3.5.1 Photosynthesis, LDR and LIR (Unit 5 Energy Transfers)

Question 1

Describe how NADP+ is reduced in the LDR of photosynthesis.

Answer 1

2e^- from electron carrier protein (originally from chlorophyll) are gained.

H+ is gained from stroma.

Question 2

What are the products of the light dependent reactions of photosynthesis?

Answer 2

ATP

NADPH (Reduced NADP)

Oxygen

Question 3

Identify the labels.

Answer 3

Question 4

Identify the labels.

Answer 4

Question 5

Why is ATP sometimes referred ot as an immediate energy source of energy?

Answer 5

Because only one bond needs ot be broken to release energy.

ATP is rapidly resynthesised.

Question 6

In biology what is meant by OXIDATION?

Answer 6

The loss of electrons

The loss of hydrogen

The gain of oxygen

Question 7

For what are the products of the light dependent reactions used for?

Answer 7

NADPH and ATP are required in the light independent reacitons of photosynthesis (Calvin cycle)

Oxygen is used in respiraiton or exits the plant via the stomata.

Question 8

Why does the plant need to carry out the respiration if the light dependent reactions produce ATP?

Answer 8

Not enough ATP is produced.

ATP is difficult to transport around the plant.

So ATP can be produced in the dark.

Not all plant cells contain chlorophyll

ATP is not a stable store of energy.

Question 9

Identify the labels.

Answer 9

Question 10

In biology, what is meant by REDUCTION?

Answer 10

The gain of electrons.

The gain of hydrogen.

The loss of oxygen.

Question 11

Describe the Light Dependent Reactions of photosynthesis.

Answer 11

In photoionisation, light excites the electrons in chlorophyll II and they move to carrier proteins in the thylakoid membrane.
The electrons are replaced by the e- produced by splitting water (photolysis), which also produces oxygen and H+.
Electrons move along carrier proteins in a series of redox reactions losing energy as they go. This is used to pump H+ into the thylakoid space creating a chemiosmotic gradient.
H+ move down the gradient through ATP synthase during photophosphorylation producing ATP from ADP+Pi
The electrons are donated to chlorophyll I and more are excited by light, travelling along another ETC until they reduce NADP to NADPH with H+ from photolysis.

Question 12

Identify the labels.

Answer 12

Question 13

Identify the labels.

Answer 13

Question 14

What does the diagram show?

Answer 14

The thylakoid membrane of a chloroplast.

Where the light dependent reactions of photosynthesis take place.

Question 15

What is NADP?

Answer 15

A coenzyme/cofactor that works alongside an enzyme, in this case it is a hydrogen carrier and electron acceptor.

Question 16

How can we measure the rate of the light dependent reactions of photosynthesis?

Answer 16

Measure the volume of oxygen produced.

Over time.

Question 17

In the light-dependent reaction of photosynthesis, light energy generates ATP. Describe how. (5 marks)

Answer 17

1. Light (energy) excites / raises energy level of electrons in chlorophyll;
2. Electrons pass down electron transfer chain;
3. (Electrons) reduce carriers / passage involves redox reactions;
4. Electron transfer chain / role of chain associated with chloroplast
   membranes / in thylakoids / grana;
5. Energy released / carriers at decreasing energy levels;
6. ATP generated from ADP and phosphate / Pi / phosphorylation of ATP;

Question 18

When investigating how light intensity affects plant growth what variables should you control?

Answer 18

temperature

concentration carbon dioxide

volume of water

concentation of ions in soil

pH of soil

Question 19

Describe the light independent reaction

Answer 19

CO2 is fixed, combining with RuBP using the enzyme Rubisco
This produces two glycerate-3-phosphate (GP)
GP is reduced to Triose phosphate (TP)
Using energy from ATP and reduced NADP
TP can be regenerated to RuBP using energy from ATP,
1C from TP is converted into organic molecules e.g. glucose, amino acids, glycerol

Question 20

How many carbon atoms in Ribulose Bisphosphate (RuBP)?

Answer 20

5

Question 21

Name the enzyme that catalyses the fixation of carbon dioxde into RuBP to produce glycerate-3-phosphate.

Answer 21

Rubisco

Question 22

How many turns of the calvin cycle take place to produce 1 molecule of glucose?

Answer 22

6

Question 23

How many carbon atoms in glycerate-3-phosphate?

Answer 23

3

Question 24

What are the products of every 6 turns of the carbon cycle?

Answer 24

1 x glucose molecule/carbon containing molecule

5 x RuBP

Question 25

What are the products of the LIR

Answer 25

Organic compounds e.g. glucose, amino acids, lipids

RuBP (Ribulose Bisphosphate)

Question 26

How many carbon atoms in triose phosphate?

Answer 26

3

Question 27

Does the Calvin Cycle require light to function?

Answer 27

No

BUT

The reactions will stop eventually in the absence of light because essential ATP and NADPH from light reactions will run out.

Question 28

During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how. (6 marks)

Answer 28

1. Carbon dioxide combines with ribulose bisphosphate / RuBP;
2. Produces two glycerate-3-phosphate / GP;
3. GP reduced to triose phosphate / TP;
4. Using reduced NADP; and…
5. …Using energy from ATP;
6. Triose phosphate converted to glucose / RuBP / ribulose bisphosphate

Question 29

Heat stress decreases the LDR - why does this lead to a decrease in the LIDR?

Answer 29

Less ATP

Less reduced NADP

Question 30

A decrease in the activity of the enzyme rubisco would limit photosynthesis - why?

Answer 30

Less carbon dioxide reacts with RuBP

so

Less GP

Question 31

where is rubisco found?

Answer 31

stroma (of chloroplast)