Cell Biology
1. Introduction to Cell Biology
- Definition: Cell biology is the branch of biology that studies the structure, function, and behavior of cells.
- Cell: The basic structural and functional unit of life. All living organisms are composed of cells.
- Cell Theory (proposed by Schleiden and Schwann):
- All living organisms are made up of cells.
- The cell is the basic unit of life.
- All cells arise from pre-existing cells (added by Rudolf Virchow).
2. Types of Cells
Prokaryotic Cells
- Definition: Cells without a nucleus or membrane-bound organelles.
- Examples: Bacteria, Archaea.
- Features:
- Small in size (1–10 µm).
- DNA is circular and found in the nucleoid region.
- Lack of complex organelles.
Eukaryotic Cells
- Definition: Cells with a true nucleus and membrane-bound organelles.
- Examples: Plants, animals, fungi, and protists.
- Features:
- Larger in size (10–100 µm).
- DNA enclosed in a nucleus.
- Possess complex organelles.
3. Structure of a Eukaryotic Cell
A. Cell Membrane (Plasma Membrane)
- Semi-permeable membrane made of a phospholipid bilayer.
- Controls the movement of substances in and out of the cell.
- Contains proteins and cholesterol.
B. Cytoplasm
- Jelly-like substance where organelles are suspended.
- Site for most cellular processes.
C. Nucleus
- Control center of the cell.
- Contains DNA in the form of chromatin.
- Surrounded by the nuclear envelope with pores.
D. Mitochondria
- Known as the "powerhouse of the cell."
- Site of cellular respiration (ATP production).
- Has its own DNA.
E. Endoplasmic Reticulum (ER)
- Rough ER: Studded with ribosomes; synthesizes proteins.
- Smooth ER: No ribosomes; synthesizes lipids and detoxifies chemicals.
F. Ribosomes
- Site of protein synthesis.
- Found free in the cytoplasm or on rough ER.
G. Golgi Apparatus
- Modifies, sorts, and packages proteins and lipids for secretion or use.
H. Lysosomes
- Contain digestive enzymes.
- Break down waste materials and cellular debris.
I. Vacuoles
- Storage sacs.
- Large central vacuole in plant cells (stores water, nutrients).
J. Centrosome and Centrioles
- Help in cell division (especially in animal cells).
K. Cytoskeleton
- Network of fibers (microtubules, microfilaments).
- Maintains cell shape and helps in movement.
4. Differences Between Plant and Animal Cells
5. Cell Organelles and Their Functions
6. Cell Division
A. Mitosis
- Produces two identical daughter cells.
- Occurs in somatic cells.
- Phases: Prophase → Metaphase → Anaphase → Telophase → Cytokinesis.
B. Meiosis
- Produces four genetically different haploid cells.
- Occurs in germ cells (sperm, eggs).
- Involves two rounds of division (Meiosis I and II).
7. Cellular Processes
- Diffusion: Movement of molecules from high to low concentration.
- Osmosis: Diffusion of water across a semi-permeable membrane.
- Active Transport: Movement of substances against the concentration gradient using energy (ATP).
- Endocytosis/Exocytosis: Processes for large molecules entering/leaving the cell.
8. Specialized Cells
- Cells are specialized to perform specific functions:
- Red blood cells: carry oxygen.
- Neurons: transmit signals.
- Muscle cells: contraction.
- Guard cells (plants): regulate stomata.
9. Stem Cells
- Definition: Undifferentiated cells with the ability to develop into different cell types.
- Types:
- Embryonic stem cells.
- Adult stem cells.
- Uses: Regenerative medicine, tissue repair, disease treatment.
10. Microscopy in Cell Biology
- Light Microscope: Uses light; limited resolution.
- Electron Microscope:
- Transmission EM (TEM): internal structure.
- Scanning EM (SEM): surface structure.
11. Cell Communication
- Cells communicate through chemical signals (hormones, neurotransmitters).
- Receptors on the cell membrane receive these signals.
- Signal transduction pathways convert signals into cellular responses.
12. Cell Cycle
- Phases: Interphase (G1, S, G2) + M phase (mitosis + cytokinesis).
- Checkpoints: Ensure correct DNA replication and division.
13. Apoptosis
- Programmed cell death.
- Essential for development and removing damaged cells
Cell Biology – MCQs
1. Who discovered the cell?
A) Robert Hooke
B) Anton van Leeuwenhoek
C) Matthias Schleiden
D) Theodor Schwann
Answer: A
2. The powerhouse of the cell is:
A) Nucleus
B) Mitochondria
C) Ribosome
D) Golgi apparatus
Answer: B
3. Which organelle is responsible for protein synthesis?
A) Lysosome
B) Ribosome
C) Golgi body
D) Mitochondria
Answer: B
4. Which structure is found only in plant cells?
A) Nucleus
B) Mitochondria
C) Cell wall
D) Ribosome
Answer: C
5. The basic unit of life is:
A) Atom
B) Tissue
C) Cell
D) Organ
Answer: C
6. What is the function of the lysosome?
A) Protein synthesis
B) Energy production
C) Digestion and waste removal
D) Transport
Answer: C
7. The fluid inside the cell is called:
A) Cytosol
B) Nucleoplasm
C) Plasma
D) Protoplasm
Answer: A
8. DNA is located in:
A) Ribosome
B) Cytoplasm
C) Nucleus
D) Mitochondria
Answer: C
9. Which part of the cell contains the genetic material?
A) Cytoplasm
B) Nucleus
C) Golgi body
D) Cell wall
Answer: B
10. Cell theory was proposed by:
A) Watson and Crick
B) Hooke and Leeuwenhoek
C) Schleiden and Schwann
D) Darwin and Wallace
Answer: C
11. The semi-permeable structure that surrounds the cell is:
A) Cell wall
B) Nuclear envelope
C) Plasma membrane
D) Cytoskeleton
Answer: C
12. Which of the following is not a cell organelle?
A) Ribosome
B) Mitochondria
C) Centriole
D) Glucose
Answer: D
13. Animal cells lack:
A) Mitochondria
B) Chloroplasts
C) Nucleus
D) Plasma membrane
Answer: B
14. The jelly-like substance within the cell is:
A) Cytoplasm
B) Nucleus
C) Mitochondria
D) Ribosome
Answer: A
15. What do plant cells have that animal cells do not?
A) Mitochondria
B) Ribosome
C) Cell wall and chloroplast
D) Nucleus
Answer: C
16. What is the function of the Golgi apparatus?
A) Digestion
B) Packaging and transporting proteins
C) Photosynthesis
D) Respiration
Answer: B
17. The process by which a cell divides into two daughter cells is:
A) Meiosis
B) Fertilization
C) Mitosis
D) Photosynthesis
Answer: C
18. Which organelle is responsible for photosynthesis?
A) Mitochondria
B) Chloroplast
C) Ribosome
D) Golgi body
Answer: B
19. Which of the following is not found in a prokaryotic cell?
A) Plasma membrane
B) Nucleus
C) Ribosome
D) Cytoplasm
Answer: B
20. The smallest living organism is:
A) Virus
B) Bacteria
C) Fungus
D) Algae
Answer: B
21. Which structure controls the activities of a cell?
A) Mitochondria
B) Nucleus
C) Golgi apparatus
D) Ribosome
Answer: B
22. Which of the following is a unicellular organism?
A) Amoeba
B) Human
C) Tree
D) Dog
Answer: A
23. The site of ATP production is:
A) Chloroplast
B) Nucleus
C) Mitochondria
D) Endoplasmic reticulum
Answer: C
24. Cells of multicellular organisms are:
A) Independent
B) Identical
C) Specialized
D) All the same
Answer: C
25. The cell membrane is made up of:
A) Protein and cellulose
B) Protein and lipid
C) Lipid and starch
D) Starch and cellulose
Answer: B
26. Which organelle detoxifies harmful substances in liver cells?
A) Golgi body
B) Lysosome
C) Smooth ER
D) Ribosome
Answer: C
27. Chromosomes are made up of:
A) DNA and protein
B) RNA and lipid
C) DNA and lipid
D) Protein and starch
Answer: A
28. In which organelle does respiration take place?
A) Golgi body
B) Mitochondria
C) Lysosome
D) Ribosome
Answer: B
29. Which is a membrane-bound organelle?
A) Ribosome
B) Lysosome
C) Nucleoid
D) Centriole
Answer: B
30. Which cell organelle helps in cell division in animal cells?
A) Centrosome
B) Ribosome
C) Nucleus
D) Mitochondria
Answer: A
31. Who coined the term ‘protoplasm’?
A) J.E. Purkinje
B) Robert Brown
C) Schleiden
D) Schwann
Answer: A
32. Which of the following is present in animal but not in plant cells?
A) Lysosome
B) Cell membrane
C) Ribosome
D) Vacuole
Answer: A
33. The structural and functional unit of life is:
A) Atom
B) Cell
C) Organelle
D) Tissue
Answer: B
34. Ribosomes are made up of:
A) DNA
B) RNA and protein
C) Protein and lipid
D) Carbohydrate
Answer: B
35. What is the role of vacuoles in plant cells?
A) Store water and nutrients
B) Photosynthesis
C) Respiration
D) Protein synthesis
Answer: A
36. Which organelle has its own DNA?
A) Ribosome
B) Nucleus
C) Mitochondria
D) Lysosome
Answer: C
37. Cell wall in plants is made up of:
A) Glucose
B) Cellulose
C) Starch
D) Lipid
Answer: B
38. Which organelle modifies, sorts, and packages proteins?
A) Nucleus
B) ER
C) Golgi apparatus
D) Lysosome
Answer: C
39. Which type of cell lacks a true nucleus?
A) Animal
B) Plant
C) Bacterial
D) Fungal
Answer: C
40. Which of the following organelles is double membrane bound?
A) Ribosome
B) Mitochondria
C) Lysosome
D) Centrosome
Answer: B
41. Which phase comes first in cell division?
A) Telophase
B) Prophase
C) Metaphase
D) Anaphase
Answer: B
42. Who proposed the term “cell theory”?
A) Schleiden and Schwann
B) Hooke and Pasteur
C) Watson and Crick
D) Darwin and Mendel
Answer: A
43. Which structure gives the cell its shape and support?
A) Cytoplasm
B) Cytoskeleton
C) Mitochondria
D) Ribosome
Answer: B
44. The process of engulfing particles by the cell is called:
A) Diffusion
B) Osmosis
C) Endocytosis
D) Exocytosis
Answer: C
45. What is the site of lipid synthesis?
A) Rough ER
B) Ribosome
C) Smooth ER
D) Lysosome
Answer: C
46. Which is the largest organelle in a plant cell?
A) Nucleus
B) Mitochondria
C) Central Vacuole
D) Chloroplast
Answer: C
47. The process by which plants make their food is:
A) Respiration
B) Digestion
C) Photosynthesis
D) Fermentation
Answer: C
48. The chromatin material condenses to form chromosomes during:
A) Interphase
B) Metaphase
C) Prophase
D) Anaphase
Answer: C
49. Which of the following is not part of the cytoskeleton?
A) Microfilaments
B) Microtubules
C) Intermediate filaments
D) Lysosomes
Answer: D
50. The outermost layer of an animal cell is:
A) Cell wall
B) Cytoplasm
C) Plasma membrane
D) Nucleus
Answer: C.
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