CAIE A-Level Biology A2 12.1 Energy Questions

Practise cellular-energy questions by explaining ATP as an energy currency, comparing respiratory substrates and calculating RQ from equations or respirometer data.

Exam points

explain ATP hydrolysis, regeneration, solubility and high turnover in cellular energy use
compare carbohydrate, lipid and protein energy values using C-H bonds and reduced carriers
calculate RQ from respiration equations, gas volumes or respirometer CO2 absorption data

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: 3]

In aerobic respiration，most ATP is produced by oxidative phosphorylation．

Outline the features of ATP that make it suitable as the universal energy currency．

[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.

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Covered syllabus points

Question 1

Question 2

Question 3

Question (a)

Question (b)

Question (i)

Question (c)

Question (i)

Question (ii)