biology-transport in plants

• What do plants need water for?

  Photosynthesis, chemical reactions, and to keep cells turgid
• Why can't plants obtain necessary substances by simple diffusion?

  Because they are multicellular and have a large surface area: volume ratio
• What do plants have instead of simple diffusion for transport?

  Mass transport systems
• What are the two types of vessels in plants that transport substances?

  Xylem and phloem vessels

  
• What do xylem vessels transport?

  Water and dissolved mineral ions from the roots

  
• What do phloem vessels transport?

  Dissolved substances such as sucrose and amino acids

  
• What is the arrangement of xylem and phloem in the plant stem?

  Xylem is on the inside, phloem is in the middle, and sclerenchyma fibres are on the outside
• How does the arrangement of xylem vessels provide strength to the stem?

  Having stronger xylem vessels in the center acts like internal scaffolding
• What is the structure of xylem vessels?

  Made up of dead, hollow cells with no end cell walls
• What substance strengthens the xylem vessel?

  Lignin

  
• What do phloem vessels transport from sources to sinks?

  Dissolved substances like sucrose and amino acids

  
• What are the two types of cells in phloem vessels?

  Sieve tube elements and companion cells

  
• What is the function of companion cells in phloem vessels?

  They provide energy for the active loading of sucrose

  
• How do sieve tube elements connect with companion cells?

  Through plasmodesmata

  
• What is the method to dissect plant stems for viewing vascular bundles?

  1. Cut a thin section of the plant stem with a scalpel.
  2. Place the tissue sample in water.
  3. Stain the sample with toluidine blue O.
  4. Rinse and place on a microscope slide.
• How does water move from the soil into root hair cells?

  By osmosis
• What are the two pathways for water to enter xylem vessels?

  The symplast pathway and the apoplast pathway

  
• How does water travel through the symplast pathway?

  From cell to cell through the cytoplasm

  
• What is the main pathway that water uses to move from the roots to the xylem?

  The apoplast pathway

  
• What is the function of the Casparian strip in roots?

  It forces water to go through a cell membrane to control substance entry
• What forces allow water to move upwards in the xylem?

  Tension, cohesion, and adhesion

  
• What is transpiration?

  The loss of water vapour through evaporation from a plant's surface
• Through which structures does transpiration mainly occur?

  Stomata
• What factors affect the rate of transpiration?

  Light intensity, temperature, wind, and humidity
• How does light intensity affect transpiration?

  Increased light intensity increases the rate of transpiration
• How does temperature affect the rate of transpiration?

  Increased temperature increases the rate of transpiration
• How does wind affect the rate of transpiration?

  Windier conditions increase the rate of transpiration
• How does humidity affect the rate of transpiration?

  More humid conditions decrease the rate of transpiration
• What are the key components of plant transport systems?

  • Xylem vessels: transport water and minerals
  • Phloem vessels: transport sugars and amino acids
  • Vascular bundles: arrangement of xylem and phloem
  • Casparian strip: regulates water entry in roots
  • Transpiration: loss of water vapor

  
• How does increasing light intensity affect the rate of transpiration?

  It increases the rate of transpiration due to more gas exchange for photosynthesis
• Why does increasing temperature increase the rate of transpiration?

  More heat energy gives water molecules more kinetic energy, increasing diffusion
• How does wind affect the rate of transpiration?

  Wind increases transpiration by blowing away water molecules that diffuse out
• What effect does humidity have on the rate of transpiration?

  Higher humidity decreases the rate of transpiration
• What is the method for measuring transpiration rate using a potometer?

  1. Cut a shoot underwater to prevent air entry.
  2. Insert the shoot into the potometer underwater.
  3. Submerge the capillary tube in water.
  4. Dry the leaves and acclimatise for 30 mins.
  5. Control other variables like light and humidity.
  6. Create an air bubble in the capillary tube.
  7. Record the starting position and time the bubble's movement.
  8. Calculate the speed of the bubble to estimate transpiration rate.
• What are xerophytes?

  Xerophytes are plants adapted to living in regions with scarce water
• What is one adaptation of xerophytes that reduces evaporation?

  A waxy layer on the epidermis
• How do sunken stomata help xerophytes conserve water?

  They shelter stomata from wind, reducing the water potential gradient
• What role do hairs on the epidermis play in xerophytes?

  They trap water vapor, reducing the water potential gradient
• How do spines help xerophytes?

  Spines reduce the surface area for water loss
• What is the function of rolled leaves in xerophytes?

  They trap water vapor and reduce surface area for water loss