ZOOLOGY: CELL BIOLOGY (ZOODSC-151) FYUG Even Semester Exam, 2025

UNIT-I

Question 1 (a) 2 Marks

Define cell biology.

Cell biology is a branch of biology that studies the structure, function, and behavior of cells, which are the fundamental units of life.

Question 1 (b) 2 Marks

Who proposed the cell theory? Mention the factors which control the shape of the cell.

The cell theory was formally proposed by Theodor Schwann and Matthias Jakob Schleiden in 1839.

Factors controlling cell shape include:

• Cytoskeleton: Microtubules and microfilaments provide structural support.
• Cell Wall: In plants and bacteria, it provides a rigid shape.
• Surface Tension: Influences the rounding of free-floating cells.
• Internal Pressure: Turgor pressure in plant cells.

Question 1 (c) 2 Marks

Define virus. What are viroids?

Virus: A submicroscopic infectious agent that replicates only inside the living cells of an organism, consisting of genetic material (DNA or RNA) wrapped in a protein coat.

Viroids: These are the smallest infectious pathogens known, consisting solely of a short strand of circular, single-stranded RNA without a protein coat.

Question 2 (a) 10 Marks

Describe the structure of an animal cell with labelled diagram. State the functions which are attributed to different cell organelles.

An animal cell is a eukaryotic cell enclosed by a plasma membrane and containing a membrane-bound nucleus and organelles.

Key Organelles and Functions:

• Nucleus: Contains genetic material (DNA) and coordinates cell activities like growth and reproduction.
• Mitochondria: The "powerhouse" of the cell; site of ATP production through cellular respiration.
• Ribosomes: Sites of protein synthesis.
• Endoplasmic Reticulum (ER): Rough ER (with ribosomes) handles protein folding; Smooth ER handles lipid synthesis.
• Golgi Apparatus: Modifies, sorts, and packages proteins for secretion.
• Lysosomes: Contain digestive enzymes to break down waste materials.
• Centrioles: Play a crucial role in organizing microtubule assembly during cell division.

Question 2 (b) 10 Marks

Write short notes on any two: (i) Bacterial Cell, (ii) Organization of Virus, (iii) Prion.

(i) Structure of a bacterial cell: Prokaryotic, lacking a nucleus. Contains a nucleoid, plasmids, cell wall (peptidoglycan), and flagella for movement.

(ii) Structural organization of virus: Consists of a Capsid (protein shell) and Nucleic Acid (DNA/RNA). Some have an outer envelope derived from host membranes.

UNIT-II

Question 3 (a) 2 Marks

Name two models of plasma membrane structure. Mention two functions of plasma membrane.

Models: 1. Fluid Mosaic Model (Singer and Nicolson), 2. Unit Membrane Model (Robertson).

Functions: 1. Selective permeability, 2. Protection and cell signaling.

Question 3 (b) 2 Marks

What is cell permeability? Define the process of passive transport.

Cell Permeability: The ability of a cell membrane to allow the passage of specific molecules or ions through it by diffusion or specialized channels.

Passive Transport: The movement of substances across a cell membrane without the expenditure of energy (ATP), moving along the concentration gradient.

Question 3 (c) 2 Marks

What are desmosomes? Mention their functions.

Desmosomes are specialized adhesive protein complexes that localized to intercellular junctions. They act like "spot welds" to provide mechanical strength to tissues.

Question 4 (a) 10 Marks

Describe the ultrastructure of plasma membrane with diagram. Differentiate between active and passive transport. Add a note on facilitated transport.

The plasma membrane follows the Fluid Mosaic Model, composed of a phospholipid bilayer with embedded proteins (integral and peripheral) and cholesterol.

Facilitated Transport: A type of passive transport where molecules move across the membrane via specific transmembrane integral proteins (carriers or channels) without using energy.

UNIT-III

Question 5 (a) 2 Marks

Name the cell type in which mitochondria are absent. Give reason for absence.

Mitochondria are absent in Mature Mammalian Red Blood Cells (RBCs). They are absent to maximize space for hemoglobin and to prevent the RBC from consuming the oxygen it carries.

Question 6 (b) (i) 5 Marks

Structure and function of mitochondria.

Mitochondria are double-membrane structures. The inner membrane is folded into cristae to increase surface area for ATP production. They contain their own DNA and ribosomes.

UNIT-V

Question 10 (a) 10 Marks

Describe the different phases of mitotic cell division with illustration. Add a note on significance and define karyokinesis.

1. Prophase: Chromatin condenses, nuclear envelope breaks down.
2. Metaphase: Chromosomes align at the equatorial plate.
3. Anaphase: Sister chromatids separate to opposite poles.
4. Telophase: Nuclear envelopes reform around separated chromatids.

Karyokinesis: The division of the cell nucleus during cell division.

Significance: Essential for growth, tissue repair, and asexual reproduction.