Light Dependent Reaction

Question 1

What is the light dependent reaction?

Answer 1

First stage of photosynthesis that requires absorbance of light from chlorophyll

Question 2

Where does the light dependent reaction occur?

Answer 2

In the thylakoids within the chloroplast of a leaf cell

Question 3

First step of LDR name

Answer 3

Photoionisation of chlorophyll

Question 4

Photoionisation of chlorophyll

Answer 4

When chlorophyll in thylakoids membranes absorb light energy from sun
So electrons in chlorophyll are excited to a higher energy level
Then lost from the molecule

Question 5

Where are the electrons from the Photoionisation of chlorophyll lost to?

Answer 5

The electron transfer chain: chain of proteins in thylakoids membrane to transport the electrons

Question 6

Electron transfer chain

Answer 6

Chain of proteins that will transport e- across the thylakoid membrane

Question 7

What happens when electrons in electron transfer chain pass the proton pump protein?

Answer 7

This supplies energy so H+ ions can actively be bumped against their electrochemical gradient from stroma into thylakoid empty space

Question 8

Proton pump protein

Answer 8

A protein pump that actively pumps H+ ions into thylakoid empty space using energy from electrons passing through from the electron transfer chain

Question 9

Electrochemical gradient

Answer 9

A gradient of H+ ions that is created by the proton pump protein so it is higher inside the thylakoid empty space than outside in the stroma

Question 10

H+ ions movement once in the thylakoid empty space

Answer 10

Move out back into the stroma again via facilitated diffusion using the channel protein ATP synthase

Question 11

Facilitated diffusion of H+ ions allows…

Answer 11

The synthesis of ATP from ADP and Pi as the movement of H+ ions releases energy catalysed by enzyme ATP synthase

Question 12

ATP synthase and what it does?

Answer 12

A channel protein and enzyme
Facilitates diffusion of H+ ions down electrochemical gradient out the thylakoid
To also catalyse the synthesis of ATP from ADP and Pi using this energy

Question 13

What do we use synthesised ATP for?

Answer 13

Used for light independent reaction

Question 14

Chemisomosis

Answer 14

The process of the facilitated diffusion of H+ ions down an electrochemical gradient to provide the energy needed for ATP synthesis, that is aided by the enzyme ATP synthase

Question 15

What is at the end of the electron transfer chain?

Answer 15

The enzyme dehydrogenase

Question 16

What does Dehydrogenase enzyme do?

Answer 16

Used electrons from electron transfer chain
And H+ ions from the stroma
To reduce NADP

Question 17

Reduction of NADP

Answer 17

NADP + e- + H+ ——> NADPH

Question 18

Reduced NADP

Answer 18

NADPH

Question 19

How do we replace electrons lost from the chlorophyll?

Answer 19

Using the photolysis of water

Question 20

Photolysis of water

Answer 20

‘Splitting’ water
H2O ——> H+ + O2 + e-

Question 21

Products of photolysis of water

Answer 21

O2 is one of the overall products of photosynthesis, so diffuses out of chloroplast, plant cell then stomata
E- replaces electrons lost of the chlorophyll
H+ ions enters thylakoid space contributing to electrochemical gradient and chemiosmosis

Question 22

What is NADPH used for?

Answer 22

Used for light independent reaction

Question 23

What triggers photolysis of water?

Answer 23

When electrons are lost from chlorophyll which is caused by chlorophyll absorbing light
NOT directly by absorbing light energy

Question 24

Does temperature have much of an effect of light dependent reaction?

Answer 24

No light is a bigger factor
AND does not effect rate of enzyme catalysed reaction: dehydrogenase enzyme is bound to thylakoid membrane so increasing its Ek has little effect

Question 25

Where does photolysis of water occur?

Answer 25

Water splitting enzyme near chlorophyll