AQA GCSE Combined Science: Trilogy · 4.8

Key ideas - biology

50 revision questions with answers for 4.8 Key ideas - biology 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 · Links 4.2.2.1
A mutation changes an enzyme's active site. How could this affect digestion?
Answer:
The substrate may no longer fit, so catalysis slows and fewer small soluble digestion products are produced.
Question 2 · Links 4.1.1.2
Why does a photosynthetic cell need both chloroplasts and mitochondria?
Answer:
Chloroplasts make glucose using light; mitochondria support aerobic respiration, transferring energy for the cell's activities.
Question 3 · Links 4.4.2.3
How can the products of protein digestion support muscle growth?
Answer:
Amino acids are absorbed and used to build new proteins; respiration supplies energy for synthesis.
Question 4 · Links 4.2.2.1
How does bile demonstrate that physical structure affects reaction rate?
Answer:
Emulsification creates smaller fat droplets with a larger total surface area, allowing faster lipase action.
Question 5 · Links 4.4.1.3
Why can nitrate deficiency limit plant growth even when glucose is available?
Answer:
Nitrate supplies nitrogen for amino acids. Without enough nitrogen, plants cannot make sufficient proteins for growth.
Question 6 · Links 4.5.1
Why does homeostasis help enzyme-controlled reactions continue effectively?
Answer:
It keeps internal conditions near suitable levels, reducing changes in enzyme activity caused by temperature or other conditions.
Question 7 · Links 4.2.1
Explain how a heart muscle cell contributes to an organ system.
Answer:
Muscle cells form tissue; tissues form the heart; the heart pumps blood as part of the circulatory system.
Question 8 · Links 4.1.1.3
Why would a contracting muscle cell benefit from many mitochondria?
Answer:
Muscle contraction needs energy, and mitochondria provide the main site for aerobic respiration.
Question 9 · Links 4.1.3.1
Why does an intestine need villi as well as a blood supply?
Answer:
Villi provide a large exchange area; blood flow carries absorbed molecules away and maintains a concentration gradient.
Question 10 · Links 4.2.2.2
How do the lungs and circulatory system cooperate during exercise?
Answer:
Lungs exchange gases; blood carries extra oxygen to muscles and returns carbon dioxide, supporting a higher respiration rate.
Question 11 · Links 4.2.2.3
How does a red blood cell's structure support the whole organism?
Answer:
Its haemoglobin and large surface area help transport oxygen, supporting aerobic respiration in body tissues.
Question 12 · Links 4.2.2.4
Why can a narrowed coronary artery reduce the heart's ability to pump?
Answer:
Less oxygen reaches heart muscle, limiting aerobic respiration and energy transfer for contraction.
Question 13 · Links 4.1.3.3
How are root hair cells' large surface area and respiration linked to ion uptake?
Answer:
Large area provides more exchange surface; respiration supplies energy for active transport when ions move against a gradient.
Question 14 · Links 4.2.3.2
How do xylem and stomata together support photosynthesis?
Answer:
Xylem supplies water; stomata allow carbon dioxide to enter. Both reactants are needed for photosynthesis.
Question 15 · Links 4.1.2.2
Why can mitosis repair a damaged patch of skin?
Answer:
It produces new genetically identical cells that replace damaged cells and restore the protective barrier.
Question 16 · Links 4.7.1.1
How can loss of a pollinating species affect a plant population?
Answer:
Reduced pollination can reduce fertilisation and seed production, lowering plant reproduction and affecting dependent species.
Question 17 · Links 4.7.1.3
How could a plant disease indirectly affect herbivore numbers?
Answer:
Reduced plant growth lowers available food, potentially reducing herbivore survival and reproduction.
Question 18 · Links 4.7.1.1
Why can introducing one competitor change several populations?
Answer:
The new species uses shared resources, affecting existing species and the organisms that depend on them.
Question 19 · Links 4.7.1.4
How can both structure and behaviour reduce water loss in a desert organism?
Answer:
A water-loss-resistant surface reduces evaporation; sheltering during hot periods reduces exposure to drying conditions.
Question 20 · Links 4.7.1.2
Why might the same plant species grow differently in two habitats?
Answer:
Environmental differences, such as light, water and mineral availability, affect growth despite shared species characteristics.
Question 21 · Links 4.7.2.1
Why should a distribution study measure environmental conditions as well as abundance?
Answer:
This allows possible links between abiotic conditions and species distribution to be investigated.
Question 22 · Links 4.7.2.1
Why is a large random sample more convincing than one carefully chosen quadrat?
Answer:
It is less vulnerable to selection bias and more likely to represent variation across the habitat.
Question 23 · Links 4.3.1.5
How does malaria illustrate interdependence between species?
Answer:
The protist's life cycle involves mosquitoes and humans; changing mosquito numbers affects transmission between humans.
Question 24 · Links 4.7.3.6
How could removing hedgerows affect both biodiversity and crop pollination?
Answer:
It removes habitat for many species, including some pollinators, potentially reducing biodiversity and pollination services.
Question 25 · Links 4.4.1.1
Trace the source of carbon in a rabbit's tissues.
Answer:
Carbon dioxide is fixed into plant molecules by photosynthesis. The rabbit eats plants and incorporates carbon-containing nutrients into tissues.
Question 26 · Links 4.4.1.1
Why does most life ultimately depend on energy from the Sun?
Answer:
Photosynthetic producers absorb sunlight and build organic molecules, supporting most food chains.
Question 27 · Links 4.4.1.3
How can a plant keep growing during a short period of darkness?
Answer:
Stored carbohydrates can supply glucose for respiration and provide material for growth, although photosynthesis stops without light.
Question 28 · Links 4.3.1.2
Connect TMV infection to reduced crop yield.
Answer:
Leaf damage reduces photosynthesis, leaving less glucose for respiration and synthesis of new biomass.
Question 29 · Links 4.2.3.2
Why can very dry conditions reduce both water loss and carbon dioxide uptake?
Answer:
Stomata may close, reducing transpiration but also restricting carbon dioxide entry for photosynthesis.
Question 30 · Links 4.4.1.2 · Higher only
Why can adding greenhouse carbon dioxide have little effect at low light intensity?
Answer:
Light may be the limiting factor, so more carbon dioxide cannot increase photosynthesis until light supply improves.
Question 31 · Links 4.4.2.1
Why is breathing different from cellular respiration?
Answer:
Breathing moves air into and out of lungs. Respiration is a set of energy-transferring chemical reactions inside cells.
Question 32 · Links 4.1.3.3
Why can reduced respiration limit nutrient uptake even if a root remains intact?
Answer:
Less energy is available for active transport of mineral ions against their concentration gradient.
Question 33 · Links 4.4.2.1
How can the same glucose molecule support either storage or an immediate energy need?
Answer:
It may be built into storage carbohydrate or broken down during respiration, depending on the organism's needs.
Question 34 · Links 4.4.2.2
Why do exercise responses involve both transport and chemical reactions?
Answer:
Faster circulation and ventilation deliver reactants; faster respiration transfers energy needed for muscle contraction.
Question 35 · Links 4.4.2.1
How do yeast and human muscles differ when oxygen is unavailable?
Answer:
Yeast produces ethanol and carbon dioxide; human muscle produces lactic acid. Both transfer less energy than aerobic respiration.
Question 36 · Links 4.7.2.2
How do microorganisms link dead leaves to future plant growth?
Answer:
Decomposers break down leaves and return mineral ions to soil, where plant roots can absorb them.
Question 37 · Links 4.7.2.2
Why is carbon cycling different from energy transfer through ecosystems?
Answer:
Carbon atoms are reused in cycles. Energy enters mainly as sunlight and is transferred, eventually dissipating to surroundings.
Question 38 · Links 4.7.3.4
Explain two links between forest clearance and the carbon cycle.
Answer:
Clearance reduces photosynthetic carbon dioxide uptake; burning or decomposition transfers stored carbon back to the atmosphere.
Question 39 · Links 4.2.3.2
How does transpiration connect a plant's transport system to the water cycle?
Answer:
Water absorbed by roots travels through xylem and is released as vapour from leaves to the atmosphere.
Question 40 · Links 4.7.3.3
Why can conserving peat protect both biodiversity and carbon stores?
Answer:
Peat habitats support distinctive species and contain stored carbon that could be released if peat is disturbed or burned.
Question 41 · Links 4.6.1.3
How can DNA influence a visible characteristic through a protein?
Answer:
A gene codes for an amino acid sequence, producing a protein whose structure and function can affect the characteristic.
Question 42 · Links 4.6.2.1
Identical plant clones reach different heights. Must their DNA differ?
Answer:
No. Environmental differences, such as water or light availability, can produce different phenotypes from the same genotype.
Question 43 · Links 4.6.1.1
Why can siblings resemble each other without being genetically identical?
Answer:
They inherit alleles from the same parents but receive different combinations through sexual reproduction.
Question 44 · Links 4.6.1.5
How can a harmful recessive allele remain in a population?
Answer:
It can be carried by heterozygous individuals who do not show the associated disorder.
Question 45 · Links 4.6.2.4
How does genetic engineering use the link between genes and characteristics?
Answer:
Introducing a gene can enable cells to produce a particular protein and show a desired characteristic.
Question 46 · Links 4.6.3.4
Why is antibiotic resistance an example of evolution rather than purposeful adaptation?
Answer:
Random inherited variation exists or arises; antibiotics select resistant survivors, changing the population across generations.
Question 47 · Links 4.6.2.2
Why must useful variation be inherited for natural selection to change later generations?
Answer:
Only inherited differences can be passed to offspring and become more common through differential reproduction.
Question 48 · Links 4.6.2.3
Compare the selecting agents in selective breeding and natural selection.
Answer:
Humans choose breeding parents in selective breeding; environmental pressures affect survival and reproduction in natural selection.
Question 49 · Links 4.6.4
Why can genetic evidence help establish evolutionary relationships?
Answer:
More similar inherited DNA often indicates a more recent common ancestor, alongside other evidence.
Question 50 · Links 4.6.2.2
How can environmental change lead to either evolution or extinction?
Answer:
Populations may change as advantageous inherited traits spread; if organisms cannot survive and reproduce, the species may become extinct.

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Key ideas - biology

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