Page 120 - NCERT Science Class 10 English Medium

REPRODUCTION
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REPRODUCTION
REPRODUCTION
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MODES
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7.2 M ODES OF R EPRODUCTION U SED BY SINGLE
7 7.2.2
. 7 7.2
2
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ORGANISMS
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Activity 7.17.1
Activity 7.1
Activity 7.1
Activity 7.1
Activity
n Dissolve about 10 gm of sugar in 100 mL of water.
n Take 20 mL of this solution in a test tube and add a pinch of yeast
granules to it.
n Put a cotton plug on the mouth of the test tube and keep it in a
warm place.
n After 1 or 2 hours, put a small drop of yeast culture from the test
tube on a slide and cover it with a coverslip.
n Observe the slide under a microscope.
Activity
Activity 7.27.2
Activity 7.2
7.2
Activity
Activity 7.2
n Wet a slice of bread, and keep it in a cool, moist and dark place.
n Observe the surface of the slice with a magnifying glass.
n Record your observations for a week.
Compare and contrast the ways in which yeast grows in the first
case, and how mould grows in the second.
Having discussed the context in which reproductive processes work,
let us now examine how different organisms actually reproduce. The
modes by which various organisms reproduce depend on the body
design of the organisms.
7.2.1 Fission
For unicellular organisms, cell division, or fission, leads to the creation
of new individuals. Many different patterns of fission have been observed.
Many bacteria and protozoa simply split into two equal halves during
cell division. In organisms such as Amoeba, the splitting of the two cells
during division can take place in any plane.
Activity 7.3
Activity 7.37.3
Activity 7.3
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Activity 7.3
n Observe a permanent slide of
Amoeba under a microscope.
n Similarly observe another Figure 7.1(a) Binary fission in Amoeba
Figure 7.1(a)7.1(a)
Figure
Figure 7.1(a)
Figure 7.1(a)
permanent slide of Amoeba
showing binary fission.
n Now, compare the observations of
both the slides.
However, some unicellular organisms
show somewhat more organisation of their
bodies, such as is seen in Leishmania (which
(a) (b) (c) (d) (e) (f)
cause kala-azar), which have a whip-like
Figure 7.1(b)7.1(b)
Figure
Figure 7.1(b)
Figure 7.1(b)
structure at one end of the cell. In such Figure 7.1(b) Binary fission in Leishmania
organisms, binary fission occurs in a definite orientation in relation to
How do Organisms Reproduce? 115
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