CSEC Biology key terms

The smallest unit of life that can carry out all the basic activities of living things. Some organisms consist of one cell; others, such as humans, are built from many.

A thin, flexible layer surrounding a cell that controls which substances enter and leave. It allows some materials through and blocks others, a property called selective permeability.

The membrane-bound structure in a eukaryotic cell that holds the chromosomes and directs the cell's activities. It is the control centre for growth, repair and reproduction.

The jelly-like fluid that fills the space inside a cell, outside the nucleus. Many chemical reactions of life occur here, and organelles are suspended within it.

A specialised structure inside a cell that performs a particular job, such as a mitochondrion releasing energy or a chloroplast trapping light. Each organelle has a distinct structure suited to its function.

An organelle where aerobic respiration takes place, releasing energy from glucose. Cells that need a lot of energy, such as muscle cells, contain many mitochondria.

A green organelle found in plant cells that contains chlorophyll and carries out photosynthesis. It traps light energy to make glucose from carbon dioxide and water.

The movement of particles from a region of higher concentration to a region of lower concentration, caused by random motion. It needs no energy from the cell and continues until concentrations are balanced.

The diffusion of water across a partially permeable membrane from a dilute solution to a more concentrated one. It explains how plant roots absorb water and how cells gain or lose water.

The movement of substances across a cell membrane from a lower to a higher concentration, using energy released by respiration. It allows cells to take in minerals even when soil levels are low.

A protein that speeds up a chemical reaction in living things without being used up. Each enzyme works best at a particular temperature and pH, and is denatured if conditions change too much.

The permanent loss of an enzyme's shape and function when it is heated too much or exposed to the wrong pH. The active site changes so the substrate no longer fits.

The process by which green plants use light energy to combine carbon dioxide and water into glucose, releasing oxygen. It takes place mainly in the leaves and stores energy in chemical form.

The green pigment in chloroplasts that absorbs light energy for photosynthesis. It absorbs mainly red and blue light and reflects green light, which is why leaves look green.

The chemical breakdown of glucose in cells to release energy for life processes. Aerobic respiration uses oxygen and produces carbon dioxide and water; anaerobic respiration occurs without oxygen.

A simple sugar produced by photosynthesis and used by cells as their main fuel. It is broken down during respiration to release energy, and its units join to form starch and cellulose.

A nutrient made of sugar units, such as starch, glucose and cellulose, that supplies energy. Foods like bread, rice and potatoes are rich sources.

A nutrient built from amino acids, needed for growth, repair and making enzymes. Meat, fish, eggs and beans are good sources; proteins are digested into amino acids before absorption.

A fat or oil used by the body for long-term energy storage and insulation. Lipids are digested into fatty acids and glycerol before they can be absorbed.

The building block from which proteins are made. About twenty different amino acids are used by living things, and their order determines the shape and function of a protein.

The molecule that carries genetic information in the form of a code. It is found in chromosomes and controls inherited characteristics by determining which proteins a cell makes.

A section of DNA that carries the instructions for one characteristic or for making one protein. Genes are passed from parents to offspring and may exist in different forms called alleles.

A thread-like structure of DNA and protein found in the nucleus, carrying genes. Human body cells contain 46 chromosomes arranged in 23 pairs.

One of the alternative forms of a gene, such as the tall and short forms of a plant height gene. An organism inherits one allele from each parent for each gene.

Describing an allele that shows its effect in the organism even when only one copy is present. The dominant characteristic appears in the offspring whenever at least one dominant allele is inherited.

Describing an allele that only shows its effect when two copies are present, one from each parent. A recessive characteristic can remain hidden for a generation if a dominant allele is also inherited.

The combination of alleles an organism carries for a particular characteristic, such as two identical or two different alleles. It is not always visible, unlike the phenotype.

The observable characteristics of an organism, produced by its genotype interacting with the environment. Eye colour and plant height are examples of visible phenotypes.

The control of conditions inside the body so they stay steady, despite changes outside. Examples include keeping body temperature near 37 degrees Celsius and controlling blood glucose and water levels.

A control mechanism in which a change is detected and a response reverses it, bringing conditions back towards normal. It keeps body temperature, blood glucose and water balance stable.

A chemical messenger made by a gland and carried in the blood to target organs, where it alters their activity. Insulin and adrenaline are examples.

The removal from the body of waste products made by chemical reactions inside cells, such as carbon dioxide and urea. It is different from egestion, which removes undigested food.

An organ that filters the blood, removing urea and excess water and salts to form urine. It also helps control water balance and blood pressure.

The firm, swollen state of a plant cell when it is full of water and the cell contents press against the cell wall. Turgor keeps soft plant parts upright; loss of it causes wilting.

The loss of water vapour from the leaves of a plant, mainly through small pores called stomata. It pulls water up the stem and cools the plant.

A community of living organisms together with the non-living parts of their environment, such as soil, water and air, interacting as a system. Energy flows through it and nutrients are recycled.

A diagram showing the transfer of energy from one organism to the next, beginning with a producer. Arrows point in the direction the energy moves, from eaten to eater.

An organism, usually a green plant or alga, that makes its own food by photosynthesis. Producers form the base of every food chain and supply energy to all other organisms.

An organism that cannot make its own food and must eat other organisms to obtain energy. Primary consumers eat producers; secondary consumers eat other animals.

An organism such as a bacterium or fungus that breaks down dead material and waste, releasing nutrients back into the soil. Decomposers recycle materials so producers can use them again.