Cells and movement across membranes

• Cells

  Basic unit of life. Unicellular organisms only have one cell. Multicellular organisms have many cells that work together.
• Animal cell structure

  • Nucleus
  • Cell membrane
  • Cytoplasm
  • Mitochondria
• Plant cell structure

  • Chloroplasts
  • Cell wall
  • Large central vacuole
• Summary of features found in cells and their functions

  • Cell membrane - Controls the movement of substances into and out of the cell
  • Cytoplasm - Jelly-like substance, where chemical reactions happen
  • Nucleus - Carries genetic information and controls what happens inside the cell
  • Mitochondria - Where respiration takes place, releasing energy for the cell
  • Large central vacuole - Contains a liquid called cell sap, which keeps the cell firm
  • Cell wall - Made of a tough substance called cellulose, which supports the cell
  • Chloroplasts - Contain the green pigment chlorophyll, which absorbs light energy. This is where photosynthesis occurs.
• All living things are made of cells which are differentiated to perform different functions
• Substances move into or out of the cell and enzymes are catalysts contributing to cell metabolism
• Light microscope


  Uses focused light passed through the object and two lenses to magnify an image of the object
• Using a light microscope

  1. Light passes through the object

  2. Light passes through the ×4 objective lens

  3. Light passes through the ×10 eyepiece lens

  4. Image is magnified 40 times
• Using light microscopy

  • It is possible to magnify using a ×40 objective lens which magnifies the image 400 times
  • Using an objective lens with higher magnification than this will make the image bigger but will not improve image clarity
• Electron microscopy

  Uses electrons to form images of dead organic matter
• Making a glass slide

  1. Rub a clean cotton bud gently on the inside of your cheek

  2. Smear the sample across a clean glass slide

  3. Place a few drops of methylene blue dye onto the smear

  4. Use a mounted needle to gently lower a glass coverslip onto the sample
• Before undertaking any practical activity it is important to carry out a risk assessment
• Things to consider in a risk assessment

  • Hazard
  • Risk
  • Control measure
• Methylene blue is an irritant
• If methylene blue comes into contact with the skin or eyes


  It could cause irritation
• Control measures for methylene blue

  • Wear laboratory gloves
  • Wear safety glasses
  • Use low concentrations of the chemical
• Glass coverslips are easily broken and are sharp
• Glass coverslips can cut the skin


  When trying to lower onto the slide
• Control measures for glass coverslips

  • Handle carefully
  • Report breakages
• Magnification

  Calculated as image size divided by actual size
• Katie's drawing was 40 mm in length and the actual cells were 0.4 mm in length

  The magnification of her drawing was ×100
• Terry's drawing was 60 mm in length and the actual cells were 0.4 mm in length


  The magnification of his drawing was ×150
• Zygote

  A fertilised egg cell with a full set of genes
• Differentiation

  1. Unspecialised cell becomes a more specialised cell type

  2. Controlled by genes
• Tissue

  Cells with a similar function grouped together
• Organ

  A collection of different tissues carrying out a particular function
• Organ system

  Several different organs working together to perform specific functions
• Organism

  Organ systems working together
• A solution with a low solute concentration has a high water concentration. Pure water has the highest water concentration.
• • going from high to low concentration is going down the concentration gradient
• • going from low to high concentration is going against the concentration gradient
• Diffusion

  The process by which molecules move from an area of higher concentration to an area of lower concentration.
• Concentration gradient

  A difference in the concentration of a substance across a space, which drives diffusion.
• Osmosis

  The movement of water molecules from an area of higher concentration to an area of lower concentration through a selectively permeable membrane.
• Alveoli


  Small sacs at the end of bronchioles where gas exchange occurs, exchanging O2 and CO2 between lungs and bloodstream
• Gas Exchange in Alveoli

  Oxygen molecules diffuse from alveoli into bloodstream, while carbon dioxide molecules diffuse in the reverse direction; facilitated by thin capillary walls and hemoglobin function
• Turgid cell

  A cell that absorbs water and swells due to a hypotonic environment.
• Flaccid cell

  A cell that loses water and shrinks due to a hypertonic environment.
• Carrier Proteins

  Proteins that pick up specific molecules and transport them through the cell membrane against the concentration gradient.
• Root Hair Cell

  A type of plant cell found at the tip of a root hair, responsible for absorbing water and minerals from the soil.