Test 2 Metabolism Modified True/False



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Test 2 - Metabolism

Modified True/False

Indicate whether the sentence or statement is true or false. If false, change the identified word or phrase to make the sentence or statement true.

____ 1. Aerobic cellular respiration requires that oxygen be present. _________________________

____ 2. Cellular respiration results in the relatively rapid, uncontrolled release of energy from a molecule of glucose to produce ATP for use by cells for various functions. _________________________

____ 3. Enzymes lower activation energy. _________________________

____ 4. The ultimate metabolic waste product from the metabolism of nucleic acids and proteins is ammonia. _________________________

____ 5. The organelle that is unique to eukaryotic photoautotrophs is the chromoplast. _________________________

____ 6. Light is a form of energy that travels in wave packets called protons. _________________________

____ 7. The reactions of carbon fixation depend on the light reactions to supply ATP and NADPH. _________________________

____ 8. Most plants are green because that is the colour of light they need for photosynthesis. ___________________________________________________________________________

Multiple Choice

Identify the letter of the choice that best completes the statement or answers the question.

____ 9. During aerobic cellular respiration, which of the following is the most common type of reaction to take place in the cell?



a.

hydrolysis

d.

redox

b.

condensation

e.

dehydration

c.

neutralization

____ 10. Glycolysis can best be described as which of the following kinds of pathways?



a.

catabolic and synthetic

d.

anaerobic and catabolic

b.

glycolytic and aerobic

e.

anaerobic and anabolic

c.

aerobic and catabolic

____ 11. Where in the electron transport chain does the energy come from for the synthesis of ATP?



a.

the combination of hydrogen ions, electrons, and oxygen to form water

b.

the breakdown of water

c.

the cytochromes

d.

an electrochemical gradient across the inner mitochondrial membrane

e.

oxygen

____ 12. At the end of the electron transport chain, the final product is which of the following?



a.

cytochrome oxidase

d.

ATP

b.

pyruvate

e.

water

c.

co-enzyme A

____ 13. Oxygen that is consumed during cellular respiration is returned to the environment once it has been combined with which of the following substances?



a.

ATP or inorganic phosphates

d.

glucose or nitrogen

b.

elemental carbon

e.

carbon or hydrogen

c.

nitrates or sulfates

____ 14. In which of the following forms is energy immediately made available for use by living cells?



a.

ATP

d.

fats

b.

glucose

e.

starch

c.

ADP

____ 15. Anaerobic respiration is less efficient than aerobic respiration for which of the following reasons?



a.

less ATP is produced in anaerobic respiration

b.

aerobic respiration allows for rapid oxidation during strenuous exercise

c.

blood carries more than enough oxygen to support aerobic respiration

d.

only bacteria and yeast use anaerobic respiration

e.

most animals have to breathe air in order to survive

____ 16. A particular organism releases carbon dioxide and alcohol as its end products. The organism is most likely which of the following?



a.

an animal

d.

an alga

b.

a green plant

e.

a yeast

c.

a virus

____ 17. From the following list, which is the best definition of anaerobic respiration?



a.

respiration by a particular species of yeast

b.

cellular metabolism with adequate oxygen

c.

cellular metabolism in the absence of oxygen

d.

metabolism in the presence of ample oxygen

e.

a form of respiration making use of cytochromes

____ 18. Amino acids can enter cellular respiration, but first they have to be



a.

deaminated

d.

converted to glucose

b.

hydrolyzed

e.

converted into protein

c.

phosphorylated

____ 19. The alternate fates of pyruvate in various organisms is primarily due to



a.

optimizing the concentration of important biochemical intermediates

b.

regenerating NAD+ for further reduction in the cytoplasm

c.

maximizing ATP production in the mitochondrion

d.

maximizing electron flow through the electron transport chain

e.

none of the above

____ 20. Which of the following most accurately describes the location of chloroplasts in the leaves of most plants?



a.

the palisade mesophyll tissue only

b.

the palisade and spongy mesophyll tissue only

c.

the upper epidermis and palisade mesophyll tissues only

d.

the upper epidermis, palisade, and spongy mesophyll tissues only

e.

the palisade and spongy mesophyll tissues, and the guard cells of epidermal tissue

____ 21. In terms of the spectrum of white light, which of the following is the most effective for photosynthesis?



a.

geen light

d.

yellow light

b.

red light

e.

violet light

c.

blue light

____ 22. The fact that 18O is found in the oxygen produced by photosynthesis, but not in the carbohydrate products, when photosynthesizing organisms are water labelled with 18O leads to which of the following conclusions?



a.

the oxygen in the carbohydrate may come from carbon dioxide

b.

both water and carbon dioxide are sources of gaseous oxygen

c.

carbon dioxide is a possible source of oxygen gas

d.

oxygen from water ends up in the carbohydrates

e.

water is the only possible source of oxygen gas

____ 23. Land plants get the CO2 they need for photosynthesis mostly from



a.

breakdown of starch

d.

carbon fixation in the roots

b.

carbonates in the soil

e.

water via the roots

c.

the atmosphere

____ 24. Which one of the following is not a characteristic of the light reactions?



a.

electrons are displaced

b.

carbon fixation happens

c.

reduction happens

d.

energy is converted from a physical to a chemical form

e.

they take place in the thylakoids of chloroplasts

____ 25. Which of the following statements concerning the Calvin cycle is true?

I. ATP molecules are needed to keep the reactions going

II. the process makes NADPH + H+

III. reduction occurs

IV. oxygen is a product

V. photophosphorylation occurs

VI. carbon fixation occurs

VII. takes place in the thylakoids of chloroplasts

a.

IV, V and VII

d.

II, IV, and V

b.

I, VI, and VII

e.

I, II, III and VI

c.

I, III, and VI

____ 26. Photophosphorylation specifically refers to the



a.

synthesis of glucose via carbon fixation

b.

splitting water as a result of light

c.

synthesis of ATP by photolysis

d.

reduction of NADPH by electron transport

e.

synthesis of ATP using light

____ 27. In photosynthesis, the function of water is to



a.

supply free electrons

d.

supply hydrogen ions

b.

supply oxygen

e.

buffer pH

c.

activate chlorophyll

____ 28. What does carbon dioxide combine with during photosynthesis?



a.

G3P

d.

NAD+

b.

ribulose bisphosphate

e.

water

c.

ribulose

____ 29. What is the name of the first enzyme in the C3 pathway?



a.

ribulose bisphosphate carboxylase/oxygenase (rubisco)

b.

phosphoenolpyruvate carboxylase (PEP carboxylase)

c.

oxaloacetate carboxylase (OAA carboxylase)

d.

succinate dehydrogenase

e.

pyruvate kinase

____ 30. Photorespiration occurs principally because of



a.

elevated carbon dioxide levels in the leaves due to photosynthesis

b.

elevated oxygen levels in the leaves due to cellular respiration

c.

an increase in oxygenase activity relative to carboxylase activity as temperature increases

d.

an increase in light intensity

e.

none of the above

____ 31. C4 refers to



a.

Canada, Chile, China and Cambodia, the countries trying to reduce their CO2 emissions

b.

the number of carbons is takes to produce one molecule of PGA

c.

the number of different types of cells needed to run the Calvin cycle

d.

the number of carbons in the first product of the Calvin cycle

e.

the number of carbons joined together when PEP is carboxylated

____ 32. No Question, be sure to leave this blank on the ScanTron

____ 33. Spatial separation refers to

a.

the Calvin cycle

d.

cellular respiration

b.

the C4 pathway

e.

oxidative phosphorylation

c.

the CAM pathway

____ 34. There is a cost associated with the C4/CAM pathways. This cost consists of



a.

NADPH

d.

ATP

b.

NADH

e.

none of the above

c.

cytochrome oxidation

Use the following information to answer questions 35 and 36 only. Imagine you have five small glass jars that are sealed to the atmosphere. All the jars are filled with a bicarbonate solution (as a source of carbon dioxide) and an indicator. The differences between each jar are described below:

Jar #1: Has a small fish.

Jar #2: Has one small fish in addition to some aquatic plants.

Jar #3: Has three small fish in addition to some aquatic plants.

Jar #4: Has some aquatic plants.

Jar #5: Has some aquatic plants, but the jar is completely surrounded by aluminum foil.

The indicator shows you how much carbon dioxide is in each jar. The following table shows the relative amounts:



Colour of pH indicator solution

Relative amount of carbon dioxide

red

high

green

medium (equivalent to atmosphere)

blue

low

The following table shows the results of an experiment where the tubes were allowed to stand under natural light for several hours.



Observation

Jar #1

Jar #2

Jar #3

Jar #4

Jar #5

Starting colour of indicator

green

green

green

green

green

Final colour of indicator

red

green

red

blue

green

____ 35. The following are statements regarding the above results:

I. respiration is taking place in all five test tubes

II. respiration is exceeding photosynthesis in Jar#3

III. photosynthesis is occurring in Jar#5

IV. the lowest concentration of carbon dioxide is found in Jar#2


Which of the above statements are correct?

a.

II and III

d.

II and IV

b.

I and II

e.

III and IV

c.

I and IV

____ 36. Under what circumstance would the indicator change from green to blue in Jar#5?



a.

taking away some of the aquatic plants

b.

illuminating the jar with green light

c.

adding more fish to the jar

d.

adding more aquatic plants to the jar

e.

taking the aluminum foil off of the jar

____ 37. Under what circumstance would the indicator change from red to green in Jar#3?



a.

removing some of the aquatic plants

b.

illuminating the jar with green light

c.

adding some aquatic plants to the jar

d.

adding some fish to the jar

e.

covering the jar with tin foil


Completion (10 marks)

Complete each sentence or statement.

38. In comparing the structure and function of the mitochondrion and chloroplast, the following can be noted. The mitochondrion has an inner membrane called the ____________________. One of the functions of this inner membrane is ___________________________________. The hydrogen ion reservoir is located in the ______________________________ and ATP is synthesized in the ____________________. In the chloroplast, electron transport takes place on membranes of the ____________________, and one of its functions is ________________________________________. The hydrogen ion reservoir is located in the ____________________ and ATP synthesis occurs in the ____________________. In order to facilitate reproduction, independent of cell division, both of these organelles have _________________________ and _________________________.



Matching

Match each item with the correct statement below.

a.

cell membrane

e.

chloroplast

b.

nucleus

f.

cytoplasm

c.

intermembrane space

g.

outer mitochondrial membrane

d.

mitochondrial matrix

h.

inner mitochondrial membrane

____ 39. Where does glycolysis occur?

____ 40. Where does the oxidation of pyruvate occur?

____ 41. Where does the Krebs cycle occur?

____ 42. Where is the electron transport chain located?

____ 43. What membrane does glucose have to cross?

____ 44. Where does the most substrate level phosphorylation occur?

____ 45. Where is most NADH oxidized to NAD+?

____ 46. What membrane do protons cross in the synthesis of ATP?

Match each item with the correct statement below.

a.

ground state

g.

photosystem I

b.

excitation

h.

photosystem II

c.

fluorescence

i.

noncyclic electron flow

d.

primary electron acceptor

j.

Z protein

e.

antenna complex

k.

photophosphorylation

f.

reaction centre

l.

cyclic electron flow

____ 47. The release of energy as light as an electron returns to ground state.

____ 48. The absorption of energy by an electron.

____ 49. The lowest possible potential energy level of an electron.

____ 50. Photon-energized electrons move to produce ATP and NADPH.

____ 51. Compound that is reduced by an excited chlorophyll electron.

____ 52. Contains chlorophyll P680.

____ 53. Transmembrane protein of chlorophyll a that absorbs light energy.

____ 54. Contains chlorophyll P700.

____ 55. Web of chlorophyll molecules that transfers energy to a reaction centre.

____ 56. Light-dependent formation of ATP.

____ 57. Photon-energized electrons move to produce only ATP.

____ 58. Protein that helps split water into hydrogen ions, oxygen and electrons.
Short Answer – point form answers are adequate.



  1. Explain, in a general way, how fats can be used to generate energy. (4 marks)



  1. What are the pigments most commonly found in the chloroplasts of leaves in higher plants? (2 marks) What are the advantages, if any, to a plant having several different pigments? (2 marks)

61. Photosystem I usually converts most of the light energy it receives to ATP and NADPH by noncyclic electron flow. There are times when some of the energy is used by cyclic electron flow.

a. What is cyclic electron flow? (2 marks)

b. Why is it called 'cyclic'? (1 mark)


c. At what times does cyclic electron flow occur? (2 marks)

62. You are touring a local greenhouse and you notice that many of the plants in one of the rooms of the greenhouse are not as large when compared to the same plants being grown in other parts of the greenhouse. You speak with the manager who says s/he has been having a problem recently with growing plants in this particular room. Later in the conversation you learn that the manager has looked at factors such as light levels, temperature and soil nutrients, yet all these are the same in both rooms. What factors would you suggest testing for, and how would each of these factors affect the growth of plants?



Essay:

63. Choose only one of the following two questions, and write a short essay that answers the question.

Choice 1 Compare and contrast C4 and CAM photosynthesis in terms of their abilities to counter the process known as photorespiration.

Choice 2 Imagine you are a molecule of glucose inside a cell. Describe your journey as you are converted into carbon dioxide and energy, and how the molecule in your bonds is converted to energy useful for cellular reactions. It is not necessary to name all the intermediates and enzymes, but try to point out the important points as you go along.

64. Imagine that an extraterrestrial life-form has been recovered from a meteorite by a deep space probe that has a ravenous appetite for sand. Your job is to come up with a preliminary analysis of its bioenergetic pathway. On close examination you note that the biochemical pathway employed by this creature has some features in common with your own. You note that the alien has a basic cellular structure similar to that of Earth-based creatures. It has what you would consider to be a cytoplasm, nucleus, and other basic organelles. In addition, the creature appears to be capable of using oxygen in the course of its metabolism. Following a rigorous biochemical analysis, you note the following points:

a. A glycolysislike process begins with the alien's basic food stuff of sand particles. Specifically, the first molecule in the pathway contains 256 silicon atoms (Si256).

b. In the process of metabolizing the Si256, you note that the creature uses up 50 energy- carrying molecules that you have named ZTP (since it is an unknown triphosphate-bearing molecule that gives the creature 'zip') in converting the Si256 to 4 molecules of Si64. Also, in the process of breaking down one molecule of Si256, ten (10) molecules of an electron-carrying substance you have called EADH are formed.

c. Each Si64 molecule is broken into two molecule with the creation of 5 ZTP molecules and 4 EADH molecules. Each molecule of Si64 gives off four (4) SiO2 molecules in this step (Si30 left).

d. Each Si30 goes through a cyclic process in an organelle similar in structure to our own mitochondrion in which the Si30 is completely oxidized to SiO2. In the process, 8 ZTP, 4 EADH, and 7 EADH2 are released.

e. Each molecule of EADH is converted to 10 ZTP, and each molecule of EADH2 is converted to 5 ZTP. (NOTE: Each EADH formed in step (b) is converted to two molecules of EADH2 when it passes into the mitochondrion-like structure.)
How many ZTP and SiO2 molecules will be formed in the complete metabolism of 1 molecule of Si256? Show your work in the space below.

Test 2 - Metabolism

Answer Section

MODIFIED TRUE/FALSE

1. ANS: T REF: K/U OBJ: 2.1

LOC: MP1.06

2. ANS: F

relatively slow

controlled

REF: K/U OBJ: 2.1 LOC: MP1.06

3. ANS: T REF: K/U OBJ: 2.2

LOC: MP1.05

4. ANS: T REF: K/U OBJ: 2.3

LOC: MP1.05

5. ANS: F, chloroplast REF: C OBJ: 3.1

LOC: MP1.05

6. ANS: F, photons REF: C OBJ: 3.2

LOC: MP2.01

7. ANS: T REF: K/U OBJ: 3.2

LOC: MP1.01

8. ANS: F, because the combination of pigments absorbs light at the blue and red end of the spectrum, and green is left to reflect back to our eyes.

REF: MC OBJ: 3.3 LOC: MP3.03

MULTIPLE CHOICE

9. ANS: D REF: K/U OBJ: 2.1 LOC: MP1.04

10. ANS: D REF: K/U OBJ: 2.2 LOC: MP1.06

11. ANS: D REF: K/U OBJ: 2.2 LOC: MP1.05

12. ANS: E REF: K/U OBJ: 2.2 LOC: MP1.05

13. ANS: E REF: K/U OBJ: 2.2 LOC: MP1.05

14. ANS: A REF: K/U OBJ: 2.2 LOC: MP1.05

15. ANS: A REF: K/U OBJ: 2.2 LOC: MP1.06

16. ANS: E REF: K/U OBJ: 2.3 LOC: MP1.05

17. ANS: C REF: K/U OBJ: 2.3 LOC: MP1.06

18. ANS: A REF: K/U OBJ: 2.3 LOC: MP1.05

19. ANS: B REF: K/U OBJ: 2.3 LOC: MP1.05

20. ANS: E REF: C OBJ: 3.1 LOC: MP2.05

21. ANS: C REF: C OBJ: 3.2 LOC: MP3.01

22. ANS: A REF: K/U OBJ: 3.2 LOC: MP1.05

23. ANS: C REF: C OBJ: 3.3 LOC: MP1.06

24. ANS: B REF: C OBJ: 3.3 LOC: MP1.04

25. ANS: C REF: C OBJ: 3.3 LOC: MP1.06

26. ANS: E REF: K/U OBJ: 3.3 LOC: MP1.05

27. ANS: A REF: K/U OBJ: 3.3 LOC: MP1.05

28. ANS: B REF: K/U OBJ: 3.3 LOC: MP1.05

29. ANS: A REF: K/U OBJ: 3.4 LOC: MP1.03

30. ANS: C REF: K/U OBJ: 3.4 LOC: MP1.03

31. ANS: D REF: I OBJ: 3.4 LOC: MP1.06

32. ANS: E REF: C OBJ: 3.4 LOC: MP2.03

33. ANS: B REF: C OBJ: 3.4 LOC: MP2.01

34. ANS: D REF: K/U OBJ: 3.4 LOC: MP1.05

35. ANS: B REF: I OBJ: 3.6 LOC: MP2.06

36. ANS: E REF: I OBJ: 3.6 LOC: MP2.06

37. ANS: C REF: I OBJ: 3.6 LOC: MP2.06



COMPLETION

38. ANS:

cristae (pl.), crista (s.)

electron transport / H+ ion transport / ATP synthesis

intermembrane space

matrix


thylakoid(s)

electron transport / H+ ion transport / ATP synthesis

thylakoid interior

stroma


DNA / ribosomes

ribosomes / DNA

REF: K/U, C OBJ: 3.6 LOC: MP1.06, MP2.05

MATCHING

39. ANS: F REF: K/U OBJ: 2.2 LOC: MP1.05

40. ANS: D REF: K/U OBJ: 2.2 LOC: MP1.05

41. ANS: D REF: K/U OBJ: 2.2 LOC: MP1.05

42. ANS: H REF: K/U OBJ: 2.2 LOC: MP1.05

43. ANS: A REF: K/U OBJ: 2.2 LOC: MP1.05

44. ANS: F REF: K/U OBJ: 2.2 LOC: MP1.05

45. ANS: H REF: K/U OBJ: 2.2 LOC: MP1.05

46. ANS: H REF: K/U OBJ: 2.2 LOC: MP1.05

47. ANS: C REF: C OBJ: 3.3 LOC: MP1.06

48. ANS: B REF: C OBJ: 3.3 LOC: MP1.06

49. ANS: A REF: C OBJ: 3.3 LOC: MP1.06

50. ANS: I REF: C OBJ: 3.3 LOC: MP1.06

51. ANS: D REF: C OBJ: 3.3 LOC: MP1.06

52. ANS: H REF: C OBJ: 3.3 LOC: MP1.06

53. ANS: F REF: C OBJ: 3.3 LOC: MP1.06

54. ANS: G REF: C OBJ: 3.3 LOC: MP1.06

55. ANS: E REF: C OBJ: 3.3 LOC: MP1.06

56. ANS: K REF: C OBJ: 3.3 LOC: MP1.06

57. ANS: L REF: C OBJ: 3.3 LOC: MP1.06

58. ANS: J REF: C OBJ: 3.3 LOC: MP1.06

SHORT ANSWER

59. ANS:

894 ZTP and 256 SiO2
Si256

|

| ¬ -50 ZTP (ii)



| ® 10 EADH ® 20 EADH2 ® 20 X 5 ZTP = +100 ZTP (ii) and (v)

¯

4 X Si64



|

| ® 4 X 4 SiO2 = 16 SiO2 (iii)

| ® 4 X 5 ZTP = 20 ZTP (iii)

| ® 4 X 4 EADH ® 16 X 10 ZTP = 160 ZTP (iii) and (v)

¯

8 X Si30



|

| ® 8 X 30 SiO2 = 240 SiO2 (iv)

| ® 8 X 8 ZTP = 64 ZTP (iv)

| ® 8 X 4 EADH ® 32 X 10 ZTP ® 320 ZTP (iv) and (v)

| ® 8 X 7 EADH2 ® 56 X 5 ZTP ® 280 ZTP (iv) and (v)
By adding up all of the underlined quantities, you will get a total of: 256 SiO2 and 894 ZTP.

REF: I OBJ: 2.2 LOC: MP2.03

60. ANS:

- Fat cannot be used directly to produce energy for a cell.

- First, fat must by hydrolyzed into glycerol and fatty acids. The glycerol can enter glycolysis after either being converted to glucose (via gluconeogenesis) or changed into dihydroxyacetonephosphate (DHAP).

- The fatty acids are broken down to two-carbon units (acetyl-CoA) in a process called b-oxidation, which can be fed directly into Krebs cycle.

REF: K/U OBJ: 2.3 LOC: MP1.05

61. ANS:

- The main pigments found in the leaves of higher plants are the chlorophylls (a and b and to a lesser extent c and d) and carotenoids.

- All but chlorophyll a are accessory pigments since only chlorophyll a is able to transfer the energy of light to the carbon fixation reactions.

- By having several different pigments a plant can absorb many different wavelengths of light most efficiently.

REF: K/U OBJ: 3.2 LOC: MP1.05

62. ANS:

a. In cyclic electron flow when photosystem I is struck by a photon with the correct energy, it will release electrons to the same carrier molecules as non-cyclic electron flow. These electrons move through a cytochrome system and cause hydrogen ions to move from the stroma across the thylakoid membrane to the inside of the thylakoid. The higher concentration of hydrogen ions inside the thylakoids can be used to make ATP. The chlorophyll molecule of PS I oxidizes the final electron carrier, gaining electrons to return to its reduced form.

b. The term 'cyclic' is used because the chlorophyll of PS I serves as both the electron donor and electron acceptor.

c. Cyclic electron flow would appear to occur when reserves of NADP+ are low, which would imply that levels of NADPH are high. These means there will be a shortage of electron acceptors, which results in electrons being accepted by the cytochrome electron carrier system.

REF: K/U OBJ: 3.3 LOC: MP1.05

63. ANS:

Factors that might also be considered could be

a. carbon dioxide level: If the carbon dioxide level is not adequate, then the rate of carbon fixation would be reduced and the plants would not increase in mass at the same rate.

b. water availability: If soil water levels are low then the stomata will tend to close, thereby limiting the amount of carbon dioxide available for photosynthesis. In addition water will be needed for photolysis so if water is limiting photosynthesis cannot occur at its maximal rate.

REF: I OBJ: 3.5 LOC: MP2.06



ESSAY

64. ANS:

Photorespiration is the oxidation of ribulose bisphosphate by rubisco and oxygen in light to form glycolate, which upon subsequent metabolism releases carbon dioxide. It is seen as a wasteful process both in terms of the carbon dioxide lost that could have become photosynthetic product, and the energy used along the way in releasing the carbon dioxide. This is a process that typically occurs in C3 plants such as many deciduous trees. Two mechanisms have evolved in higher plants to counteract the process of respiration, they are C4 and CAM photosynthesis.
C4 photosynthesis is one response some plants have evolved to the problem of photorespiration. Plants such a corn and sugar cane are examples of such plants. The enzyme that fixes carbon dioxide in these plants is PEP carboxylase in the mesophyll cells of the vascular bundles, and the first product formed is oxaloacetate, a four carbon compound. PEP carboxylase has no oxygenase function as rubisco has so there is no initial problem with photorespiration. The oxaloacetate is converted to malate and shuttled into the bundle sheath cells where it is decarboxylated to pyruvate with the release of carbon dioxide which can now be fixed by rubisco which is present in these cells. However, the oxygen concentration in these cells is very low so photorespiration has been effectively eliminated but at the expense of some ATP. C4 represents a spatial separation of photosynthesis.
CAM stands for crassulacean acid metabolism and is so named because it was first discovered in members of the plant family known as a the Crassulacea (e.g., cacti, pineapples, aloe). CAM is a way that some plants have evolved to avoid the problem of photorespiration. In this process the stomata of the plants are open during the night when it is cooler and less water can be lost. Carbon dioxide can enter, but the usual method of fixing the carbon, by using the energy produced in the light-dependent reactions obviously is not available. PEP carboxylase is used to fix carbon dioxide into organic acids which are stored in the vacuoles of the mesophyll cells. During the day, when the stomata are closed, the organic acids are decarboxylated and the carbon dioxide that is released is fixed by rubisco in the Calvin cycle which is located in the bundle sheath cells. There is a cost of some ATP in the process. CAM represents a temporal separation of photosynthesis.

REF: K/U OBJ: 3.4 LOC: MP1.05

65. ANS:

In the cytoplasm, the molecule of glucose (6C) would undergo the process of aerobic cellular respiration. The first stage of this process involves glycolysis, a multistep, enzyme-catalyzed series of reactions that occurs in the cytoplasm. In order to get glycolysis going, some ATP needs to be added, and so there is a small cost in starting the whole process. By the end of glycolysis, the molecule of glucose has been broken into two molecules of pyruvate (3C). In addition, four molecule of ATP have been produced (for net production of 2 ATP), as well as two molecules of NADH.


The pyruvate molecules then move to the inner mitochondrial membrane where a process called oxidative decarboxylation occurs. In this process each pyruvate molecule is joined onto a CoA unit, and a carbon dioxide (1C) is released. This results in the production of an acetyl-CoA (2C) and a molecule of NADH from each pyruvate.
The acetyl-CoA molecules are now in the mitochondrial matrix. At this point they enter the Krebs cycle, a multistep, enzyme-catalyzed pathway that loops back on itself. Each acetyl-CoA (2C) combines with a molecule of oxaloacetate (4C) to form citrate (6C). As citrate moves through the cycle, there are two points at which intermediate molecules are decarboxylated (lose carbon dioxide (1C)), three points at which NADH is produced, one point at which FADH2 is produced, and one point at which substrate level phosphorylation produces a molecule of GTP. At this point, all of the carbon atoms that were originally in glucose have been converted to carbon dioxide.
Most of the energy from the molecule of glucose is still in the molecules of NADH and FADH2. Electrons from NADH are passed to the enzyme NADH dehydrogenase, which is embedded in the inner mitochondrial membrane (a similar reactions occurs with FADH2, but it enters the chain further down, and the NADH from the oxidative decarboxylation of pyruvate is converted to FADH2 as it passes into the mitochondrion). The hydrogen that is released from the NADH is pumped to the inter membrane space, thus establishing a proton and pH gradient. The electrons move from electron carrier to electron carrier in the inner mitochondrial membrane in a series of redox reactions and ultimately combine with oxygen and protons at the cytochrome oxidase complex to form water. As electrons move along this pathway, more protons, from the dissociation of water, are pumped from the matrix to the intermembrane space, adding to the proton and pH gradient. The protons from the intermembrane space return to the matrix via special ATP synthase molecules embedded in the inner mitochondrial membrane. As they do so, they help to catalyze the formation of ATP from ADP and Pi. The theoretical yield from the complete oxidation of one molecule of glucose is 36 ATP, but the actual yield is closer to 30 ATP.

REF: K/U OBJ: 2.2 LOC: MP1.05
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