key terms

• abundance

  a measure of how common something is
• active site

  the site on an enzyme where the reactants bind
• active transport

  the movement of substances from a low concentration to high concentration requiring energy from respiration due to being against the concentration gradient
• adaptations

  special features that make an organism well suited to the environment where it lives
• ADH

  anti-diuretic hormone helps control the water balance of the body and affects the amount of urine produced by the kidney
• adrenaline

  hormone that prepares the body for fight or flight
• adult stem cells

  stem cells that are found in adults that can differentiate and form a limited number of cells
• aerobic respiration

  an exothermic reaction in which glucose is broken down using oxygen to produce carbon dioxide and water and release energy for the cells
• agar gel

  widely used gel culture medium used for growing microorganisms
• algae

  simple aquatic organisms (protista) that make their own food by photosynthesis
• alleles

  different forms of the same gene, sometimes referred to as variants
• alveoli

  tiny air sacs in the lungs that increase the surface area for gaseous exchange
• amino acids

  molecules made up of carbon hydrogen and oxygen
• amylase

  enzyme that speeds up the digestion of starch into sugars
• anaerobic respiration

  exothermic reaction in which glucose is broken down in the absence of oxygen to produce lactic acid in animals and ethanol and carbon dioxide in plants and yeast
• aorta

  the artery that leaves the heart from the left ventricle and carries oxygenated blood to the body
• aphids

  insects that penetrate the plant phloem and feed on the dissolved food. they act as vectors that carry pathogenic viruses, bacteria and fungi into healthy plant tissue
• archaea

  one of the three domains containing primitive forms of bacteria that can live in many of the extreme environments of the world
• arteries

  blood vessels that carry blood away from the heat. they usually carry oxygenated blood and have a pulse
• asexual reproduction

  involves only one individual and the offspring is identical to the parent. there is no fusion of gametes or mixing of genetic information
• atria

  the upper chambers of the heart
• auxin

  a plant hormone that controls responses of plants to light (phototropism) and gravity (geotropism)
• bacteria

  single-celled prokaryotic organisms
• bases (DNA)

  nitrogenous compounds that make up part of the structure of DNA and RNA, they are represented by the letter A, T, C and G
• benign tumours

  growths of abnormal cells that are contained in one area, usually within a membrane and do not invade other tissues
• bile

  neutralises stomach acid to give a high pH for the enzymes from the pancreas and small intestine to work well. is not an enzyme
• biodiversity

  a measure of the variety of all the different species of organisms on earth
• binary fission

  reproduction by simple cell division, e.g. in bacteria
• biomass

  the amount of biological material in an organism
• cancer

  the common name for a malignant tumour, formed as a result of changes in cells that lead to uncontrolled growth and division
• capillaries

  the smallest blood vessels, they run between individual cells and have a wall that is only one cell thick
• carbohydrases

  enzymes that speed up the breakdown of carbohydrates into simple sugars
• carbohydrates

  molecules that contain only carbon, hydrogen and oxygen. they provide energy for the metabolism and are found in foods such as rice, potatoes and bread
• carbon cycle

  the cycling of carbon through the living and non-living world
• carcinogens

  agents that cause cancer of significantly increase the risk of developing cancer
• carriers

  individuals who are heterozygous for a recessive allele linked to genetic disorder. carriers have one healthy allele so aren't affected themselves but can pass the affected allele onto their offspring
• catalyst

  a substance that speeds up the rate of another reaction but is no used up or changes itself
• causal mechanism

  something that explains how one factor influences another
• cell cycle

  the three stage process of cell division in a body cell that involves mitosis and results in the formation of two identical daughter cells
• cell membrane

  the membrane around the contents of cell that controls what moves in and out of the cell