Topic 2: Cells and Control

• Prophase (mitosis)

  1. Chromosomes condense and are now visible under a microscope.
  2. Nuclear envelope breaks down, leaving the chromosomes free in the cytoplasm.
• Give 3 benefits of using stem cells in medicine.

  1. used to replace damaged/diseased cells
  2. used for testing new drugs before being used on people
  3. can be studied to show how cells become damaged, so new treatments can be developed
• Telophase (mitosis)

  1. Chromatids uncoil to become long and thin again when they reach opposite poles of the cell
  2. nuclear envelope forms around each set of chromosomes to form 2 nuclei
• Give 2 risks of using stem cells in medicine.

  1. Stem cells may continue to divide inside the body to produce cancer.
  2. Stem cells from another person may be rejected by the patients immune system.
• Adult stem cells:

  • Can replace damaged cells but don't form any new tissue
  • They can only differentiate into specialised cells from the organ/tissue where they reside
  • Example: Bone marrow - found in the centre of big bones and contain adult stem cells which can divide by mitosis but can only differentiate into types of blood cells e.g red, white and platelets
• Why is differentiation important in the development of specialised cells?

  It allows cells to specialise and perform specific functions in an organism. Without specialisation, complex multicellular animals/plants wouldn't exist.
• Cytokinesis (after mitosis but part of cell cycle)

  Cytoplasm divides to produce 2 identical diploid daughter cells
• 2 drawbacks of using embryonic stem cells in medicine:

  • Limited supply of them
  • risk of rejection
  • ethical issues
• Plant stem cells:

  • found in meristems (roots and shoots of plants)
  • unspecialised stem cells will differentiate into e.g. root hair cells or palisade cells
  • last for plant's entire life (unlike embryonic stem cells which differentiate + disappear by the time we are fully developed)
• Embryonic stem cells:

  • can differentiate into any type of specialised cell while the embryo is dividing + growing so we have all the specialised cells needed to form a baby by 9 months.
• Describe growth in plants (cell division, elongation + differentiation)

  • Cell division - mitosis
  • Elongation - all plant cells are able to elongate to become longer as they grow. This occurs all though out the plant, not only in the meristems.
  • Differentiation - meristems (plant stem cells) in plants differentiate into specialised cells.
• Describe growth in animals (cell division + differentiation)

  • Cell division - mitosis, a zygote divides by mitosis to form an embryo and eventually a foetus
  • Differentiation - embryonic stem cells can differentiate into any type of specialised cell
• Describe cancer

  the result of mutations in cells that lead to uncontrolled cell division
• describe the division of a cell by mitosis

  the production of 2 identical diploid daughter cells

  each has identical sets of chromosomes in the nucleus to the parent cell
• What are the 3 reasons that mitosis is important to organisms?

  1. growth in an organism
  2. repair for when an organism/tissue is damaged
  3. asexual reproduction in bacteria + plants
• Anaphase (mitosis)

  spindle fibres contract to pull the chromatids to opposite ends of the cell
• metaphase (mitosis)

  The chromosomes line up in the middle of the cell
• The nervous system

  Stimulus (change in environment) - receptor - sensory neuron - cns (brain + spine) + relay neuron - motor neuron - effector (e.g. muscles) - response
• What is a stimulus and what is it's function?

  • a change in internal or external environments
  • allows your nervous system to react to the stimuli to keep you from harm
• What is the structure and function of receptors?

  • structure - a group of cells that are sensitive to stimuli
  • function - they stimulate electrical impulses in response to stimuli
• structure and function of neurons?

  • a bundle of neurons is a nerve
  • axon - long and thin, carry electrical impulses around the body
  • myelin sheath - insulates axon to increase efficiency of electrical signal transfer as it need to be fast
  • dendrons + dendrites - tiny branches that increase surface area to connect more neurons to each other
• describe how a synapse works

  • electrical impulse reaches end of nerve (or neuron)
  • causes a release of chemicals - neurotransmitters
  • these diffuse across the gap to the next nerve and trigger another electrical impulse at the beginning of the next nerve
• What are the 2 parts of the CNS?

  Brain and spinal cord (where the thinking happens)
• What is the function of an effector and give 2 examples

  An effector will bring about a response, e.g. muscles = contract (response), glands = release hormones (response)
• name 2 ways of responding to stimuli

  voluntary - you think about a response

  involuntary - you don't think about the response, it happens automatically
• reflex arc

  stimulus - receptor - sensory neuron - relay neuron - motor neuron - effector - response

  doesn't involve the conscious part of the brain or the CNS, unlike the nervous system .
• What is the function of the reflex arc?

  To involuntarily contract the muscles (bring about an response) to protect the body from harm and minimise the potential harm caused