Food supply, plant growth and productivity (b)

Question 1

Why and what absorbs light energy?

Answer 1

Light energy is absorbed by photosynthetic pigments to generate ATP and for photolysis.

Question 2

What happens to light energy that isn’t absorbed?

Answer 2

It is either transmitted or reflected.

Question 3

Define ‘carotenoids’

Answer 3

Carotenoids extend the range of wavelengths absorbed and pass energy to the chlorophyll for photosynthesis.

Each pigments absorbs a different range of wavelengths of light

Question 4

Describe the ‘light reaction’ stage?

Answer 4

Absorbed light energy excites the electrons in the pigment molecule. Transfer of these electrons through the electron transport chain releases energy to generate ATP by ATP synthase. Energy is also used for photolysis, in which water is split into oxygen, which is evolved, and hydrogen ions, which are transferred to coenzyme NADP.

Question 5

Describe the ‘Carbon fixation’ stage?

Answer 5

In the carbon fixation stage (Calvin Cycle), the enzyme RuBisCO fixes carbon dioxide by attaching it to RuBP. 3PG produced is phosphorylated by ATP and combined with hydrogen ions from NADPH to form G3P. G3P is used to regenerate RuBP and for the synthesis of glucose.

Question 6

What is the fate of glucose?

Answer 6

Glucose may be used as a respiratory substrate, synthesised into starch or cellulose or passed to other biosynthetic pathways.

Question 7

Describe biosynthetic pathways?

Answer 7

These biosynthetic pathways can lead to the formation of a variety of metabolites such as DNA, protein and fat.