B2 - Cells and Control

• Chromosomes


  • Coiled up DNA molecules found in the nucleus
  • Body cells usually have 2 copies of each
• Mitosis


  • division of a parent cell to produce 2 genetically identical daughter cells (diploid cells)
• Cell cycle

  1. Interphase
  2. Prophase, Metaphase, Anaphase, Telophase
  3. Cytokenesis
• Interphase


  • DNA duplicates and forms pairs of chromosomes
• Prophase


  • nucleus membrane starts to break down
  • spindle fibres start to appear
• Metaphase


  • Chromosomes line up at the centre of the cell
• Anaphase


  • Spindle fibres pull single arms of chromosomes to opposite ends of the cell
• Telophase


  • a new membrane forms around each set of chromosomes
  • forms new nuclei
• Cytokinesis 


  • cell is divided
• Cell Differentiation


  • when stem cells become specialised
• Cell Division 


  • reproduction of cells
  • mitosis/meiosis
• Cell Elongation


  • growth of plants
  • occur in the roots and shoot (Meristems)
• Tumours (Benign/cancerous)


  • uncontrolled cell division (change in a gene)
  • Cancerous - tumour invades and destroys surrounding tissues
• Stem Cells (embryonic)

  • pluripotent (can differentiate into any cell)
  • growth and development
• Stem cells (adult)


  
  

  • multipotent - only produce certain cells (skin cells, blood cells)
  • mainly found in bone marrow
  • replaced damaged cells
• Stem cells


  • unspecialised cell which can differentiate into specialised cells
  • divide by mitosis
• Percentile charts 


  • monitor a child's growth using weight & age
  • good for highlighting problems
• Plant stem cells


  • cells that divide by mitosis are found in meristems
  • meristems are found in growing parts (roots and shoots)
  • produce unspecialised cells (can form any cell)
  • e.g xylem, phloem
• Medical uses of stem cells

  1. Bone Marrow transplant

  • adult stem cells produce new blood cells
  • can cure sickle cell anaemia
• Medical uses of stem cells


  1. Replacement

  • stem cells from embryos
  • stimulate them into different specialised cells
  • e.g replace damaged neurones
• Risks of embryonic stem cells 


  
  

  • tumour development - cells divide too quickly
  • disease transmission - donor stem cells might carry disease
  • rejection - immune response
  • ethical concerns
• Spinal cord 


  • Long column of Neurones that run from the brain down the spine
  • Relays info from the brain to the rest of the body
• Cerebrum 


  • largest part of brain
  • divided into 2 halves (right and left hemisphere)
  • controls movement, intelligence, memory, language, vision
• Cerebellum


  • under cerebrum
  • controls balance, muscle coordination (fine motor skills)
• Medulla Oblongata (brain stem)


  • controls unconscious activities (heart rate, breathing)
  • connect brain and spinal cord
• Lobes of the Cerebrum

  1. frontal lobe
  2. pariental lobe
  3. temporal lobe
  4. occipital lobe
• CT scans 


  • uses x-rays to produce an image of the brain
  • shows main structures of brain
  • can see potential brain damage
• PET scans 


  • use radioactive chemicals to show brain activity
  • useful for comparing
  • show function and structure
• Treating CNS problems

  • hard to repair damage
  • not easy to access
  • cause permanent damage
• CNS (components)

  • Brain & spinal cord
• CNS coordinated response


  1. Receptors detect stimuli (change in environment)
  2. Electrical impulse sent to CNS (coordinator) by the sensory neurones
  3. CNS coordinates response to stimuli
  4. Impulse travels through the CNS by relay neurones
  5. Response sent by motor neurones to the effector
• Myelin sheath


  • electrical insulator
  • speeds up electrical impulse
• Sensory neurone


  • carries nerve impulse from receptor to CNS (coordinator)
  • one long dendron (carries impulse from receptor)
  • cell body in the middle
  • short axon (carries impulse to CNS
• Motor neurone 


  • carries nerve impulse given by relay neurone from CNS (coordinator) to effector
  • short dendrites surround cell body
  • Long axon (carries nerve impulse form cell body to effector cell)
• Relay neurone 


  • connect sensory and motor neurones
  • many short dendrites (impulse from sensory neurone to cell body
  • axon (carries impulse to motor neurone)
• Synapses


  • connect neurones
  • nerve signals transferred by chemical neurotransmitters
  • they diffuse across the gap
  • this sets off a new electrical signal in the next neurone
• Reflex arc


  • Stimuli detected by receptor
  • Electrical impulse travels along sensory neurone to spinal cord to relay neurone
  • Spinal cord coordinates response (skips brain to make it quicker)
  • motor neurone to effector
• Cornea


  • bends the light to the eye
• Iris


  • controls how much light enters the pupil
• Lens


  • refracts light and focuses it into the retina