Transport in Plants

• What are the different types of plant tissues?

  Epidermis, palisade mesophyll, spongy mesophyll, xylem vessels, phloem vessels, meristem tissue
• What does the epidermis do?

  Covers the outer surfaces of the plant for protection
• What does the palisade mesophyll do?

  The main site of photosynthesis in the leaf
• What does the spongy mesophyll do?

  Air spaces between the cells allow gases to diffuse through the leaf
• What do the xylem vessels do?

  Transports water and minerals through the plant, from roots to leaves. Also supports the plant
• What do phloem vessels do?

  Transports dissolved food materials through the plant
• What does the meristem tissue do?


  Found mainly at the tips of the roots and shoots, where it can produce new cells for growth
• Describe plant tissues.


  . Plant tissues are gathered together to form organs

  . The leaf is a plant organ

  . The structures of tissues in the leaf are related to their functions
• What are all the parts of a leaf structure?

  Upper epidermis, vacuoles, nucleus, lower epidermis, wax cuticle, palisade mesophyll, spongy mesophyll, stoma, guard cell with chloroplasts, air space
• Describe certain aspects about leaf structures.

  . Many chloroplasts close to the top of the leaf to trap maximum sunlight

  . Lots of air spaces to allow gases to diffuse

  . Stomata allow the diffusion of gases in and out of the leaf and can be opened and closed by guard cells
• What is water transport like in plants?

  . Water enters the plant from the soil, through the root hair cells, by osmosis

  . Root hair, xylem and phloem cells are specialised to transport water, minerals and sugars around the plant

  . This water contains dissolved minerals

  . The water and minerals are transported through the xylem vessels, from the roots to the stems and leaves

  . At the leaves, most of the water will evaporate and diffuse out of the stomata (small pores)

  . The loss of water rom the leaves is called transpiration

  . It helps to draw water up the xylem vessels from the roots
• What factors and affect the rate of transpiration?

  - An increase in temperature will increase the rate, as more energy is transferred to the water to allow it to evaporate

  - Faster air flow will increase the rate, as it will move away water vapour allowing more to evaporate

  - Increased light intensity will increase the rate, as it will cause stomata to open

  - An increase in humidity decreases the rate. The air contains more water vapour so the concentration is lower
• Stomata


  Openings in the leaf surface
• Guard cells


  Cells that open and close the stomata
• Role of guard cells

  1. Open stomata

  2. Close stomata
• At night


  Stomata are closed
• Carbon dioxide is not needed for photosynthesis at night, so closing the stomata reduces water loss
• When water is plentiful

  Guard cells take up water and bend, causing the stomata to open
• Gases for photosynthesis are free to move in and out of the open stomata along with water from transpiration
• When water is scarce


  Losing water makes the stomata change shape and close, stopping the plant from losing more water through transpiration
• What is a key point to remember about the stomata?

  In most plants, the stomata are mainly found on the bottom surface of the leaf. This means that the sun does not shine directly on them, reducing water loss
• What is a key point to remember abut transpiration?

  Plants cannot stop transpiration completely. This is because carbon dioxide is needed for photosynthesis, so water will always escape
• What is translocation?


  . Phloem tissue transports dissolved sugars from the leaves to the rest of the plant

  . This movement of food through phloem tissue is called translocation

  . Phloem cells are adapted for this function
• Can the rate of transpiration from a cut shoot be estimated?

  . The rate of transpiration from a cut shoot can be estimated by measuring the rate at which the shoot takes up water

  . This is only an estimate because not all of the water taken up by a shoot is lost - a very small percentage is used in the leaf