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• Processing data from investigations involving stomata and transpiration rates

  Find arithmetic means, understand the principles of sampling, calculate surface areas and volumes
• Importance of sugars, amino acids, fatty acids and glycerol in metabolism


  • Conversion of glucose to starch, glycogen and cellulose
  • Formation of lipid molecules from glycerol and fatty acids
  • Use of glucose and nitrate ions to form amino acids for protein synthesis
  • Respiration
  • Breakdown of excess proteins to form urea for excretion
• Meiosis halves the number of chromosomes in gametes, and fertilisation restores the full number
• Genome


  The entire genetic material of an organism
• Understanding the human genome is important for identifying genes linked to diseases and treating inherited disorders
• DNA


  The genetic material in the nucleus of a cell, composed of a chemical called DNA
• DNA


  • A polymer made up of two strands forming a double helix
  • Contained in structures called chromosomes
• Gene


  A small section of DNA on a chromosome that codes for a particular sequence of amino acids to make a specific protein
• Nucleotide


  The basic unit of DNA, consisting of a common sugar and phosphate group with one of four different bases attached
• DNA contains four bases: A, C, G and T
• Sequence of three bases


  The code for a particular amino acid
• The order of bases controls the order in which amino acids are assembled to produce a particular protein
• Protein synthesis


  Proteins are synthesised on ribosomes, according to a template. Carrier molecules bring specific amino acids to add to the growing protein chain in the correct order
• Protein folding


  When the protein chain is complete it folds up to form a unique shape, enabling the proteins to do their job as enzymes, hormones or forming structures in the body
• Mutation


  A change in the DNA structure that may result in a change in the protein synthesised by a gene
• Most mutations do not alter the protein, or only alter it slightly so that its appearance or function is not changed
• A few mutations code for an altered protein with a different shape, which may cause an enzyme to no longer fit the substrate binding site or a structural protein to lose its strength
• Not all parts of DNA code for proteins. Non-coding parts of DNA can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed
• Gamete


  A reproductive cell, such as a sperm or egg cell, that fuses with another during fertilisation
• Chromosome


  A structure in the nucleus of a cell that contains genes
• Gene


  A section of DNA that codes for a particular characteristic
• Allele


  Different forms of the same gene
• Dominant


  An allele that is always expressed, even if only one copy is present
• Recessive


  An allele that is only expressed if two copies are present (no dominant allele present)
• Homozygous


  Having two identical alleles for a particular characteristic
• Heterozygous


  Having two different alleles for a particular characteristic
• Genotype


  The alleles present in an organism
• Phenotype


  The observable characteristics of an organism
• Some characteristics are controlled by a single gene, while most are a result of multiple genes interacting
• Polydactyly (having extra fingers or toes) is caused by a dominant allele, while cystic fibrosis is caused by a recessive allele
• Ordinary human body cells contain 23 pairs of chromosomes, with one pair determining sex (XX in females, XY in males)
• Variation


  Differences in the characteristics of individuals in a population, due to genetic and/or environmental factors
• Mutations occur continuously, and very rarely a mutation will lead to a new phenotype that is suited to an environmental change, leading to a relatively rapid change in the species
• Evolution


  A change in the inherited characteristics of a population over time through a process of natural selection
• Natural selection


  The process by which individuals with characteristics best suited to their environment are more likely to survive and reproduce, passing on their advantageous traits to the next generation
• If two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring, they have formed two new species
• Selective breeding


  The process by which humans breed plants and animals for particular genetic characteristics
• Selective breeding


  Choosing parents with the desired characteristic from a mixed population, breeding them together, and continuing this process over many generations until the desired characteristic is present in all offspring
• Genetic engineering


  The process of modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
• Genetically modified (GM) crops include ones that are resistant to insect attack or to herbicides, and generally show increased yields