A. Fill in the blanks
- All living organisms are made up of cells.
- The cell wall provides rigidity and protection to the plant cell.
- All cellular activities are controlled by the nucleus.
- The mitochondria is known as the powerhouse of the cell.
- Tissue is a group of cells performing a specific function.
- It was Robert Hooke who observed cells for the first time.
B. Match the following
| Column I | Column II |
|---|---|
| 1. Golgi Complex | (d) packaging centre |
| 2. Ribosomes | (e) protein synthesis |
| 3. Chromosomes | (a) genes |
| 4. Dead cells | (b) cork |
| 5. Photosynthesis | (c) chloroplasts |
C. Tick (✓) the correct option
- The cell organelle which acts as a storage bag for a cell is known as the —
✅ vacuole - Hen’s egg is —
✅ a single cell - The nucleus is separated from the cytoplasm by the —
✅ nuclear membrane - Which of the following will not be found in an egg cell, human liver cell and an Amoeba?
✅ cell wall - Which of the following represents the correct sequence?
✅ cell → tissue → organ → organ system - Which, amongst the following pairs, can be found only in a plant cell but not in an animal cell?
✅ cell wall and plastids - D. Answer the following questions in brief
1. List the (main) factors that determine the shape of a cell.
The shape of a cell depends mainly on:
the function performed by the cell,
its location in the body,
and the structure of the cell membrane and cell wall.
For example, nerve cells are long and branched to help in carrying messages, while red blood cells are round and flat to transport oxygen easily.
2. Distinguish between unicellular and multicellular organisms. Give two examples of each.
Unicellular Organisms
Multicellular Organisms
Made up of only one cell.
Made up of many cells.
A single cell performs all life activities.
Different cells perform different functions.
Usually microscopic in size.
Usually larger and more complex.
Examples of unicellular organisms: Amoeba, Paramecium
Examples of multicellular organisms: Human beings, Mango tree
This difference shows how nature creates both simple and highly organized forms of life.
3. Give reasons for the following:
(a) The cell is called the structural and functional unit of life.
A cell is called the structural and functional unit of life because:
all living organisms are made up of cells,
and all life processes such as respiration, growth, nutrition and reproduction take place inside cells.
Just as bricks form a building, cells form the body of every living organism. Therefore, cells are the basic units that build and run life.
(b) Plant cells are more rigid than animal cells.
Plant cells are more rigid because they have a cell wall outside the cell membrane.
The cell wall provides:
strength,
shape,
protection,
and rigidity to the plant cell.
Animal cells do not have a cell wall, so they are softer and more flexible.
4. Which cell organelle is known as the “Powerhouse of the cell”? Why is it so called?
Mitochondria are known as the “powerhouse of the cell”.
They are called so because they produce energy by breaking down food during respiration. This energy is stored in the form of ATP and is used for all activities of the cell.
Without mitochondria, cells would not get the energy needed to survive and work.
5. Name the cell organelles responsible for imparting colour to the leaves and fruits of a plant.
The cell organelles responsible for imparting colour are called plastids.
Chloroplasts give green colour to leaves due to chlorophyll.
Chromoplasts give red, yellow and orange colours to fruits and flowers.
These colours make plants beautiful and also help in photosynthesis and attraction of insects for pollination.
| Basis | Cilia | Flagella |
|---|---|---|
| Definition | Short, hair-like structures present on the surface of a cell. | Long, whip-like structures present on the surface of a cell. |
| Function (Similarity) | Help in movement of the cell or substances around it. | Help in movement of the cell. |
| Size and Number (Dissimilarity) | Short and numerous. | Long and few in number. |
E. Answer the following questions
1. “All cells in an organism do not have the same shape.” Justify the statement by drawing at least three different cell types found in human beings.
All cells in the human body perform different functions. Therefore, they have different shapes and sizes suited to their work. The shape of a cell helps it to carry out its function efficiently.
Examples of different types of human cells
(a) Nerve Cell (Neuron)
- Long and branched in shape.
- Helps in carrying messages from one part of the body to another.
(b) Red Blood Cell (RBC)
- Round and biconcave disc-shaped.
- Helps in transporting oxygen in the blood.
(c) Muscle Cell
- Long and spindle-shaped.
- Helps in movement of body parts.
Thus, different cells have different structures because each cell is specialized for a particular function.
2. Where, and how, are chromosomes formed? State their significance.
Chromosomes are formed inside the nucleus of a cell.
They are formed from a thread-like material called chromatin. During cell division, chromatin fibres shorten and thicken to form chromosomes.
Chromosomes contain genes, which carry hereditary characters from parents to offspring.
Significance of chromosomes
- They control hereditary traits.
- They transfer genetic information from one generation to another.
- They help in cell division and growth.
- They control many activities of the cell.
Thus, chromosomes play an important role in maintaining continuity of life.
3. With the help of well labelled diagrams, highlight three differences between a plant cell and an animal cell.
| Plant Cell | Animal Cell |
|---|---|
| Cell wall is present. | Cell wall is absent. |
| Plastids are present. | Plastids are absent. |
| Vacuole is large and permanent. | Vacuoles are small and temporary. |
| Usually rectangular or fixed in shape. | Usually round or irregular in shape. |
| Centrosome is absent. | Centrosome is present. |
Additional Differences
- Plant cells usually have a fixed rectangular shape.
- Animal cells are generally irregular or round in shape.
Simple Diagram Idea
Plant Cell: Rectangular with cell wall, chloroplasts and large vacuole.
Animal Cell: Round or irregular without cell wall and plastids.
4. Write the functions performed by the following cell organelles.
(a) Endoplasmic Reticulum (ER)
- Helps in transport of materials inside the cell.
- Rough ER helps in protein synthesis.
- Smooth ER helps in fat synthesis.
(b) Golgi Complex
- Modifies, packages and secretes substances.
- Acts as the packaging and dispatch centre of the cell.
(c) Nucleus
- Controls all activities of the cell.
- Contains chromosomes and hereditary material.
(d) Chromoplasts
- Impart colour to fruits and flowers.
- Help attract insects and animals for pollination and seed dispersal.
(e) Vacuoles
- Store food, water and waste materials.
- Help maintain turgidity in plant cells.
(f) Mitochondria
- Release energy from food.
- Known as the powerhouse of the cell.
5. The cell membrane is a very important component of a cell. How is damage to the cell membrane likely to impact the functions of the cell?
The cell membrane controls the movement of substances into and out of the cell. It protects the internal contents of the cell and maintains proper balance.
If the cell membrane gets damaged:
- harmful substances may enter the cell,
- useful substances may leak out,
- exchange of materials becomes disturbed,
- and normal cellular activities stop.
As a result, the cell may not function properly and can even die. Therefore, the cell membrane is essential for the survival of the cell.
6. Define the term ‘cell’, for plants/animals. Name the different organelles that make a cell. Explain why none of these is called the structural and functional unit individually.
A cell is the basic structural and functional unit of life. All living organisms, including plants and animals, are made up of cells.
Main cell organelles
- Cell membrane
- Cytoplasm
- Nucleus
- Mitochondria
- Endoplasmic reticulum
- Golgi complex
- Ribosomes
- Vacuoles
- Plastids (in plant cells)
Each organelle performs a specific function, but no single organelle can perform all life activities independently.
For example:
- the nucleus controls activities,
- mitochondria provide energy,
- ribosomes make proteins,
- vacuoles store substances.
Only when all organelles work together does the cell function properly. Therefore, the entire cell—not any single organelle—is called the structural and functional unit of life.
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