Download 1. COMPOUND MICROSCOPE

(A) Core Experiments :
Unit - 1
In the first unit of core experiments you will study the parts of a compound microscope,
method of using it, characteristic of living organism and their identification. You will also
study the biological studies of nearby areas by undertaking local excursions.
1. COMPOUND MICROSCOPE
Objects which are ordinarily not visible
by naked eye are seen with microscope.
Generally an object smaller than 0.1 mm
cannot be seen by our eyes. Therefore, to
observe an object smaller than this, compound
microscope is very helpful. Hand lens
(magnifying lens) is also a type of microscope
but its magnifying capacity is very low.
Dissecting microscope is also used to visualize
tiny things, but it has only one lens. Compound
microscope is generally used in the
laboratories. Therefore, description, use and
maintenance of ordinary compound
microscope is mentioned here.
base of this, stage is fixed. On the top
of the arm body tube of the microscope
is fixed and two knobs are fitted. One is
for the coarse adjustment and the other
for the fine adjustment. These are used
for focussing the body tube.
(c) Body Tube : This is attached to the knob of
the arm. It has one lens on the upper
end known as eye piece. This lens can
be changed according to the required
magnificaton. On the bottom of this
tube there is a nose piece. Two to four
lenses can be fitted in this nose piece.
Because the lenses are fitted on the
objective, these are known as
objective lenses. These are fitted in
the body tube, known as objective
lens body. The objective lens body is
fitted into the noise piece.
1.1 Parts of a Compound
Microscope
Take out the microscope from the box
holding the arm by one hand and supporting
the base by another hand. Place carefully on
the table and study the names and functions of
the parts as mentioned in the figure. The parts
of a compound microscope can been divided
into 4 main parts:
(d) Stage : It is a platform having a circular hole
in the centre to allow the passage for
light from below. It is fixed to the base
by the stand. One mirror is fixed to the
stand. It is known as reflecting mirror.
Below the stage is a condenser through
which concentrated beam of light passes.
Iris diaphragm is also attached to the
condenser. The reflecting mirror reflects
the light upward through the iris and
diaphragm. This beam of light passes
through the hole in the stage and provide
light to the object kept on the slide.
There are two clips for holding
(a) Base : This is U-shaped lower portion of the
microscope on which the other parts of
the microscope lie. Above the U-shaped
portion, there is a perpendicular portion
known as the pillar. On the top of this,
another arm is fixed. This is known as
inclination joint. This can be used to tilt
the microscope at a desired angle.
(b) Arm : It supports the body tube and base of
the microscope. This portion is used to
hold or carry the microscope. On the
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the slide above the hole on the stage.
Operation (Use) : Keep a clean prepared slide
in the centre of the stage. Use clips to
fix the slide on the stage so that it does
not move. Now move the body tube
by the help of coarse adjustment
knobs. Bring the slide in focus under
the objective lens. Focussing should
be made sharp by the use of fine
adjustment knobs. When the focus is
sharp then study the slide. The
specimen is viewed by keeping one
eye on the eye piece and the second
eye should be kept open. This type of
compound microscope is known as
monocular compound microscope.
Some compound microscopes have two
body tubes. So there are 2 eye pieces and
specimen can be viewed by both the eyes. Such
type of compound microscope is known as
binocular compound microscope. In the
research work generally bioncular compound
microscope is used.
1.2 How to use a Compound
Microscope
PRACTICAL BIOLOGY - XI
are also available. The multiplication of
magnification of eye piece and nose piece
denotes the size of the object under
observation.
Maintenance of Microscopes:
Microscope is a costly equipment.
Therefore, it should be handled carefully.
Always keep the microscope in an upright
position while taking it from one place to
another. As far as possible don’t tilt the arm.
Clean the lenses of the microscope with the
lens paper or muslin cloth, never with the filter
or any other kind of paper. If you are using the
high power objective lens then after the
observation is over, turn the nose piece and
bring low power objective lens in line with the
hole in the stage. Objective lens should be kept
atleast 1 cm above the stage. After using the
microscope always keep it in the box. Take
care to see that the stage of microscope, the
eye piece, the objective lens are dry and clean.
No chemical should stick to these. Adjustment
knobs and joints should be protected from
rusting by applying vaseline.
To use the microscope first of all rotate
the nose piece until the low power objectives
is in line with the body tube and clicks into
position. Open the iris diaphragm. Look
through the eye piece, adjust the mirror and
diaphragm to set a complete field of vision.
Place the slide you want to examine on the
stage of the microscope and by the help of
the clips fix it. Move the slide till the object
comes roughly to the centre of the hole or the
stage. Bring the object into focus using the
coarse adjustment knob. Turn the fine
adjustment knob to bring the object into
sharp focus.
How much magnification the object
needs will be learnt through experience.
Eye lenses of 5x, 10x or 15x are available.
Some way objective lenses of 4x, 10x & 40x
Fig. 1.1 A compound microscope
CORE EXPERIMENTS
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2. Living and Non Living
In this world of living organisms it is normal
to differentiate between the living and the nonliving. Unknowingly without seeing their special
characters can we say which is living or nonliving
? While doing this we observe some character
such a locomotion and movement, nutrition,
growth, respiration, reproduction and response
to stimuli. But it is not necessary that all the above
characters are visible in all living organisms.
Without learning the characteristics
anybody can say that a table, chair or a stone
is non living, but there are some objects which
cannot be called either living or nonliving by
observing them. For example the seeds of
various plants. It is difficult to say whether seed
is livng or non living as non of the given
characteristics are seen in a seed. But as the
seed germinates to produce a new plant it is
definitely living. Similary the larvae of many
insects are motile, they take in nutrition also
and show growth, but as soon as they change
into pupa, all the activities of the living stop.
The pupa remains in the same place without
moving or rating for many days. But one day
the adult insects emerges out of it and flies
away. This proves that pupa is living and inside
it all living functions take place.
Let us know the characters of living and
on the basis of these characters let us
differentiate between living and non living.
1.
under the microscope.
Flagella
Basal bodies
Cytoplasm
Stigma
nucleolus
nucleus
cup shaped
chloroplat
pyrenoid
cell wall
Two
Contractile
vacuole
Fig. 2.1 Chlamydomonas
Nutrition :
We can observe the entire animal world
taking in nutrition. But the members of the plant
kingdom do not take nutrition like us. You must
have studied that the leaves of a plant have
chlorophyll and in the presence of sunlight they
prepare starch by the process of photosynthesis
and store it. To prove this we can perform starch
test in leaves of plants and in algae also.
Activity :
(a)
Boil the leaves of a plant in alcohol (rectified
spirit). By doing this the green chlorophyll
will be removed and the leaf will become
colourless. Now dip these leaves in iodine
solution. You will see that the leaves become
dark blue or black in colour. This iodine
test confirms the presence of starch in the
leaves.
(b)
If a potted plant is kept in the dark room
for 2-4 days and then the above activity
is performed with the leaves of the same
plant, they will not give the starch test.
Locomtion and movement :
These characteristics are usually found in
the animal kingdom but plants also show these
characters. For eg dehiscence of fruits, their seed
dispersal and the closing of the touch me not leaves
on being touched all show movements in plants.
Unicellular corals also move around like
animals. The protists like chlamydomonas and
volvox etc. also show movement, when observed
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PRACTICAL BIOLOGY - XI
This is because in the dark the leaves could
not perform photosynthesis and the plant
used up its stored starch.
If the above activity is repeated with a non
living object like stone or dry twig then we
will not get the starch test.
3.
Growth :
This is an important characteristic of living
organisms. All around us we see the seeds
of plants germinate and grow into big trees
over a period of time. In the animals also
young one’s slowly grow to become adults.
But non-living objects remain the same even
after long duration of time.
Activity : To observe growth, take any
kind of seeds and sow them in small pots or plastic
containers. Water them regularly and observe
them at regular intervals. You will observe the
seeds will germinate and the length of the seedling
will be increasing. Soon branches and leaves will
also develop.
You can maintain a daily record of the
changes taking place in the different kinds of
seeds. From that you can understand the
difference in the rate of growth of different
seeds.
4. Respiration :
To understand whether an object is living
or non living its breathing is very important. If
it is not breathing them it is clear that the
organism is dead. But plants do not breathe in
this manner, although we know that they also
respire. Seeds which appear to be lifeless also
perform respiration and on observing that we
can understand that it is living.. To do this we
will perform the following acitivity.
Activity :
Take a widemouthed long test tube. Fill
it partially with pink coloured phenolphthalein
solution. Now place a cotton plug inside the test
cork
dry seeds
pebbles
or
boiled
seeds
cotton plug
Test
solution
Fig. 2.2 To show respiration in seed
tube a little above the indicator solution. On the
cotton plug place a few dry seeds of wheat or
gram. Close the mouth of the test tube with cork
and seal it with wax. (as shown in figure)
After few hours you will find that the
indicator solution has lost its pink colour. This
happens because CO 2 decolouresis
phenolpthalein. Thus it is clear that the dry
seeds have given out CO2 due to respiration.
You can also perform a similar control
experiment where you place boiled seeds or
pebbles on the cotton plug. This time there is
no change in the colour of the indicator
solution. This proves that seeds are living
boiled seeds are not living and so are pebbles,
therefore they donot respire.
5. Reproduction :
We can easily see reproduction in animals
like bitches producing puppies cows producing
calves and women producing children. But to see
reproduction in small animals and plants, we can
perform the following activities.
(a)
If you find eggs on the leaves of plants like
lemon then take the leaves and put them in
a glass bottle along with few more leaves
cover the mouth of the bottle with a lid and
make holes in the lid. Keep observing the
set up from time to time.
CORE EXPERIMENTS
You will find larvae hatch out of the egg.
The larvae will feed on the leaves. If
leaves start drying replace them with
fresh leaves. Soon the larvae convert into
pupa, which lie inside the bottle without
eating or moving. Finally a small
butterfly or other insect will emerge out
of the pupa.
(b)
6.
A similar experiment has been described in
the section of investigatory projects (lifecycle of house fly). You can do it also as
you have studied the structure of a flower.
Fruits develop from the ovary of a flower.
In many flowers ovaries do not develop into
flowers because in then the reproductive
activities are not completed such as
pollination or any other defect. You can
remove the androecium of flowers or the
anthers from the flowers and study the
effect. None of the non-living object shows
reproduction.
Response to stimule :
Every animal responds to changes in its
external or internal environment by doing some
kind of activity. We experience hunger and
thirst. In some other animals effect of
temperature can be observed. For example if
we keep earthworms in such a bottle which is
partially covered by a black paper and we keep
the bottle in sunlight, we will see that after
sometime most of the earthworms move to the
dark part of the bottle.
Similarly the leaves of touch me not
plant close down as soon as it is touched and
slowly the entire branch droops. To see the
changes taking place in the behaviour of
cockroaches with changes in the environment,
the following activity can be performed.
Cockroach is a domestic insect
belonging to class insecta. Almost all
organisms have the ability to respond to changes
in the environment. How cockroaches adapt
themselves to sudden changes in their surroundings
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Open leaves
before being
touched
Leaves closed
after touching
Fig. 2.3 Branch of a touch me not plant
can be studied by planning an activity.
The major changes taking place in the
environment moisture content. Therefore cages
with nets have to be designed to keep the
cockroaches through which the activities of the
cockroaches can be observed. The timings for
these activities could be long or short but it
can be carried out for 3-4 months.
The cages should be of the size 1ft long
× 8” wide × 9” high. Inside these cages
different conditions can be created. For
temperature different cages can be fitted with
bulbs of different wattage. In a cage a
cardboard can be placed on one side so that in
the cage the temprature remains same but
conditions of strong light dim light or darkness
can be created.
Similarly conditions of dry and humid
environment can be created and their behaviour
can be observed.
If cages are not available then wide
mouthed glass bottles can be used to keep the
cockroaches and their mouths can be closed
with cotton plugs. To bring sudden changes in
the environment the use of bottles is a better
option. The bottles should first be kept in the
sun and then food for the cockroaches should
be kept. After sometime the same bottle should
be kept in the fridge and the behaviour of the
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PRACTICAL BIOLOGY - XI
cockroaches can be compared.
the effect on their reproduction can also be
To create humid conditions water vapour
can be introduced into the bottles.
observed. Their intake of different varieties of food
Their intake of food at normal
temperature, high temperature and low
temperature can also be studied.
Cockroach is omnivorous, so enough of different
can also be studied under changed circumstances.
kinds of food should be supplied to them.
The differences in the behaviour observed
Observation :
under different circumstances indicate the
From these activities we can understand
how the behaviour of the cockroaches differ with
change in environmental conditions like how for
they can tolerate extreme changes in the conditions
can be found out. If observed for long duration
adaptability of the cockroaches. For eg if at very
low temperatures cockroaches become less active
and take rest, it suggests that due to changed
circumstances, they are conserving their energy
by reducing their activities
3. Biological Studies of Nearby Areas
Biology is the study of nature. The more
closely we observe, the closer we go to nature.
We can learnt most concepts from the text books
but directly observing even some portions of the
curriculum in nature is a great opportunity for
students of. Biology Thus a student of Biology
should keep observing keenly all around himself
whenever he is out in the nature. You will find that
nature has different varieties of plants and animals.
You will find animals showing different kinds of
behaviour (such as hunting, defending, eating,
making different kinds of sounds etc.) The plants
and animals in your neighbourhood will be different
along with the atmospheric conditions from those
found in other places. So arrange for field trips
near the school and study plants and animals found
there.
Go for field trips during different seasons
so that variety within the same locality can be
observed.
Preparation for field trips :
Before going for a trip you must make
necessary arrangements such as carry notebook,
pencil, pen, forceps, polythene bags of different
size, old newspapers, hand lens, a few jars with
plastic lids, thermometer (if available) blade etc.
in a bag.
What should you do no a trip :
Divide your class into small groups of
maximum 4 students and be alert white observing
nature. While observing you can collect leaves,
flowers of different kinds small plants which can
be uprooted easily, small sized harmless animals
etc. These things can be kept in the polythene
bags/ jars or between newspapers. It you do not
capture the animals, their behaviour can be
observed and noted.
After returning from the trip :
Classify the items collected and keep them
safely. The plant materials should be dried by
keeping between newspapers folds. They can be
later used to make herbarium. The animals can
be preserved in 5% formaline solution.
All the activities undertaken by you during
the trip should be noted in the notebook. To note
the observations the following points can be
considered -
CORE EXPERIMENTS
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(1)
Date and time of field trip
animal - You can make a table about this. It
(2)
Place of visit (like farms, fields ponds,
gardens etc.)
is not necessary that you should know the
Weather conditions – Summer, monsoon
or winter season, approximate
temperature, sunlight present or hot.
collect their names from friends/teacher/
(3)
(4)
names of all plants and animals. If you can
passers-by, note it down. If you do not get
the name of any plant / animal just give them
a number on the table and note their details.
Information about observed plants and
Plant Kingdom
Name of plants
observed
Root
stem
Leaf
Flower
Inflorescence Fruit
Any other
information
1. .................
2. .................
3. .................
4. .................
5. .................
Animal Kingdom
Name of
Animal
Colour, shape
Appearance
No. of wings
What kind of
legs
activity it was doing
Special
comment
1. .................
2. .................
3. .................
4. .................
5. .................
Report : On the basis of the tabulated information make a report of the trip undertaken. In this way
report on the obseravations of different trips, mutual discussion conclusions etc. can be
entered in the practical record and can be presented to the examiner during examination.