Biology course

1. 1.Cell Structure and Function

   The cell is the smallest unit that carries out all the processes of life. Prokaryotic cells, such as bacteria, are small and have no nucleus; their DNA floats in the cytoplasm. Eukaryotic cells, found in plants, animals, fungi and protists, keep their DNA in a nucleus and divide their work among membrane-bound organelles.

   • Plant cells have a cell wall, chloroplasts and a large central vacuole; animal cells do not.
   • Diffusion and osmosis move substances down a concentration gradient without energy; active transport uses ATP to move them up it.
   • Surface-area-to-volume ratio limits how large a cell can grow.
   Quick check: Which organelle carries out photosynthesis?

   The chloroplast

   Includes a worked example, 3 common mistakes and 3 practice questions with answers. Study cell structure and function

2. 2.Genetics

   Genetics explains how traits pass from parents to offspring. Genes are stretches of DNA, and each gene can come in different versions called alleles. You inherit one allele of each gene from each parent, and the combination, your genotype, determines the trait you show, your phenotype.

   • Homozygous: two identical alleles ($AA$ or $aa$); heterozygous: two different ($Aa$).
   • Each parent passes on one allele at random, which is why outcomes are probabilities.
   • A test cross with $aa$ reveals whether a dominant-looking individual is $AA$ or $Aa$.
   Quick check: In $Aa \times aa$, what fraction of offspring show the recessive trait?

   $\frac{1}{2}$

   Includes a worked example, 3 common mistakes and 3 practice questions with answers. Study genetics

These topics belong to the course outline. Full explainers for them have not been written yet, so they are summarised here rather than given pages of their own.

Evolution

Natural selection and Hardy-Weinberg equilibrium.

Ecology

Population growth, energy flow and ecosystems.

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