Cambridge IGCSE Biology 0610 – Unit Summaries

Free overview of every unit in the Cambridge IGCSE Biology (0610) syllabus, written by Dr. Khaled Dabour for Dabour Hub students. Each unit below starts with the key ideas you need to know. The complete revision notes, diagrams, quizzes and question banks are available to registered students.

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1. Characteristics and classification of living organisms – IGCSE Biology 0610

The seven characteristics of living organisms Learn them as a list and define each one, because the question is usually worth one mark per definition, not per word. Movement – an action by an organism causing a change of position or place. Respiration – the chemical reactions in cells that break down nutrient molecules and release energy. Sensitivity – the ability to detect stimuli and to make responses. Growth – a permanent increase in size and dry mass. Reproduction – the processes that make more of the same kind of organism. Excretion – removal of the waste products of metabolism, toxic materials and substances in excess. Nutrition – taking in materials for energy, growth and development. Where marks are lost: growth is a permanent increase in dry mass. A plant that takes up water gets bigger and heavier without growing. And excretion is not egestion – faeces were never inside the cells, so they are not a product of metabolism.…

2. Organisation of the organism – IGCSE Biology 0610

The structures in a cell, and what each one does Cell membrane – controls what enters and leaves the cell. Present in every cell. Cytoplasm – where the chemical reactions of the cell happen. Nucleus – contains the DNA and controls the activities of the cell. Mitochondria – the site of aerobic respiration. Ribosomes – the site of protein synthesis. Cell wall (plants only) – made of cellulose, stops the cell bursting and gives it shape. Chloroplasts (plants) – contain chlorophyll, the site of photosynthesis. Permanent vacuole (plants) – filled with cell sap, keeps the cell turgid. Where marks are lost: animal cells do have vacuoles – small, temporary ones. Only the large permanent vacuole is a plant feature. And a root hair cell has no chloroplasts, because there is no light underground. Bacterial cells A bacterial cell has a…

3. Movement into and out of cells – IGCSE Biology 0610

Diffusion The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of their random movement. It is a passive process – no energy from respiration is needed. Rate increases with: a steeper concentration gradient, a higher temperature (particles have more kinetic energy), a larger surface area, and a shorter distance. Osmosis The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane. Where marks are lost: say water molecules, not water; say partially permeable, not…

4. Biological molecules – IGCSE Biology 0610

What each molecule is made of Starch and glycogen are large molecules built from many glucose units. Starch is the storage carbohydrate in plants, glycogen in animals; both are insoluble, which is exactly why they are good for storage – they do not affect osmosis. Protein structure A protein is a chain of amino acids folded into a specific three-dimensional shape. There are about 20 different amino acids, and the sequence of them determines how the chain folds – which is…

5. Enzymes – IGCSE Biology 0610

What an enzyme is A protein that functions as a biological catalyst: it speeds up a chemical reaction and is not changed or used up by it. Because it is unchanged, one enzyme molecule works over and over. The lock and key model The substrate fits into the enzyme’s active site, which is complementary in shape to it. This is why enzymes are specific – one enzyme catalyses one reaction. The enzyme-substrate complex forms, the reaction happens, and the products leave. Temperature As temperature rises, molecules move faster, there are more successful collisions between…

6. Plant nutrition – IGCSE Biology 0610

The reaction Photosynthesis is the process by which plants make carbohydrates from raw materials using energy from light. Word equation: carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll. Balanced equation: 6CO2 + 6H2O → C6H12O6 + 6O2 Chlorophyll is not a reactant. It transfers light energy to chemical energy in the glucose, and it is not used up. What happens to the glucose Used in respiration to release energy. Converted to starch for storage, because starch is insoluble and does not affect osmosis. Converted to cellulose for cell…

7. Human nutrition – IGCSE Biology 0610

The nutrients Energy needs are higher in an active person, higher in a pregnant woman, and higher per kilogram in a growing child. Teeth Incisors cut, canines tear, premolars and molars grind. Tooth decay: bacteria on the tooth feed on sugar and make acid; the acid dissolves the enamel. Prevent it by brushing with fluoride toothpaste, eating less sugar, and visiting the dentist. The alimentary canal in order Mouth → oesophagus → stomach → small intestine (duodenum then ileum) → large intestine (colon then rectum) → anus. The pancreas,…

8. Transport in plants – IGCSE Biology 0610

Xylem and phloem compared In the root the xylem is in the centre; in the stem the vascular bundles are in a ring near the outside; in the leaf they form the veins, with xylem on the upper side. The path of water Soil → root hair cell by osmosis → across the root → xylem → up the stem in a continuous column → leaf mesophyll → evaporates → diffuses out of the…

9. Transport in animals – IGCSE Biology 0610

Double circulation Blood passes through the heart twice for each circuit of the body. The pulmonary circuit carries blood to the lungs and back; the systemic circuit carries it to the rest of the body and back. The advantage is that blood leaves the heart at high pressure on the way to the body, so it travels faster and delivers oxygen more quickly. Through the heart in order Vena cava → right atrium → tricuspid valve → right ventricle → pulmonary artery…

10. Diseases and immunity – IGCSE Biology 0610

Key words A pathogen is a disease-causing organism. A transmissible disease is one in which the pathogen can be passed from one host to another. Transmission is either direct, through blood or other body fluids, or indirect, through contaminated food, water, surfaces or animal vectors. The body defences Antibodies Every pathogen carries antigens on its surface. A lymphocyte that recognises a particular antigen divides rapidly and makes antibodies with a complementary…

11. Gas exchange in humans – IGCSE Biology 0610

The pathway of air Nose → trachea → bronchi → bronchioles → alveoli. The trachea is held open by rings of cartilage so it cannot collapse. Inspired and expired air The lime-water test: expired air turns lime water milky faster than inspired air, showing it contains more carbon dioxide. Breathing movements Alveolar adaptations There are millions of them, giving a very large surface area. The wall is…

12. Respiration – IGCSE Biology 0610

What respiration is Respiration is the chemical reaction in cells that breaks down nutrient molecules to release energy. It happens in every living cell, all the time. It is not the same as breathing. The energy released is used for muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses and maintaining a constant body temperature. Aerobic respiration Word equation: glucose + oxygen → carbon dioxide + water. Balanced equation: C6H12O6 + 6O2 → 6CO2 +…

13. Excretion in humans – IGCSE Biology 0610

What excretion means Excretion is the removal from the body of the waste products of metabolism, toxic materials and substances in excess of requirements. Passing out undigested food is egestion, not excretion, because that food never entered the cells. The liver first Excess amino acids cannot be stored. In the liver they are deaminated: the amino group is…

14. Coordination and response – IGCSE Biology 0610

The nervous system It is made of the central nervous system – brain and spinal cord – and the peripheral nervous system, the nerves that reach the rest of the body. The reflex arc in order Stimulus → receptor → sensory neurone → relay neurone in the spinal cord → motor neurone → effector → response. A reflex action is rapid and automatic because the impulse does not travel up to the brain before the response happens. That speed is what protects the body from damage. The synapse Where two neurones meet there is a tiny gap. The impulse arrives, a neurotransmitter is released into the…

15. Drugs – IGCSE Biology 0610

What a drug is A drug is any substance taken into the body that modifies or affects chemical reactions in the body. Antibiotics Antibiotics kill or stop the growth of bacteria. They have no effect on viruses, because a virus has no cell processes of its own to attack – it reproduces inside the host’s cells using the host’s machinery. How resistance develops: In any large population of…

16. Reproduction – IGCSE Biology 0610

The two kinds The flower Self-pollination is the transfer of pollen to the stigma of the same flower or another flower on the same plant; cross-pollination is transfer to a different plant of the same species, and gives more variation. Fertilisation: a pollen tube grows down the style to…

17. Inheritance – IGCSE Biology 0610

The words, defined exactly Humans have 46 chromosomes in 23 pairs. A gamete has 23 – the haploid number. Mitosis and meiosis DNA and protein synthesis DNA is a double helix; the bases pair A with T and C with G. A sequence of three bases codes for one amino acid. The base sequence of a gene therefore determines the sequence of amino acids in a protein, and so the protein’s shape and job. Every cell carries every gene, but only some are switched on in any one cell – that is why a nerve cell and a muscle cell…

18. Variation and selection – IGCSE Biology 0610

Two kinds of variation Mutation A mutation is a change in the base sequence of DNA. It is the only source of new alleles. Most are neutral or harmful; a few are useful, and those are the raw material of evolution. The rate is increased by ionising radiation such as X-rays and gamma rays, and by chemical mutagens such as the tar in tobacco smoke. Natural selection, step by step There is genetic variation within…

19. Organisms and their environment – IGCSE Biology 0610

Energy enters once The Sun is the principal source of energy for all biological systems. Producers convert light energy to chemical energy in photosynthesis, and every other organism gets its energy from them. Why chains are short Only about 10% of the energy at one trophic level passes to the next. The rest is lost as heat from respiration, in undigested material passed out as faeces, and in urine. After four or five levels there is not enough energy left to support another. This is also why feeding people…

20. Human influences on ecosystems – IGCSE Biology 0610

Eutrophication, in order Excess fertiliser is washed off fields into a river or lake. Nitrates and phosphates make algae grow rapidly – an algal bloom. The bloom blocks light, so plants below die. Decomposers multiply as they break down the dead material. The decomposers use up the dissolved oxygen in respiration. Fish and other aerobic organisms suffocate. Untreated sewage causes exactly the same sequence, for the same reason. Air pollution The greenhouse effect: short-wave radiation from the Sun passes through the atmosphere and warms…

21. Biotechnology and genetic modification – IGCSE Biology 0610

Why bacteria They reproduce very rapidly in ideal conditions. They have few ethical concerns compared with animals. They can be grown on a wide range of cheap materials, including waste. Their plasmids make it straightforward to insert a new gene. They have no complex internal structures to…