All Free Biology MCQs with Answers

• A. A bacterial cell has 70S ribosomes, whereas a plant cell has 80S ribosomes.
• B. A bacterial cell divides by binary fission, whereas a plant cell divides by mitosis.
• C. Bacterial cells lack a nuclear membrane, whereas plant cells possess one.
• D. None of the above

Explanation: All of the provided statements accurately represent differences between bacterial and plant cells. Prokaryotic cells like bacteria have 70S ribosomes, lack a nuclear membrane, and divide by binary fission. In contrast, plant cells, which are eukaryotic, have 80S ribosomes, a defined nucleus with a nuclear membrane, and undergo mitosis for cell division. Therefore, the option 'None of the above' is correct because it acknowledges that no incorrect differences are presented in the statements.

• A. Nucleus
• B. Ribosomes
• C. Cell membrane
• D. DNA

Explanation: The correct answer is the nucleus. Animal cells, as eukaryotes, have a well-defined nucleus enclosed by a nuclear membrane, which houses the cell's genetic material. In contrast, bacterial cells, being prokaryotic, do not have a true nucleus. Their genetic material is located in the nucleoid, a region within the cytoplasm without a surrounding membrane. Ribosomes, the cell membrane, and DNA are all present in both animal and bacterial cells, though they may differ in size and organization.

• A. Cilia
• B. Plasma membrane
• C. Membranous organelles
• D. Ribosomes

Explanation: Membrane-bound organelles are a characteristic feature of eukaryotic cells. Eukaryotic cells have a defined nucleus enclosed by a nuclear membrane, and they also contain various membrane-bound organelles such as the endoplasmic reticulum, Golgi apparatus, mitochondria, chloroplasts (in plant cells), lysosomes, and more.

• A. Ribosomes
• B. Nucleus
• C. Cell membrane
• D. Cell wall

Explanation: The defining structural difference between eukaryotic and prokaryotic cells is the presence of a nucleus. Eukaryotic cells have a true nucleus enclosed by a nuclear membrane, which houses their genetic material. In contrast, prokaryotic cells lack a true nucleus and instead have a nucleoid region where their genetic material is located. Additionally, eukaryotic cells contain various membrane-bound organelles, which are absent in prokaryotic cells.Incorrect Options:Ribosomes: Present in both cell types, differing only in size (80S in eukaryotes, 70S in prokaryotes).Cell membrane: Found in both cell types, serving a similar protective role.Cell wall: Found in both cell types but differs in composition and presence.

• A. Phospholipid bilayer
• B. Channel proteins
• C. Both A and B
• D. None of the above

Explanation: The correct answer is the phospholipid bilayer, as this structure acts as a barrier to ions due to its hydrophobic nature. Ions, being charged particles, cannot easily diffuse through the bilayer without the help of membrane proteins. In contrast, channel proteins are specifically designed to facilitate the passage of ions across the plasma membrane, allowing for regulated transport. Therefore, while the phospholipid bilayer restricts the movement of ions, channel proteins enable it. Options C and D are incorrect because they misrepresent the roles of these components in ion transport.

• A. Permeable to large ionic polar molecules
• B. Permeable to small ionic molecules
• C. Permeable to only polar molecules
• D. None of the above

Explanation: The lipid bilayer of the plasma membrane is selectively permeable. It allows small, non-polar molecules such as oxygen and carbon dioxide to pass through easily. Small polar molecules like water can also cross the membrane via osmosis, but larger or charged molecules, such as ions and large polar molecules, typically require transport proteins to facilitate their passage. Hence, the correct answer is 'None of the above' because none of the first three options correctly describe the permeability of the lipid bilayer.

• A. Extracellular
• B. Intracellular
• C. Both A and B
• D. Plasma membrane

Explanation: Glycolipids and glycoproteins are crucial components of the extracellular matrix (ECM) in animal cells and the bacterial cell wall. They help maintain cell structure and facilitate communication between cells and their environment. The ECM is a complex network composed of proteins, carbohydrates, and lipids, providing structural support to cells. Although glycolipids and glycoproteins are also present in plasma membranes, their primary structural function lies in the extracellular matrix, not within the intracellular space.

• A. Microtubules
• B. Microfilaments
• C. Intermediate filaments
• D. Cilia

Explanation: Microtubules are hollow microscopic tubular structures with an external diameter of 24 nm and of variable length. They are composed of tubulin. Intermediate filaments are the numerous microscopic protein fibers of about 10 nm thickness that form part of the cytoskeleton. They are intermediate in size between microtubules and microfilaments.They are made up of a variety of proteins e.g. keratin in nails. Microfilaments are fine, thread-like protein fibers, 7nm in diameter. They are composed predominantly of a contractile protein called actin.

• A. Genes
• B. Nucleotides
• C. Nucleosomes
• D. Base pairs

Explanation: Nucleosomes appear as 'beads ­on a ­string' in the chromosomes when viewed under an electron microscope. The beads in 'beads ­on a ­string' arrangement are complexes of histones and DNA. The beads, plus the connecting DNA that leads to the next bead, form the nucleosome. A nucleosome is the fundamental unit of organisation on which the higher-order packaging of chromatin is built. The bead of each nucleosome contains eight histone molecules, in which two copies each of H2A, H2B, H3, and H4 are found.

• A. Is
• B. Are
• C. Is being
• D. Are being

Explanation: The correct answer is is because 'neither' is a singular pronoun that requires a singular verb form. In this context, the sentence indicates that out of the two provided answers, neither is correct, hence the use of 'is' is appropriate. The options 'are' and 'are being' are incorrect as they denote a plural form, which does not agree with the singular subject 'neither.' Although 'is being' is grammatically correct, it implies a continuous action that does not fit the context of the sentence, which seeks to convey a firm conclusion about the correctness of the answers.