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 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

  Process where cells specialise 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
• Measurements used for growth monitoring

  • Mass
  • Length
  • Head circumference
• 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
  • Differentiation process not fully understood
  • Removal of stem cells destroys embryo
  • Religious/ethical objections
  • Risk of contamination and infection
  • 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, sneezing
• Removal of stem cells

  • Results in destruction of the embryo
• Research into the process of differentiation
• If the growing stem cells are contaminated with a virus

  An infection can be transferred to the individual
• 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
• Highly invasive

  Cutting the skull open and physically examining the brain 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
  • Not recommended for pregnant women and children as it exposes the patient to higher doses of radiation than a normal X-ray
• 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 as these use more blood than normal tissue
• Investigating brain function and treating brain damage and disease

  • 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


  • They can push against other structures and blood vessels in the brain, restricting their function
  • Often, tumours can be buried deep in the brain or spinal cord, making them especially difficult to remove
• Nervous system 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 appropriate response is coordinated, resulting in an electrical impulse being sent along motor neurons to effectors

  4. Effectors carry out the response
• Reflex

  Automatic responses which take place before you have time to think, important to prevent the individual from getting hurt
• Reflex arc

  1. Stimulus is detected by receptors

  2. Impulses are sent along a sensory neuron

  3. In the CNS the impulse passes to a relay neuron

  4. Impulses are sent along a motor neuron

  5. The impulse reaches an effector resulting in the appropriate response
• Synapse


  The gaps between two neurons, when the impulse reaches the end of the first neuron, a chemical called a neurotransmitter is released into the synapse, this neurotransmitter diffuses across the synapse and triggers the impulse to begin again in the next neuron
• Myelinated nerves


  Nerves surrounded by a myelin sheath, allows the nerve transmission (or action potential) to travel faster, myelin is produced by Schwann cells
• Retina

  • Layer of light sensitive cells found at the back of the eye, when light hits this, the cells are stimulated and impulses are sent to the brain, which interprets the information to create an image
  • Contains rod cells and cone cells, rod cells are more sensitive to light so better for seeing in low light, cone cells allow colour vision