Lecture 8

Question 1

True or false? All CAM plants are succulents.

Answer 1

False

Question 2

What is special about the CAM plants?

Answer 2

Uses both C4 pathway and Calvin cycle but its separate temporally all within the same cell

Question 3

How does CAM photosynthesis work?

Answer 3

At night, they fix CO2
Day, decarboxylated and CO2 transferred to the Calvin cycle
Stomata closed during the day to reduce water loss

Question 4

How does the night portion of CAM photosynthesis work?

Answer 4

Fix CO2 using PEP carboxylase
Oxaloacetate is reduced to malate and stored in a large vacuole as malic acid

Question 5

How does the day portion of CAM photosynthesis work?

Answer 5

Decarboxylated and CO2 is transferred to the Calvin cycle.
It forms pyruvate and stored as starch

Question 6

True or false? CAM plants have lower photosynthetic efficiency.

Answer 6

True

Question 7

What are the three organelles used to get rid of the toxic waste produced by the binding of O2 and Rubisco?

Answer 7

Chloroplast
Peroxisome
Mitochondrion

Question 8

While trying to get rid of the toxic waste produced by binding O2 snd Rubisco, in which organelle is O2 being fixed?

Answer 8

Chloroplast

Question 9

In peroxisome, what happens to the O2?

Answer 9

It is just reacting, not fixed so it is not consumed

Question 10

Why is the process of dealing with toxic waste of oxygenase of Rubisco called photophosphorylation?

Answer 10

Oxygen is being consumed and CO2 is being produced from the salvaging of glycolate

Question 11

Where in photophosphorylation is CO2 being produced?

Answer 11

Mitochondrion

Question 12

In order, what are the products of the salvaging of glycolate?

Answer 12

Turns into glyoxylate then glycine

Question 13

How many times can net photosynthetic rate of C4 plants be more efficient higher than C3 plants?

Answer 13

3 or 4

Question 14

What is the first detectable product of C4 pathway?

Answer 14

Oxaloacetate

Question 15

What is a mobile intermediate and what is it in C4 plant?

Answer 15

When something can move about
Malate

Question 16

What are the two separate places of the C4 pathway?

Answer 16

Mesophyll cell and bundle sheath cell

Question 17

Where does teh carbon cycle take place in the C4 pathway?

Answer 17

Bundle sheath

Question 18

What enzyme fixes CO2 to PEP to form oxaloacetate?

Answer 18

Pep carboxylase

Question 19

What is advantageous about PEP carboxylase?

Answer 19

It has a higher affinity with CO2 than Ripubisco, only reacts to hydrated CO2 (HCO3-)

Question 20

What is special about phosphoanhydride bonds?

Answer 20

Releasing this bond will create a lot of energy like ATP

Question 21

What are the two products that oxaloacetate can be transformed into and how?

Answer 21

Malate by reduction
Aspartate by transamination

Question 22

How are the C4 pathway and Calvin cycle separated in C4 plants?

Answer 22

Spatially

Question 23

What happens in the bundle-sheath cells?

Answer 23

Decarboxylated to pyruvate and CO2
CO2 enters the Calvin cycle
Pyruvate returns to mesophyll and reacts with ATP
Regenerates PEP

Question 24

Are there granum in the bundle sheath and why?

Answer 24

No because the light reactions are in the mesophyll cell

Question 25

How does aspartane or malate move through the mesophyll to the bundle sheath?

Answer 25

Diffusion

Question 26

True or false? All C4 plants are monocots.

Answer 26

False

Question 27

What is Kranz anatomy?

Answer 27

The plant has two concentric layers of cells
Present in monocot plant leaves (C4)

Question 28

True or false? Mesophyll cells are exposed to air, so both O2 and CO2, but only reacts to hydrated CO2.

Answer 28

True

Question 29

What allows dispersion and diffusion of malate and aspartate between the mesophyll and bundle-sheath cells?

Answer 29

Plasmodesmata

Question 30

What is the amount of Rubisco that C4 plants has compared to C3 plants and why?

Answer 30

1/3 to 1/6 less
There isn’t a CO2 or O2 competition thanks to PEP carboxylase so there is no need for that many Rubisco

Question 31

How would a C3 plant fair in optimal conditions for C4 plants?

Answer 31

It would die

Question 32

How are C4 plants without Kranz anatomy and how does their photosynthesis work?

Answer 32

Photosynthesis occurs within the same cell. It has dimorphic chloroplasts within the same cell. They carry out C4 carboxylation and the Calvin cycle.
They have equivalent mesophyll and bundle-sheath cells
Chloroplast seperate do either periphery vs centre or top and bottom

Question 33

What are dimorphic chloroplast?

Answer 33

Chloroplast separated in the same cell

Question 34

What are C3 plants limited by to be just as good as C4 plants in higher temperatures?

Answer 34

Limited by CO2, heat rising and energy cost to photosynthetic apparatus (N)

Question 35

In which type of climate do C3 plants perform equally well or even better then C4 plants while doing photosynthesis?

Answer 35

Cool climate

Question 36

What is the cost of C4 pathway compared to C3 photosynthesis?

Answer 36

2 more ATP
With a total pf 5 ATP versus E ATP

Question 37

Why have C4 plants not taken over the globe?

Answer 37

Fixation of Carbon has a larger energy cost then C3 plants of 2 ATP for each molecule of CO2 fixed per molecule of PEP

Question 38

What are the advantages that C4 plants have over C3 plants?

Answer 38

It maintains a high CO2/O2 ratio
Favours the work of Rubisco
If photorespiration occurs, the CO2 is released back to the mesophyll where it can be trapped by PEP carboxykase
CO2 does not escape the leaf
Hor climate advantage
No need to open their stomata so no loss of water
Not as many Rubisco
Less nitrogen use and more efficient nitrogen use
Less water use because more efficient water use

Question 39

How many times higher can the photosynthetic rate of C4 plants be compared to C3 plants?

Answer 39

3/4