8 - Transport in Plants

• Xylem:

  • transport of water and mineral ions
  • prodivedes structural support to the plant
• Structure and function of xylem vessels - 

  • xylem cells are long and thin
  • cells arranged end-to-end to form vessels (tube) 
  • when mature, the cells lack cross walls, making a long, continuous tube
  • they lack cell contents such as cytoplasm and nuclei 
  • cell walls become lignified
  • function is to transport water and mineral ions from roots to leaves 
  • lignin provides strength for the stem and makes the vessels waterproof

  A) water

  B) minerals

  C) no end between cells

  D) one-way transport only

  E) outer cells aren't living

  F) thickened walls stiffened with lignin

  G) thickened walls stiffened with lignin

  
• Phloem: 

  • transport of sucrose and amino acids
• Identifying the xylem and phloem in sections of root:

  A) cortex

  B) epidermis

  C) endodermis

  D) phloem

  E) root hair

  F) xylem

  G) root

  H) phloem

  I) xylem

  J) cortex

  K) epidermis

  L) stem

  
• Root-hair cell:

  • large surface area of root hairs increase uptake in of water and mineral ions

  A) ribosomes

  B) mitochondrion

  C) nucleus

  D) cytoplasm

  E) vacuole

  F) root hair

  G) cell wall

  H) cell membrane

  
• Transpiration:

  Is the loss of water vapour from leaves

  • water forms a thin layer on the surfaces of mesophyll cells and evaporates into air spaces in the spongy mesophyll
  • loss of water vapour in transpiration's related to large surface area provided by the cell surfaces in mesophyll cells, the interconnecting air spaces in spongy mesophyll and stomata
  • creates a high concentration of water molecules = water'll diffuse out the leaf through the stomata as water vapour
  • water evaporating from leaves causes suction = pulls water up the stem
• Water movement in the xylem - 

  1. water evaporating from leaf creates suction (transpiration pull) as water molecules are held together by forces of attraction between them (cohesion)

  • cohesion = attraction that gives stickiness

  1. water forms a column and travels through the xylem
  2. creates a transpiration stream, pulling water up from the root
  3. xylem vessels draw water up the stem by capillary action
  4. roots produce a root pressure, forcing water up xylem vessels
• Factors that affect the rate on transpiration (Part 1) -

  • Increase in temperature
  • Increases transpiration rate (increases the kinetic (movement) energy of the water molecules, so they diffuse faster - transpiration is likely to be faster on a hot day than on a cold day)
  • Increase in wind speed
  • Increases transpiration rate (because the concentration of water molecules outside the leaf is lowered, increasing the concentration gradient for diffusion
• Factors that affect the rate on transpiration (Part 2) -

  • Increase in humidity
  • Decreases transpiration rate (because it increases the concentration of water molecules outside the leaf,reducing the concentration gradient for diffusion)
• Translocation -

  • translocation is the movement of sucrose(sugars) and amino acids in phloem from sources to sinks
  • sources = the parts of plants that release sucrose or amino acids (usually leaves)
  • sinks = the region sucrose/amino acids are transported to
  • may be for storage  (e.g. in the roots or developing parts of the plants – new leaves, fruits and seed)
  • or use for respiration
  • or for growth
  • during the life of a plant, a region that originally acted as a sink may become a source
• Wilting:

  1. young plant stems and leaves rely on their cells being turgid to keep them rigid
  2. if the amount of water lost from the leaves of a plant is greater than the amount taken into the roots, the plant will have a water shortage
  3. cells become flaccid if they lack water, and they will no longer press against each other
  4. stems and leaves then lose their rigidity and wilt
• Transpiration:

  The loss of water vapour from leaves
• Translocation:

  The movement of sucrose and amino acids in the phloem from sources to sinks