biology

• Evolution is the gradual change in inherited traits in a population over time, occurs due to natural selection.
• Theory of natural selection

  1. Genetic variation exists due to spontaneous mutations
  2. Selection pressures exist
  3. Random mutations give organisms a selective advantage
  4. Organism is better adapted to the environment and survives
  5. Organism reproduces, passing on its beneficial alleles
  6. Frequency of advantageous alleles increases
• Competition between organisms in a habitat exists because the resources within a habitat required for survival are limited.
• 1. Genetic variation exists due to spontaneous mutations
  2. Antibiotics act as selection pressure
  3. Random mutations give bacteria antibiotic resistance
  4. If an antibiotic is administered, the bacterium is better adapted and survives, whilst other bacteria is killed
  5. Bacteria reproduces, passing on its resistant variant
  6. Frequency of antibiotic resistant alleles increases
• How does the pentadactyl limb provide evidence for evolution?


  The presence of the pentadactyl limb suggests that all species which possess it have descended from a common ancestor
• Describe the methods used by scientists to date tools

  • Carbon- 14 dating- estimating the age of carbon-containing material that is found in tools or alongside tools
  • Stratigraphy- using the age of the layers of sediment surrounding the tool as an indication of the age of the tool
• How has the development of more complex tools provided as evidence for evolution?

  • Correlation between the development of more complex tools and an increase in brain size
  • Primitive tools are older than complex tools. Brain size has increased over time as brain size increased, advancements in tool use were made
• How did Leakey's findings provide evidence for human evolution?


  He discovered many hominid fossils. The 1.6 million year old fossil 'Turkana Boy' showed no comparable to that of modern day humans e.g. brain size
• Digestive enzymes

  • Lipase breaks down lipids into glycerol and fatty acids. It is made in the pancreas and the small intestine. It works in the small intestine
  • Protease breaks down proteins into amino acids, made in the pancreas, stomach and small intestine. It works in the stomach and small intestine.
  • Amylase breaks down starch into sugars, made in pancreas, small intestine and salivary glands, works in mouth and small intestine
• Carbon dioxide is going to be diffused from the blood into the lungs so it can be breathed out. Oxygen is going to be diffused from the lungs into the blood so it can be taken around the body.
• Uses of stem cells

  • treating Parkinsons- growing new brain cells
  • bone and spinal injury- growing new bone cells
  • organ failure- growing new organs/parts of organs
• Method

  • nuclei removed from the egg cell
  • nuclei from patient cell inserted into empty egg
  • egg starts to develop into embryo
  • stem cells removed from embryo
  • stem cells turned into new cells
• What are the risks of stem cell use in medicine?

  • Transplanted stem cells could cause tumours
  • Finding suitable sperm donors is a difficult task
  • Stem cells may be rejected by the body
  • Potential side effects
  • Long term risks unknown
  • Stem cells may become contaminated during preparation and transmit infection to the patients, making them sicker
• Neurones


  Dendrites receive electrical impulses from other neurones. Nerve endings can connect to receptors or effectors like muscles. They contain a long insulated fibre called myelin sheath, they are long to help transmit electrical impulses up and down the body

  
• Egg cell


  Cell membrane- changes after fertilisation to prevent sperm entry

  Cytoplasm- contains nutrients for developing embryo

  
• Onion cell- Microscopy Practical

  1. Take a thin layer of cells from your sample either by peeling them or using a cotton bud
  2. Add a small amount of the correct chemical stain
  3. Apply the cells to your glass slide by placing them on or wiping a cotton bud against it
  4. Carefully place a coverslip onto your slide, taking care to avoid air bubbles
  5. Place the slide on the stage and look through the eyepiece lens
  6. Turn the focus wheel to obtain a clear image
  7. Start with the lowest objective lens magnification
  8. Increase the magnification of the objective lens and refocus
• Effect of pH on enzyme activity


  1. Place single drops of iodine solution on each well of a tray

  2. Label a test tube with the pH to be tested

  3. Place it in a beaker with 50ml cold water and place this above a Bunsen Burner for 3 minutes

  4. Place 2cm^3 of amalyse solution, 2cm^3 of starch solution and 1cm^3 of buffer pH solution in a test tube and start a stop watch

  5. After 10 seconds, use the pipette to drop a solution into one of the wells containing iodine solution

  6. Keep repeating until solution remains orange, and record the time taken

  7. Repeat steps 1-5 with a buffer solution of different pH
• The mixture should turn blue-black to indicate starch is still present
• Blood type is recessive to blood type A and B.