All Free Biology MCQs with Answers

• A. Primary cell wall
• B. Secondary cell wall
• C. Middle lamella, if present
• D. Cell surface membrane

Explanation: The cell wall in plants and few algae consists of three important layers: 1) The primary cell wall is the outermost thin, flexible and extensible layer. 2) The secondary cell wall is a thick layer present inside the primary cell wall. 3) The middle lamella is a layer rich in pectins which form plasmodesmata connections between adjacent cell walls. This layer cements the cell walls of two adjacent plant cells. It is the first formed outermost layer (cell plate formed during cell division forms the middle lamella or lamellum). So, the correct answer is 'Middle lamella, if present'

• A. Nucleolus
• B. Mitochondrion
• C. Centriole
• D. Golgi apparatus

Explanation: The correct answer is the Golgi apparatus. It is located near the nucleus and is characterized by its stack of flattened, membrane-bound sacs or cisternae. These cisternae are involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles. The other options are incorrect: the nucleolus is part of the nucleus and does not contain cisternae; mitochondria contain cristae rather than cisternae and are not specifically near the nucleus; the centriole is part of the cytoskeleton and lacks cisternae.

• A. 4X
• B. 10X
• C. 40X
• D. 400X

Explanation: The total magnification of a microscope is the product of the magnifications of the eyepiece and the objective lens. In this case, you need to find the magnification power of the objective lens. Given that the eyepiece magnification is 10X and the total magnification is 40X, you calculate the objective lens magnification as follows: 40X / 10X = 4X.Other options are incorrect because they either confuse the eyepiece magnification with the objective lens magnification or misunderstand the relationship between total magnification and the magnifications of the individual components of the microscope.

• A. Galactose
• B. Glucose
• C. Phospholipid
• D. Carbohydrate

Explanation: Fluid mosaic model of the plasma membrane describes the arrangement of phospholipids in two layers, stabilized interiorly by the hydrophobic interactions while hydrophilic interactions at intracellular and extracellular faces with embedded proteins randomly.

• A. Ribosome
• B. Lysosome
• C. Chloroplast
• D. Nucleus

Explanation: Chloroplasts and mitochondria are unique among cellular organelles as they possess their own circular DNA, similar to bacterial DNA. This is a key characteristic that allows them to function semi-autonomously within the cell. In contrast, ribosomes and lysosomes do not contain any DNA, and the nucleus, while it does contain DNA, has it in a linear form organized into chromosomes. Therefore, the correct answer is chloroplasts, as they not only perform photosynthesis but also have the circular DNA structure akin to that of prokaryotes.

• A. Tetraploid
• B. Triploid
• C. Haploid
• D. Diploid

Explanation: Germ cells are products of meiosis, a process that reduces the chromosome number by half, resulting in haploid cells. This is essential for maintaining the species' chromosome number through sexual reproduction. Haploid cells carry one set of chromosomes, so during fertilization, the fusion of two haploid cells restores the diploid state. In contrast, tetraploid and triploid chromosome numbers are abnormal in the context of germ cells, while diploid refers to somatic cells, which have two sets of chromosomes.

• A. Five subunits
• B. Four subunits
• C. Three subunits
• D. Two subunits

Explanation: Ribosomes are essential organelles in the process of protein synthesis, consisting of two subunits: the large subunit and the small subunit. These subunits are crucial as they come together to form a functional ribosome capable of translating mRNA into a polypeptide chain. Options suggesting more than two subunits are incorrect because the ribosomal structure does not include additional subunits.

• A. Mitochondria
• B. Lysosome
• C. Nucleus
• D. Chloroplast

Explanation: The correct answer is Lysosome, as it is the only organelle among the options that is enclosed by a single membrane. This membrane encloses enzymes crucial for breaking down cellular components and waste. In contrast, Mitochondria, the Nucleus, and Chloroplasts all have double membranes. Mitochondria have a double membrane with an inner folded structure for ATP production, the Nucleus is enclosed by the nuclear envelope consisting of two lipid bilayers, and Chloroplasts have double outer membranes supporting the photosynthetic machinery within.

• A. i, ii, iii, iv, v
• B. v, iv, iii, ii, i
• C. ii, iv, i, iii, v
• D. ii, v, iv, iii, i

Explanation: The correct sequence for the events in Tay-Sachs disease is: ii, v, iv, iii, i. The disease begins with the inheritance of an abnormal gene (ii), which affects the synthesis of a specific lysosomal enzyme, leading to its absence (v). Without this enzyme, the catabolism of lipids is impaired (iv), resulting in their accumulation in brain cells (iii). This biochemical dysfunction ultimately manifests as mental retardation (i). Incorrect options either start with the wrong event or misplace the sequence of the biochemical and genetic progression.

• A. i, ii, iii, iv, v
• B. i, iv, v, iii, ii
• C. v, iv, iii, ii, i
• D. ii, iii, iv, v, i

Explanation: Mutations (i) in the genes responsible for lysosomal enzymes result in their deficiency (iv). This deficiency leads to metabolic sluggishness (v), as the substances that need to be broken down are not processed efficiently. Consequently, these substances accumulate within the cells (iii), culminating in storage diseases (ii). The incorrect options either misplace the events or start with outcomes rather than causes.