biology cell and control

• Chromosomes


  Poiled up lengths of DNA molecules that contain genetic information
• Body cells


  • Normally have two copies of each chromosome (diploid cells)
  • One chromosome comes from the organism's mother, one from its father
• Mitosis


  1. Cell division to produce two cells identical to the original cell

  2. Nucleus of each new cell contains the same number of chromosomes as the original cell
• Cell cycle

  Process by which body cells divide to produce new cells for growth and repair
• Stages of cell cycle


  1. Interphase

  2. Mitosis and cytokinesis
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase
• At the end of mitosis, the cell has produced two new daughter cells that are genetically identical to the parent cell
• Cell growth

  • Cell division
  • Cell differentiation
  • Cell elongation
• Cell differentiation


  Process by which a cell changes to become specialised for its job
• All growth in animal cells happens by cell division. Animals tend to grow while they're young - when young cells divide quickly but as adults most cell division is for repair = in most animals cell differentiation is lost young
• In plants, growth in height is mainly due to cell elongation, while cell division occurs in meristems. Plants often grow continuously.
• Cancer

  Uncontrolled cell division due to changes in genes that control cell division
• Percentile charts

  Used to assess a child's growth over time and identify any problems
• Stem cells

  Undifferentiated cells that can divide and differentiate into different cell types
• Embryonic stem cells

  • Found in early human embryos, can produce any cell type
• Adult stem cells

  • Found in certain places like bone marrow, can only produce certain cell types
• Doctors already use adult stem cells to cure some diseases, and scientists are experimenting with using stem cells to create specialised cells for replacement therapy
• Meristems

  Plant tissues where cells divide by mitosis are found
• Meristematic zones

  Areas of a plant that are growing, e.g. the tips of the roots and shoots
• Meristems

  • Produce unspecialised cells that are able to divide and form any cell type in the plant
  • Act like embryonic stem cells
  • Unlike human stem cells, these cells can divide and differentiate to generate any type of cell for as long as the plant lives
  • The unspecialised cells go on to form specialised tissues like xylem and phloem
• Stem cells

  Cells that can be used in medicine
• Diseases cured with adult stem cells

  • Sickle cell anaemia can sometimes be cured with a bone marrow transplant (containing adult stem cells which produce new blood cells)
• Using embryonic stem cells

  1. Extracting stem cells from very early human embryos

  2. Growing the stem cells

  3. Stimulating the stem cells to differentiate into specialised cells
• It might be possible to use stem cells to create specialised cells to replace those which have been damaged by disease or injury, e.g. new cardiac muscle cells could be transplanted into someone with heart disease
• Potential risks of using stem cells

  • Tumour development
  • Disease transmission
  • Rejection
• Research using embryonic stem cells raises ethical issues

  • Some people argue that human embryos shouldn't be used for experiments because each one is a potential human life
  • Others think that the aim of curing patients who are suffering should be more important than the potential life of the embryos
• Nervous system

  Lets you act in response to what goes on around you. It is made up of neurones (nerve cells) which go to all parts of the body.
• Central Nervous System (CNS)

  • Coordinates a response to a stimulus
• Responding to a stimulus

  1. Receptors detect a stimulus

  2. Information is converted to a nervous (electrical) impulse

  3. Impulse sent along sensory neurones to the CNS

  4. CNS coordinates the response

  5. CNS sends information to an effector along motor neurones

  6. Effector responds accordingly
• Reaction time

  The time it takes to respond to a stimulus
• Neurones

  • Have a cell body with a nucleus, dendrites/dendrons that carry impulses towards the cell body, and an axon that carries impulses away from the cell body
  • Some axons are surrounded by a myelin sheath which acts as an electrical insulator, speeding up the impulse
  • Neurones can be very long, which also speeds up the impulse
• Types of neurones

  • Sensory neurone
  • Motor neurone
  • Relay neurone
• Synapse

  The connection between two neurones
• Transmission of a nerve impulse across a synapse

  1. Neurotransmitters are released and diffuse across the gap

  2. Neurotransmitters set off a new electrical signal in the next neurone
• Transmission of a nervous impulse is very fast, but is slowed down a bit at the synapse because the diffusion of neurotransmitters across the gap takes time
• Reflex

  An automatic, rapid response to a stimulus that can reduce the chances of injury
• Pathway of a reflex arc

  1. Receptor detects stimulus

  2. Impulses sent along sensory neurone to relay neurone in the CNS

  3. Impulses trigger release of neurotransmitters at synapse with motor neurone

  4. Impulses travel along motor neurone to effector (muscle)
• Reflexes are quicker than normal responses because you don't have to spend time thinking about the response
• Pupillary light reflex

  1. Light receptors in the eye detect bright light

  2. Impulses sent to the brain

  3. Brain sends impulses to muscles in the iris to contract, making the pupil smaller