GCSE Combined Science Biology 2 — Questions and Answers
Question 1: In genetics, what does the term 'heterozygous' mean?
- Having two identical alleles for a gene
- Having two different alleles for a gene (Correct answer)
- Having only one allele for a gene
- Having no alleles for a gene
Correct answer: Having two different alleles for a gene
Heterozygous means having two different alleles for a particular gene — one inherited from each parent (e.g., Bb). If both alleles are the same (e.g., BB or bb), the organism is homozygous.
Question 2: Which ecological term describes a community of organisms and their physical environment interacting together?
- Population
- Habitat
- Ecosystem (Correct answer)
- Niche
Correct answer: Ecosystem
An ecosystem includes all the living organisms (biotic factors) and non-living components (abiotic factors) in an area, and the interactions between them. Examples include a pond, a woodland, or a coral reef.
Question 3: During exercise, which substance builds up in muscles when there is insufficient oxygen for aerobic respiration?
- Carbon dioxide
- Ethanol
- Lactic acid (Correct answer)
- Glucose
Correct answer: Lactic acid
When muscles cannot get enough oxygen during intense exercise, they switch to anaerobic respiration, which produces lactic acid. This causes muscle fatigue and cramps. The oxygen debt must be repaid after exercise to break down the lactic acid.
Question 4: What is the function of the stomata in a leaf?
- To absorb water from the soil
- To allow gas exchange and control water loss (Correct answer)
- To produce chlorophyll
- To transport sugars around the plant
Correct answer: To allow gas exchange and control water loss
Stomata are tiny pores on the leaf surface (mainly underside) that allow carbon dioxide in for photosynthesis and oxygen out. Guard cells open and close the stomata to regulate gas exchange and reduce water loss through transpiration.
Question 5: Which type of pathogen causes diseases such as measles and influenza?
- Bacteria
- Viruses (Correct answer)
- Fungi
- Protists
Correct answer: Viruses
Viruses cause measles and influenza. Viruses are not living cells — they are small particles containing genetic material (DNA or RNA) inside a protein coat. They can only reproduce inside living host cells, damaging them in the process.
Question 6: What happens to the rate of enzyme activity if the temperature exceeds the enzyme's optimum?
- It continues to increase
- It stays the same
- It decreases because the enzyme becomes denatured (Correct answer)
- It doubles with every 10°C rise
Correct answer: It decreases because the enzyme becomes denatured
Above the optimum temperature, the enzyme's active site changes shape (denatures) because the bonds holding its 3D structure break. The substrate can no longer fit, so the rate of reaction decreases sharply.
GCSE Combined Science Biology 2
In genetics, what does the term 'heterozygous' mean?