Cell The Building Block of Life Class 9 Extra Questions and Answers Science Chapter 2

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Class 9 Science Chapter 2 Cell The Building Block of Life Extra Questions

Class 9 Science Chapter 2 Extra Questions on Cell The Building Block of Life

Cell The Building Block of Life Class 9 Very Short Question Answer

Question 1.
Where does the synthesis of ribosomal subunits take place?
Answer:
Nucleolus.

Question 2.
What is the limit of resolution of the human eye?
Answer:
0.1 mm.

Question 3.
Define osmosis.
Answer:
The movement of water from a region of a higher to a lower concentration through a selectively permeable membrane.

Question 4.
What is the cell wall made of in plant cells?
Answer:
Cellulose.

Question 5.
Name the green pigment found in chloroplasts.
Answer:
Chlorophyll.

Question 6.
What is a nucleoid?
Answer:
A nucleoid is a region in prokaryotic cells where the genetic material (DNA) is present, not enclosed by a nuclear membrane.

Question 7.
What is ATP?
Answer:
Adenosine Triphosphate (ATP) is energy currency of the cell.

Question 8.
Name the first stage of cell division.
Answer:
Prophase.

Question 9.
What is contact inhibition?
Answer:
Cell division stops when cells contact with neighbouring cells, preventing overcrowding and uncontrolled cell growth in the body.

Question 10.
What is the result of errors in mitosis?
Answer:
Tumours or abnormal chromosomes.

Cell The Building Block of Life Class 9 Short Question Answer

Question 1.
Why do plant cells have a cell wall but animal cells do not?
Answer:
Plant cells have a cell wall because they need extra support and protection. Plants usually stay fixed in one place, so their cells must be strong enough to keep the plant upright and maintain its shape.

The cell wall also prevents the cell from bursting when water enters it by osmosis. Animal cells do not have a cell wall because animals need their cells to be flexible for movement, bending, and changing shape.

Question 2.
State the Cell Theory.
Answer:
Cell Theory says that:

• All living organisms are made of cells.
• Cell is the basic structural and functional unit of life.
• All cells arise from pre-existing cells.

Question 3.
What happens when a plant cell and animal cell are placed in a concentrated sugar solution?
Answer:
A concentrated sugar solution is hypertonic, so water moves out of the cells by osmosis. In a plant cell, the cell membrane pulls away from the cell wall, and the cytoplasm shrinks.

The rigid cell wall prevents the cell from collapsing completely. In an animal cell, there is no cell wall, so the entire cell shrinks and becomes smaller.

Question 4.
Differentiate between RER and SER.
Answer:
The Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER) differ mainly in structure and function.

The RER has ribosomes attached to its surface, which gives it a rough appearance, and it is mainly involved in the synthesis and transport of proteins. In contrast, the SER does not have ribosomes and appears smooth; it is responsible for the synthesis of lipids (fats), hormones, and also helps in detoxification and storage within the cell.

Question 5.
Why does the skin of your finger shrink when you wash clothes for a long time? (NCERT Exemplar)
Answer:
When fingers stay in soapy water for a long time, water moves out of the skin cells by osmosis. The soap solution is more concentrated than the fluid inside the cells, so it acts as a hypertonic solution. Due to this, the cells lose water and shrink, making the skin of the fingers appear wrinkled or shrunken.

Question 6.
Which kind of plastid is more common in (NCERT Exemplar)
(a) roots of the plant
(b) leaves of the plant
(c) flowers and fruits
Answer:
(a) Leucoplast: These are found mostly in roots and other storage parts of the plant. They store food, especially starch, oils, and proteins. Since roots do not carry out photosynthesis, they do not need chlorophyll.

(b) Chioroplast: These are common in leaves because leaves prepare food by photosynthesis. They contain chlorophyll, the green pigment that absorbs sunlight. This helps the plant make its food.

(c) Chromoplast: These are found in flowers and fruits. They contain pigments like yellow, orange, and red, which are source of bright colours in flowers and fruits. These bright colours attract pollinators and animals that help in seed dispersal.

Question 7.
Why are onion root tips used to study cell division?
Answer:
Onion root tips are used because they are actively growing regions. Cells at the root tip divide continuously to help the root grow longer. Because many cells are dividing there, different stages of mitosis can be easily observed under a microscope after staining.

Question 8.
Why do plant cells possess large vacuoles? (NCERT Exemplar)
Answer:
Large vacuoles contain cell sap, which helps maintain the turgidity of a cell. This is especially important for plant cells because they are always exposed to the environmental changes. A vacuole also stores important substances such as water, nutrients, and waste products.

Question 9.
Why do cancer cells form tumors?
Answer:
Cancer cells form tumors because they lose control over cell division. Normally, cells stop dividing when they touch neighbouring cells, a process called contact inhibition. Cancer cells ignore this signal and keep dividing again and again. This uncontrolled growth forms a mass of cells called a tumor.

Question 10.
A person takes a concentrated solution of salt, and after some time, he starts vomiting. What is the phenomenon responsible for such a situation? Explain. (NCERT Exemplar)
Answer:
Swallowing a concentrated solution of salt results in osmosis from the cells of the alimentary canal. Due to this, dehydration occurs in the person, leading to irritation and imbalance in the digestive system. As a result, the person starts vomiting.

Question 11.
If you are provided with some vegetables to cook, you generally add salt into the vegetables during cooking process. After adding salt, veqeta bies release water. What mechanism is responsible for this?
Answer:
When salt is sprinkled on vegetables, the surrounding medium becomes hypertonic. This facilitates movement of water outside the cells. Due to this. vegetables release water when salt is added to them.

Question 12.
What is contact inhibition and what happens when it fails?
Answer:
Contact inhibition is the natural process by which normal cells stop dividing when they come into contact with neighbouring cells, ensuring controlled growth and proper tissue organisation. When this mechanism fails, cells lose control over their division and continue to multiply even after touching other cells. This uncontrolled division leads to the formation of abnormal masses of cells called tumors, which may further develop into cancerous growths if not regulated.

Question 13.
How is a bacterial cell different from an onion peel cell?
Answer:

Bacterial cell	Onion peel cell
(i) These are prokaryotes.	These are eukaryotes.
(ii) Nucleus is absent.	Nucleus is present.
(iii) Vacuole is absent.	Vacuole is present.
(iv) Membrane-bound organelles absent.	Membrane-bound organelles present.

Cell The Building Block of Life Class 9 Long Question Answer

Question 1.
Explain the differences between prokaryotic and eukaryotic cells.
Answer:
A prokaryotic cell carries out most of its activities directly in the cytoplasm because it does not have membrane-bound organelles. A eukaryotic cell, on the other hand, has well-developed, membrane-bound organelles that divide cellular functions, which makes its functioning more organised and efficient.

Feature	Prokaryotic cells	Eukaryotic cells
Nucleus	Absent; nucleoid Present	Present
Nuclear membrane	Absent	Present
Membrane-bound organelles	Present	Absent
Size	Usually 1 – 10 µm	Usually 10 – 100 µm
Number of cells	Usually unicellular	Unicellular or multicellular
DNA	Circular	Linear chromosomes
Ribosomes	Smaller	Larger
Examples	Bacteria	Plant and animal cells

Question 2.
Explain the lipid bilayer with proteins; a flexible and dynamic structure with a well- labeled diagram.
Answer:
The cell membrane is made of a lipid bilayer with proteins embedded in it. The lipids form two layers, with water-attracting heads facing outward and water-repelling tails facing inward, creating a barrier that separates the cell from its surroundings. Proteins are placed within or on the surface of this bilayer and help in transport. cell signaling, and recognition.

This structure is described by the fluid-mosaic model because the membrane is not rigid. The lipids and some proteins can move sideways within the layer, so the membrane is flexible and dynamic. This flexibility helps the cell membrane function properly during the movement of substances in and out of the Cell.

Question 3.
Differentiate between plant, and animal cell.
Answer:

Cell Structures	Plant Cell	Animal cell
1. Cell membrane	Present	Present
2. Cell wall	Present	Absent
3. Cytoplasm	Present	Present
4. Well-defined nucleus (genetic material enclosed by a membrane)	Present	Present
5. Primitive nucleus (nucleoid) (genetic material without membrane around it)	Absent	Absent
6. Membrane-bound organelles	Present	Present

Question 4.
Describe structure/function of
(i) Nucleus
(ii) Ribosomes
(iii) Endoplasmic Reticulum (ER).
Answer:
(i) Nucleus: The nucleus is the control centre of the cell. It is surrounded by a double membrane called the nuclear membrane, which has pores for exchange of materials between the nucleus and cytoplasm.

Inside the nucleus, chromatin contains DNA, which condenses into chromosomes during cell division. The nucleolus inside the nucleus helps in the formation of ribosomal subunits.

The nucleus stores hereditary information and passes it from one generation of cells to the next. It also regulates cell activities by controlling the expression of genes. Because of this, the nucleus is essential for growth, repair. and reproduction.

(ii) Ribosomes: These are tiny particles found either free in the cytoplasm or attached to rough endoplasmic reticulum. They are the sites of protein synthesis, meaning they help assemble amino acids into proteins according to genetic instructions. Ribosomes are essential because proteins are needed for growth, repair, enzymes. hormones, and many other cell functions. In both prokaryotic and eukaryotic cells, they are present, but eukaryotic ribosomes are larger and more complex.

(iii) Endoplasmic Reticulum (ER): The endoplasmic reticulum is a network of membranes spread throughout the cytoplasm. It is continuous with the nuclear envelope and helps in transport and synthesis inside the cell. There are two main types: RER and SER.

RER has ribosomes on its surface, so it looks rough, and it mainly helps in protein synthesis and transport. SER does not have ribosomes, so it looks smooth, and it mainly helps in lipid synthesis and storage. The ER acts like an internal transport and manufacturing system of the cell.

Question 5.
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.
Answer:
(a) Nucleus
(b) Golgi body
(c) Cell wall
(d) Cytoplasm

Question 6.
Draw a well-labelled diagram of an eukaryotic nucleus. How is it different from nucleoid?
Answer:

Nucleus	Nucleoid
(i) Nuclear membrane is present.	(i) Nuclear membrane absent.
(ii) Nucleolus present.	(ii) Nucleolus absent.
(iii) Genetic materials are enclosed in nucleus.	(iii) Genetic materials are not contained in any closed structure.
(iv) Found in eukaryotes.	(iv) Found in prokaryotes.

Question 7.
A student observes two slides in the lab under the microscope, slide A and slide B. The diagrams of the same are shown below:

(a) Which slide contained the plant cell?
(b) How were you able to distinguish the difference?
(c) Draw plant ccli you see under the microscope, and label the following parts Cell wall, cell membrane, nucleus, cytoplasm and vacuole.
Answer:
(a) The slide A shows plant cell.
(b) The plant cells have a cell wall and several vacuoles.
(c)

Cell The Building Block of Life Class 9 Quiz Questions

Question 1.
What is the function of mitochondria?
Answer:
Energy production

Question 2.
Which microscope is used to observe proteins?
Answer:
Electron microscope

Question 3.
What is the full form of ATP?
Answer:
Adenosine Triphosphate

Question 4.
Which organelle is responsible for packages proteins?
Answer:
Golgi apparatus

Question 5.
Which infectious agent lacks protein coat?
Answer:
Viroid

Question 6.
How many cells are formed in meiosis?
Answer:
Four

Question 7.
What is the maximum magnification of a light microscope?
Answer:
Approx. 1000X

Question 8.
What does “resolution” mean in microscopy?
Answer:
Ability to distinguish two close objects

Question 9.
Which organelle controls cell activities?
Answer:
Nucleus

Question 10.
Which type of cell division produces identical cells?
Answer:
Mitosis

Cell The Building Block of Life Class 9 Skill Based Questions

Question 1.
Draw a well-labeled diagram of the microscope that is used in your school laboratory. Also, mention the following:
(i) Its uses.
(ii) Formula to calculate the estimated size of cell.

(i) It is used to observe the cells and microorganisms not visible to the naked eye. To study plant and animal tissues.
To examine the fine structures of various structures.

(ii) Estimated size of cell:
\(=\frac{\begin{array}{c}
\text { Diameter of the visible field in } \\
\text { micrometre }
\end{array}}{\text { Number of cells along the diameter }}\)

Question 2.
(i) Draw a well-labelled diagram showing a typical structure of a nucleus.
(ii) Identify the parts of an animal cell with the help of the given clues.
(a) A – It is the packaging organelle
(b) B – Provides energy
(c) C – Helps in the transport of material
(d) D – Carries the information.

Answer:

(ii)
(a) A – Golgi apparatus
(b) B – Mitochondria
(e) C – Endoplasmic Reticulum
(d) D – Nucleus

Cell The Building Block of Life Class 9 Case Based Questions

Question 1.
Early Earth had extreme conditions such as high temperature, volcanic activity, and intense radiation. Scientists believe life may have originated in water bodies like hot springs. In places like Puga Valley (Ladakh), thermophilic bacteria survive even today. Calcium carbonate deposits in such environments may have protected early molecules and helped form primitive cell membranes. These membranes allowed the first cells to exist and function.
I. Why are hot springs considered important in the origin of life?
II. What are thermophiles?
III. How did calcium carbonate help early life?
OR
What is the importance of a cell membrane?
Answer:
I. Hot springs provide conditions similar to early Earth, such as high temperature and mineral-rich environments, which may have supported the formation of life.
II. Thermophiles are heat-loving microorganisms.
III. Calcium carbonate helped protect early organic molecules from harsh conditions and may have provided a surface for the formation of primitive cell membranes.
OR
The cell membrane acts as a selectively permeable protective boundary, regulating the movement of substances in and out of the cell, which is essential for survival.

Question 2.
A student compared two types of cell division based on number of divisions and daughter cells formed. One process produced two identical daughter cells, while the other produced four non-identical cells with half chromosome number. This comparison helps in understanding their roles in growth and reproduction.
Data Table:

Feature	Process X	Process Y
No.of Divisions	1	2
No.of Daughter cells	2	4
Chromosome number in daughter cells	Same	Half

Answer the following questions based on the above information.
(i) Identify process Y:
(a) Mitosis
(b) Meiosis
(c) Fusion
(d) Budding
Answer:
(b) Meiosis

(ii) Which process causes variation?
(a) Y
(b) X
(c) Both
(d) None
Answer:
(a) Y

(iii) Why is chromosome number halved in process Y?
(i) Reduce size
(ii) Maintain number after fertilisation
(iii) Stop division
(iv) Increase energy
OR
How many daughter cells are formed in mitosis?
(a) 1
(b) 3
(c) 2
(d) 4
Answer:
(b) or (c)

Suggested Projects and Activities

Question 1.
Make a 3D plant or animal cell model using food items (e.g., Jell-O for cytoplasm, candies for organelles like mitochondria as powerhouse grapes, nucleus as fruit ball) to represent the tiny living factory analogy. Justify organelle placements and functions (e.g., Golgi as post office with stacked wafers), then evaluate: How does fluidity of the lipid bilayer affect worker (protein) movement?

Question 2.
Stage a skit showing mitosis/meiosis errors (e.g., uncontrolled division as cancer tumor growth, meiosis faults causing genetic disorders), using puppets for stages and chromosomes. Students evaluate the loss of contact inhibition in animal cells and compare it with the role of the plant cell wall in regulating cell growth and division.

Question 3.
Using wilted versus swollen leaves (e.g., spinach in salt water overnight), measure length /weight changes and hypothesise vacuole role in turgor pressure. Apply cell wall permeability, create/demonstrate a model showing plasmolysis (membrane pulls from wall) vs. animal cell shrinkage. Finally, evaluate plant survival without cell wall and justify your reasoning.

Cell The Building Block of Life Extra Questions for Practice

Multiple Choice Questions

Question 1.
Which cells lack well-defined nucleus?
(a) Plant cells
(b) Animal cells
(c) Bacterial cells
(d) Fungal cells

Question 2.
In potato osmosis experiment, the potato piece in salt solution
(a) swells
(b) shrinks
(c) remains same
(d) bursts.

Question 3.
What is the basic structure of a virus?
(a) Only protein
(b) Only DNA
(c) Genetic material + protein coat
(d) Cell membrane + cytoplasm

Question 4.
Read the given statements and select the correct option.
Assertion (A): Ribosomes are the sites of protein synthesis.
Reason (R): Ribosomes are made up of RNA and proteins.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.

Question 5.
Match the items in Column A to those in Column B.

Column A	Column B
(i) Nucleus	(p) Protein synthesis
(ii) Mitochondria	(q) Photosynthesis
(iii) Ribosomes	(r) Control centre
(iv) Chioroplast	(s) Energy production

(a) (i) -(r) (ii)-(s), (iii)-(p), (iv)-(q)
(b) (i)-(s), (ii)-(r), (iii)-(p), (iv)-(q)
(c) (i)-(r), (ii)-(p), (iii)-(s), (iv)-(q)
(d) (i)-(q), (ii)-(s), (iii)-(r), (iv)-(p)

Very Short Answer Type Questions

Question 1.
What are thermophiles?

Question 2.
Name the two main types of cell division.

Question 3.
Why do cells divide instead of just growing bigger?

Question 4.
What happens in meiosis regarding chromosome number?

Question 5.
How do substances like carbon dioxide (CO₂) and water (H₂O) move in and out of the cell?

Short Answer Type-I Questions

Question 1.
Differentiate between osmosis and diffusion.

Question 2.
What is the fluid-mosaic model of cell membrane?

Question 3.
What are consequences of errors in meiosis?

Question 4.
Why do plant cells have a cell wall but animal cells do not?

Question 5.
What happens when a plant cell and animal cell are placed in a concentrated sugar solution?

Short Answer Type-II Questions

Question 1.
Explain mitosis and meiosis.

Question 2.
How do microscopes help in studying cells?

Question 3.
Explain hypotonic, hypertonic, and isotonic solution.

Question 4.
Why are plant cells rectangular and animal cells irregular in shape? Also, write the functions of cell wall.

Question 5.
Write down the importance of nucleus.

Long Answer Type Questions

Question 1.
Describe functions of following cell organelles. Endoplasmic Reticulum, Golgi, Mitochondria, Lysosomes, Plastids, Vacuole.

Question 2.
Explain cell membrane structure (fluid-mosaic) and functions with a well-labelled diagram.

Question 3.
Describe the observations made in a potato osmosis experiment when potato pieces are placed in different solutions. Explain the reason for these observations.

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