Page 312 - Biology_F5

Gas exchange and respiration
The process of respiration in plants
occurs throughout the day and night,
providing energy to the plants. The light
dependent phase of photosynthesis can
only occur during the day time and stops
at night or during darkness. One product
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of respiration is carbon dioxide gas.
This can be used by the plant directly
for photosynthesis. However, during the
day, the rate of photosynthesis can be 10
or even 20 times faster than respiration
(depending on light intensity). Therefore,
the stomata must stay open for longer
periods to allow adequate diffusion of
carbon dioxide from the atmosphere into
the plant cells.
Activity 6.2: Observation of stomata
on a plant leaf
Materials
A potted Tradescantia plant, water, for-
ceps, needle, surgical or razor blade,
watch glasses, light microscope, slide,
slide cover, blotting paper, safranin, and
glycerin
Procedure
(a) Remove a healthy leaf from the
potted plant.
(b) Use a surgical or razor blade and
forceps to remove a thin outer layer
from the lower surface of the leaf.
(Alternatively, you can do this by
folding the leaf, and gently pulling
the thin layer apart using forceps).
(c) Place the leaf layer in a watch glass
containing water.
(d) Add a few drops of safranin stain in
a watch glass containing a thin layer
of the leaf, then leave it for 2 to 3
minutes.
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(e) Using forceps and a needle, take
out the layer of the leaf and place
it on a slide.
(f) Add a drop of glycerin over the leaf
layer to prevent the leaf layer from
getting dry, then place a slide cover
over it.
(g) Use a blotting paper to remove the
excess stain and glycerin.
(h) Observe the leaf layer on a slide
under the microscope.
Questions
1. Describe what you have observed.
2. What conclusion can you make from
your observation?
Safety precaution
Be careful when working with sharp
objects, such as needle, surgical or razor
blade.
6.3 Respiration
Respiration is a process by which food
substances are oxidised to release
energy in the form of ATP, which is
needed for metabolic activities in the
body. Respiration takes place within the
mitochondria of a cell. Since respiration
takes place in a living cell, it is commonly
referred to as cellular respiration. There are
two types of respiration, namely aerobic
respiration and anaerobic respiration.
Aerobic respiration occurs in the presence
of oxygen, while anaerobic respiration
occurs in the absence of oxygen (due
to that, it is sometimes referred to as
fermentation). Aerobic respiration
involves three main stages or processes,
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