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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The Light Reactions Of Photosynthesis

Summary box Light energy behaves both as electromagnetic waves and discrete particles, measured in photons. Pigments absorb visible light – important pigments in photosynthesis ar chlorophyll a, chlorophyll b and carotenoid The light-dependent reactions of photosynthesis make ATP and NADPH Photosystems I and II are complexes that work together to absorb light and produce ATP …

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Overview Of Photosynthesis

Summary box Green plants and other organisms convert light energy into chemical energy through photosynthesis Photosynthesis is essential for almost all light on earth – either directly or indirectly Chloroplasts in the leaves of plant cells are the organelles in which photosynthesis takes place Chloroplasts contain chlorophyll which absorbs the light energy Thylakoids are disc-shaped …

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Types Of Mutations

Summary box Mutations occur through various mechanisms that can impact genes, chromosomes, and outcomes differently. Mutations can occur on a single nucleotide scale (at the level of point mutations), or on a much larger scale (where segments of whole chromosomes are affected. Substitution of nucleotides can be synonymous (silent) or non-synonymous (change amino acid). The …

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Summary box Mutations describe changes to a DNA sequence and are associated with both disease and evolution Mutations can occur spontaneously in all cell types, but will only become part of the future generation’s genome sequence when they occur in the parental germ line Mutations can occur due to exposure to chemicals, environmental factors, or …

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RNA – Structure and Types

Ribonucleic acid (RNA) is a complex compound with high molecular weight. It participates in protein synthesis within cells and also has the ability to carry genetic codes instead of DNA in some viruses. When examining the structure of RNA, it is possible to notice that it’s made up of ribose nucleotides which are nitrogenous bases …

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The Immune System

Definitions: Immunity – can be defined as the capacity to recognise the intrusion of material foreign to the body and to mobilise cells and cell products to remove that sort of foreign material with great speed and effectiveness. Pathogen – a disease-causing micro-organism. Reservoir – The place where the pathogen is usually found. Endemic – …

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Genetics is the study of DNA and hereditary changes in living organisms. The idea that species of organisms can change over time was first thought about and later published by the famous English naturalist, Charles Darwin in 1859. He wrote a book called “On the Origin of Species”, which continued to highlight views such as …

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Homeostasis – Anatomy & Physiology

Homeostasis is the control of internal conditions, be it temperature, specific blood conditions or other variables within living organisms. The term ‘Homeostasis’ was first defined by the French physiologist, Claude Bernard, in 1865. The purpose of homeostasis is to provide a consistent internal environment for set processes to occur. Each process, or reaction, has a …

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Chloroplasts are large organelles, usually in a biconvex shape, and about 4-10μm long and 2-3μm wide. Within plants most chloroplasts are found in the mesophyll cells of leaves. The stages of photosynthesis take place within the chloroplast, stage 1 within the granum and stage 2 within the stroma.   Stage 1 – Light Dependent Photosynthesis …

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