Photosynthesis Experiments
End product of
photosynthesis is STARCH. Therefore, experiments can be performed to find
out what affects starch production in a leaf and
hence photosynthesis.
Obviously, the answer is Light and carbon
dioxide! Before the
experiments are carried out, the leaves of a plant must be 'de-starched'.
This is done by placing the plant in darkness for 24 hours. Once the
leaves are de-starched, the plant can be left in light for 24 hours with some
leaves deprived of CO2, some of light and others left
alone. They are then tested for starch using IODINE. Iodine can
stain starch. If the leaf being tested for starch turns blue/black with
iodine, then starch is present. This show that photosynthesis had taken
place. If the iodine stays yellow/brown then there is no starch, which
indicates that the leaf could not perform photosynthesis because it did not have
either CO2 or light. Up take of
water by the plant can be investigated by using a POTOMETER. It allows you
to test the rate of water uptake by a plant in different atmospheric
conditions. The apparatus is setup as below. As soon as the water
evaporates from the leaves, it is drawn up the xylem tubes and the air bubble
moves along the glass tube. The further along the bubble moves in a given
time, the faster the rate of TRANSPIRATION or WATER UPTAKE. A Plant can be
exposed to different conditions, such as wind/heat/humidity etc., to find out
how it affects the rate of TRANSPIRATION.
Testing
for Starch with IODINE:
Testing
WATER UPTAKE or Transpiration:
Test your understanding of leaf testing, starch production, and experimental variables. 1. Why must a leaf be boiled in ethanol before testing it with iodine? 2. When using a variegated leaf, which part of the leaf will turn blue-black after the iodine test? 3. What substance is used to absorb carbon dioxide in an experiment investigating if CO2 is needed for photosynthesis? 4. Why is a plant left in the dark for 48 hours before starting a photosynthesis experiment? 5. In the light intensity experiment using Elodea (pondweed), how is the rate of photosynthesis measured?🔬 Knowledge Check: Photosynthesis Experiments
Click to Reveal Answers
2. Only the green parts (Only cells with chlorophyll can photosynthesize and produce starch).
3. Soda lime (It acts as an absorber to remove CO2 from the air inside a container).
4. To 'destarch' the plant (Ensures any starch found later was produced during the experiment).
5. Counting oxygen bubbles (The more bubbles produced per minute, the faster the rate of photosynthesis).
Tags:Photosynthesis, Water uptake, Transpiration, Starch, Iodine