Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
The Cell — Exercise Solutions
Use this page alongside the official Samacheer Kalvi textbook. Solve every exercise question on your own first, then check the solutions below.
I. Multiple Choice Questions (MCQs)
Q1. The unit of measurement used for expressing dimension (size) of cell is
- (a) centimetre
- (b) millimetre
- (c) micrometre
- (d) metre
Cells are microscopic and their sizes are typically measured in micrometres (µm). One micrometre equals one-thousandth of a millimetre. Most cells range from 1 to 100 micrometres in size.
Q2. Under the microscope Priya observes a cell that has a cell wall and a distinct nucleus. The cell that she observed is
- (a) a plant cell
- (b) an animal cell
- (c) a nerve cell
- (d) a bacteria cell
A cell wall is present only in plant cells, not in animal cells. The presence of a distinct nucleus confirms it is a eukaryotic cell (plant cells are eukaryotic). Bacteria are prokaryotic and lack a distinct nucleus.
Q3. A 'control centre' of the eukaryotic cell is
- (a) Cell wall
- (b) Nucleus
- (c) Vacuoles
- (d) Chloroplast
The nucleus regulates all cell activities — growth, metabolism, protein synthesis, and cell division — earning it the title "control centre" of the cell.
Q4. Which one of the following is not a unicellular organism?
- (a) Yeast
- (b) Amoeba
- (c) Spirogyra
- (d) Bacteria
Spirogyra is a multicellular green alga made up of many cells arranged in a filament. Yeast, Amoeba, and Bacteria are all unicellular (single-celled) organisms.
Q5. Most organelles in a eukaryotic cell are found in the
- (a) Cell wall
- (b) Cytoplasm
- (c) Nucleus
- (d) Vacuole
The cytoplasm is the jelly-like substance that fills the cell and houses most organelles such as mitochondria, ribosomes, endoplasmic reticulum, Golgi body, and vacuoles. The cell wall is outside the cell and the nucleus contains its own contents.
Q6. Which one is a prokaryotic cell?
- (a) Plant cell
- (b) Animal cell
- (c) Nerve cell
- (d) Cyanobacteria cell
Cyanobacteria (blue-green algae) are prokaryotic organisms. They lack a well-defined nucleus and membrane-bound organelles. Plant cells, animal cells, and nerve cells are all eukaryotic.
Q7. The habitat of Escherichia coli bacteria is
- (a) Soil-inhabiting
- (b) Human intestine
- (c) Aquatic
- (d) Air
E. coli is a bacterium that naturally lives in the intestines of humans and warm-blooded animals. It helps in digestion and produces vitamin K.
Q8. A typical cell consists of ___ major parts.
- (a) Two
- (b) Four
- (c) Three
- (d) Five
A typical cell consists of three major parts: (1) Cell membrane, (2) Cytoplasm, and (3) Nucleus.
Q9. The approximate number of cells in the human body is
- (a) 3.7 × 10¹²
- (b) 3.7 × 10¹³
- (c) 3.7 × 10¹⁴
- (d) 3.7 × 10¹⁵
The human body contains approximately 37 trillion (3.7 × 10¹³) cells. These cells vary in size and shape depending on their function.
Q10. Prokaryotic cell type of nucleus is called
- (a) Nucleolus
- (b) Nuclear membrane
- (c) Organelles
- (d) Nucleoid
Prokaryotic cells do not have a well-defined nucleus. Their genetic material is found in a region called the nucleoid, which is not enclosed by a nuclear membrane.
II. Fill in the Blanks
1. The instrument used to observe the cell is microscope.
2. I control the food production of a cell. Who am I? Chloroplast
3. I am like a policeman. Who am I? Cell wall
4. The term "cell" was coined by Robert Hooke.
5. The egg of an Ostrich is the largest single cell.
6. Cell is the basic structural and functional unit of every living organism.
7. Nowadays an electron microscope is used to magnify the cells.
8. In Latin, the word 'cellula' means a small chamber.
9. The branch of science that deals with the study of cells is called cell biology.
10. The outer covering part of the cell is called cell membrane.
11. Prokaryotic cells were the first form of life on earth.
12. Chloroplast is present in plant cells only.
13. Plants prepare food with the help of chlorophyll.
III. True or False (with Corrections)
Q1. A cell is the smallest unit of life.
The cell is indeed the smallest structural and functional unit of life. All living organisms are made up of cells.
Q2. Nerve cell is the longest cell.
Nerve cells (neurons) can extend up to a metre or more in length, making them the longest cells in the human body. They connect the spinal cord to the toes.
Q3. Prokaryotes were the first form of life on earth.
Prokaryotic organisms (like bacteria) appeared about 3.5 billion years ago, long before eukaryotic cells evolved.
Q4. The organelles of both plants and animals are made up of cells.
Organelles are structures within cells. Since both plant and animal bodies are made up of cells, their organelles are also contained within cells.
Q5. New cells are produced from existing cells.
This is a fundamental principle of cell theory: all cells arise from pre-existing cells through cell division.
Q6. The cell is self-sufficient and carries out all the fundamental and essential functions of an organism.
Each cell performs essential life functions like respiration, nutrition, excretion, and reproduction, making it self-sufficient.
Q7. Robert Hooke saw many objects like Butterfly's compound eyes, Bee's wings, etc.
Correction: Robert Hooke observed thin slices of cork under his microscope and saw honeycomb-like structures. It was Antonie van Leeuwenhoek who observed living microorganisms and various other objects like butterfly wings, bee compound eyes, etc.
Q8. All cells can be seen with our naked eye.
Correction: Most cells are microscopic and cannot be seen with the naked eye. Only a few cells, like the egg of an ostrich (the largest single cell), are large enough to be seen without a microscope.
Q9. The size of a bacterial cell ranges from 0.01 micrometre to 0.5 micrometres.
Bacterial cells are among the smallest cells, typically ranging from 0.5 to 5 micrometres. Some very small bacteria can be as small as 0.1–0.5 micrometres.
Q10. Spirogyra and human beings are unicellular.
Correction: Spirogyra and human beings are multicellular organisms. Spirogyra is a filamentous alga made of many cells, and human beings have trillions of cells.
IV. Match the Following
| # | Column A | Column B | Correct Match |
|---|---|---|---|
| 1 | Control centre | (a) Cell membrane | Nucleus |
| 2 | Food producer (Plant cell) | (b) Mitochondria | Chloroplasts |
| 3 | Gate of the nucleus | (c) Nucleus | Nuclear membrane |
| 4 | Gate of the cell | (d) Chloroplasts | Cell membrane |
| 5 | Energy producer | (e) Nuclear membrane | Mitochondria |
Explanations:
1. Nucleus — Controls all activities of the cell; hence called the control centre. 2. Chloroplasts — Contain chlorophyll and produce food through photosynthesis in plant cells. 3. Nuclear membrane — Surrounds the nucleus and acts as its gate, controlling what enters and exits. 4. Cell membrane — Surrounds the cell and controls the movement of substances in and out; acts as the gate of the cell. 5. Mitochondria — Produce energy in the form of ATP; called the "powerhouse" of the cell.
V. Arrange in Correct Sequence
Q1. Elephant, Cow, Bacteria, Mango, Rose plant
Arrange from smallest to largest. Bacteria is a microscopic unicellular organism. Rose plant and mango tree are multicellular plants (mango tree grows larger). Cow and elephant are multicellular animals, with the elephant being the largest.
Q2. Hen egg, Ostrich egg, Insect egg
Arrange from smallest to largest cell/egg. Insect eggs are tiny (often less than 1 mm), hen eggs are a few centimetres, and ostrich eggs are the largest single cells (about 15 cm long).
VI. Analogy
Complete the analogy by filling in the missing term.
1. Prokaryote : Bacteria :: Eukaryote : Plant or animal cell
Prokaryotes are organisms without a true nucleus (like bacteria). Eukaryotes have a well-defined nucleus (like plant and animal cells).
2. Spirogyra : Plant cell :: Amoeba : Animal cell
Spirogyra is a plant (alga) and Amoeba is an animal-like protozoan.
3. Food producer : Chloroplasts :: Powerhouse : Mitochondria
Chloroplasts produce food (by photosynthesis), and mitochondria produce energy (ATP) — hence called the powerhouse.
4. Smallest cell : Bacteria :: Biggest cell : Ostrich egg
Bacteria are among the smallest cells; the ostrich egg is the largest single cell.
5. No true nucleus : Prokaryotic cell :: True nucleus : Eukaryotic cell
Prokaryotic cells lack a true nucleus (nuclear membrane), while eukaryotic cells have a well-defined nucleus.
6. Plant cell : Chloroplast :: Animal cell : Centrioles
Chloroplasts are unique to plant cells. Centrioles are unique to animal cells (they help in cell division).
VII. Very Short Answer Questions
Q1. Who discovered the cell in 1665?
Q2. What type of cells do we have?
Q3. What are the essential components of a cell?
Q4. What are the organelles found only in plant cells?
Q5. Give any three examples of eukaryotic cells.
Q6. Which one is called the "Area of movement"?
Q7. Shiva said, "Bigger onion has larger cells when compared to the cells of smaller onion!" Do you agree?
VIII. Short Answer Questions
Q1. Why are cells called the building blocks of life?
Q2. Identify any four parts of a plant cell.
Q3. Distinguish between prokaryotic and eukaryotic cells.
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| Size | Small (1–2 µm) | Large (10–100 µm) |
| Nucleus | No well-defined nucleus (nucleoid) | Well-defined nucleus with nuclear membrane |
| Nuclear membrane | Absent | Present |
| Membrane-bound organelles | Absent | Present (mitochondria, ER, Golgi, etc.) |
| Nucleolus | Absent | Present |
| Cell wall | Present (made of peptidoglycan in bacteria) | Present in plant cells (cellulose); absent in animal cells |
| Examples | Bacteria, Cyanobacteria | Plant cell, Animal cell, Fungi |
Q4. Make sketches of animal and plant cells that you observe under the microscope. List the differences.
Plant Cell
- Larger in size
- Rectangular in shape
- Has a rigid cell wall outside the cell membrane
- Contains chloroplasts (green organelles for photosynthesis)
- Has a large central vacuole
- Stores food as starch
- Does not have centrioles
Animal Cell
- Smaller in size
- Round or irregular in shape
- No cell wall; only cell membrane
- No chloroplasts
- Has many small vacuoles or none
- Stores food as glycogen
- Has centrioles (help in cell division)
Q5. Write about the contribution of Robert Hooke in cell biology.
1. He improved the design of the compound microscope in the 17th century. 2. In 1665, he observed thin slices of cork (the bark of an oak tree) under his microscope. 3. He saw many small, identical, hexagonal chambers that resembled the small rooms (cells) in which monks lived. 4. He coined the term "cell" (from the Latin word cellula meaning "small chamber") to describe these structures. 5. He published his observations in a famous book called Micrographia in 1665, which contained detailed drawings of what he saw under the microscope.
Robert Hooke's discovery marked the beginning of cell biology as a field of study.
IX. Detailed / Long Answer Questions
Q1. Tabulate any five cell organelles and their functions.
| S.No. | Cell Organelle | Function |
|---|---|---|
| 1 | Nucleus | Controls all cell activities; contains genetic material (DNA); called the "brain" or "control centre" of the cell |
| 2 | Mitochondria | Produces energy in the form of ATP through respiration; called the "powerhouse of the cell" |
| 3 | Chloroplast | Prepares food by photosynthesis using sunlight, CO₂, and water; contains the green pigment chlorophyll; present only in plant cells |
| 4 | Cell wall | Provides rigidity, shape, and protection to the cell; acts as a supporter and protector; present only in plant cells |
| 5 | Vacuole | Stores water, nutrients, and waste products; plant cells have a large central vacuole; animal cells have small or no vacuoles |
Other important organelles:
| S.No. | Cell Organelle | Function |
|---|---|---|
| 6 | Cell membrane | Controls the movement of substances in and out of the cell; called the "gate of the cell" |
| 7 | Nuclear membrane | Surrounds the nucleus; controls movement of materials in and out of the nucleus; called the "gate of the nucleus" |
| 8 | Endoplasmic reticulum | Transports materials within the cell; helps in protein and lipid synthesis |
| 9 | Golgi body | Packages and distributes materials within and outside the cell |
| 10 | Ribosomes | Site of protein synthesis |
Q2. Compare plant cell and animal cell.
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Size | Larger (10–100 µm) | Smaller (10–30 µm) |
| Shape | Rectangular (fixed shape due to cell wall) | Round or irregular (no fixed shape) |
| Cell wall | Present (made of cellulose) | Absent |
| Cell membrane | Present (inside the cell wall) | Present (outermost boundary) |
| Chloroplasts | Present (for photosynthesis) | Absent |
| Vacuoles | One large central vacuole | Small and many, or absent |
| Centrioles | Absent | Present (help in cell division) |
| Nucleus | Present | Present |
| Mitochondria | Present (fewer) | Present (more numerous) |
| Food storage | Stores food as starch | Stores food as glycogen |
| Lysosomes | Few or absent | Present |
Q3. Describe the structure and function of the nucleus.
Structure of the Nucleus
The nucleus is a large, spherical or oval structure located near the centre of the cell. It consists of:
1. Nuclear membrane — A double-layered membrane that surrounds the nucleus. It has pores that allow the transfer of materials between the nucleus and the cytoplasm. It is called the "gate of the nucleus." 2. Nucleoplasm — The jelly-like substance inside the nucleus, similar to the cytoplasm. 3. Chromatin / Chromosomes — Thread-like structures made of DNA and proteins. They carry the genetic information that is passed from parent to offspring. 4. Nucleolus — A small, dense, spherical body inside the nucleus that produces ribosomes.
Functions of the Nucleus
1. Control centre — Controls all metabolic activities of the cell. 2. Genetic information — Stores and transmits genetic material (DNA) from one generation to the next. 3. Cell division — Directs cell division by controlling chromosome replication. 4. Protein synthesis — Controls protein synthesis by sending instructions through messenger RNA (mRNA).
Q4. Draw a neat labelled diagram of a prokaryotic cell and describe its features.
A prokaryotic cell (e.g., a bacterial cell) has the following features:
1. Cell wall — Outermost rigid layer that gives shape and protection. 2. Cell membrane — Thin membrane just inside the cell wall; controls entry and exit of materials. 3. Capsule — A slimy outer layer in some bacteria that provides extra protection. 4. Nucleoid — The region where the genetic material (DNA) is present. It is NOT enclosed by a nuclear membrane — this is the key difference from eukaryotic cells. 5. Ribosomes — Small particles for protein synthesis; these are NOT membrane-bound. 6. Flagellum (plural: flagella) — A whip-like tail for movement (present in some bacteria). 7. Plasmid — A small circular DNA separate from the main DNA.
Key differences from a eukaryotic cell:
- No well-defined nucleus
- No nuclear membrane
- No membrane-bound organelles (no mitochondria, no chloroplast, no Golgi body, no endoplasmic reticulum)
Q5. Write a note on the microscope and its importance in cell biology.
What is a Microscope?
A microscope is an instrument used to see objects that are too small to be seen with the naked eye. It magnifies tiny structures so we can study them.
Types of Microscopes
1. Simple Microscope — Uses a single lens to magnify objects. It was the earliest type of microscope used. 2. Compound Microscope — Uses two or more lenses (eyepiece lens + objective lens) to produce higher magnification. Robert Hooke used a compound microscope to observe cork cells. This is the type commonly used in school laboratories. 3. Electron Microscope — Uses a beam of electrons instead of light. It can magnify up to 2 million times, revealing the ultrastructure of cells and organelles.
Importance in Cell Biology
- Discovery of cells — Robert Hooke used a microscope to discover cells in 1665.
- Understanding cell structure — Microscopes revealed the details of cell organelles like mitochondria, chloroplasts, and ribosomes.
- Studying microorganisms — Antonie van Leeuwenhoek observed bacteria, protozoa, and other microorganisms using a microscope.
- Medical diagnosis — Microscopes help identify disease-causing microorganisms, cancer cells, and blood disorders.
- Cell research — Electron microscopes allow scientists to study the detailed internal structure of cells at the molecular level.
Common Mistakes to Avoid
1. Confusing cell wall with cell membrane. The cell wall is the outermost rigid layer found only in plant cells. The cell membrane is a thin, flexible layer found in all cells (both plant and animal). In plant cells, the cell membrane lies just inside the cell wall.
2. Saying "cell is the smallest unit" without clarifying. Always say: "The cell is the smallest structural and functional unit of life." A cell is not just small — it is the fundamental unit that performs all life functions.
3. Confusing prokaryotic with eukaryotic cells. Prokaryotic cells lack a well-defined nucleus and membrane-bound organelles. Eukaryotic cells have both. Remember: Pro = "before" (primitive), Eu = "true" (well-developed).
4. Saying "bacteria have no nucleus at all." Bacteria do have genetic material (DNA), but it is in a region called the nucleoid, not enclosed by a nuclear membrane. They lack a "true" or "well-defined" nucleus — not genetic material itself.
5. Forgetting that the ostrich egg is the largest SINGLE cell. The ostrich egg is the largest single cell by size, but nerve cells (neurons) are the longest cells in the body. Size and length are different.
6. Saying "all plant cell organelles are absent in animal cells." Only cell wall and chloroplasts are absent in animal cells. Both cell types share the nucleus, mitochondria, cell membrane, endoplasmic reticulum, Golgi body, ribosomes, and cytoplasm. Animal cells also have centrioles, which plant cells lack.
7. Writing "Robert Hooke discovered living cells." Robert Hooke observed cork cells, which were dead (empty chambers without living contents). It was Antonie van Leeuwenhoek who first observed living cells (bacteria, protozoa).
Exam Checklist
Before your exam, make sure you can:
- [ ] Define a cell and explain why it is called the "building block of life"
- [ ] Name who discovered the cell, in which year, and from what material
- [ ] List and describe the three essential parts of a cell (cell membrane, cytoplasm, nucleus)
- [ ] Identify cell organelles and state their functions (nucleus, mitochondria, chloroplast, cell wall, vacuole, cell membrane, ribosome)
- [ ] Distinguish between prokaryotic and eukaryotic cells with at least 4 differences
- [ ] Compare plant cell and animal cell with at least 6 differences
- [ ] Explain the structure and function of the nucleus (nuclear membrane, nucleolus, chromosomes)
- [ ] Describe the role of the microscope in cell biology and name its types
- [ ] Define key terms: organelle, cytoplasm, nucleoid, unicellular, multicellular
- [ ] Give examples of unicellular organisms (Amoeba, bacteria, yeast) and multicellular organisms (Spirogyra, human, mango)
- [ ] Explain why a bigger onion does not mean bigger cells
- [ ] Arrange cells/organisms by size (bacteria → plant → animal cell → ostrich egg)
- [ ] Answer analogy questions connecting cell structures to their functions