Practicle

• Transpiration

  The evaporation of water from the leaves or through the stomata
• Transpiration stream

  The movement of water up the plant from the roots to the leaves
• Water transport in plants

  1. Water is brought to the leaves in the xylem

  2. Evaporates from the xylem into the spongy mesophyll

  3. Leaves the plant through the stomata
• Stomata

  • Have guard cells on either side
• Factors affecting transpiration

  • Temperature
  • Humidity
  • Light intensity
  • Air movement
  • Number, size and position of stomata
  • Presence of waxy cuticle
  • Water availability
• Higher temperature

  Higher kinetic energy, more water evaporates
• Higher humidity


  Lower diffusion gradient, less water evaporates
• Higher light intensity


  Higher rate of photosynthesis, more gas exchange through stomata, more water evaporates
• Higher air movement


  Water vapor surrounding stomata blown away, steeper vapor gradient, more water evaporates
• More/larger/higher positioned stomata

  More water evaporates
• Thicker waxy cuticle


  Less water evaporates
• More water available


  More water can be lost through transpiration
• Potometer


  Device used to measure water uptake by plants
• Setting up a potometer

  1. Select healthy plant

  2. Cut stem under water at an angle

  3. Dry leaves

  4. Use same age and species with same leaf area

  5. Set up under water and introduce air bubble
• Potometer does not accurately measure water uptake as some water is used for turgor pressure and photosynthesis
• To calculate water uptake using a potometer, you need to know the diameter/radius, length of bubbles, and time
• Auxin experiment 1

  1. Tips removed

  2. Auxin made in shoot tips

  3. No upward growth of shoot

  4. Potential for more lateral growth
• Auxin experiment 2

  1. Shoot tips covered

  2. Auxin still present

  3. Growth in all directions
• Auxin experiment 3

  1. Shoot lit from one side

  2. Auxin made on lit side

  3. Auxin broken down on lit side

  4. Shaded side grows more
• Auxin experiment 4

  1. Shoot tip covered by transparent cap

  2. Light can break down auxin in shoot tip

  3. Shoot grows towards light
• Auxin experiment 5


  1. Base covered by opaque shield

  2. Light impacts shoot tip, not base
• Auxin experiment 6

  1. Tip separated by agar block

  2. Auxin can spread down shoot

  3. Shoot bends towards light
• Auxin experiment 7

  1. Mica prevents auxin diffusion down shoot

  2. Shoot does not bend
• Gibberellins


  Higher concentration leads to more plant growth, including stem growth
• Designing experiments

  • Identify variable being changed and how
  • Identify variables being kept constant and how
  • Identify what is being measured and how
  • Repeat experiments to identify anomalous results
  • Calculate mean and perform statistics like standard deviation
• Acronym for designing experiments: CSMR (Change, Same, Measure, Repeat)
• Purifying DNA by precipitation

  1. Crush sample

  2. Add detergents

  3. Add protease enzyme

  4. Filter to remove solids

  5. Add salt

  6. Pour cold alcohol over top
• Crushing the sample

  • Breaks down the cellular cell wall
• Adding detergents


  • Dissolves the cell surface or plasma membrane
• Adding protease enzyme


  • Breaks down histones (proteins associated with DNA) to allow extraction
• Adding salt


  • Helps clump the DNA together for easier precipitation
• Pouring cold alcohol over the top

  • DNA is insoluble in alcohol so it floats to the top
• Pineapple juice contains the protease enzyme
• Eating/drinking a lot of pineapple can hurt the inside of your mouth
• This practical is normally performed using a strawberry or a kiwi