FYUG EVEN SEMESTER EXAM 2024 ZOOLOGY (2nd Semester) Course No.: ZOODSC-151T

Time: 3 Hours | Full Marks: 70

Subject: Zoology

Paper Code: ZOODSC-151T

Semester: 2nd Semester (FYUG)

Year: 2024

SECTION-A

Answer any ten questions. (All solved below for full coverage)

1. Who had discovered the cell? Write the cell theory. [2]

Robert Hooke discovered the cell in 1665.

Cell Theory: All living organisms are composed of one or more cells; the cell is the basic unit of structure and organization in organisms; and cells arise from pre-existing cells.

2. Mention four differences between prokaryotic and eukaryotic cells. [2]

Feature Prokaryotic Cell Eukaryotic Cell
Nucleus Absent (Nucleoid) Present (True Nucleus)
Organelles Membrane-bound organelles absent Present (Mitochondria, Golgi, etc.)
DNA Circular DNA Linear DNA
Ribosomes 70S type 80S type

3. Why viruses are not considered as true cells? Give reasons. [2]

Viruses are not considered true cells because they lack a cellular structure, cytoplasm, and independent metabolic machinery. They cannot reproduce outside a living host cell.

4. Define plasma membrane. Name two enzymes present in the plasma membrane. [2]

The plasma membrane is a semi-permeable biological membrane that separates the interior of all cells from the outside environment.

  • Adenylate cyclase
  • Alkaline phosphatase

5. What is active transport? Give example. [2]

Active transport is the movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration, requiring energy in the form of ATP.

Example: Sodium-Potassium pump (Na+/K+ pump).

6. Define gap junction. In which tissue gap junctions are mostly found? [2]

A gap junction is a specialized intercellular connection that directly connects the cytoplasm of two cells, allowing molecules and ions to pass freely between cells. They are mostly found in cardiac muscle tissue and epithelial tissues.

7. What is oxidative phosphorylation? Where does it occur within the cell? [2]

Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing energy which is used to produce ATP. It occurs in the inner mitochondrial membrane.

8. Define ribosome. Who first described ribosomes? [2]

Ribosomes are complex molecular machines found within all living cells that serve as the site of biological protein synthesis. They were first described by George Palade.

9. Why is mitochondria considered as semi-autonomous organelle? [2]

Mitochondria are considered semi-autonomous because they contain their own circular DNA and ribosomes, allowing them to synthesize some of their own proteins and self-replicate.

10. Who first discovered and named nucleus? Name one eukaryotic cell that does not contain nucleus. [2]

Robert Brown first discovered and named the nucleus. A eukaryotic cell that lacks a nucleus is the Mature Mammalian Red Blood Cell (RBC).

11. Differentiate between euchromatin and heterochromatin. [2]

  • Euchromatin: Lightly packed form of chromatin that is enriched in genes and often under active transcription.
  • Heterochromatin: Tightly packed form of DNA which comes in multiple varieties and is generally transcriptionally inactive.

12. What is intermediate filament? Mention its functions. [2]

Intermediate filaments are cytoskeletal structural components found in the cells of many animal species. They provide mechanical strength to cells and help maintain cell shape.

13. Write at least four differences between mitosis and meiosis. [2]

Mitosis Meiosis
Occurs in somatic cells Occurs in germ cells
Produces two daughter cells Produces four daughter cells
Chromosome number remains same (2n) Chromosome number is halved (n)
No genetic variation (clones) Genetic variation occurs via crossing over

14. Define cell cycle. What is cyclin? [2]

The cell cycle is the series of events that take place in a cell leading to its division and duplication of its DNA to produce two daughter cells. Cyclin is a family of proteins that controls the progression of a cell through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes.

15. What are secondary messengers? Give example. [2]

Secondary messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules (primary messengers).

Example: Cyclic AMP (cAMP) or Calcium ions (Ca2+).

SECTION-B

Answer any five questions. (All solved below for full coverage)

16. Define a cell. Describe the structure of a typical eukaryotic cell with a properly labelled diagram. Name the factors which control the shape of the cells. Mention at least two differences between an animal cell and a plant cell. [1+6+1+2=10]

Definition: A cell is the structural, functional, and biological unit of all known living organisms.

Structure of Eukaryotic Cell: A typical eukaryotic cell consists of three main parts: the plasma membrane, the cytoplasm containing various organelles, and a membrane-bound nucleus. Key organelles include mitochondria (powerhouse), Golgi apparatus (packaging), Endoplasmic Reticulum (transport), and lysosomes (digestion).

Factors Controlling Cell Shape: Cell shape is controlled by the cytoskeleton (microtubules, microfilaments), internal pressure, and the function the cell performs.

Animal Cell vs Plant Cell:

  • Cell Wall: Plant cells have a rigid cellulose cell wall; animal cells do not.
  • Chloroplasts: Plant cells contain chloroplasts for photosynthesis; animal cells do not.

17. Describe general organization of viruses. Why are viruses considered both living as well as non-living? What are viroids? Name two diseases caused by prions. [6+2+1+1=10]

Organization of Viruses: Viruses consist of a genetic material (DNA or RNA) enclosed in a protein coat called a capsid. Some viruses also have an outer lipid envelope. They lack cellular organelles and metabolic systems.

Living vs Non-living: Viruses are considered living because they possess genetic material and can replicate within a host. They are non-living because they can be crystallized, lack metabolism, and cannot reproduce independently.

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

Prion Diseases: 1. Mad Cow Disease (BSE), 2. Creutzfeldt-Jakob Disease (CJD).

18. Who put forward the concept of unit membrane? Give an account of the fluid-mosaic model of plasma membrane with illustration. Mention the functions of the plasma membrane. [1+7+2=10]

Unit Membrane Concept: Put forward by J.D. Robertson.

Fluid-Mosaic Model: Proposed by Singer and Nicolson in 1972. It describes the membrane as a "mosaic" of proteins floating in or on a fluid lipid bilayer. Phospholipids have hydrophilic heads facing outward and hydrophobic tails facing inward. Proteins can be integral (spanning the membrane) or peripheral.

Functions:

  • Protects the cell and maintains its shape.
  • Regulates the transport of substances (Selective Permeability).
  • Cell signaling and communication.

19. Write short notes on: (a) Golgi apparatus (b) Lysosomes. [5+5=10]

(a) Golgi Apparatus: Discovered by Camillo Golgi. It consists of flattened sacs called cisternae. Its main function is the processing, packaging, and secretion of proteins and lipids synthesized in the ER.

(b) Lysosomes: Known as "suicidal bags" of the cell. They are spherical sacs containing hydrolytic enzymes. They function in intracellular digestion, breaking down waste materials, cellular debris, and foreign particles.

20. Describe the structure of mitochondria with proper illustration. Mention the important functions of mitochondria. Write briefly about the endosymbiotic hypothesis. [6+2+2=10]

Structure: Mitochondria are double-membrane organelles. The outer membrane is smooth, while the inner membrane is folded into cristae to increase surface area. The space inside the inner membrane is the matrix, containing DNA and enzymes.

Functions: ATP production via cellular respiration, regulation of metabolism, and calcium storage.

Endosymbiotic Hypothesis: This theory suggests that mitochondria originated as free-living bacteria that were engulfed by a larger host cell, eventually becoming a permanent organelle.

21. Write short notes on: (a) Prokaryotic ribosomes (b) Peroxisomes. [5+5=10]

(a) Prokaryotic Ribosomes: These are 70S type, consisting of two subunits: 50S and 30S. They are found freely in the cytoplasm and are responsible for protein synthesis.

(b) Peroxisomes: Small, membrane-bound organelles containing oxidative enzymes like catalase. They function in breaking down fatty acids and detoxifying hydrogen peroxide (H2O2) into water and oxygen.

22. Describe the structure of nucleus with proper illustration. Throw light on its role in inheritance. Mention at least two differences between nucleus and nucleolus. [6+2+2=10]

Structure: The nucleus is enclosed by a double-layered nuclear envelope with nuclear pores. It contains the nucleoplasm, chromatin (DNA and proteins), and the nucleolus.

Role in Inheritance: The nucleus houses the genetic material (DNA) in the form of chromosomes, which carries the hereditary information passed from parents to offspring.

Nucleus vs Nucleolus:

  • The nucleus is the whole organelle; the nucleolus is a structure inside the nucleus.
  • The nucleus contains DNA; the nucleolus is primarily involved in rRNA synthesis and ribosome assembly.

23. What are microtubules? Briefly describe the structure and functions of microtubules. Define microfilament. What are the functions of microfilament in the cell? [6+2+2=10]

Microtubules: Hollow, cylindrical structures made of tubulin protein. They provide structural support, form the spindle apparatus during cell division, and assist in intracellular transport.

Microfilaments: Thin, solid rods made primarily of the protein actin.

Functions: They are involved in muscle contraction, cell movement (amoeboid movement), and maintaining cell shape.

24. Describe the Prophase-I of first meiotic division with proper diagram. Write a note on significance of meiosis. Define cytokinesis. [6+2+2=10]

Prophase-I: A complex stage divided into five substages: Leptotene, Zygotene (pairing of chromosomes), Pachytene (crossing over), Diplotene, and Diakinesis. It is characterized by the exchange of genetic material between homologous chromosomes.

Significance: Meiosis ensures the maintenance of a constant chromosome number across generations and introduces genetic variation via crossing over.

Cytokinesis: The physical process of cell division, which divides the cytoplasm of a parental cell into two daughter cells.

25. Write short notes on: (a) Regulation of cell cycle (b) GPCR and its role in cell signalling. [5+5=10]

(a) Regulation of Cell Cycle: Controlled by internal checkpoints (G1, G2, and M checkpoints) and regulatory proteins like Cyclins and Cyclin-Dependent Kinases (CDKs). These ensure the cell is ready to proceed to the next phase without errors.

(b) GPCR (G-Protein Coupled Receptors): The largest family of cell-surface receptors. They detect molecules outside the cell and activate internal signal transduction pathways, ultimately leading to cellular responses.

Exam Focus Enhancements

Important Formulas & Laws

  • Cell Theory: All cells come from pre-existing cells.
  • 70S Ribosome = 50S + 30S subunits (Prokaryotic).
  • 80S Ribosome = 60S + 40S subunits (Eukaryotic).

Exam Tips

  • Always draw neat, labeled diagrams for long questions to score full marks.
  • In Section B, use bullet points for functions and features.
  • Differentiate between "Living" and "Non-living" features clearly for Virus questions.

Answer Presentation Strategy

For questions worth 10 marks (Section B), follow the structure: Introduction/Definition -> Detailed Explanation -> Diagram -> Conclusion. This ensures clarity and satisfies the marks weightage requirements.