TCE Biology exam 2026Exam: Mon 16 Nov · TASC timetable

The response acts in the opposite direction to the stimulus: a rise produces responses that cause a fall, and a fall produces responses that cause a rise.

Leak channels are always open and help set the resting potential. Voltage-gated channels open only when the membrane potential changes, producing the action potential.

A hormone reaches almost every cell, but only cells with complementary receptors respond. This is why one hormone can have a precise effect.

In vasodilation and vasoconstriction, the arterioles supplying the skin widen or narrow. The blood vessels do not move closer to or further from the skin surface.

The pathogen is the agent (the virus SARS-CoV-2); the disease is the illness it causes (COVID-19). Name both where you can.

Innate responses do not target a particular antigen and do not produce memory. They respond quickly, within minutes to hours, while the adaptive response takes days to build up.

Humoral: B cells and antibodies, against pathogens and toxins in body fluids. Cell-mediated: cytotoxic T cells, against infected body cells. Helper T cells are needed for both.

Only active immunity produces memory cells, so only active immunity gives long-term protection. Passive immunity fades as the borrowed antibodies are broken down.

Every evaluation mark needs a specific limitation linked to a specific improvement and its effect, for example "the lamp also heated the water, so temperature was not controlled; use a heat shield or water bath to keep temperature constant, improving validity".

Biodiversity is the variety of all living things, considered at the genetic, species, and ecosystem levels within a defined area.

An ecosystem is all the living organisms in an area together with the non-living physical environment, interacting as a functional unit through the flow of energy and the cycling of matter.

A trophic level is a feeding position in a food chain, defined by how many steps an organism is from the original energy source. Producers are the first trophic level, primary consumers the second, and so on.

Carrying capacity is the maximum population size of a species that an environment can support indefinitely, given the available resources such as food, water, and space.

An enzyme is a globular protein that acts as a biological catalyst, speeding up a specific chemical reaction by lowering its activation energy, without being permanently changed or consumed in the process.

Water is used and oxygen is made in the light-dependent stage (thylakoids). Carbon dioxide is used and glucose is made in the light-independent stage (stroma). ATP from the light-dependent stage can limit the light-independent stage.

Glycolysis: 2 ATP (cytoplasm). Krebs cycle: 2 ATP (matrix). Electron transport chain: most of the ATP (inner membrane). Aerobic total: about 36 to 38. Anaerobic total: 2.

An organelle is a specialised structure within a cell that carries out a particular function. Most are bounded by one or more membranes that separate their contents from the surrounding cytoplasm.

The hydrogen bonds between bases are weak, so the two strands can be separated for replication and transcription, while the strong bonds of the sugar-phosphate backbone keep each strand intact.

A gene is a length of DNA that codes for a functional product, usually a polypeptide (protein) but sometimes a functional RNA molecule.

Lactose does not switch the genes on directly. It inactivates the repressor. The operon is "off" by default and "on" only when the repressor is removed from the operator.

The genetic code is read in non-overlapping triplets from a fixed start point. Adding or removing one base changes every triplet that follows, whereas a substitution changes only one.

An adaptation is an inherited feature that increases an organism's chance of surviving and reproducing in its environment. Adaptations are the product of natural selection acting over many generations.

Microevolution is a change in the allele frequencies of a population over a small number of generations, driven by selection, drift, gene flow, mutation, or non-random mating.

Reproductive isolation is the prevention of gene flow between populations, so that they no longer interbreed successfully. It is the essential step that allows two populations to diverge into separate species.