Biology

• Cell Division/Mitosis


  1. Cell divides to form two identical daughter cells

  2. Needed to produce new cells for growth and repair of damaged cells

  3. Maintains diploid chromosome complement
• Mother cell


  Cell that undergoes cell division
• Stages of mitosis


  1. Chromosomes uncoil and each forms 2 identical chromatids

  2. Chromatids join at centromere to form chromosomes

  3. Nuclear membrane disintegrates and spindle fibers form

  4. Chromosomes line up at equator, spindle fibers attach to centromere

  5. Chromatids pulled apart to opposite ends

  6. Nuclear membrane forms around each set

  7. Separated chromatids now called chromosomes

  8. 2 daughter cells with same number of chromosomes as mother cell
• Chromosomes


  • Found in the nucleus and carry genetic information
  • Genetic information made from DNA
  • Visible only when cell is ready to divide
• Humans have 46 chromosomes arranged in 23 pairs
• Gametes do not have pairs of chromosomes in their nuclei
• Bacteria and blood cells do not have a nucleus
• DNA (deoxyribonucleic acid)


  • Consisting of phosphate and deoxyribose sugar molecules
  • Each individual DNA is unique except in identical twins
• Stem cells


  • Unspecialised cells that can self-renew and develop into other cell types
  • Involved in growth and replacement of worn out/damaged cells and tissues
• Types of stem cells

  • Embryonic stem cells
  • Adult stem cells
• Embryonic stem cells


  Present in embryos, can make all various types of cells
• Adult stem cells


  Obtained from some tissues in the body of an adult
• Bone marrow is a rich source of stem cells used to treat some types of cancer and blood diseases
• Stem cells are important in treatment of some conditions of cancer and birth defects
• Replacement of damaged tissue

  Possibility of producing stem cells which are then directed to develop into specific types of cells, providing a source of new cells, tissues and even organs for transplants
• Stem cells could be used to test drugs and chemicals, allowing drugs to be tested on human cells rather than animals
• Stem cell tissues can be grown to test response to certain chemicals and screen for toxins
• Ethical issues with embryonic stem cells

  • Embryo is destroyed, potential loss of human life
  • But stem cell discovery can be used for new medicines and treatments to stop suffering
• Plants maintain all their embryonic cells and it is very easy to clone plants for this reason
• Sources of stem cells

  • Embryos
  • Foetus
  • Umbilical cord blood
  • Amniotic fluid
  • Bone marrow and blood (permanent tissue cells)
• Unicellular organisms


  Consisting of only one cell, which shows all characteristics of life and carries out all functions required for survival
• Multicellular organisms


  Made up of many cells, with a division of labour where cells are specialised and each carries out a particular function
• Levels of cell organisation

  • Cells
  • Tissues
  • Organs
  • Systems
  • Organism
• Types of specialised cells

  • Motor neuron
  • Sperm cell
  • Red blood cell
• Nervous system


  Coordinates the activities of cells, tissues and organs so they can perform specific functions at any given time
• Components of the nervous system

  • Brain
  • Spinal cord
  • Nerves
• Central nervous system (CNS)


  Brain and spinal cord, connected to all parts of the body with nerves
• Types of neurons


  • Sensory neuron
  • Interneuron
  • Motor neuron
• Nervous system function


  1. Stimulus detected by sensory receptors

  2. Stimulus travels to CNS

  3. Response sent from CNS to effectors
• Synapse


  Gap between neurons, where a chemical (neurotransmitter) transfers the electrical impulse
• Reflex arc


  Automatic response to stimuli, bypassing the brain
• Main parts of the brain

  • Cerebrum
  • Cerebellum
  • Medulla
• Cerebrum


  Largest part of the brain, processes information from sensory neurons and sends impulses to body parts
• Cerebellum


  Controls balance and coordinated muscle action
• Medulla


  Controls breathing, digestion, heart rate, swallowing and sneezing
• Endocrine system


  • Involved in communication around the body
  • Consists of endocrine glands that release hormones into the bloodstream
• Hormonal control


  1. Stimulus detected by endocrine organs

  2. Hormones released into blood

  3. Hormone receptors on target cells

  4. Response by target cells
• Insulin


  Hormone made in the pancreas that stimulates liver and muscle cells to absorb glucose, lowering blood glucose levels
• Glucagon


  Hormone made in the pancreas that converts stored glycogen in the liver and muscles into glucose, increasing blood glucose levels
• Homeostasis


  Internal mechanism that controls blood glucose levels to prevent dangerously low or high levels