biology paper 1

• Magnification

  image size/actual object size
• Light microscope

  • 1000 um in 1 mm
  • 1000 nm in 1 um
  • Can see nucleus and cell wall but not mitochondria (too small and not stained)
  • Electron microscope has much more resolution and magnification
• Osmosis

  The movement of water from an area with high concentration of water to an area of low concentration of water
• Solute


  Something that dissolves in water
• High concentration of sugar in solution

  Water moves out of potato cells into the solution, potato gets smaller
• Low concentration of sugar in solution

  Potato gets bigger
• Investigating osmosis

  • Control variables: amount of solution
  • Remove excess water with paper towels before weighing to ensure change in mass is due to change in water content
• Test for starch

  Add iodine, turns black if starch present
• Test for protein

  Add biuret, turns purple
• Test for reducing sugar

  Add benedicts and heat for 2 mins, turns red
• Test for lipid

  Add ethanol then add water, turns cloudy
• Investigating amylase enzyme

  • Need a water bath to maintain correct temperature, as temperature affects reaction rate
  • Test at pH 3,4,5,6,7,8,9&10 to find exact optimum pH
• Measuring, starting and stopping timers are sources of error and weaknesses in investigating amylase enzyme
• The closer the lamp

  The quicker the bubbles are produced, so higher rate of photosynthesis
• Difficult to count very small bubbles, each bubble counts as 1 no matter how big it is, so results may be inaccurate in light and photosynthesis experiments
• Leave the plant for a few minutes before starting to count bubbles, as it takes time for the plant to adjust to the light/temperature and for photosynthesis to reach the correct rate
• Place a glass screen in front of beaker to allow light to get through but block the heat, to avoid heat from the lamp as a source of error in light and photosynthesis experiments
• Apart from light, other limiting factors for photosynthesis are temperature and CO2
• Rate of photosynthesis will level off, even with maximum light, because the plant also needs enough temperature and CO2
• Investigating reaction time

  • Repeat to calculate mean, range of results, resolution of measurements
• Quadrat

  Apparatus used to measure population size
• Cell membrane


  • Determines what goes in and out of the cell
• Cell wall


  • Provides structure
• Cytoplasm

  • Where reactions occur
• Ribosomes

  • Responsible for protein synthesis
• Mitochondria


  • Produce energy
• Things in an animal cell

  • Cell membrane
  • Mitochondria
  • Ribosomes
  • Cytoplasm
  • Nucleus
• Things in a plant cell that are not in an animal cell

  • Cell wall
  • Vacuole
  • Chloroplasts
• Things in a bacterial cell

  • Cell membrane
  • Cytoplasm
  • Chromosomes
  • Flagella
  • Ribosomes
  • Cell wall
• Cell specialisation

  Cells start off looking the same, then various different genes will be turned off and on, causing the cells to specialise and differentiate
• Magnification equation

  Magnification = image height / object height
• Mitosis

  DNA in nucleus condenses into chromosomes, line up down the middle, then chromosomes get pulled apart to either side of the cell, new nuclei will form and then separate
• Stem cells

  Unspecialized cells from which differentiated cells develop
• Stem cells can be used to grow new brain cells, new bones, new organs
• To make stem cells, the nucleus is taken out of an egg cell and the nucleus from the patient's cell is inserted, causing the egg to develop into an embryo
• A downside of making stem cells is that human embryos will be created and destroyed
• Diffusion

  The movement of particles from an area of high concentration to an area of low concentration
• Osmosis

  The diffusion of water across a selectively permeable membrane from an area of high water concentration to low
• Active transport

  Movement across a membrane from a low to high concentration
• Active transport occurring

  • Glucose in gut
  • Minerals in roots