GCSE-readyGCSE and International GCSE Biology: common mistakes
The wrong answers students pick most often in our Biology questions, and why they are wrong. Read these before a test, then open the lesson for anything that surprises you.
Getting started
- Getting started: cells and the light microscope
- Not “Cytoplasm”. The cytoplasm is where reactions happen, but it does not hold the genetic material.
- Not “Cell membrane”. The membrane controls what enters and leaves, not the cell's activities.
- Not “Vacuole”. The vacuole holds cell sap.
- Getting started: life processes, photosynthesis and respiration
- Not “Carbon dioxide and water”. These are the reactants, not the products.
- Not “Glucose and carbon dioxide”. Carbon dioxide is used up, not made.
- Not “Oxygen and water”. Water is a reactant in photosynthesis.
- Getting started: variables, fair tests and means
- Not “The time taken for the reaction”. This is what is measured: the dependent variable.
- Not “The volume of enzyme”. This should be kept the same: a control variable.
- Not “The pH”. pH should be kept the same: a control variable.
1 Key concepts in biology
- Animal, plant and bacterial cells
- Not “Ribosomes”. Ribosomes make proteins.
- Not “Nucleus”. The nucleus holds the genetic material.
- Not “Cell wall”. The cell wall strengthens plant cells.
- Microscopes and magnification
- Not “It uses coloured stains”. Light microscopes also use stains. Stains do not reveal tiny structures.
- Not “The cells are alive”. Samples for electron microscopes are not alive.
- Not “It uses a brighter bulb”. Brightness does not change how much detail can be separated.
- Core practical: using a light microscope
- Not “1 × 10-6 m”. That is a micrometre.
- Not “1 × 10-9 m”. That is a nanometre.
- Not “1 × 10-3 m”. That is a millimetre.
- Enzymes
- Not “The enzyme is killed”. Enzymes are molecules. They are not alive, so they cannot be killed.
- Not “The substrate is used up”. The substrate is still there. It just no longer fits.
- Not “The enzyme moves too fast”. Faster movement speeds reactions up until the shape changes.
- Core practical: pH and enzyme activity
- Not “The enzyme is denatured”. Adding substrate does not denature the enzyme.
- Not “The substrate runs out”. There is lots of substrate at high concentrations.
2 Cells and control
- Mitosis and the cell cycle
- Not “Prophase”. In prophase the chromosomes condense and the nuclear membrane breaks down.
- Not “Anaphase”. In anaphase the chromatids are pulled apart.
- Not “Telophase”. In telophase new nuclei form.
- The nervous system and reflexes
- Not “Motor neurone”. Motor neurones carry impulses away from the CNS to effectors.
- Not “Relay neurone”. Relay neurones are inside the CNS.
- Not “Effector neurone”. There is no such neurone. Effectors are muscles or glands.
3 Genetics
- Meiosis and reproduction
- Not “It only needs one parent”. Needing only one parent is an advantage of asexual reproduction.
- Not “It is faster than asexual reproduction”. Asexual reproduction is usually faster.
- Not “Offspring are identical to the parent”. Identical offspring come from asexual reproduction.
- DNA and the genome
- Not “All the DNA in an organism”. That is the genome.
- Inheritance and Punnett squares
- Not “The alleles an organism has”. That is the genotype.
1 The nature and variety of living organisms
- Characteristics and groups of living things
- Not “Excretion”. All organisms excrete waste.
- Not “Respiration”. All organisms respire.
- Not “Reproduction”. All organisms reproduce.
2(a) to (d) Cells, biological molecules and movement of substances
- Levels of organisation and cell structure
- Not “A chloroplast”. A chloroplast is an organelle.
- Not “A palisade cell”. This is a single cell.
- Not “Muscle tissue”. This is a tissue.
- Investigating enzymes: temperature and pH
- Not “The temperature”. Temperature is the independent variable.
- Not “The time taken”. Time is the dependent variable.
2(e) to (f) Nutrition and respiration
- Leaf structure, minerals and starch tests
- Not “Nitrate”. Lack of nitrate causes stunted growth, often with yellow older leaves. This plant is growing normally, so magnesium (needed for chlorophyll) is the better answer.
- The human digestive system
- Not “Storing faeces”. Faeces are stored in the rectum.
2(g) to (h) Gas exchange and transport
- Blood and the immune response
- Not “Oxygen bound to haemoglobin”. Oxyhaemoglobin is inside red blood cells.
2(i) to (j) Excretion, co-ordination and response
- Excretion in plants and humans
- Not “Removal of undigested food”. That is egestion.
- Homeostasis and temperature control
- Not “They move deeper into the skin”. Blood vessels do not move. The arterioles narrow.
3(b) Inheritance
- Family pedigrees and probability
- Not “1 : 2 : 1”. 1 : 2 : 1 is the ratio of genotypes, not phenotypes.
4 Ecology and the environment
- Air pollution and the greenhouse effect
- Not “Nitrous oxide”. Nitrous oxide is a greenhouse gas.