AS Biology definitions

A result that is really close to the true answer

The energy required that needs to be supplied before a chemical reaction will start

The part of an enzyme where a substrate molecule binds

Movement of molecules and ions across plasma membranes, against a concentration gradient thus requiring energy

A characteristic that increases and organism's chance of survival

The tendency a molecule has to bind with oxygen

An alternative form of a gene

A microscopic air sac in the lungs where gas exchange occurs

A monomer of proteins

A balloon-like swelling of an artery

Measurements that fall outside the range of values you'd expect or any pattern you have

A chemical used to treat bacterial diseases

When bacteria are able to survive in the presence of antibiotics

A protein produced by B-cells in response to the presence of a pathogen

A molecule found on the surface of a cell. A foreign antigen triggers an immune response

Where pathogens change their antigens

A route that water takes through a plant root to the xylem, through cell walls

A blood vessel that branches off of an artery

A respiratory condition where the airways become irritated and inflamed, usually because of an allergic reaction to substances such as pollen and dust

A fibrous plaque caused by the build up and hardening of white blood cells, lipids and connective tissue

A group of cells in the heart wall that are responsible for passing waves of electrical activity from the SAN on to the bundle of His

A valve in the heart linking the atria to the ventricles

A type of white blood cell involved in the immune response by producing antibodies

A nitrogen-containing molecule that forms part of a DNA nucleotide

A biochemical test for the presence of sugars

The variety of living organisms and ecosystems on Earth

A biochemical test for the presence of polypeptides and proteins

An effect by which an increase of carbon dioxide in the blood results in a reduction of haemoglobin's affinity for oxygen

A group of muscle fibres in the heart, responsible for conducting waves of electrical activity from the AVN to the Purkyne fibres

A tumour that invades surrounding tissue

A network of capillaries

An enzyme that catalyses the hydrolysis of carbohydrates

An ongoing sequence of contraction and relaxation of the atria and ventricles that keeps the blood continuously circulating around the body

• The volume of blood pumped by the heart per minute
• Measured in cm^3 per minute

Any disease associated with the heart and blood vessels

A waxy strip in the cell wall of an endodermis cell

A chemical that speeds up a chemical reaction without being used up itself

Where a change in one variable causes the change in another

The process that all body cells from multicellular organisms use to grow and divide

A method that separates the organelles in a cell

• The membrane found on the surface of animal cells (and just inside the cell wall of plant and prokaryotic cells
• Regulates the movement of substances into and out of the cell

The outermost cell layer found in plant cells

The immune response that involves T-cells

A polysaccharide made of long unbranched chains of beta-glucose

The point at which two strands of a chromosome are joined together

A green substance found in chloroplasts

An organelle present in cells where photosynthesis occurs

One 'arm' of a double stranded chromosome

A thread-like structure made up of one long DNA molecule

The act of arranging organisms into groups based on their similarities and differences

An organism from which all other organisms in a particular taxonomic group have evolved

A molecule that has a similar shape to a substrate and blocks an enzyme's active site

A reaction that releases a small molecule (eg water) when it links molecules together

When two bacteria come together and exchange genetic material

An extra experiment set up to eliminate the effect of some variables that can't be controlled

A group in a study that is treated in exactly the same way as the experimental group, apart from the factor you're investigating

A variable that is kept constant throughout an experiment

An artery that supplies the heart muscle with blood

When the coronary arteries have lots of atheromas in them, which restricts blood flow to the heart

A relationship between two variables

The outer layer of cells in a plant root

The system in which blood flows in the opposite direction to water in the gills of a fish

Behaviour carried out by organisms to attract a mate of the right species

When chromatids twist around each other and bits of them swap over during meiosis

A gel-like substance where most of the chemical reactions in a cell take place

The point at which an enzyme no longer functions as a catalyst

The pentose sugar in DNA

The variable you measure in an experiment

A type of flowering plant

The process of a cell becoming specialised

Net movement of particles from an area of higher concentration to an area of lower concentration

The process of breaking down food into substances that can be used by the body

A molecule formed from two amino acids

When a cell contains two copies of each chromosome

A molecule formed from two monosaccharides

The molecule in cells that stores genetic information

An enzyme that breaks the hydrogen bonds between two polynucleotide DNA strands during DNA replication

The process of determining the base order of a section of DNA

An enzyme that joins together the nucleotides on a new strand of DNA during DNA replication

A study involving a control group and an experimental group where neither the scientists involved nor the participants know which group the participants are in

• The structure of a DNA molecule
• - Two separate strands wound together in a spiral

A lung disease caused by smoking or long-term exposure to air pollution, where foreign particles in the smoke or air become trapped in the alveoli

A single layer of cells between the cortex and the xylem

• A system of membranes enclosing a fluid-filled space
• Involved with lipid and protein processing

The inner lining of a blood vessel

A protein that speeds up the rate of chemical reactions

The intermediate formed when a substrate molecule binds to the active site of an enzyme

The outermost layer of cells on a leaf

Organism made up of a cell (or cells) containing a nucleus

An organ specialised to exchange substances

A section of DNA within a gene that codes for amino acids

The diffusion of particles through carrier proteins or channel proteins in the plasma membrane

A test in which only the independent variable has been allowed to affect the dependant variable

When a haploid sperm fuses with a haploid egg to generate a diploid zygote

The formation of scar tissue in the lungs' which can be the result of an infection or exposure to substances such as asbestos or dust

Model describing the arrangement of molecules in a cell membrane

The reduction in genetic diversity that occurs when just a few organisms from a population start a new colony

A sex cell

The process of taking in gases that are needed for life processes and getting rid of waste gases

A boundary between the outside environment and the internal environment of an organism, over which gas exchange occurs

A section of DNA which codes for a protein

Different alleles being moved between populations when individuals migrate from one population into another

The complete range of alleles in a population

An event that causes a big reduction in a population and reduces genetic diversity

Differences in DNA

The alleles an organism has

The respiratory organ of a fish

A thin plate in a fish's gill

A polysaccharide made from a long, very branched chain of alpha-glucose

A bond formed between monosaccharides

• A group of fluid-filled flattened sacs
• Involved with processing and packaging lipids and proteins, and making lysosomes

A structure in chloroplasts formed from the stacking of thylakoid membranes

A cell that controls the opening and closing of stomata

An oxygen-carrying protein found in red blood cells

When a cell contains one copy of each chromosome

The number of heartbeats per minute

When unvaccinated people are protected because the occurrence of the disease is reduced by the number of people who are vaccinated

Protein the DNA is wound around in order to fit into the nucleus

A pair of matching chromosomes- each chromosome contains the same gene but may contain different alleles

When genes are passed on horizontally to other members of the same or different species, without reproduction occurring

The immune response that involves B-cells and the production of antibodies

A chemical reaction that uses a water molecule when it breaks bonds between molecules

Attracts water

Repels water

A specific testable statement, based on a theory, about what will happen in a test situation

The ability to respond quickly to an infecrion

Using antibodies to determine how similar proteins are

How many people suffer from a disease

The random division of maternal and paternal chromosomes into gametes during meiosis

The variable you change in an experiment

A measure of species diversity that takes into account the number of species present and the number individuals of each species

A disease caused by an infection with a pathogen

Variation between members of the same species

A period of the cell cycle in which the cell grows and DNA is replicated

Variation between different species

A section of DNA within a gene that does not code for amino acids

A biochemical test for the presence of starch

A solution with the same water potential as another solution or cell

The inability to digest lactose due to an insufficient amount of the enzyme lactase

A thin, flat piece of thylakoid found in the chloroplasts

A tiny structure found on the gill filament in a fish

An enzyme that catalyses the hydrolysis of lipids

The action of an oxygen molecule binding with a haemoglobin molecule

The position on a chromosome where a particular allele is found

A network of tubes which transports excess tissue fluid back into the circulatory system

A round organelle that contains digestive enzymes

How much bigger an image from a microscope is compared to the specimen

A system that carries substances to and from individual cells

The average of the values collected in a sample

A type of cell division where a parent cell divides to create four genetically different haploid cells

A white blood cell that remains in the body and remembers how to respond to infections

A type of plant cell present in a leaf and the main gas exchange surface in a plant

The rate at which energy is used by an organism

A strong fibre formed by chains of cellulose linked together by hydrogen bonds

A fold in the plasma membrane that increases the surface area

• An oval-shaped organelle with a double membrane
• The site of anaerobic respiration

A type of cell division where the parent cell divides to produce two genetically identical daughter cells

An antibody produced from a single group of genetically identical B-cells

A small, basic molecular unit

A monomer of carbohydrates

Staphylococcus aureus bacteria that are resistant to the antibiotic methicillin

An organism that has more than one cell

A section of repetitive DNA found outside of genes- does not code for amino acids

A change in the base sequence of an organism's DNA

Heart attack