All Free Biology MCQs with Answers

• A. Proton Nucleus
• B. Nucleus
• C. Nucleoplasm
• D. Nucleoid

Explanation: The name of the region where double-stranded circular DNA is found in the prokaryotic cell is the nuclecid. The nucleoid is a region of the cytoplasm that contains the genetic material of the cell. In prokaryotic cells, the nucleoid is not surrounded by a membrane, as it is in eukaryotic cells. Instead, the DNA is simply condensed and held together by proteins.

• A. Ribosomes
• B. Endoplasmic Reticulum
• C. Nucleolus
• D. Smooth Endoplasmic Reticulum

Explanation: The site of protein synthesis in the cell are ribosomes. These are present attached to the surface of the rough endoplasmic reticulum and also in the free state in the cytoplasm. These organelles are involved in the process of translation which is the conversion of the mRNA to protein.

• A. Tonoplast
• B. Plasma membrane
• C. Epidermis
• D. Both Options B and C are correct

Explanation: The correct answer is option a) Tonoplast. The tonoplast is the specialized membrane surrounding the vacuole in plant cells, distinguishing it from other cellular membranes. It plays a vital role in regulating the transport of substances between the vacuole and the cytoplasm, helping maintain osmotic balance and store nutrients or waste products.Option b) Plasma membrane refers to the general outer boundary of the cell, not specific to the vacuole. Option c) Epidermis is a tissue type, not a cell membrane. Option d) Both Options B and C are correct is incorrect because neither option B nor C is the correct term for the vacuole's membrane.

• A. 6
• B. 9
• C. 12
• D. 15

Explanation: Animal cells, cells of some microorganisms, and lower plants contain two centrioles located near the exterior surface of the nucleus. In cross-section, each centriole consists of a cylindrical array of nine microtubules. However, each of the nine microtubules is further composed of three tubules. Centrioles are made up of nine microtubule triplets.

• A. Phospholipid
• B. Intrinsic proteins
• C. Extrinsic proteins
• D. All of these

Explanation: The fluid mosaic model describes the plasma membrane as a dynamic structure consisting of a phospholipid bilayer with proteins scattered throughout in a mosaic-like pattern. Phospholipids provide the foundational bilayer, allowing for fluidity and selective permeability. Intrinsic proteins are embedded within this bilayer, facilitating transport and signaling, while extrinsic proteins are attached to the membrane surface, contributing to signaling and structural support. Thus, the correct answer, 'All of these,' acknowledges the integral roles of phospholipids, intrinsic proteins, and extrinsic proteins in forming the plasma membrane. Options A, B, and C are incorrect individually because they only represent partial aspects of the model.

• A. Schwann
• B. Schleiden
• C. Robert Hooke
• D. Both a and b

Explanation: The first time the word cell was used to refer to these tiny units of life was in 1665 by a British scientist named Robert Hooke. When he looked at a thin slice of cork under his microscope, he was surprised to see what looked like a honeycomb. He realised that the cork was made up of many tiny units, which Hooke called cells.

• A. Nucleus
• B. Cell membrane
• C. Mitochondria
• D. All of these

Explanation: The cell membrane is essential for maintaining the cell's internal environment by regulating the passage of substances in and out of the cell. Damage to this structure leads to the uncontrolled loss of cell contents, resulting in immediate cell death. While the nucleus and mitochondria are crucial for cell functions, their damage does not result in instant cell death, as the cell can maintain short-term viability through other mechanisms.

• A. Cell membrane
• B. Golgi apparatus
• C. Mitochondria
• D. Nucleoid

Explanation: The correct answer is the cell membrane, as it is the universal cellular structure that is present in both prokaryotic and eukaryotic cells. It functions as a selective barrier that allows cells to maintain homeostasis by controlling the movement of substances in and out of the cell. In contrast, the Golgi apparatus and mitochondria are organelles specific to eukaryotes, while the nucleoid is a characteristic of prokaryotic cells. Thus, the cell membrane is the only structure common to both types of cells.

• A. Plasma membrane
• B. Ribosomes
• C. Endoplasmic reticulum
• D. Mitochondria

Explanation: Amphipathic means having both polar and non-polar heads. Hence, the only suitable option in this question is "plasma membrane" which is made up of phospholipids that have a polar phosphate head and a non-polar hydrocarbon tail.

• A. Cell wall
• B. Tonoplast
• C. Cell membrane
• D. Nuclear membrane

Explanation: The living part of the cell is the protoplasm (nucleus and cytoplasm surrounded by a membrane). The cell wall is an extracellular product and is non-living. It is a completely passive structure.