Introduction
The cell is called the fundamental unit of life because all living organisms are made up of cells, and all life processes occur within cells. From the simplest bacteria to complex human beings, every organism is composed of one or more cells. The study of cells is known as cytology, and understanding cell structure and function is essential for biology.
Discovery of the Cell
- In 1665, Robert Hooke observed a thin slice of cork under a microscope and saw small compartments which he named “cells.”
- Later, Antonie van Leeuwenhoek observed living cells such as bacteria and protozoa using his improved microscope.
- The cell theory was later proposed by Matthias Schleiden and Theodor Schwann.
Cell Theory
The Cell Theory states:
- All living organisms are made up of one or more cells.
- The cell is the basic structural and functional unit of life.
- All cells arise from pre-existing cells (added by Rudolf Virchow).
Importance of Cell Theory
- Explains growth and reproduction.
- Establishes unity among living organisms.
- Forms the foundation of modern biology.
Types of Organisms Based on Number of Cells
1. Unicellular Organisms
- Made up of a single cell.
- Example: Amoeba, Paramecium, Bacteria.
- One cell performs all life processes.
2. Multicellular Organisms
- Made up of many cells.
- Cells specialize to perform different functions.
- Example: Humans, plants, animals.
Cell Structure
Cells vary in size, shape, and structure depending on their function. However, all cells have certain basic components.
Basic Components of a Cell
- Cell membrane
- Cytoplasm
- Nucleus
Prokaryotic and Eukaryotic Cells
Prokaryotic Cells
- Primitive cells.
- No true nucleus.
- Genetic material not enclosed in membrane.
- Example: Bacteria.
Eukaryotic Cells
- Advanced cells.
- True nucleus with nuclear membrane.
- Membrane-bound organelles present.
- Example: Plant and animal cells.
Cell Organelles and Their Functions
1. Cell Membrane (Plasma Membrane)
- Thin, flexible outer covering.
- Selectively permeable.
- Made of lipids and proteins.
- Controls movement of substances.
Functions
- Protection.
- Exchange of materials.
- Maintains shape.
2. Cell Wall (Plant Cells Only)
- Present in plant cells.
- Made of cellulose.
- Provides rigidity and support.
3. Cytoplasm
- Jelly-like substance.
- Contains organelles.
- Site of metabolic reactions.
4. Nucleus
- Control center of the cell.
- Contains DNA and chromosomes.
- Surrounded by nuclear membrane.
Functions
- Controls activities.
- Inheritance.
- Protein synthesis regulation.
5. Mitochondria
- Called the “powerhouse of the cell.”
- Site of respiration.
- Produces ATP (energy).
6. Ribosomes
- Small particles.
- Site of protein synthesis.
- Present in cytoplasm and on ER.
7. Endoplasmic Reticulum (ER)
Types:
- Rough ER (with ribosomes)
- Smooth ER (without ribosomes)
Functions:
- Protein synthesis (RER)
- Lipid synthesis (SER)
- Transport system
8. Golgi Apparatus
- Modifies and packages proteins.
- Forms vesicles.
9. Lysosomes
- Contain digestive enzymes.
- Known as “suicide bags.”
- Destroy waste and damaged organelles.
10. Vacuoles
- Storage sacs.
- Large central vacuole in plant cells.
- Maintains turgor pressure.
11. Plastids (Plant Cells)
Types:
- Chloroplast (photosynthesis)
- Chromoplast (color)
- Leucoplast (storage)
Chloroplast contains chlorophyll and performs photosynthesis.
Comparison Between Plant and Animal Cells
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present | Absent |
| Vacuole | Large | Small |
| Plastids | Present | Absent |
| Shape | Rectangular | Irregular |
Cell Division
Cell division is essential for growth and reproduction.
Types of Cell Division
1. Mitosis
- Occurs in somatic cells.
- Produces two identical daughter cells.
- Helps in growth and repair.
2. Meiosis
- Occurs in reproductive cells.
- Produces four haploid cells.
- Important for sexual reproduction.
Cell Transport
Diffusion
Movement of particles from high concentration to low concentration.
Osmosis
Movement of water through a semi-permeable membrane.
Types of Osmosis
- Hypotonic solution
- Hypertonic solution
- Isotonic solution
Cell Size and Shape
- Small size ensures efficient diffusion.
- Shape depends on function:
- Nerve cells – long.
- Muscle cells – elongated.
- RBC – biconcave.
Specialized Cells
Examples:
- Neuron – transmits impulses.
- RBC – transports oxygen.
- Muscle cell – movement.
- Root hair cell – absorption.
Importance of the Cell
- Basis of life.
- Responsible for metabolism.
- Controls heredity.
- Maintains body structure.
- Helps in growth and reproduction.
Differences Between Prokaryotic and Eukaryotic Cells
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | Absent | Present |
| Organelles | Absent | Present |
| Size | Small | Large |
| Examples | Bacteria | Plants, Animals |
Cell as a Living System
Each cell performs:
- Nutrition
- Respiration
- Excretion
- Growth
- Reproduction
- Response to stimuli
Cells work together to form tissues, tissues form organs, organs form organ systems, and organ systems form an organism.
Modern Developments in Cell Biology
- Electron microscope discovery.
- DNA structure discovery.
- Stem cell research.
- Cell cloning.
- Genetic engineering.
These developments have revolutionized medicine and biotechnology.
Conclusion
The cell is rightly called the fundamental unit of life because it forms the structural and functional basis of all living organisms. From unicellular bacteria to complex human beings, life begins at the cellular level. Understanding cell structure, organelles, and functions helps us understand growth, reproduction, heredity, and disease. The discovery of cells opened new pathways in science, leading to advancements in medicine, genetics, and biotechnology. Thus, studying the cell is essential for understanding life itself.
🧬 Fundamental Unit of Life – 100 MCQs with Answers
✅ Multiple Choice Questions (1–25)
1. Who discovered the cell?
A) Leeuwenhoek
B) Robert Hooke
C) Schwann
D) Virchow
Answer: B
2. Cell was discovered in which year?
A) 1665
B) 1674
C) 1838
D) 1855
Answer: A
3. The basic structural and functional unit of life is:
A) Tissue
B) Organ
C) Cell
D) Nucleus
Answer: C
4. Which scientist observed living cells first?
A) Robert Hooke
B) Schleiden
C) Schwann
D) Leeuwenhoek
Answer: D
5. Cell theory was proposed by:
A) Hooke & Virchow
B) Schleiden & Schwann
C) Darwin & Lamarck
D) Mendel & Morgan
Answer: B
6. “All cells arise from pre-existing cells” was given by:
A) Schwann
B) Schleiden
C) Virchow
D) Hooke
Answer: C
7. Prokaryotic cells lack:
A) Cytoplasm
B) Cell membrane
C) Nucleus
D) Ribosomes
Answer: C
8. Which organism is unicellular?
A) Human
B) Amoeba
C) Mango plant
D) Dog
Answer: B
9. Plasma membrane is:
A) Permeable
B) Impermeable
C) Selectively permeable
D) Rigid
Answer: C
10. Cell wall is present in:
A) Animal cell
B) Plant cell
C) Human cell
D) RBC
Answer: B
11. Cell wall is made up of:
A) Protein
B) Lipid
C) Cellulose
D) Starch
Answer: C
12. Powerhouse of the cell is:
A) Ribosome
B) Mitochondria
C) Nucleus
D) Golgi body
Answer: B
13. Site of protein synthesis:
A) Mitochondria
B) Lysosome
C) Ribosome
D) Vacuole
Answer: C
14. Suicide bags of the cell are:
A) Ribosomes
B) Lysosomes
C) Plastids
D) ER
Answer: B
15. Rough ER has:
A) DNA
B) Ribosomes
C) Lysosomes
D) Chloroplast
Answer: B
16. Smooth ER helps in:
A) Protein synthesis
B) Lipid synthesis
C) Respiration
D) Photosynthesis
Answer: B
17. Golgi apparatus is responsible for:
A) Respiration
B) Digestion
C) Packaging and secretion
D) Photosynthesis
Answer: C
18. Largest cell organelle in plant cell:
A) Nucleus
B) Vacuole
C) Ribosome
D) ER
Answer: B
19. Chloroplast is found in:
A) Animal cells
B) Plant cells
C) Bacteria
D) Fungi
Answer: B
20. Photosynthesis occurs in:
A) Mitochondria
B) Chloroplast
C) Nucleus
D) Golgi
Answer: B
21. Genetic material is present in:
A) Cytoplasm
B) Nucleus
C) Cell wall
D) Vacuole
Answer: B
22. Diffusion is movement of particles from:
A) Low to high concentration
B) High to low concentration
C) Equal concentration
D) Inside to outside only
Answer: B
23. Osmosis involves movement of:
A) Solute
B) Water
C) Gas
D) Protein
Answer: B
24. Mitosis produces:
A) 4 cells
B) 2 identical cells
C) 2 different cells
D) 1 cell
Answer: B
25. Meiosis produces:
A) 2 diploid cells
B) 4 haploid cells
C) 1 cell
D) 8 cells
Answer: B
✅ MCQs (26–50)
26. Control center of cell is: Nucleus
Answer: A) Nucleus
27. Smallest living unit is:
A) Organ
B) Cell
C) Tissue
D) Atom
Answer: B
28. Plant cells are generally:
A) Round
B) Rectangular
C) Irregular
D) Oval
Answer: B
29. Animal cells lack:
A) Mitochondria
B) Nucleus
C) Cell wall
D) Ribosomes
Answer: C
30. Bacteria are:
A) Eukaryotic
B) Prokaryotic
C) Multicellular
D) Complex
Answer: B
31. Nucleolus is present in: Nucleus
Answer: B
32. ATP is produced in: Mitochondria
Answer: C
33. Jelly-like substance is: Cytoplasm
Answer: A
34. Transport system of cell: ER
Answer: D
35. Chromosomes are made of: DNA
Answer: B
36. Turgor pressure is maintained by: Vacuole
Answer: C
37. Chromoplast gives: Color
Answer: D
38. Leucoplast stores: Food
Answer: A
39. Ribosomes are made of: RNA & protein
Answer: C
40. Cell membrane is made of: Lipids & proteins
Answer: D
41. Smallest cell is: Bacteria
Answer: A
42. Largest cell in human body: Ovum
Answer: B
43. Longest cell in body: Nerve cell
Answer: C
44. Lysosomes contain: Digestive enzymes
Answer: D
45. Selective permeability means: Controls entry & exit
Answer: A
46. In hypertonic solution cell: Shrinks
Answer: B
47. In hypotonic solution plant cell: Swells
Answer: C
48. Eukaryotic cells have: True nucleus
Answer: D
49. Prokaryotic DNA lies in: Cytoplasm
Answer: A
50. Cell division helps in: Growth
Answer: B
✅ MCQs (51–100)
51. Basic unit of heredity: Gene – Answer: C
52. Nuclear membrane is: Double layered – Answer: B
53. Chromatin forms: Chromosomes – Answer: A
54. Organelle absent in prokaryotes: Mitochondria – Answer: D
55. Energy currency of cell: ATP – Answer: C
56. Cell wall is absent in: Animals – Answer: A
57. Protein synthesis starts in: Nucleus – Answer: B
58. Ribosomes are: Non-membranous – Answer: C
59. Vacuole contains: Cell sap – Answer: D
60. Plasma membrane is: Living – Answer: A
61. Site of respiration: Mitochondria – Answer: B
62. Green pigment is: Chlorophyll – Answer: C
63. Control of cell activities: Nucleus – Answer: D
64. Cell theory does not apply to: Viruses – Answer: A
65. Chromosomes carry: Genes – Answer: B
66. ER helps in: Transport – Answer: C
67. Golgi modifies: Proteins – Answer: D
68. Suicide bag term refers to: Lysosome – Answer: A
69. Plant cell outermost layer: Cell wall – Answer: B
70. Animal cell outermost layer: Cell membrane – Answer: C
71. Fluid mosaic model explains: Membrane – Answer: D
72. Biconcave cell: RBC – Answer: A
73. Root hair cell function: Absorption – Answer: B
74. Meiosis occurs in: Reproductive cells – Answer: C
75. Mitosis occurs in: Somatic cells – Answer: D
76. Haploid cells have: Half chromosomes – Answer: A
77. Diploid cells have: Full set chromosomes – Answer: B
78. Prophase is stage of: Mitosis – Answer: C
79. Crossing over occurs in: Meiosis – Answer: D
80. Cytokinesis means: Division of cytoplasm – Answer: A
81. Cell plate forms in: Plant cells – Answer: B
82. Centrioles present in: Animal cells – Answer: C
83. Plastids are absent in: Animals – Answer: D
84. Semi-permeable membrane allows: Selective movement – Answer: A
85. Diffusion requires: No energy – Answer: B
86. Active transport requires: Energy – Answer: C
87. DNA stands for: Deoxyribonucleic acid – Answer: D
88. RNA is present in: Ribosomes – Answer: A
89. Cell was observed in cork by: Hooke – Answer: B
90. Living cell first seen by: Leeuwenhoek – Answer: C
91. Plant cell shape due to: Cell wall – Answer: D
92. Vacuole size in animals: Small – Answer: A
93. Organelle for detoxification: SER – Answer: B
94. Site of photosynthesis: Chloroplast – Answer: C
95. Organelle with cristae: Mitochondria – Answer: D
96. Unit of life: Cell – Answer: A
97. Group of cells forms: Tissue – Answer: B
98. Tissue forms: Organ – Answer: C
99. Organs form: Organ system – Answer: D
100. Study of cells is called: Cytology – Answer: A
✅ 100 Very Short Answer Questions (1–2 lines each)
🔹 Very Short Answer Questions (1–25)
1. What is the fundamental unit of life?
Cell.
2. Who discovered the cell?
Robert Hooke.
3. In which year was the cell discovered?
1665.
4. Who first observed living cells?
Antonie van Leeuwenhoek.
5. What is cytology?
The study of cells.
6. Name the basic components of a cell.
Cell membrane, cytoplasm, and nucleus.
7. What is the outermost covering of an animal cell?
Plasma membrane.
8. What is the outermost covering of a plant cell?
Cell wall.
9. What is the cell wall made of?
Cellulose.
10. What is the control center of the cell?
Nucleus.
11. What does the nucleus contain?
DNA and chromosomes.
12. What is the jelly-like substance inside the cell?
Cytoplasm.
13. Which organelle is called the powerhouse of the cell?
Mitochondria.
14. What is ATP?
Energy currency of the cell.
15. Where does protein synthesis occur?
Ribosomes.
16. What are lysosomes known as?
Suicide bags of the cell.
17. What is diffusion?
Movement of particles from high to low concentration.
18. What is osmosis?
Movement of water through a semi-permeable membrane.
19. What is a unicellular organism?
An organism made of one cell.
20. Give one example of unicellular organism.
Amoeba.
21. What is a multicellular organism?
An organism made of many cells.
22. Name one plastid responsible for photosynthesis.
Chloroplast.
23. What is the function of vacuole in plant cells?
Storage and maintaining turgor pressure.
24. What are chromosomes made of?
DNA and protein.
25. What is cell theory?
All living organisms are made of cells.
🔹 Very Short Answer Questions (26–50)
26. Who added that cells arise from pre-existing cells?
Rudolf Virchow.
27. What is a prokaryotic cell?
A cell without a true nucleus.
28. Give one example of prokaryote.
Bacteria.
29. What is a eukaryotic cell?
A cell with a true nucleus.
30. What is the function of Golgi apparatus?
Packaging and secretion of proteins.
31. What is rough ER?
ER with ribosomes attached.
32. What is smooth ER?
ER without ribosomes.
33. What is the function of smooth ER?
Lipid synthesis and detoxification.
34. What is chromatin?
Thread-like material in nucleus.
35. What is the function of nucleolus?
Formation of ribosomes.
36. What is tonoplast?
Membrane surrounding vacuole.
37. What is plasmolysis?
Shrinkage of cell in hypertonic solution.
38. What is cytokinesis?
Division of cytoplasm.
39. How many cells are formed in mitosis?
Two.
40. How many cells are formed in meiosis?
Four.
41. What is the longest cell in human body?
Nerve cell.
42. What is the largest cell in human body?
Ovum.
43. What is selective permeability?
Allows some substances to pass.
44. Where is chlorophyll present?
Chloroplast.
45. What is cell sap?
Liquid inside vacuole.
46. What is the site of respiration?
Mitochondria.
47. What is the function of ribosomes?
Protein synthesis.
48. What is a gene?
Unit of heredity.
49. What is nucleoid?
DNA region in bacteria.
50. What is the fluid mosaic model related to?
Cell membrane structure.
🔹 Very Short Answer Questions (51–75)
51. What gives rigidity to plant cells?
Cell wall.
52. What maintains shape of animal cells?
Cell membrane.
53. What is the function of lysosomes?
Intracellular digestion.
54. What is hypertonic solution?
Solution with higher solute concentration.
55. What is hypotonic solution?
Solution with lower solute concentration.
56. What happens in isotonic solution?
No net movement of water.
57. What is the full form of DNA?
Deoxyribonucleic Acid.
58. What is the full form of RNA?
Ribonucleic Acid.
59. What are plastids?
Organelles in plant cells.
60. Name three types of plastids.
Chloroplast, Chromoplast, Leucoplast.
61. What is the function of chromoplast?
Provides color to fruits and flowers.
62. What is the function of leucoplast?
Storage of food.
63. What is mitosis?
Cell division for growth.
64. What is meiosis?
Cell division for reproduction.
65. What are somatic cells?
Body cells.
66. What are gametes?
Reproductive cells.
67. What is active transport?
Movement using energy.
68. What is passive transport?
Movement without energy.
69. What is the basic unit of heredity?
Gene.
70. What is cristae?
Inner folds of mitochondria.
71. What is dictyosome?
Golgi apparatus in plants.
72. What is peptidoglycan?
Material of bacterial cell wall.
73. What is glycolysis?
Breakdown of glucose in cytoplasm.
74. What is ATP full form?
Adenosine Triphosphate.
75. What is semi-autonomous organelle?
Organelle with its own DNA.
🔹 Very Short Answer Questions (76–100)
76. Name one semi-autonomous organelle.
Mitochondria.
77. What is the function of ER?
Transport of materials.
78. What is chromosomal number in humans (diploid)?
46.
79. What is haploid number in humans?
23.
80. What is the study of heredity called?
Genetics.
81. What are centrioles?
Structures aiding cell division.
82. Where are centrioles present?
Animal cells.
83. What is cell plate?
Structure formed during plant cell division.
84. What forms tissues?
Group of similar cells.
85. What forms organs?
Group of tissues.
86. What forms organ systems?
Group of organs.
87. What is metabolism?
Chemical reactions in cell.
88. What is the smallest cell organelle?
Ribosome.
89. What is cell differentiation?
Specialization of cells.
90. What is endocytosis?
Intake of materials by cell.
91. What is exocytosis?
Release of materials from cell.
92. What is nucleus discovered by?
Robert Brown.
93. What is cell membrane made of?
Lipids and proteins.
94. What is the function of nucleus?
Controls cell activities.
95. What is reproduction at cellular level?
Cell division.
96. What is the function of mitochondria?
Energy production.
97. What is inheritance?
Transmission of traits.
98. What is chromosomal condensation?
Formation of chromosomes.
99. What is the basic building block of organisms?
Cell.
100. Why is cell called fundamental unit of life?
Because all organisms are made of cells.
✅ Short Answer Questions
🔹 Short Answer Questions (1–20)
1. Why is the cell called the fundamental unit of life?
The cell is called the fundamental unit of life because all living organisms are made up of cells. Every life process such as respiration, nutrition, growth, and reproduction occurs within cells. Cells form tissues, tissues form organs, and organs form organ systems.
2. Describe the discovery of the cell.
The cell was discovered in 1665 by Robert Hooke while observing a thin slice of cork under a microscope. He noticed small box-like compartments and named them “cells.” Later, Antonie van Leeuwenhoek observed living cells using an improved microscope.
3. State the main points of cell theory.
Cell theory states that all living organisms are made of cells, the cell is the basic structural and functional unit of life, and all cells arise from pre-existing cells. This theory forms the foundation of modern biology.
4. Differentiate between prokaryotic and eukaryotic cells.
Prokaryotic cells lack a true nucleus and membrane-bound organelles. Their DNA lies freely in the cytoplasm. Eukaryotic cells have a well-defined nucleus and membrane-bound organelles like mitochondria and Golgi apparatus. Prokaryotes are simpler and smaller than eukaryotes.
5. Explain the structure of the plasma membrane.
The plasma membrane is a thin, flexible boundary made of lipids and proteins arranged in a bilayer. It follows the fluid mosaic model and is selectively permeable, allowing only certain substances to enter or leave the cell.
6. What are the functions of the cell wall?
The cell wall is present in plant cells and is made of cellulose. It provides rigidity, shape, and protection to the cell. It prevents the cell from bursting in hypotonic solutions and supports the plant structure.
7. Describe the structure and function of nucleus.
The nucleus is a membrane-bound organelle containing genetic material in the form of DNA. It controls all cellular activities including growth, metabolism, and reproduction. The nucleolus inside the nucleus helps in ribosome formation.
8. Write short notes on mitochondria.
Mitochondria are double-membraned organelles known as the powerhouse of the cell. They produce ATP through cellular respiration. The inner membrane has folds called cristae. Mitochondria contain their own DNA and are considered semi-autonomous organelles.
9. What is the role of ribosomes in a cell?
Ribosomes are small, non-membranous organelles responsible for protein synthesis. They may be free in the cytoplasm or attached to rough endoplasmic reticulum. They are composed of RNA and proteins.
10. Explain the functions of endoplasmic reticulum.
The endoplasmic reticulum acts as a transport system within the cell. Rough ER synthesizes proteins due to ribosomes attached to it. Smooth ER synthesizes lipids and helps in detoxification of drugs and poisons.
11. What is the function of Golgi apparatus?
The Golgi apparatus modifies, packages, and transports proteins and lipids produced in the ER. It forms vesicles for secretion and plays an important role in cell secretion and membrane formation.
12. Why are lysosomes called suicide bags?
Lysosomes contain powerful digestive enzymes that break down waste materials and damaged organelles. If lysosomes burst, they can digest the entire cell, hence they are called suicide bags of the cell.
13. Describe the structure and function of vacuole.
Vacuoles are membrane-bound sacs filled with cell sap. In plant cells, they are large and central, helping maintain turgor pressure and storing nutrients and waste products. In animal cells, vacuoles are smaller.
14. What are plastids? Name their types.
Plastids are organelles found in plant cells. They are of three types: chloroplasts (for photosynthesis), chromoplasts (provide color), and leucoplasts (store food). Chloroplasts contain chlorophyll for capturing sunlight.
15. Explain diffusion and osmosis.
Diffusion is the movement of particles from high concentration to low concentration without energy. Osmosis is the movement of water across a semi-permeable membrane from lower solute concentration to higher solute concentration.
16. What happens to a cell in hypertonic solution?
In a hypertonic solution, water moves out of the cell by osmosis. The cell shrinks due to water loss. In plant cells, this process is called plasmolysis.
17. Describe mitosis briefly.
Mitosis is a type of cell division that produces two identical daughter cells. It occurs in somatic cells and helps in growth, repair, and replacement of damaged cells.
18. Describe meiosis briefly.
Meiosis is a type of cell division that produces four haploid cells. It occurs in reproductive cells and is essential for sexual reproduction and maintaining chromosome number.
19. Write differences between plant and animal cells.
Plant cells have a cell wall, chloroplasts, and a large central vacuole. Animal cells lack cell wall and plastids and have smaller vacuoles. Plant cells are usually rectangular, while animal cells are irregular in shape.
20. Explain the importance of cell division.
Cell division helps in growth, repair of damaged tissues, and reproduction. Mitosis ensures identical cell formation, while meiosis maintains chromosome number across generations and promotes genetic variation.
21. What is cytoplasm and what are its functions?
Cytoplasm is the jelly-like substance present between the cell membrane and nucleus. It contains organelles and is the site of most metabolic reactions such as glycolysis. It helps in the movement of materials within the cell.
22. Explain selective permeability of plasma membrane.
Selective permeability means the plasma membrane allows certain substances to pass through while restricting others. Small molecules like oxygen pass easily, while larger molecules require special transport mechanisms. This helps maintain internal balance.
23. What is nucleolus and its function?
The nucleolus is a dense structure inside the nucleus. It is responsible for the formation of ribosomal RNA and assembling ribosome subunits. It plays a key role in protein synthesis.
24. Why are mitochondria called semi-autonomous organelles?
Mitochondria are called semi-autonomous because they have their own DNA and ribosomes. They can replicate independently within the cell and synthesize some of their own proteins.
25. What is chromatin material?
Chromatin is a thread-like network present inside the nucleus. It is composed of DNA and proteins. During cell division, chromatin condenses to form visible chromosomes.
26. What is active transport?
Active transport is the movement of substances across a membrane against their concentration gradient using energy in the form of ATP. It is important for maintaining proper concentration of ions inside the cell.
27. What is passive transport?
Passive transport is the movement of substances across a membrane without using energy. It includes diffusion and osmosis, where substances move along their concentration gradient.
28. Describe the structure of chloroplast.
Chloroplast is a double-membraned organelle containing chlorophyll. Inside, it has thylakoids arranged in stacks called grana. It performs photosynthesis by converting sunlight into chemical energy.
29. What is the role of smooth ER?
Smooth endoplasmic reticulum synthesizes lipids and steroids. It also helps in detoxifying drugs and poisons, especially in liver cells.
30. What is the role of rough ER?
Rough endoplasmic reticulum has ribosomes attached to its surface. It synthesizes and transports proteins to the Golgi apparatus for further modification and packaging.
31. What are centrioles?
Centrioles are cylindrical structures present in animal cells. They help in cell division by forming spindle fibers during mitosis and meiosis.
32. Explain the term plasmolysis.
Plasmolysis is the shrinkage of the cytoplasm away from the cell wall when a plant cell is placed in a hypertonic solution due to water loss.
33. What is turgor pressure?
Turgor pressure is the pressure exerted by the cell contents against the cell wall in plant cells. It helps maintain rigidity and keeps plants upright.
34. What is glycolysis?
Glycolysis is the breakdown of glucose into pyruvate in the cytoplasm. It is the first step of cellular respiration and produces a small amount of ATP.
35. What is a gene?
A gene is a segment of DNA that carries information for a specific trait. It is the basic unit of heredity passed from parents to offspring.
36. What is nucleoid?
Nucleoid is the region in prokaryotic cells where genetic material is present. It is not enclosed by a nuclear membrane.
37. Why do plant cells have large vacuoles?
Plant cells have large central vacuoles to store cell sap and maintain turgor pressure. This helps in providing structural support.
38. What is the function of chromoplast?
Chromoplasts provide color to fruits and flowers by storing pigments other than chlorophyll. They help attract pollinators.
39. What is the difference between diffusion and osmosis?
Diffusion involves movement of any particles from high to low concentration, while osmosis specifically refers to movement of water across a semi-permeable membrane.
40. Why is cell membrane called living?
The cell membrane is called living because it regulates exchange of materials and actively participates in cell functions.
🔹 Questions (41–60)
41. Describe the role of lysosomes.
Lysosomes contain digestive enzymes that break down waste materials and damaged organelles. They help in intracellular digestion and recycling of materials.
42. What are plastids?
Plastids are membrane-bound organelles found in plant cells. They include chloroplasts, chromoplasts, and leucoplasts, each performing specific functions like photosynthesis and storage.
43. What is the function of leucoplast?
Leucoplast stores food materials such as starch, oils, and proteins in plant cells.
44. What is the significance of mitosis?
Mitosis ensures growth, repair, and replacement of cells. It produces two identical daughter cells.
45. What is the significance of meiosis?
Meiosis produces gametes and maintains chromosome number across generations.
46. What is the function of Golgi apparatus?
It modifies, packages, and secretes proteins and lipids.
47. What is cell differentiation?
Cell differentiation is the process by which cells specialize to perform specific functions.
48. What is the importance of nucleus?
The nucleus controls cell activities and stores genetic information.
49. What is semi-permeable membrane?
A membrane that allows selective substances to pass through.
50. What are somatic cells?
Somatic cells are body cells involved in growth and repair.
🔹 Questions (61–100)
61. What are gametes?
Reproductive cells involved in sexual reproduction.
62. What is the function of ribosomes?
They synthesize proteins.
63. What is ATP?
ATP is the energy currency of the cell.
64. Why are viruses excluded from cell theory?
Viruses are not made of cells and can reproduce only inside host cells.
65. What forms tissues?
Group of similar cells.
66. What forms organs?
Group of tissues.
67. What forms organ systems?
Group of organs.
68. What is metabolism?
All chemical reactions occurring inside a cell.
69. What is the function of ER?
Transport and synthesis of proteins and lipids.
70. What is chromosomal condensation?
Condensing of chromatin into chromosomes during division.
71. What is diploid number in humans?
46 chromosomes.
72. What is haploid number in humans?
23 chromosomes.
73. What is prophase?
First stage of mitosis.
74. What is cytokinesis?
Division of cytoplasm.
75. What is cell plate?
Structure formed during plant cell division.
76. What is cell sap?
Liquid inside vacuole.
77. What is cristae?
Folds of inner mitochondrial membrane.
78. What is tonoplast?
Membrane surrounding vacuole.
79. What is endocytosis?
Taking material into cell.
80. What is exocytosis?
Releasing material from cell.
81. What is the smallest organelle?
Ribosome.
82. What is the role of chlorophyll?
Absorbs sunlight for photosynthesis.
83. What is DNA?
Genetic material carrying hereditary information.
84. What is RNA?
Molecule involved in protein synthesis.
85. What is cytoskeleton?
Network providing structural support to cell.
86. Why are cells small in size?
To maintain efficient surface area to volume ratio.
87. What is inheritance?
Transmission of traits from parents to offspring.
88. What is genetic variation?
Differences in traits among individuals.
89. What is reproduction at cellular level?
Cell division.
90. What is nucleus discovered by?
Robert Brown.
91. What is the function of mitochondria?
Energy production.
92. What is the function of cell wall?
Protection and support.
93. What is selective permeability?
Allows specific substances to pass.
94. What is cell membrane made of?
Lipids and proteins.
95. What is unicellular organism?
Organism made of one cell.
96. What is multicellular organism?
Organism made of many cells.
97. What is the basic building block of life?
Cell.
98. What is cytology?
Study of cells.
99. What is chromosome?
Structure carrying genes.
100. Why is cell important?
It performs all life processes
✅ Assertion–Reason Questions
Directions:
A) Both Assertion (A) and Reason (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.
🔹 Assertion–Reason (1–10)
1.
A: Cell is the basic structural unit of life.
R: All organisms are made up of cells.
Answer: A
2.
A: Robert Hooke discovered living cells.
R: He observed cork under a microscope.
Answer: D
3.
A: Prokaryotic cells lack membrane-bound organelles.
R: They do not have a true nucleus.
Answer: A
4.
A: Mitochondria are called powerhouse of the cell.
R: They produce ATP through respiration.
Answer: A
5.
A: Plant cells do not have a cell wall.
R: Cell wall is made of cellulose.
Answer: D
6.
A: Ribosomes are sites of protein synthesis.
R: They are composed of RNA and proteins.
Answer: B
7.
A: Lysosomes are called suicide bags.
R: They contain digestive enzymes.
Answer: A
8.
A: Diffusion requires energy.
R: It occurs along the concentration gradient.
Answer: D
9.
A: Osmosis is movement of water.
R: It occurs through a semi-permeable membrane.
Answer: A
10.
A: Golgi apparatus modifies proteins.
R: It packages proteins into vesicles.
Answer: A
🔹 Assertion–Reason (11–20)
11.
A: Chromatin condenses into chromosomes during cell division.
R: Chromosomes carry genetic information.
Answer: B
12.
A: Mitosis produces four daughter cells.
R: It occurs in somatic cells.
Answer: D
13.
A: Meiosis reduces chromosome number by half.
R: It occurs in reproductive cells.
Answer: A
14.
A: Cell membrane is selectively permeable.
R: It allows all substances to pass freely.
Answer: C
15.
A: Chloroplast performs photosynthesis.
R: It contains chlorophyll pigment.
Answer: A
16.
A: Animal cells have plastids.
R: Plastids are found only in plant cells.
Answer: D
17.
A: Vacuoles maintain turgor pressure in plant cells.
R: They store cell sap.
Answer: A
18.
A: Rough ER synthesizes lipids.
R: It has ribosomes attached to its surface.
Answer: D
19.
A: Smooth ER helps in detoxification.
R: It lacks ribosomes.
Answer: B
20.
A: Ribosomes are membrane-bound organelles.
R: They are present in cytoplasm.
Answer: D
🔹 Assertion–Reason (21–30)
21.
A: Cell wall is freely permeable.
R: It has pores.
Answer: A
22.
A: Nucleus controls all cell activities.
R: It contains DNA.
Answer: A
23.
A: Centrioles are present in plant cells.
R: They help in cell division.
Answer: D
24.
A: Active transport requires energy.
R: It moves substances against gradient.
Answer: A
25.
A: Cytoplasm is the site of metabolic reactions.
R: It contains cell organelles.
Answer: B
26.
A: Prokaryotic cells are larger than eukaryotic cells.
R: They lack nucleus.
Answer: D
27.
A: Mitochondria have their own DNA.
R: They are semi-autonomous organelles.
Answer: A
28.
A: Golgi apparatus is also called dictyosome in plants.
R: It helps in packaging of proteins.
Answer: B
29.
A: Lysosomes help in intracellular digestion.
R: They contain hydrolytic enzymes.
Answer: A
30.
A: Plasmolysis occurs in hypotonic solution.
R: Water moves out of the cell.
Answer: D
🔹 Assertion–Reason (31–40)
31.
A: Diffusion occurs from high to low concentration.
R: It does not require energy.
Answer: B
32.
A: Nucleolus helps in ribosome formation.
R: It is present inside nucleus.
Answer: B
33.
A: Chromosomes are visible during interphase.
R: Chromatin condenses during division.
Answer: D
34.
A: Hypertonic solution causes plant cell to shrink.
R: Water moves out by osmosis.
Answer: A
35.
A: Isotonic solution causes no net water movement.
R: Concentration inside and outside is equal.
Answer: A
36.
A: Mitosis is responsible for growth.
R: It produces identical daughter cells.
Answer: A
37.
A: Meiosis increases chromosome number.
R: It produces haploid cells.
Answer: D
38.
A: Ribosomes are smallest organelles.
R: They synthesize proteins.
Answer: B
39.
A: Plant cells are rectangular in shape.
R: They have rigid cell wall.
Answer: A
40.
A: Cell theory applies to viruses.
R: Viruses are made of cells.
Answer: D
🔹 Assertion–Reason (41–50)
41.
A: DNA carries genetic information.
R: Genes are segments of DNA.
Answer: A
42.
A: ER acts as transport system.
R: It forms a network of membranes.
Answer: A
43.
A: Chloroplast is double-membraned.
R: It performs respiration.
Answer: C
44.
A: Cell membrane is composed of lipids and proteins.
R: It follows fluid mosaic model.
Answer: B
45.
A: Vacuoles are larger in plant cells.
R: They maintain turgidity.
Answer: A
46.
A: Bacteria are eukaryotic.
R: They lack true nucleus.
Answer: D
47.
A: Crossing over occurs in meiosis.
R: It increases genetic variation.
Answer: A
48.
A: Cytokinesis is division of nucleus.
R: It follows karyokinesis.
Answer: D
49.
A: ATP is produced in mitochondria.
R: Mitochondria are site of respiration.
Answer: A
50.
A: Cell is the fundamental unit of life.
R: All life processes occur within cells.
Answer:a
✅ Long Answer Questions
1. Explain the Cell Theory.
Cell theory was proposed by Matthias Schleiden and Theodor Schwann in 1838–39. Later, Rudolf Virchow added that all cells arise from pre-existing cells. The cell theory states that: (1) All living organisms are composed of one or more cells. (2) The cell is the basic structural and functional unit of life. (3) New cells arise from pre-existing cells through cell division. This theory laid the foundation of modern biology. It explains that all life processes such as respiration, digestion, and reproduction occur at the cellular level. Even multicellular organisms begin as a single cell (zygote). Though viruses are exceptions because they are acellular, the theory remains universally accepted for living organisms.
2. Describe the structure and functions of the plasma membrane.
The plasma membrane is the outermost covering of the cell that separates the cell contents from the external environment. It is composed mainly of lipids and proteins and follows the fluid mosaic model. The membrane is selectively permeable, meaning it allows only certain substances to pass through it. Small molecules like oxygen and carbon dioxide move through diffusion, while water moves through osmosis. Active transport requires energy (ATP) to move substances against the concentration gradient. The plasma membrane also helps in cell communication through receptor proteins. It maintains the internal balance of the cell and protects the cell from harmful substances. In animal cells, it is the outer boundary, while in plant cells, it lies just inside the cell wall.
3. Differentiate between Prokaryotic and Eukaryotic cells.
Prokaryotic cells are simple, small cells that lack a true nucleus and membrane-bound organelles. Their genetic material is present in a region called the nucleoid. Examples include bacteria and cyanobacteria. In contrast, eukaryotic cells are larger and more complex. They have a well-defined nucleus surrounded by a nuclear membrane and possess membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus. Prokaryotic cells divide by binary fission, whereas eukaryotic cells divide by mitosis or meiosis. Prokaryotes usually have a single circular chromosome, while eukaryotes have multiple linear chromosomes. Plant and animal cells are examples of eukaryotic cells. Thus, eukaryotic cells show a higher level of organization compared to prokaryotic cells.
4. Explain the structure and functions of the nucleus.
The nucleus is a spherical, membrane-bound organelle found in eukaryotic cells. It is surrounded by a double membrane called the nuclear envelope, which has pores for exchange of materials. Inside the nucleus is nucleoplasm containing chromatin and the nucleolus. Chromatin consists of DNA and proteins; during cell division, it condenses to form chromosomes. The nucleolus is responsible for ribosome formation. The nucleus controls all cellular activities by regulating gene expression. It stores hereditary information in the form of DNA and passes it to the next generation. Because it controls growth, metabolism, and reproduction, the nucleus is often called the “control center” of the cell.
5. Describe mitochondria and their functions.
Mitochondria are double-membraned organelles found in eukaryotic cells. The outer membrane is smooth, while the inner membrane forms folds called cristae. The inner space is called the matrix. Mitochondria are known as the powerhouse of the cell because they produce energy in the form of ATP through cellular respiration. They contain their own DNA and ribosomes, making them semi-autonomous organelles. They play an important role in metabolism, apoptosis (programmed cell death), and regulation of cellular activities. The number of mitochondria varies depending on the energy requirement of the cell. Muscle cells, for example, contain a large number of mitochondria due to high energy demands.
6. Explain the structure and functions of the Endoplasmic Reticulum (ER).
The endoplasmic reticulum is a network of membrane-bound tubules present in the cytoplasm. It is of two types: Rough ER (RER) and Smooth ER (SER). RER has ribosomes attached to its surface and is involved in protein synthesis and transport. SER lacks ribosomes and is involved in lipid synthesis, detoxification of drugs, and calcium storage. The ER acts as a transport system within the cell, moving materials from one part to another. It also contributes to membrane biogenesis. The ER is continuous with the nuclear membrane, facilitating communication between the nucleus and cytoplasm.
7. Describe the Golgi apparatus and its functions.
The Golgi apparatus consists of flattened membranous sacs called cisternae. It modifies, sorts, and packages proteins and lipids received from the ER. These materials are packed into vesicles and transported to their destination inside or outside the cell. In plant cells, it is also known as dictyosome. The Golgi apparatus plays an important role in secretion, formation of lysosomes, and cell wall formation in plants. It ensures that proteins are properly modified before they are released. Thus, it acts as a packaging and distribution center of the cell.
8. Explain lysosomes and why they are called suicide bags.
Lysosomes are membrane-bound organelles containing powerful digestive enzymes. These enzymes can break down waste materials, foreign particles, and worn-out organelles. Lysosomes help in intracellular digestion and recycling of cellular components. Under certain conditions, if the lysosome membrane ruptures, the enzymes may digest the entire cell, leading to cell death. Therefore, lysosomes are called “suicide bags” of the cell. They are more abundant in animal cells and help maintain cell cleanliness by removing debris and harmful substances.
9. Describe plastids and their types.
Plastids are double-membraned organelles found only in plant cells. They are of three types: chloroplasts, chromoplasts, and leucoplasts. Chloroplasts contain chlorophyll and perform photosynthesis. Chromoplasts contain colored pigments other than green and give color to fruits and flowers. Leucoplasts are colorless and store food materials like starch, oil, and proteins. Plastids have their own DNA and ribosomes, making them semi-autonomous. They play a significant role in food production and storage in plants.
10. Explain the process of osmosis.
Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration through a semi-permeable membrane. It does not require energy and is a type of passive transport. In plant cells, osmosis helps maintain turgor pressure, which keeps the plant upright. When a cell is placed in a hypotonic solution, it swells due to water entry. In a hypertonic solution, it shrinks due to water loss (plasmolysis). In an isotonic solution, there is no net movement of water. Osmosis is essential for maintaining water balance in living organisms.
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