A Level Biology

Biological Molecules

The shared chemistry of life. Work explores the few groups of carbon-based compounds common to all cells — carbohydrates, lipids, proteins and nucleic acids — how enzymes work, how DNA carries the genetic code, and why the universal chemistry of life, and its dependence on water, provides indirect evidence for evolution.

Cells

Life’s fundamental unit. Work explores the structure of prokaryotic and eukaryotic cells, division by binary fission, mitosis and meiosis, and the plasma membrane that controls what crosses it — along with cell signalling, antigens, and how the immune system recognises ‘self’ from ‘foreign’.

Trading with the environment. Work explores how substances cross exchange surfaces, and why large organisms need mass transport systems — associated with exchange surfaces — to carry substances around the body and maintain the diffusion gradients that supply every cell.

Diversity, decoded. Work explores genes and loci, how genetic diversity arises through mutation, meiosis and fertilisation, and how natural selection acts on it — measuring variation through DNA and protein sequences, and biodiversity through species richness and an index of diversity.

Life depends on the continuous transfer of energy. Work explores photosynthesis, in which chlorophyll absorbs light to drive the production of ATP — as protons diffuse through ATP synthase embedded in organelle membranes — a process common to all photoautotrophs, and further evidence for evolution.

Energy Transfers: Respiration

From one organism to the next. Work explores how the molecules made in photosynthesis are consumed and respired by animals, bacteria and fungi, how respiratory substrates are hydrolysed to produce ATP, and why neither photosynthesis, respiration nor the transfer of biomass through a community is ever fully efficient.

Stimulus and response. Work explores receptors, coordinators and effectors, the rapid, localised action of nerve impulses set against the slow, widespread effect of hormones, plant growth substances — and the control of gene expression, where cells translate only part of their genome, shaped by environmental and epigenetic factors.

Evolution, in full. Work explores common ancestry and phylogenetic classification, how genetic drift and natural selection change allele frequencies, and how reproductive isolation gives rise to new species — before the interplay of competition, biotic and abiotic factors that shapes populations within an ecosystem.

Controlling the code. Work explores how we are learning to alter the epigenome, genome and proteome, the medical and technological applications this brings, and how DNA technology aids the diagnosis and treatment of disease — alongside essay preparation for Paper 3.

The final stretch. Revision is active: the eight topics revisited, required practicals and data-analysis skills sharpened, essay technique practised, and past papers worked through — turning two years of biology into confident, exam-ready understanding.