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D. Through the lenticels or any cracks in the bark of woody stems.

N.B.: Carbon dioxide resulting from respiration of the plant is expelled to the external environment by direct diffusion from plant cells that are directly exposed to the external environment. While in case of deep-seated cells, gaseous exchange occurs by mutual diffusion of CO2 in return to xylem and vessels or phloem tissue which passes CO2 in return to stomata, then to the external atmosphere.

The relation between photosynthesis and respiration in plants:

The following figure represents the cycle of cellular respiration and photosynthesis. Study it and create your own comparison between the two processes.

Experiments on Respiration

Experiment 1:

To illustrate the evolution of CO2 gas during aerobic respiration:

A. In non-green parts of the plant (seeds):

Put some Potassium hydroxide solution (KOH) in a beaker. Insert some dry seeds (peas) in a glass retort, and dip the end of the retort stem in the Potassium hydroxide solution in the beaker. (apparatus no. 1)

Put some Sodium chloride solution (NaCl) in a beaker. Insert some soaked seeds in another retort, and dip the end of the retort stem in the Sodium chloride solution in that beaker. (apparatus no. 2)

Put another quantity of Potassium hydroxide solution (KOH) in a third beaker. Insert some soaked seeds in a third glass retort, and dip the stem of that retort in the Potassium hydroxide solution in that third beaker. (apparatus no. 3)

Leave the three retorts for some time.

Observation:

No change occurs in apparatus 1 and 2.

In case of retort 3: Potassium hydroxide solution rises up in the stem of the retort.

Interpretation:

In case of apparatus 1:

Dry seeds do not respire actively, therefore no change occurs under these conditions.

In case of apparatus 2:

Seeds soaked in water need to germinate and grow, therefore they must respire actively to obtain energy. They absorb Oxygen from the surrounding air, and they release an equal volume of CO2. So, no change is observed in the volume of the air inside the retort. This is because the released CO2 is not absorbed by Sodium chloride solution. So, the components of the air inside the retort have changed, but the total volume remains constant.

In case of apparatus 3:

The germinating seeds are actively respiring. CO2 gas is released in a volume equal to that of the absorbed Oxygen. The released CO2 will be absorbed by Potassium hydroxide solution. So, the solution rises up the stem of the retort.

This proves that CO2 gas is produced as a result of respiration in non-green parts of the plant (seeds).

By comparing the 3 cases, it is clear that:

Dry seeds do not respire actively. So, the volume and the components of air remains without change.



Germinating seeds respire actively, and the volume of air remains constant during respiration because the released CO2 is equal in volume to the absorbed Oxygen.

3. When germinating seeds (which are non green parts of the plant) respire, they release Carbon dioxide gas.

B. Green parts of the plant:

Take a green potted plant, and place it on a glass plate together with a small beaker containing clear lime water. Invert a glass bell-jar over the two. Then cover the jar with a black piece of cloth.


Date: 2015-12-11; view: 776


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This is known as Muscular Fatigue. If Oxygen is available, Lactic acid is converted into Pyruvic acid again and then into Acetyl Co-A. | Prepare a similar apparatus, with a pot empty of any cultivated plant.
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