RBSE Class 9 Science Important Questions Chapter 5 The Fundamental Unit of Life

Rajasthan Board RBSE Class 9 Science Important Questions Chapter 5 The Fundamental Unit of Life Important Questions and Answers.

RBSE Class 9 Science Chapter 5 Important Questions The Fundamental Unit of Life

Objective Type Questions

Question 1.
Which of the following can be made into crystal?
(a) A bacterium
(b) An amoeba
(c) A virus
(d) A sperm
Answer:
(c) A virus

Question 2.
Chromosomes are made up of :
(a) DNA
(b) protein
(c) DNA and protein
(d) RNA
Answer:
(c) DNA and protein

Question 3.
Which of the following are covered by a single membrane?
(a) Mitochondria
(b) Vacuole
(c) LysosOme
(d) Plastid
Answer:
(b) Vacuole, (c) Lysosome

Question 4.
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
Answer:
(c) Smooth endoplasmic reticulum

Question 5.
The undefined nuclear region of prokaryotes are also known as :
(a) nucleus
(b) nucleolus
(c) nucleic acid
(d) nucleoid
Answer:
(a) nucleus

Question 6.
The undefined nuclear region of prokaryotes are also known as:
(a) nucleus
(b) nucleolus
(c) nucleic acid
(d) nucleoid
Answer:
(d) nucleoid

Question 7.
The cell organelle involved in forming complex sugars from simple sugars are :
(a) endoplasmic reticulum
(b) ribosomes
(c) plastids
(d) golgi apparatus
Answer:
(d) golgi apparatus

Question 8.
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
Answer:
(d) Locomotion

Question 9.
Amoeba acquires its food through a process, termed :
(a) exocytosis
(b) endocytosis
(c) plasmolysis
(d) exocytosis and endocytosis both
Answer:
(b) endocytosis

Question 10.
Cell wall of which one of these is not made up of cellulose?
(a) Bacteria
(b) Hydrilla
(c) Mango tree
(d) Cactus
Answer:
(a) Bacteria

Question 11.
Silver nitrate solution is used to study :
(a) endoplasmic reticulum
(b) Golgi apparatus
(c) nucleus
(d) mitochondria
Answer:
(b) Golgi apparatus

Question 12.
Organelle other than nucleus, containing DNA is :
(a) endoplasmic reticulum
(b) Golgi apparatus
(c) mitochondria
(d) lysosome
Answer:
(c) mitochondria

Question 13.
Kitchen of the cell is :
(a) mitochondria
(b) endoplasmic reticulum
(c) chloroplast
(d) Gogli apparatus
Answer:
(c) chloroplast

Question 14.
Lipid molecules in the cell are sythesised by :
(a) smooth endoplasmic reticulum
(b) rough endoplasmic reticulum
(c) Golgi apparatus
(d) plastids
Answer:
(a) smooth endoplasmic reticulum

Question 15.
Cell arises from pre-existing cell was stated by :
(a) Haeckel
(b) Virchow
(c) Hooke
(d) Schleiden
Answer:
(b) Virchow

Question 16.
Cell theory was given by :
(a) Schleiden and Schwann
(b) Virchow
(c) Hooke
(d) Haeckel
Answer:
(a) Schleiden and Schwann

Question 17.
The only cell organelle seen in prokaryotic cell is :
(a) mitochondria
(b) ribosomes
(c) plastids
(d) lysosomes
Answer:
(b) ribosomes

Question 18.
Organelle without a cell membrane is :
(a) ribosome
(b) Golgi apparatus
(c) chloroplast
(d) nucleus
Answer:
(a) ribosome

Question 19.
1 μm is :
(a) 10^-6 m
(b) 10^-9 m
(c) 10^-10m
(d) 10^-3m
Answer:
(a) 10^-6 m

Question 20.
Lysosome arises from :
(a) endoplasmic reticulum
(b) Golgi apparatus
(c) nucleus
(d) mitochondria
Answer:
(b) Golgi apparatus

Question 21.
Living cells were discovered by :
(a) Robert Hooke
(b) Purkinje
(c) Leeuwenhoek
(d) Robert Brown
Answer:
(c) Leeuwenhoek

Question 22.
Name the organelles which show the analogy written as under :
(a) Transporting channels of the cell …………………
(b) Powerhouse of the cell …………………
(c) Packaging and dispatching unit of the cell …………………
(d) Digestive bag of the cell …………………
(e) Storage sacs of the cell …………………
(f) Kitchen of the cell …………………
(g) Control room of the cell …………………
Answer:
(a) endoplasmic reticulum
(b) mitochondria
(c) golgi body
(d) lysosome
(e) vacuole
(f) chloroplast
(g) nucleus

Question 23.
Match the items in column A with column B :

Column A	Column B
(i) Smooth endoplasmic reticulum	(a) Amoeba
(ii) Lysosome	(b) Nucleus
(iii) Nucleoid	(c) Bacteria
(iv) Food vacuoles	(d) Detoxification
(v) Chromatin material and nucleolus	(e) Suicidal bags

Answer:

Column A	Column B
(i) Smooth endoplasmic reticulum	(d) Detoxification
(ii) Lysosome	(e) Suicidal bags
(iii) Nucleoid	(c) Bacteria
(iv) Food vacuoles	(a) Amoeba
(v) Chromatin material and nucleolus	(b) Nucleus

Question 24.
Read the statements carefully and identify whether they are True or False-
1. Cell was first observed in radish plant.
2. Phagocytosis is the intake of liquid droplets.
3. Cell division takes place in prokaryotic cells.
4. Ribosomes are the smallest cellular organelle.
5. In the eukaryotic cells, mitochondria is absent.
Answer:
1. False
2. False
3. True
4. True
5. False

Very Short Answer Type Questions

Question 1.
What is plasma membrane made up of?
Answer:
Plasma membrane is made up of proteins and lipids.

Question 2.
Name the autonomous organelles in the cell.
Answer:
Chloroplast and mitochondria are the autonomous organelles in the cells.

Question 3.
Name the smallest cell and the longest cell in human body.
Answer:
The smallest cell is the red blood cell or sperm cell in male. The longest cell is the nerve cell.

Question 4.
What is diffusion?
Answer:
The process when gases like CO₂ and O₂, move across the cell membrane, is called diffusion.

Question 5.
What is the full form of DNA?
Answer:
DNA (Deoxyribose Nucleic Add).

Question 6.
Name the cell organelle that helps in packaging.
Answer:
Golgi apparatus.

Question 7.
Which organelle makes the digestive enzyme of lysosomes?
Answer:
Rough endoplasmic reticulum makes the digestive enzyme of lysosomes.

Question 8.
What are cisterns?
Answer:
The Golgi bodies consist of a system of membrane-bound vesides arranged in stacks called cisterns.

Question 9.
Name the cell organelles that have their own DNA and ribosomes.
Answer:
The cell organelles with their own DNA and ribosomes are mitochondria and plastids.

Question 10.
What is the role of cell organelles in the cell?
Answer:
Each kind of cell organelles performs a specific function such as making new material, dearing of the waste, transporting material, etc.

Question 11.
What is the energy currency of the cell?
Answer:
ATP – Adenosine Triphosphate.

Question 12.
What is the function of ribosomes?
Answer:
Ribosome helps in protein synthesis.

Question 13.
Where are genes located in the cell?
Answer:
Genes are located in the chromosomes in the nucleus of the cell.

Question 14.
Name the cell organelle which helps in the transportation of material.
Answer:
Endoplasmic reticulum.

Question 15.
Name the cell organelle due to which leaves, flowers and fruits get their colour.
Answer:
Chromoplast.

Question 16.
Name the cell organelle which helps in the formation of lysosomes.
Answer:
Golgi apparatus.

Question 17.
Name the cleaning organelle in the cell.
Answer:
Lysosomes.

Question 18.
(i) Name the largest animal cell.
(ii) Name the smallest cell.
Answer:
(i) An ostrich egg.
(ii) Pleuro pneumonia like organisms.

Question 19.
What is cell wall?
Answer:
Cell wall is the rigid outer covering of plasma membrane in plant cells.

Question 20.
What is the cell wall composed of?
Answer:
The cell wall is composed of cellulose.

Question 21.
Name the type of organism in which a single cell constitutes the whole organism.
Answer:
Organism in which a single cell constitutes the whole organism is unicellular organism.

Question 22.
Where are proteins synthesised inside the cell?
Answer:
The proteins are synthesised in the ribosomes, known as protein factories too.

Question 23.
Name two cells with cell wall.
Answer:
Onion cell (plant cell) and fungi are two cells with cell wall.

Question 24.
What is the function of chromosomes?
Answer:
Chromosomes contain information for the hereditary pattern of features from parents to next generation in the form of DNA molecules.

Question 25.
Name the organelles present in liver of animals which detoxifies many poisons and drugs.
Answer:
In the liver of animal cells, smooth endoplasmic reticulum .helps in detoxifying many poisons and drugs.

Question 26.
What are genes?
Answer:
Gene is a part of DNA. They are located on chromosomes in linear fashions. One gene may perform one or more functions. Genes are carrier of genetic characters.

Question 27.
What is the function of DNA?
Answer:
They are responsible for storing and transmitting hereditary information from one generation to another. They contain the information necessary for constructing and organising cells.

Question 28.
How are new cells reproduced?
Answer:
Cells multiply by dividing themselves again and again. Cells divide to produce cells of their own kind.

Question 29.
How does a living cell perform basic functions?
Answer:
A living cell perform basic functions by division of labour among specific components within it is known as cell organelles.

Question 30.
Write a function of cell membrane.
Answer:
Its major function is to hold cellular contents and control passage of materials in and out of the cell.

Question 31.
Give example of working of chromoplasts.
Answer:
Spinach looks green due to the presence of chloroplasts, papaya is yellow and edible part of watermelon is red due to the presence of chromoplasts.

Question 32.
Name various cell organelles.
Answer:
The cell organelles are : Endoplasmic Reticulum, Ribosomes, Golgi apparatus, Lysosomes, Mitochondria, Plastids, Vacuoles, Peroxisomes and Centrosomes.

Question 33.
Which cell organelle transmits the heredity information from parents to offspring?
Answer:
Genes are the functional units of chromosomes which transmit the heredity information from parents to offspring. These are located on chromosomes.

Short Answer Type Questions

Question 1.
How does fungi and bacteria can withstand much greater changes in the surrounding medium than animal cells?
Answer:
The cell wall present in fungi and bacteria permits these cells to resist very dilute external medium without bursting. Water is taken up by osmosis. Hence, cells swell up and build the pressure against the cell wall. The wall exerts an equal pressure against the swollen cell. It is because of the cell wall, such cells can resist much greater changes in the surrounding medium than animal cells.

Question 2.
State the difference between smooth endoplasmic reticulum and rough endoplasmic reticulum.
Answer:

Smooth endoplasmic reticulum	Rough endoplasmic reticulum
1. It looks smooth.	1. It looks rough.
2. SER helps in the manufacturing of fat molecules or lipids.	2. Ribosomes are attached to RER which synthesise proteins.

Question 3.
All cells come from pre-existing cells, justify.
Answer:
All organisms around are made up of one or more cells. There are single cells organism called unicellular like amoeba whereas some single bodies are made up of many cells called multicellular organism. Cells divide to produce cells of their own kind. Hence, all cells come from pre-existing cells.

Question 4.
What is the function of plastids?
Answer:
Plastids are present only in plant cells. There are two types of plastids, chromoplasts (coloured plastids) and leucoplasts (white or colourless).

Chromoplast : Consists of coloured pigments and gives different colours to flowers, fruits and leaves. The green colour pigment present in leaf is called chlorophyll which helps in the photosynthesis and a plastid with chlorophyll is called chloroplast.
Leucoplast: It stores starch, oil and protein granules in it.

Question 5.
What is the difference in chromatin, chromosomes and genes?

Chromatin	Chromosomes	Genes
It is a fine network of thread-like structure made up of DNA or RNA. It gets condensed to form chromosomes.	The chromosomes cue made from chromatin material and are located in the cell.	Genes are found in chromosomes.

Question 6.
List any six functions of nucleus of a cell.
Answer:

1. Nucleus plays a central role in cellular reproduction.
2. It plays an important role in determining the way the cell will develop.
3. It also determines what form the cell will exhibit at maturity.
4. It contains chromosome thus inherits characters.
5. It is the control centre of the cell.
6. It directs chemical activities of the cell.

Question 7.
What would happen when we put an animal cell into a solution of sugar or salt in water?
Answer:
The following three things could happen :

• If the solution surrounding the cell is very dilute than cytoplasm, the water will move into the cell, i.e. the cell will gain water.
• If the solution has exactly similar water concentration as that of cytoplasm of cell, there will be no net movement of water across the cell membrane, i.e. no gain or loss of water from the cell.
• If the medium (solution) has a lower concentration of water than the cell, i.e. the solution is concentrated, the cell will lose water by osmosis.

Question 8.
Who discovered cells in living organisms? Give an example of unicellular organism.
Answer:
Leeuwenhoek (1674) was the first to observe the free living cells in pond water.
Example of unicellular organisms: Amoeba, Chlamydomonas, Paramoeeium, Bacteria, etc.

Question 9.
Explain the structure and functions of Golgi bodies.
Answer:
Structures: Golgi bodies consist of a system of membrane-bound vesicles arranged in stacks parallel to each other called cisterns. These membranes have connections with the membrane of endoplasmic reticulum (ER).

Functions :

• The material synthesised near the ER is packaged and dispatched to various targets inside and outside the cell through Golgi apparatus.
• It also stores, modifies and helps in the packaging of products in vesicles.
• In some cases, complex sugars may be made from simple sugars in it.
• It also helps in the formation of lysosomes.

Question 10.
Name some organelles which are found only in animal cells and those which occur only in plant cells.
Answer:
1. Structures found only in animal cells: centrosomes, lysosome.
2. Structures found only in plant cells: cell wall, plastids and big vacuoles.

Question 11.
Give brief introduction of Prokaryotic and Eukaryotic cell.
Answer:
Prokaryotic cell:

1. Cell size is generally small.
2. Only a single chromosome is present.
3. Nucleolus is absent.
4. Cell division takes place by fission or budding.

Eukaryotic cell:

1. Cell size is generally large.
2. More than one chromosome is present.
3. Nudeolus is present.
4. Cell division takes place by mitotic or meiotic.

Question 12.
Give difference between organs and organdiles.
Answer:

Organs	Organelles
1. They are found in multicellular organisms.	1. They are found in all eukaryotic cells.
2. They are large sized.	2. They are very small sized.
3. They may be external or internal to the body of organisms.	3. They are mostly internal.

Question 13.
Give difference between light and electron microscope.
Answer:

Light microscope	Electron microscope
1. It uses glass lenses.	1. It uses electromagnets.
2. It uses a beam of light to illuminate the object.	2. It uses a beam of electrons instead of light.
3. Internal vacuum is not required.	3. Internal vacuum is essential.

Question 14.
Give difference between diffusion and osmosis.
Answer:

Diffusion	Osmosis
1. Diffusion can occur in any medium.	1. It occurs only in liquid medium.
2. The diffusing molecules may be solids, liquids or gases.	2. It involves movement of solvent molecules only.
3. Semipermeable membrane is not required.	3. Semipermeable membrane is required.
4. An equilibrium in the free energy of diffusion molecules is achieved in the system.	4. An equilibrium in the free energy of solvent molecules is never achieved.

Question 15.
Explain endocytosis.
Answer:
Endocytosis is the ingestion of material by the cells through the plasma membrane. It is a collective term that describes three similar processes : phagocytosis (cell eating), potocytosis (cell drinking) and receptor-mediated endocytosis. These processes are pathways of specifically internalise solid particles, small molecules and macromolecules, respectively.

Question 16.
Why do plant cells have more in number and big-sized vacuoles as compared to the animal cells?
Answer:
Plants cells attain turgidity and rigidity due to the more number of vacuoles as well as large-sized vacuoles help the plant cells to withstand the wear and tear, external environmental conditions. They also help in the storage of essential material required by plants for their growth like amino adds, sugar and various organic substances.

Question 17.
What is membrane biogenesis?
Answer:
The endoplasmic reticulum helps in the manufacture of proteins and fat molecules or lipids which are important for the cell function. These proteins and lipids help in the building of the cell membrane. This process is known as membrane biogenesis.

Question 18.
Expand the term ATP. What is the use of ATP?
Answer:
ATP stands for Adenosine Tri-phosphate
Application: ATP molecules are rich in chemical energy. The body cells use this energy for synthesis of new chemical compounds, and for mechanical work done by cells.

Question 19.
Name the cell organelles which are known as :
1. Control centre of the cell
2. Demolition squads/suicidal bags of the cell
3. Export firms
4. Powerhouse of the cell
5. Kitchen of the cell
6. Internal transport system
Answer:
1. Nucleus
2. Lysosomes
3. Golgi bodies
4. Mitochondria
5. Chloroplast
6. Endoplasmic reticulum

Question 20.
(i) What will happen when eukaryotic cells are placed in hypotonic solution?
(ii) What will happen if eukaryotic cells are placed in hypertonic solution?
(iii) What will happen if eukaryotic cells are placed in isotonic solution?
Answer:
(i) When eukaryotic cells are placed in hypotonic solution, the water molecules will enter into the cell and the cell will swell up.
(ii) If eukaryotic cells are placed in hypertonic solution, the water molecules will come out of the cell and the cell will shrink.
(iii) If the eukaryotic cell is placed in isotonic solution, the amount of water molecule will remain the same; it will neither move out nor will go inside. The cell will remain same sized.

Question 21.
What is lacking in a virus which makes it dependant on a living cell to multiply?
Answer:
Viruses do not have a basic structural organisation to perform various life processes in their own as they look selectively permeable process membrane. After entering in a living cell, a virus utilises its own genetic material and machinery of host cell to multiply.

Question 22.
What are the types of cell on the basis of the type of organisation?
Answer:

1. Prokaryotic cells: Cells which have less developed nudes and without nuclear membrane and nucleolus. These are primitive and incomplete cells, eg. bacteria.
2. Eukaryotic cells: Cells which have well developed nudes with nuclear membrane and nucleolus, e.g. plants and animals.

Question 23.
What are vacuoles?
Answer:
Vacuoles are fluid-filled structures surrounded by a membrane. The fluid in the vacuoles is called cell sap. In animal cells, either they are absent or are very small in size.

Question 24.
Give difference between Chloroplasts and Chromoplasts.
Answer:

Chloroplasts	Choromopiasts
1. They are green plastids.	1. They are non-green coloured plastids.
2. They contain chlorophylls and carotenoids.	2. Chlorophylls are absent.
3. Lamellae are present.	3. Lamellae are absent.
4. Chloroplasts are sites of photosynthesis.	4. They add colour to the organs for attracting animals to perform pollination and fruit dispersal.

Question 25.
Give difference between ribosome and centrosome.
Answer:

Ribosome	Cetotrosome
1. It is found in both animal cell and plant cell.	1. Centrosome is found only in animal cells.
2. These are dense, spherical and granular particles which occur freely in the matrix or remain attached to the endoplasmic reticulum.	2. It consists of two granules like centrioles.

Question 26.
What are the functions of endoplasmic reticulum and lysosome?
Answer:
(a) Functions of endoplasmic reticulum :

• It forms supporting skeletal framework of the cell.
• ER provides a pathway for the distribution of nuclear material from one cell to the other.

(b) Functions of lysosomes :

• Lysosomes serve as intracellular digestive system. They destroy any foreign material which enters in the cells such as bacteria and virus.
• Lysosomes also remove the worn out and poorly working cellular organelles by digesting them to make way for their new replacements.

Long Answer Type Questions

Question 1.
Give differences between hypotonic, isotonic solution and hypertonic solution.
Answer:

Hypotonic Solution	Isotonic Solution	Hypertonic Solution
1. External solution having higher concentration of water than the cell cytoplasm is known as hypotonic solution.	1. External solution having exactly the same concentration of water as that of cell cytoplasm is called isotonic solution.	1. External solution having lower concentration of water than the cell cytoplasm is called hypertonic solution.
2. Cell swells up in this solution.	2. Cell size does not alter.	2. Cell shrinks in this solution.

Question 2.
Write a note on the structure of a cell.
Answer:
(a) Cell is the basic unit of all living organisms. It is surrounded by an outer selectively permeable plasma membrane. Plant cells have an additional covering called “cell wall” outer to the plasma membrane.

(b) Inside the plasma membrane there is a translucent viscous substance, the cytoplasm in which the organelles are embedded. The control centre of the cell is the nucleus; it contains all the information necessary for the cell to function and reproduce. Surrounding of the nucleus is the endoplasmic reticulum (ER) on which ribosomes may be embedded. Ribosomes are granular structures which are the site of protein synthesis.

(c) The powerhouse of cell is the mitochondria. It helps in releasing energy by the oxidation of food in cell. There are flat membranous secretory structures in the cell which are called the Golgi bodies. In plant cells, an additional structure located near the nucleus called the chloroplast, is also present. They are the site of photosynthesis.

(d) Cells also contain lysosomes which are also called suicidal bags. They digest and remove the unwanted debris of the cell. Centriole located near the nucleus helps in cell division. Cytoplasm also contains vacuoles filled with the cell sap. In plant cells, vacuole is large and centrally placed.

Question 3.
Draw a neat labelled diagram of plant cell. Explain any two parts of it?
Answer:

1. Plastids : These are only found in plant cells. These are of two types :

• Chromoplast (coloured) and
• Leucoplast (Colourless)

(i) Chromoplast : Chromoplasts containing the pigment chlorophyll are known as chloroplasts. Chloroplasts are important for photosynthesis in plants. They also contain various yellow or orange pigments in addition to chlorophyll.

(ii) Leucoplast: These are white or colourless. These are primarily organelles in which materials such as starch, oils and protein granules are stored.

The internal organisation of the chloroplast consists of numerous membrane layers embedded in a material called the stroma. These are similar to mitochondria in external structure. These also have their own DNA and ribosomes like mitochondria.

2. Vacuoles: These are storage sacs for solid or liquid contents. In animal cells they are small sized but in plant cells, a single, prominent large vacuole is present. Many important substances for the life of plants are stored in vacuoles. It is helpful in expelling excess water.

Question 4.
Describe an activity to demonstrate endosmosis and exosmosis. Draw a diagram also.
Answer:
1. Endosmosis: The movement of water in the cell or a body through a semipermeable membrane is called endosmosis. It can be demonstrated as follows :
(i) Take some raisins with stalks and put them in plain water in a beaker.
(ii) Observation: Raisins absorb water and swell. Raisins have high concentration of sugar than surrounding plain water. Because of this, water from the outside passing through semipermeable membrane enters into the cell. This is endosmosis.

2. Exosmosis: The movement of water out from a cell or a body through a semipermeable membrane is called exosmosis. This can be demonstrated as follows :
(i) We place the swollen raisins (from above activity) into a beaker containing a concentrated solution of sugar or salt.
(ii) Observation: When swollen raisins are placed in concentrated sugar or salt solution, they shrink because the solution surrounding the raisins is having low water concentration. Thus, raisins loose water by osmosis, this process is called exosmosis.

Question 5.
Explain the structure of a nucleus. Give a neat labelled diagram of a nucleus of the cell. Give brief information about nucleus.
Answer:

Nucleus is the control centre of the cell. It is covered by a double layered envelope called nuclear membrane. The nuclear membrane has some pores which allow the transfer of material from inside the nucleus to cytoplasm. Inside the nuclear membrane some thread like structures are present. This is known as chromatin material.

The chromatin material is mainly formed through DNA (deoxyribonucleic acid) and proteins. When a cell starts to divide, chromatin material condenses into rat-shaped structures called chromosomes. The chromosomes contain DNA which are called genes.

The nucleus is a large, centrally located spherical cellular component. It is bounded by two nuclear membranes, both forming a nuclear envelope. The nuclear envelope separates the nucleus from the cytoplasm. Within nucleoplasm two types of nudear structures are embedded : the nucleolus and chromatin material. The nucleolus may be one or more in number and is not bounded by any membrane. It is rich in protein and RNA molecules and acts as the site for ribosome formation.

Question 6.
How do all cells look alike in, terms of shape and size?
Answer:
Cells vary in shapes and sizes according to the fusion. Generally, cells are spherical but they may be long and branched as in nerve cell, kidney shaped as guard cell in plant’s leaves, discoid as RBC, spindle shaped as musde cell, etc. Size of cell varies from 0.2 mm to 18 cm in diameter. Some are microscopic while some are visible with naked eyes.

For example :

• Size of a typical cell in a multicellular organism ranges from 20-30 mm.
• The largest cell is ostrich egg (15 cm in diameter with shell and 8 cm in diameter without shell).
• The longest cell is nerve cell (up to 1 m or more) and red blood cells are the smallest cell in our body.
• Smallest cells so far known are PPLOs, e.g. mycoplasma (0.1 mm in diameter).
• Human egg is 0.1 mm in diameter.

Question 7.
Explain fluid mosaic model of plasma membrane.
Answer:
According to fluid mosaic model, plasma membrane is made up of a bilayer of phospholipids. There are two types of protein molecules: Intrinsic proteins, which completely covers the lipid bilayer and Extrinsic proteins, which occur either on the outer surface or on the inner surface of the lipid membrane.

The fluid mosaic membrane has been described as “a number of protein icebergs floating in the sea of lipids”.

Question 8.
Give information about the mitochondria. Describe the structure of mitochondria.
Answer:
The mitochondria are tiny bodies of varying shapes and sizes. Each mitochondria is bounded by a double membrane envelope. Outer membrane is porous. The inner membrane is thrown into folds. These folds are called cristae and studded with small rounded bodies known as oxysomes. The interior cavity of the mitochondria is filled with a protein matrix which contains a few small-sized ribosomes, a circular DNA molecule and phosphate granules. Mitochondria are sites of cellular respiration.

Mitochondria are the membrane bound cell organelles found in the cytoplasm. Each mitochondria is a double membrane bounded structure. The outer membrane of mitochondria is smooth but, the inner membrane of the mitochondria is folded inwardly, into the matrix of mitochondria forming finger like projections. The inward finger like projections of inner membrane is called cristae. Cristae greatly increases the surface area of inner membrane. Mitochondria contains extra nuclear DNA.

Question 9.
Draw a labelled diagram of animal cell. Explain the structure and function of any four organelles.
Answer:

(1) Mitochondria: These are found in both animal cells and plant cells. It has two-membrane coverings. The outer membrane is porous while inner membrane is deeply folded. These folds increase surface area for ATP generating chemical reactions. They have their own DNA and ribosomes.

Function: It is known as the powerhouse of the cell. The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP molecules. ATP is called the energy currency of the cell. The body uses this energy stored in ATP for making new chemical compounds and for mechanical work.

(2) Lysosomes: Lysosomes are membrane-bound sacs filled with digestive enzymes. These enzymes are made by RER. So these are kind of waste disposal system of the cell.

Function: Lysosomes help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles. Foreign materials entering the cell like bacteria or food, as well as old organelles end up in the lysosomes which break complex substances into simpler substances. Lysosomes are able to do this because they contain powerful digestive enzymes capable of breaking down all organic material.

(3) Golgi bodies: Golgi bodies consist of a system of membrane-bound vesicles arranged in stacks parallel to each other called cisterns. These membranes have connections with the membrane of endoplasmic reticulum (ER).

Functions:

• The material synthesised near the ER is packaged and dispatched to various targets inside and outside the cell through Golgi apparatus.
• It also stores, modifies and helps in the packaging of products in vesicles.
• In some cases, complex sugars may be made from simple sugars in it.
• It also helps in the formation of lysosomes.

(4) Endoplasmic Reticulum (ER): It is a large network of membrane-bound tubes and sheets. It is similar in structure to the plasma membrane. They looks like long tubules or round or oblong bags.

There are two types of ER-rough ER (RER) and smooth ER (SER). RER looks rough under a microscope because it has particles called ribosomes to its surface. So these are sites of protein manufacture. SER does not have ribosomes, so it helps in manufacture of fat molecules or lipids. Some of these proteins and lipids help in building the cell membrane and this process is known as membrane biogenesis.

Function: ER serves as channels for the transport of materials between various regions of the cytoplasm or between the cytoplasm and nucleus. It also helps in manufacture of nucleus cell and golgi bodies. It helps in protein synthesis.