Biology topic 2 edexcel cell and control

• Chromosomes


  Genetic information found in the nucleus, containing coils of DNA
• Gene


  Short section of DNA that codes for a protein and controls a characteristic
• There are 23 pairs of chromosomes in each cell of the body, resulting in 46 chromosomes in total
• Sex cells (gametes) have half the number of chromosomes, resulting in 23 chromosomes in total
• Diploid number of chromosomes

  Amount found in body cells (46 in humans)
• Haploid number of chromosomes

  Half the diploid amount (23 in humans), found in gametes
• Cell cycle


  1. Interphase

  2. Mitosis

  3. Cytokinesis
• Mitosis


  • Chromosomes line up at the equator
  • Cell fibres pull each chromosome to either side
  • Two identical daughter cells form
• Mitosis


  Cell division that produces two genetically identical diploid daughter cells
• Cell division by mitosis in multicellular organisms is important for growth, development, and replacing damaged cells
• Mitosis is also a vital part of asexual reproduction
• Cell differentiation


  Cells specialising to perform specific functions
• In animals, almost all cells differentiate at an early stage and then lose this ability
• In plants, many types of cells retain the ability to differentiate throughout life
• Cancer


  Uncontrolled cell division resulting in a tumour
• Percentiles


  Charts used to measure the growth of an organism compared to others
• Stem cell


  Undifferentiated cell that can undergo division to produce more similar cells, some of which will differentiate
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
  • Meristems in plants
• Therapeutic cloning


  Producing an embryo with the same genes as the patient to obtain embryonic stem cells
• Benefits and problems of stem cell research

  • Can replace damaged/diseased body parts
  • Unwanted embryos from fertility clinics could be used
  • Research into differentiation
  • People may have religious/ethical objections
  • Risk of contamination
  • Money and time could be better spent elsewhere
• Cerebral hemispheres


  • Responsible for consciousness, memory, intelligence, visual and sensory processing
• Cerebellum


  • Responsible for controlling fine muscle movements and coordination
• Medulla oblongata


  • Responsible for maintaining basic autonomic bodily functions like breathing, digestion, swallowing, and sneezing
• Adult stem cells


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


  The third stage of mitosis in which the chromatids are pulled to opposite poles of the cell by spindle fibres
• Asexual reproduction


  A form of reproduction involving a single parent that creates genetically identical offspring
• Embryos from fertility clinics

  • Could be used as they would otherwise be discarded
• Axon


  A long fibre that conducts nerve impulses away from the cell body
• Removal of stem cells


  • Results in destruction of the embryo
• Research into the process of differentiation
• Cancer


  A non-communicable disease caused by changes in the cell that lead to uncontrolled growth and division
• Objections to using embryos for research

  • Religious
  • Ethical
  • Seen as interference with the natural process of reproduction
• 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
• If the growing stem cells are contaminated with a virus

  An infection can be transferred to the individual
• Cell differentiation


  The process by which an undifferentiated cell becomes specialised for its function
• Money and time


  Could be better spent on other areas of medicine
• Cell elongation


  The process by which cells expand and enlarge, enabling the growth of a plant
• Medulla oblongata


  A small 'elongated' structure found in the brainstem, at the base of the brain, responsible for maintaining basic autonomic bodily functions such as breathing, digestion, swallowing and sneezing
• Central nervous system (CNS)


  The brain and spinal cord