osmosis and plant transport

• osmosis


  diffusion of water molecules from a dilute solution to a more concentrated solution through a selectively permeable membrane
• describe what happens when water moves into a plant cell by osmosis (turgid)


  the vacuole increases in size.

  the cell membrane is pushed against the cell wall

  the cell becomes turgid
• why would an animal cell burst?


  no cell wall, cell lysis will occur (a cell wall is said to be limiting)
• what happens when water moves out of a plant cell by osmosis (plasmolysis)?


  its contents shrink

  the cell membrane pulls away from the cell wall

  external solution enters

  vacuole gets smaller

  cell becomes flaccid
• in plasmolysis, why does the space between the cell wall and cell membrane fill with external solution?


  cell wall is fully permeable
• Investigate the process of osmosis by measuring the change in length or mass of plant tissue, method

  1. Set up 5 labelled beakers, each containing a different concentration of sucrose.

  2. Using a cork borer cut five potato cylinders of equal length and width.

  3. Weigh/measure the length of each potato cylinder.

  4. Add 1 potato cylinder to each beaker.

  5. Leave the beakers for 1 hour.

  6. Pat the potato cylinders dry to remove excess water.

  7. Reweigh/measure the length of each potato cylinder.

  8.Record the results in a table
• Investigating the process of osmosis by measuring the change in length or mass of model cells, using Visking tubing, method


  1. Add sucrose solution to a section of Visking tubing - a selectively permeable substance used to model a cell membrane.

  2.Weigh the Visking tubing and its contents.

  3. Add the Visking tubing to a beaker of water.

  4. Leave for 1 hour.

  5. Pat the Visking tubing dry to remove excess water.

  6. Reweigh the Visking tubing and its contents.
• transpiration


  the evaporation of water from the spongy mesophyll cells followed by the diffusion of water through the air spaces and out of the stomata.
• why is the transpiration stream important

  It provides leaves with a continuous supply of water (for photosynthesis).

  It continually transports minerals from the roots to the leaves and other parts of the plant.

  It provides plant cells with support from turgor.

  It provides water for transpiration.
• what is the role of water in plants?


  1. support

  2. photosynthesis

  3. transpiration

  4. transport of dissolved substances
• what is the affect of surface area on transpiration?


  Smaller leaves will contain less stomata causing a decrease in transpiration.
• what is the affect of wind on transpiration?


  A higher wind speed will increase transpiration. This is because moving air removes water vapour incresing rate of diffusion of water vapour from the leaf as diffusion gradient for water vapour is steeper
• what is the affect of temperature on transpiration?


  A higher temperature will increase the rate of evaporation causing an increase in transpiration.
• what is the affect of humidity on transpiration?


  A higher humidity level will reduce the rate of evaporation causing a decrease in transpiration. This is because diffusion of water vapour out of leaf slows down if the leaf is already surrounded by moist air as there is a reduced diffusion gradient for water vapour.
• what is the affect of light intensity on transpiration?


  Darkness will cause the stomata to close causing a decrease in transpiration
• what does a potometer measure?


  water loss from leaves
• what does a bubble potometer measure?


  rate of water lost from a plant by transpiration
• what does a weight potometer measure?


  amount of water lost by plant through transpiration
• what does the washing line method prove

  most water loss occurs through the lower surface of the leaf
• in the bubble potometer experiment, why is it important it is properly sealed at the junction between the shoot and the neck of the potometer?


  to prevent air leaks which hinder water uptake into the plant and therefore prevents water movement in the xylem
• why must the potometer be set up under water?

  prevent unwanted air bubbles which would prevent water movement in xylem
• how would you introduce an air bubble into a bubble potometer?

  remove the capillary tubing from the beaker of water to draw in a small column of air and then return the tubing to the beaker
• in a bubble potometer, what measurements will be needed to work out the rate of water uptake by the shoot?


  distance moved by bubble and time
• why is the bubble potometer apparatus left for five minutes before starting the experiement?

  allow plant to climatise
• describe the transpiration stream

  1. water is pulled up the xylem in the stem from the roots.

  2. water is used for photosynthesis and to stop the plant from wilting, giving it support

  3. water will evaporate from the leaf cells and pass out into the air through the pores called the stomata

  4. the stomata are found on the underside of the leaf

  5. as more water is used up or lost from the leaves, more is pulled up in the xylem vessels

  6. movement of water up the xylem is a continuous flow from roots to leaves
• What are the main functions of transpiration in plants?

  - Cooling the plant - Moving nutrients through the plant - Maintaining turgor pressure in cells
• What are the main steps involved in the process of transpiration?

  The main steps are water absorption, water transport, evaporation, and diffusion.
• Through which plant structure does water primarily leave during transpiration?

  Water primarily leaves the plant through stomata.
• Why does higher temperature lead to increased transpiration rates?

  Higher temperature increases kinetic energy, lowers air humidity, and causes wider stomatal opening.
• What is the effect of increased temperature on the water potential gradient?

  Increased temperature creates a higher water potential gradient between the leaf and the air.
• How do plants respond to extreme temperatures regarding transpiration?

  Plants may close their stomata to prevent excessive water loss.
• What would a scientist expect to observe about transpiration rates in two identical plants at different temperatures?

  The plant at the higher temperature would have a higher transpiration rate.
• Why is it more accurate to use mass rather than length in osmosis experiments?

  Potatoes have different initial masses
• How can plants reduce transpiration?

  By closing their stomata
• What is the purpose of a reservoir or syringe in a bubble potometer?

  To reset the air bubble for reliability
• Why must the potometer be airtight?

  To prevent air leaks affecting measurements
• What limitation does a potometer have regarding water uptake measurement?

  It doesn't indicate water used for photosynthesis
• Selectively Permeable Membrane


  A semipermeable membrane that allows certain substances to pass through while restricting others.
• describe a turgid cell 


  large vacuole, cell membrane pushed against cell wall.

  • large vacuole
  • cell mem. pushed against cell wall

  
• describe a flaccid cell


  a cell lacking turgidity. They are not plump and swollen but floppy or loose, and cells have drawn in and pulled away from the cell wall.