Multicellular Organisms

• Mitosis events


  1. Chromosomes replicate and double, forming 2 identical chromatids joined in the centre by a centromere

  2. Nuclear membrane breaks down and chromosomes shorten and thicken, becoming visible under a microscope

  3. Chromatids line up along the equator of the cell

  4. Spindle fibres attach to the chromatids

  5. Spindle fibres shorten pulling the chromatids apart to opposite poles of the cell

  6. Cytoplasm divides and a nuclear membrane forms

  7. 2 diploid cells produced, containing the same genetic information as the original parent cell
• Response


  A rapid action from a muscle, or a slower response from a gland by the release of a chemical
• Nervous system


  Made up of the central nervous system (CNS) and other nerves
• Central nervous system (CNS)

  Consists of the spinal cord and the brain
• Functions


  • Cerebrum - controls conscious thought and actions, memories and personality
  • Cerebellum - controls balance and movement
  • Medulla - controls heart rate and breathing rate
• Communication between cells in a multicellular organism

  Occurs by use of nerve impulses or hormones
• Central nervous system


  Produces electrical impulses for rapid response
• Reflex action


  Rapid automatic response to a stimulus
• Reflex arc


  Pathway of information from a sensory neuron through an inter neuron to a motor neuron
• Structure of Brain

  Name each structure of the brain

  A) Cerebrum

  B) Cerebellum

  C) Medulla

  D) Top of spinal cord

  
• Functions of neurones

  • Sensory neuron - Pass information from the senses to the CNS
  • Inter neuron - Located in the CNS and processes information from the senses that require a response
  • Motor neuron - enable a response to occur at an effector (a muscle or gland)
• Synapse


  A tiny gap at the junction between two nerve cells, which nerve signals must cross
• Stages of a reflex action

  1. Hand touches hot plate and the high temperature stimulates a pain receptor at the end of a sensory neuron

  2. An electrical impulse is transmitted along the sensory neuron

  3. The electrical impulse reaches the end of the sensory neuron. Chemicals are released that cross the synapse and trigger an electrical impulse that is transmitted along the inter neuron

  4. The electrical impulse reaches the end of the inter neuron. Chemicals are released that cross the synapse and trigger an electrical impulse that is transmitted along the motor neuron

  5. The electrical impulse is transmitted along the motor neuron. When it reaches the end of the neuron chemicals are released that cross the synapse to the muscle. They cause the muscle to contract (the response) and the hand is pulled away from the hot object
• Hormone


  A chemical messenger released into the bloodstream
• Reflex arcs in humans

  • Responses to pain
  • Blinking
• Target tissue

  • Contains special receptor proteins that will recognise the hormone
  • Ensures only the target tissues are affected by the hormone
• Communication between cells in a multicellular organism occurs by use of nerve impulses or hormones
• The central nervous system produces electrical impulses for rapid response
• Increase in blood glucose

  1. Pancreas releases insulin

  2. Liver detects insulin

  3. Liver converts excess glucose to glycogen

  4. Blood glucose levels fall
• Decrease blood glucose


  1. The pancreas responds by releasing the hormone glucagon

  2. Receptors in the liver detect the glucagon

  3. In response the liver starts to convert glycogen back into glucose

  4. The blood glucose levels rise
• When the glucose is gone, it is time for glucagon!
• Diploid chromosone complement


  The bodies of most animals and plants contain body (somatic) cells, eg skin cells, nerve cells, liver cells etc and gametes (sex cells). The body cells of most animals and plants each contain two sets of chromosomes in their nuclei. Every chromosome in one set has a matching partner in the other set that has the same length of DNA and the same genes. Cells that contain two sets of chromosomes are said to be diploid.
• Sexual reproduction


  New organisms are produced from the fusing of the nucleus of a male sex cell with the nucleus of a female sex cell. This is called fertilisation.
• In mammals, male and female reproductive structures are found in separate individuals
• Male gamete


  Sperm cell
• Sperm


  • Continuously produced in the testes close to adult male mammals
  • Travel through the sperm duct, into the urethra and are released out of the end of the penis during sexual intercourse
• A gamete contains a single set of chromosomes in its nucleus and is said to be haploid.
• Sites of gamete production in flowering plants

  • Anthers produce male gametes (pollen grains)
  • Ovary produces female gametes (ovules)
• Female gamete


  Egg cell
• Gametes


  Haploid male and female reproductive cells
• Fertilisation in flowering plants

  Male and female haploid gametes fuse to produce a new organism
• Egg cells


  • Produced in the ovaries of the female mammal
  • Released from the ovaries into the oviducts
  • If fertilised by a sperm in the oviduct, it divides and implants into the wall of the uterus where it grows and develops into a new individual
• Sites of gamete production in mammals

  • Testes (male)
  • Ovaries (female)
• Fertilisation


  1. Fusion of male and female haploid gametes

  2. Creation of diploid zygote
• Sperm cells reach the oviducts by swimming up through the vagina and the uterus
• Sites of gamete production in flowering plants

  • Anthers (male)
  • Ovaries (female)
• In mammals, gametes are produced in the testes or ovaries of individuals but anthers and ovaries are on the same flowering plant.
• Zygote


  • Diploid cell that receives one set of chromosomes from the female gamete and one set from the male gamete
• Cell division after fertilisation

  1. Mitotic cell division

  2. Specialisation of new cells to form body tissues
• Fertilisation


  1. Nuclei of 2 haploid gametes fuse together

  2. Forms a diploid zygote

  3. Zygote divides to form an embryo