biology

• Chromosome


  Linear DNA molecule tightly coiled around proteins that carries genetic information in the form of genes
• Chromosomes are found in pairs (one from each parent) in all body cells. Human body cells contain 23 pairs of chromosomes (46 chromosomes in total)
• Chromosome pairs are not identical as they may contain different alleles (versions of a gene)
• Sex chromosomes


  A pair of chromosomes that determine sex. Males have an X and a Y chromosome, females have two X chromosomes.
• Mitosis


  Division of a cell to produce two genetically identical daughter cells with a full set of chromosomes (46 chromosomes)
• Mitosis


  • Important for growth, replacement of old cells, and repair of damaged tissues
• Meiosis


  A type of cell division that creates four genetically different daughter cells known as gametes. Involves two divisions and produces cells with half the number of chromosomes (23 chromosomes)
• Meiosis


  • Important for creating genetic variation and ensuring the resultant zygote has a full set of chromosomes
• Cancer


  A non-communicable disease in which uncontrolled mitosis (due to damaged DNA) leads to the formation of a primary tumour. Tumour cells break off and spread to other tissues forming secondary tumours.
• Cell differentiation


  Produces specialised cells with specific functions. Some genes are switched on or off, determining cell type. Once a cell differentiates, it cannot divide to make an unspecialised cell, nor a cell which has a different specialised function.
• Stem cells


  Unspecialised cells capable of differentiating into a range of different cell types
• Types of stem cells

  • Embryonic stem cells - unspecialised and capable of differentiating into any cell type, enable the growth and development of tissues in embryos
  • Adult stem cells - can differentiate into a limited range of cell types, enable the replacement of dead or damaged cells
• In plants, stem cells are found in meristematic tissue in the root and shoot tips. They are capable of differentiating into any cell type throughout the life of a plant.
• Advantages of stem cell technology

  • Used to treat damage or disease e.g. type 1 diabetes, heart disease
  • Used to treat diseases that would otherwise be untreatable
  • Not rejected by the body
  • Do not have to be matched to the patient's tissue type
  • Can be used to grow organs for transplants
• Disadvantages of stem cell technology

  • May become contaminated during preparation and when transplanted transmit infections to the patient
  • Difficult to find suitable stem cell donors
  • No guarantee that treatment will work
  • Transplanted stem cells could cause tumours
  • Long term risks are unknown
  • Potential side effects
• There are also ethical issues surrounding the use of stem cells, in particular embryonic stem cells. Embryos used to provide these stem cells are usually destroyed which is controversial on ethical grounds.
• Groups organisms can be broadly classified into

  • Plants (flowering and non-flowering)
  • Animals (vertebrate and invertebrate)
  • Fungi
  • Protoctists (single celled organisms)
  • Bacteria
• Classification


  The organisation of organisms into groups
• Importance of classification


  • Makes it easier to identify organisms
  • Aids communication between scientists
• Scientific name


  • Given in two words
  • First name (genus) begins with a capital letter
  • Second name (species) begins with a lowercase letter
  • Words written in italics, or if handwritten underlined
• Types of adaptation


  • Morphological (structural)
  • Behavioural
• Adaptation


  Characteristics of an organism that increase its chance of survival, maintained by natural selection
• Resources organisms require from the environment


  • Light
  • Food
  • Oxygen
  • Carbon dioxide
  • Water
  • Minerals
• Resources are limited, creating competition between organisms
• Competition, as well as predation, disease and pollution, limits population sizes within a community
• Competition is the driving force of evolution by natural selection
• Components of biodiversity


  • Species diversity (variety of living organisms)
  • Genetic diversity (number of different genes)
  • Ecosystem diversity (range of ecosystems)
• Importance of biodiversity


  • Safeguards future food supplies
  • May contain chemicals for future medicines
  • Reduces damage to food chains
  • Protects valuable future resources
  • Creates stable ecosystems
  • Aesthetic reasons
  • Ecotourism benefits communities
• DNA


  Double-stranded polymer of nucleotides, wound to form a double helix
• Ways to maintain biodiversity

  • Protection of endangered species
  • Conservation schemes to protect ecosystems
  • Reforestation
  • Sustainable farming
  • Minimising global greenhouse gas production
  • Legislation to protect habitats
  • Seed banks
• Passing legislation to protect habitats can be difficult because the needs of the human population sometimes conflict with the conservation of the environment
• DNA structure


  • Each strand consists of alternating sugar and phosphate molecules
  • The two strands are joined by a pair of bases
  • There are four bases: A (adenine), T (thymine), C (cytosine) and G (guanine)
  • A pairs with T and C pairs with G
• Gene


  A section of DNA that codes for a protein
• It is important to balance the need for resources with the need to preserve the biodiversity of ecosystems
• Genetic information


  • A sequence of three bases in a gene forms a triplet
  • Each triplet codes for an amino acid
  • Order of amino acids determines the structure and function of the protein formed
• Quadrats


  • Square frame divided into smaller square sections
  • Used to count members of each species present or estimate % coverage
• Using quadrats to sample biodiversity

  1. Position two 20m tape measures at right angles

  2. Use random number generator to select x and y coordinates

  3. Place quadrat at coordinate point

  4. Identify and record numbers or % coverage of each species
• The larger the sample size, the more representative of the area and the greater its validity
• Genetic profiling


  1. Sample of cells collected

  2. DNA extracted from cells

  3. DNA sample cut into fragments using enzymes

  4. Fragments separated into bands, creating a genetic profile
• Genetic profiling


  Comparing DNA to view similarities in the DNA sequences