Transport in plants Flashcards iGCSE Biology

[q] Explain the mechanism of water movement from the roots up the tree to the leaves?

[a]

1. Water move into xylem from the roots down the water potential gradient by osmosis;
2. Transpiration / transpiration pull creates tension (in water column in xylem);
   • Cohesion of water molecules / described;
   • Adhesion of water to cell wall / xylem;
3. Water moves up the xylem ;
   • Continuous column of water (in xylem) / transpiration stream ;
4. Water move into leaf cells from the xylem down the water potential gradient by osmosis;
5. Water evaporates into airspaces in mesophyll;
6. Water vapour diffuses out through stomata;

[q] What are the Factors of Rate of Transpiration?

[a]

• Temperature
  • ↑ Temperature → ↑ Transpiration
  • Warm air can hold more water vapour than cold air. 
  • Sun heats up leaves and increases the rate of evaporation of water.

• Humidity
  • ↓ Humidity → ↑ Transpiration
  • Less water loss by transpiration
    • Increased humidity at lower surface will reduce transpiration rate;
    • Causes lower water demand / less water loss / reduces chances of wilting;
    • Reduced concentration gradient (water vapour) / water potential gradient;
    • Creates a boundary layer / AW;

• Air movements
  • ↑ Wind → ↑ Transpiration
  • In moving air, water vapour will be swept away from the leaf as fast as it diffuses out. This will speed up transpiration.

• Light intensity
  • ↑ Light Intensity → ↑ Transpiration
    The stomata closes when there is no light intensity.

[q] What is the Function of Cortex Cells?

[a]

• Cell vacuoles have high water potential;
  • Water is absorbed by osmosis
• Cells are turgid;
  • Cell contents / vacuole / cell membrane pushes out against cell wall;
  • Cell wall is inelastic / is rigid;
• Cells are tightly packed;

[q] What is the Function of Phloem?

[a] Transport of organic products of photosynthesis and amino acids from source to sink.

A.k.a Translocation

[q] What is the Function of Xylem?

[a] Transport water and mineral ions from the roots to the stem and leaves.

[q] Functions of Stomata

[a]

• Allow Movement of gas like oxygen and carbon dioxide, into and out of leaf;
  • For photosynthesis / respiration;
• Allows transpiration;
  • Enables water to be pulled up the plant / AW;

[q] How does water from the roots reach the leafs?

[a]

• Water moves from root cells, into xylem;
• Cohesion / adhesion AW, of water molecules;
• (This) pulls on / creates tension [negative pressure] (in water column in xylem);
• Water moves up / through, the xylem;
• Mass flow of water (in xylem) / transpiration stream;
• Water moves into leaf by osmosis (from xylem);
• Loss of water from leaf (cells) lowers water potential;
• A ref to water potential gradient
• Evaporation, from surfaces of (mesophyll) cells / into air spaces (in leaf);

[q] How does water pass from a leaf cell to the atmosphere?

[a]

• Diffusion / osmosis / move, from cell (to air space);
• (water moves) through cell wall / membrane;
• Evaporates into the air spaces (inside the leaf);
• Water vapour moves out through the stomata;
• (vapour) diffuses (through stomata);
• Transpiration;

[q] Identify the Xylem and Phloem

[a]

[q] Identify the Xylem and Phloem

[a]

[q] Investigating the role of environmental factors in determining the rate of transpiration from a leafy shoot

[a]

• Cut a shoot underwater to prevent air entering the xylem and place in tube
• Set up the apparatus as shown in the diagram and make sure it is airtight, using vaseline to seal any gaps
• Dry the leaves of the shoot (wet leaves will affect the results)
• Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water
• Set up the environmental factor you are investigating
• Allow the plant to adapt to the new environment for 5 minutes
• Record the starting location of the air bubble
• Leave for a set period of time
• Record the end location of air bubble
• Change the light intensity or wind speed or level of humidity or temperature (only one – whichever factor is being investigated)
• Reset the bubble by opening the tap below the reservoir
• Repeat the experiment
• The further the bubble travels in the same time period, the faster transpiration is occurring and vice versa

[q] Label the Phloem and Xylem in a stem

[a]

[q] What is the Function of Root Hair Cell?

[a] Take up water from the soil by osmosis and absorb mineral salts (as ions) by active transport.

[q] What is Translocation?

[a] The movement of sucrose and amino acids in the phloem, from regions of production (the ‘source’) to regions of storage OR to regions where they are used in respiration or growth (the ‘sink’) is called Translocation.

[q] What is Transpiration?

[a] The loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata is called Transpiration.

[q] Transport in the phloem

[a] Transport in the phloem goes in many different directions depending on the stage of development of the plant or the time of year; however dissolved food is always transported from source (where it’s made) to sink (where it’s stored or used):

• During winter, when many plants have no leaves, the phloem tubes may transport dissolved sucrose and amino acids from the storage organs to other parts of the plant so that respiration can continue
• During Spring, leaves are growing
  • Source: Roots
  • Sink: Leaves
• During Summer, leaves are fully grown
  • Source: Leaves
  • Sink: Roots

[q] What is Wilting?

[a]