Multicellular Biology

• Mitosis


  The process of cell division where the parent cell splits to form two cells, each genetically identical to the original
• Mitosis


  • Provides new cells for growth and repair of damaged cells
  • Maintains the diploid chromosome complement
• Sequence of events in mitosis

  1. Stage 1: Nuclear membrane intact, chromosomes replicating and doubling

  2. Stage 2: Chromosomes coiled and visible, made of two identical chromatids

  3. Stage 3: Nuclear membrane dispersed, chromosomes line up at equator, spindle fibres attach

  4. Stage 4: Chromatids detach and move to opposite poles, cell begins to pinch

  5. Stage 5: New nuclear membranes form, 2 new nuclei

  6. Stage 6: Cytoplasm divides, cell membrane forms on each new daughter cell
• Stem cells


  Unspecialised cells that can divide to produce more stem cells or develop into specialised cells, involved in growth and repair
• Hierarchy of organisation


  • Cells
  • Tissues
  • Organs
  • Organ systems
• Nervous system


  Consists of the central nervous system (brain and spinal cord) and other nerves
• Main parts of the brain

  • Cerebrum
  • Cerebellum
  • Medulla
• Types of neurons


  • Sensory
  • Inter
  • Motor
• Reflex arc


  Automatic and protective actions like sneezing, blinking, coughing
• Hormones


  Chemical messengers released by endocrine glands that travel in the bloodstream and affect target tissues
• Insulin is released from the pancreas

  To stimulate the conversion of glucose into the storage carbohydrate glycogen

  
• Glucagon is released from the pancreas

  To stimulate the conversion of glycogen back into glucose

  
• Gametes


  Sex cells that are haploid (contain one set of chromosomes)

  
• Zygote


  Diploid cell formed when male and female gametes fuse, containing two sets of chromosomes

  
• Mammalian gametes


  • Female: ova (egg)
  • Male: sperm cell
• Plant gametes


  • Female: ovule
  • Male: pollen grain
• Fertilisation


  Fusion of the nuclei of two haploid gametes to produce a diploid zygote

  
• Variation


  Differences that exist between individual members of a species
• Types of variation


  • Discrete
  • Continuous
• Discrete variation


  Characteristic falls into distinct groups, controlled by a single gene
• Continuous variation


  Characteristic has any value in a range, controlled by many genes (polygenic)
• Genes


  Different areas of the chromosome that code for proteins
• Alleles


  Different forms of the same gene
• Dominant alleles


  Always show up in the appearance of an organism, even if only one copy is present
• Recessive alleles


  Only show up in the appearance of an organism if there are two copies present
• Genotype


  The alleles an organism carries for a particular characteristic
• Phenotype


  The physical features of a characteristic
• Monohybrid cross


  Genetic cross between two organisms that differ in one way only
• Predicted phenotype ratios among offspring are not always achieved as fertilisation is a random process
• Plant organs involved in transport

  • Roots
  • Stems
  • Leaves
• Leaf structure


  • Waxy cuticle: waterproof outer layer
  • Epidermis: protective outer layer
  • Xylem: transports water
  • Phloem: transports glucose
  • Palisade mesophyll: contains chloroplasts for photosynthesis
  • Spongy mesophyll: loosely arranged for gas exchange
  • Stomata: allow carbon dioxide in and oxygen out
  • Guard cells: open and close stomata

  
• Xylem


  Transports water and dissolved minerals upwards towards the leaves
• Phloem


  Transports sugars and organic molecules around the plant, both upwards and downwards
• Transpiration


  Evaporation of water into the atmosphere from leaves of plants
• Root hairs increase the surface area for absorption of water from the soil. Water moves into the root hair cells by osmosis, then up the stem and into the leaves through the xylem.
• Factors affecting transpiration rate

  • Temperature
  • Humidity
  • Wind speed
  • Surface area
• The transpiration rate can be increased by: increase in temperature, increase in wind speed, increase in surface area and a decrease in humidity.
• Circulatory system


  Made up of the heart, blood and blood vessels

  
• Components of mammalian blood

  • Plasma
  • Red blood cells
  • White blood cells
• Red blood cells


  Specialised to efficiently transport oxygen in the form of oxyhaemoglobin