Transport in Plants Flashcards
Draw and describe where xylem and phloem are distributed in different parts of a plant
- Stems - vascular bundles are arranged forming a ring around the outer part of the stem
- Roots - vascular bundles are found in the centre
- Leaf - they form networks of veins in the leaf
How does water move across the cells of a leaf?
- Water vapour in the air spaces of the leaf diffuse out of the leaf into the stomata
- Water evaporates from mesophyll cells into the air spaces of the leaf
- Water is pulled out of the xylem vessels into the mesophyll cells to replace what was lost
Explain the 4 factors that increase transpiration rate
- High light intensity - higher rate of photosynthesis so more stomata open to obtain more carbon dioxide
- High temperature - more kinetic energy means water evaporates faster, there will also be a higher level of photosynthesis
- High wind intensity - maintains a steep water vapour diffusion gradient between air spaces in the leaf and environmental air
- Low humidity
What are the steps for using a potometer?
- Fill the potometer with water
- Cut a shoot underwater and fix it to the potometer
- Dry the leaves, allow time for the shoot to acclimatise and then shut the tap
- Record the starting position of the air bubble
- Start a timer and record the distance moved by the potometer
- Calculate the rate of transpiration and distance moved by water uptake / time taken
Describe the two main pathways taken by water in a plant’s roots to reach the xylem
- Apoplast - water moves through spaces in cell walls and between cells, due to the cohesive and adhesive properties of water
- Symplast - water moves from cell to cell through the cytoplasm and plasmodesmata, due to the water potential gradients
What is adhesion in the context of water transport in plants?
- The attraction of polar water molecules to the non-polar cellulose in xylem vessel cell walls
- This helps water to rise through the plant against gravity
How is the structure of plant leaves adapted for efficient gas exchange?
- Many stomata - ensure short diffusion distances
- Air spaces throughout the mesophyll - allow rapid diffusion from stomata to photosynthetic cells
- Large surface area of mesophyll cells - allows rapid gas exchange
What are examples of xerophytes and what adaptations do they have to reduce water loss?
- Cacti and marram grass
- Thick waxy cuticle to reduce water loss by evaporation
- Small, needle like leaves - reduce the surface area through which water can be lost
- Hairs on leaves - trap moist air next to leaf surface, reducing water potential gradient
- Water storage organs to conserve water
What is an example of a hydrophyte and what adaptations does it have to help it live in water?
- Water lilies
- Thin waterproof waxy cuticle
- Stomata located on upper surface of leaves so gas exchange with the air instead of water
- Reduced veins in the leaves - xylem significantly reduced as no need to transport water
What is the role of hydrogen ions and companion cells in the mass flow theory?
- Hydrogen ions are actively transported out of companion cells into surrounding source cells
- H+ is co-transported with along its concentration gradient back into companion cells with sucrose
- Sucrose can then diffuse along its concentration gradient through plasmodesmata from companion cells into sieve tube elements
Describe the processes in translocation that require energy
- Active loading at source cells - actively transporting sucrose from source cells into companion cells, and subsequently into phloem sieve tube elements for translocation
- Active unloading - actively transporting sucrose from the phloem sieve tube elements into companion cells, and subsequently into sink cells where it is used or stored
