PLANT NUTRITION PART 8: IS OXYGEN PRODUCED DURING PHOTOSYNTHESIS?

Let us recall back the equation:


From the equation, it can be concluded that oxygen is produced as a by product of photosynthesis. Now, how do we know that oxygen is really produced? OK, here's the procedure:

• Set up the apparatus as shown in the following figure and make sure that the test tube is completely full of water.
• Place the apparatus in bright sunlight for a few days.
• Carefully remove the test tube from the top of the funnel, allowing the water to run out but not allowing the gas to escape.
• Light a wooden splint and then blow it out so that it is just glowing. Carefully put it into the gas in the test tube. If it relights the glowing splint, then the gas is oxygen.
  

CONTROLS
When setting up an experiment and a control, which of the two procedures constitutes the CONTROL depends on the way the prediction is worded. For example, if the prediction is that "in the absence of light, the pondweed will not produce oxygen", then the control is the plant in the light. If the prediction is that "the pondweed in the light will produce oxygen", then the control is the plant in darkness.

MUSCLE CRAMP

What is cramp?

A cramp is an involuntary and forcibly contracted muscle that does not relax. If you haven't experienced it, count yourself lucky. Try clenching your thigh muscles. Then imagine squeezing them so hard it hurts and holding them like that for a minute. Cramp locks up your leg in a painful grip, you certainly can't pedal. Sometimes, you'll get a small cramp where you can soft pedal but if you're racing, the chances are it's game over as you're not going to be able to force the pace much and often this small tension is a sign that you're going to cramp up a lot.

What causes cramp?

• Dehydration
• Accumulation of Lactic Acid
• Electrolyte imbalance
  

PLANT NUTRITION PART 7: IS CHLOROPHYLL NEEDED?

This experiment makes use of plants having variegated leaves (leaves in which in some parts chlorophyll is absent). The following figure shows an example of such plants.



PROCEDURE

• Destarch a potted plant with variegated leaves.
• Choose a leaf and make a simple drawing of the leaf showing clearly the regions which are green in colour as well as the regions which are not green in colour.
• Expose the plant to bright sunlight for 2 hours.
• After 2 hours removed the pre-chosen leaf and test it for the presence of starch using Iodine solution.

OBSERVATION

• Iodine solution changed to blue-black only in the green regions of the leaf whereas the Iodine solution remain unchanged in the non-green regions.
  

CONCLUSION

• Chlorophyll (in the green regions) is needed by green plants to photosynthesize.
  

PLANT NUTRITION PART 6: IS CARBON DIOXIDE NEEDED?

Carbon dioxide is one of the four requirements for photosynthesis to take place. Again, since it is a requirement, photosynthesis will not take place without it.

PROCEDURE:

• Set up two destarched potted plants as shown in the following figure.
• In set up X, a container containing saturated sodium hydrogen carbonate is placed (This is to provide the plant with carbon dioxide) whereas in set up Y, soda lime is used instead (This is to absorb the carbon dioxide inside the polythene bag as well as the carbon dioxide given off by microorganisms in the soil).
• Expose bot set ups to bright sunlight for two hours.
• After 2 hours, remove one leaf from each set up and test each leaf for the presence of starch using Iodine solution.
  

OBSERVATION

• The Iodine solution in the leaf taken from set up X turns blue black whereas the Iodine solution in the leaf taken from set up Y remain unchanged.
  

CONCLUSION

• The outcome of the experiment shows that carbon-dioxide must be present for plants to photosynthesize.
  

PLANT NUTRITION PART 5: IS LIGHT NEEDED?

The objective of this experiment is to investigate if light is one of the requirements for plants to photosynthesize.

PROCEDURE

• Destarch a potted plant.
• Cover one leaf of this destarched plant with a black paper with patterns cut in it (See the following figure).
• Expose the plant to bright sunlight for two hours.
• After 2 hours, test the leaf for the presence of starch using Iodine solution (Remember the procedure outlined in the previous post)
  

OBSERVATION

• The Iodine solution will change colour to Blue-black in the uncovered region whereas in the regions which is covered with black paper, the Iodine solution remain unchanged.

CONCLUSION

• Light is unable to penetrate in the region which is covered with the black paper, so no photosynthesis and therefore no starch is produced.
• Light penetrates in the uncovered region, so photosynthesis takes place and therefore starch is produced and detected when the leaf is tested with Iodine solution.
• The experiment shows that light from the sun is necessary for photosynthesis to take place.
  

PLANT NUTRITION PART 4: DESTARCHING AND TEST FOR STARCH IN LEAF

In the next part (part 5) of this chapter, practical investigations to prove whether chlorophyll, light and carbon dioxide are really needed for green plants to photosynthesize will be discussed. Before these practical investigations can be discussed, it is SOOOOO necessary for you to know HOW and WHY destarching is necessary.

First thing first. In investigating these three requirements, we need to ask ourselves - How do we know whether photosynthesis is really taking place or not? And then ask further - How do we know whether these requirements are responsible or involved in any ways, in photosynthesis? Well, the answer to the first one - If photosynthesis is really taking place, starch must have been produced, right? And the second question - By conducting an investigation where one requirement is deprived from the photosynthesizing plants. OK, enough about this. Lets move on to the real objective of this part of the chapter.

WHAT IS DESTARCHING?

• Removal of starch from the leaves.

WHY DESTARCHING?

• To ensure that at the beginning of the above mentioned investigations, there are no starch in the leaves of the plants to be used in the investigations. We really need to ensure that starch is really produced or not as a result of photosynthesis in the presence or absence of the above mentioned requirements.
  

HOW IS IT CONDUCTED?

• By placing the plants to be used in the investigations in a dark place, for example a dark cupboard for 24 to 48 hours (Darkness will stop photosynthesis in these plants and as a result all starch stored in the leaves will be used as a source of energy)
  

HOW DO WE KNOW IF DESTARCHING IS SUCCESSFUL?

• If we want to know whether the destarching is successful or not, we may take one of the leaf and test it for the presence of starch using Iodine solution.
• SUCCESSFUL??? It means, the outcome of the starch test must be NEGATIVE, the brown Iodine should not change. This means that starch is absent in the tested leaf - meaning, the DESTARCHING IS SUCCESSFUL.

IODINE TEST ON LEAF FOR THE PRESENCE OF STARCH
Starch test using Iodine solution? Hmm... peculiar right? You must be thinking about the same test like the one you did in your food test practical classes? Well....not that easy missy or mister. Here's the procedures:

Procedures:

• Heat some water to boiling point in a beaker and then TURN OUT the Bunsen flame.
• Use forceps to dip a leaf in the hot water for about 30 seconds (This kills the cytoplasm, denatures the enzymes and makes the leaf more permeable to Iodine solution)
• Push the leaf to the bottom of a test tube and pour in some alcohol (ethanol) into the test tube (The alcohol will boil and dissolve out most of the chlorophyll. This makes colour changes with Iodine easier to see)
  

• Pour the green alcohol into a spare beaker.
• Remove the leaf (brittle at this stage) and dip it once more into the hot water to soften it.
• Spread the decolourized leaf flat on a white tile and place a few drops of Iodine solution on to it.
• If the Iodine solution changed colour to Blue black, it means that starch is still present and it means that the destarching is not successful.
• If the Iodine solution does not changed colour, it means that starch is absent in the leaf and it means that the destarching is successful

Once you get the successful outcome, then you can start to investigate!!!

PLANT NUTRITION PART 3: PHOTOSYNTHESIS

Autotrophs such as green plants contain green pigments called chlorophyll (in the chloroplasts). A pigment absorbs certain wavelengths of light and reflects other. A chlorophyll pigment absorbs blue and red light and reflects green light. Therefore the leaves appear to be green.



When light is absorbed by green plants, the light energy is used to synthesize organic compounds such as sugars from inorganic compounds, water (absorbed by the roots of the plants from the soil) and carbon dioxide (obtained from the atmosphere and enters the plants through the stomata of the leaves by diffusion). This process is known as photosynthesis and can be summarized by the following equation.



The GLUCOSE produced during photosynthesis can be converted into other forms of carbohydrates such as starch (for storage) and other complex sugars (sucrose). Notice in the equation, oxygen is also produced as a by product. This oxygen is useful and can be used by other organisms and the plants themselves for respiration.

REQUIREMENTS (CONDITIONS) FOR PHOTOSYNTHESIS:

• Carbon dioxide
• Water
• Chlorophyll
• Light energy

These requirements must be present for plants to photosynthesize. Without one, plants will not be able to photosynthesize.

WHERE IN THE LEAF DOES PHOTOSYNTHESIS TAKING PLACE?
CHLOROPLASTS...... CHLOROPLASTS..... CHLOROPLASTS.... *Hitting the white screen with my purple broom stick*

NOTE: SINCE THE STUDENTS' PRESENTATIONS, I LONGED FOR MY PURPLE BROOM STICK!!!

PLANT NUTRITION PART 2: MODES OF NUTRITION

Living things may be classified according to their modes of nutrition. They may be HETEROTROPHS or AUTOTROPHS.

AUTOTROPHS

• These are organisms that can synthesize their organic materials from inorganic materials in the environment (OR in other words, they are able to make their own food).
• GREEN PLANTS must have come to you mind at this moment right? You are right. Yes green plants are examples of autotrophs but there are other organisms which can be considered as autotrophs like some bacteria.
• BUT for some bacteria, they are using chemical energy instead of light energy so for these bacteria we say that they are chemo-synthesizing instead of photosynthesizing (Remember, since green plants are using light energy from the sun, we say that they are photosynthesizing)
• An autotroph can be a multicellular organism or unicellular organism such as Euglena (Notice the chloroplasts containing chlorophyll?)

HETEROTROPHS

• These are organisms which cannot make their own food.
  
• A heterotroph obtains its food (hence source of energy) from the organic molecules that have already been produced by the autotrophs.