multicellular organisms

• Chromosomes

  Thread-like structures made of DNA found in the nucleus of plant and animal cells
• Chromosome complement

  Definite and characteristic number of chromosomes present in each cell of a species
• Every normal human body cell contains 46 chromosomes as 23 pairs
• Karyotype

  Diagram of all the chromosomes found in a male human organised in size order
• Diploid

  Cell that contains 2 matching sets of chromosomes
• Mitosis

  1. Nucleus divides into 2 daughter nuclei, each receiving the same number of chromosomes

  2. Original cell is the mother cell, nuclei produced are daughter cells

  3. Required for growth and repair
• Stages of mitosis

  • Chromosomes condense
  • Nuclear membrane breaks down
  • Spindle fibres attach to centromeres and line up chromatids at equator
  • Spindle fibres contract, separating sister chromatids to opposite poles
  • Chromatids become chromosomes, new nuclear membranes form, cytoplasm divides
• Centromere

  Holds the 2 chromatids of a chromosome together
• Chromatid

  Half of a duplicated chromosome
• Equator

  The centre of the whole cell
• Spindle fibre

  Fibres that pull chromatids to poles of the cell
• Pole of cell

  Opposite end of the cell
• Mother cell

  The original cell that undergoes mitosis
• Daughter cell

  The cells produced by mitosis
• Stem cells

  Unspecialised animal cells that are capable of growth and repair
• Stem cells

  • Divide to produce more stem cells
  • Reproduce themselves forever by repeated mitosis while remaining unspecialised
  • Develop into various types of specialised cells when required
• Types of stem cells

  • Embryonic stem cells
  • Tissue stem cells
• Embryonic stem cells

  Found in early embryos, able to develop into all cell types in the human body
• Tissue stem cells

  Found in fully formed humans, have more limited ability to produce different cell types than embryonic stem cells
• Levels of organisation

  • Cells
  • Tissues
  • Organs
  • Systems
• Tissues

  Group of cells specialised to perform a particular function
• Parts of the nervous system

  • Central nervous system (CNS)
  • Peripheral nervous system
• Central nervous system (CNS)

  Made up of the spinal cord and the brain
• Peripheral nervous system

  All the nerves in the body that aren't in the spinal cord
• Parts of the brain

  • Cerebrum
  • Cerebellum
  • Medulla
• Cerebrum

  Controls memory, conscious thought and intelligence
• Cerebellum

  Controls balance and coordination
• Medulla

  Controls heart rate and breathing
• The cerebellum is below the cerebrum and in control of balance
• Flow of information in the nervous system

  1. Sensory nerves carry information from receptors to the CNS

  2. CNS sorts and stores information

  3. Motor nerves carry nerve impulses from the CNS to effectors
• Information is passed along neurons in the form of an electrical impulse
• Types of neurons

  • Sensory
  • Inter
  • Motor
• Sensory neurons

  Pass information from a receptor to an interneuron in the CNS
• Interneurons

  Found in the CNS, pass information from a sensory neuron to a motor neuron
• Motor neurons

  Pass information from the CNS to an effector such as a muscle or gland
• Synapse

  Small gap between neurons where chemical messengers diffuse to pass information
• Reflex arc

  1. Sense organs detect stimulus

  2. Sensory neuron passes information to interneuron in spinal cord

  3. Interneuron passes information to motor neuron

  4. Motor neuron causes effector (muscle) to respond
• Reflexes

  • Fast
  • Automatic
  • Protective
• Hormones

  Chemical messengers released directly into the bloodstream by endocrine glands
• Target tissues

  Areas of the body where a hormone acts