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A molecule consisting of two amino acids joined by a peptide bond.


The process of taking materials into a cell by surrounding them with plasma membrane, which pinches off to form a vesicle inside the cell. This is an active process requiring ATP.

Exchange surface

A specialised area adapted to make it easier for molecules to cross from one side of the surface to the other.


Taxonomic group used in the classification of living organisms. Contains related genera.


A vessel used to grow microorganisms in large numbers.


Sex cells, usually haploid (one set of chromosomes). Fuse during sexual reproduction to form zygotes (diploid).

Gene pool

The sum total and variety of all the genes in a population or species at a given time.

Glycosidic bond

The covalent bond formed when carbohydrate molecules are joined together in condensation reactions.


The place where an organism or population lives. It includes the climatic, topographic and edaphic factors as well as the plants and animals that live there.


The iron-containing prosthetic group found in haemoglobin.

Haemoglobinic acid

The acid produced when haemoglobin takes up hydrogen ions.


The rupturing of animal cell surface membranes, and subsequent release of their contents, when cells placed in a solution of higher water potential and water enters by osmosis.


Complete mental, physical and social wellbeing.


Type of protein associated with DNA in eukaryotes. DNA is wound around them to form chromatin.


Chemicals made in endocrine glands that are carried in the blood to target cells/tissues/organs. They act as chemical messengers.

Hydrocarbon chain

A chain of carbon atoms bonded together with hydrogen atoms bonded onto the carbons.

Immune response

A response to an antigen, which involves the activation of lymphocytes.

Immunological memory

Ability of the immune system to respond very quickly to antigens that it recognises as they have entered the body before.


The number of new cases of a disease in a certain time period.

Induced fit (hypothesis)

The theory of enzyme action in which the enzyme molecule changes shape to fit the substrate molecule more closely as it binds to it.


A group of factors with non-specific antiviral activity. They also affect the immune system.


Inside the cell.


An atom (or group of atoms) carrying a positive or a negative charge.

Ionic bond

Attraction between oppositely charged ions.


Fibrous protein found in skin, hair and nails.


A diverse group of chemicals that includes triglycerides, fatty acids and cholesterol.

Lock-and-key hypothesis

The simple theory of enzyme action where the active site is directly complementary to the substrate molecule.


A cavity surrounded by a cell wall in cells, such as xylem vessels, which have lost their cell contents. Also used for the central cavities of blood vessels.


A type of white blood cell activated as part of the immune response.


Membrane-bound vesicles made by pinching off from the Golgi body. They usually contain digestive enzymes.


Large, phagocytic, amoeba-like white blood cells that engulf, ingest and destroy bacteria, damaged cells and worn-out red blood cells.


The number of time greater an image is than the object.

Messenger RNA (mRNA)

A type of RNA polynucleotide involved in protein synthesis. Carries the information coding for a polypeptide from the nucleus to the ribosomes in the cytoplasm.

Microtubule motors

Proteins associated with microtubules. The proteins can move along microtubules. Kinesin moves towards the (+) end of the microtubules and dynein moves towards the (-) end.


Nuclear division that results in the formation of cells that are genetically identical to the parent cell.


A crop of plants of a single species bred to be very similar.


A small molecule that is one of the units bonded together to form a polymer.


A simple sugar molecule. The monomer of polysaccharides.


The proportion of people in a population who are ill with a particular disease at any one time.


The number of people who die from a disease in a certain time period.


A slimy substance secreted by goblet cells in animal epithelial tissues. It is made up mostly of glycoproteins and protects and/or lubricates the surface on to which it is secreted.


A change in the structure of DNA, or in the structure and number of chromosomes.


The mass of filaments (hyphae) that make up the body of a fungus.

Natural selection

The mechanism for evolution in which the best-adapted organisms in a population can outcompete those that are less well-adapted.


The exact role of an organism in the ecosystem - its use of the living and non-living components of the ecosystem.

Non-competitive inhibitor

An inhibitor of an enzyme-controlled reaction that binds to the enzyme molecule in a region away from the active site.

Nuclear envelope

The double membrane structure surrounding the nucleus in eukaryotic cells.


The monomer of nucleic acids consisting of a phosphate, a sugar and an organic base.


A large, membrane-bound organelle found in eukaryotic cells, which contains the genetic material in the form of chromosomes.


The total substances taken into an animal or plant for use in metabolism (the sum total of its diet).


Steroid hormone made in ovaries.


An animal that eats plant and animal material.

Opportunistic infection

Infection caused by an organism that infects a host with a weakened (compromised) immune system.


A collection of tissues that work together to perform a specific overall function or set of functions within a multicellular organism.


Structure inside a cell. Each has a specific function and many are surrounded by membrane.

Organic base

Nitrogenous coompound in nucleic acid: adenine, thymine, uracil, cytosine, guanine are examples.

Oxygen tension

The amount of oxygen in the air expressed as the pressure created by the presence of oxygen, expressed in kilopascals (kPa).


Describes blood carrying oxygen in the form of oxyhaemoglobin.


Haemoglobin with oxygen molecules attached.


Describes a disease that is spreading worldwide or over continents.


Relatively unspecialised plant cells. They have living contents and thin, permeable cellulose cell walls. They may be able to photosynthesise, store food or support young plants.

Partial pressure

The proportion of total pressure provided by a particular gas as part of a mixture of gases.

Partially permeable membrane

A membrane that will allow some molecules to pass through but will not allow some others to pass through.

Passive immunity

Immunity acquired indirectly without activation of the lymphocytes, such as through the placenta, from breast milk, or by injection.


An organism that causes disease.


A molecule consisting of a small number of amino acids bonded together by (covalent) peptide bonds.

Peptide bond

The covalent bond formed when amino acids are joined together in condensation reactions.


Muscular contractions of muscle layers of gut to squeeze food along.


Gives measure of acidity/alkalinity of a solution. It is the reciprocal of the logarithmic value of the hydrogen ion concentration.


A cell that can carry out phagocytosis and ingest bacteria or small particles. Macrophages and neutrophils are phagocytes.


A vacuole inside a phagocyte which is created by an infolding of the plasma (cell surface) membrane to engulf a foreign particle. The foreign particle is held inside this.


A tissue in plants that is used to transport dissolved sugars and other substances.


A molecule consisting of a glycerol molecule, two fatty acid molecules and a phosphate group covalently bonded together. Forms the basis of cell membranes.


Process by which plants, some bacteria and some protoctists make food using carbon dioxide, water and sunlight energy.


The evolutionary relationships between organisms.


A taxonomic group used in classification of living organisms. Contains similar classes.


The process of endocytosis involving the bulk movement of liquids into a cell.

Pits (or bordered pits)

Thin areas in the lignified walls of xylem tissue cells that allow communication between adjacent cells.


Fatty material built up under the endothelium of an artery.

Plasma cells

Mature B-lymphocytes (white blood cells) that secrete a specific kind of antibody.

Plasma proteins

Proteins made in the liver that are found in the non-cellular fraction of the blood.


Small, circular piece of DNA present in some bacterial cells. May have genes for antibiotic resistance and can also be used as vectors in genetic engineering.


A fine strand of cytoplasm that links the protoplasm of adjacent cells through a thin area of cell wall called a pit.


Detachment of the plasma membrane from the cell wall as the cytoplasm shrinks when water is lost from a plant cell.


Fragments of cells in the blood that play a part in blood clotting.


Stem cells capable of differentiating to become a limited number of cell types found in the organism (e.g. cells of an early embryo).


A large molecule made up of many/repeating similar, smaller molecules (monomers) covalently bonded together.


A polymer consisting of many nucleotide monomers covalently bonded together (DNA and RNA are examples).


A polymer consisting of many amino acid monomers covalently bonded together.


A polymer consisting of many monosaccharide monomers covalently bonded together.


Apparatus used to measure water uptake in a leafy shoot and so to estimate rate of transpiration.


A suspension of small solid particles in a liquid, produced by a chemical reaction.


The number of people with a particular disease at a certain time.

Primary defences

The defences that prevent the entry of a pathogen into the body.

Primary structure

The sequence of amino acids found in a protein molecule.


An organism with cells that do not contain a true nucleus.


The phase of mitosis where the chromosomes become visible as a pair of sister chromatids joined at the centromere.

Prosthetic group

A non-protein organic molecule that forms a permanent part of a functioning protein molecule.


An enzyme capable of digesting proteins.


A polymer consisting of many amino acid monomers covalently bonded together.

Pulmonary circulation

The circulation of the blood through the lungs.

Pulmonary vein

The vein carrying oxygenated blood from the lungs to the left atrium of the heart.


Adenine and guanine - nitrogenous bases consisting of a double ring structure.

Purkyne tissue (Purkinje tissue)

Specialised tissue (muscle fibres) in the septum of the heart that conducts the electrical stimulus from the sinoatrial node to the ventricles.


Thymine, cytosine and uracil - nitrogenous bases consisting of a single ring structure.


A square frame used for sampling in field work.


A study is that does not involve quantity (numbers). For example, simple observations to see if a particular species lives in a selected area.


A study involving quantity (numbers). For example, if you count the number of individuals of a species in a selected area.

Quaternary structure

Protein structure where a protein consists of more than one polypeptide chain e.g. Haemoglobin and insulin.

Receptor sites

Protein or glycoprotein molecules on cell surfaces, used for attachment of specific substances such as hormones or viruses.

Reducing sugar

A carbohydrate monomer or dimer that gives a positive result in Benedict's test because it is able chemically to reduce copper sulfate in solution.


Chemical reaction involving the gain of electrons or the addition of hydrogen.


The ability to distinguish two separate points as distinct from each other.


The process in which energy is released from complex molecules, such as glucose, within cells and transferred to molecules of ATP.


The 5-carbon (pentose) sugar found in RNA nucleotides.

Ribosomal RNA (rRNA)

The nucleic acid found in ribosomes.


The organelle on which proteins are synthesised inside the cell.

Risk factor

A factor that increases the chance that you may develop a particular disease.


A single-stranded polynucleotide molecule that exists in three forms. Each form plays a part in the synthesis of proteins within cells.

Root hair cells

Cells in the epithelium of roots that have long extensions to increase surface area for the absorption of water and minerals.

Secondary defences

Defences that attempt to kill or inactivate pathogens that have already invaded the body.

Secondary structure

The local coiling or folding parts of a protein molecule due to the formation of hydrogen bonds formed as the protein is synthesised. E.g. a-helix and b-pleated sheets.


The release of a substance made inside the cell using the process of exocytosis.

Selection pressure

An external pressure that drives evolution in a particular direction.

Semi-conservative replication

The replication of a DNA strand where the replicated double helix consists of one old strand and one newly synthesised strand.

Semilunar valves

Valves between the ventricles and the main arteries leading out of the heart, which prevent backflow of blood.


The wall separating the ventricles of the heart.

Sexual reproduction

Production of a new individual formed by the fusing of gametes from two different parents so that the offspring have a unique combination of alleles from both parents.

Sieve tube element

A cell in phloem tissue through which sap is transported. It has very little cytoplasm, no nucleus, and non-thickened cellulose cell walls, with the end walls perforated.

Simple diffusion

The movement of molecules from a region of their higher to lower concentration.

Single circulatory system

A circulation in which blood flows through the heart once during each circulation of the body.


A part of a plant that removes sugars from the phloem.

Sinoatrial node (SAN)

The patch of tissue that initiates the heartbeat by sending waves of excitation over the atria.

Smooth muscle

A type of muscle (involuntary muscle) found mostly in certain internal organs and involved in involuntary movements such as peristalsis.


A solid that dissolves in a liquid.

Solute potential (Ys)

The component of water potential that is due to the presence of solutes - the potential energy of a solution provided by the solutes.


Liquid with dissolved solids.


A liquid that dissolves solids.


A part of the plant that releases sugars into the phloem.


The formation of a new species.


A group of organisms whose members are similar to each other in shape, physiology, biochemistry and behaviour, and can interbreed to produce fertile offspring.


A structure consisting of protein fibres found in eukaryotic cells during cell division. They guide the movement of chromosomes to opposite end of the cell at telophase.


A polysaccharide found in plant cells. It is formed from the covalent bonding together of many glucose molecules.

Stem cells

Undifferentiated cells that are capable of becoming differentiated to a number of possible cell types.

Stoma (pl: stomata)

Pore in leaf epidermis, surrounded by two guard cells. Changes in turgidity of the guard cells can open or close the stoma. Allow gaseous exchange and transpiration in plants.


The gel-like matrix found in chloroplasts. The membranes of the thylakoids/grana are embedded in it.


The substance that is used up in an enzyme-controlled reaction, leading to the formation of product. It fits into the active site of the enzyme at the start of the reaction.

Surface tension

The 'skin' on the surface of water formed as a result of hydrogen bonding in water molecules pulling the surface molecules downwards.


A chemical that can reduce the surface tension of a film of water.

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