Transport in plants

• Why do plants require a transport system?

  To ensure all cells receive a strong supply of the nutrients they require.
• What is especially important about a plant's transport system?

  It must be able to transport substances up their stem against gravity.
• What is the structure of xylem and how does it relate to its function?

  • Long, continuous columns made of dead tissue for water transport.
  • Contains pits for sideways water movement between vessels.
  • Thickened with a tough substance for structural support.
• What is the structure of phloem and how does it relate to its function?

  • Sieve tube elements transport sugars around the plant.
  • Companion cells are designed for active transport of sugars into tubes.
  • Plasmodesmata allow flow of substances between cytoplasm of different cells.
• Describe the structure and function of the vascular system in the roots.

  • Consists of xylem and phloem.
  • Xylem arranged in an X shape for resistance against force.
  • Surrounded by endodermis, providing a water supply.
• Describe the structure and function of the vascular system in the stem.

  • Consists of xylem and phloem.
  • Xylem on the inside for support and flexibility, phloem on the outside.
  • Layer of meristem cells produces new xylem and phloem tissue when required.
• Describe the structure and function of the vascular system in the leaves.

  • Consists of xylem and phloem, forming the midrib and veins.
  • Involved in transport and support.
• What is transpiration?

  The evaporation of water from the leaves of a plant.
• What is a consequence of gaseous exchange in plants?

  Transpiration occurs when the plant opens the stomata to exchange oxygen and CO2.
• Name factors that affect the rate of transpiration.

  • Increased light increases transpiration.
  • Increased temperature increases transpiration.
  • Increased humidity decreases transpiration.
  • Increased air movement increases transpiration.
  • Waxy cuticle prevents transpiration.
• How can we measure the transpiration rate?

  Using a potometer to measure the movement of an air bubble in a water-filled tube.
• Define water potential as a mechanism of movement in plants.

  • Water potential is the tendency of water to move by osmosis from high water potential to low.
  • Pure distilled water has the highest water potential of 0.
  • This is the basis for water movement to areas needed within plants.
• What is meant by the apoplastic pathway?

  Water moves through the cell walls and intercellular spaces by mass flow until it reaches the Casparian strip.
• What is meant by the symplastic pathway?

  Water moves through the cytoplasm via plasmodesmata after being actively transported into cells.
• Explain the cohesion-tension theory.

  Water molecules form hydrogen bonds, causing them to stick together, allowing water to be drawn up the stem from the roots as it is lost through transpiration.
• What are adaptations of xerophytes that allow them to live in dry conditions?

  • Small or rolled leaves.
  • Densely packed mesophyll.
  • Thick waxy cuticle.
  • Stomata often closed.
  • Hairs to trap moist air.
• What are adaptations of hydrophytes that allow them to live in wet conditions?

  • Thin or absent waxy cuticle.
  • Stomata often open.
  • Wide, flat leaves.
  • Air spaces for buoyancy.
• Summarise the mechanism of translocation.

  • Sucrose produced in leaves is loaded into sieve tubes via active transport.
  • Lowers water potential, causing water to move in from xylem.
  • Assimilates move along the sieve tube towards areas of lower hydrostatic pressure (sink).
  • Sucrose diffuses into surrounding cells where it is needed.
• What do plants require to ensure all cells receive sufficient nutrients?

  A transport system
• How do xylem and phloem contribute to nutrient transport in plants?

  Xylem transports water and minerals, while phloem transports sugars
• What are the components of the vascular bundle in plants?

  • Xylem
  • Phloem
  • Provides transport and structural support
• How are xylem vessels arranged in the vascular bundle?

  In an X shape
• What mechanical forces can the X shape arrangement of xylem vessels withstand?

  Various mechanical forces such as pulling
• What surrounds the xylem vessels in the vascular bundle?

  The endodermis
• What is the function of the endodermis in relation to xylem vessels?

  It supplies xylem vessels with water
• What is the inner layer of meristem cells in the vascular bundle called?

  The pericycle
• What is the arrangement of xylem and phloem in the stem of non-woody plants?

  • Xylem is located on the inside
  • Phloem is found on the outside
  • Cambium layer is between xylem and phloem
• What do vascular bundles form in leaves?

  • The midrib
  • The veins of a leaf
• What type of leaves have a network of veins starting at the midrib?

  Dicotyledonous leaves
• What are the features of xylem vessels?

  • Transport water and minerals
  • Provide structural support
  • Long cylinders made of dead tissue
  • Open ends for continuous column
  • Contain pits for sideways water movement
  • Thickened with lignin for flexibility
  • Water flows only upwards
• What are the features of phloem vessels?

  • Tubes made of living cells
  • Involved in translocation of nutrients
  • Consist of sieve tube elements and companion cells
  • Sieve tube elements transport sugars in sap
  • Companion cells produce ATP for active processes
  • Plasmodesmata link cytoplasm of cells
• What is transpiration in plants?

  The process of absorbing water through roots and releasing it as vapor through leaves
• What is the role of the transpiration stream?

  It supplies water and minerals necessary for photosynthesis, growth, and temperature control
• What processes are involved in transpiration?

  Osmosis, evaporation, and diffusion
• What tool can be used to investigate the rate of transpiration?

  A potometer
• What factors affect the rate of transpiration?

  • Number of leaves
  • Size/position of stomata
  • Presence of waxy cuticle
  • Amount of light
  • Temperature
  • Humidity
  • Air movement
  • Water availability
• What adaptations do xerophytes have for dry conditions?

  • Smaller leaves to reduce surface area
  • Densely packed mesophyll
  • Thick waxy cuticles
  • Stomata closure to prevent water loss
  • Hairs and pits to trap moist air
  • Rolling leaves to reduce exposure
• What adaptations do hydrophytes have for living in water?

  • Thin or absent waxy cuticle
  • Constantly open stomata on upper leaf surfaces
  • Wide, flat leaves for light absorption
  • Air sacs to keep leaves afloat
  • Large air spaces for buoyancy
• How does water enter the plant through root hair cells?

  Water enters due to a water potential gradient
• What is the purpose of root hair cells?

  To provide a large surface area for water movement