Biology: Cell biology: Key terms

• Diffusion


  the natural movement of particles from an area of high concentration to an area of low concentration
• Concentration gradient


  the amount of substance in a given volume, normally measured in units of mol/dm3
• Surface area to volume ratio


  a way of comparing the surface area of an organism to its volume - the smaller this ratio, the harder it is to exchange substances with the environment at a fast enough rate
• Osmosis


  the movement of water, through a partially permeable membrane, into a solution with a lower water concentration
• Active transport

  the movement of substances against a concentration gradient; requires energy
• Chromosome


  long molecules found in the nucleus of all cells; made from DNA
• DNA


  nucleic acid molecules that contain genetic information and make up chromosomes
• Gene


  part of a chromosome, made of DNA, which codes for a protein
• Cell cycle


  the series of growth and division events that a cell goes through during its life
• Mitosis


  cell division that forms two daughter cells, each with the same number of chromosomes as the parent cell
• Undifferentiated


  a cell that has not yet become specialised
• Stem cell


  a human embryo cell or adult bone marrow cell that has yet to differentiate
• Embryonic stem cell


  cells found in an embryo that can differentiate into any type of cell
• Adult stem cell


  cells that can differentiate into limited types of cells
• Therapeutic cloning


  process in which clones are produced to treat diseases, but will not be allowed to develop into new offspring
• Meristems


  areas of cells in plants that can divide to form new cells
• Resolution


  the smallest distance apart two objects can be and still be seen as separate objects
• Electron microscope


  a device that fires electrons at a specimen to obtain a high resolution image
• Magnification


  how many times larger an image is than the real object
• Sub-cellular structures


  structures found in cells that include the nucleus, mitochondria, chloroplasts and ribosomes
• Nucleus

  the positively charged, dense region at the centre of an atom, made up of protons and neutrons, orbited by electrons
• Cytoplasm


  the substance found in living cells (outside the nucleus), where chemical reactions take place
• Mitochondria


  the structures in the cytoplasm where energy is produced from chemical reactions
• Ribosome


  small structures found in the cytoplasm of living cells where protein synthesis takes place
• Cell wall

  a protective layer, found outside the cell membrane of plant, fungal and bacterial cells, that helps to support the cell
• Cellulose


  a carbohydrate that makes up the cell wall of plants
• Vacuole


  a fluid-filled cavity in a cell that is used for storage and support
• Chloroplast


  a sub-cellular structure containing chlorophyll, which is found in plants and algae that carry out photosynthesis
• Prokaryotic


  organisms, such as bacteria, that do not have a nucleus or organelles such as mitochondria
• Eukaryotic


  describes cells that have a nucleus and sub-cellular organelles such as mitochondria
• Plasmid


  a small circle of bacterial DNA that is independent of the main bacterial chromosome
• Flagella


  a long tail-like structure that is used by some cells for movement