Unit 3 AOS 2 Biochemical pathways

Question 1

What is the formula for photosynthesis?

Answer 1

6 CO2 + 12 H2O (sunlight) C6H12O6 + 6 O2 + 6 H2O

Question 2

What are the main cells in the leaves called?

Answer 2

Mesophyll cells

Question 3

What organelle is the site of photosynthesis?

Answer 3

Chloroplast

Question 4

What is the photosynthetic pigment in the chloroplast called?

Answer 4

chlorophyll

Question 5

What occurs to allow carbon dioxide to diffuse into the leaf (C3)?

Answer 5

The stomata open

Question 6

What is water transported through?

Answer 6

Xylem

Question 7

Where does the light-dependent stage occur?

Answer 7

Thylakoid membranes which make up the grana inside the chloroplast

Question 8

What is the purpose of the light-dependent stage?

Answer 8

Generate high energy coenzymes such as NADH and ATP

Question 9

What are the inputs of the light-dependent stage?

Answer 9

H2O
NADP+
ADP + Pi

Question 10

What is the purpose of photosynthesis?

Answer 10

To convert light energy into chemical energy

Question 11

What are the outputs of the light-dependent stage?

Answer 11

O2
NADPH
ATP

Question 12

What does NADPH do?

Answer 12

Transfer ions

Question 13

What does ATP do?

Answer 13

Transfer energy

Question 14

What are the two coenzymes that cycle through both stages of photosynthesis between their loaded and unloaded forms?

Answer 14

NADPH (NADP+)
ATP (ADP + Pi)

Question 15

What happens to the outputs of the light-dependent stage?

Answer 15

O2 is released
NADPH and ATP become inputs of the light-independent stage

Question 16

Where does the light-independent (Calvin cycle) stage occur?

Answer 16

Stroma of the chloroplast

Question 17

What are the inputs of the light-independent stage?

Answer 17

CO2
NADPH
ATP

Question 18

What are the outputs of the light-independent stage?

Answer 18

C6 H12 O6 (glucose)
NADP+
ADP + Pi
H2O

Question 19

What is the enzyme involved in the light-dependent stage?

Answer 19

Rubisco

Question 20

What is the problem with Rubisco?

Answer 20

Uses O2 as a substrate instead of CO2

Question 21

What process occurs instead of photosynthesis when O2 is used instead of CO2?

Answer 21

Photorespiration

Question 22

What factors contribute to whether Rubisco binds to CO2 or O2?

Answer 22

Substrate concentration
-Stomata will close if a plant needs to conserve water
-O2 will build up, leading to more photorespiration

Temperature
-Low temperatures, Rubisco is likely to bind to CO2
-High temperatures, Rubisco is likely to bind to O2

Question 23

What environment does photorespiration occur more in?

Answer 23

Hot and dry weather due to both substrate concentration and temperature

Question 24

Characteristics of C3 plants

Answer 24

-Possess no adaptations to reduce photorespiration
-Entire pathway occurs in a single mesophyll cell

Question 25

Characteristics of C4 plants

Answer 25

-Initial carbon fixation occurs in mesophyll cell, but the remaining Calvin cycle occurs in bundle-sheath cells -Initial carbon fixation uses PEP carboxylase (instead of Rubisco), which will not bind to O2 -Use more energy to undertake photosynthesis, but results in reduced photorespiration in hot environments

Question 26

Characteristics of CAM plants

Answer 26

-CAM plants open their stomata at night to bring in CO2 -Undergoes light-dependent stage during daytime -Controlled release of CO2 out of vacuoles ensures a high concentration of CO2 is maintained near Rubisco -CAM pathways use more energy, but is better in hot, dry environments

Question 27

What are the factors affecting the rate of photosynthesis (describe them)?

Answer 27

Light intensity - plateaus at a certain point due to other limiting factor Light colour - Every colour EXCEPT black, white or green Temperature - Enzymes optimal temperature is ideal, above enzymes denature pH - Same as temperature Carbon dioxide - Low CO2 is bad, as it can lead to greater photorespiration. Plateaus at certain point Water - Reduced can lead to greater photorespiration in C3 plants (rarely a limiting factor in itself) Enzyme inhibition - Many herbicides are inhibitors. Competitive reversible inhibitors can be overcome if the substrate concentration is continually increased

Question 28

What are the factors affecting the rate of cellular respiration (describe them)?

Answer 28

Temperature - Below: enzymes and substrates move slower. Above: enzymes denature pH - enzymes denature above or below optimal pH Glucose - Increase of glucose availability increases rate of cellular respiration and ATP production. Maximum level will be reached causing respiration rate to plateau Oxygen - Increase in oxygen levels the rate of aerobic respiration increases Enzyme inhibition - Inhibited: greater rate of reaction with substrate concentration Competitive reversible inhibitor: great rate of reaction with increased substrate concentration Non-competitive and/or irreversible inhibitor: Lower rate of reaction