Lecture 9 - Photosynthesis

Question 1

Where does photosynthesis occur?

Answer 1

In two parts in the chloroplast

Question 2

What two parts of the chloroplast does photosynthesis occur

Answer 2

Thylakoid

Stroma

Question 3

What are the three membranes of chloroplast?

Answer 3

Outer
Inner
Thylakoid

Question 4

What are the three compartments of the chloroplast

Answer 4

Intermembrane space
Stroma
Thylakoid space

Question 5

What is the thylakoid space

Answer 5

Space within thylakoids where we build up proton gradient

Question 6

Where do light reactions take place?

Answer 6

On the thylakoid membrane

Question 7

Where does carbon fixation occur?

Answer 7

Stroma

Question 8

What are pigments

Answer 8

Pigments are molecules that can absorb light. Pigments enable complexes to absorb light.

Question 9

What is the purpose of light reactions?

Answer 9

To capture light energy and convert it to chemical energy. This happens with pigment and protein complexes embedded in the thylakoid membrane.

Question 10

What is a photosystem?

Answer 10

They are protein complexes that contains the chlorophyll

Question 11

How do photo systems capture light energy and what is it then used for?

Answer 11

The chlorophyll present in the photosystem absorbs light energy. This light energy then produces high energy level electrons. These high energy electrons then travel through the photosynthetic electron transport chain.

Question 12

What proteins are involved in the photosynthetic electron transport chain?

Answer 12

Photosystem ll 
Cytochrome complex
Photosystem l 
Electron carrying molecule (NADP+H+)
ATP synthase

Question 13

What happens at photosystem ll in the photosynthetic electron transport chain?

Answer 13

Light energy come in and excites the electrons. This causes the movement of 2 electrons from the chlorophyll to move through photosystem ll and then leave photosystem ll. The electrons then move to the cytochrome complex

Question 14

What happens at the cytochrome complex in the photosynthetic electron transport chain?

Answer 14

The two electrons then move through the cytochrome complex which causes it to lose some of their energy. The energy lost is then used to pump protons from one side of the membrane to the other. The 2e- then go to photosystem l.

Question 15

What happens at photosystem l in the photosynthetic electron transport chain?

Answer 15

The 2e- then travel through photosystem l. Photosystem l absorbs more light energy which transfers to the electrons to excite them. The electrons then sit in electron carrying molecule NADP+ + H+ creating NADPH.

Question 16

What happens at ATP synthase in the photosynthetic electron transport chain?

Answer 16

The protons that where pumped through the membrane by the cytochrome complex is used to create a proton gradient which is used to drive ATP synthase to convert ADP + Pi to ATP

Question 17

How does photosystem ll replace the two electrons?

Answer 17

Photosystem ll can draw electrons from water. When electrons are drawn from water O2 is also produced. As long as water is available there will be a continual chain of electrons.

Question 18

What happens in the Calvin cycle?

Answer 18

In the Calvin cycle (carbon fixation) the ATP and NADPH produced in the light reactions are used to fix CO2 and produce carbohydrates.

Question 19

Explain the steps of the Calvin cycle

Answer 19

1. Fixation: 5 carbon molecule + CO2 -> 2 x 3 carbon molecules
2. Reduction: 3 carbon molecule is converted into a different 3 carbon molecule and one carbon molecule leaves the system. (6ATP to 6ADP)(6NADPH to 6NADP+)
3. Regeneration: convert the 3 carbon molecule back into the 5C molecule.

Question 20

What is the output of the Calvin cycle?

Answer 20

A 3 carbon sugar that is converted to glucose.

6CO2 to C6H12O6

Question 21

What happens with the glucose produced from photosynthesis?

Answer 21

The plant cells break down the glucose in the mitochondria using cellular respiration.

Question 22

What is the ATP and NADPH formed during light reactions used for?

Answer 22

The Calvin cycle only, not for other cellular processes.

Question 23

What are the inputs and outputs of photosynthesis?

Answer 23

Input: light, water and carbon

Output: glucose and oxygen

Question 24

Describe the energy supply in plants and animals : Glucose

Answer 24

Both plants and animals breakdown glucose in cellular respiration to generate ATP. Animals have external source of glucose whilst plants generate glucose.

Question 25

Describe the energy supply in plants and animals: ATP

Answer 25

ATP is generated in both respiration and photosynthesis. ATP synthase is responsible for ATP generation in both processes. A proton gradient is required across a membrane for this process to occur.