Photosynthesis and respiration

Question 1

Describe photoionisation of chlorophyll

Answer 1

Light energy is absorbed by the chlorophyll and
the energy results in the electrons becoming
excited and raising up an energy level to leave
the chlorophyll. Therefore the chlorophyll has
been ionised by light. Some of the energy from
the released electrons is used to make ATP and
reduced NADP in chemiosmosis.

Question 2

Where does the light-dependent reaction (LDR) occur?

Answer 2

thylakoid membrane

Question 3

What are the three key reactions in the LDR?

Answer 3

1. photolysis
2. photoionisation of chlorophyll
3. chemiosmosis
   -> produces ATP and NADP

Question 4

describe chemiosmosis in 4 key
stages

Answer 4

Step 1: The electrons that gained energy and left the
chlorophyll move along a series of proteins embedded
within the thylakoid membrane.
Step 2: As they move along, they release energy and some of
the energy from electrons is used to pump the protons
across chloroplast membranes.
Step 3: An electrochemical gradient is created. The protons
pass through the enzyme ATP synthase, which results in
the production of ATP.
Step 4: The protons combine with the co-enzyme NADP to
become reduced NADP. As the protons move from a high to
low concentration gradient this is known as chemiosmosis.

Question 5

Why is the LIR temperature sensitive?

Answer 5

It involves the enzyme Rubisco

Question 6

What is the role of ATP in the Calvin cycle?

Answer 6

To provide the energy to reduce GP to TP
To provide the energy to regenerate RuBP from
TP

Question 7

What is the role of NADPH in the Calvin cycle?

Answer 7

To provide an H to reduce GP to TP

Question 8

What is the triose phosphate used for?

Answer 8

1 To donate one carbon each turn of the cycle to
go towards making a hexose sugar
2 To regenerate RuBP so the cycle can continue

Question 9

Which molecules from the LDR are used in the
LIR?

Answer 9

1 ATP
2 Reduced NADP

Question 10

Where does the LIR occur?

Answer 10

The stroma of the chloroplast

Question 11

What can the hexose sugars made be used
for?

Answer 11

Whilst glucose is the product, this
monosaccharide can join to form disaccharides
such as sucrose, and
polysaccharides such as cellulose and starch. It
can also be converted into glycerol and
therefore combine with fatty acids to make
lipids for the plant.

Question 12

describe the key stages in glycolysis

Answer 12

Substrate level phosphorylation
- The glucose has 2 phosphate
groups added to it from 2 ATP
molecules.
Phosphorylation makes the
glucose-2-phosphate unstable
and it splits into two x 3-carbon
compounds, triose phosphate
(TP).
The 2 TP molecules are oxidised
to form 2 pyruvate molecules by
removing an H from each. The H
is picked up by 2 NAD molecules
to become reduced NAD. This
process also releases 4 ATP.

Question 13

What are the products of glycolysis?

Answer 13

2 x pyruvate
Net gain of 2 ATP
2 X reduced NAD

Question 14

Where do the four stages of aerobic
respiration occur?

Answer 14

1. Glycolysis - cytoplasm
2. Link reaction - Mitochondrial matrix
3. Krebs cycle - Mitochondrial matrix
4. Oxidative Phosphorylation - Cristae /inner
   mitochondrial membrane

Question 15

describe the key stages in
the link reaction.

Answer 15

The pyruvate made in
glycolysis is oxidised to
acetate.
NAD picks up the hydrogen
and becomes reduced NAD.
A carbon atom is lost as
carbon dioxide.
Acetate combines with
coenzyme A to produce acetyl
coenzyme A.

Question 16

What are the products of the link reaction
(from 1 glucose molecule originally)?

Answer 16

The link reaction occurs twice for every glucose
molecule creating:
2 x Acetyl CoA
2 x CO2 released
2 x reduced NAD

Question 17

describe the key stages in the
Krebs cycle.

Answer 17

the acetyl CoA reacts with a four-carbon molecule, releasing
coenzyme A and producing a six-carbon molecule that enters the
Krebs cycle.
In a series of oxidation-reduction reactions, the Krebs cycle
generates 8 reduced coenzymes, 2 ATP by substrate-level
phosphorylation, and 4 carbon dioxides are lost.

Question 18

what are the products of the Krebs cycle (from 1
glucose molecule originally) ?

Answer 18

6 x reduced NAD
2 x reduced FAD
4 x carbon dioxide
2 x ATP

Question 19

what is the role of oxygen in oxidative
phosphorylation?

Answer 19

Oxygen is the final electron acceptor in the electron
transport chain. The oxygen combines with the
electrons and the protons to form water.

Question 20

What happens to the reduced co-enzymes in this
stage?

Answer 20

All of the accumulated reduced coenzymes release
the hydrogens which are split into protons (H+) and
electrons (e-).

Question 21

Describe how ATP is produced in oxidative
phosphorylation.

Answer 21

electrons are passed down a series of electron carrier proteins
embedded in the inner mitochondrial membrane, losing energy as they
move along (electron transport chain). The small amount of energy the
electrons release pumps protons from the mitochondrial matrix into the
intermembrane space by active transport.
This creates an electrochemical gradient across the membrane.
Therefore, the protons move down the electrochemical gradient back
into the matrix via ATP synthase making ATP.

Question 22

Where does anaerobic respiration occur?

Answer 22

The cytoplasm

Question 23

Why is it important that NAD is re-oxidised in
anaerobic respiration?

Answer 23

So that it can be reused in glycolysis and ensure ATP
continues to be produced.