Biology,
one step at a time.

A messenger RNA copy carries the gene's information from the nucleus to a ribosome. The ribosome joins amino acids in the order specified by the mRNA; detailed transcription and translation mechanisms are not required here.

Watch for: Do not name a biological process without explaining the mechanism. For What is the genome and what does it do?, link the relevant structure or condition to the resulting effect.

Every human egg carries an X chromosome, while sperm carry either X or Y. Fertilisation by a Y-carrying sperm produces the usual XY chromosomal combination associated with male development.

Watch for: Do not name a biological process without explaining the mechanism. For How is genetic information inherited?, link the relevant structure or condition to the resulting effect.

Some variants are associated with disease risk or drug response, so genome information may guide screening or treatment choice. Predictions are probabilistic and must be interpreted alongside environment and clinical evidence.

Watch for: Do not name a biological process without explaining the mechanism. For How can and should gene technology be used?, link the relevant structure or condition to the resulting effect.

HIV attacks immune-system cells and can progress to AIDS, leaving the body less able to control opportunistic infections such as tuberculosis. HIV is transmitted through infected body fluids, not ordinary social contact.

Watch for: Do not name a biological process without explaining the mechanism. For What are the causes of disease?, link the relevant structure or condition to the resulting effect.

Antimicrobial compounds can inhibit or kill pathogens and are chemical defences. A cuticle and cell wall are physical barriers, while stomatal closure in darkness is not the specified chemical defence response.

Watch for: Do not name a biological process without explaining the mechanism. For How do organisms protect themselves against pathogens?, link the relevant structure or condition to the resulting effect.

Risk is rarely zero. A defensible decision uses the probability and severity of outcomes, vaccine effectiveness, uncertainty, individual circumstances and effects on other people rather than treating either benefit or harm as absolute.

Watch for: Do not name a biological process without explaining the mechanism. For How can we prevent the spread of infections?, link the relevant structure or condition to the resulting effect.

Plant disease diagnosis uses visible symptoms, distribution patterns and diagnostic tests, while first ruling out environmental causes. Plants also resist attack using barriers such as cuticle and cell walls and defensive chemicals.

Watch for: Do not name a biological process without explaining the mechanism. For How can we identify the cause of an infection?, link the relevant structure or condition to the resulting effect.

The association is consistent with a causal contribution but other factors, measurement differences and population composition may confound it. Stronger evidence uses individual exposure data, plausible mechanisms and controlled comparisons.

Watch for: Do not name a biological process without explaining the mechanism. For How can lifestyle, genes and the environment affect health?, link the relevant structure or condition to the resulting effect.

After laboratory and animal preclinical testing, phased clinical trials assess safety, suitable dose and effectiveness in people, using controls and increasingly large groups. No trial can guarantee zero side effects.

Watch for: Do not name a biological process without explaining the mechanism. For How can we treat disease?, link the relevant structure or condition to the resulting effect.

Plants convert glucose into cellulose for cell walls and also use it in respiration, store it as starch, make amino acids with nitrate ions, and make lipids. These uses support growth and metabolism.

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

A potometer records water uptake by a shoot. Most replaces water lost through transpiration, but a small amount is used in photosynthesis, growth or maintaining cells, so uptake is only an estimate of transpiration.

Watch for: Do not name a biological process without explaining the mechanism. For How do producers get the substances they need?, link the relevant structure or condition to the resulting effect.

Transpiration releases water vapour from leaves. Water cycles through evaporation, transpiration, condensation, precipitation and flows, while decomposers and microorganisms also drive carbon and nitrogen cycling.

Watch for: Do not name a biological process without explaining the mechanism. For How are organisms in an ecosystem interdependent?, link the relevant structure or condition to the resulting effect.

Replicated measurements of pollutant levels, oxygen, temperature and abundance on both sides of the discharge provide a comparison and reveal whether the biological pattern tracks the proposed cause. One observation cannot control natural variation.

Watch for: Do not name a biological process without explaining the mechanism. For How are populations affected by conditions in an ecosystem?, link the relevant structure or condition to the resulting effect.

Complete aerobic breakdown of glucose transfers substantially more energy to ATP than anaerobic pathways. Anaerobic respiration can continue without oxygen but releases less usable energy per glucose molecule.

Watch for: Do not name a biological process without explaining the mechanism. For What happens during cellular respiration?, link the relevant structure or condition to the resulting effect.

A scientific biological drawing uses clear, unbroken lines, no artistic shading and ruled label lines. It should represent the observed specimen and include scale or magnification where appropriate.

Watch for: Do not name a biological process without explaining the mechanism. For How do we know about mitochondria and other cell structures?, link the relevant structure or condition to the resulting effect.

Plant meristems retain cells that divide and differentiate throughout growth. Embryonic animal stem cells can form many cell types, whereas adult stem cells such as bone-marrow cells usually have a more limited range.

Watch for: Do not name a biological process without explaining the mechanism. For How do organisms grow and develop?, link the relevant structure or condition to the resulting effect.

A valid evaluation tests dose-response, crop damage, persistence, environmental movement and non-target effects. Selective action is useful only if risks and application conditions are understood.

Watch for: Do not name a biological process without explaining the mechanism. For How is plant growth controlled?, link the relevant structure or condition to the resulting effect.

An ethical clinical decision communicates the quality of evidence, possible benefits, severity and probability of harm, alternatives and uncertainty. The patient's informed values then matter alongside medical judgement.

Watch for: Do not name a biological process without explaining the mechanism. For Should we use stem cells to treat damage and disease?, link the relevant structure or condition to the resulting effect.

The liver forms urea from excess amino acids, and blood plasma carries it to the kidneys. Blood also transports oxygen, carbon dioxide, water and dissolved nutrients according to tissue requirements.

Watch for: Do not name a biological process without explaining the mechanism. For How do substances get into, out of and around our bodies?, link the relevant structure or condition to the resulting effect.

Brain injuries often differ in position and extent, may damage interconnected regions and are rare, so one case study is difficult to generalise. Researchers must also balance useful evidence against consent and welfare concerns.

Watch for: Do not name a biological process without explaining the mechanism. For How does the nervous system help us respond to changes?, link the relevant structure or condition to the resulting effect.

Testimonials are vulnerable to placebo effects, natural variation and selective reporting. A valid test needs defined outcomes, hormone measurements, an appropriate control and enough representative participants.

Watch for: Do not name a biological process without explaining the mechanism. For How do hormones control responses in the human body?, link the relevant structure or condition to the resulting effect.

ADH makes collecting ducts more permeable to water, so more water returns to the blood and a smaller volume of concentrated urine forms. Kidney failure may require dialysis or transplant; urea is made in the liver from excess amino acids.

Watch for: Do not name a biological process without explaining the mechanism. For Why do we need to maintain a constant internal environment?, link the relevant structure or condition to the resulting effect.

Barrier methods reduce sperm transfer and can reduce STI transmission. Hormonal methods alter reproductive hormone control but do not protect against infection; effectiveness, contraindications and user preference should be compared.

Watch for: Do not name a biological process without explaining the mechanism. For What role do hormones play in human reproduction?, link the relevant structure or condition to the resulting effect.

Function depends on precise long-distance connections, support cells and signal pathways. Transplanted cells must integrate safely, and scar tissue or ongoing damage may prevent recovery, so forming a neuron-like cell is not sufficient.

Watch for: Do not name a biological process without explaining the mechanism. For What can happen when organs and control systems stop working?, link the relevant structure or condition to the resulting effect.

If populations are isolated, different selection pressures and mutations can change their allele frequencies. Over many generations the differences may become large enough to prevent successful interbreeding, producing separate species.

Watch for: Do not name a biological process without explaining the mechanism. For How was the theory of evolution developed?, link the relevant structure or condition to the resulting effect.

Replicated populations exposed to the same controlled changes allow survival to be related to reproductive mode and variation. One case or uncontrolled species comparison cannot separate reproductive mode from other differences.

Watch for: Do not name a biological process without explaining the mechanism. For How do sexual and asexual reproduction affect evolution?, link the relevant structure or condition to the resulting effect.

Nested taxa organise diversity and communicate relationships, with species grouped into broader categories. Modern systems increasingly aim to reflect evolutionary ancestry supported by morphological and molecular evidence.

Watch for: Do not name a biological process without explaining the mechanism. For How does our understanding of biology help us classify the diversity of organisms on Earth?, link the relevant structure or condition to the resulting effect.

Replicated abundance data paired with pollution measurements can test the proposed association. Recording plausible confounders such as substrate, light and moisture helps assess whether distance from traffic rather than another factor explains the pattern.

Watch for: Do not name a biological process without explaining the mechanism. For How is biodiversity threatened and how can we protect it?, link the relevant structure or condition to the resulting effect.

Surface liquid is not part of the potato tissue and would falsely increase the measured mass. Blotting consistently removes this source of measurement error without extracting water from the cells.

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

Risk is reduced by choosing an appropriate organism, limiting contamination and growth of pathogens, keeping plates closed and following approved disposal procedures. The controls address both exposure and environmental release.

Watch for: Do not name a biological process without explaining the mechanism. For What needs to be considered when investigating a phenomenon scientifically?, link the relevant structure or condition to the resulting effect.

An unusual result may be genuine variation. Transparent analysis retains it or applies a stated pre-agreed rule; repeating the measurement and showing analyses with and without it can clarify its influence.

Watch for: Do not name a biological process without explaining the mechanism. For What conclusions can we make from data?, link the relevant structure or condition to the resulting effect.

Independent failure to reproduce lowers confidence and prompts examination of hidden conditions, errors, analysis and reporting. The original result is not automatically fraudulent, but the explanation needs stronger evidence.

Watch for: Do not name a biological process without explaining the mechanism. For How are scientific explanations developed?, link the relevant structure or condition to the resulting effect.

The proposal combines technical uncertainty with ethical questions about consent, inheritance, equity and acceptable intervention. A reasoned decision makes these assumptions explicit and compares less heritable alternatives.

Watch for: Do not name a biological process without explaining the mechanism. For How do science and technology impact society?, link the relevant structure or condition to the resulting effect.