Question 1

Give a comparative account of the following:
(a) Apoptosis and necrosis
(b) Autocrine and paracrine signaling
(c) Anabolic and catabolic pathways
(d) Totipotent and pluripotent cells

Accepted Answer

Answer:
(a) Apoptosis vs Necrosis:
- Apoptosis is programmed cell death, a controlled and energy-dependent process that helps in removing unwanted cells without causing inflammation.
- Necrosis is uncontrolled cell death due to injury or damage, leading to cell swelling, rupture, and inflammation.

(b) Autocrine vs Paracrine signaling:
- Autocrine signaling occurs when a cell secretes signaling molecules that bind to receptors on its own surface, affecting itself.
- Paracrine signaling involves signaling molecules affecting nearby cells in the local environment.

(c) Anabolic vs Catabolic pathways:
- Anabolic pathways build complex molecules from simpler ones, requiring energy (e.g., protein synthesis).
- Catabolic pathways break down complex molecules into simpler ones, releasing energy (e.g., glycolysis).

(d) Totipotent vs Pluripotent cells:
- Totipotent cells can differentiate into all cell types including extraembryonic tissues (e.g., zygote).
- Pluripotent cells can differentiate into almost all cell types but not extraembryonic tissues (e.g., embryonic stem cells). — Each pair is compared based on definition, function, and characteristics to highlight differences.

Question 2

Explain how stem cells are different from blood cells in terms of potency?

Accepted Answer

Stem cells are undifferentiated cells capable of self-renewal and differentiation into various specialized cell types. They are multipotent or pluripotent depending on their type. Blood cells, on the other hand, are differentiated cells with specific functions and limited or no ability to differentiate further. Thus, stem cells have higher potency compared to blood cells which are terminally differentiated. — Stem cells possess the ability to differentiate into multiple cell types (potency), whereas blood cells are specialized and cannot differentiate further.

Question 3

How many mitotic divisions will produce 64 cells out of a single cell?

Accepted Answer

Each mitotic division doubles the number of cells. Starting from 1 cell:
Number of cells after n divisions = 2^n
We need 2^n = 64
64 = 2^6
Therefore, n = 6 mitotic divisions are required. — Since each mitotic division doubles the cell number, the number of divisions needed to reach 64 cells is the exponent of 2 that equals 64, which is 6.

Question 4

Match the following
(a) Centromere
(b) Kinetochore
(c) Metaphase
(d) Zygotene
(e) Pachytene
(f) Meiosis I
(g) Meiosis II
with
(i) Reductional division
(ii) Holds the two sister chromatids together
(iii) Pairing of homologous chromosomes
(iv) Equational division
(v) Assembly of homologous chromosomes on metaphase plate
(vi) Site of attachment of chromosomes to spindle fibers
(vii) Crossing over between homologous chromosomes occurs

Accepted Answer

Matching pairs:
(a) Centromere - (ii) Holds the two sister chromatids together
(b) Kinetochore - (vi) Site of attachment of chromosomes to spindle fibers
(c) Metaphase - (v) Assembly of homologous chromosomes on metaphase plate
(d) Zygotene - (iii) Pairing of homologous chromosomes
(e) Pachytene - (vii) Crossing over between homologous chromosomes occurs
(f) Meiosis I - (i) Reductional division
(g) Meiosis II - (iv) Equational division — Each term is matched with its correct definition or characteristic based on meiosis and chromosome structure.

Question 5

How is cell migration important for the development of an embryo?

Accepted Answer

Cell migration is crucial during embryonic development as it allows cells to move from their origin to specific locations where they differentiate and form tissues and organs. This process helps in shaping the embryo, establishing body plan, and ensuring proper organ formation. — Migration enables cells to reach their target sites, facilitating tissue organization and morphogenesis during embryogenesis.

Question 6

What is the significance of citric acid cycle?

Accepted Answer

The citric acid cycle (Krebs cycle) is significant because it is a central metabolic pathway that oxidizes acetyl-CoA to CO2 and generates high-energy electron carriers (NADH and FADH2) and GTP/ATP. These electron carriers then feed into the electron transport chain to produce ATP, the energy currency of the cell. It also provides intermediates for biosynthetic pathways. — It plays a key role in energy production and supplies precursors for synthesis of amino acids and other biomolecules.

Question 7

The first reaction in glycolysis is catalysed by which of the following enzymes:
(a) Glucokinase
(b) Phosphoglycerate kinase
(c) Phosphofructokinase
(d) Hexokinase

Accepted Answer

The first reaction in glycolysis is the phosphorylation of glucose to glucose-6-phosphate. This reaction is catalyzed by Hexokinase (option d). Hexokinase transfers a phosphate group from ATP to glucose, trapping glucose inside the cell and preparing it for further metabolism. — Hexokinase catalyzes the first step of glycolysis, which is essential for glucose utilization. Glucokinase is a hexokinase isoform in liver cells but generally hexokinase is the correct answer. Phosphoglycerate kinase and phosphofructokinase catalyze later steps.

Question 8

Which of the following statements regarding cell signaling is NOT true?
(a) In endocrine signaling, the ligand reaches the target cell through bloodstream after being synthesised in the extracellular space.
(b) Synaptic signaling is an example of paracrine signaling.
(c) Ligands bind to receptors in a non-specific manner.
(d) Cancer cells exhibit autocrine signaling.

Accepted Answer

Option (c) is NOT true. Ligands bind to receptors in a highly specific manner to trigger appropriate cellular responses. Non-specific binding would not allow precise signaling.

Explanation of other options:
(a) True - Endocrine signaling involves hormones traveling through the bloodstream.
(b) True - Synaptic signaling is a specialized form of paracrine signaling.
(d) True - Cancer cells often use autocrine signaling to promote their own growth. — Specific ligand-receptor binding is fundamental to cell signaling specificity and function.

Question 9

Dark reaction in photosynthesis is named so because—
(a) It occurs independent of light energy
(b) It occurs in dark
(c) It cannot occur in daylight
(d) All of the above

Accepted Answer

Option (a) is correct. The dark reaction (Calvin cycle) is called so because it does not require light directly; it uses ATP and NADPH produced in the light reactions to fix CO2 into carbohydrates. It can occur in light or dark conditions as long as ATP and NADPH are available. — The name 'dark reaction' is historical and refers to the light-independent nature of the Calvin cycle, not that it only occurs in darkness.

Question 10

Differentiate between cyclic and non-cyclic photophosphorylation.

Accepted Answer

Cyclic photophosphorylation:
- Involves only Photosystem I.
- Electrons cycle back to Photosystem I.
- Produces ATP only.
- No NADPH or oxygen is produced.

Non-cyclic photophosphorylation:
- Involves both Photosystem I and II.
- Electrons flow from water to NADP+.
- Produces ATP, NADPH, and oxygen (from water splitting).
- Electrons do not cycle back but move linearly. — The key difference is electron flow and products formed. Cyclic produces ATP only, non-cyclic produces ATP, NADPH, and oxygen.

Question 11

Briefly describe Calvin cycle.

Accepted Answer

The Calvin cycle is the set of light-independent reactions in photosynthesis that fix atmospheric CO2 into organic molecules. It occurs in the stroma of chloroplasts and involves three phases:
1. Carbon fixation: CO2 is attached to ribulose bisphosphate (RuBP) by the enzyme Rubisco.
2. Reduction: ATP and NADPH are used to convert 3-phosphoglycerate into glyceraldehyde-3-phosphate (G3P).
3. Regeneration: Some G3P molecules regenerate RuBP to continue the cycle.
The cycle produces G3P which can be used to form glucose and other carbohydrates. — Calvin cycle uses energy from light reactions to convert CO2 into sugars, essential for plant growth.

Question 12

Which of the following best describes catabolism in cellular processes?

Accepted Answer

Breakdown of molecules to release energy — Catabolism refers to the metabolic pathways that break down complex molecules into simpler ones, releasing energy that the cell can use. This contrasts with anabolism, which synthesizes complex molecules and requires energy input.

Question 13

Assertion (A): Glycolysis occurs in the cytoplasm and does not require oxygen.
Reason (R): Glycolysis is an anaerobic process that breaks down glucose into pyruvate producing ATP and NADH.

Accepted Answer

A — Assertion is true because glycolysis occurs in the cytoplasm and does not require oxygen. Reason is true because glycolysis is an anaerobic process that breaks glucose into pyruvate, producing ATP and NADH. The reason correctly explains the assertion.

Question 14

Fill in the blank: The process in which glucose is broken down into two molecules of pyruvate in the cytoplasm is called _____.

Accepted Answer

glycolysis — Glycolysis is the metabolic pathway that breaks down glucose, a six-carbon sugar, into two molecules of pyruvate in the cytoplasm. This process yields ATP and NADH and does not require oxygen.

Question 15

Which organelle is primarily involved in the Krebs cycle and electron transport chain?

Accepted Answer

Mitochondria — The Krebs cycle and electron transport chain occur in the mitochondria. The Krebs cycle takes place in the mitochondrial matrix, while the electron transport chain is located in the inner mitochondrial membrane.

Cellular Processes

Cellular Processes — Study Notes

Introduction to Cellular Processes

Metabolism of Carbohydrates

Metabolism of Lipids

Practice Questions — Cellular Processes

All 12 Chapters in Biotechnology