specification

• green plants and other photosynthetic organisms use chlorophyll to absorb light energy and convert carbon dioxide and water into glucose, producing oxygen as a by-product
• limiting factors of photosynthesis -

  1. carbon dioxide concentration
  2. light intensity
  3. temperature
• sodium hydroxide is used to absorb carbon dioxide
• How to test a leaf for starch -

  1. heat a plant leaf in boiling water for 30 seconds (this kills the leaf, stopping any chemical reactions)
  2. add the leaf to boiling ethanol in a water bath for a few minutes (the boiling ethanol dissolves the chlorophyll and removes the green colour from the leaf - it turns white so it is easy to see the change in colour)
  3. wash with water to rehydrate and soften the leaf and spread onto a white tile
  4. add iodine solution from a dropping pipette
• The steps within the method for testing a leaf for starch include: killing the leaf by placing in boiling water, decolouration using ethanol, washing to soften, testing with iodine. Understand the need for de-starching the leaf prior to the procedure
• the uses made by plant cells of the glucose produced in photosynthesis:

  • respired to release energy
  • converted to starch for storage
  • used to make cellulose, proteins and oils
• structures of leaves -

  • cuticle
  • epidermis,
  • stomata
  • palisade layer
  • spongy layer
  • xylem and phloem
• the stomata can open and close to regulate transpiration and allow gas exchange
• plants use water for photosynthesis, transport of minerals and support
• Water provides support by filling the vacuoles which push against cell walls. This keeps cells turgid and prevents cells becoming flaccid and wilting
• root hairs are specialised cells that have a large surface area to absorb water and minerals
• the role of osmosis in the uptake and movement of water through a plant
• Cells that are carrying out active transport are actively respiring.
• the uptake of mineral salts by root hairs by active transport
• Water is carried through the xylem from the root, up the stem and to all parts of the plant.
• transpiration is the loss of water vapour from the leaves of the plant, via the stomata
• A potometer can be used to measure the effect of different environmental conditions. However it is an indirect measure of transpiration.
• the role of phloem in carrying sucrose from the photosynthetic areas to other parts of the plant for use in respiration or converted into starch for storage
• two things happen to the sugar transported by phloem -

  1. it can be used straight away to provide energy, by respiration - important for growing the tips of plants
  2. If it is not needed immediately, the sugar is stored as starch, both in the leaves and in other parts of the plant
• lack of nitrogen (in the form of nitrates) causes poor growth
• deficiency of potassium results in yellowing of the leaf
• deficiency of phosphate results in poor root growth
• Light is one of the factors which affects the rate of photosynthesis.
• a green plant named Canadian pondweed (Elodea) will produce bubbles of oxygen as a result of photosynthesis.
• The number of bubbles of oxygen produced is affected by light intensity.
• investigation of the factors affecting photosynthesis -

  A) boiling tube

  B) lamp

  C) elodea

  D) metre ruler

  
• Method of investigating how light intensity affects photosynthesis

  1. Place the Elodea in a beaker containing 200cm3 of water

  2. Add one spatula of sodium hydrogen carbonate to the water

  3. Stick 3 small pieces of plasticine to the rim of the funnel and place it upside down over the plant

  4. Completely fill a test tube with water and carefully place over the end of the funnel with the end under the water, clamp into place

  5. Place the lamp 5cm away from the apparatus

  6. Start the stopwatch and record the number of bubbles of oxygen produced in one minute

  7. Repeat the experiment with the lamp 10cm, 15cm, 20cm, 25cm and 30cm from the apparatus
• Analysis of investigating how light intensity affects photosynthesis -

  1. Plot a graph of the distance against number of bubbles produced in 1 minute.
  2. What conclusions can be reached from your results?
  3. Evaluate your method and state how it could be improved.
• Risk Assessment of investigating how light intensity affects photosynthesis -

  Hazard - Hot lamps can burn

  Risk - Contact with skin will cause burns when {handling/touching/moving} apparatus

  Control Measure - Do not touch lamp until it has cooled down
• Transpiration is the evaporation of water from the leaves of a plant, which causes the uptake of water from the roots.
• It is assumed that the volume of water taken up at the roots is equal to evaporation from the leaves.
• In this investigation a freshly cut plant stem will carry out transpiration. The rate of transpiration can be measured by the distance travelled by an air bubble along a capillary tube in a particular time.
• Investigation into factors affecting transpiration -

  A) leafy shoot

  B) water reservoir

  C) graduated scale

  D) capillary tube

  E) air bubble

  
• Method of Investigation into factors affecting transpiration

  1. Immerse the potometer in the bowl of water and make sure the apparatus is full of water with no air bubbles

  2. Put the cut end of the leafy shoot in the water, taking care to keep the leaves above the surface

  3. Diagonally cut the last centimetre from the stem underwater

  4. With the potometer and stem still underwater, gently push the stem into the bung as shown in the diagram. Make sure it is a tight fit

  5. Remove the assembled apparatus from the water and apply Vaseline to all the joints to avoid air entering the apparatus

  6. Gently dab the leaves with the paper towel to remove excess water

  7. Clamp the potometer in an upright position with the capillary tube in the beaker of water

  8. Remove the capillary tube from the beaker to allow an air bubble to form and then return it to the beaker

  9. When the air bubble reaches the start of the scale begin timing

  10. After a set amount of time record how far the air bubble has travelled along the scale

  11. Repeat steps 8-10 twice more
• Analysis of Investigation into factors affecting transpiration -

  Calculate the mean water loss per minute
• Risk Assessment of Investigation into factors affecting transpiration -

  1. Hazard - Scissors are sharp. Risk - Cutting hand when cutting stem. Control Measure - Cut away from hand.
  2. Hazard - Delicate capillary tubing easily breaks. Risk - Cutting hand on smashed tubing due to pressure of inserting bung/stem. Control Measure - Use minimal pressure to push stem into bung and bung into tubing