Cells and Control

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  • Section 2 - Cells and Control
    • Mitosis
      • genetic material > chromosomes
        • Body cells are diploid
      • Produces two cells identical to original
      • Cell cycle
        • Interphase - cell grows to increase mitochondria and ribosomes. Duplicates DNA ( X shape)
        • Mitosis in Cytokinesis: PROPHASE = membrane breaks down METAPHASE = chromosomes line up at centre ANAPHASE = cell fibres pull them apart TELOPHASE = Membranes form around two sets, cytoplasm and membrane divide to form two cells
    • Cell division and growth
      • CELL DIFFRENTIATION = cell changes to be more specialised
      • CELL DIVISION = by mitosis
      • CELL ELONGATION = plant cell expands
      • cancer is a case of uncontrolled cell division
        • abnormal cells = tumour attacks surrounding tissue
      • Percentile charts are used to monitor growth
    • Stem Cells
      • embryonic stem cells hae the potential to produce any cell
      • Important for growth and development of organisms
      • Meristems contain plant stem cells
        • generate any cell type for as long as the plant lives (xylem and phloem)
      • use in medicine
        • used to replace damaged specialised cells
        • RISKS: tumour development, disease transmission, rejection
    • The Nervous System
      • Sensory receptors convert stimulus to nervous impulse - sent to CNS
        • CNS coordinates a response sending info to effector by a motor neurone
      • dendrites and dendrons towards cell body / axons away
        • myelin sheath acts as insulator - speeds up impulse
      • sensory neuron: one long dendron & one short axon
      • motor neurone: many short dendrites & one long axon
      • relay neurone: many short dendrites & an axon
    • Synaoses and reflexes
      • Synapses connect neurones
      • reflexes help prevent injury
        • neurones in reflex arc go through spinal cord - they reach a synapse and neurotransmitters are released - impulses sent to effector
          • quicker than normal responses - no thinking
        • reflex protects the eye: light receptors > sensory neurone > relay neurone > motor neurone > circular muscles in iris contract > smaller pupil


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