Test: The Fundamental Unit of Life- 1 - UPSC MCQ

The plasma membrane, also referred to as the cell membrane, is the outermost covering of a cell that controls the movement of substances in and out of the cell. This selective permeability is essential for maintaining cellular functions and homeostasis.

- Option A: Hypertonic solution - Cell swells up
 Incorrect. In a hypertonic solution, the outside solution has a higher solute concentration than inside the cell, causing the cell to lose water and shrink, not swell up.

- Option B: Hypotonic solution - Cell shrinks
Incorrect. In a hypotonic solution, the outside solution has a lower solute concentration than inside the cell, causing the cell to gain water and swell up, not shrink.

- Option C: Isotonic solution - No net movement of water
Correct. In an isotonic solution, the concentration of solutes outside the cell is the same as inside the cell, resulting in no net movement of water across the cell membrane. Thus, the cell maintains its shape and size.

- Option D: Diffusion - Movement of water molecules
Incorrect. Diffusion is the movement of molecules (excluding water molecules) from a region of higher concentration to a region of lower concentration. The movement of water molecules specifically through a selectively permeable membrane is known as osmosis.

• Assertion Correctness: The assertion is correct. Robert Hooke did indeed first observe cells in a cork slice in 1665.
• Reason Correctness: The reason is also correct. The cell theory was indeed formulated by Schleiden and Schwann, stating that cells are the basic unit of life.
• Explanation: While both the assertion and reason are factually accurate, the reason provided does not directly explain the assertion. The discovery of cells by Hooke and the formulation of the cell theory by Schleiden and Schwann are two separate events in the history of cell biology.

- Option A: Smooth Endoplasmic Reticulum - Protein Synthesis
The Smooth Endoplasmic Reticulum (SER) is primarily involved in the synthesis of lipids and detoxification of drugs and poisons, not protein synthesis. Protein synthesis is the function of the Rough Endoplasmic Reticulum (RER). Therefore, this pair is incorrectly matched.

- Option B: Golgi Apparatus - Formation of Lysosomes
The Golgi Apparatus is involved in the formation of lysosomes. It packages and dispatches materials within the cell and is essential for the synthesis of complex sugars and the formation of lysosomes from simple vesicles. Therefore, this pair is correctly matched.

- Option C: Lysosomes - Photosynthesis
Lysosomes are responsible for digesting cellular waste and foreign materials within the cell. Photosynthesis is a process carried out by chloroplasts in plant cells. Therefore, this pair is incorrectly matched.

- Option D: Mitochondrion - Detoxification of Drugs
Mitochondria are known as the powerhouses of the cell, involved in energy production through cellular respiration. Detoxification of drugs is a function of the Smooth Endoplasmic Reticulum, not mitochondria. Therefore, this pair is incorrectly matched.

Thus, the correctly matched pair is Option B: Golgi Apparatus - Formation of Lysosomes.

The ER membrane is structurally similar to the plasma membrane, which is a crucial feature of the endoplasmic reticulum.

Mitochondria are known as the powerhouses of the cell primarily because they are responsible for generating ATP (Adenosine triphosphate), which is the energy currency of the cell. This process occurs through chemical reactions within the mitochondria, providing energy for various cellular activities essential for life.

- Option A: Chromatin material - Visible as rod-shaped structures when cell is about to divide
Incorrect. Chromatin material is visible as an entangled mass of thread-like structures when the cell is not dividing. It organizes into chromosomes, which are rod-shaped structures, when the cell is about to divide.

- Option B: Prokaryotes - Cells with membrane-bound organelles
Incorrect. Prokaryotes are organisms whose cells lack a nuclear membrane and most of the other membrane-bound organelles found in eukaryotic cells.

- Option C: Nucleoid - Well-defined nuclear region with nuclear membrane
Incorrect. The nucleoid is a poorly defined nuclear region in prokaryotes that lacks a nuclear membrane.

- Option D: Functional segments of DNA - Genes
Correct. Genes are the functional segments of DNA that contain the information necessary for constructing and organizing cells.

The correct answer is Option D because it accurately describes the relationship between functional segments of DNA and genes, while the other options contain inaccuracies based on the provided content.

Chromosomes are structures in the nucleus that contain DNA and protein, visible as rod-shaped bodies when a cell is preparing to divide.

Leucoplasts primarily function in storage within a cell. They are specialized organelles that store various substances such as proteins, lipids, and starch. This storage function is essential for the cell's metabolic processes and long-term energy needs.

- Option A: Prokaryotic Cell - Membrane-bound cell organelles present
Incorrect. Prokaryotic cells do not have membrane-bound cell organelles. They lack structures such as mitochondria, Golgi apparatus, and endoplasmic reticulum, which are found in eukaryotic cells.

- Option B: Eukaryotic Cell - Single chromosome
Incorrect. Eukaryotic cells have multiple chromosomes contained within a well-defined nucleus, unlike prokaryotic cells which typically have a single, circular chromosome.

- Option C: Prokaryotic Cell - Nuclear region not well defined
Correct. Prokaryotic cells have a nuclear region that is not well defined and is known as the nucleoid. This region is not enclosed by a nuclear membrane.

- Option D: Eukaryotic Cell - Nuclear region not well defined
Incorrect. Eukaryotic cells have a well-defined nuclear region that is surrounded by a nuclear membrane, distinguishing them from prokaryotic cells.

The correct answer, therefore, is Option C: Prokaryotic Cell - Nuclear region not well defined.

• Meiosis involves two consecutive rounds of division (meiosis I and meiosis II) and results in four non-identical cells, each with half the number of chromosomes as the original cell. This reduction is crucial for sexual reproduction because it ensures that when gametes (sperm and egg) fuse during fertilization, the resulting zygote will have the correct diploid number of chromosomes.

• Mitosis involves a single round of division and produces two identical daughter cells, each with the same number of chromosomes as the original cell.

Here's a quick breakdown of the other options:

• Option A: Correct in stating that meiosis involves two divisions, while mitosis involves one. However, Option B more directly addresses the key distinction in the number of cells and chromosome count.

• Option C: Incorrect because meiosis occurs in gamete-producing cells (sex cells), while mitosis occurs in somatic cells (body cells).

• Option D: While meiosis does result in genetic variation, mitosis also results in identical genetic copies. This option is partially correct but doesn’t directly address the difference in the number of cells or chromosomes.

Therefore, Option B is the best answer, accurately describing the key difference in terms of cell division outcomes.

Cells are enclosed by a plasma membrane composed of lipids and proteins. The plasma membrane regulates the movement of materials between the interior of the cell and the outer environment.

1. Vacuoles are only found in plant cells and not in animal cells.
   This statement is incorrect. Vacuoles are found in both plant and animal cells, although they are more prominent and have a larger central vacuole in plant cells.

2. The central vacuole in some plant cells can occupy 50-90% of the cell volume.
   This statement is correct. In plant cells, the central vacuole can be very large, occupying a significant portion of the cell's volume, ranging from 50-90%.

3. Plant cells generally have smaller vacuoles than animal cells.
   This statement is incorrect. Plant cells typically have a very large central vacuole, whereas animal cells have smaller vacuoles.

4. Vacuoles are large and centrally located in animal cells.
   This statement is incorrect. In animal cells, vacuoles are typically small and scattered throughout the cytoplasm. It is in plant cells that a large, central vacuole is commonly found.

Correct Answer: The central vacuole in some plant cells can occupy 50-90% of the cell volume.

- Option A: Mitosis - Four new cells
Incorrect. Mitosis results in the formation of two identical daughter cells, not four. Each daughter cell has the same number of chromosomes as the mother cell.

- Option B: Meiosis - Two new cells
Incorrect. Meiosis leads to the creation of four new cells, each with half the number of chromosomes compared to the mother cell, not just two.

- Option C: Golgi apparatus - Storage and packaging of substances
Correct. The Golgi apparatus is responsible for the storage, modification, and packaging of substances manufactured in the cell.

- Option D: Nucleus - Manufacture of proteins
Incorrect. The nucleus directs the life processes of the cell and contains genetic material, but the actual manufacture of proteins occurs in the ribosomes, which are either free in the cytoplasm or attached to the endoplasmic reticulum.

Thus, the correctly matched pair is Option C: (c) Golgi apparatus - Storage and packaging of substances.