GCSE Biology Paper 2: what to revise (and where marks are lost)

Biology Paper 2 is on Monday 8 June. One student sitting next to my boys spent last Sunday doing brilliant revision on cells and enzymes. Wrong paper. Those are Paper 1 topics. Paper 2 is homeostasis, inheritance and ecology.

Different content, different calculations, same exam pressure. This post covers what Paper 2 actually tests, where the marks get dropped, and what the final days before the exam should look like.

What is on GCSE Biology Paper 2

Paper 1 covers cells, transport in cells, organisation, infection and response, and bioenergetics. Paper 2 shifts to homeostasis, the nervous system, hormones, inheritance, evolution and ecology. The split matters because students who revise the wrong topics in the wrong week arrive well-prepared for the paper they already sat.

Homeostasis: the topic worth the most marks

Homeostasis is the maintenance of a stable internal environment. That sentence sounds like a definition to memorise. It is actually the framework for every homeostasis question on the paper.

Every homeostasis question has the same structure: something in the body changes, a receptor detects the change, a control centre processes the signal, an effector responds, and the variable returns to its normal level. That loop is called negative feedback. Name it.

Nervous vs endocrine: two ways the body coordinates

Before the detail, know the two systems that run every response, because the compare question comes up most years. The nervous system sends fast electrical impulses along neurones to a precise target, and the effect is short-lived. The endocrine system releases chemical hormones into the blood, so the message travels more slowly, spreads widely around the body, and the effect lasts longer.

Blood glucose control

Blood glucose is the highest-frequency homeostasis topic on GCSE Biology Paper 2. Questions come in three forms: describe the mechanism, explain what happens after eating, and explain what happens during exercise. All three use the same underlying loop.

Glucagon does the opposite. When blood glucose falls (during exercise or between meals), the pancreas releases glucagon. Glucagon causes the liver to break down glycogen into glucose, which is released into the blood. Students often confuse insulin and glucagon. A simple check: insulin in, glucagon out.

Type 1 vs Type 2 diabetes

Diabetes is the disease side of blood glucose control, and the compare question comes up regularly. In Type 1 diabetes the pancreas cannot produce enough insulin, usually from a young age, so blood glucose can rise to dangerously high levels. It is treated with insulin injections. In Type 2 diabetes the pancreas still produces insulin, but the body cells stop responding to it. It is linked to obesity and is usually controlled by a carbohydrate-controlled diet and exercise.

Thermoregulation

Temperature control questions use the same negative feedback structure but a different set of effectors. When body temperature rises: sweat glands produce sweat (evaporation cools the skin), blood vessels near the skin surface dilate (vasodilation increases heat loss), and body hair lies flat. When temperature falls: blood vessels constrict (vasoconstriction reduces heat loss), you shiver (muscle contractions generate heat), and body hair stands up (traps air as insulation).

ADH and water balance

ADH (antidiuretic hormone) controls water reabsorption in the kidneys. When blood water concentration is too low (for example, after not drinking enough), the pituitary gland releases more ADH. The kidneys reabsorb more water, producing small amounts of concentrated urine. When water concentration is high, less ADH is released and more water is lost in urine.

The two marks students lose: (1) saying ADH is released by the kidneys instead of the pituitary gland, and (2) saying ADH "makes" water reabsorb rather than stating that it increases the permeability of the kidney tubules to water.

Inheritance: three types of question, three common errors

Inheritance questions come in three forms: Punnett squares, probability calculations, and phenotype-versus-genotype distinctions. Each has one error that appears constantly in mark schemes.

Punnett squares

Phenotype vs genotype

Genotype is the combination of alleles an organism carries (TT, Tt, or tt). Phenotype is the observable characteristic (can roll tongue, cannot roll tongue). Questions that ask you to "state the phenotype" want the visible outcome, not the letter combination. Questions that ask you to "state the genotype" want the letters.

Homozygous means both alleles are the same (TT or tt). Heterozygous means the alleles are different (Tt). A carrier is an individual who is heterozygous for a recessive condition: they do not show the condition but can pass the allele on. This is tested almost every year.

The magnification calculation

Magnification appears in the inheritance and cell biology sections. It comes up every sitting and it is easy marks if you have drilled the formula. It is dropped because students reverse the calculation.

Ecology: what the calculations actually test

Ecology is the section where students lose confidence. The topics feel abstract (biodiversity, nutrient cycles) and the calculations look unfamiliar. But the calculations follow a fixed method every time. Students who practise them score them reliably.

Quadrat sampling

Food chains and energy transfer

Food chain questions ask you to trace energy flow and explain why only about 10% of energy transfers between each trophic level. The answer has two parts: energy is lost through respiration (as heat), and energy is lost in waste materials (faeces, urine). Both parts are needed for 2 marks.

Students write "energy is used up." Energy is not used up. It is transferred to the environment as heat via respiration, or it is not absorbed by the next organism because it passes through as waste. These are specific mechanisms, not vague losses.

The carbon and nitrogen cycles

Carbon cycle questions ask about the processes that move carbon between stores: photosynthesis (atmospheric CO2 into plants), respiration (carbon released back as CO2), feeding (carbon moves along food chains), decomposition (carbon released by microorganisms), and combustion (burning releases stored carbon).

Nitrogen cycle questions focus on the role of bacteria: nitrogen fixation (converting atmospheric nitrogen into nitrates in the soil), nitrification (ammonium ions converted to nitrates), denitrification (nitrates converted back to nitrogen gas). Students confuse nitrification and denitrification. Nitrification builds nitrates, denitrification destroys them.

What to do in the last 6 days

The exam is Monday 8 June. Six days. Broad learning is over. These days are about activating what is already in your head under timed conditions.

One timed past paper section per day. Not the whole paper if time is short, but a complete section under exam conditions. No notes, timer running. Mark it immediately with the mark scheme. Find the three things you got wrong. Work on those three things specifically. Start again tomorrow.

Biology Paper 2 students often lose marks not because they do not know the biology, but because they write descriptions when the question asks for explanations. "Describe" wants what happens. "Explain" wants why it happens. Check the command word before you write anything.

If you use GCSE Biology revision on PrepWise, the adaptive quiz builds your daily plan around the topics you keep getting wrong. It finds that you are dropping the insulin mechanism before you do. But the principle works without an app too: test yourself, mark immediately, fix the gap. Do not re-read. Do not highlight. Test and fix.

Related reading

• GCSE Chemistry Paper 2: what to revise (and where marks are lost)
• GCSE Physics Paper 2: what to revise (and where marks are lost)
• GCSE Biology revision: every topic, flashcards and quizzes