A Level Biology Revision Notes

Comprehensive A Level Biology revision notes providing information and assistance for all UK examination boards (AQA, OCR, Edexcel) as well as international curriculum (CIE).

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Meiosis

Summary Meiosis is a specialised type of cell division that produces gametes, which require a haploid genome in order to participate in sexual reproduction Meiosis is fairly similar to mitosis, but the differences can be remembered with the pneumonic DISCOPUG (division, independent, synapsis, crossover, outcome, ploidy, use, genetics Meiosis can be divided into two stages, …

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Oxidative Phosphorylation

Summary Oxidative phosphorylation is comprised of the electron transport chain and chemiosmosis. It is the most efficient producer of ATP in the process of aerobic respiration Electrons carried from previous steps of respiration enter the electron transport chain, and are sequentially passed through membrane bound proteins The final member of the chain is oxygen, which …

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Variation

Summary Variation describes diversity in the genetic make-up of a species Variation arises from mutations Variations usually have a small effect on phenotype (continuous variation), but there are examples where a variant has a large effect on a phenotype, and generates distinct categories (discontinuous variation) Variation in a population can be influenced by mutation rate, …

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Lipids Structure & Functions

Summary Lipids are most often triglycerides, which are made up of 3 fatty acids and glycerol Triglycerides are generated by a condensation reaction, and the bond between glycerol and the fatty acid is called an ester bond Fatty acids can be saturated (single bonds between all carbons) or unsaturated, at least one double bond between …

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Water

Summary Water is made up of two hydrogens covalently bonded to oxygen. Water molecules are polar, and are attracted to one another by hydrogen bonding Water is an excellent solvent, breaking up compounds so that the components can take part in biological processes It is also important in regulating temperature fluctuations in living organisms Water …

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Biological Catalysts – Enzymes

Summary Enzymes are biological catalysts that speed up the rate of the majority of chemical reactions that occur in the cell. They do this by lowering the activation energy required for the reaction to proceed. Enzymes are essential, the rate of most reactions would be too slow without them and the cell would fail to …

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Proteins

Summary Proteins carry out the majority of the functions of the cell Proteins have hugely diverse components, sizes, structures, and functions Proteins are made up of chains of amino acids, which progressively fold to form the final structure of the protein Primary, secondary, tertiary and quaternary structures classify the distinct layers of polypepide folding structures, …

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The Cell Cycle – Interphase & Mitosis

Summary The cell cycle is made up of two main stages: interphase and mitosis During interphase, cells are duplicating their material and synthesising proteins to prepare to divide. Interphase encompasses 3 phases: G1, S and G2. During S phase, DNA is replicated. Mitosis encompasses prophase, prometaphase, metaphase, anaphase telophase. During these phases, the nuclear envelope …

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Movement – Diffusion & Osmosis

Summary Diffusion is the passive movement of molecules from a high concentration to a lower concentration Diffusion can also be facilitated by membrane proteins such as channels or carriers Osmosis is a water-specific type of diffusion, where water moves from a high to a low concentration across a selectively-permeable membrane Larger molecules are transported into …

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Inorganic ions

Summary Inorganic ions are crucial components of cells Inorganic ions have an electrical charge, owing to loss or gain of electrons. A positively charged ion is called a cation, whereas a negatively charged ion is called anion. Sodium, potassium and calcium ions are all important for creating membrane potentials across cell membranes. They regulate cellular …

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