Page 60 - Understanding NCERT Science 09

C hapter 5

HE F FUNDAMENTALUNDAMENTAL U UNITNIT OFOF L LIFEIFE
T T T T THEHE F FUNDAMENTALUNDAMENTAL U UNITNIT OFOF LIFEIFE
HE FUNDAMENTAL UNIT OF L LIFE
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While examining a thin slice of cork, Robert avoid air bubbles while putting the
Hooke saw that the cork resembled the cover slip with the help of a mounting
needle. Ask your teacher for help. We
structure of a honeycomb consisting of many
have prepared a temporary mount of
little compartments. Cork is a substance onion peel. We can observe this slide
which comes from the bark of a tree. This
under low power followed by high
was in the year 1665 when Hooke made this
powers of a compound microscope.
chance observation through a self-designed
microscope. Robert Hooke called these boxes
Eyepiece
cells. Cell is a Latin word for ‘a little room’.
This may seem to be a very small and
insignificant incident but it is very important
in the history of science. This was the very first Coarse adjustment
Body tube
time that someone had observed that living
Fine adjustment
things appear to consist of separate units. The
use of the word ‘cell’ to describe these units is Arm
Clip Objective lens
being used till this day in biology.
Microscope slide
Let us find out about cells. Stage
Swivel
Condenser
5.1 What are Living Organisms Mirror
Made Up of? Base

Activity ______________ 5.1 Fig. 5.1: Compound microscope

• Let us take a small piece from an onion What do we observe as we look through
bulb. With the help of a pair of forceps, the lens? Can we draw the structures that
we can peel off the skin (called we are able to see through the microscope,
epidermis) from the concave side (inner
layer) of the onion. This layer can be on an observation sheet? Does it look like
put immediately in a watch-glass Fig. 5.2?
containing water. This will prevent the
peel from getting folded or getting dry.
What do we do with this peel?
• Let us take a glass slide, put a drop of Nucleus
water on it and transfer a small piece
of the peel from the watch glass to the
Cells
slide. Make sure that the peel is
perfectly flat on the slide. A thin camel
hair paintbrush might be necessary to
help transfer the peel. Now we put a
drop of safranin solution on this piece
followed by a cover slip. Take care to Fig. 5.2: Cells of an onion peel

Rationalised 2023-24