Unit 7

• Chromosomes


  Found in the Nucleus
• Nucleus


  Contains genetic material in the form of chromosomes
• DNA


  A long list of instructions on how to put an organism together and make it work
• Genome


  All of an organism's DNA
• Gene


  A chemical instruction that codes for a particular protein
• Proteins


  • They control most processes in the body
  • They determine inherited characteristics eg eye colour, blood type
• Alleles


  Different versions of the same gene
• DNA molecule


  • It has two strands coiled together in the shape of a double helix
  • The two strands are held together by chemical bases (adenine, cytosine, guanine, thymine)
  • The bases are paired in a complementary way (A-T, C-G)
• Diploid


  Human body cells have two copies of each chromosome, arranged in pairs
• Every living organism has DNA
• Protein synthesis


  1. Transcription (DNA to mRNA)

  2. Translation (mRNA to protein)
• Codon


  A sequence of three bases in a gene that codes for a particular amino acid
• DNA also contains non-coding regions
• Asexual reproduction


  Mitosis (cell division to produce genetically identical cells)
• Mitosis


  • DNA is duplicated
  • Chromosomes line up and are pulled apart
  • New nuclei and cells form
• Gametes


  Sperm and egg cells that contain half the normal number of chromosomes (haploid)
• Sexual reproduction


  1. Fusion of male and female gametes to form a zygote

  2. Zygote undergoes cell division and develops into an embryo
• Fertilisation is random, producing genetic variation in offspring
• Gametes


  Sperm cells and egg cells
• Gametes


  • Haploid - have half the number of chromosomes in a normal cell
  • In humans, each gamete contains 23 chromosomes
• Fertilisation


  1. Male gamete fuses with female gamete to form a zygote (fertilised egg)

  2. Zygote undergoes cell division (mitosis) and develops into an embryo

  3. Embryo inherits features from both parents
• Fertilisation of gametes is random, producing genetic variation in the offspring
• Sexual reproduction


  Involves the fusion of male and female gametes
• Offspring contain a mixture of their parents' genes
• Meiosis


  1. Produces gametes for sexual reproduction

  2. Involves two divisions

  3. Produces four haploid cells that are genetically different
• Meiosis produces gametes, mitosis produces two genetically identical cells
• Flower


  • Contains both male (stamen) and female (carpel) reproductive parts
• Pollination


  1. Transfer of pollen from anther to stigma

  2. Cross-pollination is when pollen is transferred from one plant to another
• Plants adapted for insect pollination

  • Have brightly coloured petals, nectar glands, sticky pollen grains, sticky stigma
• Plants adapted for wind pollination

  • Have small dull petals, no nectar glands, produce lots of small light pollen grains, have long filaments and feathery stigmas
• Fertilisation in plants


  1. Pollen grain lands on stigma

  2. Pollen tube grows down to ovary

  3. Male nucleus fuses with female nucleus to form zygote
• Flowering plants can only be fertilised by pollen from the same or closely related species
• Seed germination


  1. Seed takes in water

  2. Root and shoot start to grow

  3. Plant uses food reserves until it can photosynthesize
• Seed


  • Contains an embryo and food reserves, wrapped in a hard seed coat
• Germination only starts when conditions (water, oxygen, temperature) are suitable