AQA GCSE Combined Science: Trilogy · 4.4

Bioenergetics

50 revision questions with answers for 4.4 Bioenergetics in AQA GCSE Combined Science: Trilogy (spec 8464). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

All 50 questions and answers

Question 1 · Spec 4.4.1.1
State the word equation for photosynthesis.
Answer:
Carbon dioxide + water → glucose + oxygen, using energy transferred by light.
Question 2 · Spec 4.4.1.1
Identify CO₂, H₂O, O₂ and C₆H₁₂O₆.
Answer:
Carbon dioxide, water, oxygen and glucose, respectively.
Question 3 · Spec 4.4.1.1
Why is photosynthesis described as endothermic?
Answer:
Energy is transferred from the environment to chloroplasts by light.
Question 4 · Spec 4.4.1.1
What is chlorophyll's role in photosynthesis?
Answer:
It absorbs light energy in chloroplasts.
Question 5 · Spec 4.4.1.2
Name four factors affecting photosynthesis rate.
Answer:
Light intensity, carbon dioxide concentration, temperature and the amount of chlorophyll.
Question 6 · Spec 4.4.1.2
How does increasing light intensity affect photosynthesis when light is limiting?
Answer:
The rate increases because more energy is available for photosynthesis.
Question 7 · Spec 4.4.1.2
Why can increasing carbon dioxide concentration increase photosynthesis rate?
Answer:
Carbon dioxide is a reactant; when its supply is limiting, more is available for the reaction.
Question 8 · Spec 4.4.1.2
Why does photosynthesis slow at temperatures far above the optimum?
Answer:
Enzymes involved become denatured, reducing the reaction rate.
Question 9 · Spec 4.4.1.2
Why can reduced chlorophyll lower photosynthesis rate?
Answer:
Less light energy is absorbed, so the energy supply for photosynthesis decreases.
Question 10 · Spec 4.4.1.2
What does a plateau on a rate-light intensity graph show?
Answer:
Further increases in light intensity do not increase the rate under those conditions.
Question 11 · Spec 4.4.1.2 · Higher only
How can two photosynthesis curves reveal a limiting factor?
Answer:
If raising carbon dioxide increases the rate at the same light intensity and temperature, carbon dioxide was limiting the lower-rate condition.
Question 12 · Spec 4.4.1.2 · Higher only
State the inverse-square relationship between lamp distance and light intensity.
Answer:
Light intensity is proportional to 1 / distance², for a suitable point-source approximation.
Question 13 · Spec 4.4.1.2 · Higher only
A lamp moves from 10 cm to 20 cm away. How does intensity change?
Answer:
Distance doubles, so intensity becomes 1 / 2² = one-quarter of its original value.
Question 14 · Spec 4.4.1.2 · Higher only
Why might maximising greenhouse photosynthesis fail to maximise profit?
Answer:
Extra heating, lighting or carbon dioxide may cost more than the value of the additional crop produced.
Question 15 · Spec 4.4.1.2 · Required practical
How can pondweed be used to investigate light intensity?
Answer:
Change a lamp's distance and measure oxygen output per unit time, keeping other conditions constant.
Question 16 · Spec 4.4.1.2 · Required practical
Why is collected oxygen volume often better than bubble count?
Answer:
Bubbles may differ in size, so volume gives a better estimate of the amount of oxygen produced.
Question 17 · Spec 4.4.1.2 · Required practical
Which variables should be controlled in the pondweed practical?
Answer:
Temperature, carbon dioxide availability, pondweed species or length and the measurement time.
Question 18 · Spec 4.4.1.2 · Required practical
Why allow pondweed to adjust after changing lamp distance?
Answer:
Its photosynthesis rate needs time to stabilise before measurement.
Question 19 · Spec 4.4.1.2 · Required practical
Pondweed produces 6.0 cm³ oxygen in 4.0 min. Calculate the rate.
Answer:
Rate = 6.0 / 4.0 = 1.5 cm³ per minute.
Question 20 · Spec 4.4.1.2 · Required practical
How can the pondweed investigation be made more reliable?
Answer:
Repeat each condition, check anomalies and calculate a mean from valid repeats.
Question 21 · Spec 4.4.1.3
Name five possible uses of glucose made in photosynthesis.
Answer:
Respiration; starch storage; fat or oil storage; cellulose production; amino acid production for proteins.
Question 22 · Spec 4.4.1.3
Why is glucose converted to starch for storage?
Answer:
Starch is insoluble, so it can be stored without creating a large dissolved-solute concentration.
Question 23 · Spec 4.4.1.3
How is glucose linked to stronger plant cell walls?
Answer:
Glucose molecules are used to make cellulose, which strengthens cell walls.
Question 24 · Spec 4.4.1.3
Why do plants need nitrate ions to make proteins?
Answer:
Nitrate ions supply nitrogen needed to make amino acids, which are joined to form proteins.
Question 25 · Spec 4.4.2.1
Define cellular respiration.
Answer:
Chemical reactions in living cells that transfer energy from glucose for living processes.
Question 26 · Spec 4.4.2.1
Why is respiration described as exothermic?
Answer:
It transfers energy to the surroundings; some transferred energy is used for cellular processes.
Question 27 · Spec 4.4.2.1
State the word equation for aerobic respiration.
Answer:
Glucose + oxygen → carbon dioxide + water.
Question 28 · Spec 4.4.2.1
Give three uses of energy transferred by respiration.
Answer:
Building larger molecules, movement through muscle contraction and maintaining body temperature.
Question 29 · Spec 4.4.2.1
Do plants respire in darkness?
Answer:
Yes. Living plant cells respire continuously, both in light and in darkness.
Question 30 · Spec 4.4.2.1
State the word equation for anaerobic respiration in muscles.
Answer:
Glucose → lactic acid.
Question 31 · Spec 4.4.2.1
Why does anaerobic respiration transfer less energy per glucose molecule?
Answer:
Glucose is incompletely oxidised, so less energy is transferred than in aerobic respiration.
Question 32 · Spec 4.4.2.1
State the word equation for anaerobic respiration in yeast.
Answer:
Glucose → ethanol + carbon dioxide.
Question 33 · Spec 4.4.2.1
How does yeast fermentation help bread rise?
Answer:
Carbon dioxide gas is produced and forms bubbles in the dough.
Question 34 · Spec 4.4.2.1
How is fermentation useful in alcoholic drink production?
Answer:
Yeast respires anaerobically, converting sugars into ethanol and carbon dioxide.
Question 35 · Spec 4.4.2.1
Compare aerobic respiration with anaerobic respiration in human muscles.
Answer:
Aerobic uses oxygen, produces carbon dioxide and water, and transfers more energy. Anaerobic uses no oxygen and produces lactic acid.
Question 36 · Spec 4.4.2.2
What happens to heart rate, breathing rate and breath volume during exercise?
Answer:
They increase, delivering more oxygen and glucose to working muscles and removing carbon dioxide faster.
Question 37 · Spec 4.4.2.2
Why do muscles respire anaerobically during vigorous exercise?
Answer:
The oxygen supply may be insufficient for the muscles' increased energy demand.
Question 38 · Spec 4.4.2.2
How is lactic acid linked to fatigue?
Answer:
It accumulates during anaerobic respiration; during prolonged vigorous activity muscles become fatigued and contract less efficiently.
Question 39 · Spec 4.4.2.2 · Higher only
What happens to lactic acid after exercise?
Answer:
Blood carries it from muscles to the liver, where it can be converted back into glucose.
Question 40 · Spec 4.4.2.2 · Higher only
What is oxygen debt?
Answer:
The extra oxygen required after exercise to deal with accumulated lactic acid and restore the body following anaerobic respiration.
Question 41 · Spec 4.4.2.2
A pulse rises from 60 to 150 beats/min. Find the percentage increase.
Answer:
Increase = 90 beats/min; percentage increase = 90 / 60 × 100 = 150%.
Question 42 · Spec 4.4.2.2
How could you investigate exercise's effect on heart rate fairly?
Answer:
Measure resting pulse, perform a standard exercise, then record pulse at fixed intervals. Control exercise duration and repeat with adequate recovery.
Question 43 · Spec 4.4.2.3
Define metabolism.
Answer:
The sum of all chemical reactions in a cell or organism.
Question 44 · Spec 4.4.2.3
Why is respiration important to metabolism?
Answer:
It transfers energy needed for continual enzyme-controlled reactions, including the synthesis of new molecules.
Question 45 · Spec 4.4.2.3
Name three large carbohydrates made from glucose.
Answer:
Starch, glycogen and cellulose.
Question 46 · Spec 4.4.2.3
What smaller molecules are used to build a lipid molecule?
Answer:
One glycerol molecule and three fatty acid molecules.
Question 47 · Spec 4.4.2.3
What happens to excess proteins in metabolism?
Answer:
They are broken down, producing urea for excretion.
Question 48 · Spec 4.4.2.3
How do digestion and synthesis differ?
Answer:
Digestion breaks large molecules into smaller ones. Synthesis builds larger molecules from smaller units, using energy.
Question 49 · Spec 4.4.2.3
How are photosynthesis and aerobic respiration linked by their materials?
Answer:
Photosynthesis produces glucose and oxygen used in respiration. Respiration produces carbon dioxide and water used in photosynthesis.
Question 50 · Spec 4.4.2.3
Why is saying that respiration creates energy incorrect?
Answer:
Energy is transferred between stores during reactions; it is conserved and cannot be created.

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