Topic 5.1 - Photosynthesis

Question 1

What is ATP?

Answer 1

Adenosine Triphosphate. It is the source of energy for use at the cellular level.

Question 2

Can ATP be stored? Why?

Answer 2

No, ATP cannot be stored as it is unstable.

Question 3

Where do animals get their nitrate ions from?

Answer 3

From plants that contain nitrates, or from eating other animals that have eaten plants.

Question 4

Where do plants get their nitrate ions from?

Answer 4

Soil.

Question 5

What does ATP break down into?

Answer 5

ADP + Pi

Question 6

When ATP is broken down, energy is released. What is the four processes that use this energy? Give an example of each process.

Answer 6

1. Chemical - Synthesis.
2. Osmotic - Active Transport.
3. Mechanical - Muscle Contraction.
4. Electrical - Motor neuron nerve cells.

Question 7

Give 5 reasons why ATP is useful.

Answer 7

1. It is a single-step reaction (therefore is an immediate source of energy.)
2. The energy released is large enough for most processes and has minimal waste.
3. The activation energy is low, so the bonds are easier to break.
4. It can be reformed.
5. It cannot be transported out of the cell.

Question 8

What kind of reaction converts ATP to ADP + Pi? What is used?

Answer 8

A hydrolysis reaction using the enzyme ATP hydrolase and a molecule of water.

Question 9

What is released from the hydrolysis reaction?

Answer 9

Energy is available for cellular work.

Question 10

What kind of reaction converts ADP + Pi to ATP? What is used?

Answer 10

A condensation reaction uses energy from sunlight or food and releases a molecule of water. The enzyme ATP synthase is used.

Question 11

Describe how an ATP molecule is formed from its component molecules. (4 marks)

Answer 11

ADP (consisting of adenine, a ribose sugar and 2 phosphate ions) joins with a phosphate ion in a condensation reaction. This forms ATP. In this reaction, an enzyme called ATP synthase is used, and a molecule of water is released.

Question 12

What is the LDR?

Answer 12

The Light-Dependent Reaction.

Question 13

What is the first stage in the LDR?

Answer 13

Photoionisation.

Question 14

What happens in Photoionisation?

Answer 14

Light energy (photons) hits the chlorophyll molecule of photosystem II. This excited the electrons in the chlorophyll, causing them to leave the chlorophyll molecule.

Question 15

What happens to the chlorophyll in photoionisation?

Answer 15

It is oxidised.

Question 16

The chlorophyll loses electrons, how are they replaced?

Answer 16

Chlorophyll gains electrons from photolysis (has been reduced.)

Question 17

What is oxidation?

Answer 17

Loss of electrons and hydrogen ions, gain of oxygen.

Question 18

What is reduction?

Answer 18

Loss of oxygen, gain of electrons and hydrogen ions.

Question 19

Where do the electrons that have been emitted by the chlorophyll molecule go to?

Answer 19

Primary acceptors.

Question 20

Where do the electrons from the primary acceptor of Photosystem II go to?

Answer 20

They go through a series of reduction and oxidation reactions, passing through 3 electron carriers until it hits the chlorophyll molecule of photosystem I. (The electron carrier is first reduced as it gains an electron and then oxidised as it passes the electron.)

Question 21

What is the process of electrons passing through electron carriers called?

Answer 21

Photophosphorylation.

Question 22

What is the chain of electron carriers called?

Answer 22

The Electron Transport Chain.

Question 23

Once the electron hits the chlorophyll of photosystem I, what happens?

Answer 23

The chlorophyll is oxidised again as photoionisation occurs.

Question 24

Where do the electrons emitted by the primary acceptor of photosystem I go to?

Answer 24

NADP Reductase.

Question 25

What is NADP Reductase?

Answer 25

An enzyme that reduces NADP by giving it electrons (from photosystem I) and H+.

Question 26

Energy pumps H+ into the thylakoid lumen from the stroma. What happens to the H+?

Answer 26

The proton gradient is dissipated and leaves the interior of the thylakoid.

Question 27

How do the H+ ions leave the thylakoid?

Answer 27

Through a complex of a proton pure and ATP synthase.

Question 28

What happens during the proton pores?

Answer 28

As the protons pass the pores, energy is released. This energy helps in the synthesis of ATP.

Question 29

What is the name for actively pumping in H+?

Answer 29

Chemiosmosis.

Question 30

Crops use light energy to produce photosynthetic products. Describe how crop plants use light energy during the light-dependent reaction (5)

Answer 30

1. Light energy (photons) hit the chlorophyll molecule in photosystem ll causing the electrons in the chlorophyll to become excited. Due to this, electrons are emitted from chlorophyll will transferred to the primary acceptor. This causes the chlorophyll to become oxidised and the primary acceptor reduced. 2. The electrons then go through a series of redox reactions when passing, 3 electron carriers in the electron transport chain, where the electron carrier is first reduced (gains the electron) and then oxidised (loses it to the next) releasing energy. 3. This energy is used to join ADP and Pi to form ATP. In photosystem I another photon hits the chlorophyll and photoionisation occurs again. Electrons from the electron carriers replace the lost electrons and the chlorophyll has been reduced. 4. Photolysis is when water is split up to form electrons, hydroxide ions and hydrogen ions (the electrons go back into the chlorophyll to make up for the ones lost.) The process is known as photoionisation. 5. The electrons then leave photosystem I and go to NADP reductase. NADP reductase takes these electrons and extra H+ ions and gives them to NADP, reducing it to form reduced NADP.

Question 31

What does the LIR stand for?

Answer 31

Light - independent reaction.

Question 32

What is another name for the LIR?

Answer 32

The Calvin cycle.

Question 33

Where does the Calvin cycle take place?

Answer 33

In the stroma of the chloroplast.

Question 34

What does the LIR use from the LDR?

Answer 34

It uses the products of the LDR, which is reduced NADP and ATP.

Question 35

What are the three main stages of the Calvin cycle?

Answer 35

1. Fixation of Carbon. 2. Reduction phase. 3. Regeneration phase.

Question 36

Roughly, what happens in the fixation of Carbon?

Answer 36

An enzyme called rubisco adds a CO2 molecule to RuBP to form GP.

Question 37

Where does the CO2 come from?

Answer 37

The atmosphere.

Question 38

What is the full name of RuBP? What is it made up of?

Answer 38

Ribulose bisphosphate. 5 carbons, 2 phosphates.

Question 39

What does GP stand for? What is it made up of?

Answer 39

Glycerate -3phosphate. It has 3 Carbons, 1 phosphate. There are usually 2 of these molecules formed.

Question 40

Generally, what happens in the reduction phase?

Answer 40

GP is reduced to form 2 molecules of TP. It is reduced as it gains electrons and hydrogen ions from reduced NADP (a product of the LDR). It also gains energy to do this from the break down of ATP to ADP + Pi. The NADP has been oxidised and goes back to the LDR to be reduced. The ADP + Pi also go back so they can be synthesised by H+.

Question 41

What does TP stand for? What does it consist of?

Answer 41

Triose Phosphate. It has 2 molecules of 3 carbons and 1 phosphate.

Question 42

TP can join together to form what?

Answer 42

Glucose.

Question 43

What are some uses of glucose?

Answer 43

1. Respiration. 2. Starch. 3. Lipids / Oils. 4. Cellulose. 5. When joined with Ammonium ions and Nitrate ions, it can form amino acids. These can create proteins which can make enzymes. Enzymes are useful (for example rubisco for the fixation of carbon.)

Question 44

Generally what happens in the regeneration phase?

Answer 44

TP loses a carbon (an enzyme takes it out). This forms RuP. Another molecule of ATP breaks down to form ADP and Pi. The Pi is what is added to RuP to form RuBP. RuBP is then ready to start the cycle again.

Question 45

What does RuP stand for? What is it made of?

Answer 45

Ribulose Phosphate. 5 carbons and 1 phosphate.

Question 46

What is the equation for Photolysis?

Answer 46

H20 -> 2e- + 2H+ + 1/2 O2