Download class 9 biology chapter- 1 fundamental unit of life introductory

CLASS 9
BIOLOGY
CHAPTER- 1
FUNDAMENTAL UNIT OF LIFE
INTRODUCTORY QUESTIONS
Ques. 1 What is the functional unit of life?
Ans. Cell is the functional unit of life.
Ques. 2 Why cell is called functional unit of life?
Ans. Because single cell perform all the vital activities of life.
Ques.3 How does a living cell perform these basic function?
Ans. All multicellular organisms including human being , show division of labour.
NCERT QUES.S
Ques. 1 Who discovered cells, and how?
Ans. Robert Hooke discovered cells while examining a thin slice of cork under his self designed
microscope. He observed that the cork resembled the structure of a honeycomb consisting of
many little compartments, which he named cells. Cell in Latin means "a little room".
Concept insight: Most popular Exam Ques. from this topic.
Ques. 2 Why is the cell called the structural and functional unit of life?
Ans. All living organisms are made up of cells. The number of cells in various living organisms
varies greatly depending on the size of the organism. Many cells group together to form tissues,
many tissues join together to form organ, many organs form organ system and finally all
systems make up an organism, hence called structural unit of life.
A cell is able to live and perform the various functions of life. Each component in the cell carries
out a specific function. In other words, it is a self-sufficient living entity. All the metabolic
activities of life like respiration, digestion, excretion etc. occur at the cell level. So it is called the
functional unit of life.
Concept insight: Most popular Exam Ques. from this topic.
Ques. 3 How do substances like CO2 and water move in and out of the cell? Discuss.
Ans. Substances like CO2 move in and out of the cell by the process of diffusion. When the
concentration of CO2 accumulates in the cell and is higher than the cell's external environment,
it moves out and is thus excreted. Similarly, when its concentration is lower in the cell as
compared to outside the cell, it moves into the cell.
Water also moves in and out of the cell by the same principle of difference of concentration,
but the process through which water moves across a selectively permeable membrane is called
osmosis.
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Concept insight: Osmosis is a special type of diffusion in which movement of water takes place
through semi permeable membrane whereas in diffusion movement of molecules takes place
without a semi permeable membrane.
Ques. 4 Why is the plasma membrane called a selectively permeable membrane?
Ans. Plasma membrane allows only some selected substances to move in and out of the cell,
and prevents the entry and exit of the other substances, so it is called a selectively permeable
membrane.
Concept insight: Plasma membrane is also called as cell membrane. Students should not get
confused between cell membrane and cell wall. Cell wall is not selectively permeable in nature.
Ques. 5 Fill in the gaps in the following table illustrating differences between prokaryotic and
eukaryotic cells.
1. Size: generally small (1-10
m)
1. Size: generally large (5-100 m).
-6
1 m=10 m.
2. Nuclear region:
_______________
and known as___
3. Chromosome: single
2. Nuclear region: Well defined and surrounded by a
nuclear membrane.
3. More than one chromosome.
4. Membrane-bound cell
4. _____________________ _______
organelles absent.
Ans. Fill in the gaps in the following table illustrating differences between prokaryotic and
eukaryotic cells.
Prokaryotic cell
1. Size: generally small (1-10 m)
1 m=10-6m.
Eukaryotic cell
1. Size: generally large (5-100 m).
2. Nuclear region: Undefined nuclear region 2. Nuclear region: Well defined and
containing only nucleic acids is called a
surrounded by a nuclear membrane.
nucleoid.
3. More than one chromosome.
3. Chromosome: single
4. Membrane bound cell organelles (e.g.,
4. Membrane-bound cell organelles are
chloroplasts, golgi bodies, mitochondria etc.)
absent.
are present.
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Concept insight:
• Differences should always be written in tabular form.
• Differences should be written in terms of their significance.
• Write only those many numbers of differences as stated in the Ques..
• Give example wherever possible.
Ques. 6 Can you name the two organelles we have studied that contain their own genetic
material?
Ans. Plastids and Mitochondria.
Concept insight: Apart form nucleus, plastids and mintochondria are the two cell orgenelles
that contains their own genetic material and make some of their proteins. They are also called
semi autonomous organelles.
Ques. 7 If the organisation of a cell is destroyed due to some physical or chemical influence,
what will happen?
Ans. Cell organelles are responsible for the organisation of a cell. Each cell organelle perform
some specific function. If a few of these cell organelles are destroyed due to some physical or
chemical influence , some of the important function of the cell will stop and it may result in the
death of the cell.
Concept insight: Each cell acts as a single entity. Death of few cell components will result into
the death of cell itself.
Ques. 8 Why are lysosomes konwn as suicide bags?
Ans. Lysosomes are known as suicide bags because whenever there is a disturbance in the
cellular metabolism and the cell gets damaged or destroyed, the lysosomes burst and the
powerful hydrolytic enzymes digest or eat their own cell. That is why they are called suicide
bags.
Concept insight: Important from Exam point of view.
Ques. 9 Where are proteins synthesized inside the cell ?
Ans. Proteins are synthesized in the ribosomes which are either attached to the surface of the
rough endoplasmic reticulum or lying freely in the cytoplasm.
Concept insight: Important from Exam point of view.
Ques. 10 Make a comparison and write down ways in which plant cells are different from
animal cells.
Ans. The differences between plant cells and animal cells are as follows:
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Plant Cells
1.Plant cell are larger in size.
2.Cell wall is present.
3.Plastids (Chloroplast,chromoplast and
leucoplast) are present.
4.Centrole is absent.
5.Larger vacuoles are present.
6.Food is stored in the form of starch.
7.Lysosomes are either absent or if present they
are very few in number.
8.Golgi apparatus exist as small subunits called
dictyosomes.
Animal Cells
1.Animal cells are comparatively smaller in
size.
2.Cell wall is absent.
3.Plastids are absent.
4.Centriole with centrosome is present.
5.Vacuoles are either absent or if present
they are very small in size.
6.Food is stored in the form of glycogen.
7.Lysosomes are present and are more in
number.
8.Highly complex Golgi apparatus is present.
Concept insight:
• Differences should always be written in tabular form.
• Differences should be written in terms of their significance.
• Write only those many numbers of differences as stated in the Ques..
• Give example wherever possible.
Ques. 11 How is a prokaryotic cell different from a eukaryotic cell?
Ans.
Difference between prokaryotic cell and eukaryotic cell are as under:
Prokaryotic cell
1.Generally small in size (1-10 m) 1 m = 10-6m.
2.Undefined nuclear region containing only nucleic
acids is called a nucleoid.
3.Single chromosome.
4.Membranne-bound cell organelles are absent.
Example: Bacteria and blue green algae.
Eurkaryotic Cell
1.Generally large in size(5-100 m).
2.Well defined nucleus surrounded by a
Nuclear membrane.
3.More than one chromosome.
4.Membrane-bound cell organelles are
present.
Example: Plant cell and animal cell.
Concept insight:
• Differences should be written in tabular form.
• Differences should be written in terms of their singnificance.
• Write only those many numbers of differences as stated in the Ques..
• Give example wherever possible.
Ques. 12 What would happen if the plasma membrane ruptures or breaks down?
Solution:
Plasma membrane is the selectively permeable membrane that surrounds the cell and allows
the entry and exit of selected materials into and out of the cell. If it ruptures, then
(i) The contents of the cell will come in direct contact with the outside medium and not only
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unwanted material will be able to enter freely into the cell, but useful material will also diffuse
out of the cell.
(ii) The cell will lose its shape.
Concept insight: Plasma membrane is the outermost covering of both plant and animal cells
protecting the inside material.
This Ques. is important from Exam point of view.
Ques. 13 What would happen to the life of a cell if there was no Golgi apparatus?
Ans. Golgi apparatus helps in the packaging, storage and transport of substances in the cell. If
there were no Golgi apparatus then the following things will happen:
(i) The material synthesised by Endoplasmic reticulum would not be carried to the various parts
inside and outside the cell.
(ii) Synthesised materials could not be stored and modified further, as the Golgi apparatus
performs the function of storage and modification.
(iii) There will be no production of lysosomes which will cause the accumulation of waste
material, worn out and dead cell organelles within the cell which will ultimately lead to cell
death.
Concept insight: Important from Exam point of view.
Ques. 14 Which organelle is known as the powerhouse of the cell? Why?
Ans. Mitochondria is called the powerhouse of the cell as it produces energy by oxidizing the
food and storing it in the form of ATP (Andenosine Tri phosphate), which is called the energy
currency of the cell. This energy is later used for various activities by the cell.
Concept insight: Most popular Exam Ques. from this topic.
Ques. 15 Where do the lipids and proteins constituting the cell membrane get synthesised?
Ans. The lipids and proteins constituting the cell membrane are synthesised in the endoplasmic
reticulum. Lipids are synthesised in the Smooth Endoplasmic Reticulum (SER) and the proteins
are synthesised in the ribosomes attached to the Rough Endoplasmic Reticulum (RER).
Concept insight: Smooth endoplasmic reticulum and rough endoplasmic reticulum are two
different organelles. Ribosomes are attached only to the surface of rough endoplasmic
reticulum.
Ques. 16 How does an Amoeba obtain its food?
Ans. Amoeba is a unicellular organism. It obtain its food through the false feet called
pseudopodia. Whenever it sees food particle its flexible membrane protrudes and engulfs the
food. This food is then broken down into the food vacuole which contains digestive enzymes.
This process is known as endocytosis.
Concept insight: Most popular Exam Ques. from this topic.
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Ques. 17 What is osmosis?
Ans. Movement of water molecules from the region of its higher concentration to the region of
its lower concentration through a selectively permeable membrane is called osmosis.
It is a special type of diffusion.
Concept insight: Osmosis takes place through selectively permeable membrane only.
Ques. 18. Carry out the following
Take four peeled potato halves and scoos each one out to make potato cups. One of these
potato cups should be made from a boiled potato. Put each potato cup in a trough containing
water.
Now,
(a) Keep cup A empty
(b) Put one teaspoon sugar in cup B
(c) Put one teaspoon salt in cup C
(d) Put one teaspoon sugar in the boiled potato cup D
Keep these for two hours. Then observe the four potato cups and answer the following:
(i) Explain why water gathers in the hollowed portion of B and C.
(ii) Why is potato A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed out portions of A and D.
Ans. (i) Water gathers in the hollowed portion of B and C because of the process of osmosis.
The cell membrane of a potato is selectively permeable. As the cups B and C are filled with
sugar and salt respectively and their outer part is in contact with the water, the concentration
of water outside the cups is higher than inside the cups, so water moves from its higher
concentration towards the lower concentration, i.e., inside the cup. This process of osmosis
(moving in of the solvent) is known as endosmosis.
(ii) Potato A acts as a control for the experiment. It helps in comparing the result of the
experiment.
(iii) Water does not gather in the hollowed out portion of A because there is no concentration
difference and hence no osmosis takes place. Water also does not gather in the cup D as the
cells of boiled potato are dead and hence no osmosis takes place.
Concept insight:
(i) Follow the instructions properly.
(ii) Observe the activity carefully.
(iii) Give reason for your observation.
VALUE BASED QUESTIONS
Ques.1 Shilpa told her sister, who studies in ix standards, that cells were discovered by
Robert Hook in 1665. Based on his observation, cell theory was developed.As Shilpa does not
have a microscope she was not able to show her the structure of a cell. As her sister
understood this, she asked Shilpa to show her a cell.
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(i) What will Shilpa show to her sister to give her an idea of a typical cell?
Ans.Shilpa can show her a behive, each chamber of which looks like a cell.
(ii) What is the life of a cell?
Ans.Different cells have different life span. Some cells live for few days whereas few live upto a
year.
(iii) What values are shown by shilpa and her sister?
Ans.The value shown by Shilpa is adequate knowledge on the subject and the scientific
approach to find solution to a problem. The value shown by her sister is the attitude to go for
detail.
Ques. 2 Naman has being told by his teacher that plants posses mostly dead cells in their
body and on the other hand most of the animal cells are alive. A student wants to know from
his teacher that wheather the dead cells in organisms gives an equal advantage like that of
plants.
(i) What advantage do plants get by having mostly dead cells?
Ans.Plant are static. Dead cells give them rigidity. They also do not need any energy to maintain
the dead cells.
(ii) Why should we protect trees?
Ans.Trees give us oxygen to breath. They give us cool breeze. We get fruits, vegetables and
many other food items from trees. Trees help in conserving the biodiversity.
(iii) What value is shown by the students?
Ans.The value shown by Naman is adequate knowledge of subject.
HOTS QUIESTION ANSWER
Ques. 1 (a) Name the phenomenon which helps fresh water unicellular organism (eg.
Amoeba) continuously gain water in their bodies. Also name the mechanism by which these
organisms throw out excess of water from their bodies.
(b)Give atleast two examples in plants where similar phenomenon is used to gain of water.
Ans.(a) Fresh water unicellular organisms (eg. Amoeba) continuoulsy gain water in their bodies
due to osmosis. These organisms have contractile vacuoles to throw out excess of water from
their bodies.
(b) (i)Absorbtion of water by the plant roots from the soil through root hairs occurs due to
osmosis.
(ii)In plants, cells, tissues and soft organs (leaves, young shoots, flowers) maintain turgidity
due to osmotic absorption of water.
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ACTIVITIE
To study endosmosis and exosmosis in raisins procedure
 Half-fill a Petridis with water and place 4-5 dried raisins in it.
 Observe after 30 minutes. note down your observation (observation i)


now place these raisins in concentrated suger or salt solution.
Observe after 0.3 minutes. Note down your observation (observation ii)
OBSERVATION AND INFERENCE
Observation i
The raisins swell up when placed in water due to endosmosis (water moves into the rains).
Observation ii
These swollen raisins shrink when placed in concentrated sugar or salt solution due to
exosmosis (water moves out of raisins).
ACTIVITY- II
To study plasmolysis and deplasmolysis in plant cells
Procedure
step 1. mount the peel of Rheo on a clean slide in a drop of
water and cover with a cover slip.
 Observe the cells under high power of the microscope,
identify different parts of the cells and draw a diagram. (observation I).
Step2. Take 10% sugar or salt take solution.
 Remove cover slip from the mount and put 2-3 drops of the above solution on the
mounted peel.
 Cover it with cover slip and remove excess of fluid with a blotting paper.
 After two minutes observe it under high power of microscope. (observation II)
 Draw the diagram and compare it with the previous one. What change has occurred?
Step3.put some fresh water on the peel. Leave for two minutes.
 Observe under the microscope. What change has taken place?(observation III
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Observation
1. A normal rheo leaf has cell well, a large central vacuole, a nucleus, cytoplasm, greencoloured chloroplasts.
2. In sugar solution the cytoplasm in rheo leaf cells shrinks and vacuole disappears.
3. When cells are placed in fresh water, they regain their original turgid shape.
Interfence


In 10% sugar/salt solution the shrinkage of cell cytoplasm has occurred due to
exosmosis. The water from cell moves out from hypotonic external medium. The
shrinkage of cell cytoplasm in hypertonic medium is called plasmolysis.
These plasmolysed cells become normal because water from hypotonic external
mediummoved into the cells. This is due to endosmosis and this is called deplasmolysis.
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