Bio Topic 2 (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
  • 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
• Being in a high percentile (e.g. 90th percentile or higher) can indicate a health problem
• 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
  • Contamination risk
  • Money and time could be better spent
• Cerebral hemispheres


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


  • Responsible for controlling fine movements of muscles
• Medulla oblongata


  • Responsible for maintaining basic autonomic bodily functions like breathing, digestion, swallowing, and sneezing
• Doctors often need to look inside the brain to examine brain structure and function
• 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
• 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
• 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

  • Doctors can look inside the brain to examine brain tissue for injury and disease without cutting the skull open, which is highly invasive
• CT scans


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


  Use a radioactive 'tracer' injected into the blood, the scan is sensitive to the tracer so areas with greater blood flow are highlighted, 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 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, and are 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, response occurs