TOPIC 2 BIOLOGY PAPER 1

• 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
• 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
  • 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
• Research into the process of differentiation
• People may have religious or ethical objections


  • As it is 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 ('automatic) bodily functions, such as breathing, digestion, swallowing and sneezing
• Doctors often need to look inside the brain


  • To examine brain tissue for injury and disease
  • This is highly invasive and often does not provide any clues about brain function
• CT (Computerised Tomography) scans


  Fire X-Ray radiation at the brain from several different angles to generate a 3D image of the brain, useful for examining bleeding within the skull, and damage to brain structures
• PET (Positron Emission Tomography) scans


  A radioactive 'tracer' is injected into the blood before the scan, the scan is sensitive to the tracer so areas where the tracer builds up (which will also be areas with greater blood flow) will be highlighted more brightly, useful for identifying cancerous tumours
• Investigating brain function and treating brain damage and 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 tumours in the brain

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


  Allows us to react to our surroundings, and coordinate actions in response to stimuli
• Response to stimuli


  1. Receptor cells convert a stimulus into an electrical impulse

  2. Electrical impulse travels along sensory neurons to the central nervous system (CNS)

  3. Information is processed and the appropriate response is coordinated, resulting in an electrical impulse being sent along motor neurones to effectors

  4. Effectors carry out the response