Xylem and phloem

• What do xylem tubes transport in plants?

  Water and mineral ions
• What do phloem tubes transport in plants?

  Sugars and amino acids
• What are the two main types of transport tissues in plants?

  Xylem and phloem
• What is the primary function of xylem tissue?

  To transport water and mineral ions from the roots to other parts of the plant
• What is the primary function of phloem tissue?

  To transport dissolved sugars and other soluble food molecules from the leaves to other areas of the plant
• How does water enter the roots of a plant?

  Water enters the roots by osmosis
• What is translocation in plants?

  Translocation is the movement of dissolved sugars from the leaves to other parts of the plant
• What structure do xylem and phloem tissues form together?

  A vascular bundle
• What is the structure of xylem tissue?

  Xylem vessels are made from dead xylem cells with thickened cellulose cell walls
• What is the structure of phloem tissue?

  Phloem vessels are made of living cells with sieve plates that allow dissolved sugars to pass through
• How do vascular bundles provide support to different parts of a plant?

  They form a network in leaves, provide strength in stems, and anchor roots
• What happens to a plant if it loses water faster than it takes it in?

  The plant may wilt
• What is transpiration?

  Transpiration is the loss of water from a plant's leaves
• What is the transpiration stream?

  The transpiration stream is the constant flow of water from the roots, through the xylem, and out of the leaves
• How does water enter the xylem from the soil?

  Water diffuses from the soil into the root hairs by osmosis
• How do stomata control water loss from leaves?

  Guard cells open and close the stomata to regulate water loss
• Why is the upper surface of many leaves covered in a thick, waxy cuticle?

  To prevent uncontrolled water loss
• What happens to the stomata when a plant wilts?

  The stomata close to prevent further water loss
• What is the formula to calculate the rate of movement of an air bubble in a potometer?

  Rate of movement = distance (mm) / time (s)
• If an air bubble travels 18 mm in 90 seconds, what is the rate of movement?

  $0.2 \text{ mm s}^{-1}$
• What are the factors affecting transpiration?

  • Temperature
  • Humidity
  • Wind speed
  • Light intensity
• How does a potometer work to measure transpiration?

  1. An air bubble is introduced into the capillary tube.
  2. Water moves into the shoot and evaporates from leaves.
  3. The air bubble moves towards the plant.
  4. Measure the speed of the air bubble to determine transpiration rate.
• What are the structural differences between xylem and phloem tubes?

  • Xylem:
  • Made of dead cells
  • Thickened cell walls
  • One-way flow
  • Phloem:
  • Made of living cells
  • Sieve plates present
  • Two-way flow
• Why is a constant supply of glucose and water important to plant cells?

  • Glucose is needed for energy and growth.
  • Water is essential for photosynthesis and maintaining turgor pressure.
• Why is the distribution of vascular bundles different in various parts of a plant?

  • To provide support where needed:
  • In leaves: network for support
  • In stems: strength against bending
  • In roots: anchoring the plant
• What happens to a plant's stomata in response to low water availability?

  • Stomata close to reduce water loss.
  • This limits photosynthesis but conserves water.
• How does transpiration help in water movement into root hairs?

  • Transpiration creates a negative pressure in the xylem.
  • This pulls water up from the roots, facilitating osmosis into root hairs.
• What is the role of guard cells in the regulation of stomata?

  • Guard cells control the opening and closing of stomata.
  • They regulate gas exchange and water loss.
• Anything that increases the rate of photosynthesis increases the rate of transpiration. This is because more stomata open to allow more carbon dioxide into the plant. As a result the plant loses more water by evaporation.
• Temperature

  If you increase the temperature, water evaporates more quickly from leaf cells. Diffusion of water vapour out of the leaf becomes more rapid. This increases the rate of transpiration

  
• Light intensity

  Stomata open in the light and close in the dark. If you increase the light intensity more water evaporates. The rate of transpiration increases until all the stomata are open. Transpiration is now at its maximum rate

  
• Air movement

  When air moves over the surface of leaf, it moves evaporated water molecules away from the leaf. The faster the air moves, the faster the water molecules are moved. This increases the concentration gradient between the leaf and the air, as fewer water molecules are present in the air surrounding the leaf, compared to inside the leaf. This means that water diffuses more quickly out of the leaf

  
• Humidity

  Humidity is the amount of water in the air. The higher the humidity, the more water it contains. If you decrease the humidity, this increases the concentration gradient between the leaf and the air so water diffuses out more quickly. This increases the rate of transpiration