biology

• Passive Transport


  The most basic form is diffusion - the random movement of particles in liquids and gases from an area of high concentration to low concentration, without needing energy (ATP)
• Concentration gradient


  • The difference in concentration between two areas
• Factors affecting rate of diffusion

  Size and temperature
• Osmosis


  The movement of water particles across a semi-permeable membrane from an area of high water concentration to low water concentration
• Types of solutions


  • Hypotonic (dilute/weak)
  • Hypertonic (concentrated/strong)
  • Isotonic (same concentrations)
• Osmoregulation


  • Animal/plant cells will lose water in hypertonic solutions, and gain water in hypotonic solutions
• Animal cells in different solutions

  • Cell crenation in hypertonic
  • Normal state in isotonic
  • Cell lysis in hypotonic
• Plant cells in different solutions

  • Plasmolysed (flaccid) in hypertonic
  • Turgid in hypotonic due to turgor pressure
• Active Transport


  Requires energy in the form of ATP to move molecules and/or ions against their concentration gradient (from low to high concentration)
• Energy is always involved in the movement/removal/addition of membranes, so ALL forms of cytosis is active transport
• Semi-permeable membrane


  A membrane that is partially permeable to certain types of materials
• Factors affecting rate of diffusion

  • Size of molecules
  • Concentration gradient
  • Surface area
• Cell state in hypertonic solution

  Animal cells crenate (shrink), plant cells get plasmolysed (flaccid)
• Cell state in hypotonic solution

  Animal cells lyse (burst), plant cells get turgid due to increase in turgor pressure
• Turgid state is most beneficial for non-woody plants as it provides support
• Active Transport


  Can be identified by the use of energy (ATP)
• Number of mitochondria


  Related to the amount of active transport occurring
• Seawater is a hypertonic solution due to the abundance of dissolved minerals
• Drinking seawater will make an individual thirstier
• Diffusion is the movement of particles from an area of high to low concentration
• Osmosis is the movement of water particles from an area of high water concentration to low water concentration through a semi-permeable membrane
• Cells in isotonic solution


  Water concentration inside and outside the cell are equal, so no net movement of water
• Cells in hypotonic solution

  Water concentration outside the cell is higher than inside, so water moves into the cell causing it to increase in size

  
• Cells in hypertonic solution (seawater)


  Water concentration outside the cell is lower than inside, so water moves out of the cell causing it to shrink/crenate

  
• Drinking seawater


  Causes water to be lost from cells, leading to cell crenation and inability to function properly, triggering signals to the brain to drink more water (feeling thirsty)
• Continued drinking of seawater will likely lead to death from internal dehydration as normal metabolic functions in cells cannot resume
• Cell wall


  Found outside the cell membrane of plant cells
• Primary cell wall formation

  1. Formed in young plant cells

  2. Consist of cellulose bundled together into microfibrils

  3. Water and ions able to move freely through the mesh of microfibrils
• Secondary cell wall formation

  1. Form as the plant matures

  2. Contain lignin which help stiffen cells

  3. Affects the dead cells in living material

  4. Develops to become the wood of the tree
• Function of cell wall

  Prevents the plant cell from taking on too much water through osmosis, and exploding, when in a hypotonic environment
• Chloroplast


  • Sites of photosynthesis of the plant
  • Large organelles found in leaf cells or at the green parts of a stem
  • Absorb red and blue wavelengths of light and reflect the green light
• Structure of chloroplast


  1. Inside the chloroplast is the thylakoid, arranged in stacks known as granum

  2. Chlorophyll membranes have a large surface area that "catches" the solar energy required for photosynthesis

  3. Inside the fluid filled matrix is the stroma, where CO2 and H2 join to form glucose in the light independent phase (Calvin Cycle) of photosynthesis
• Chloroplasts


  • Have their own DNA and ribosomes
  • Able to reproduce themselves
  • Indicates some evolutionary origin to the development of plant cells
• Centrioles


  • Present in all animal cells and not in plant cells
  • Made up of microtubules
  • Responsible for forming the spindles during cell division
• Microtubule organizing centres (MTOC)


  Produce microtubules during cell division and cytokinesis in plant cells