Biology,
one step at a time.

A lilac or purple Biuret result shows that peptide bonds are present, so the sample contains protein. Iodine tests starch, Benedict's reagent tests reducing sugars and an emulsion test detects lipids.

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

Important brain regions are interconnected and difficult to access without harming healthy tissue. Neurones have limited replacement, so damage is hard to reverse even when imaging identifies the affected region.

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

Genome data can help identify disease-associated variants, trace migration and ancestry, and guide research. It does not remove environmental effects or ethical concerns about privacy and discrimination.

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

The same underlying five-digit bone plan in limbs used for walking, flying or swimming is homologous evidence for descent from a common ancestor. Fossils, tools and genetic comparisons provide additional evidence for human evolution.

Watch for: Do not name a biological process without explaining the mechanism. For Natural selection and genetic modification, 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 Health, disease and the development of medicines, link the relevant structure or condition to the resulting effect.

Translocation is the movement of dissolved assimilates, especially sucrose, through phloem from sources such as leaves to sinks such as roots, fruits and growing tissues.

Watch for: Do not name a biological process without explaining the mechanism. For Plant structures and their functions, 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 Animal coordination, control and homeostasis, link the relevant structure or condition to the resulting effect.

Arteries withstand and maintain higher pressure using thick muscular elastic walls. Veins return blood at lower pressure, have wider lumens and valves that reduce backflow.

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