Cells and movement across cell membranes

• A cell is the smallest unit of life - all living things are made of at least one cell.

  Scientific name for living things is organis.
• Parts of a cell:

  • Cell wall - contains cellulose, structural support (plant cell)
  • Cell membrane - controls the entry and exit of substances (plant+ animal cell)
  • Cytoplasm - site of most cell reactions (plant + animal cell)
  • Nucleus - has chromosomes carrying genetic information, controls cell activity (plant + animal cell)
  • Cell vacuole - contains watery sap and helps make the cell firm (plant cell)
  • Chloroplasts - site of photosynthesis (plant cell)
  • Mitochondria - site of aerobic respiration (plant + animal cell)
• Plant cells have chloroplasts but animal cells don’t as they carry out photosynthesis and also absorb light.
• SPECIALISED CELLS

  Cells with special features that make them more efficient at performing a specific function.
• Specialised cells:

  • Palisade cell - plant leaves for photosynthesis.
  • Egg cells
  • Ciliated cell - in animal airways to protect lungs from damage.
  • Root hair cell - large surface area to absorb.
  • Red blood cell - transport of oxygen, no nucleus, biconcave, haemoglobin.
  • Sperm cell - lots of mitochondria, fertilise inside egg through enzymes in head.
  • Nerve cell - carries signals over long distance.
• Microscopes

  Let us see things we can’t with the naked eye.

  Total magnification = eyepiece x objective lens

  Biological cell staining is a technique to enable better visualisation of cells under the microscop.
• LIGHT microscopes

  • Limited magnification
  • Natural colouring unless stained
  • Used to view dead or alive specimens
• ELECTRON microscope

  • Higher magnification (x2,000,000)
  • False colouring can be added
  • Black and white images
  • Specimens must be dead to view
• Diffusion is the movement of particles from an area of high concentration (down concentration gradient) until the concentration are equal.
• Diffusion does NOT require energy so it’s a passive process.

  Cell membrane is selectively permeable - only allows certain substances to pass through, e.g. CO2 and oxygen.
• Visking tubing:

  Can be used as a model for cell membrane as has pores, allowing particles that are small enough to pass through pores can diffuse, particles that are too large cannot.

  E.g. Glucose and iodine are small so can pass, but starch is too large - starch stays in the tube, iodine diffuses into tube down the concentration gradient, tube turns blue/black
• Osmosis is the movement of water molecules from an area of high water concentration to an area of low water concentration, down a water concentration gradient, across a selectively permeable membrane.
• Concentration gradient:

  The greater the difference in the water concentration on either side of the membran, the steeper the concentration gradient so faster rate of reaction.

  If water concentration was equal on both sides of the membrane - no NET movement of water overall.
• Flaccid

  when a plant cell had lost some water but membrane hasn’t peeled away
• Plasmolyed

  when a plant cell has lost lots of water and the membrane has peeled away
• Turgid

  when a plant cell had lots of water and the cell is firm - the vacuole pushes on the cell wall
• Tubes of a vegetable can be used to show osmosis - in pure water it will gain length/mass (osmosis into cells), in low salt solution there will be no change (no net osmosis), high salt solution it will lose length/mass (osmosis out of cells).
• Active transport:

  Moves molecules from an area of low concentration to an area of high concentration - against concentration gradient.

  This process requires energy, in form of ATP from respiration - if respiration doesn’t occur, neither can active transport.

  Occurs in small intestine and plant roots.
• Factor that can affect the rate of respiration:

  • Temperature
  • pH
  • Number of mitochondria
  • Toxic substances
• Similarities and differencies

  
• ROOT HAIR CELLS

  Large surface area to increase rate of absorption- water and mineral ions.

  They absorb mineral ions by active transport.
• Multicellular Organisms

  1. Atoms (oxygen)
  2. Molecules (sugar)
  3. Organelles (nucleus)
  4. Cells (sperm cell)
  5. Tissues (muscle tissue) - group of similar cells with similar functions.
  6. Organs (liver) - consists of several tissues performing specific functions.
  7. Organ systems (digestive system) - consists of number of organs working together to perform an overall function.
  8. Organism
• • If a diagram is magnified 100 times larger, to calculate the size of the actual cell, you need to make the drawing 100 times smaller.