Biology, 7: Transport in plants

• Xylem and phloem

  
• The xylem consists of cells forming a long tube

  The tubes are hollow remains of dead cells

  They act as thick strong cell walls supporting the plant
• The xylem carries water and mineral ions from the roots to the leaves and all parts of the plant that needs it

  It supplies water for leaf cells to photosynthesise
• The phloem is involved in translocation

  It is bidirectional
• The xylem Is involved in transpiration

  It is unidirectional
• What is the key takeaways of water uptake:

  Water + dissolved minerals absorbed from the soil through the root hair cells

  Water enters through osmosis, as w.p in root hair cell is lower than in soil

  Since minerals cannot enter by diffusion, root hair cell membranes adapts to take minerals in via active transport
• Water uptake

  
• What is the process of water uptake?

  Water enters the root hair cell via osmosis

  Water passes from cortex cell to cortex cell by osmosis

  Water enters xylem tissue in root

  It is transported to other parts of the plants

  In the leaves, water moves out of the xylem cell and goes to cells of spongy mesophyll by osmosis
• How do you investigate water movement through plant?

  Add food coloring to water given to plant

  It will be carried through xylem, and visible in veins
• Transpiration is the process that transports water from roots to other parts of the plant | It is the loss of water vapor from plant leaves by evaporation of water at the surfaces of mesophyll cells followed by diffusion of water vapor through the stomata
• Translocation is the process that moves sucrose and amino acids from region of production to regions of storage or use.
• What happens in transpiration?

  Water molecules cross cell membrane of spongy mesophyll into air spaces (evaporates)

  Liquid water becomes vapor in air spaces

  If stomata is open, water vapor molecules diffuse out
• In transpiration:

  • Very little water is loss in waxy cuticle
  • Water passes from xylem cells to other cells by osmosis
  • Water evaporates from the cell into air surfaces of spongy mesophyll layger
  • Water vapor diffuses out through the open stomata
• How is transpiration affected when the air is dry (low humidity)?

  There is a steeper concentration w.p gradient between leaf and air, making rate of transpiration water
• How is transpiration affected when the temperature is higher?

  Particles have more energy, moving faster

  It is easier to evaporate from cell into air spaces

  Gives higher rate of transpiration
• How is transpiration affected when it is humid?

  Lower concentration gradient between air and leaf

  Lower rate of transpiration
• Transpiration


  1. Loss of water from spongy mesophyll to air spaces

  2. Water molecules move from surrounding cells into spongy mesophyll by osmosis

  3. Water moves into them by osmosis, all the way back to the xylem

  4. Water moves out of xylem into surrounding cells by osmosis

  5. Water molecules show cohesion

  6. Tension pulls water molecules out of root cortical cells into xylem

  7. W.p gradient continues through root cortical cells into soil water
• Loss of water from spongy mesophyll to air spaces


  Increases w.p of cell's cytoplasm
• Water molecules move from surrounding cells into spongy mesophyll by osmosis


  This creates a w.p gradient between cells throughout the leaf
• As water moves out of xylem in leaf

  Tension is created throughout the xylem
• Transpiration and water potential (overall):

  • Evaporation creates w.p gradient that pulls water through the plamt
  • Water moves by osmosis, but cohesion and tension in xylem allows for long distance transport
• Sucrose is made directly from glucose produced in photosynthesis

  It is less active than glucose, so easier to transport around plant
• Amino acids are produced using glucose cells from photosynthesis

  Nitrogen ions are taken from the soil
• Sucrose is transported in the phloem to:

  • Convert back into glucose for respiration
  • Convert back into glucose and other molecules needed for cell growth
  • Convert into starch to store until needed
• What is the source?

  Where the substance is produced, or supplied to the plant
• What is the sink?

  Where the substance is used or converted into another substance
• What is the source of glucose in translocation?

  Photosynthesising cells of leaf
• What is the sink of translocation?

  Root, shoot tips, flowers

  Some plants direct glucose to storage organs like root and stem tubers

  Some convert back into starch and use for next growing season for rapid growth
• Transport in animals take place in the circulatory system
• The circulatory system is a system of continuous tubes

  It carries blood around the body

  It is connected to a pump, the heart

  Valves in heart and some blood vessels ensure correct flow
• The mammalian circulatory system is a double circulation
• Separating circulation to lungs and body allows for blood to be circulated at different pressures
• To the lungs:

  • Blood is pumped at a lower pressure as it does not travel far
  • Lower pressure prevents damage to capillaries in lung tissue
• To the rest of the body:

  • Pumped at a higher pressure for long distance
  • Loses pressure by the time it reaches capillaries in body tissue
• Th heart is a muscular organ pumping blood by expanding in size as it fills, and contracting to force the blood through the blood vessels
• Arteries pumps blood away from the heart
• Veins returns blood to the heart
• The right and left side of the heart is separated by the septum
• The right side of the heart pumps de-oxygenated blood to the lung to collect oxygen
• The left side of the heart pumps oxygenated blood around the rest of the body