Biology

• Define diffusion

  The net spreading out of particles from a high concentration to a low concentration.
• Name 4 factors will speed up diffusion

  short diffusion distance, temperature, surface area, high conc gradient
• Give an example of a biological system adapted for fast diffusion

  Alveoli ---> large diffusion gradient, thin walls, large surface area
• Define osmosis


  Osmosis is the movement of free water particles from an area of high water potential to an area of low water concentration over a semi-permeable membrane
• Dilute = ..... water concentration


  HIGH (many water molecules)
• Concentrated = .... water concentration

  LOW (few water molecules)
• Design an experiment to test osmosis in lettuce

  • Take 2 samples of lettuce.

  • Add distilled water to one watchglass

  • Add concentrated salt solution to a second watchglass

  • Measure the mass of one lettuce sample and place the lettuce in the distilled water

  • Measure the mass of the other lettuce sample and place the lettuce in the concentrated salt solution.
• What is visking tubing?

  it is partially permeable - water can move through but not other substances
• How do you use visking tubing?

  • Put mystery solution into 2 visking tubings (add bulldog clip to seal)

  • Weigh the visking tubings water

  • Place in known solutions (different concentrations of sugar solution)

  • Wait 40 minutes - complete questions below in this time

  • Reweigh the visking tubing

  • Calculate % mass lost/gain
• How can we improve the accuracy of using visking tubing?

  - More time - ensure osmosis has finished and reached equilibrium

  - Control temperature - water bath

  - Repeats

  - More of different concentrations
• % change in mass formula

  change in mass/initial mass
• Name the process that causes the change in the level of the water and the level of the

  sucrose solution.

  Osmosis
• Characteristics of diffusion

  - against a concentration gradient

  - oxygen leaves the leaf

  - is passive

  - occurs in nature

  - involves the transport of solutes

  - particles move randomly

  - doesn't require a membrane

  - does not require cell energy for movement

  - movement from an area of high to low concentration

  - doesn't need water for movement
• Characteristics of osmosis

  - involves a partially permeable membrane

  - involves water only

  - is passive

  - occurs in nature

  - always passes a membrane

  - does not require cell energy for movement

  - movement from an area of high to low concentration

  - particles move randomly

  - water moves down a concentration gradient
• Characteristics of active transport

  - requires energy

  - uses carrier proteins

  - occurs in nature

  - involves the transport of solutes

  - always passes a membrane
• Define turgid

  • cell membrane and cytoplasm pressing against cell wall

  • in dilute solution

  • water moved into cell by osmosis
• Define plasmolysed

  • cell membrane pulled away from cell wall, as cytoplasm decreased

  
  

  • in concentrated salt solution

  
  

  • water moved out of cell by osmosis
• Define hypotonic

  - Higher water concentration

  - Lower solute concentration
• Define hypertonic

  - Lower water concentration

  - Higher solute concentration
• Which substance moves by osmosis?

  Water
• What happens to plant cells that take up water by osmosis, and what do you call the cell?

  Turgid
• What happens to plant cells that lose water by osmosis, and what do you call the cell?

  Plasmolysed
• Where is water absorbed by a plant?


  Root hair cells
• What process requires water in plants?

  Photosynthesis
• Where does photosynthesis happen?

  Chloroplasts
• Which direction does water need to flow in? (it is a one way journey)

  Up through the roots
• How do plants make sugar (glucose) ?

  As a product of photosynthesis
• What does a plant need sugar for?

  Respiration
• Where do plants store their excess sugar?

  In the roots as starch
• Where is sugar needed in a plant?

  Everywhere - all cells that respire
• Will sugar (in solution) flow in only one direction, or will it flow all over the plant?

  All over (through the phloem)
• Characteristics of upper epidermis

  Transparent - lets light through
• Characteristics of waxy cuticle

  Prevents water loss
• Characteristics of palisade mesophyll

  Lots of cells tightly packed to hold as much chlorophyll as possible
• Characteristics of spongy mesophyll

  Lots of air pockets to allow for gas exchange
• Role of the xylem

  Transports water
• Role of the phloem

  Transports food and mineral ions
• Characteristics of xylem

  - solution moves up only

  - no end between cells

  - transports water and mineral ions

  - dead

  - lignin strengthens the walls which stops xylem collapsing in
• Characteristics of phloem

  - transports sucrose and amino acids

  - alive

  - has a sieve plate

  - very few organelles (little bit of cytoplasm)

  - solution moves up and down

  - companion cells keep phloem alive
• Define transpiration

  Transpiration is the evaporation of water at the surfaces of the spongy mesophyll cells in leaves, followed by loss of water vapour through the stomata.