CAIE A-Level Biology A2 12.1 Energy Questions

Practise how cells spend and regenerate ATP, compare respiratory-substrate energy values, and use RQ equations and respirometer results to investigate respiration.

Exam points

Explain ATP demand in active transport, cell movement and anabolic synthesis such as protein formation.
Explain ATP's small, soluble form, immediate energy release on hydrolysis and rapid regeneration.
Distinguish substrate-linked phosphorylation from chemiosmosis as the two ATP-synthesis routes.
Locate ATP production in glycolysis, Krebs and oxidative phosphorylation from a respiration-stage table.
Compare chemiosmosis in cristae and thylakoid membranes, including proton movement and phosphorylation.
Compare carbohydrate, lipid and protein energy values; explain lipid's greater ATP yield from C–H bonds.
Define RQ as CO₂ produced ÷ O₂ taken in; use its value to identify respiratory substrates.
Calculate RQ from CO₂ and O₂ coefficients in respiration equations for named substrates.
Plan seed or blowfly-larva RQ trials with a respirometer, CO₂ absorbent and paired control readings.

Covered syllabus points

12.1.1—Energy needs in living organisms 12.1.2—ATP features as universal energy currency 12.1.3—ATP synthesis 12.1.4—Energy values of respiratory substrates 12.1.5—Respiratory quotient (RQ)12.1.6—RQ calculations 12.1.7—Respirometer investigations

[Maximum number: 4]

There are many mitochondria located in the presynaptic knobs of neuromuscular junctions and in the sarcomeres of muscle fibres of striated muscle.

Explain the need for many mitochondria in the presynaptic knobs and in the sarcomeres.

any four from:

1 mitochondria produce ATP ;

presynaptic knob

2 for production of, acetylcholine / ACh ;

3 for, making / moving, vesicles ; A exocytosis

sarcomere

4 active transport of $\mathrm{Ca}^{2+}$ into, sarcoplasmic reticulum ;

5 detachment of myosin heads / break cross bridge

or

allows myosin head to move back to original position ;

6 AVP ; e.g. ref. to sodium potassium pump / active transport of $\mathrm{Ca}^{2+}$ out of synaptic knob

[Maximum number: 6]

(a)

Describe how ATP is produced from ADP in the Krebs cycle.

[ 2 ]

any two from:
1 transfer of phosphate group to ADP / ADP phosphorylated / ADP $+\mathrm{P}_{\mathrm{i}} \rightarrow$ ATP ;
2 substrate-linked phosphorylation ;
A substrate-level phosphorylation
R if oxidative phosphorylation
3 enzyme (catalysed reaction) ;

(b)

Describe and explain the features of ATP that make it suitable as the universal energy currency.

[ 4 ]

any four from:

1 small / water-soluble, so can move around cell ;

2 loss of phosphate / hydrolysis, leads to energy release ;

3 (release energy) immediately / in small packets

or

ref. $30.5 \mathrm{~kJ}\left(\mathrm{~mol}^{-1}\right)$ ;

4 can be, recycled / regenerated or

ATP ⇆ ADP + Pi ;

5 link between energy-yielding and energy-requiring reactions / AW ;

6 high turnover / described ;

7 ref to ATPase ;

[Maximum number: 7]

(a)

In respiration, most ATP is synthesised during oxidative phosphorylation. Some ATP is made by substrate-linked reactions in glycolysis and Krebs cycle.

Describe how ATP is made by substrate-linked reactions.

[ 2 ]

(b)

Lipids can be metabolised to provide ATP.
- The enzyme lipase hydrolyses lipids to glycerol and fatty acids.
- The hydrocarbon chain of the fatty acid breaks down into smaller, 2C compounds.
- Each 2 C compound reacts with coenzyme A to form acetyl coenzyme A.

[ 2 ]

(i)

Explain why lipids have a higher energy value than carbohydrates.

[ 2 ]

(c)

The respiratory quotient, RQ, is used to show which substrate is being metabolised by cells. It can be determined using the equation below.

\mathrm{RQ}=\frac{\text { molecules of carbon dioxide released }}{\text { molecules of oxygen taken in }}

Lauric acid is a saturated fatty acid found in coconuts and has a chain of 12 carbon atoms.

[ 3 ]

(i)

Complete the equation below which outlines the aerobic respiration of lauric acid.

\mathrm{C}_{12} \mathrm{H}_{24} \mathrm{O}_{2}+\ldots \ldots \mathrm{O}_{2} \longrightarrow 12 \mathrm{CO}_{2}+12 \mathrm{H}_{2} \mathrm{O}

[ 1 ]

(ii)

Calculate the RQ value for lauric acid.

Show your working. Give your answer to 2 decimal places.

answer =

[ 2 ]

$RQ=12\div17=0.71$

Accept error carried forward from (i) for one mark.

[Maximum number: 4]

Describe and explain the features of ATP that make it suitable as the universal energy currency.

[Maximum number: 2]

Describe how ATP is produced from ADP in the Krebs cycle.

[Maximum number: 2]

Explain why lipids have a higher energy value than carbohydrates.

[Maximum number: 4]

(a)

The rufous hummingbird, Selasphorus rufus, feeds on the nectar produced by flowers. Nectar is a liquid containing sugars. Hummingbirds hover to maintain a position next to a flower while they feed. This requires a lot of energy.

Fig. 6.2 is a rufous hummingbird.

Fig. 6.2

Hummingbirds that have not fed for some time have a respiratory quotient (RQ) value of 0.7 . After feeding their RQ value is 1.0 .

[ 4 ]

(i)

Define the term respiratory quotient.

[ 2 ]

(ii)

Explain why a hummingbird that has not fed for some time has an RQ value of 0.7 , while a hummingbird that has fed has an RQ value of 1.0.

[ 2 ]

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Covered syllabus points

Question 1

Question 2

Question (a)

Question (b)

Question 3

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Question (b)

Question (i)

Question (c)

Question (i)

Question (ii)

Question 4

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Question 7

Question (a)

Question (i)

Question (ii)