When grading your essays, the TAs and I strive to make the score that you receive on your essay accurately indicate how well you have answered the question. At times it is possible that the score that you received on your essay does not correlate with how well you answer the question so this essay resubmission policy is designed to correct those rare occurances.
Rules for Submitting Essays
1. Answers written in pencil can not be submitted for regrading.
2. Do not turn in essays until you have carefully examined the answer keys (provided below or on bulletin board). Take a look at the answer key and carefully compare your answer to the key. Ask the following questions. Did your answer actually answer the question that was asked? Did your answer include all of the details shown on the answer key? Was your answer as well organized as the answer key?
3. I only want to look at tests where you feel there is a severe difference between the score you earned and how well you answered the question (that means 3 or more poingt). I do NOT want to see any 19/20s!
4. To resubmit an essay please type out a brief paragraph describing why you think that your answer deserved more points that it was awarded. Staple the essay to this sheet (make sure you put your name on it) and leave the sheet in a box that is located outside of my office in McClellan Hall (room 215) by 5:00 PM on Monday March 26.
Answer Key For First Midterm
Essay
Exponential population growth is a model of population growth that only occurs when the per capita growth rate is constant. In populations experiencing exponential growth, the population size keeps increasing over time at ever increasing rates. Thus, populations growing exponentially would keep increasing in size forever. Obviously, we do not see this pattern of growth in nature, so this must not be a realistic model of population growth.
The problem with exponential growth is that the per capita growth rate is not constant. In fact, in most species we expect that the per capita growth rate should be negatively density dependent. The per capita growth rate (r) can be calculated by subtracting the per capita death rate (d) from the per capita birth rate (r). Because both per capita birth rates and per capita death rates are density dependent, it is not surprising that per capita growth rate is also density dependent and thus not a constant.
The per capita birth rate is negatively density dependent. As population sizes increase there are more individuals competing for the same amount of food, so each individual gets less food. Because the number of babies that a female produces is related to the amount of resources she has, as each female has less food, they should have fewer births resulting in a lower per capita birth rate.
The per capita death rate is positively density dependent. Per capita death rates increase with population size for three possible reasons. First, as population size increases competition causes each individual to get less food which increases their chance of dying of starvation. Second, predation rates could be higher in larger populations if predators were attracted to areas of high prey density or if prey were easier to catch when population sizes were high (maybe there are not enough hiding places to go around). Finally, mortality caused by disease could be higher in more dense populations because it is easier to spread disease throughout the population when individuals are in close contact.
Because per capita birth rates decrease and per capita death rates increase as population size increases, the per capita growth rate decreases as population sizes increases which results in a non-exponential pattern of growth.
Essay
The process of natural selection causes traits that increase the survival, reproduction, and mating ability of organisms. Thus, long tails in peacocks have been molded by this process.
If we assume that the long tails of peacocks can be explained by the handicap principle, then the reason that females choose to mate with the males with the longest tails is that the long tails are a “handicap” to effective survival in the peacocks natural environment. Thus, males that have managed to survive with large tails must have genes that code for phenotypic characteristics that make them especially good at surviving (finding food, escaping predation , etc.). Thus, by choosing to mate with a male with the most extreme tail, a female hopes to benefit by passing on those good survival genes to their offspring so both her sons and her daughters should have higher survival.
For the process of natural selection to occur there must be variation in phenotype within a population, the variation must be heritable, and variation in traits must affect fitness. Assume that tail length has a genetic component and that there is variation in tail length within a population of peacock ancestors. If females are choosing males with the most extreme trait because of the handicap principle then males with longest tails should be chosen to mate more often and the offspring of females that mate with long tails should survive better. Thus, there is a fitness benefit associated with mating with a male with the longest tail.
If this is true, then over time the frequency distribution of tail length in males should move to the right (directional selection) so we see increases in both the maximum, minimum, and mean tail length. The introduction of new mutations that allow males to produce even longer tails should allow directional selection to continue so that the mean tail length of males increases. We would expect directional selection to continue until the mating benefit of having the longest tail was offset by the survival disadvantage of having an extremely long tail and the fitness advantage of having the longest tail disappears. At this point stabilizing slection would kick in and direction selection would cease.
Answer Key for Retest
Posted on the wall where I posted MC answers.
Answer Key for Second Midterm
Graph A.
As light intensity increases the rate of photosynthesis increases until the rate of photosynthesis reaches a plateau. Initially, increases in light intensity greatly increase the rate of photosynthesis but as light intensity increases, the rate of increase in photosynthesis decreases until it equals zero.
Graph B.
As the concentration of carbon dioxide increases the rate of photosynthesis increases until the rate of photosynthesis reaches a plateau. Initially, increases in carbon dioxide concentration greatly increase the rate of photosynthesis but as carbon dioxide levels increase, the rate of increase of photosynthesis decreases until it equals zero.
Graph C
As temperature increases the rate of photosynthesis increases until it reaches a maximum and then decreases until the rate of photosynthesis is zero.
Essay
The rate of photosynthesis can be limited by a variety of environmental factors including light intensity, atmospheric carbon dioxide concentration, temperature, and soil nutrient content.
Increasing light intensity results in an increase in photosynthetic rates until photosynthetic rates reach a maximum suggesting that light intensity can limit the rate of photosynthesis. Light intensity limits the rate of photosynthesis by limiting the production of ATP and NADPH that are required to power the Calvin Cycle.
When further increases in light intensity fail to increase photosynthetic rates then other factors such as atmospheric carbon dioxide concentration or the amount of RuBP carboxylase have become the rate limiting step. The fact that the same increase in light intensity results in diminishing increases in photosynthetic rate as light intensity increases suggests that multiple factors can be limiting at the same time. When light levels are low light appears to be most limiting, but as light intensity increases other factors in addition to light levels appear to limit photosynthetic rates.
Increasing atmospheric carbon dioxide concentrations results in an increase in photosynthetic rates until photosynthetic rates reach a maximum suggesting that the atmospheric concentration of carbon dioxide can also limit the rate of photosynthesis. Carbon dioxide limits the rate of photosynthesis because carbon dioxide is used in the Calvin Cycle to produce glucose.
When further increases in atmospheric carbon dioxide concentration fail to increase photosynthetic rates then other factors such as light availability or the amount of RuBP carboxylase have become the rate limiting factors. The fact that the same increase in carbon dioxide content results in diminishing increases in photosynthetic rate as light intensity increases suggests that multiple factors can be limiting at the same time. When carbon dioxide concentrations are low carbon dioxide concentration appears to be most limiting factor, but as carbon dioxide concentration increases other factors in addition to light levels appear to limit photosynthetic rates.
Essay
Humans require energy to do biological work. The energy used to power biological work in humans come in the form of energy released by ATP. Energy in ATP is converted from energy stored in chemical bonds of glucose by the process of cellular respiration. Humans are capable of breaking down sugar to release ATP in both aerobic and anaerobic conditions so they use both aerobic and anaerobic respiration.
Aerobic respiration breaks down glucose in the presence of oxygen to release 38 ATP per glucose. Glycolysis, which occurs in the cytosol of the cell, breaks down glucose into two molecules of pyryuvate + H+ which requires the input of energy from 2 ATPs to release energy in 4 ATPs. Hydrogen ions are picked up by the hydrogen carrier NADH and then released to react with oxygen to form water. The pyruvate moves into the mitochondria where is is broken down to produce acetyl Co A and CO2. The Acetyl Co A enters the Krebs cycle where one molecule of ATP is release for each Acetyl CoA that enters the cycle. An excited electron undergoes electron transport which produces a large number of ATP. The ATPs are produced by chemiosmosis which is powered by a hydrogen ion concentration gradient that is produced when energy released by electron transport is used to actively transport H+. Aerobic respiration is a very effective way of converting glucose into ATP.
When oxygen is not available to remove the H+ from the system then organisms must use an anaerobic pathway. Glucose is still broken down by glycolysis with the same net gain of 2 ATP per glucose. In order to keep glycolysis going forward the pyruvate and H+ react to form acetaldehyde which is converted to ethanol (alcohol fementation). Alcohol fermentation is not as advantageous to the cells because alcohol can be poisonous to cells and potential energy in pyruvate can not be released. Humans need to use anaerobic respiration when they are so active that they are using oxygen faster than their system can supply it such that cells momentarily become anoxic environments.
Tuesday, March 9, 2010
Thursday, March 4, 2010
Multiple Choice Answers for Midterm #2 and BAC Report
Here are the final answers to the multiple choice portion of the second midterm. The original answers I posted contained several mistakes (sorry for the confusion and extra stress) so please compare your answers to these.
Form 1 (Blue Test)
1. b
2. c
3. d
4. a
5. e
6. all answers considered correct (BAC)
7. d
8. d
9. a
10. all answers considered correct (BAC)
11. e
12. a
13. b
14. c
15. d
16. b
17. a
18. a
19. b
20. a
21. e
22. b
23. a
24. e
25. d
26. a
27. e
28. d
29. b
30. c
Form 2 (Pink test)
1. a
2. e
3. b
4. c
5. b
6. c
7. d
8. a
9. e
10 all answers correct (BAC)
11. d
12. e
13. d
14. a
15. all answers correct (BAC)
16. e
17. a
18. b
19. c
20. d
21. b
22. a
23. a
24. b
25. a
26. e
27. b
28. d
29. a
30. d
BAC Report
Thanks to the members of the BAC (Brittany Luker, Isaac Perez, Sarah Qureshi, Brady Douglas, Patrick Thomas, Paulina Ramirez, Jordan Ardoin, Kadie Bowman, Ashlei Taylor, Kim Gorton, James Walls, Jonathan Hickey, Kendall Kennedy, Britney Williams, and Reid Smalley) for the work yesterday afternoon. I think they broke the record for the longest BAC meeting in history. They brought forward a number of questions for discussion.
DENIED
Most of the problems that students had with the questions appeared to arise because they were not answering the question that I asked.
9-pink, 5-blue
The question asks which species is most efficient at converting energy stored in glucose into ATP. The process that does this is cellular respiration. All three of the organisms listed as possible answers conduct aerobic respiration under the conditions described in the question so they are equally efficient at converting glucose into ATP. Thus, the correct answer is E.
13-pink, 8- blue
The question asks which human activities have increased the rate that carbon dioxide is ADDED to the atmosphere. Both burning coal and burning trees increases the rate that carbon dioxide is added to the atmosphere. Cutting down trees decreases the rate that carbon dioxide is removed from the atmosphere. Although it is true that decreasing the rate that carbon is removed from the atmosphere will result in an increase in atmospheric carbon dioxide content over time, this is not what the question asks. Correct answer D
20-pink, 15-blue
Chemiosmosis is the process that adds energy to ATP during both photosynthesis and aerobic respiration. Chemiosmosis is powered by the concentration gradient that is created when hydrogen ions are actively transported from the stroma inside the thylakoid space which occurs during electron flow. The process of chemiosmosis does not result in active transport of hydrogen ions, but depends on it. Correct answer D.
21-pink, 16-blue
This question asks when ATP is produced during LINEAR electron flow. Because the question asks about linear electron flow anything that happens during cyclic electroon flow is irrelevant! The only correct answer that refers to linear flow is B.
22-pink, 17-blue
This question asks about things that occur during the Calvin Cycle. Several students tried to artue that Carbon dioxide combines with RuBP to produce glyceraldehyde phosphate. The actual product produced during this reaction are an unstable 6-carbon intermediate which breaks down to PGA (either of those would have been correct answers if they were choices). Although it is true that glyceraldehyde phosphate is produced several steps down the line in the Calvin Cycle, you can't possibly think that any chemist would ever define the results of a chemical reaction in that way. Correct answer A
26-pink, 21-blue
This questions asks about the net gain of ATP during ALCOHOL FERMENTATION. Alcohol fermentation occurs as part of anaerobic respiration. All of the ATP released during anaerobic respiration comes from glycolysis. NO ATPS ARE PRODUCED BY ALCOHOL FERMENTATION. The only possible answer is E.
BAC recomendations accepted
10-pink, 6-blue
The seeds consumed by sparrows are angiosperms. These seeds are not dispersed by the birds they are consumed by the birds (seed predation). So I think the correct answe chould be D. However, in the book (PG. 625) is discusses seeds as "dispersable stage". While it is true that seeds are dispersable, the adaptations that allow seeds to be dispersed are produced by the fruit. However, I see that this statement could have been misleading and we didn't spend very much time discussing seed dispersal. Thus, all answers to this questions will be graded as correct.
15-pink, 10- blue
The statement in answer (a) is garbled enough that there is no best answer to this question. Thus, all answers will be considered to be correct.
Form 1 (Blue Test)
1. b
2. c
3. d
4. a
5. e
6. all answers considered correct (BAC)
7. d
8. d
9. a
10. all answers considered correct (BAC)
11. e
12. a
13. b
14. c
15. d
16. b
17. a
18. a
19. b
20. a
21. e
22. b
23. a
24. e
25. d
26. a
27. e
28. d
29. b
30. c
Form 2 (Pink test)
1. a
2. e
3. b
4. c
5. b
6. c
7. d
8. a
9. e
10 all answers correct (BAC)
11. d
12. e
13. d
14. a
15. all answers correct (BAC)
16. e
17. a
18. b
19. c
20. d
21. b
22. a
23. a
24. b
25. a
26. e
27. b
28. d
29. a
30. d
BAC Report
Thanks to the members of the BAC (Brittany Luker, Isaac Perez, Sarah Qureshi, Brady Douglas, Patrick Thomas, Paulina Ramirez, Jordan Ardoin, Kadie Bowman, Ashlei Taylor, Kim Gorton, James Walls, Jonathan Hickey, Kendall Kennedy, Britney Williams, and Reid Smalley) for the work yesterday afternoon. I think they broke the record for the longest BAC meeting in history. They brought forward a number of questions for discussion.
DENIED
Most of the problems that students had with the questions appeared to arise because they were not answering the question that I asked.
9-pink, 5-blue
The question asks which species is most efficient at converting energy stored in glucose into ATP. The process that does this is cellular respiration. All three of the organisms listed as possible answers conduct aerobic respiration under the conditions described in the question so they are equally efficient at converting glucose into ATP. Thus, the correct answer is E.
13-pink, 8- blue
The question asks which human activities have increased the rate that carbon dioxide is ADDED to the atmosphere. Both burning coal and burning trees increases the rate that carbon dioxide is added to the atmosphere. Cutting down trees decreases the rate that carbon dioxide is removed from the atmosphere. Although it is true that decreasing the rate that carbon is removed from the atmosphere will result in an increase in atmospheric carbon dioxide content over time, this is not what the question asks. Correct answer D
20-pink, 15-blue
Chemiosmosis is the process that adds energy to ATP during both photosynthesis and aerobic respiration. Chemiosmosis is powered by the concentration gradient that is created when hydrogen ions are actively transported from the stroma inside the thylakoid space which occurs during electron flow. The process of chemiosmosis does not result in active transport of hydrogen ions, but depends on it. Correct answer D.
21-pink, 16-blue
This question asks when ATP is produced during LINEAR electron flow. Because the question asks about linear electron flow anything that happens during cyclic electroon flow is irrelevant! The only correct answer that refers to linear flow is B.
22-pink, 17-blue
This question asks about things that occur during the Calvin Cycle. Several students tried to artue that Carbon dioxide combines with RuBP to produce glyceraldehyde phosphate. The actual product produced during this reaction are an unstable 6-carbon intermediate which breaks down to PGA (either of those would have been correct answers if they were choices). Although it is true that glyceraldehyde phosphate is produced several steps down the line in the Calvin Cycle, you can't possibly think that any chemist would ever define the results of a chemical reaction in that way. Correct answer A
26-pink, 21-blue
This questions asks about the net gain of ATP during ALCOHOL FERMENTATION. Alcohol fermentation occurs as part of anaerobic respiration. All of the ATP released during anaerobic respiration comes from glycolysis. NO ATPS ARE PRODUCED BY ALCOHOL FERMENTATION. The only possible answer is E.
BAC recomendations accepted
10-pink, 6-blue
The seeds consumed by sparrows are angiosperms. These seeds are not dispersed by the birds they are consumed by the birds (seed predation). So I think the correct answe chould be D. However, in the book (PG. 625) is discusses seeds as "dispersable stage". While it is true that seeds are dispersable, the adaptations that allow seeds to be dispersed are produced by the fruit. However, I see that this statement could have been misleading and we didn't spend very much time discussing seed dispersal. Thus, all answers to this questions will be graded as correct.
15-pink, 10- blue
The statement in answer (a) is garbled enough that there is no best answer to this question. Thus, all answers will be considered to be correct.
Sunday, February 28, 2010
Errors in Answer Key to Past Midterms
Several students have informed me that the answers provided in the back of the lab manual are not correct. I don't have access to the lab manual so I can't check this out.
I am sorry if I did not post the correct answer (no idea what went wrong). You can find the correct answers
http://biol1404.blogspot.com/2009/02/answer-key-for-second-midterm.html
Sorry for the inconvenience.
I am sorry if I did not post the correct answer (no idea what went wrong). You can find the correct answers
http://biol1404.blogspot.com/2009/02/answer-key-for-second-midterm.html
Sorry for the inconvenience.
Thursday, February 25, 2010
Plant Diversity- Gymnosperms and Angiosperms
Gymosperms and angiosperms are the "seed plants".
Gymnosperms
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- defne and contrast homospory and heterospory
- discuss the evolutionary advantage of heterosporty over homospory
- identify the parts of a seed and discuss why reproducing by seeds is an advantaged compared to reproducing by spores
- discuss the life cycle of a pine
- discuss the characteristics of pines that are advanced relative to the ferns and those that are primitive relative to the angiosperms
Angiosperms
Expected Learning Outcomes
At the end of the course a fully engaged student should be able to
- discuss the parts of a flower
- discuss the evolutionary advantage of reproducing by flowers rather than by cones
- discuss the life cycle of an angiosperm
- discuss the characteristics of angiosperms that are advanced relative to the pines and those that are primitive relative to the angiosperms
- discuss why angiosperms are the most successful of all plant groups
Plant Diversity- Ferns
Ferns are examples of the first vascular plants.
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- discuss the components of the vascular system
- discuss the advantage of a having a vascular system
- diagram the life cycle of a fern
- discuss the morphological and physiological characteristics of ferns
- discuss the characteristics of ferns that makes them considered to be advanced relative to mosses but primitive relative to the gumnosperms
- discuss how the morphological and life history characteristics limits their size and geographic distrubution
Plant Diversity- Algae and Mosses
As I mentioned in class, plants are interesting to me because the are so different than we are. At first these differences will cause unfamiliarity but eventually you will not be so bogged down by learning new vocabulary and you will hopefully come to realize that plants are more interesting than you might have thought (and besides, no plants means no dorritos, french fries, or beer?).
Further Viewing
1) Here is the slideshow that I will use in class for the final three lectures.
http://www.slideshare.net/secret/DBv71wnKTH1YBN
2) Here is a powerpoint presentation from a group called "world of teaching" that covers plant diversity? There are many "quiz questions" that should be helpful to look at.
http://www.worldofteaching.com/powerpoints/biology/Plant%20Divisions.ppt
Primitive Plants
Expected Learning Outcomes
A the end of this course a fully engaged student should be able to
- functionally define a plant
- discuss the characteristics of a primitive plant such as Chlamydomonas
- diagram a life cycle of a human
- diagram the life cycle of Chlamydomonas
- distinguish between oogamy and isogamy
- discuss the evolutionary advantage of multicellularity, diploid dominance, and oogamy
Transition to Land
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- discuss the problems plants face when moving to the land
- discuss the characteristics of the ancestor of land plants
- diagram the life cycle of a moss
- discuss the morphological and physiological characteristics of mosses
- discuss the characteristics of mosses that makes them considered to be advanced relative to primitive plants but primitive relative to the ferns
- discuss how the morphological and life history characteristics of mosses limits their growth and geographic distribution
Cellular Respiration
Cellular respiration converts chemical energy in glucos to chemical energy in ATP which is the ultimate source of energy used to do "biological work".
Glycolysis
1) Glycolysis animation
http://www.youtube.com/watch?v=7hiwSCUoSZY
2) Another Glycolysis animation- this one goes into a little more chemical detail so it might be useful if you are intersted in knowing more about the chemistry
http://www.youtube.com/watch?v=x-stLxqPt6E
Anaerobic Respiration
Alcohol Fermentation and Lactic Acid Fermentation
Further Reading
Alcohol Fermentation- http://www.tempeh.info/fermentation/alcohol-fermentation.php
Lactic Acid Fermentation- http://www.tempeh.info/fermentation/lactic-acid-fermentation.php
Further Viewing
http://www.youtube.com/watch?v=y_k8xLrBUfg
Aerobic Respiration
1) Aerobic Respiration
http://www.youtube.com/watch?v=iXmw3fR8fh0
2) Krebs Cycle
http://www.youtube.com/watch?v=aCypoN3X7KQ&feature=related
3) Electron Transfer Chain
http://www.teachertube.com/view_video.php?viewkey=a67b8fcdafb25c122359
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- discus glycolysis, anaerobic respiration, alcohol fermentation, lactic acid fermentation, aerobic respiration, the Kreb's Cycle, and electron transport
- compare and contrast aerobic respiration with anaerobic respiration
- discus why the breakdown of glucose to produce ATP is so much more efficient when oxygen is present
- describe where in the cell the different parts of cellular respiration take place
Factors Limiting the Rate of Photosynthesis
The rate of photosynthesis can be limited by a variety of environmental factors including
1) light
2) concentration of carbon dioxide
3) water
4) soil nutrients
Which factor most limits photosynthesis varies between environments.
Light- Can directly limit the rate of photosythesis by limiting the rate at which ATP and NADPH are produced
Carbon dioxide- can directly limit the rate of photosynthesis by limiting the rate at which the Calvin Cyle takes place
Water- can indirectly limit the rate of photosynthesis. When plants are water stressed they close their stomata (long before the concentration of water in the cell becomes too low for water to supply electrons to P680). Thus, the rate of photosynthesis is water stressed plants is directly limited by the amount of carbon dioxide in the leaf.
Soil Nutrients- Sometimes the rate limiting step in photosynthesis is the rate at which carbon dioxide + RuBP ==> PGA. This reaction is catalyzed by the enzyme RuBP carboxylase. Increasing the amount of RuBP carboxlyase in the cell can increase the rate at which this reaction occurs. Fertilizing plants with nitrogen will increase the amount of RuBP Carboxylase produced by the plant.
Expected Learning Outcomes
By the end of this class a fully engaged student should be able to
- discuss the factors that can directly or indirectly limit the rates of photosynthesis
- discuss how the most limiting factors should vary between environments
- discuss how the activities of farmers such as irrigation and fertilization can increase photosynthetic rates
- interpret the graph at the top of the post (irradiance measures light intensity and the three lines represent different concentrations of carbon dioxide)
- explain what why the graph shows that shape
Why Are Plants Green or Why Aren't Plants Black?
If I was hired as an engineer to design a machine whose job was to convert light energy into chemical energy I probably would not choose to use a green pigment. Instead, I would choose to use a black pigment because black pigments would absorb more energy because they would absorb all wavelengths of light. If you look at a field of plants you will notice that they are green (OK this doesn't work too well around Lubbock in the winter)and we have learned that chlorophyll, a green pigment, is the dominant photosynthetic pigment. What is going on?
Here is one theory about why chlorophyll is the dominant photosynthetic pigment in plants today. Early on there were photosynthetic bacteria with purple pigments (purple is a combination of red and violet). These aquatic bacteria had a very simple sort of cyclic electron flow that was able to convert light energy into energy in ATP (they didn't have non-cyclic flow or the Calvin Cycle).
Origin of chlorophyll- The purple pigment absorbed all wavelengths of light except for the reds and violets. Thus, any bacteria using purple pigments that lived deeper in the water than the purple bacteria on the surface would have no light to use because it had all been absorbed by the surface bacteris (exploitative competition). Because red and violet wavelengths pass through to deeper water, bacteria that contained a pigment that was able to absorb these wavelengths would be able to coexist with the purple bacteria. This was the origin of chlorophyll.
Competition purple and green photosynthetic pigments. Over time there was competition between organisms with purple photosynthetic pigments and green photosynthetic pigments. Obviously, the green photosynthetic pigments won this competition because chlorophyll is the dominant photosynthetic pigment today (there are still examples of photosynthetic bacteria with purple pigments, but they are limited to very harsh environments). Interestingly, chlorophyll came to dominate, not because it was a better at absorbing light energy, but rather because the cyclic flow machinery associated with chlorophyll was more efficient at producing ATP than the machinery associated with the purple pigment was. Thus, it is an evolutionary accident that modern plants are green.
Black Plants
It would be possible for modern plants to be black if they had enough accessory pigments to allow them to absorb all wavelengths of light. In fact, some red algae that live deep below the surface where light levels are low are basically black. Because the amount of light is not the factor that limits the rate of photosynthesis in most terrestrial plants, it is not worth the cost of producing extra accessory pigments. However, deep in the ocean where light levels are low, plants benefit from being able to absorb all wavelengths of light so deep marine algae have invested in extra accessory pigments.
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- discuss why terrestrial plants to not invest in the accessory pigments required to make them black
Carbon Fixation
Technically, arbon fixation is defined as the first chemical reaction that incorporates carbon dioxide into an organic molecule (a molecule with more than one carbon atom).
In C3 photosynthesis the following step is considered to be carbon fixation-
carbon dioxide + RuBP ==> PGA
In CAM photosynthesis the following is considered to be carbon fixation-
carbon dioxide ===> malate
Note: CAM plants also have the reaction- carbon dioxide + RuBP ===> PGA, but in this case this step is not considered to be carbon fixation.
Sometimes people will loosely use the term carbon fixation to mean the production of glucose by photosynthesis. Be sure that you are aware of how different authors are using the term and you should attempt to use the term as precisely as possible in your own work.
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- define carbon fixation
- identify carbon fixation in C3 and CAM photosynthesis
Leaf Structure
In most plants, leaves are the major sites of photosynthesis. Thus, we can think of leaves as "photosynthesis machines" and use our knowledge of natural selection to try to understand aspects of leaf structure.
Further Reading
http://micro.magnet.fsu.edu/cells/leaftissue/leaftissue.html
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- discuss important differences between animals and plants in gas uptake
- diagram the cross section of a leaf
- explain the adaptive basis of leaf structure
Photosynthesis - Summary
Once you understand the light dependent reactions, the light independent reactions, and how these two sets of interactions are linked together then you understand the basics of photosynthesis. The pattern of photosythesis that we have discussed so far is known as "C3 photosynthesis" (it is named this becasue the first stable product of the Calvin Cycle is a molecule that contains three carbon atoms). C3 photosynthesis is considered to be the basic mechanism of photosynthesis.
As I have mentioned in class the best way to assure that you understand what is going on is that you should be able to describe photosynthesis at different levels of detail.
1) the one sentence answer
2) the one paragraph answer
3) the full detail answer
In my experience, students quickly get lost by worrying about the details. Thus, I suggest that you start at the one sentence answer, then move to the one paragraph answer, and finally finish up with the full detail answer. You will find that by thinking about the one sentence and the one paragraph answers you will have already figured out how to organize your full detail answer.
I suggest that you try writing out the answers to these questions at the three levels.
1) What is photosynthesis?
2) What are the light dependent reactions of photosynthesis?
3) What are the light independent reactions of photosynthesis?
4) What is a photosystem?
I encourage you to post your answers here and then to provide critical feedback to your classmates about their answers.
Friday, February 19, 2010
Retest Answers and BAC
I met with the BAC on Wednesday afternoon. The results of the BAC are included on the answer key,
1. c
2. c
3. c
4. b
5. e
6. b
7. d
8. e
9. c
10. a
11. d
12. a
13. a
14. d
15. b
16. a
17. e
18. b
19. b
20. c
21. c
22. e
23. d and e
24. e
25. a
26. c
27. c
28. e
29. a
30. a
1. c
2. c
3. c
4. b
5. e
6. b
7. d
8. e
9. c
10. a
11. d
12. a
13. a
14. d
15. b
16. a
17. e
18. b
19. b
20. c
21. c
22. e
23. d and e
24. e
25. a
26. c
27. c
28. e
29. a
30. a
Wednesday, February 17, 2010
Photosynthesis- Light Independent Reactions- Calvin Cycle
In the light independent reactions the energy stored in ATP and NADPH is converted to energy stored in glucose. This invovles a chemical cycle known as the Calvin Cycle.
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- discuss what links the light dependent and light independent reactions of photosynthesis
- describe the initial step of the Calvin Cycle
- describe the chemical reaction catalyzed by the enzyme RuBP carboxylase
- discuss some interesting characteristics of RuBP carboxylase
- define "carbon fixation" and identify the carbon fixation step in the different modes of photosynthesis
- diagram the Calvin Cycle (at the level of detail that I talked about in class)
- discuss where and why ATP and NADPH are required in the Calvin Cycle
- disucus where in the cell that the Calvin Cycle takes place
Further Viewing
1) This is an excellent animation (narrated by a man with a perfect "announcer's voice"). This animation goes into the amount of detail you are required to know for this class. It even has its own quiz, so see how you do.
http://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.html
2) I didn't know that photosynthesis was such a popular subject for musicians (I can't belive I gave up what would surely have been a lucrative career as a rock star to become a biologist- who knew I could have combined the two). The guy in the video is kind of a dufus, but the song is pretty cool, and I learned something from watchig it.
http://www.youtube.com/watch?v=OYSD1jOD1dQ
3)This is quite a good video (sorry, no song involved). Note, this video concludes that glyceraldehyde phosphate is the result of the Calvin Cycle. For our purposes in this class we are going to conclude that glucose is the end result of this cycle.
http://www.youtube.com/watch?v=mHU27qYJNU0
4) Maybe you will find this animation to be helpful
http://www.science.smith.edu/departments/Biology/Bio231/calvin.html
Tuesday, February 16, 2010
Photosynthesis- Light Dependent Reactions
Photosythesis takes place in two steps. In the first step, known as the light dependent reactions, light energy is converted into chemical energy held in the bonds of ATP and NADPH.
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- list the parts of a photosystem
- discuss the function of a photosystem
- describe where the light dependent reactions of photosythesis occur and discuss why these reactions occur in this location
- describe cyclc electron flow, be able to explain both the energetic result and what chemcical changes occur
- describe non-cyclic electron flow, be able to explain both the energetic result and what chemical changes occur
- describe the cause and the result of chemiosmosis
- answer the question- "why doesn't photosynthesis stop after the production of ATP and NADPH in the light dependent reactions
Further Reading
Here is a link to some fairly detailed info about photosynthesis (it contains some very good diagrams).
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html
Further Viewing
These videos contain animations that might help you to understand what is happening in the light dependent reactions. I encourage you to watch each of these videos.
1) This video has some great animations of what is going on in the light dependent reactions.
http://www.youtube.com/watch?v=hj_WKgnL6MI
2) This short video is a good review of the light dependent reactions.
http://www.youtube.com/watch?v=eY1ReqiYwYs&feature=related
3) This is a video of a woman with a very southern accent talking about photosyntheis with some decent animations.
http://www.youtube.com/watch?v=RFl25vSElaE&feature=related
4) This one comes complete with a "Photosyntheis Song." I guarantee that you will be humming this as you walk around campus!
http://www.teachertube.com/view_video.php?viewkey=dc9810ac32b3c413fb29
Sunday, February 14, 2010
Introduction to Energetics
Energy is required to do work. In order to understand the two important energetic processes taking place in living organims (photosynthesis and cellular respiration) it is useful to understand some basics of energetics.
Expected Learning Outcomes
By the end of the course a fully engaged student should be able to
- give examples of biological work
- list different forms of energy, give examples of the different forms, and give examples of energy conversions
- define the First and Second Laws of Thermodynamics and discuss why these laws are important for biologists
- discuss electromagnetic energy, including the wavelengths associated with different forms of electromagnetic energy and the relationship between wavelength and energy
- define a photon
- discuss the three things that can happen when a photon of light hits a molecule
- define a pigment
- draw and interpret an absorption spectrum
Further Reading
Electromagnetic radiation- http://www.eoearth.org/article/Electromagnetic_radiation
Homework Assignment- Photosynthesis
The next homework assignment, photosynthesis, is currently available on Mastering Biology.
Due Date: 11:59 PM Monday February 22nd
Point Value: 15 points
Homework Format: In order to reduce the chance that students are able to exchange answers, we will not make the answers of the quiz avaialble until after the quiz is due. When we choose this option, the Mastering Biology website does not allow you to have multiple chances to answer each question. Thus, you will only be able to attempt each qustion one time.
We will begin talking about energetics and photosynthesis on Monday, Feb 15th. Hopefully, I will have covered all of the information that you need in order to answer these questions by Friday, but certainly we will have covered all of this material by next Monday. Thus, I suggest that you not try the homework until after we have completed talking about both the light dependent and light independent reactions of photosynthesis
Things Students Have Sent Me About Climate Change
Hello,
I appreciate the links that students have sent me about climate change including the cartoon posted above and the link to the newspaper article posted below. Keep them coming!!
Bill Nye the Science Guy: Climate Change Deniers are Unpatriotic
http://rawstory.com/2010/02/bill-nye-climate-change-deniers-unpatriotic/
Thursday, February 11, 2010
Intersesion Courses at Junction Campus
Texas Tech offers courses during Intersession (May 12 - May 27th, 2010) the period between the end of Spring Semester and the start of the First Summer Session at our field station in Junction, TX. http://www.depts.ttu.edu/hillcountry/junction/junction%20acad%
The Department of Biological Sciences offers a number of courses at Junction during Intersession-
BIOL 4301-180 - Herpetology (Reptiles and Amphibians) - Dr. Lou Densmore
BIOL 3301-180 - Field Ecology - Dr. Mark McGinley
ZOOL 4406-180 - Mammalogy - Dr. Robert Bradley
ZOOL 4408-180 - General Ornithology - Dr. Kent Rylander
Courses taught in Junction are intense so you can basically plan on being involved in class mornng, afternoon, and evenings virtually every day of intersession. Because the classes are hands-on and there is lots of interaction between faculty and students, most students think that taking classes during intersession is a great opportunity (and you can get three credit hours in less than three weeks).
If you are interested in learning more about any of these classes then contact the professor. Of course, Field Ecology is the absolute bestest class offered in Junction, so if any of you are interested in learning more please let me know.
Global Carbon Cycle and Climate Change
Human activity, including burning fossil fuels, deforestation, and buring trees, has altered the global carbon cycle. This alternation of the global carbon cycle is the proposed cause of global climate change (global warming).
Obviously, global climate change is a very imporant issue facing us today. If you are alive and paying any attention, then you probably know that there is some disgreement out there about (1) whether global warming is occuring, (2) if it is occuring is it a natural occurence or is it caused by humans, and (3)what should we as individuals and a society do about these issues. As I mentioned in class, it is very important that you understand what components of the debate are facts and what components of the debate are based on mathematical models or other forms of argument. I think that it is important that you should be able to explain to other people why scientists will never be able to conduct the experiment that will nail down whether or not humans are causing global warming (we have only one earth).
I think that it is important for you to have access to good information. Here are some links to what I consider to be some of the best and most reliable sources of information about this topic. Although some of these articles go into much more detail than are required for this class you should know where to find reliable information about this topic.
Further Reading
Carbon cycle- http://www.eoearth.org/article/Carbon_cycle
Global warming- http://www.eoearth.org/article/Global_warming
Global warming Frequenty Asked Questions- http://www.eoearth.org/article/Global_warming_frequently_asked_questions
Climate change FAQ- http://www.eoearth.org/article/Climate_change_FAQs
Intergovenmental Panel on Climate Change- http://www.eoearth.org/article/Intergovernmental_Panel_on_Climate_Change_%28IPCC%29
IPCC Assessment for Policymakers- http://www.eoearth.org/article/IPCC_Fourth_Assessment_Report%2C_Working_Group_I%3A_Summary_for_Policymakers
If you would like additional information about global climate change then you can take a look at a presentation I developed for another class.
Global Carbon Cycle and Global Climate Change
http://www.slideshare.net/secret/C6iDTujQlIh73C
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- diagram the global carbon cycle
- discuss how humans have altered the global carbon cycle
- discuss how the atmospheric concentration of carbon dioxide varies annually
- discuss the proposed relationship between human caused changes in the global carbon cycle and global warming
- discuss alternative causes of global warming
- discuss the experiment that would be required to determine whether or not human activity is the cause of global warming
- articulate and defend their own personal view of how they intend to deal with the global warming issue
Ecosystem Ecology
Ecosystem ecologists focus on the flow of enery and the cycling of nutrients through the ecosystem.
Further Readings
Ecosystems- http://www.eoearth.org/article/Ecosystem
Ecological energetics- http://www.eoearth.org/article/Ecological_energetics
Nitrogen cycle- http://www.eoearth.org/article/Nitrogen_cycle
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- diagram and discuss the flow of energy through an ecosystem
- diagram, discuss the causes of, and discuss some of the implications of the enegy pyramid
- diagram nitrogen cycle within an ecosystem
- discuss the factors that influence the rate of flow from dead bodies to the soil and discuss the implications of differences in this rate
Community Ecology: The Portal Experiment
Here are some photos from the research site in Portal, Arizona. For more information about the research project at Portal you can look at their website at
http://www.biology.usu.edu/labsites/ernestlab/portal/index.html
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- distinguish between direct and indirect, positive and negative effects
- describe the experiemental design that Dr. Brown and his colleagues used to study exploitative competition between desert rats and rodents
- discuss the "search the the missing indirect positive effect of rodents on ants" and how that dilema was solved
-discuss why and how the outcome of studies of interactions betwen organisms can vary over time
- discuss the way that the ecological community responded when they learned the importance of long term studies
- discuss how indirect interactions influence my facvorite phrase "the world is complicated"
Cool Video From Kruger Park in South Africa
A past BIOL 1404 student sent me a link to this video. It seems like almost everything that we have talked about so far in BIOL 1404 is going on in this video. The highlight of my biology life was visiting Kruger Park when I was about 13 (how sad to peak so young). I saw lots of amazing animals, but I didn't see anything like this. This video keeps getting better so watch it all the way to the end. Enjoy!!
http://www.youtube.com/watch?v=LU8DDYz68kM
Wednesday, February 10, 2010
First Midterm Answers and BAC Report
Here are the final answers for the multiple choice questions on the first midterm. First I want to explain the answers to a couple of the questions that clearly baffled a lot of people and second I want to give a report from the BAC.
Question 6 (on both form 1 and form 2) was my favorite question on the test. Because it talks about Hamilton's Rule we know that we need to determine B, C, r and n and then plug them into Hamilton's Rule equation. The question states that we need to assume that "the probability of survival in wild dogs is directly correlated with the amount of food they eat". This statement should allow us to calculate both the benefit received by the recipients and the costs to the actor. First, the actor regurgitates 1 pound of food which she should have been able to eat herself. Thus, by sharing food she reduces her probability of survival one pound's worth. Thus, C = 1 unit worth of survival.
Next we can calculate the benefit received that the dogs that share her food. Because the food is divided evenly among all individuals that are sharing, the benefit of receiving food depends on the number of sisters sharing the food. When( the actor is sharing with only one sister that sister receives 1 pound of meat which increases her survival by 1 pound worth (B = 1 survival unit). Now we can plug into Hamilton's Rule Equation. Does
(1 survival unit)(1/2) > 1 survival unit?
because the answer to this question is no, the the actor should be selfish.
When two sisters share the regurgitated food, then both sisters receive 1/2 extra pound of meat which increases their chance of survival by 1/2 survival units (B = 1/2). Plug into Hamilton's Rule
2(1/2 survival units)(1/2) > 1 survival unit
Again this is not true so the actor should be selfish.
When three sisters share the regurgitated food, each sister getw 1/3 pound of extra meet for a benefit of 1/3 survival unit. Plug into Hamilton's Rule
3(1/3 survival units)(1/2) > 1 survival unit
Again this is not true so the actor should be selfish.
Becasue the benefit received by each helped sister declines as the food is spread among more sisters, then the actor will NEVER be slected to be altruistic.
Question 23 (both form 1 and form 2)asks you determine if and why the population size of lions should change if the populstion size of hyenas was increased. Because they are scavengers, hyenas have an interesting relationship with lions. Becuase hyenas don't kill their own food (they only eat food killed by other species) they are not exploitative competitors with lions. Because they chase lions away from kills they are interference competitors with lions. Thus, increasing the population size of hyenas should decrease the population size of lions, but only by a direct interaction (interference competition).
BAC Report
The members of the BAC met with me on Wednesday afternoon to discuss test questions. They went through a large number of your comments and brought a number of questions to me for further discussion. I agreed with them on two questions.
Question 11 (both form 1 and form 2) dealt with mate choice in frigatebirds (one of my favorite birds). Frigatebirds, which were featured in the website I listed on the blog, have a bright red throat sac (skin!!!) that they use to attract females. Becuse we discussed how skin was used to indicate resistance of disease to females I chose answer (e) as being the best answer so this answer will receive credit. The BAC suggested that it was not clear whether or not the sac was make out of skin or feathers (although I suggest they called the sac a "ballon" should have been a good hint) that students thought that because females chose males with the "biggest and shiniest" throat sac that they might be choosing as a result of female choice. Because I did not clearly use the term "skin" in the discussion and because the word "biggest" suggested the sexy sons hypothesis, I have decided to award credit for answer (a) as well.
Question 18 (on both form 1 and form 2) asked why the population growth rate is initally very negative when the initialy population size is much larger than the carrying capacity in logistic growth. Because dN/dt = rN, dN/dt will be the most negative when you multiply a large negative value of r times a large N (answer (c) gets credit). Several students argued that
b - d = r and that r = (dN/dt)/N and that if you set these two equations equal to each other and did some algebra that it would be clear that answer (b) was equally correct. Although I think my answer is the best answer, coming up with answer (b) showed not only an understanding of the topic, but some clever creativity, so I will give credit for both answers.
You BAC representatives spent a considerable amount of time discussing these questions. I appreciate their efforts and I hope that you let them know how much you appreciate their hard work. You should discuss with them how to write more effective comments to the BAC on future exams.
Final Answers
1. b
2. c
3. d
4. d
5. e
6. d
7. d
8. d
9. e
10. c
11. a or e
12. b
13. c
14. c
15. e
16. a
17. a
18. b or c
19. d
20. c
21. d
22. d
23. b
24. b
25. b
26. d
27. a
28. d
29. e
30. a
Sunday, February 7, 2010
Evolution of Sex
I realized that I failed to post info about the Evolution of Sex. You are reponsible for this material on the first midterm.
Based on our understanding of natural selection, at first glance sexual reproduction doesn't appear to be advantageous from the female perspective (due to the two-fold cost of sex). However, the fact that sexual reproduction is so common in all groups of organisms suggests that there must be some major benefits of sex that outweight the costs.
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- explain "the two-fold costs of sex"
- discuss possible benefits of sexual reproduction including adaptation to environmental uncertainty and fighting disease
- be able to discuss the problem of the evolution of antiobiotic resistant microbes
- be able to discuss what the medical field may be able to learn from observing how nature fights disease.
Past Exam Question (answer at the bottom of the post)
1. What is the “two fold cost of sex”?
(a) female gametes are twice as expensive to produce as male gametes
(b) the genetic variation produced by sexually reproducing females provides a benefit if there is environmental uncertainty
(c) individuals reproducing asexually pass on twice as many of their genes
(d) a and b
(e) b and c
2. Which of the following hypotheses can explain a benefit of sex?
(a) males pass on more genes in sexual reproduction than in asexual reproduction
(b) the genetic variation produced by sexual reproductions provides a benefit in uncertain environments
(c) females reproducing asexually pass on twice as many of their genes
(d) a and b
(e) b and c
Further Readings
Although I am usually a little skeptical of articles form Wikipedia, this one is pretty good. It goes into more detail than you need to know, but provides some useful information
Evolution of Sexual Reproduction http://en.wikipedia.org/wiki/Evolution_of_sex
Life in Local Playa Lakes
If you would like to learn a little more about local playa lakes-
Playa Lakes http://www.eoearth.org/article/Playa_lake
Drawings of cladocerans similar to those inhabiting playa lakes.
Based on our understanding of natural selection, at first glance sexual reproduction doesn't appear to be advantageous from the female perspective (due to the two-fold cost of sex). However, the fact that sexual reproduction is so common in all groups of organisms suggests that there must be some major benefits of sex that outweight the costs.
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- explain "the two-fold costs of sex"
- discuss possible benefits of sexual reproduction including adaptation to environmental uncertainty and fighting disease
- be able to discuss the problem of the evolution of antiobiotic resistant microbes
- be able to discuss what the medical field may be able to learn from observing how nature fights disease.
Past Exam Question (answer at the bottom of the post)
1. What is the “two fold cost of sex”?
(a) female gametes are twice as expensive to produce as male gametes
(b) the genetic variation produced by sexually reproducing females provides a benefit if there is environmental uncertainty
(c) individuals reproducing asexually pass on twice as many of their genes
(d) a and b
(e) b and c
2. Which of the following hypotheses can explain a benefit of sex?
(a) males pass on more genes in sexual reproduction than in asexual reproduction
(b) the genetic variation produced by sexual reproductions provides a benefit in uncertain environments
(c) females reproducing asexually pass on twice as many of their genes
(d) a and b
(e) b and c
Further Readings
Although I am usually a little skeptical of articles form Wikipedia, this one is pretty good. It goes into more detail than you need to know, but provides some useful information
Evolution of Sexual Reproduction http://en.wikipedia.org/wiki/Evolution_of_sex
Life in Local Playa Lakes
If you would like to learn a little more about local playa lakes-
Playa Lakes http://www.eoearth.org/article/Playa_lake
Drawings of cladocerans similar to those inhabiting playa lakes.
This is what they don't look like.
answer- 1. c 2. b
Community Ecology
Community Ecology will be the final topic covered on the First Midterm (Monday's lecture will be included on the exam). You are responsible for the material on pages 1198 - 1210 on this exam. You are NOT responsible for any material on Ecosystems on this exam.
Suggested Readings
Community Ecology- http://www.eoearth.org/article/Community_ecology
Competition- http://www.eoearth.org/article/Competition
Interspecific Competition- http://www.eoearth.org/article/Interspecific_competition
Exploitative Competition- http://www.eoearth.org/article/Exploitative_competition
Predation- http://www.eoearth.org/article/Predation
Mutualism- http://www.eoearth.org/article/Mutualism
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- define competition, exploitative competition and interference competition
- identify and explain examples of exploitative and interference competition from a variety of environments
- define predation (narrow and broad sense), herbivory, and parasitms
- identify and explain examples of predation, herbivory, and parasitism from a variety of environments
- identify examples of morphological and behavioral adaptations that animals have to help capture their food
- identify examples of morphological, biochemical, or behavioral adaptations that animals have to protect them from predators
- identify and explain examples of mutualisms from a variety of habitats
- explain the results of Connell's experiment examining competition between two species of barnacles (Fig. 54.3) and Paine's experiment examining predation by the starfish Pisaster (Fig. 54.15)
- define a keystone species and an ecosystem engineer and provide examples of each.
Past Test Questions (answers at bottom of post)
In the southeastern United States, a weedy plant called Kudzu has caused a great deal of problems. Because Kudzu has such high growth rates it is able to rapidly overgrow buildings and other plants.
1. Which of the following would best describe the ecological relationship between Kudzu and a species of pine tree that is commonly overgrown by Kudzu?
(a) mutualism
(b) parasitism
(c) exploitative competition
(d) herbivory
(e) none of the above
Answer- 1. c
Tuesday, February 2, 2010
Human Population Growth
Because we missed a class for the snow day, I will not be able to give a lecture on human population growth. The good news, of course, is that you are still responsible for the expected learning outcomes associated with this topic (listed at the bottom of this post). You should be able to get all of the information you need from this post and from the readings I have listed here.
I have spent a lot of time telling you that exponential growth is an unrealistic model of population growth. Interestingly, human populations have experienced exponential-like growth. How can this be?
What makes humans different from other species?
In other species per capita birth rates and per capita deaths rates are density dependent. However, as human populations have increased there has been no corresponding decline in per capita birth rates or increase in per capita death rates. What makes humans different from other species?
Humans have the ability to alter their environment so that they can avoid the density dependent effects on birth and death rates. 1) Humans have increased food production by improvements in agriculture (e.g., irrigation, fertilization, mechanized farming, genetically improved crops). 2) Humans have been able to decrease death rates by improvements in medicine and public health (things as simple as not pooping in the water you drink helps a lot!). 3) Humans have elimnated most human predators (ocassionally, someone gets killed by a shark or a mountain lion).
Where is human population growth occuring?
The rates of human population growth are not the same in all regions. Today, human populations are increasing in size much faster in developing countries (e.g., Mexico, other countries in Central America, Africa, and Southeast Asia) than they are in developed countries (e.g, USA, Canda, Western Europe). The figure at the top of this post shows the patterns of population growth in developed and developing nations.
Thus we see that populations are increasing most rapidly in the countries that are least able to deal with a rapidly increasing population. See "Population Challenges-The Basics" that can be downloaded from the Population Institute's website.
http://www.populationinstitute.org/population-issues/index.php
Human Population Growth Problem?
There is a great deal of debate about whether increasing human populations are a problem or not, and if they are what should be done about it. Unfortunately, we don't have time to discuss this issue in very much detail in class. My personal opinion is that we have too many people consuming too many resources and the last thing that we need are billions more people living on the planet. This is an issue that I am always intersted in talking more about if you would like to chat.
Further Reading
The section on Human Population Growth in your textbook is quite good.
Also see the article "Human Population Explostion" from the EoE.
http://www.eoearth.org/article/Human_population_explosion
Both of these contain a good discussion of the "demographic transition".
Really Cool Video
Here is a link to a YouTube video on "World Population" The first minute and a half or so is a little boring, so you can skip over it if you wish. However, I think the animation showing when and where human population growth has been occuring is really cool.
http://www.youtube.com/watch?v=4BbkQiQyaYc
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- describe patterns of human population growth in developed and developing nations
- discuss some reasons why the pattern of population growth in humans is so different from that in other species
- describe the demographic transition
- discuss their own personal view of human population growth.
Past Test Questions (answers at bottom of post)
1. In developing countries, why have per capita birth rates not decreased as human populations have increased in size?
(a) because we have increased rates of food production
(b) because of the improvements in education of women
(c) because of improvements in medical care
(d) a and c
(e) a, b, and c
2. Why do some people consider the high growth rates of human populations in developing countries to be of concern?
(a) because many people are born into conditions that do not provide them enough food
(b) because many people are born into conditions without clean water and adequate sanitation
(c) because increasing population sizes have led to increasing habitat destruction
(d) a, b, and c
(e) none of the above
answers- 1.d, 2.d
Population Growth- Final Thoughts
We have discussed how population ecologists have tried to develop a model (the logistic growth model) that helps them to understand the factors that affect population growth.
We talked a lot about the graph plotting how the population size would vary over time in a population that started much smaller than the carrying capacity (the s-curve). Why does logistic growth show this pattern?
Initially, the population is growing slowly. When populations are small the per capita growth rate is large but because there are only a few individuals in the population rN is small. Over time, the population growth rate increases becasue populations are still small enough that r is still relatively large and now a larger N allows rN to be a bigger number. Population growth rate starts to slow as populations reach their carrying capacity because in large populations the per capitat growth rate is small and even though N is large rN is small. When the population reaches its carrying capacity b = d, so population growth stops.
Density Dependent Population Regulation
We notice that populations don't keep increasing in size forever. That is because populations are naturally self regulating. As population size increases the per capita birth rate declines for the biological reasons that we discused earlier. (When a parameter decreases as population size increases that parameter is said to be negatively density dependent. As population size increases the per capitat death rates increase for the biological reasons that we discussed earlier. (when a parameter increases as the population size increases that parameter is said to be positively density dependent). Thus, the per capita birth and death rates are naturally density dependent in such a way that eventually causes the population size of species to stop growing.
Past Test Questions (answers at bottom of post)
1. In logistic growth, what is the per capita growth rate when N = 1/2K?
(a) rmax
(b) 2(rmax)
(c) ½ (rmax)
(d) it is a maximum
(e) you can not answer this questions with the information provided.
2. How can you calculate the population growth rate?
(a) subtract B from D
(b) add the per capita death rate to the per capita birth rate
(c) multiply r by N
(d) divide dN/dt by N
(e) a and c
3. Why don’t we expect raccoons to show exponential growth?
(a) per capita birth rates increase as population sizes increase
(b) per capita death rates increase as population sizes increase
(c) per capita birth rates decrease as population sizes increase
(d) b and c
(e) none of the above
4. Which of the following are true when populations are at their carrying capacity?
(a) dN/dt > 0
(b) r < 0
(c) b = d
(d) B > D
(e) a and d
answers- 1.e, 2.c, 3.d, 4.c
We talked a lot about the graph plotting how the population size would vary over time in a population that started much smaller than the carrying capacity (the s-curve). Why does logistic growth show this pattern?
Initially, the population is growing slowly. When populations are small the per capita growth rate is large but because there are only a few individuals in the population rN is small. Over time, the population growth rate increases becasue populations are still small enough that r is still relatively large and now a larger N allows rN to be a bigger number. Population growth rate starts to slow as populations reach their carrying capacity because in large populations the per capitat growth rate is small and even though N is large rN is small. When the population reaches its carrying capacity b = d, so population growth stops.
Density Dependent Population Regulation
We notice that populations don't keep increasing in size forever. That is because populations are naturally self regulating. As population size increases the per capita birth rate declines for the biological reasons that we discused earlier. (When a parameter decreases as population size increases that parameter is said to be negatively density dependent. As population size increases the per capitat death rates increase for the biological reasons that we discussed earlier. (when a parameter increases as the population size increases that parameter is said to be positively density dependent). Thus, the per capita birth and death rates are naturally density dependent in such a way that eventually causes the population size of species to stop growing.
Past Test Questions (answers at bottom of post)
1. In logistic growth, what is the per capita growth rate when N = 1/2K?
(a) rmax
(b) 2(rmax)
(c) ½ (rmax)
(d) it is a maximum
(e) you can not answer this questions with the information provided.
2. How can you calculate the population growth rate?
(a) subtract B from D
(b) add the per capita death rate to the per capita birth rate
(c) multiply r by N
(d) divide dN/dt by N
(e) a and c
3. Why don’t we expect raccoons to show exponential growth?
(a) per capita birth rates increase as population sizes increase
(b) per capita death rates increase as population sizes increase
(c) per capita birth rates decrease as population sizes increase
(d) b and c
(e) none of the above
4. Which of the following are true when populations are at their carrying capacity?
(a) dN/dt > 0
(b) r < 0
(c) b = d
(d) B > D
(e) a and d
answers- 1.e, 2.c, 3.d, 4.c
Fun With Graphs- Quiz Yourself
Here are some questions that I have designed to let you know if you are understanding the graphs well enough to meet the course expected learning outcomes. I suggest that you do not try to answer these questions until you have thoroughly reviewed all of the information about the population ecology graphs. (I will put the answers for the multiple choice questions at the bottom of this post, for the others you need to find out whether your answers are correct or not).
1. What are the correct axes for a graph showing how population growth rate depends on population size in logistic growth?
a) x- N y- t
b) x- N y- dN/dt
c) x- dN/dt y- N
d) x- dN/dt y- t
e) x- N y- r
2. Which of the following best describes the graph that shows how the per capita growth rate varies over time in exponential growth?
a) the per capita growth rate decreases over time
b) the per capita growth rate increases over time
c) the per capita growth rate does not change over time
d) the per capita growth rate increases until it reaches a maximum and then decreases to zero when the population reaches the carrying capacity
e) the per capita death rate is initially very negative and gets less negative over time.
3. What would I ask to make you draw this graph?
a) show how the population size varies over time in logistic growth when the initial population size is much smaller than the carrying capacity
b) show how the population growth rate depends on the population size in logistic growth when the intitial population is much smaller than the carrying capacity
c) show how the population size depends on population size in logistic growth when the initial population size is much smaller than the carryuing capacity
d) show how the population size varies over time in logistic growth when the intitial population is much larger than the carrying capacity
4. What are the axes of a graph showing how the per capita growth rate depends on the population size in logistic growth?
a) x- logistic y- exponential
b) x- logistic y- r
c) x-N y-r
d) x-r y-N
e) x-N y-dN/dt
5. Which of the following is true when populations are at their carrying capacity?
a) N = 100 individuals
b) dN/dt = 0
c) b > d
d) b = d
e) b and d
6. Describe how the population growth rate varies over time in logistic growth when the intial population size is much larger than the carrying capacity.
7. Draw the graph that shows how the population size varies over time in logistic growth when the initial population size is much smaller than the carrying capacity.
Answers. 1.b, 2.c, 3.b, 4.c, 5.e
1. What are the correct axes for a graph showing how population growth rate depends on population size in logistic growth?
a) x- N y- t
b) x- N y- dN/dt
c) x- dN/dt y- N
d) x- dN/dt y- t
e) x- N y- r
2. Which of the following best describes the graph that shows how the per capita growth rate varies over time in exponential growth?
a) the per capita growth rate decreases over time
b) the per capita growth rate increases over time
c) the per capita growth rate does not change over time
d) the per capita growth rate increases until it reaches a maximum and then decreases to zero when the population reaches the carrying capacity
e) the per capita death rate is initially very negative and gets less negative over time.
3. What would I ask to make you draw this graph?
a) show how the population size varies over time in logistic growth when the initial population size is much smaller than the carrying capacityb) show how the population growth rate depends on the population size in logistic growth when the intitial population is much smaller than the carrying capacity
c) show how the population size depends on population size in logistic growth when the initial population size is much smaller than the carryuing capacity
d) show how the population size varies over time in logistic growth when the intitial population is much larger than the carrying capacity
4. What are the axes of a graph showing how the per capita growth rate depends on the population size in logistic growth?
a) x- logistic y- exponential
b) x- logistic y- r
c) x-N y-r
d) x-r y-N
e) x-N y-dN/dt
5. Which of the following is true when populations are at their carrying capacity?
a) N = 100 individuals
b) dN/dt = 0
c) b > d
d) b = d
e) b and d
6. Describe how the population growth rate varies over time in logistic growth when the intial population size is much larger than the carrying capacity.
7. Draw the graph that shows how the population size varies over time in logistic growth when the initial population size is much smaller than the carrying capacity.
Answers. 1.b, 2.c, 3.b, 4.c, 5.e
Monday, February 1, 2010
Population Ecology- Logistic Growth
We are trying to develop a mathematical model that helps us to understand patterns of population growth. So far our first attempt, the exponential growth model, did not help us to understand population growth (for reasons that I hope that you understand by now).
The "Real" world
In our attemtp to think about population growth in the real world, we attempted to examine how per capitat birth rates and per capitat death rates should vary as population size varies. The model that describes this pattern of growth is known as the logistic growth model. It is important to realize that although this model is much more realistic, and therefore useful to us, than the exponential growth model, the logistic growth model still only exmaines what I call "the theoretical real world". That is, this model applies to our ideas about how populations should generally behave and do not thus relate directly to studying the population sizes of white tailed deer in central Texas or parrot fish on a coral reef in Fiji. These real world situations are much harder to understand than the simple "idealized" populations that I am talking about in BIOL 1404. You can take an Advanced Population Biology course if you want to learn more about how to apply these models to the "real real world".
Logistic Growth
We have discussed why, in the real world, r should decrease as population sizes increase. If this is the case then there is a population size at which the per capita birth rate equals the per capita death rate. We call this population size the carrying capacity.
1) When populations are smaller than the carrying capacity we expect them to increase in size until they reach the carrying capacity.
2) When populations are larger than carrying capacity we espect them to decrease in size untile they reach the carrying capacity.
3) When the population size equals the carrying capacity we expect no change in the size of the population.
The logistic growth equation is a mathematical equation developed by biologists to describe patterns of population growth consistent with the ideas above. Before focusing on the biological isights that we can gain from the logistic growth model (the real purpose of everything we have been doing) it is important to really understand patterns of logistic growth. Hopefully, this powerpoint presentation will help you understand these patterns better.
Powerpoint Presentation
Click here for a powerpoint presentation entitled "Fun With Graphs- Logistic Growth"
http://www.slideshare.net/secret/gyB3cjnSplLw41
Expected Learning Outcomes
By the end of this course a fully engaged students should be able to
- define the carrying capacity
- draw, and interpret the following graphs associated with logistic growth
-how population size changes over time in logistic growth when the initial population size is much smaller than the carrying capacity
-how the population size changes over time in logistic growth when the initial population size is much larger than the carrying capacity
-how population growth rate changes over time in logistic growth when the initial population size is much smaller than the carrying capacity
-how the population growth rate changes over time in logistic growth when the initial population size is much larger than the carrying capacity
-how the per capita growth rate varies over time in logistic growth
-how the population growth rate varies over time in logistic growth
- discuss the causes for the shape of the s-curve (this answer will need to include a discussion of both math and biology)
- discuss the factors that regulate population size, be able to distinguish between density dependent and density independent factors that regulate population growth and give examples
Fun With Graphs- Exponential Growth
How do I know which graph to draw?
1) In the population ecology portion of this course we will be discussing two models of population growth- exponential growth and logistic growth. Thus, you need to know which growth model you are describing before you know which graph to draw.
2) You can't draw a graph until you know what the axes are.
Hopefully, this is a review, but it is probably worth talking about. The x-axis (the horizontal axis) is known as the independent variable. The y-axis (the vertical axis) is the dependent variable. Changing the value of the independent variable results in a change in the dependent variable. Id DOES matter which variable goes on which axis so try to get it right.
In population ecology there will be two main independent variables that we are interested in studying. Because we are interested in patterns of population growth, we will often want to observe how variables change over time. Time is always the independent variable, so it always goes on the x-axis. Sometimes we are interested in how parameters depend on population size. In this case, population size is always the independent variable.
Powerpoint Presentation
This powerpoint presentation "Fun With Graphs: Exponential Growth) reviews the graphs you are expected to be able to draw, understand, and interpret.
http://www.slideshare.net/secret/mavlOD8flFs67G
Exponential Population Growth
From the first lesson on Population Ecology we learned that the population growth rate (dN/dt) can be calculated as the product of the per capita growth rate (r) and the population size (N).
dN/dt = rN
This is the fundamental equation describing population growth and this equation is always true.
If we want to use this equation to analyze how population sizes change over time, then it makes sense to start by examining the simplest formulation of this equation which occurs when the per capita growth rate is constant. The equation dN/dt = rN when r is constant is known as the exponential growth equation and this equation describes a patter on growth known as exponential growth.
The graph plotting how population size changes over time is shown in the Exponential Growth article. This graph shows an exponential growth curve (sometimes known as the "j-curve"). If you have questions about why the graph has this shape let me know and I will try to explain it more thoroughly.
It is important that you are able to look at this graph and determine all of the information held in the graph. The exponential growth curve allows us to discuss how two parameters change over time- 1) the population size (shown by the x-axis) and 2) the population growth rate (shown by the slope of the line). I find that it is easier to discuss only one parameter at a time so let's start with the population size.
1) Over time, the population size increases (we know this because the line has a positive slope).
Now let's think about the population growth rate.
2) Over time, the population growth rate increases (we know this becasue the line gets steeper over time.
3) Over time, the rate at which the population growth rate increases over time, increases over time (we know this because the slope increases faster and faster over time).
Thus, if populations are growing exponentially then they keep increasing in size at an ever faster rate forever and ever.
Now try this-
Can you draw the following graphs?
1) plot how the population growth rate varies over time.
(hint- we have alredy described what this pattern will look like using words- just turn these words into pictures).
2) plot how the population growth rate depends on population size.
(hint- this graph is a little trickier, but we do have an equation that relates the two variables)
3) plot how the per capita growth rate varies over time.
(hint- think about what the basic assumption we made aboiut exponential growth)
4) plot how the per capita growth rate
(see the hint from number 3)
Exponential Growth is Unrealistic
Because population sizes keep increasing at ever faster rates for ever, exponential growth does not seem to be an accurate description of population growth in most animals, plants, and microbes. If this is an unrealistic model then why did I teach it to you? I started with exponential growth becasue it is the simplest model of population growth and scientists always like to describe the world using the simplest models that they can.
Obviously, in this case we have started with a model that is too simple to realistically describe the world. What is wrong with the exponential growth model? The fundamental assumption we made about exponential growth is that the per capita growth rate is constant. This must not be a realistic assumtpion.
It is important that you understand, and are able to explain, both the mathematical reasons and biological reasons that exponential growth is an unreasonable model of population growth. I tried to explain biologically why exponential growth is unrealistic in the "Exponential Growth" article and the attached Powerpoint presentation so take a look at those.
Suggested Readings
Here are some articles you should look at from the Encyclopedia of the Earth. I wrote these so they are brilliant!!!
Population Ecology http://www.eoearth.org/article/Population_ecology
Exponential Growth http://www.eoearth.org/article/Exponential_growth
Logistic Growth http://www.eoearth.org/article/Logistic_growth
Carrying Capacity http://www.eoearth.org/article/Carrying_capacity
Intraspecific Competition http://www.eoearth.org/article/Intraspecific_competition
Powerpoint Presentation
Click here for the Powerpoint presentation "Why is Exponential Growth Unrealistic?"
http://www.slideshare.net/secret/IDPugQtl2wvONv
Expected Learning Outcomes
By the end of this course a fully engaged student should be able to
- draw and interpret the following graphs associate with exponential growth
a) how population size change over time in exponential growth
b) how population growth rate varies over time in exponential growth
c) how the population growth rate depends on the population size
d) how per capita growth rate changes over time in exponential growth
e) how per capita growth rate depends on population size
- explain why exponential growth is an unrealistic pattern of growth for most species
- define and explain the carrying capacity
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