Cells and control

• Adult stem cells


  Stem cells that can differentiate into a limited range of cell types, e.g. bone marrow stem cells
• Asexual reproduction


  A form of reproduction involving a single parent that creates genetically identical offspring
• Axon


  A long fibre that conducts nerve impulses away from the cell body
• Cancer


  A non-communicable disease caused by changes in the cell that lead to uncontrolled growth and division
• Cataract


  A cloudy patch which forms on the lens of the eye and prevents light from entering normally. Affected individuals have blurred vision, difficulty seeing the intensity of colours and problems with glare. It is treated using surgery to exchange the clouded lens for a synthetic one
• Cell cycle


  A series of events that take place in a cell, involving cell growth, DNA replication and cell division
• Cell differentiation


  The process by which an undifferentiated cell becomes specialised for its function
• Cell elongation


  The process by which cells expand and enlarge, enabling the growth of a plant
• Central nervous system (CNS)


  The brain and spinal cord
• Cerebellum


  The region of the brain that controls muscle coordination and non-voluntary movement (e.g. balance, posture)
• Cerebral hemisphere


  One half of the cerebrum. The left hemisphere controls muscles on the right side of the body and vice versa
• Cerebrum


  The largest region of the brain consisting of two hemispheres. It is responsible for movement, memory, intelligence, language and vision
• Chromatid


  One 'arm' of a replicated chromosome
• Chromosome


  A long, coiled molecule of DNA that carries genetic information in the form of genes
• Colour blindness


  A deficiency of the eye that makes it difficult to distinguish between colours
• Cone cells


  Cells found in the retina that are sensitive to high light intensity (bright light) and which detect different colours
• Cornea


  The transparent outer covering that reflects light entering the eye
• Cytokinesis


  The division of the cytoplasm at the end of mitosis to produce two new daughter cells
• Dendrites


  Short, branched extensions of dendrons that provide a large surface area to receive nerve impulses from other neurones
• Dendron


  Branched extensions of a nerve cell body that connect to other neurones and carry impulses towards the body
• Diploid cell


  A cell that contains two copies of each chromosome (i.e. a full set of chromosomes)
• Effector


  An organ, tissue, or cell that produces a response to a stimulus
• Eye


  A sense organ containing receptors sensitive to light intensity and colour
• Growth


  An increase in mass or size
• Haploid cell


  A cell that contains a single copy of each chromosome (i.e. half the number of chromosomes)
• Interphase


  The longest stage of the cell cycle that involves cell growth, the synthesis of new organelles and DNA replication
• Iris


  A pigmented ring of muscles that controls the size of the pupil to alter how much light enters the eye
• Lens


  A transparent, biconvex structure that refracts light, focusing it onto the retina
• Long-sightedness


  A defect of the eye where nearby objects appear out of focus due to the convergence of light rays behind the retina. This occurs when the eyeball is too short or the lens is less elastic. It is corrected using a convex lens
• Medulla oblongata


  The region of the brain that regulates unconscious activities such as breathing and heart rate
• Meristem tissue


  Plant tissues containing undifferentiated stem cells
• Metaphase


  The second stage of mitosis in which the chromosomes align at the cell equator
• Mitosis


  A form of cell division that produces two genetically identical daughter cells (with a full set of chromosomes) from one parent cell
• Motor neurone


  A neurone that carries nerve impulses from the central nervous system to the effectors
• Myelin sheath


  An electrically insulating layer that surrounds the axon and increases the speed of nerve impulses
• Neurones


  Nerve cells adapted to quickly transmit nerve impulses. They are the functional units of the nervous system
• Neurotransmitters


  Chemicals that are used for communication between neurones and their target cells
• Percentile chart


  A chart used to monitor growth or time. Measurements (e.g. fetal length or head circumference) can be compared to the expected values at a certain age enabling the identification of abnormal patterns in development
• PET scan


  An imaging technique used to assess the structure and function of the brain through the use of radioactive chemicals. Comparisons to a normal brain can highlight unusually active or inactive areas
• Prophase


  The first stage of mitosis in which the chromosomes condense and the nuclear membrane breaks down