JCE Biology cheat sheet

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles; eukaryotic cells have both. Bacteria are prokaryotes; plants, animals, fungi and protoctists are eukaryotes.

Plant cell features absent from animal cells: cellulose cell wall, large permanent vacuole with sap, chloroplasts with chlorophyll, and (in some tissues) plasmodesmata.

Animal cell features absent from plant cells: centrioles, cholesterol-containing flexible cell membrane, and lysosomes as a distinct organelle (plant cells use vacuoles and enzymes).

Organelle functions: nucleus = DNA and genetic control; mitochondrion = aerobic respiration and ATP; ribosome = protein synthesis; rough ER = protein transport; smooth ER = lipid synthesis; Golgi = modification and packaging; lysosome = hydrolysis of material.

Magnification = image size / actual size. Convert all lengths to the same unit before dividing. Actual size = image size / magnification.

Diffusion moves particles from high to low concentration down a gradient without energy input. Osmosis is diffusion of water across a partially permeable membrane from high to low water potential. Active transport moves substances against the gradient and requires ATP.

Water potential: pure water = 0 kPa; solutes lower water potential, so solutions are negative. Water moves from less negative (higher) to more negative (lower) water potential.

Enzymes are biological catalysts; they lower activation energy. Activity is affected by temperature (denaturation above optimum), pH (denaturation away from optimum), and substrate concentration (rate plateaus when all active sites are occupied).

Mitosis produces two genetically identical diploid daughter cells for growth, repair and asexual reproduction; stages are prophase, metaphase, anaphase, telophase, followed by cytokinesis.

Photosynthesis equation: 6CO2 + 6H2O -> C6H12O6 + 6O2, requiring light energy and chlorophyll. Light energy is converted to chemical energy in glucose.

Limiting factor: the factor in shortest supply that restricts the rate. Increasing light, CO2 or temperature raises the rate only until another factor becomes limiting.

Leaf adaptations: large flat surface for light capture, thin for short diffusion distance, stomata for gas exchange, palisade mesophyll with many chloroplasts, and a spongy mesophyll with air spaces.

Mineral deficiencies: nitrate for amino acids and proteins (stunted growth, yellowing); magnesium for chlorophyll (yellow leaves); phosphate for roots and respiration; potassium for enzyme function.

Balanced diet components: carbohydrates (energy), proteins (growth and repair), lipids (energy, insulation, membranes), vitamins A, C and D, minerals calcium and iron, water and dietary fibre.

Deficiency diseases: vitamin C = scurvy; vitamin D or calcium = rickets; iron = anaemia; protein-energy deficiency = kwashiorkor (with oedema) or marasmus (severe wasting).

Teeth: incisors cut, canines tear, premolars and molars crush and grind. Enamel is the hardest layer; dentine lies beneath; pulp contains nerves and blood vessels.

Dental decay results from bacteria fermenting sugars into acid that dissolves enamel. Prevention: reduced sugar frequency, fluoride, brushing, and regular checks.

Food tests: Benedict's for reducing sugar (blue to brick-red on heating); iodine for starch (brown to blue-black); Biuret for protein (blue to purple); ethanol emulsion for lipid (white emulsion).

Root hair cells increase surface area for water and mineral uptake. Water enters by osmosis; most minerals enter by active transport.

Xylem transports water and dissolved minerals upward only; vessels are dead, hollow, lignified tubes. Transpiration pull, cohesion and adhesion move water up the stem.

Transpiration rate rises with higher temperature, wind, and lower humidity, and with more open stomata in bright light. It falls when stomata close at night or in wilting.

Phloem transports sucrose and amino acids bidirectionally from sources (leaves) to sinks (roots, fruits, growing tips). Translocation requires living cells and energy.

Mammalian heart: right side pumps deoxygenated blood to the lungs via the pulmonary artery; left side pumps oxygenated blood to the body via the aorta. The left ventricle wall is thickest.

Blood vessels: arteries carry blood away from the heart at high pressure, with thick elastic muscular walls; veins carry blood to the heart at low pressure and have valves; capillaries are one cell thick for exchange.

Blood components: red cells (haemoglobin, oxygen transport, no nucleus in mammals), white cells (phagocytes engulf, lymphocytes make antibodies), platelets (clotting), plasma (transports dissolved substances).

Aerobic respiration: C6H12O6 + 6O2 -> 6CO2 + 6H2O, releasing about 38 ATP per glucose (in practice about 30-32 in eukaryotes). Anaerobic in muscle: glucose -> lactic acid, releasing much less energy.

Excretion: kidneys remove urea, excess salts and water; lungs remove CO2; skin removes water and salts. The nephron filters at the glomerulus and reabsorbs glucose, some salts and most water in the tubule.

Nervous pathway: stimulus -> receptor -> sensory neurone -> relay neurone in the CNS -> motor neurone -> effector (muscle or gland) -> response.

Reflex arc features: it bypasses conscious brain processing for speed. A synapse is a gap across which a neurotransmitter diffuses; this slows and directs impulses.

Neurone structure: dendrites receive, a long axon conducts, and the myelin sheath insulates and speeds conduction. The resting potential is maintained by the sodium-potassium pump.

The eye: the cornea refracts most light; the lens fine-focuses by accommodation. In bright light the iris constricts the pupil. The fovea has the highest cone density for sharp colour vision.

Hormones are chemical messengers secreted by endocrine glands into the blood, acting on target organs with specific receptors. Effects are slower and longer-lasting than nerve impulses.

Blood glucose control: high glucose -> insulin from the pancreas -> liver and muscle take up glucose and store glycogen. Low glucose -> glucagon -> glycogen is broken down to glucose.

Thermoregulation: too hot -> sweating and vasodilation; too cold -> shivering, vasoconstriction, hair erection and reduced sweating. The hypothalamus is the control centre.

Negative feedback reverses a deviation from the set point (e.g. temperature, blood glucose, water balance). Positive feedback amplifies a change and is rare (e.g. oxytocin in labour).

Tropisms: phototropism is controlled by auxin, which accumulates on the shaded side and causes cell elongation, bending the shoot toward light. Geotropism makes roots grow downward.

Asexual reproduction produces genetically identical offspring from one parent (e.g. runners, tubers, binary fission, cuttings). Sexual reproduction involves gamete fusion and produces genetic variation.

Human male reproductive system: testes make sperm and testosterone; sperm travel via the sperm duct and urethra, with seminal fluid added by the prostate and seminal vesicles.

Human female reproductive system: ovaries release eggs; fertilisation occurs in the oviduct (Fallopian tube); the zygote implants in the uterus lining.

Menstrual cycle: FSH from the pituitary matures the follicle; oestrogen thickens the uterus lining and triggers the LH surge; LH causes ovulation; progesterone maintains the lining.

Fertilisation: a sperm's acrosome enzymes digest the egg membrane; only one sperm nucleus fuses with the egg nucleus to form a diploid zygote.

Pregnancy: the placenta exchanges nutrients, oxygen and waste between mother and fetus and secretes progesterone. The amniotic fluid cushions the fetus.

Contraception: barrier methods block sperm; hormonal pills prevent ovulation by suppressing FSH and LH; IUDs affect implantation; sterilisation blocks the gamete ducts.

Growth in plants occurs at meristems (tips and cambium) by cell division and elongation. In animals, growth is usually determinate and occurs throughout the body by mitosis.

Developmental stages: seed germination needs water, oxygen and a suitable temperature; in humans the embryo develops into a fetus by about 8 weeks and is born at about 38-40 weeks.

A gene is a section of DNA coding for a protein. Alleles are alternative forms of a gene. Genotype is the allele combination; phenotype is the observable characteristic.

Dominant alleles are expressed when present in one copy (capital letter); recessive alleles require two copies (lowercase). Homozygous = identical alleles; heterozygous = different alleles.

Monohybrid cross: use a Punnett square. Heterozygous x heterozygous (Aa x Aa) gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio.

Test cross: cross an unknown dominant phenotype with a homozygous recessive to reveal its genotype (1:1 ratio if heterozygous, all dominant if homozygous).

Codominance: both alleles are expressed in the heterozygote (e.g. AB blood group). Incomplete dominance produces an intermediate phenotype.

Sex determination: human females are XX, males are XY. The father's sperm determines sex (X or Y).

DNA structure: a double helix of two strands joined by complementary base pairs, A with T and C with G, held by hydrogen bonds, with a sugar-phosphate backbone.

Mutation is a change in DNA sequence. It may be neutral, harmful or beneficial, and is the source of new alleles. Most mutations occur in body cells and are not inherited.

Genetic terms: pedigree shows inheritance across generations; carriers are heterozygous for a recessive disorder and show no symptoms (e.g. cystic fibrosis, sickle cell).

Population = individuals of one species in a habitat. Community = all populations in an area. Ecosystem = the community plus its abiotic environment.

Food chains show energy flow; arrows point in the direction of energy transfer. Only about 10% of energy passes to the next trophic level, so food chains rarely exceed five levels.

Energy is lost between trophic levels via respiration, heat, movement, egestion and excretion. Pyramids of biomass or energy are usually wider at the base.

Carbon cycle: photosynthesis removes CO2; respiration, combustion and decomposition release it. Nitrogen cycle: nitrogen fixation, nitrification, assimilation, denitrification.

Decomposers (bacteria and fungi) break down dead matter and recycle nutrients; their activity increases with warmth, moisture and oxygen.

Population size is affected by birth rate, death rate, immigration and emigration, and by biotic factors (predation, competition, disease) and abiotic factors (light, temperature, water, pH).

Quadrats estimate population density by counting in randomly placed squares; capture-recapture estimates population size using (number marked x total caught) / number recaptured.

Conservation strategies: protected areas, captive breeding and reintroduction, seed banks, habitat corridors, and sustainable resource use.

Indicator species reflect pollution: lichens indicate clean air; mayfly larvae indicate clean, oxygen-rich water; rat-tailed maggots indicate polluted water.

Pathogens include bacteria, viruses, fungi and protoctists. Viruses cannot reproduce outside a host cell and are not killed by antibiotics.

Transmission routes: airborne droplets, contaminated food and water, direct contact, blood, and vectors (e.g. mosquitoes for malaria, which is caused by a protoctist).

Body defences: skin, mucus and cilia, stomach acid, and white blood cells (phagocytes engulf, lymphocytes produce antibodies).

Immunity: active immunity follows infection or vaccination and involves antibody production and memory cells; passive immunity is short-lived antibody transfer (e.g. across the placenta).

Vaccination exposes the body to weakened or inactive antigens, triggering an immune response and memory cells, giving protection without disease.

Non-communicable diseases include cancer, coronary heart disease, diabetes and obesity. Risk factors include smoking, diet, alcohol, inactivity and genetic predisposition.

Experimental design: identify independent, dependent and controlled variables; use a control group; repeat and calculate a mean to reduce random error.

Validity requires controlling variables so the result can be attributed to the independent variable. Reliability improves with repeats; accuracy improves with suitable apparatus and technique.

Data presentation: line graphs for continuous data, bar charts for categories, and scatter graphs with a line of best fit for correlation. Correlation does not prove causation.

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles; eukaryotic cells have both. Bacteria are prokaryotes; plants, animals, fungi and protoctists are eukaryotes.

Plant cell features absent from animal cells: cellulose cell wall, large permanent vacuole with sap, chloroplasts with chlorophyll, and (in some tissues) plasmodesmata.

Animal cell features absent from plant cells: centrioles, cholesterol-containing flexible cell membrane, and lysosomes as a distinct organelle (plant cells use vacuoles and enzymes).

Organelle functions: nucleus = DNA and genetic control; mitochondrion = aerobic respiration and ATP; ribosome = protein synthesis; rough ER = protein transport; smooth ER = lipid synthesis; Golgi = modification and packaging; lysosome = hydrolysis of material.

Magnification = image size / actual size. Convert all lengths to the same unit before dividing. Actual size = image size / magnification.

Diffusion moves particles from high to low concentration down a gradient without energy input. Osmosis is diffusion of water across a partially permeable membrane from high to low water potential. Active transport moves substances against the gradient and requires ATP.

Water potential: pure water = 0 kPa; solutes lower water potential, so solutions are negative. Water moves from less negative (higher) to more negative (lower) water potential.

Enzymes are biological catalysts; they lower activation energy. Activity is affected by temperature (denaturation above optimum), pH (denaturation away from optimum), and substrate concentration (rate plateaus when all active sites are occupied).

Mitosis produces two genetically identical diploid daughter cells for growth, repair and asexual reproduction; stages are prophase, metaphase, anaphase, telophase, followed by cytokinesis.

Photosynthesis equation: 6CO2 + 6H2O -> C6H12O6 + 6O2, requiring light energy and chlorophyll. Light energy is converted to chemical energy in glucose.

Limiting factor: the factor in shortest supply that restricts the rate. Increasing light, CO2 or temperature raises the rate only until another factor becomes limiting.

Leaf adaptations: large flat surface for light capture, thin for short diffusion distance, stomata for gas exchange, palisade mesophyll with many chloroplasts, and a spongy mesophyll with air spaces.

Mineral deficiencies: nitrate for amino acids and proteins (stunted growth, yellowing); magnesium for chlorophyll (yellow leaves); phosphate for roots and respiration; potassium for enzyme function.

Balanced diet components: carbohydrates (energy), proteins (growth and repair), lipids (energy, insulation, membranes), vitamins A, C and D, minerals calcium and iron, water and dietary fibre.

Deficiency diseases: vitamin C = scurvy; vitamin D or calcium = rickets; iron = anaemia; protein-energy deficiency = kwashiorkor (with oedema) or marasmus (severe wasting).

Teeth: incisors cut, canines tear, premolars and molars crush and grind. Enamel is the hardest layer; dentine lies beneath; pulp contains nerves and blood vessels.

Dental decay results from bacteria fermenting sugars into acid that dissolves enamel. Prevention: reduced sugar frequency, fluoride, brushing, and regular checks.

Food tests: Benedict's for reducing sugar (blue to brick-red on heating); iodine for starch (brown to blue-black); Biuret for protein (blue to purple); ethanol emulsion for lipid (white emulsion).

Root hair cells increase surface area for water and mineral uptake. Water enters by osmosis; most minerals enter by active transport.

Xylem transports water and dissolved minerals upward only; vessels are dead, hollow, lignified tubes. Transpiration pull, cohesion and adhesion move water up the stem.

Transpiration rate rises with higher temperature, wind, and lower humidity, and with more open stomata in bright light. It falls when stomata close at night or in wilting.

Phloem transports sucrose and amino acids bidirectionally from sources (leaves) to sinks (roots, fruits, growing tips). Translocation requires living cells and energy.

Mammalian heart: right side pumps deoxygenated blood to the lungs via the pulmonary artery; left side pumps oxygenated blood to the body via the aorta. The left ventricle wall is thickest.

Blood vessels: arteries carry blood away from the heart at high pressure, with thick elastic muscular walls; veins carry blood to the heart at low pressure and have valves; capillaries are one cell thick for exchange.

Blood components: red cells (haemoglobin, oxygen transport, no nucleus in mammals), white cells (phagocytes engulf, lymphocytes make antibodies), platelets (clotting), plasma (transports dissolved substances).

Aerobic respiration: C6H12O6 + 6O2 -> 6CO2 + 6H2O, releasing about 38 ATP per glucose (in practice about 30-32 in eukaryotes). Anaerobic in muscle: glucose -> lactic acid, releasing much less energy.

Excretion: kidneys remove urea, excess salts and water; lungs remove CO2; skin removes water and salts. The nephron filters at the glomerulus and reabsorbs glucose, some salts and most water in the tubule.

Nervous pathway: stimulus -> receptor -> sensory neurone -> relay neurone in the CNS -> motor neurone -> effector (muscle or gland) -> response.

Reflex arc features: it bypasses conscious brain processing for speed. A synapse is a gap across which a neurotransmitter diffuses; this slows and directs impulses.

Neurone structure: dendrites receive, a long axon conducts, and the myelin sheath insulates and speeds conduction. The resting potential is maintained by the sodium-potassium pump.

The eye: the cornea refracts most light; the lens fine-focuses by accommodation. In bright light the iris constricts the pupil. The fovea has the highest cone density for sharp colour vision.

Hormones are chemical messengers secreted by endocrine glands into the blood, acting on target organs with specific receptors. Effects are slower and longer-lasting than nerve impulses.

Blood glucose control: high glucose -> insulin from the pancreas -> liver and muscle take up glucose and store glycogen. Low glucose -> glucagon -> glycogen is broken down to glucose.

Thermoregulation: too hot -> sweating and vasodilation; too cold -> shivering, vasoconstriction, hair erection and reduced sweating. The hypothalamus is the control centre.

Negative feedback reverses a deviation from the set point (e.g. temperature, blood glucose, water balance). Positive feedback amplifies a change and is rare (e.g. oxytocin in labour).

Tropisms: phototropism is controlled by auxin, which accumulates on the shaded side and causes cell elongation, bending the shoot toward light. Geotropism makes roots grow downward.

Asexual reproduction produces genetically identical offspring from one parent (e.g. runners, tubers, binary fission, cuttings). Sexual reproduction involves gamete fusion and produces genetic variation.

Human male reproductive system: testes make sperm and testosterone; sperm travel via the sperm duct and urethra, with seminal fluid added by the prostate and seminal vesicles.

Human female reproductive system: ovaries release eggs; fertilisation occurs in the oviduct (Fallopian tube); the zygote implants in the uterus lining.

Menstrual cycle: FSH from the pituitary matures the follicle; oestrogen thickens the uterus lining and triggers the LH surge; LH causes ovulation; progesterone maintains the lining.

Fertilisation: a sperm's acrosome enzymes digest the egg membrane; only one sperm nucleus fuses with the egg nucleus to form a diploid zygote.

Pregnancy: the placenta exchanges nutrients, oxygen and waste between mother and fetus and secretes progesterone. The amniotic fluid cushions the fetus.

Contraception: barrier methods block sperm; hormonal pills prevent ovulation by suppressing FSH and LH; IUDs affect implantation; sterilisation blocks the gamete ducts.

Growth in plants occurs at meristems (tips and cambium) by cell division and elongation. In animals, growth is usually determinate and occurs throughout the body by mitosis.

Developmental stages: seed germination needs water, oxygen and a suitable temperature; in humans the embryo develops into a fetus by about 8 weeks and is born at about 38-40 weeks.

A gene is a section of DNA coding for a protein. Alleles are alternative forms of a gene. Genotype is the allele combination; phenotype is the observable characteristic.

Dominant alleles are expressed when present in one copy (capital letter); recessive alleles require two copies (lowercase). Homozygous = identical alleles; heterozygous = different alleles.

Monohybrid cross: use a Punnett square. Heterozygous x heterozygous (Aa x Aa) gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio.

Test cross: cross an unknown dominant phenotype with a homozygous recessive to reveal its genotype (1:1 ratio if heterozygous, all dominant if homozygous).

Codominance: both alleles are expressed in the heterozygote (e.g. AB blood group). Incomplete dominance produces an intermediate phenotype.

Sex determination: human females are XX, males are XY. The father's sperm determines sex (X or Y).

DNA structure: a double helix of two strands joined by complementary base pairs, A with T and C with G, held by hydrogen bonds, with a sugar-phosphate backbone.

Mutation is a change in DNA sequence. It may be neutral, harmful or beneficial, and is the source of new alleles. Most mutations occur in body cells and are not inherited.

Genetic terms: pedigree shows inheritance across generations; carriers are heterozygous for a recessive disorder and show no symptoms (e.g. cystic fibrosis, sickle cell).

Population = individuals of one species in a habitat. Community = all populations in an area. Ecosystem = the community plus its abiotic environment.

Food chains show energy flow; arrows point in the direction of energy transfer. Only about 10% of energy passes to the next trophic level, so food chains rarely exceed five levels.

Energy is lost between trophic levels via respiration, heat, movement, egestion and excretion. Pyramids of biomass or energy are usually wider at the base.

Carbon cycle: photosynthesis removes CO2; respiration, combustion and decomposition release it. Nitrogen cycle: nitrogen fixation, nitrification, assimilation, denitrification.

Decomposers (bacteria and fungi) break down dead matter and recycle nutrients; their activity increases with warmth, moisture and oxygen.

Population size is affected by birth rate, death rate, immigration and emigration, and by biotic factors (predation, competition, disease) and abiotic factors (light, temperature, water, pH).

Quadrats estimate population density by counting in randomly placed squares; capture-recapture estimates population size using (number marked x total caught) / number recaptured.

Conservation strategies: protected areas, captive breeding and reintroduction, seed banks, habitat corridors, and sustainable resource use.

Indicator species reflect pollution: lichens indicate clean air; mayfly larvae indicate clean, oxygen-rich water; rat-tailed maggots indicate polluted water.

Pathogens include bacteria, viruses, fungi and protoctists. Viruses cannot reproduce outside a host cell and are not killed by antibiotics.

Transmission routes: airborne droplets, contaminated food and water, direct contact, blood, and vectors (e.g. mosquitoes for malaria, which is caused by a protoctist).

Body defences: skin, mucus and cilia, stomach acid, and white blood cells (phagocytes engulf, lymphocytes produce antibodies).

Immunity: active immunity follows infection or vaccination and involves antibody production and memory cells; passive immunity is short-lived antibody transfer (e.g. across the placenta).

Vaccination exposes the body to weakened or inactive antigens, triggering an immune response and memory cells, giving protection without disease.

Non-communicable diseases include cancer, coronary heart disease, diabetes and obesity. Risk factors include smoking, diet, alcohol, inactivity and genetic predisposition.

Experimental design: identify independent, dependent and controlled variables; use a control group; repeat and calculate a mean to reduce random error.

Validity requires controlling variables so the result can be attributed to the independent variable. Reliability improves with repeats; accuracy improves with suitable apparatus and technique.

Data presentation: line graphs for continuous data, bar charts for categories, and scatter graphs with a line of best fit for correlation. Correlation does not prove causation.

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles; eukaryotic cells have both. Bacteria are prokaryotes; plants, animals, fungi and protoctists are eukaryotes.

Plant cell features absent from animal cells: cellulose cell wall, large permanent vacuole with sap, chloroplasts with chlorophyll, and (in some tissues) plasmodesmata.

Animal cell features absent from plant cells: centrioles, cholesterol-containing flexible cell membrane, and lysosomes as a distinct organelle (plant cells use vacuoles and enzymes).

Organelle functions: nucleus = DNA and genetic control; mitochondrion = aerobic respiration and ATP; ribosome = protein synthesis; rough ER = protein transport; smooth ER = lipid synthesis; Golgi = modification and packaging; lysosome = hydrolysis of material.

Magnification = image size / actual size. Convert all lengths to the same unit before dividing. Actual size = image size / magnification.

Diffusion moves particles from high to low concentration down a gradient without energy input. Osmosis is diffusion of water across a partially permeable membrane from high to low water potential. Active transport moves substances against the gradient and requires ATP.

Water potential: pure water = 0 kPa; solutes lower water potential, so solutions are negative. Water moves from less negative (higher) to more negative (lower) water potential.

Enzymes are biological catalysts; they lower activation energy. Activity is affected by temperature (denaturation above optimum), pH (denaturation away from optimum), and substrate concentration (rate plateaus when all active sites are occupied).

Mitosis produces two genetically identical diploid daughter cells for growth, repair and asexual reproduction; stages are prophase, metaphase, anaphase, telophase, followed by cytokinesis.

Photosynthesis equation: 6CO2 + 6H2O -> C6H12O6 + 6O2, requiring light energy and chlorophyll. Light energy is converted to chemical energy in glucose.

Limiting factor: the factor in shortest supply that restricts the rate. Increasing light, CO2 or temperature raises the rate only until another factor becomes limiting.

Leaf adaptations: large flat surface for light capture, thin for short diffusion distance, stomata for gas exchange, palisade mesophyll with many chloroplasts, and a spongy mesophyll with air spaces.

Mineral deficiencies: nitrate for amino acids and proteins (stunted growth, yellowing); magnesium for chlorophyll (yellow leaves); phosphate for roots and respiration; potassium for enzyme function.

Balanced diet components: carbohydrates (energy), proteins (growth and repair), lipids (energy, insulation, membranes), vitamins A, C and D, minerals calcium and iron, water and dietary fibre.

Deficiency diseases: vitamin C = scurvy; vitamin D or calcium = rickets; iron = anaemia; protein-energy deficiency = kwashiorkor (with oedema) or marasmus (severe wasting).

Teeth: incisors cut, canines tear, premolars and molars crush and grind. Enamel is the hardest layer; dentine lies beneath; pulp contains nerves and blood vessels.

Dental decay results from bacteria fermenting sugars into acid that dissolves enamel. Prevention: reduced sugar frequency, fluoride, brushing, and regular checks.

Food tests: Benedict's for reducing sugar (blue to brick-red on heating); iodine for starch (brown to blue-black); Biuret for protein (blue to purple); ethanol emulsion for lipid (white emulsion).

Root hair cells increase surface area for water and mineral uptake. Water enters by osmosis; most minerals enter by active transport.

Xylem transports water and dissolved minerals upward only; vessels are dead, hollow, lignified tubes. Transpiration pull, cohesion and adhesion move water up the stem.

Transpiration rate rises with higher temperature, wind, and lower humidity, and with more open stomata in bright light. It falls when stomata close at night or in wilting.

Phloem transports sucrose and amino acids bidirectionally from sources (leaves) to sinks (roots, fruits, growing tips). Translocation requires living cells and energy.

Mammalian heart: right side pumps deoxygenated blood to the lungs via the pulmonary artery; left side pumps oxygenated blood to the body via the aorta. The left ventricle wall is thickest.

Blood vessels: arteries carry blood away from the heart at high pressure, with thick elastic muscular walls; veins carry blood to the heart at low pressure and have valves; capillaries are one cell thick for exchange.

Blood components: red cells (haemoglobin, oxygen transport, no nucleus in mammals), white cells (phagocytes engulf, lymphocytes make antibodies), platelets (clotting), plasma (transports dissolved substances).

Aerobic respiration: C6H12O6 + 6O2 -> 6CO2 + 6H2O, releasing about 38 ATP per glucose (in practice about 30-32 in eukaryotes). Anaerobic in muscle: glucose -> lactic acid, releasing much less energy.

Excretion: kidneys remove urea, excess salts and water; lungs remove CO2; skin removes water and salts. The nephron filters at the glomerulus and reabsorbs glucose, some salts and most water in the tubule.

Nervous pathway: stimulus -> receptor -> sensory neurone -> relay neurone in the CNS -> motor neurone -> effector (muscle or gland) -> response.

Reflex arc features: it bypasses conscious brain processing for speed. A synapse is a gap across which a neurotransmitter diffuses; this slows and directs impulses.

Neurone structure: dendrites receive, a long axon conducts, and the myelin sheath insulates and speeds conduction. The resting potential is maintained by the sodium-potassium pump.

The eye: the cornea refracts most light; the lens fine-focuses by accommodation. In bright light the iris constricts the pupil. The fovea has the highest cone density for sharp colour vision.

Hormones are chemical messengers secreted by endocrine glands into the blood, acting on target organs with specific receptors. Effects are slower and longer-lasting than nerve impulses.

Blood glucose control: high glucose -> insulin from the pancreas -> liver and muscle take up glucose and store glycogen. Low glucose -> glucagon -> glycogen is broken down to glucose.

Thermoregulation: too hot -> sweating and vasodilation; too cold -> shivering, vasoconstriction, hair erection and reduced sweating. The hypothalamus is the control centre.

Negative feedback reverses a deviation from the set point (e.g. temperature, blood glucose, water balance). Positive feedback amplifies a change and is rare (e.g. oxytocin in labour).

Tropisms: phototropism is controlled by auxin, which accumulates on the shaded side and causes cell elongation, bending the shoot toward light. Geotropism makes roots grow downward.

Asexual reproduction produces genetically identical offspring from one parent (e.g. runners, tubers, binary fission, cuttings). Sexual reproduction involves gamete fusion and produces genetic variation.

Human male reproductive system: testes make sperm and testosterone; sperm travel via the sperm duct and urethra, with seminal fluid added by the prostate and seminal vesicles.

Human female reproductive system: ovaries release eggs; fertilisation occurs in the oviduct (Fallopian tube); the zygote implants in the uterus lining.

Menstrual cycle: FSH from the pituitary matures the follicle; oestrogen thickens the uterus lining and triggers the LH surge; LH causes ovulation; progesterone maintains the lining.

Fertilisation: a sperm's acrosome enzymes digest the egg membrane; only one sperm nucleus fuses with the egg nucleus to form a diploid zygote.

Pregnancy: the placenta exchanges nutrients, oxygen and waste between mother and fetus and secretes progesterone. The amniotic fluid cushions the fetus.

Contraception: barrier methods block sperm; hormonal pills prevent ovulation by suppressing FSH and LH; IUDs affect implantation; sterilisation blocks the gamete ducts.

Growth in plants occurs at meristems (tips and cambium) by cell division and elongation. In animals, growth is usually determinate and occurs throughout the body by mitosis.

Developmental stages: seed germination needs water, oxygen and a suitable temperature; in humans the embryo develops into a fetus by about 8 weeks and is born at about 38-40 weeks.

A gene is a section of DNA coding for a protein. Alleles are alternative forms of a gene. Genotype is the allele combination; phenotype is the observable characteristic.

Dominant alleles are expressed when present in one copy (capital letter); recessive alleles require two copies (lowercase). Homozygous = identical alleles; heterozygous = different alleles.

Monohybrid cross: use a Punnett square. Heterozygous x heterozygous (Aa x Aa) gives a 3:1 phenotype ratio and a 1:2:1 genotype ratio.

Test cross: cross an unknown dominant phenotype with a homozygous recessive to reveal its genotype (1:1 ratio if heterozygous, all dominant if homozygous).

Codominance: both alleles are expressed in the heterozygote (e.g. AB blood group). Incomplete dominance produces an intermediate phenotype.

Sex determination: human females are XX, males are XY. The father's sperm determines sex (X or Y).

DNA structure: a double helix of two strands joined by complementary base pairs, A with T and C with G, held by hydrogen bonds, with a sugar-phosphate backbone.

Mutation is a change in DNA sequence. It may be neutral, harmful or beneficial, and is the source of new alleles. Most mutations occur in body cells and are not inherited.

Genetic terms: pedigree shows inheritance across generations; carriers are heterozygous for a recessive disorder and show no symptoms (e.g. cystic fibrosis, sickle cell).

Population = individuals of one species in a habitat. Community = all populations in an area. Ecosystem = the community plus its abiotic environment.

Food chains show energy flow; arrows point in the direction of energy transfer. Only about 10% of energy passes to the next trophic level, so food chains rarely exceed five levels.

Energy is lost between trophic levels via respiration, heat, movement, egestion and excretion. Pyramids of biomass or energy are usually wider at the base.

Carbon cycle: photosynthesis removes CO2; respiration, combustion and decomposition release it. Nitrogen cycle: nitrogen fixation, nitrification, assimilation, denitrification.

Decomposers (bacteria and fungi) break down dead matter and recycle nutrients; their activity increases with warmth, moisture and oxygen.

Population size is affected by birth rate, death rate, immigration and emigration, and by biotic factors (predation, competition, disease) and abiotic factors (light, temperature, water, pH).

Quadrats estimate population density by counting in randomly placed squares; capture-recapture estimates population size using (number marked x total caught) / number recaptured.

Conservation strategies: protected areas, captive breeding and reintroduction, seed banks, habitat corridors, and sustainable resource use.

Indicator species reflect pollution: lichens indicate clean air; mayfly larvae indicate clean, oxygen-rich water; rat-tailed maggots indicate polluted water.

Pathogens include bacteria, viruses, fungi and protoctists. Viruses cannot reproduce outside a host cell and are not killed by antibiotics.

Transmission routes: airborne droplets, contaminated food and water, direct contact, blood, and vectors (e.g. mosquitoes for malaria, which is caused by a protoctist).

Body defences: skin, mucus and cilia, stomach acid, and white blood cells (phagocytes engulf, lymphocytes produce antibodies).

Immunity: active immunity follows infection or vaccination and involves antibody production and memory cells; passive immunity is short-lived antibody transfer (e.g. across the placenta).

Vaccination exposes the body to weakened or inactive antigens, triggering an immune response and memory cells, giving protection without disease.

Non-communicable diseases include cancer, coronary heart disease, diabetes and obesity. Risk factors include smoking, diet, alcohol, inactivity and genetic predisposition.

Experimental design: identify independent, dependent and controlled variables; use a control group; repeat and calculate a mean to reduce random error.

Validity requires controlling variables so the result can be attributed to the independent variable. Reliability improves with repeats; accuracy improves with suitable apparatus and technique.

Data presentation: line graphs for continuous data, bar charts for categories, and scatter graphs with a line of best fit for correlation. Correlation does not prove causation.