cells 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


  The amount of chromosomes found in body cells (46 in humans)
• Haploid


  Half the diploid amount of chromosomes (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 of the 'X' to either side of the cell
• Daughter cells


  Two identical cells formed when the cytoplasm and cell membranes divide
• Mitosis produces 2 genetically identical diploid daughter cells
• Growth and differentiation in animals


  • Cell division and differentiation
  • Specialised cells adapted to their function
• In mature animals, cell division mostly only happens to repair or replace damaged cells
• Growth in plants


  • Cell division and differentiation
  • Elongation - plant cells grow longer by absorbing water into vacuoles
• Many plant cell types 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
• Being in a high percentile (e.g. 90th percentile or higher) can indicate a health problem
• Stem cells


  Undifferentiated cells 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
  • Differentiation process not fully understood
  • Unwanted embryos could be used
  • Destruction of embryo
  • Religious/ethical objections
  • Risk of contamination
  • Money/time could be better spent
• The brain and spinal cord make up the central nervous system
• Embryos from fertility clinics

  • Could be used as they would otherwise be discarded
• Removal of stem cells

  • Results in destruction of the embryo
• Objections to using embryos for research


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


  An infection can be transferred to the individual
• Money and time


  Could be better spent on other areas of medicine
• Doctors often need to look inside the brain to examine brain tissue for injury and disease
• Highly invasive


  Cutting the skull open and physically examining the brain does not provide any clues about brain function
• Reasons investigating brain function and treating brain damage/disease is difficult


  • It is complex and delicate
  • It is easily damaged
  • Drugs given to treat diseases cannot always reach the brain because of the membranes that surround it
  • It is not fully understood which part of the brain does what
• Cancerous tumours can form in the brain as in any other part of the body
• Cancerous brain tumours


  • Can push against other structures and blood vessels, restricting their function
  • Often buried deep in the brain or spinal cord, making them especially difficult to remove
• Nervous system response to stimuli

  1. Receptor cells convert stimulus into electrical impulse

  2. Impulse travels along sensory neurons to central nervous system

  3. Information processed, appropriate response coordinated, impulse sent along motor neurons to effectors

  4. Effectors carry out response
• Reflex


  Automatic response which takes place before you have time to think, important to prevent injury
• Reflex arc


  1. Stimulus detected by receptors

  2. Impulses sent along sensory neuron

  3. Impulse passes to relay neuron in CNS

  4. Impulses sent along motor neuron

  5. Impulse reaches effector, resulting in response
• Reflex arcs


  • Pupils getting smaller to avoid damage from bright lights
  • Moving hand from hot surface to prevent damage
• Synapse


  • Gap between two neurons
  • Neurotransmitter released into synapse, diffuses across and triggers impulse in next neuron
• Myelinated nerves


  Surrounded by myelin sheath, allowing faster nerve transmission
• Retina


  Layer of light sensitive cells at back of eye, containing rod cells and cone cells which convert light to nerve impulses
• Cornea


  • Allows light through, curved surface bends and focuses light onto retina