11 – Cell Structure and Micro-Organism
Q 1.
Fill in the blanks.
Ans.
(1) plastids (2) fertilizers (3) chloroplasts (4) microbes/cell organelles
Q
2. What is difference between us?
(1) Plant cell and animal cell.
Plant cell
Animal cell
1.
Plant cells have cell wall made up of 1. Animal cells do not have cell
wall.
cellulose.
2. The
cytoplasm of the plant cells is lesser, 2. The cytoplasm of animal cells is more granular
and not dense.
granular and dense.
3. There is a single large vacuole located in 3. The cytoplasm is uniformly distributed in
centre
which pushes the cytoplasm to one the cell.
end.
4. There
are no lysosomes. 4. Lysosomes are
present in the animal cells. 5.
The mitochondria are few in number.
5. The mitochondria are greater in number
as compared to
the plant cells.
6
Plastids are present only in plant cells. 6. Plastids are absent in the animal
cells.
7.
Single or more but large vacuoles present. 7. Vacuoles are few and temporarily formed.
8. The vacuoles are filled up with cell sap. 8. The vacuoles are filled with food or
excretory matter.
(2) Prokaryotic cell and eukaryotic cell.
Prokaryotic cell Eukaryotic cell
1.The nucleus of prokaryotic cell is not 1. The nucleus of eukaryotic cell is
distinct distinct.
with nuclear membrane, nucleoli and
nucleoplasm.
2. Prokaryotic cells are about 1 to 10 um in 2. Eukaryotic cells are about 5 to 100 um
in size.
size. .
3. Due to the absence of nuclear membrane. 3. Due to the presence of nuclear membrane,
the nuclear material comes in contact nucleoplasm and cytoplasmn never
come
with the cytoplasm. in
physical contact with each other.
4. The cell organelles if present are without 4. The cell organelles are always bound with
membranes. membranes.
5. There is indistinct nucleoid in which 5. The nucleus is distinct with more
than
prokaryotic DNA is present. There is a one chromosomes.
single chromosome.
6. Mitochondria are absent in prokaryotic 6. Mitochondria are present in eukaryotic
cells. cells.
7. Chlorophyll is present in the vesicles and 7. Chlorophyll is always inside the
not in plastids.
chloroplasts.
8. Prokaryotic cells are found in blue-green 8. Eukaryotic cells are found in highly
algae algea and bacteria. evolved plants and animals.
Q. 3. Answer the following questions :
(1)
What is a 'cell’?
Ans.
The structural and functional unit of the body is called a cell.
(2)
Name the different organelles in a cell?
Ans.
Nucleus, endoplasmic reticulum, ribosome, Golgi body, lysosomes, mitochondria,
plastids, vacuoles are all different cell organelles.
(3) What
are micro-organisms?
Ans.
The living organisms on the earth which are in every environment but can be
seen only under compound microscope are called micro-organisms.
(4)
Which are the different types of micro-organisms?
Ans
Bactaria, virus, fungi, algae and protozoan are all the different types of
micro-organism.
(5) Who discovered the process of fermentation?
Louis
Pasteur discovered the process of fermentation.
Q 4. Explain the uses and the harmful effects of
micro-organisms.
Ans.
1. Uses of micro-organisms :
(1) Micro-organism decomposition, the wastes and sewage water. (2) By the process of
Decomposition
they keep the environment clean. Fertilizers are prepared from wastes by this
process. With the help of biogas plant, the biogas is prepared by the
micro-organisms. (3) The microbes residing in the soil and in the root nodules
of leguminous plants help in biological nitrogen fixation. This helps in
increasing fertility of soil and also in increasing the protein content of
seeds in legumes. (4) Micro-organisms help in the formation of curd and other based
products. (5) The process of fermentation is used for producing alcohol from
grains and fruits, bread from flour as well as in the production of acetic
acid, citric acid, lactic acid, vitamins, antibiotics, etc. (6) Processes like
tanning of skin, production of ropes and strings from agave are also done with
help of microbes. (7) Oil slick is cleared with the help of some specific
bacteria.
II.
Harmful effects of micro-organisms :
Micro-organisms
spoil the food. In hot and humid air there is fugal attack on food. (2)
Microbes produce enterotoxins and cause food toxic resulting into food
poisoning. (3) Harmful microbes cause diseases in plants, animals and human.
Amoebiasis, typhoid, cholera, hepatitis, gastro are caused by water and food
borne microbes. (4) Microbes cause diseases like malaria, dengue,
elephantiasis, yellow fever, chikungunya, Zika fever, etc. These diseases are
caused after mosquito transfers the miscrobes into human body. Common cold,
cough, diphtheria, pneumonia, tuberculosis are diseases of respiratory tract
which are caused by microbes.
Q
5. When will you use a simple microscope and when, a compound microscope? Explain
in detail how you will use them.
Ans.
(1) Simple microscope is of lesser magnification. One can observe, insect parts
of parts of flowers under such microscope. (2) Compound microscope is required
for the observation of microbes. (3) Here magnification is 100 to 450 times. It
is there observation of cells and tissues. (4) The simple microscope's stage
can be used for direct observation. (5) The object to be studied by compound
microscope is placed over glass slide and covered over with cover slip. The
object is sectioned into very thin slices and stained appropriately. (6) The
ocular and objective lens are brought in one line. Before that the mirror is
adjusted for optimum light. (7) The magnified view of the object is seen
through the eyepiece. (8) The coarse focus knob is adjusted first and then with
fine focus knob the accurate focussing is done. (9) In this way, simple
microscope is used for general observations and compound microscope is used for
specialized observations that require greater magnification.
Q 6. Sketch and describe in
your own words, the plant cell and animal cell.
picture
1.
Plant cell : (1) There is cellulose cell wall in plant cells which is the
outermost covering of the cell. (2) Inside the cell wall there is a plasma
membrane that encloses cytoplasm. Cell organelles are embedded in the
cytoplasm. (3) Plastid is an important cell organelle present only in plant
cells. Of these chloroplasts perform photosynthesis. (4) Nucleus endoplasmic
reticulum, Golgi body, mitochondria are the cell organelles present in the
cytoplasm. (5) Vacuole is usually single and large. Since it is present in the
centre of the cell, the cytoplasm is pushed to one end.
II.
Animal cell : (1) The outermost covering is plasma membrane. (2) Inside this
there is cytoplasm in which the cell organelles are embedded. (3) The cell
organelles are as following: Nucleus, Golgi body, endoplasmic reticulum and
many smaller vacuoles.
Q. 8.
Give scientific reasons :
(1)
Diseases spread on a large scale during periods of heavy rainfall and floods.
Ans.
The spread of disease is most likely during heavy rainfall and floods. The
water and food gets contaminated. The water logging causes growth of micro-organisms
and house flies. They spread the pathogens rapidly. The humid atmosphere
induces food spoilage. Even if flood water recedes, the poodle formed helps in
the breeding of mosquitoes. All such reasons are responsible for epidemic
spread of diseases.
(2) There is a possibility of food
poisoning if we eat stale food.
Ans.
The stale food is likely to have microbes in it. Some of the microbes produce
enterotoxins. The enterotoxins cause food poisoning. Therefore there is a
possibility of food poisoning if we eat stale food.
(3)
Soil is turned over during tilling.
Ans. There are some useful bacteria in the soil.
They help to decompose organic substances into inorganic nutrients. Thereby
they produce fertilizers. Some microbes also help in nitrogen fixation. They help the plants to get
nitrogen. Thus to have better yield of crop, the soil is turned over during
tilling to mix the bacteria.
(4)
Fungus grows quickly in moist or humid conditions.
Ans.
The fungus needs suitable conditions for the growth. The moist and humid
conditions are favourable to it. It does not grow in dry conditions.
(5) A refrigerator is used in almost
every home.
Ans. The harmful microbes do not grow in cold
temperatures. they grow only in the temperature range of 15° C to 35° C.
Refrigerator has very low temperatures. Food can be stored there without spoiling.
Therefore, to store perishable food items refrigerators have become essential
in every home.
(6)
Bread 'rises during baking.
Ans.
When the bread is prepared yeast is added to it. Yeast is a type of fungus. It
undergoes process of fermentation in the batter of bread and releases carbon
dioxide. Therefore, the bread rises during baking.
(7)
Fodder is soaked in water before offering to cattle.
Ans. By
adding the fodder into water, it is fermented. By fermentation, the vitamin
content rises in the fodder, it also becomes easier for digestion. The cattle
is thus well nourished. Therefore, fodder is soaked in water before offering to
cattle.
