Biology

• Classification


  Putting organisms into groups
• Kingdoms


  • Animal
  • Plant
  • Fungi
  • Single-celled organisms (Protoctists)
  • Bacteria
• Animal kingdom


  • Vertebrates (with a backbone)
  • Invertebrates (without a backbone)
• Plant kingdom


  • Flowering plants
  • Non-flowering plants
• Taxonomic groups


  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Binomial system


  Uses the organism's genus and species to create its name
• Scientists know the binomial system is universal and Latin is used to name organisms
• Physical adaptation


  • Gives an organism a greater chance of survival in its habitat, e.g. camels have long eyelashes to protect from sand
• Behavioural adaptation


  • A particular behaviour that gives an organism an advantage in its particular habitat, e.g. being nocturnal (becoming active at night) to avoid the heat of the day
• Biodiversity


  The variety of different species on Earth
• Ways to conserve and protect biodiversity and endangered species

  • Convention on International Trade in Endangered Species
  • Sites of Special Scientific Interest and national parks
  • Captive breeding programmes and seed/sperm banks
  • Local biodiversity action plans
• Alien species


  Organisms not native to a particular region or country and so have no natural predators to control their population growth
• Mitosis

  1. Occurs during growth

  2. Occurs to replace worn out cells

  3. Occurs to repair damaged tissue

  4. Occurs in all body cells except gamete-forming cells

  5. Produces genetically identical daughter cells
• Daughter cells produced by mitosis have a full set of chromosomes (diploid)
• When a cell divides by mitosis two daughter cells are produced
• Mitosis is carefully controlled

  When a cell becomes cancerous, it divides uncontrollably
• Cancerous cells

  Produce a growth called a tumour
• Carcinogens


  Agents that cause cancer, they cause mutations in DNA
• Factors that increase the risk of mutations

  • Ionising radiation, e.g. UV in sunlight
  • Chemical carcinogens in cigarette smoke
• Sexual reproduction


  1. Gametes join in fertilisation to form a zygote

  2. Gametes contain half the number of chromosomes in each that the organism needs - they are haploid

  3. Gametes are formed by a type of cell division called meiosis - the cell divides twice to form four gametes

  4. Gametes formed by meiosis are genetically different from each other, they show variation

  5. Meiosis only occurs in gamete forming cells
• Stem cells

  Undifferentiated cells
• Types of stem cells

  • Embryonic stem cells (will differentiate into any cell type)
  • Adult stem cells (can differentiate into related cell types only)
  • Stem cells in plants (found in regions called meristems)
• Stem cells


  • Have great potential, in treating patients with currently untreatable conditions, growing organs for transplants, and research
  • There are clinical, ethical and social issues related to the use of stem cells
• DNA backbone strands


  Made from alternating sugar and phosphate molecules
• Base pairing


  • Cross-links between the two strands in DNA are formed by pairs of bases
  • Thymine pairs with adenine (T-A)
  • Guanine pairs with cytosine (G-C)
• Alleles


  Different versions of the same gene
• Genotype


  The alleles that determine characteristics and can be expressed as a phenotype
• Dominant allele


  Expressed in the heterozygote
• Recessive allele


  Only expressed if the individual has two copies
• Human body cells have 23 pairs of chromosomes, the 23rd pair are the sex chromosomes
• Female genotype and phenotype

  X chromosome from the mother and one from the father - produces a girl (female phenotype from the XX genotype)
• Male genotype and phenotype

  X chromosome from the mother and a Y chromosome from the father - produces a boy (male phenotype from the XY phenotype)
• DNA profiling


  Cutting a sample of DNA into fragments and separating them by size
• Uses of DNA profiling

  • Identify alleles for genetic disorders
  • Determine paternity
  • Help solve crimes
  • Compare different species for classification purposes
• Variation

  Some is genetic, some is environmental, and some is a combination of both
• Offspring get half of the genetic information from one parent and half from the other
• Continuous variation

  A characteristic that changes gradually over a range of values, e.g. height, weight, hand span
• Discontinuous variation


  A characteristic with only a limited number of possible values, e.g. gender (male or female), eye colour, blood group
• Asexual reproduction


  1. Only one parent is needed

  2. Offspring are produced by mitosis and are genetically identical to the parent

  3. They are clones
• Organisms that can reproduce asexually

  • Bacteria
  • Strawberries