Unit 1 - Cell Biology

• Sperm cell - joins ovum for fertilisation

  • Contains half the genetic information of an adult cell
  • Long tail to swim
  • Streamlined to make swimming easier
  • Packed full of mitochondria - energy for swimming
  • Enzymes to digest the outer layer of the ovum
• Nerve cells - send electrical impulses around body

  • Long axon to carry electrical impulses from one part of the body to another
  • Myelin sheath - insulates and speeds up transmission of nerve impulses
  • Synapses - junctions to allow impulse to pass from nerve cells to nerve cells
  • Dendrites - increase surface area
• Muscle cells - contract

  • Protein fibres which can change length
  • Mitochondria - provides energy for muscle contraction
• Root hair cells

  • Increase surface area
  • No chloroplasts as they are underground
• Xylem cells

  • Long tubes carry water and dissolved water from roots to leaves
  • Thick walls of lignin - support to plant
  • Dead cells with no end walls - water and dissolved minerals flow easily
  • No subcellular structures - easier for water and minerals to flow
• Phloem

  • Dissolved sugars up and down
  • No nucleus and limited cytoplasm
  • Sieve plates on end walls - allow dissolved sugars to move
  • Companion cell connected to each cell with mitochondria - energy for active transport
• Ways to avoid contamination

  • Sterilise all Petri dishes, bacteria nutrient broth or agar - kills unwanted organisms, prevents contamination
  • Spray working area with disinfectant and wipe dry
  • Sterilise inoculating loop by passing through flame
  • Attach lid using adhesive tape, stops lid falling off and microorganisms entering
  • Store agar lid upside down to stop condensation dripping down
• Cell cycle

  1. Growth stage - DNA and chromosomes replicate, cell grows and subcellular structures are replicated
  2. Mitosis - one set of chromosomes pulled to each end of cell, nucleus divides
  3. Cytokinesis - cytoplasm and cell membrane divide to form 2 identical cells
• Functions of mitosis:

  • Essential for growth and development of multicellular organisms
  • Repairing (e.g. broken bone healing)
  • Asexual reproduction
• Embryonic stem cells

  1. Sperm cell joins with ovum - fertilisation
  2. Fertilised ovum undergoes mitosis to form embryo (ball of cells)
  3. These cells continue to undergo mitosis and differentiate
• Bone marrow stem cells

  • Red blood cells
  • White blood cells
  • Platelets
• Leukemia (cancer of the bone marrow) treatment

  1. Patient's existing bone marrow is destroyed using radiation
  2. Patient receives a transplant of bone marrow from a donor
  3. Stem cells in the bone marrow now divide and form new bone marrow, and differentiate to form blood cells
• Problems with bone marrow transplants

  • Donor has to be compatible or the white blood cells produced by the donated bone marrow could attack the patient's body
  • Risk that viruses can be passed from the donor to the patient
• Therapeutic cloning

  • Embryos produced with the same genes as the patient
  • Stem cells from the embryo can be transplanted into the patient without being rejected by the patient's immune system
  • Once inside the patient, the stem cells can differentiate to replace cells which have stopped working correctly