Cells & control

• Mitosis: asexual reproduction creating human body cells needed for growth & repair

  • the interphase, DNA, and organelles replicated
  • mitosis contains the prophase, metaphase, anaphase, telophase
  • cytokinesis, two genetically identical diploid daughter cells form

  Cancer occurs as a result of uncontrollable cell division creating tumours
• Differentiation:

  • in animals, cells divide in mitosis and differentiate into specialised cells
  • in plants, cells divide, elongate, and then differentiate in the meristem of the plant
• Stem cells: undifferentiated cells that can undergo cell division

  • embryonic stem cells form when a zygote forms
  • adult stem cells are found in bone marrow
  • meristems found in the root and shoot tips

  Stem cells are cloned to control the differentiation of cells, used to replace damaged/ diseased parts of the body - however, risks rejection in the body or destruction of the embryo, which is hard to obtain
• The CNS: made up of the brain and the spinal cord

  • receptor cells in our senses convert stimuli into electric impulses
  • electric impulses travel to sensory neurons, to the CNS, to relay neurons, to motor neurons, then to effectors
  • electric impulses trigger neurotransmitters that diffuse across the synapse to the next neuron
• Reflex arc: an automatic response allows vital responses to take place quickly

  • a stimulus detected by receptors, sent along sensory neurons, passed to a relay neuron, to a motor neuron, to an effector
• The brain:

  • cerebral cortex has two hemispheres, controls memory and consciousness
  • cerebellum, movement and coordination
  • medulla oblongata, autonomic bodily functions
• CT and PET scans:

  • CT scans are x-rays fired at the brain to examine its structure
  • PET scans use a radioactive tracer injected into the blood to detect cancerous tumours
• The eye:

  • optic nerve, sends electrical impulses to the brain
  • retina, detects light, containing rods (detect light intensity) and cones (detect colour)
  • cornea, focuses light
  • iris controls size of pupil
  • ciliary muscles control shape of lens
  • lens refracts light onto the retina
• Eye defects:

  • short-sightedness is fixed with a concave lens to spread out the light
  • long-sightedness is fixed with a convex lens to bring the light together
  • cataracts are the clouding of the eye lens, which can be replaced to treat it
  • colour blindness occurs when there isn't enough cone cells in the retina