Biology,
one step at a time.

Polymer properties depend on the number and sequence of monomers and, for some polymers, branching or folding. Different arrangements therefore produce different structures and functions even when the monomer types overlap.

Watch for: Do not name a biological process without explaining the mechanism. For Monomers and polymers, link the relevant structure or condition to the resulting effect.

On heating, a reducing sugar reduces blue copper(II) ions in Benedict's reagent to copper(I) oxide, producing an orange or brick-red precipitate at high concentration. The other observations correspond to tests for starch, protein and lipid.

Watch for: Do not name a biological process without explaining the mechanism. For Carbohydrates, link the relevant structure or condition to the resulting effect.

Triglycerides contain many carbon–hydrogen bonds that can release energy during oxidation. Because triglycerides are insoluble, they do not contribute many dissolved particles and therefore have little osmotic effect on water potential.

Watch for: Do not name a biological process without explaining the mechanism. For Lipids, link the relevant structure or condition to the resulting effect.

Carbohydrates contain carbon, hydrogen and oxygen, whereas proteins also contain nitrogen and may contain sulfur through amino acids such as cysteine and methionine. Elemental composition does not by itself describe the full structure.

Watch for: Do not name a biological process without explaining the mechanism. For General properties of proteins, link the relevant structure or condition to the resulting effect.

The spread suggests either natural variation or an anomalous result. Repeats under identical controlled conditions allow the anomaly to be investigated and a mean of concordant measurements to provide more reliable evidence.

Watch for: Do not name a biological process without explaining the mechanism. For Many proteins are enzymes, link the relevant structure or condition to the resulting effect.

A DNA nucleotide contains deoxyribose sugar, a phosphate group and one base: adenine, thymine, cytosine or guanine. RNA nucleotides instead contain ribose and use uracil in place of thymine.

Watch for: Do not name a biological process without explaining the mechanism. For Structure of DNA and RNA, link the relevant structure or condition to the resulting effect.

The parental strands separate and each acts as a template for a complementary new strand. Each daughter double helix therefore conserves one original strand and contains one newly polymerised strand.

Watch for: Do not name a biological process without explaining the mechanism. For DNA replication, link the relevant structure or condition to the resulting effect.

ATP is rapidly hydrolysed and regenerated. Phosphate transfer can raise a reactant's free energy or alter its reactivity, so energy released by respiration can be coupled to cellular work without ATP serving as a permanent energy store.

Watch for: Do not name a biological process without explaining the mechanism. For ATP, link the relevant structure or condition to the resulting effect.

Water has partial charges because oxygen is more electronegative than hydrogen. Water molecules orient around ions and interact with polar groups, separating and surrounding solute particles so they can remain dispersed in solution.

Watch for: Do not name a biological process without explaining the mechanism. For Water, link the relevant structure or condition to the resulting effect.

The sodium–potassium pump maintains a low Na⁺ concentration inside the epithelial cell. Na⁺ then moves in down its gradient through a co-transporter, carrying glucose into the cell against the glucose gradient.

Watch for: Do not name a biological process without explaining the mechanism. For Inorganic ions, link the relevant structure or condition to the resulting effect.

Ribosomes translate mRNA into polypeptides. Ribosomes on rough endoplasmic reticulum commonly make proteins destined for secretion or membranes, allowing the growing polypeptide to enter the endoplasmic-reticulum lumen for folding and transport.

Watch for: Do not name a biological process without explaining the mechanism. For Structure of eukaryotic cells, link the relevant structure or condition to the resulting effect.

All viruses are non-cellular structures with either DNA or RNA as their nucleic-acid core and a protein capsid. Only some viruses have an outer phospholipid envelope; viruses lack ribosomes and depend on host cells for replication.

Watch for: Do not name a biological process without explaining the mechanism. For Structure of prokaryotic cells and of viruses, link the relevant structure or condition to the resulting effect.

Resolution is the ability to distinguish two points that are close together as separate structures. Magnification only states how many times larger the image is than the specimen, so greater magnification without adequate resolution adds no new detail.

Watch for: Do not name a biological process without explaining the mechanism. For Methods of studying cells, link the relevant structure or condition to the resulting effect.

Following accurate DNA replication, mitosis distributes one copy of each chromosome to each daughter nucleus. Repeated cell division therefore increases cell number without changing chromosome number or normally changing genotype.

Watch for: Do not name a biological process without explaining the mechanism. For All cells arise from other cells, link the relevant structure or condition to the resulting effect.

Rising temperature increases molecular movement and can denature membrane proteins; greater heat disrupts bilayer organisation. More pigment crosses the tonoplast and plasma membrane, increasing supernatant absorbance.

Watch for: Do not name a biological process without explaining the mechanism. For Transport across cell membranes, link the relevant structure or condition to the resulting effect.

When a large proportion of a population is immune, an infected person is less likely to contact a susceptible host. Transmission chains are interrupted, reducing pathogen prevalence and indirectly protecting some people who cannot be vaccinated.

Watch for: Do not name a biological process without explaining the mechanism. For Cell recognition and the immune system, link the relevant structure or condition to the resulting effect.

As linear size increases, volume grows faster than surface area, while many cells lie farther from the exterior. Specialised surfaces provide area and mass transport maintains gradients over long distances.

Watch for: Do not name a biological process without explaining the mechanism. For Surface area to volume ratio, link the relevant structure or condition to the resulting effect.

Boyle's law links increased thoracic and lung volume to decreased pressure. Air then moves down the pressure gradient from the atmosphere into the lungs; the reverse pressure gradient drives quiet expiration as the muscles relax and elastic tissue recoils.

Watch for: Do not name a biological process without explaining the mechanism. For Gas exchange, link the relevant structure or condition to the resulting effect.

Specific sodium-dependent cotransporters absorb amino acids at the brush border. The sodium gradient created by basolateral pumps supplies the indirect energy, after which amino acids move toward blood through transport proteins.

Watch for: Do not name a biological process without explaining the mechanism. For Digestion and absorption, link the relevant structure or condition to the resulting effect.

As ventricular muscle contracts, ventricular pressure exceeds atrial pressure. The pressure difference forces atrioventricular valves shut, preventing backflow into the atria; semilunar valves open once ventricular pressure exceeds arterial pressure.

Watch for: Do not name a biological process without explaining the mechanism. For Mass transport in animals, link the relevant structure or condition to the resulting effect.

Sap exuding from a severed aphid stylet shows that sieve-tube contents are under positive hydrostatic pressure. This is consistent with bulk flow down a pressure gradient, although it is not alone a complete proof of every loading step.

Watch for: Do not name a biological process without explaining the mechanism. For Mass transport in plants, link the relevant structure or condition to the resulting effect.

The genetic code is read in non-overlapping triplets. Complementary transcription produces mRNA, and tRNA anticodons bring amino acids according to codon order, establishing primary structure.

Watch for: Do not name a biological process without explaining the mechanism. For DNA, genes and chromosomes, link the relevant structure or condition to the resulting effect.

RNA polymerase binds near a gene, uses the transcribed DNA strand as a template and joins complementary RNA nucleotides. The RNA sequence is complementary to the template and matches the non-transcribed strand except U replaces T.

Watch for: Do not name a biological process without explaining the mechanism. For DNA and protein synthesis, link the relevant structure or condition to the resulting effect.

Each bivalent can orient in either direction independently of other bivalents. Consequently, homologues assort into daughter cells in many combinations; random orientation of sister chromatids at metaphase II adds further variation after crossing over.

Watch for: Do not name a biological process without explaining the mechanism. For Genetic diversity from mutation, meiosis and fertilisation, link the relevant structure or condition to the resulting effect.

Allele differences and meiotic recombination create genetic variation; nutrition, climate and experience create environmental effects. Many phenotypes, such as height, reflect an interaction between genotype and environment.

Watch for: Do not name a biological process without explaining the mechanism. For Genetic diversity and adaptation, link the relevant structure or condition to the resulting effect.

A binomial is written using the genus followed by the specific epithet, conventionally italicised with the genus capitalised. Standardisation allows scientists using different languages to refer to the same species.

Watch for: Do not name a biological process without explaining the mechanism. For Species and taxonomy, link the relevant structure or condition to the resulting effect.

Farming supplies food and income, but practices can damage biodiversity and services such as pollination and soil protection. Evidence-led management seeks acceptable production with proportionate conservation safeguards.

Watch for: Do not name a biological process without explaining the mechanism. For Biodiversity within a community, link the relevant structure or condition to the resulting effect.

Phenotypes may be influenced by environment and different DNA changes may have no visible effect. Sequencing directly reveals base differences, although interpretation still requires homologous regions and suitable sampling.

Watch for: Do not name a biological process without explaining the mechanism. For Investigating diversity, link the relevant structure or condition to the resulting effect.

Electron transport powers proton movement from stroma into the thylakoid space. Photolysis also adds protons there. Protons then diffuse down their electrochemical gradient through ATP synthase to the stroma, driving ATP formation.

Watch for: Do not name a biological process without explaining the mechanism. For Photosynthesis, link the relevant structure or condition to the resulting effect.

Anaerobic conditions allow only the small substrate-linked ATP yield of glycolysis. Glucose is incompletely oxidised, and much energy remains in lactate or ethanol because electron transport and oxidative phosphorylation stop.

Watch for: Do not name a biological process without explaining the mechanism. For Respiration, link the relevant structure or condition to the resulting effect.

Each additional transfer loses usable biomass energy. Reducing weeds, pests and intermediate trophic levels can increase the fraction of primary production entering the intended human food chain, subject to wider impacts.

Watch for: Do not name a biological process without explaining the mechanism. For Energy and ecosystems, link the relevant structure or condition to the resulting effect.

Matter such as nitrogen and phosphorus remains in chemical forms that organisms and decomposers transform and reuse. Energy flows through trophic levels and is eventually transferred to the environment as heat.

Watch for: Do not name a biological process without explaining the mechanism. For Nutrient cycles, link the relevant structure or condition to the resulting effect.

A concentration series with a solvent control can reveal a dose response only if starting material, environment, duration and measurement are comparable. Replicates allow biological variation and uncertainty to be assessed.

Watch for: Do not name a biological process without explaining the mechanism. For Survival and response, link the relevant structure or condition to the resulting effect.

A tastant binds a receptor on a chemoreceptor cell, causing ion-channel changes and depolarisation. Calcium entry can stimulate neurotransmitter release onto a sensory neurone, which fires if threshold is reached.

Watch for: Do not name a biological process without explaining the mechanism. For Receptors, link the relevant structure or condition to the resulting effect.

Carbon dioxide contributes to carbonic acid formation and raises hydrogen-ion concentration. Peripheral chemoreceptors in carotid and aortic bodies and central receptors in the medulla relay this chemical change to control centres.

Watch for: Do not name a biological process without explaining the mechanism. For Control of heart rate, link the relevant structure or condition to the resulting effect.

Sodium channels inactivate while potassium channels open. K⁺ leaves, repolarising the membrane; slow closure can cause hyperpolarisation, and pumps plus diffusion restore the resting ion distribution during the refractory period.

Watch for: Do not name a biological process without explaining the mechanism. For Nerve impulses, link the relevant structure or condition to the resulting effect.

Acetylcholinesterase rapidly hydrolyses acetylcholine in the cleft into acetate and choline. Removing transmitter prevents continuous depolarisation; choline returns to the presynaptic knob for acetylcholine synthesis.

Watch for: Do not name a biological process without explaining the mechanism. For Synaptic transmission, link the relevant structure or condition to the resulting effect.

Filaments slide past one another without changing length. Greater overlap reduces regions containing only actin or only myosin, but the length of thick myosin filaments—and therefore the A band—does not change.

Watch for: Do not name a biological process without explaining the mechanism. For Skeletal-muscle contraction, link the relevant structure or condition to the resulting effect.

A receptor detects deviation from the normal range. Nervous or endocrine coordination activates muscles or glands, and their response reduces the original deviation, restoring the variable toward its set range.

Watch for: Do not name a biological process without explaining the mechanism. For Principles of homeostasis and negative feedback, link the relevant structure or condition to the resulting effect.

Insulin resistance means a given insulin concentration produces less glucose uptake and storage. Genetic susceptibility, excess visceral fat and inactivity can contribute, and pancreatic beta cells may eventually fail to compensate.

Watch for: Do not name a biological process without explaining the mechanism. For Control of blood glucose concentration, link the relevant structure or condition to the resulting effect.

The afferent arteriole is wider than the efferent arteriole, helping create high hydrostatic pressure. Water and small solutes cross fenestrated endothelium, basement membrane and podocyte filtration slits; cells and most proteins remain in blood.

Watch for: Do not name a biological process without explaining the mechanism. For Control of blood water potential, link the relevant structure or condition to the resulting effect.

A homozygous recessive tester contributes only recessive alleles. Recessive offspring show that the unknown parent supplied a recessive allele and is heterozygous; all dominant offspring support, but do not absolutely prove with a small sample, homozygosity.

Watch for: Do not name a biological process without explaining the mechanism. For Inheritance, link the relevant structure or condition to the resulting effect.

Differential reproductive success is selection and changes allele frequencies. Hardy–Weinberg equilibrium assumes no selection, mutation or migration, random mating and a sufficiently large population.

Watch for: Do not name a biological process without explaining the mechanism. For Populations, link the relevant structure or condition to the resulting effect.

A physical barrier divides the gene pool. Mutation, drift and different selection pressures change allele frequencies independently; if reproductive barriers later prevent successful interbreeding, the populations constitute separate species.

Watch for: Do not name a biological process without explaining the mechanism. For Evolution may lead to speciation, link the relevant structure or condition to the resulting effect.

Both forms can reduce growth, survival or reproduction when organisms need the same limiting resource. Intraspecific competitors often have especially similar requirements, while interspecific competition can affect realised niches and community composition.

Watch for: Do not name a biological process without explaining the mechanism. For Populations in ecosystems, link the relevant structure or condition to the resulting effect.

TYR codes for tyrosinase, an enzyme required in melanin synthesis. A mutation can alter the enzyme's amino-acid sequence and activity, producing reduced or absent melanin and the albinism phenotype.

Watch for: Do not name a biological process without explaining the mechanism. For Gene mutation can alter protein structure, link the relevant structure or condition to the resulting effect.

Stem cells maintain an undifferentiated population through self-renewal while developmental signals can direct daughter cells into specialised lineages. Potency describes the range of lineages available.

Watch for: Do not name a biological process without explaining the mechanism. For Most cellular DNA is not translated, link the relevant structure or condition to the resulting effect.

Hox genes are a conserved subset of homeobox genes that regulate developmental gene networks along body axes. Altering one regulator can therefore change the identity or placement of multiple structures rather than one enzyme alone.

Watch for: Do not name a biological process without explaining the mechanism. For Regulation of transcription and translation, link the relevant structure or condition to the resulting effect.

A controlled intervention tests direction: reducing the mark should restore transcription and protein if methylation is causal. Replication and appropriate controls address alternative explanations.

Watch for: Do not name a biological process without explaining the mechanism. For Gene expression and cancer, link the relevant structure or condition to the resulting effect.

Large sequence datasets can reveal patterns of similarity, divergence and conserved regions across genomes. Inference still depends on alignment, models, sampling and distinction between homology and analogy.

Watch for: Do not name a biological process without explaining the mechanism. For Using genome projects, link the relevant structure or condition to the resulting effect.

If the marker is linked to the transferred construct and its promoter works, transformed cells produce a fluorescent protein and can be detected. This confirms expression of the marker, though further tests may be needed for the desired protein.

Watch for: Do not name a biological process without explaining the mechanism. For Recombinant DNA technology, link the relevant structure or condition to the resulting effect.

Hybridisation requires sufficient complementarity and suitable temperature and salt conditions. Poor target preparation or detection failure can also produce a false negative.

Watch for: Do not name a biological process without explaining the mechanism. For Exploiting DNA differences within a species, link the relevant structure or condition to the resulting effect.

PCR can amplify selected variable regions and electrophoresis separates their fragments or alleles. A profile supports identity or relationship inference probabilistically, so sample quality, contamination and reference-population frequencies still matter.

Watch for: Do not name a biological process without explaining the mechanism. For Genetic fingerprinting, link the relevant structure or condition to the resulting effect.

Excessive kinetic energy disrupts hydrogen and ionic interactions. Denaturation reduces active-site complementarity and successful enzyme-substrate complex formation.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 1: effect of a named variable on an enzyme-controlled reaction, link the relevant structure or condition to the resulting effect.

Large disagreement may reflect sampling location, preparation quality or classification. Reviewing images blind and expanding the count can test these sources of variation.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 2: stained root-tip squashes, mitosis and mitotic index, link the relevant structure or condition to the resulting effect.

Different dimensions change exchange area and diffusion distance. Standardisation makes sucrose concentration the main systematic cause of response differences.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 3: dilution series and a calibration curve for plant-tissue water potential, link the relevant structure or condition to the resulting effect.

Alcohol can disrupt the cell-surface membrane and tonoplast. Escaping pigment colours the surrounding solution and provides a measure of permeability.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 4: effect of a named variable on cell-surface-membrane permeability, link the relevant structure or condition to the resulting effect.

Animal tissue can carry microorganisms and instruments can cut. Hygiene, sharps technique and specified biological-waste disposal control these hazards.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 5: dissection of a gas-exchange or mass-transport system, link the relevant structure or condition to the resulting effect.

The zone of inhibition reflects antimicrobial effect combined with diffusion. Larger zones suggest greater effectiveness only when disc loading and conditions are standardised.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 6: aseptic investigation of antimicrobial substances and microbial growth, link the relevant structure or condition to the resulting effect.

Capillary action should carry solvent past a concentrated spot on the stationary phase. Submerging the spot washes sample away and prevents separation.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 7: chromatography of leaf pigments, link the relevant structure or condition to the resulting effect.

Light-dependent electron transfer reduces DCPIP in place of the natural acceptor. Loss of blue colour therefore indicates dehydrogenase-linked electron transfer.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 8: effect of a named factor on chloroplast dehydrogenase activity, link the relevant structure or condition to the resulting effect.

Boiling destroys metabolic activity. Failure of the killed-yeast control to decolourise supports the conclusion that active respiration caused dye reduction.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 9: effect of a named variable on respiration in single-celled organisms, link the relevant structure or condition to the resulting effect.

Silica gel removes water vapour while damp material supplies it. Indicator strips confirm that the intended gradient exists before animals are introduced.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 10: effect of an environmental variable on animal movement, link the relevant structure or condition to the resulting effect.

The responses of known concentrations allow an unknown sample's absorbance to be converted into an estimated glucose concentration.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 11: glucose calibration curve and colorimetric analysis of an unknown sample, link the relevant structure or condition to the resulting effect.

If sites differ systematically in other environmental factors, herbicide may not be the sole explanation. Matched adjacent areas or baseline data strengthen inference.

Watch for: Do not name a biological process without explaining the mechanism. For Required practical 12: effect of an environmental factor on species distribution, link the relevant structure or condition to the resulting effect.