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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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

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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Photosynthesis

Photosynthesis 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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Plant Reproduction System

 Plants can reproduce two ways, via insects or the wind. Insect-pollinated flowers usually have bright colours and a scent to attract the insects while wind-pollinated plants are usually absent of both bright colours and scent. The flower is comprised of many different parts, each with a different function, it’s the organ of reproduction in …

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Phloem – Plant Tissue

Made up from 4 different parts: Phloem fibres Phloem parenchyma Sieve tubes Companion cells The sieve tubes and companion cells are both involved with the mass flow hypothesis. Sieve Tubes Cell membrane broken down Fluid cytoplasm No vacuole No nucleus With the end of the sieve wall broken down it allows inter cellular movement. Translocation …

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The Five Kingdoms Classification System

All living things can be grouped into five categories. This is called the five kingdom proposal and was introduced by Robert Whittaker in 1968 as a way to categorise all organisms. Living organisms are divided into five kingdoms: Prokaryotae Protoctista Fungi Plantae Animalia Prokaryotae Unicellular and Microscopic. Non-membrane bound (no nuclear membrane, no ER, no …

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The Digestive System

Digestion is the breaking down of chemicals in the body to a form that can be absorbed and used. Digestion begins, in mammals, with the saliva in the mouth. The Mouth This is the buccal cavity in a human and is where mechanical digestion and mastication (chewing) takes place. Saliva in the mouth consists of …

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Respiration

Respiration is a set of metabolic reactions and processes that take place with in the cells of organisms. It stores biochemical energy within adenosine triphosphate (ATP) molecules. There are two types of respiration, aerobic and anaerobic. Respiration is also the process of making ATP rather that breaking it down. ATP (Adenosine triphosphate) ATP is the …

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