5. Transport systems in plants

• Plants need water for:

  • To remain turgor
  • For photosynthesis
  • To keep cool
• Water enters the root hairs by osmosis.
• Water molecules move from a high concentration from a low concentration inside the root cells.
• Root hairs increase the surface area of the root so more water molecules and minerals can be taken up.
• Plants use tubes called xylems to transport water up through the plant.
• Xylem are hollow, dead cells that are lignified with rings of lignin.
• Phloem is used to transport sugar up and down the plant.
• Phloem cells are alive.
• Phloem cells have cells called companion cells to provide energy.
• Phloem cells

  
• Xylem cells.

  
• There are several types of plant cell layered on top of one another and Xylem and Phloem cells arranged into a vein.
• A plant cell labelled

  
• The epidermis (upper & lower) is like a skin where the stomata and guard cells are found.
• The palisade layer is where most photosynthesis takes place
• The spongy mesophyll consists of irregular shaped cells that don't fit together. This creates spaces between them for gases to move around.
• The vein is made up of bundles of xylem and phloem.
• Structure of a leaf

  
• Stomata are small pores that allow water vapour and gases out of the leaf.
• Each stomata is surrounded by two guard cells which control the opening and closing of the stomata.
• When a plant cell has a high level of water, the guard cells are turgid. This makes the guard cells curve out, opening the stoma and allow carbon dioxide in and oxygen out. Water also evaporates through the stomata.
• When a plant cell has a low level of water, the guard cells lose water and close. Gas exchange cannot take place and water is not lost.
• The movement of water vapour out the stomata is a process known as transpiration.
• Water is taken into the root hairs from the soil via osmosis. Water is then transported through the plants through the xylem tubes. Finally, water is lost by evaporation through the open stomata in the leaf.
• The rate of transpiration can change based on external conditions.
• High light intensity increases the rate of transpiration as the stomata is open.
• Warm temperatures increase the rate of transpiration as the water evaporates faster.
• Low light intensity decreases the rate of transpiration as the stomata close in the dark to reduce water loss.