Part 4

Question 1

How many G3P molecules are required to make 1 glucose molecule?

Answer 1

2

Question 2

Why is G3P a key intermediate in photosynthesis?

Answer 2

• G3P is made in the Calvin Cycle.
• It stores energy for the plant.
• G3P is used to make glucose and other sugars.
• It can be turned into amino acids, lipids, and nucleotides.
• It’s important for plant growth and metabolism.

Question 3

How many CO2 molecules are required to make 1 glucose molecule? How many turns of the Calvin cycle is needed for this?

Answer 3

6 molecules are required
6 turns of the calvin cycle (1 CO2 per turn)

Question 4

Define photorespiration

Answer 4

is an unfavourable process which decreases the production of sugars by photosynthesis.

ex.; On a hot, dry day, a plant’s stomata (pores) close to conserve water, which limits CO₂ intake. With less CO₂ available, Rubisco binds to oxygen more often, leading to photorespiration and reducing sugar production.

Question 5

Describe how CAM plants are unique

Answer 5

• Water-storing plants: CAM plants, like cacti, aloe, and pineapple, store water and thrive in dry, desert environments.
• Stomata behavior: They open stomata at night and close them during the day to conserve water (temporal separation).
• Nighttime carbon fixation: At night, stomata open, and the plant takes in CO₂, storing it as malic acid in vacuoles.
• Daytime process: During the day, stomata are closed. The stored malic acid releases CO₂, which is used in the Calvin cycle to make sugars.
• CAM stands for Crassulacean Acid Metabolism, a method of carbon fixation found in certain plants.

Question 6

Explain how the Calvin Cycle is affected for C3 plants during sunny, hot, and dry days AND during low light conditions

Answer 6

C3 Plants:
Hot, Sunny, and Dry Days:
* Stomata close to save water, but less CO₂ enters.
* RuBisCO can also bind to oxygen instead of CO₂, causing photorespiration, which wastes energy and reduces sugar production.
Low Light Conditions:
* Less light means less energy for photosynthesis.
* The Calvin Cycle works slower and produces less sugar.

Question 7

Explain how both C4 plants and CAM plants have adapted to survive sunny, hot, and dry days

Answer 7

• C4 plants: Capture CO₂ as a 4-carbon compound in mesophyll cells and move it to bundle-sheath cells, minimizing water loss and photorespiration (e.g., corn, sugar cane).
• CAM plants: Open stomata at night to capture CO₂, storing it as malic acid. During the day, stomata close to save water, and CO₂ is used for the Calvin Cycle (e.g., cacti, pineapple).