CBSE - The Fundamental Unit of Life

An English Botanist, Robert Hooke discovered cells. In 1665, he used self-designed microscope to observe cells in a cork slice.

Cells are called the structural and functional unit of life because all the living organisms are made up of cells and also all the functions taking place inside the body of organisms are performed by cells.

The substances like CO2and water move in and out of a cell by diffusion from the region of high concentration to low concentration.
When the concentration of CO2and water is higher in external environment than that inside the cell, CO2and water moves inside the cell. When the concentration outside the cell becomes low and it is high inside the cell, they moves out.

Plasma membrane called a selectively permeable membrane because it regulates the movement of substances in and out of the cell. This means that the plasma membrane allows the entry of only some substances and prevents the movement of some other materials.

Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

Answer

Mitochondria and plastids

If the organisation of a cell is destroyed due to some physical or chemical influence then cell will not be able to perform the basic functions like respiration, nutrition, excretion etc. This may stop all the life activities and may result in its death.

Lysosomes are called suicide bags because in case of disturbance of their cellular metabolism they digest their own cell by releasing own enzymes.

The proteins are synthesized in the Ribosome inside the cell.

Animal cell	Plant cell
The do not have cell wall.	They have cell wall made up of cellulose.
They do not have chloroplast.	They contain chloroplast.
They have centrosome.	They do not have centrosome.
Vacuoles are smaller in size.	Vacuoles are larger in size.
Lysosomes are larger in number.	Lysosomes are absent or very few in number
Prominent Golgi bodies are present.	Subunits of Golgi bodies known as dictyosomes are present.

Prokaryotic cell	Eukaryotic cell
Most prokaryotes are unicellular.	Most eukaryotes are multicellular.
Size of the cell is generally small (0.5- 5 µm).	Size of the cell is generally large (50- 100 µm).
Nuclear region is poorly defined due to the absence of a nuclear membrane or the cell lacks true nucleus.	Nuclear region is well-defined and is surrounded by a nuclear membrane, or true nucleus bound by a nuclear membrane is present in the cell.
It contains a single chromosome.	It contains more than one chromosome.
Nucleolus is absent.	Nucleolus is present.
Membrane-bound cell organelles such as plastids, mitochondria, endoplasmic reticulum, Golgi apparatus, etc. are absent.	Cell organelles such as mitochondria, plastids, endoplasmic reticulum, Golgi apparatus, lysosomes, etc. are present.
Cell division occurs through binary fission	Cell division occurs by mitosis.
Prokaryotic cells are found in bacteria and blue-green algae.	Eukaryotic cells are found in fungi, plants, and animal cells.

If the plasma membrane ruptures or breakdown then the cell will not be able to exchange material from its surrounding by diffusion or osmosis. Thereafter the protoplasmic material will be disappeared and the cell will die.

Golgi apparatus has the function of storage modification and packaging of the products. If there is no Golgi apparatus then the packaging and transporting of materials synthesized by cell will not happen.

Mitochondria are known as the powerhouse of cells because energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine triphosphate) molecules.

Lipids are synthesized in Smooth endoplasmic reticulum (SER) and the proteins are synthesized in rough endoplasmic reticulum (RER).

Amoeba takes in food using temporary finger-like extensions of the cell surface which fuse over the food particle forming a food-vacuole as shown in figure. Inside the food vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm. The remaining undigested material is moved to the surface of the cell and thrown out.

Osmosis is the process in which water molecules moves from the region of high concentration to a region of low concentration through a semi permeable membrane.

Carry out the following osmosis experiment:

Take four peeled potato halves and scoop 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.

Answer

(i) Water gathers in the hollowed portions of set-up B and C because water enters the potato as a result of osmosis. Since the medium surrounding the cell has a higher water concentration than the cell, the water moves inside by osmosis. Hence, water gathers in the hollowed portions of the potato cup.

(ii) Potato A in the experiment acts as a control set-up. No water gathers in the hollowed portions of potato A.

(iii) Water does not gather in the hollowed portions of potato A because potato cup A is empty. It is a control set-up in the experiment.
Water is not able to enter potato D because the potato used here is boiled. Boiling denatures the proteins present in the cell membrane and thus, disrupts the cell membrane. For osmosis, a semi-permeable membrane is required, which is disrupted in this case. Therefore, osmosis will not occur. Hence, water does not enter the boiled potato cup.

1. Which of the following can be made into crystal?
(a) A Bacterium
(b) An Amoeba
(c) A Virus
(d) A Sperm
Ans. (c) A Virus
Explanation: Virus does not have a cell; like other options. Virus is composed of nuclear material enclosed in a protein coat. Due to this, it can be into crystal.

2. A cell will swell up if
(a) The concentration of water molecules in the cell is higher than the concentration of water molecules in surrounding medium
(b) The concentration of water molecules in surrounding medium is higher than water molecules concentration in the cell
(c) The concentration of water molecules is same in the cell and in the surrounding medium
(d) Concentration of water molecules does not matter
Ans. (b) The concentration of water molecules in surrounding medium is higher than water molecules concentration in the cell
Explanation: If concentration of water molecules in surrounding medium is higher than water molecules concentration in the cell, it will result in movement of water into the cell. This will result in cell getting swelled up.

3. Chromosomes are made up of
(a) DNA
(b) protein
(c) DNA and protein
(d) RNA
Ans. (c) DNA and protein

4. Which of these options are not a function of Ribosomes?
(i) It helps in manufacture of protein molecules
(ii) It helps in manufacture of enzymes
(iii) It helps in manufacture of hormones
(iv) It helps in manufacture of starch molecules
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (iv) and (i)
Ans. (c) (iii) and (iv)
Explanation: Ribosomes are responsible for protein synthesis. Enzymes are composed of protein. Hence, options (iii) and (iv) are incorrect.

 5. Which of these is not related to endoplasmic reticulum?
(a) It behaves as transport channel for proteins between nucleus and cytoplasm
(b) It transports materials between various regions in cytoplasm
(c) It can be the site of energy generation
(d) It can be the site for some biochemical activities of the cell
Ans. (c) It can be the site of energy generation
Explanation: Energy generation is the function of mitochondria.

6. Following are a few definitions of osmosis
Read carefully and select the correct definition
(a) Movement of water molecules from a region of higher concentration to a region of
lower concentration through a semipermeable membrane
(b) Movement of solvent molecules from its higher concentration to lower concentration
(c) Movement of solvent molecules from higher concentration to lower concentration of solution through a permeable membrane
(d) Movement of solute molecules from lower concentration to higher concentration of solution through a semipermeable membrane
Ans. (a) Movement of water molecules from a region of higher concentration to a region of lower concentration through a semipermeable membrane

7. Plasmolysis in a plant cell is defined as
(a) break down (lysis) of plasma membrane in hypotonic medium
(b) shrinkage of cytoplasm in hypertonic medium
(c) shrinkage of nucleoplasm
(d) none of them
Ans. (b) shrinkage of cytoplasm in hypertonic medium
Explanation: When a cell is kept in hypertonic solution, it results in exosmosis. Most of the fluid goes out of the cell; resulting in shrinkage of cytoplasm.

8. Which of the following are covered by a single membrane?
(a) Mitochondria
(b) Vacuole
(c) Lysosome
(d) Plastid
Ans. (b) Vacuole
Explanation: Other organelles in the options are double – membrane structures.

9. Find out the false sentences
(a) Golgi apparatus is involved with the formation of lysosomes
(b) Nucleus, mitochondria and plastid have DNA; hence they are able to make their own structural proteins
(c) Mitochondria is said to be the power house of the cell as ATP is generated in them. 
(d) Cytoplasm is called as protoplasm

Ans. (a) Golgi apparatus is involved with the formation of lysosomes 
Explanation: Golgi apparatus is involved in synthesis and storage of certain
biomolecules and has no role to play in the formation of lysosomes. 

10. Find out the correct sentence
(a) Enzymes packed in Lysosomes are made through RER (rough endoplasmic reticulum)
(b) Rough endoplasmic reticulum and smooth endoplasmic reticulum produce lipid and protein respectively
(c) Endoplasmic reticulum is related with the destruction of plasma membrane
(d) Nucleoid is present inside the nucleoplasm of eukaryotic nucleus
Ans. (a) Enzymes packed in Lysosomes are made through RER (rough endoplasmic reticulum) 
Explanation: RES has ribosomes on the surface and ribosomes are responsible for protein synthesis and thus for enzymes synthesis as well. Hence, option ‘a’ is correct and option ‘b’ is incorrect. ER has no role to play in destruction of plasma membrane. The undefined nuclear region in prokaryotes is called nucleoid.

11. Which cell organelle plays a crucial role in detoxifying many poisons and drugs in a cell?
(a) Golgi apparatus
(b) Lysosomes
(c) Smooth endoplasmic reticulum
(d) Vacuoles
Ans. (c) Smooth endoplasmic reticulum
Explanation: In the river cells of vertebrate, SER plays an important role in detoxifying many poisons and drugs.

12. The proteins and lipids, essential for building the cell membrane, are manufactured by
(a) rough endoplasmic reticulum
(b) golgi apparatus
(c) plasma membrane
(d) mitochondria
Ans. (a) rough endoplasmic reticulum
Explanation: Endoplasmic reticulum synthesise both lipids and proteins. However, RER mainly synthesise proteins and SER mainly synthesise lipids.

13. The undefined nuclear region of prokaryotes are also known as
(a) nucleus
(b) nucleolus
(c) nucleic acid
(d) nucleoid
Ans. (d) nucleoid 

14. The cell organelle involved in forming complex sugars from simple sugars are 
(a) endoplasmic reticulum
(b) ribosomes
(c) plastids
(d) golgi apparatus
Ans. (d) golgi apparatus
Explanation: Golgi apparatus is involved in repackaging of many biomolecules.

15. Which out of the following is not a function of vacuole?
(a) Storage
(b) Providing turgidity and rigidity to the cell
(c) Waste excretion
(d) Locomotion
Ans. (d) Locomotion
Explanation: Locomotion is carried out by specialized structures which are outside the cell but vacuoles are inside the cell. 
 

16. Amoeba acquires its food through a process, termed
(a) exocytosis
(b) endocytosis
(c) plasmolysis
(d) exocytosis and endocytosis both
Ans. (b) endocytosis
Explanation: The Term endocytosis is composed of two term, i.e. ‘endo’ means towards inside and ‘cytosis’ means movement related to cell.

17. Cell wall of which one of these is not made up of cellulose?
(a) Bacteria
(b) Hydrilla
(c) Mango tree
(d) Cactus
Ans. (a) Bacteria
Explanation: Other options show plants in which cell wall is made of cellulose. But cell wall of bacteria is made of peptidoglycan.

18. Silver nitrate solution is used to study
(a) endoplasmic reticulum
(b) golgi apparatus
(c) nucleus
(d) mitochondria
Ans. (b) golgi apparatus
Explanation: Camillo Golgi carried out ‘black reaction’ which involved use of silver nitrate. This helped him in staining individual nerve and cell structures.

19. Organelle other than nucleus, containing DNA is
(a) endoplasmic reticulum
(b) golgi apparatus
(c) mitochondria
(d) lysosome
Ans. (c) mitochondria
Explanation: Mitochondria and chloroplast contain DNA and hence have capability of replication.

20. Kitchen of the cell is
(a) mitochondria
(b) endoplasmic reticulum
(c) chloroplast
(d) golgi apparatus
Ans. (c) chloroplast
Explanation: Food is produced in plants inside chloroplasts. Hence, chloroplast is called the kitchen of the cell.

21. Lipid molecules in the cell are sythesized by
(a) smooth endoplasmic reticulum
(b) rough endoplasmic reticulum
(c) golgi apparatus
(d) plastids
Ans. (a) smooth endoplasmic reticulum

22. Cell arises from pre-existing cell was stated by
(a) Haeckel
(b) Virchow
(c) Hooke
(d) Schleiden
Ans. (b) Virchow
Explanation: This postulation of Virchow made an addition to the earlier cell theory.

23. Cell theory was given by
(a) Schleiden and Schwann
(b) Virchow
(c) Hooke
(d) Haeckel
Ans. (a) Schleiden and Schwann
Explanation: They were the first to propose the cell theory which stated that all plants and animals are made up of cell and cell is the basic unit of life.

24. The only cell organelle seen in prokaryotic cell is
(a) mitochondria
(b) ribosomes
(c) plastids
(d) lysosomes 
Ans. (b) ribosomes
 Explanation: Other cell organelles are absent in prokaryotic cells.
 
25. Organelle without a cell membrane is
(a) ribosome
(b) golgi apparatus
(c) chloroplast
(d) nucleus
Ans. (a) ribosome
Explanation: Other cell organelles are membrane – bound.

26. 1 μm is
(a) 10–6 m
(b) 10–9 m
(c) 10–10 m
(d) 10–3 m
Ans. (a) 10–6 m

27. Lysosome arises from
(a) endoplasmic reticulum
(b) golgi apparatus
(c) nucleus
(d) mitochondria
Ans. (b) golgi apparatus

28. Living cells were discovered by
(a) Robert Hooke
(b) Purkinje
(c) Leeuwenhoek
(d) Robert Brown
Ans. (c) Leeuwenhoek
Explanation: Robert Hooke was the first to observe cells but he observed dead cells of cork. It was Leeuwenhoek who was the first to observe living cells.

29. Select the odd one out
(a) The movement of water across a semipermeable membrane is affected by the amount
of substances dissolved in it.
(b) Membranes are made of organic molecules like proteins and lipids
(c) Molecules soluble in organic solvents can easily pass through the membrane.
(d) Plasma membranes contain chitin sugar in plants
Ans. (d) Plasma membranes contain chitin sugar in plants
Explanation: This is a wrong statement, while others are correct. 

Lysosomes are known as ‘suicide-bags’ because when cell gets damaged during the disturbance in cellular metabolism, lysosomes may burst and the digestive enzymes thus released digest their own cell.

I agree with the statement that “A cell is a building block of an organism”. This is true because all living beings are made up of cells and cell is the smallest independent unit of living beings.

Soap solution is very concentrated - Hypertonic solution, so water moves out of your finger cells by osmosis.

Cell wall is absent in animals. Due to this, movement of substances inside the cells is easier in animals than in plants. Due to this, endocytosis is found in animals only.

Swallowing a concentration solution of salt results in exosmosis from cells of the alimentary canal. Due to this, dehydration occurs in the person. As a result, the person starts vomiting.

Ribosome

Diffusion and osmosis respectively

Exosmosis

If cells of onion peel and RBC are separately kept in hypotonic solution, what among the following will take place? Explain the reason for your answer.

(a) Both the cells will swell. 
(b) RBC will burst easily while cells of onion peel will resist the bursting to some extent.
(c) a and b both are correct.
(d) RBC and onion peel cells will behave similarly.
Ans. (c) a and b both are correct. When surrounding medium is hypotonic, water moves into the cells. This will result in swelling of cells. RBCs do not have cell wall and hence they will easily burst. Presence of cell wall in the cells of onion peel will prevent their bursting.

Small vesicles which are associated with plasma membrane are present in such bacteria. These vesicles contain pigments which can trap solar energy to produce food.

Match the following A and B

ANS

 a�iv; b�v; c�iii; d�i; e�ii

Flower and Fruit— Chromoplast
Leaves of the plant— Chloroplast
Root of the plant— Leucoplast

Name the organelles which show the analogy written as under
(a) Transporting channels of the cell __________
Ans. Endoplasmic reticulum
(b) Power house of the cell __________
Ans. Mitochondria
(c) Packaging and dispatching unit of the cell __________
Ans. Golgi body
(d) Digestive bag of the cell __________
Ans. Lysosome
(e) Storage sacs of the cell __________
Ans. Vacuole
(f) Kitchen of the cell __________
Ans. Chloroplast
(g) Control room of the cell __________
Ans. Nucleus

Bacterial cell	Onion peel cell
It is prokaryotic cell	It is eukaryotic cell
Nucleus is not present	It has well-developed nucleus
Circular DNA is present	DNA is present inside nucleus
It does'nt have membrane bound cell organelles	It has membrane-bound cell organelles

Carbon dioxide moves through diffusion, while water moves through osmosis.

Amoeba makes pseudopodia to surround a food particle. It then ingest the food particles; along with a drop of water and then forms food vacuole. This process of obtaining food by Amoeba is called endocytosis.

Mitochondria and plastids

Lysosomes contain enzymes which are used for destroying worn out parts of the cell. Lysosomes also destroys waste materials. Due to this, lysosomes are also known as ‘scavengers of the cells’.

Nucleus

Which kind of plastid is more common in
(a) roots of the plant
Ans. Leucoplast
(b) leaves of the plant
Ans. Chloroplast
(c) flowers and fruits
Ans. Chromoplast

Vacuoles not only store many important substances, they also contain cell sap that give turgidity to cell.

Chromosomes are made up of chromatids and chromatids are made up of chromatin. 

(a) A cell containing higher water concentration than the surrounding medium
Ans. Exosmosis
(b) A cell having low water concentration than the surrounding medium.
Ans. Endosmosis
(c) A cell having equal water concentration to its surrounding medium.
Ans. No effect

Draw a plant cell and label the parts which
(a) determines the function and development of the cell
(b) packages materials coming from the endoplasmic reticulum
(c) provides resistance to microbes to withstand hypotonic external media without bursting
(d) is site for many biochemical reactions necessary to sustain life.
(e) is a fluid contained inside the nucleus
Ans. (a) Nucleus
(b) Golgi apparatus
(c) Cell wall
(d) Cytoplasm
(e) Nucleoplasm.

Animal Cell	Plant Cell
1. Cell wall absent	1. Cell wall present
2. Plastids are absent	2. Plastids are present
3. It has a small vacuole	3. It has a large vacuole
4. Centriole present	4. Centriole absent

 Ans.

The ribosomes, which are present in all active cells, are the sites of protein synthesis. Endoplasmic reticulum helps in transporting these proteins to various places. The smooth endoplasmic reticulum help in manufacture of fat and lipids which along with proteins help in building the cell membrane.

In brief state what happens when
(a) dry apricots are left for sometime in pure water and later transferred to sugar solution?
Ans. First it swells due to endosmosis and then exosmosis occurs and it shrinks.
(b) a Red Blood Cell is kept in concentrated saline solution?
Ans. It will lose water and shrink.
(c) the Plasma-membrane of a cell breaks down?
Ans. The cell will die.
(d) rheo leaves are boiled in water first and then a drop of sugar syrup is put on it?
Ans. The cell gets killed on boiling so no plasmolysis.
(e) golgi apparatus is removed from the cell?
Ans. All sorts of vesicle formation stop.