Pathways of Photosynthesis

Question 1

What is the adaptive purpose of photosynthesis?

Answer 1

Photosynthesizers must adapt to Earth’s variable climate.

Question 2

State the chemical equation of photosynthesis.

Answer 2

6CO2 + 12H2O + Light —> C6H12O6 + 6O2 + 6H2O

     REACTANTS                  PRODUCTS

Question 3

What is the status of CO2 concentrations in the atmosphere in relation to other gases?

Answer 3

CO2 concentration is low in the atmosphere.

Question 4

How much of the water that is absorbed by the plant used for photosynthesis?

Answer 4

Less than 1%

Question 5

A plant’s light availability is dependent on what conditions?

Answer 5

1. atmospheric conditions.
2. altitude
3. season
4. latitude

Question 6

What part of a plant is considered the major “organ” of photosynthesis?

Answer 6

leaves

Question 7

Describe the process of gas exchange in a plant during photosynthesis.

Answer 7

The stomata allows for gas exchange between the mesophyll and the atmosphere.

Question 8

Where are the chloroplasts found in the plant?

Answer 8

Mesophyll

Question 9

Where is the site of light reactions found in a plant?

Answer 9

thylakoids located in the chloroplast

Question 10

What is the process of the light reactions and what do they ultimately result in?

Answer 10

“Light striking chlorophyll within the chloroplasts.”

• Converts light energy into chemical energy for the plant.

Question 11

What are the two processes that occur when the light is absorbed by the chlorophyll.

*HINT: transfer & formation

Answer 11

1. A transfer of hydrogen (from H2O) and electrons cause NADP+ to convert to NADPH.
   The NADPH is used to energize Calvin Cycle
2. Formation of ATP from ADP: Phosphorylation

Question 12

What are the inputs and outputs of the light reactions.

Answer 12

Water enters –> LIGHT RXN –> produces oxygen

Question 13

What are the inputs and outputs of the Calvin Cycle?

AKA: Light independent or dark rxn

Answer 13

carbon dioxide enters –> DARK RXN –>produces sugar
(CH2O)
*Calvin Cycle uses NADPH & ATP from the light rxns.

Question 14

What is the initial step of the Calvin Cycle?

Answer 14

STEP A. Carbon Fixation: CO2 enters Calvin cycle attached to RuBP (5carbon ribulose biphosphate)
6 carbon sugar is unstable so it splits into two 3PGA (3-carbon phosphoglycerate)

Carbon fixation is catalyzed by enzyme: Rubisco

Question 15

What is the second step of the Calvin Cycle?

Answer 15

STEP B: Each 3PGA (2 total) receives phosphate from ATP.
NADPH donates electrons, reducing 3GPA to a sugar.
1 molecule of the sugar leaves the cycle to be used in other part of plant. Remaining sugar is used to rebuild RuBP.

Question 16

What is step three of the Calvin Cycle?

Answer 16

Regeneration of RuBP via leftover sugars from second step.

Question 17

What is Rubisco? What are the two substances Rubisco has an affinity for?

Answer 17

Rubisco is the enzyme responsible for carrying CO2 and O2. (Carbon dioxide & oyygen)

Question 18

What three (3) mechanisms convert CO2 (carbon dioxide) to carbohydrates during light-independent reactions?

Answer 18

a. 3-Carbon pathway “C3” (AKA Calvin Cycle)
b. 4-Carbon pathway “C4”
c. Crassulacean Acid Metabolism “CAM”

Question 19

Define:

Photorespiration

Answer 19

Using oxygen to produce a 3-carbon compound and 2-carbon compound.

Question 20

What properties are unique to photorespiration?

Compare to photosynthesis

Answer 20

Uses O2 (oxygen), produces 2-carbon and 3-carbon compounds, output = CO2 (carbon dioxide).

Fewer carbohydrates produced.

Short-term response to hot temperatures when stomata are closed.

Question 21

What properties are unique to photosynthesis?

Compare to photorespiration

Answer 21

Uses CO2 (carbon dioxide)

produces 3-carbon compounds

output = O2

Question 22

What properties do photosynthesis and photorespiration share? (similarities)

Answer 22

Both use rubisco.
Both do light reactions.
Both do calvin cycle
Both produce carbohydrates.

Question 23

What are plants called when they have a C3 pathway? Explain why.

Answer 23

They’re called “cool season” plants because the rate of photorespiration increases with rising temperatures.

As temp. rises, the stomata close, the rubisco uses up the oxygen and therefore can’t photosynthesize as there is no glucose.

Examples of C3 plants: onions, potatoes, spinach, wheat.

Question 24

What are two adaptations that arose in order to decrease photorespiration?

Answer 24

C4 and CAM pathways

Question 25

What is the specific adaptation for C4 photosynthesis?

Answer 25

Adaptation for hot environments.

Question 26

What are the two parts of unique leaf anatomy in C4 plants?

Answer 26

Mesophyll

Bundle Sheath cells (lie adjacent to the vein of the leaf and the mesophyll. )

Question 27

Where is the Calvin cycle found in C4 plants?

Where is CO2 (carbon dioxide) incorporated and how is this done?

Answer 27

Found in bundle sheath cells

CO2 is incorporated into 4-carbon compounds in mesophyll cells.

Question 28

In C4 plants what has a higher affinity for CO2 other than the enzyme, Rubisco?

Answer 28

PEP (phosphoenolpyruvate)

Question 29

What are some advantages of C4 pathways?

List examples of C4 plants.

Answer 29

Advantages: maintaining high carbon dioxide levels, even in dry environments.

Examples: corn, sugar cane, summer grasses.

Question 30

What is the specific adaptation for CAM photosynthesis?

Answer 30

Adaptation for dry environments

Question 31

What do CAM plants do differently than other plants?

Answer 31

They bring in CO2 (carbon dioxide) at night.

Stomata open at night so the rate of water loss is minimized.

Question 32

Where does the CAM pathway occur?

*cellular level

Answer 32

mesophyll chloroplasts