11.3 Light independent reaction

Question 1

What are two main products of light dependent reaction

Answer 1

• NADPH and ATP (and O2 as waste product)

Question 2

Where does light independent reaction occur

Why could it actually be light dependent

Answer 2

Stroma of chloroplasts

Although it hypothetically doesn’t need light, it requires the products of light dependent reaction, so if in the dark it will rapidly cease

Question 3

Describe stage 1 of Calvin cycle
(With CO2 entering)

Answer 3

.CO2 from atmosphere diffuses into leaf through stomata
. It dissolves in water around the walls palisade mesophyll cells
. Then it diffuses through cell surface membrane, cytoplasm and chloroplast membranes into stroma of chloroplast

Question 4

Stage 2 of Calvin cycle

( CO2 reacting with RuBP)
What enzyme is needed

Answer 4

. In the stroma, the CO2 reacts with a 5 Carbon compound RuBP ) ribulose bisphosphate)
.This is catalysed by enzyme called ribulose bisphosphate carboxylase (aka rubisco)

Question 5

Stage 3

What is made in reaction of CO2 with RuBP
What does NADPH from light dependent reaction do to this product

Answer 5

. Two molecules of 3 carbon glycerate 3-phosphate (GP)

. NADPH reduces this to triose phosphate using energy supplied by ATP

Question 6

Stage 4

What happens to this NADP

Answer 6

It is reformed to NADP and goes back to light dependent reaction to gain protons to be reduced again

Question 7

What happens to the triose phosphate molecules

Answer 7

• Some are converted to organic substances that plant requires eg starch , cellulose, lipids, glucose, amino acids, nucleotides
• However most triose phosphate is used to regenerate ribulose biphosphate using ATP from the light dependent reaction

Question 8

Why is the chloroplast able to carry out light independent reaction so well

Answer 8

. Fluid in stroma contains all enzymes needed to carry out light independent reaction.
Stromal fluid is membrane bound in chloroplast so is a chemical environment with high concentration of enzymes, and substrates can be maintained within it.

. Stroma fluid surrounds grana so products of light dependent reaction can easily diffuse into stroma

. It contains DNA and ribosomes so can quickly and easily manufacture some proteins involved in light independent reaction