SB2

• 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 of the cell
  • Cell fibres pull each chromosome of the 'X' to either side of the cell
• Daughter cells

  Identical cells produced by mitosis
• Mitosis produces 2 genetically identical diploid daughter cells
• Growth and development in multicellular organisms

  • Cell division by mitosis
  • Replacing damaged cells
  • 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 cells

  Undifferentiated cells that can undergo division to produce many 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
• Brain

  • Cerebral hemispheres
  • Cerebellum
  • Medulla oblongata
• The brain and spinal cord make up the central nervous system
• The cerebral hemispheres perform functions like consciousness, memory, intelligence, visual and sensory processing
• The cerebellum is responsible for controlling fine movements of muscles
• The medulla oblongata maintains basic autonomic bodily functions like breathing, digestion, swallowing and sneezing
• 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 stem cell 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
• 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
• CT and PET Scanning

  • Used to look inside the brain to examine brain tissue for injury and disease
  • Less invasive than physically examining the brain
• CT scans

  Fire X-Ray radiation at the brain from several different angles to generate a 3D image of the brain
• PET scans

  Use a radioactive 'tracer' injected into the blood to highlight areas with greater blood flow, useful for identifying cancerous tumours
• 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 in the brain

  • Can push against other structures and blood vessels, restricting their function
  • Often buried deep in the brain or spinal cord, making them 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
• Synapse

  Gap between two neurons, where neurotransmitter is released to trigger impulse in next neuron