cell

Cell Biology – Detailed Notes for SSC CGL

1. Introduction to Cells

  • The cell is the smallest unit of life.

  • Cell Theory (Schleiden & Schwann, 1838-39):

    1. All living organisms are composed of one or more cells.

    2. The cell is the basic unit of life.

    3. All cells arise from pre-existing cells (Virchow, 1855).

2. Types of Cells

A. Prokaryotic Cells

  • No true nucleus (DNA is in the nucleoid region).

  • No membrane-bound organelles.

  • Examples: Bacteria & Archaea.

B. Eukaryotic Cells

  • Have a nucleus enclosed by a membrane.

  • Have membrane-bound organelles.

  • Examples: Plants, Animals, Fungi, Protists.

3. Cell Structure and Functions

A. Cell Membrane (Plasma Membrane)

  • Semi-permeable and made of a phospholipid bilayer.

  • Regulates entry & exit of substances.

  • Model: Fluid Mosaic Model (Singer & Nicolson, 1972).

B. Cytoplasm

  • Gel-like substance where organelles are suspended.

C. Nucleus

  • Contains DNA & controls cell functions.

  • Has nucleolus (produces ribosomes).

D. Cell Organelles

Organelle

Structure & Function

Mitochondria

Powerhouse of the cell, produces ATP.

Ribosomes

Site of protein synthesis (found in both prokaryotes & eukaryotes).

Endoplasmic Reticulum (ER)

Rough ER – has ribosomes, makes proteins. Smooth ER – makes lipids, detoxifies.

Golgi Apparatus

Modifies, sorts, and packages proteins.

Lysosomes

Contain digestive enzymes, known as Suicidal Bags.

Peroxisomes

Help in detoxification of harmful substances.

Centrioles

Aid in cell division (only in animal cells).

Plastids (in plants)

Chloroplast – Photosynthesis. Chromoplast – Stores pigments. Leucoplast – Stores starch.

Vacuole

Stores water & nutrients (large in plants, small in animals).

4. Cell Division

A. Mitosis

  • Produces two identical daughter cells.

  • Used for growth, repair, and asexual reproduction.

  • Occurs in somatic (body) cells.

B. Meiosis

  • Produces four haploid cells (gametes).

  • Reduces chromosome number by half.

  • Occurs in germ cells (sperm & egg formation).

5. Differences Between Plant & Animal Cells

Feature

Plant Cell

Animal Cell

Cell Wall

Present (Cellulose)

Absent

Chloroplast

Present

Absent

Vacuole

Large & Central

Small & Many

Centrioles

Absent

Present

Shape

Rectangular

Round/Irregular

6. Important Scientists & Discoveries

  • Robert Hooke (1665) – Discovered cells in cork.

  • Anton van Leeuwenhoek (1674) – Observed living cells.

  • Schleiden & Schwann (1838-39) – Cell Theory.

  • Rudolf Virchow (1855) – Cells arise from pre-existing cells.

  • Camillo Golgi – Discovered Golgi Apparatus.

MCQs for SSC CGL – Cell Biology

1. Who discovered the cell?

A) Anton van Leeuwenhoek
B) Robert Hooke
C) Rudolf Virchow
D) Theodor Schwann
✅ Answer: B) Robert Hooke

2. What is the function of mitochondria?

A) Protein synthesis
B) Digestion
C) Energy production
D) Photosynthesis
✅ Answer: C) Energy production

3. What is the powerhouse of the cell?

A) Ribosomes
B) Nucleus
C) Mitochondria
D) Golgi Apparatus
✅ Answer: C) Mitochondria

4. Which organelle is responsible for photosynthesis?

A) Mitochondria
B) Golgi Apparatus
C) Chloroplast
D) Ribosome
✅ Answer: C) Chloroplast

5. What is the function of lysosomes?

A) Protein synthesis
B) Digestion of waste materials
C) Energy production
D) DNA replication
✅ Answer: B) Digestion of waste materials

6. Which of the following is NOT found in animal cells?

A) Centrioles
B) Mitochondria
C) Cell Wall
D) Lysosomes
✅ Answer: C) Cell Wall

7. What is the smallest cell in the human body?

A) RBC
B) WBC
C) Sperm
D) Liver cell
✅ Answer: C) Sperm

8. Which of these is a semi-permeable membrane?

A) Cell wall
B) Nucleus
C) Cell membrane
D) Golgi Apparatus
✅ Answer: C) Cell membrane

9. Where is DNA found in a prokaryotic cell?

A) Nucleus
B) Ribosomes
C) Nucleoid
D) Mitochondria
✅ Answer: C) Nucleoid

10. What is the full form of ATP?

A) Adenosine Tri Phosphate
B) Amino Tri Phosphate
C) Adenine Tri Protein
D) Adenosine Tetra Phosphate
✅ Answer: A) Adenosine Tri Phosphate

Key Takeaways for SSC CGL

✔ Cells are the fundamental unit of life.
✔ Eukaryotic cells have a nucleus; prokaryotic cells do not.
✔ Mitochondria produce energy, ribosomes make proteins, and chloroplasts help in photosynthesis.
✔ Mitosis = growth & repair; Meiosis = gamete formation.
✔ Cell wall is present in plant cells but absent in animal cells.