UEE Biology cheat sheet

Prokaryotic cells lack membrane-bound organelles and a nucleus; eukaryotic cells compartmentalise reactions into organelles, which increases metabolic efficiency.

Magnification = image size ÷ actual size; use the same units on both sides, and convert µm to mm by dividing by 1000.

Surface area : volume ratio falls as cell size rises, so large cells need folds, villi or flattened shapes to sustain diffusion.

Water potential Ψ = Ψs (solute potential, always ≤ 0) + Ψp (pressure potential); water moves from higher to lower Ψ.

Enzyme rate rises with substrate concentration until active sites saturate; Vmax is reached, and Km is the substrate concentration giving half Vmax.

Competitive inhibitors raise Km but leave Vmax unchanged; non-competitive inhibitors lower Vmax without changing Km.

Condensation joins monomers with loss of water (amino acids → peptide bond; monosaccharides → glycosidic bond); hydrolysis reverses this.

Tests: Benedict's (reducing sugar, brick-red on heating), biuret (protein, purple), iodine (starch, blue-black), emulsion test (lipid, white emulsion).

ATP hydrolysis to ADP + Pi releases energy for active transport, muscle contraction and synthesis; ATP is resynthesised by respiration.

DNA is a double helix of antiparallel strands with complementary base pairing (A–T, G–C); each base pair is held by hydrogen bonds, three for G–C.

Semi-conservative replication: helicase unwinds, DNA polymerase adds nucleotides 5'→3', and each daughter molecule keeps one parental strand.

Transcription makes mRNA from the template strand; translation at the ribosome reads codons 5'→3' and tRNA anticodons deliver amino acids.

The genetic code is degenerate (several codons per amino acid), non-overlapping, and universal across most organisms.

Monohybrid cross of heterozygotes gives 3:1 phenotype and 1:2:1 genotype; a test cross with a recessive reveals the unknown genotype.

Dihybrid cross of double heterozygotes gives 9:3:3:1 only if genes assort independently; linkage distorts this ratio.

Chi-squared = Σ (O − E)² / E; compare with the critical value at the correct degrees of freedom (n − 1) to accept or reject the null hypothesis.

Mutations: substitution changes one codon (may be silent), while insertion or deletion causes a frameshift and usually a non-functional protein.

Sex-linked recessive traits appear more often in males because they have one X chromosome, so one allele is expressed.

Xylem transports water and mineral ions upward; cohesion between water molecules, adhesion to walls and transpiration pull drive the flow.

Transpiration rate rises with temperature, wind speed and light intensity and falls with high humidity; stomata close to conserve water.

Phloem translocates sucrose and amino acids from source to sink by mass flow, powered by active loading that lowers water potential.

Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2; light-dependent reactions occur on thylakoid membranes, the Calvin cycle in the stroma.

Limiting factors: at low light, light intensity limits rate; at high light, CO2 concentration or temperature becomes limiting.

Chlorophyll absorbs red and blue light and reflects green; a photosynthometer measures oxygen release or CO2 uptake to estimate rate.

Water and mineral uptake occurs through root hair cells by osmosis and active transport; root hairs increase surface area.

Plant hormones: auxin promotes elongation and shows apical dominance and phototropism; gibberellin promotes stem elongation and seed germination.

Monocots have one cotyledon and parallel veins; dicots have two cotyledons, net-like veins and a ring of vascular bundles.

Mammalian heart: right side pumps deoxygenated blood to lungs, left side pumps oxygenated blood to the body; valves prevent backflow.

Cardiac output = heart rate × stroke volume; exercise raises both, and the medulla controls rate via the autonomic nervous system.

Gas exchange surfaces need a large area, thin barrier, moist surface and a concentration gradient; alveoli and gills meet these.

Countercurrent flow in fish gills keeps a concentration gradient along the whole gill lamella, extracting more oxygen than parallel flow.

Neurone resting potential (about −70 mV) is maintained by the Na⁺/K⁺ pump; an action potential is a rapid depolarisation followed by repolarisation.

Synaptic transmission: an impulse releases neurotransmitter across the cleft, which binds receptors on the postsynaptic membrane.

Homeostasis uses negative feedback: a receptor detects change, a coordinator compares it with a set point, and an effector reverses it.

Nephron: ultrafiltration in the glomerulus, selective reabsorption of glucose and most water in the proximal tubule, and osmoregulation in the loop and collecting duct.

Insulin lowers blood glucose by promoting uptake and glycogen formation; glucagon raises it by stimulating glycogen breakdown.

Natural selection requires heritable variation, competition for resources, and differential survival and reproduction.

Directional selection shifts the mean, stabilising selection reduces variance, and disruptive selection favours both extremes.

Allele frequencies change through mutation, gene flow, genetic drift and selection; the Hardy–Weinberg model assumes none of these act.

Hardy–Weinberg: p + q = 1 and p² + 2pq + q² = 1, where p and q are allele frequencies and q² is the frequency of homozygous recessives.

Speciation occurs when populations become reproductively isolated, often after geographical separation (allopatric) or within one area (sympatric).

Evidence for evolution includes fossils, homologous structures, embryology, and molecular comparisons of DNA and protein sequences.

Convergent evolution produces analogous structures from different ancestors; divergent evolution produces homologous structures from a common ancestor.

Antibiotic resistance spreads because antibiotics select pre-existing resistant bacteria, which then reproduce and pass on the allele.

Hierarchy of classification: domain, kingdom, phylum, class, order, family, genus, species; the binomial name is Genus species.

Three domains are Bacteria, Archaea and Eukarya; the five-kingdom model uses Monera, Protista, Fungi, Plantae and Animalia.

Species definition: a group of organisms that can interbreed to produce fertile offspring; hybrids such as the mule are sterile.

Viruses are not classified as living cells: they are acellular, have no metabolism, and reproduce only inside a host cell.

Fungi have chitin cell walls, are heterotrophic and absorb nutrients; bacteria have peptidoglycan walls and no membrane-bound nucleus.

Arthropods have an exoskeleton and jointed limbs; insects have three body parts and six legs, arachnids have eight legs.

Biodiversity has three levels: genetic, species and ecosystem diversity; it is measured using species richness and evenness.

Classification now uses molecular phylogeny (rRNA and DNA sequences) to infer evolutionary relationships rather than appearance alone.

Population growth: exponential (J-shaped) when resources are unlimited; logistic (S-shaped) approaches carrying capacity K.

Population size estimate by mark–recapture: N ≈ (number marked × total in second sample) ÷ number of marked recaptures.

Energy is lost between trophic levels as heat, movement and excretion, so only about 10% passes to the next level; food chains rarely exceed five levels.

Pyramids of numbers may invert, but pyramids of energy are always upright because energy is lost at every transfer.

Carbon cycle: photosynthesis fixes CO2; respiration, combustion and decomposition release it; decomposers recycle nutrients.

Nitrogen cycle: nitrogen fixation, nitrification, assimilation, ammonification and denitrification; legumes host nitrogen-fixing bacteria in root nodules.

Eutrophication: nutrient runoff causes algal bloom, then decomposers deplete oxygen, killing fish and other aerobic organisms.

Succession: pioneer species colonise bare rock, then mosses, grasses and shrubs lead to a stable climax community.

Interspecific relationships: competition, predation, mutualism (both benefit), commensalism (one benefits, one unaffected) and parasitism.

Digestion: amylase breaks starch to maltose, protease breaks protein to amino acids, lipase breaks lipid to fatty acids and glycerol.

Villi of the small intestine increase surface area and have thin walls and a rich blood supply for efficient absorption.

Breathing: diaphragm contracts and flattens, ribs move up and out, thoracic volume rises, pressure falls and air enters.

Blood composition: red cells carry oxygen via haemoglobin, white cells defend against pathogens, platelets clot, plasma transports solutes.

Pathogens cause disease by damaging cells or releasing toxins; the immune response uses phagocytes, antibodies and memory cells.

Vaccination introduces antigens to stimulate antibodies and memory cells, giving immunity without the disease.

Health risk factors include smoking (lung cancer, cardiovascular disease), high salt intake (hypertension) and obesity (type 2 diabetes).

Type 1 diabetes is caused by insufficient insulin secretion; type 2 involves reduced cellular response to insulin.

Coronary heart disease arises when fatty deposits narrow the coronary arteries, reducing oxygen supply to cardiac muscle.

Independent variable is changed, dependent variable is measured, and controlled variables are kept constant to make the test fair.

Reliability improves with repeats and larger samples; validity depends on whether the method measures what it claims to measure.

Precision describes how close repeat readings are to each other; accuracy describes how close a value is to the true value.

Control group receives no treatment or a placebo, so the effect of the independent variable can be isolated.

A line graph suits continuous data; a bar chart suits categorical data; a scatter graph shows correlation between two variables.

Correlation does not prove causation; a third variable may explain the observed relationship.

Rate of reaction = change in quantity ÷ time; calculate the gradient of a tangent to find rate at a single point.

Random sampling with quadrats reduces bias; a transect samples organisms along an environmental gradient.

Aseptic technique and sterile equipment prevent contamination of cultures; controls check that the medium itself is not causing growth.

Prokaryotic cells lack membrane-bound organelles and a nucleus; eukaryotic cells compartmentalise reactions into organelles, which increases metabolic efficiency.

Magnification = image size ÷ actual size; use the same units on both sides, and convert µm to mm by dividing by 1000.

Surface area : volume ratio falls as cell size rises, so large cells need folds, villi or flattened shapes to sustain diffusion.

Water potential Ψ = Ψs (solute potential, always ≤ 0) + Ψp (pressure potential); water moves from higher to lower Ψ.

Enzyme rate rises with substrate concentration until active sites saturate; Vmax is reached, and Km is the substrate concentration giving half Vmax.

Competitive inhibitors raise Km but leave Vmax unchanged; non-competitive inhibitors lower Vmax without changing Km.

Condensation joins monomers with loss of water (amino acids → peptide bond; monosaccharides → glycosidic bond); hydrolysis reverses this.

Tests: Benedict's (reducing sugar, brick-red on heating), biuret (protein, purple), iodine (starch, blue-black), emulsion test (lipid, white emulsion).

ATP hydrolysis to ADP + Pi releases energy for active transport, muscle contraction and synthesis; ATP is resynthesised by respiration.

DNA is a double helix of antiparallel strands with complementary base pairing (A–T, G–C); each base pair is held by hydrogen bonds, three for G–C.

Semi-conservative replication: helicase unwinds, DNA polymerase adds nucleotides 5'→3', and each daughter molecule keeps one parental strand.

Transcription makes mRNA from the template strand; translation at the ribosome reads codons 5'→3' and tRNA anticodons deliver amino acids.

The genetic code is degenerate (several codons per amino acid), non-overlapping, and universal across most organisms.

Monohybrid cross of heterozygotes gives 3:1 phenotype and 1:2:1 genotype; a test cross with a recessive reveals the unknown genotype.

Dihybrid cross of double heterozygotes gives 9:3:3:1 only if genes assort independently; linkage distorts this ratio.

Chi-squared = Σ (O − E)² / E; compare with the critical value at the correct degrees of freedom (n − 1) to accept or reject the null hypothesis.

Mutations: substitution changes one codon (may be silent), while insertion or deletion causes a frameshift and usually a non-functional protein.

Sex-linked recessive traits appear more often in males because they have one X chromosome, so one allele is expressed.

Xylem transports water and mineral ions upward; cohesion between water molecules, adhesion to walls and transpiration pull drive the flow.

Transpiration rate rises with temperature, wind speed and light intensity and falls with high humidity; stomata close to conserve water.

Phloem translocates sucrose and amino acids from source to sink by mass flow, powered by active loading that lowers water potential.

Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2; light-dependent reactions occur on thylakoid membranes, the Calvin cycle in the stroma.

Limiting factors: at low light, light intensity limits rate; at high light, CO2 concentration or temperature becomes limiting.

Chlorophyll absorbs red and blue light and reflects green; a photosynthometer measures oxygen release or CO2 uptake to estimate rate.

Water and mineral uptake occurs through root hair cells by osmosis and active transport; root hairs increase surface area.

Plant hormones: auxin promotes elongation and shows apical dominance and phototropism; gibberellin promotes stem elongation and seed germination.

Monocots have one cotyledon and parallel veins; dicots have two cotyledons, net-like veins and a ring of vascular bundles.

Mammalian heart: right side pumps deoxygenated blood to lungs, left side pumps oxygenated blood to the body; valves prevent backflow.

Cardiac output = heart rate × stroke volume; exercise raises both, and the medulla controls rate via the autonomic nervous system.

Gas exchange surfaces need a large area, thin barrier, moist surface and a concentration gradient; alveoli and gills meet these.

Countercurrent flow in fish gills keeps a concentration gradient along the whole gill lamella, extracting more oxygen than parallel flow.

Neurone resting potential (about −70 mV) is maintained by the Na⁺/K⁺ pump; an action potential is a rapid depolarisation followed by repolarisation.

Synaptic transmission: an impulse releases neurotransmitter across the cleft, which binds receptors on the postsynaptic membrane.

Homeostasis uses negative feedback: a receptor detects change, a coordinator compares it with a set point, and an effector reverses it.

Nephron: ultrafiltration in the glomerulus, selective reabsorption of glucose and most water in the proximal tubule, and osmoregulation in the loop and collecting duct.

Insulin lowers blood glucose by promoting uptake and glycogen formation; glucagon raises it by stimulating glycogen breakdown.

Natural selection requires heritable variation, competition for resources, and differential survival and reproduction.

Directional selection shifts the mean, stabilising selection reduces variance, and disruptive selection favours both extremes.

Allele frequencies change through mutation, gene flow, genetic drift and selection; the Hardy–Weinberg model assumes none of these act.

Hardy–Weinberg: p + q = 1 and p² + 2pq + q² = 1, where p and q are allele frequencies and q² is the frequency of homozygous recessives.

Speciation occurs when populations become reproductively isolated, often after geographical separation (allopatric) or within one area (sympatric).

Evidence for evolution includes fossils, homologous structures, embryology, and molecular comparisons of DNA and protein sequences.

Convergent evolution produces analogous structures from different ancestors; divergent evolution produces homologous structures from a common ancestor.

Antibiotic resistance spreads because antibiotics select pre-existing resistant bacteria, which then reproduce and pass on the allele.

Hierarchy of classification: domain, kingdom, phylum, class, order, family, genus, species; the binomial name is Genus species.

Three domains are Bacteria, Archaea and Eukarya; the five-kingdom model uses Monera, Protista, Fungi, Plantae and Animalia.

Species definition: a group of organisms that can interbreed to produce fertile offspring; hybrids such as the mule are sterile.

Viruses are not classified as living cells: they are acellular, have no metabolism, and reproduce only inside a host cell.

Fungi have chitin cell walls, are heterotrophic and absorb nutrients; bacteria have peptidoglycan walls and no membrane-bound nucleus.

Arthropods have an exoskeleton and jointed limbs; insects have three body parts and six legs, arachnids have eight legs.

Biodiversity has three levels: genetic, species and ecosystem diversity; it is measured using species richness and evenness.

Classification now uses molecular phylogeny (rRNA and DNA sequences) to infer evolutionary relationships rather than appearance alone.

Population growth: exponential (J-shaped) when resources are unlimited; logistic (S-shaped) approaches carrying capacity K.

Population size estimate by mark–recapture: N ≈ (number marked × total in second sample) ÷ number of marked recaptures.

Energy is lost between trophic levels as heat, movement and excretion, so only about 10% passes to the next level; food chains rarely exceed five levels.

Pyramids of numbers may invert, but pyramids of energy are always upright because energy is lost at every transfer.

Carbon cycle: photosynthesis fixes CO2; respiration, combustion and decomposition release it; decomposers recycle nutrients.

Nitrogen cycle: nitrogen fixation, nitrification, assimilation, ammonification and denitrification; legumes host nitrogen-fixing bacteria in root nodules.

Eutrophication: nutrient runoff causes algal bloom, then decomposers deplete oxygen, killing fish and other aerobic organisms.

Succession: pioneer species colonise bare rock, then mosses, grasses and shrubs lead to a stable climax community.

Interspecific relationships: competition, predation, mutualism (both benefit), commensalism (one benefits, one unaffected) and parasitism.

Digestion: amylase breaks starch to maltose, protease breaks protein to amino acids, lipase breaks lipid to fatty acids and glycerol.

Villi of the small intestine increase surface area and have thin walls and a rich blood supply for efficient absorption.

Breathing: diaphragm contracts and flattens, ribs move up and out, thoracic volume rises, pressure falls and air enters.

Blood composition: red cells carry oxygen via haemoglobin, white cells defend against pathogens, platelets clot, plasma transports solutes.

Pathogens cause disease by damaging cells or releasing toxins; the immune response uses phagocytes, antibodies and memory cells.

Vaccination introduces antigens to stimulate antibodies and memory cells, giving immunity without the disease.

Health risk factors include smoking (lung cancer, cardiovascular disease), high salt intake (hypertension) and obesity (type 2 diabetes).

Type 1 diabetes is caused by insufficient insulin secretion; type 2 involves reduced cellular response to insulin.

Coronary heart disease arises when fatty deposits narrow the coronary arteries, reducing oxygen supply to cardiac muscle.

Independent variable is changed, dependent variable is measured, and controlled variables are kept constant to make the test fair.

Reliability improves with repeats and larger samples; validity depends on whether the method measures what it claims to measure.

Precision describes how close repeat readings are to each other; accuracy describes how close a value is to the true value.

Control group receives no treatment or a placebo, so the effect of the independent variable can be isolated.

A line graph suits continuous data; a bar chart suits categorical data; a scatter graph shows correlation between two variables.

Correlation does not prove causation; a third variable may explain the observed relationship.

Rate of reaction = change in quantity ÷ time; calculate the gradient of a tangent to find rate at a single point.

Random sampling with quadrats reduces bias; a transect samples organisms along an environmental gradient.

Aseptic technique and sterile equipment prevent contamination of cultures; controls check that the medium itself is not causing growth.