Free Cell Structure and Function MCQs with Answers

41. Facilitated diffusion differs from simple diffusion in that it

• A. requires energy from ATP
• B. uses specific carrier or channel proteins in the membrane
• C. moves substances against their concentration gradient
• D. occurs only through the lipid portion of the membrane

Explanation: Facilitated diffusion still follows the concentration gradient and costs no energy, but polar molecules and ions pass through specific protein channels or carriers. Needing ATP or moving against the gradient would make it active transport, a common trap in the comparison.

42. A prokaryotic cell contains all of the following EXCEPT

• A. cytoplasm
• B. a nuclear envelope
• C. ribosomes
• D. a plasma membrane

Explanation: The defining absence in a prokaryote is a membrane-bound nucleus; its DNA lies free in the nucleoid. It still has cytoplasm, 70S ribosomes and a plasma membrane, since those are requirements of every living cell.

43. The genetic material of a typical bacterium is

• A. a linear molecule wrapped around histones
• B. distributed over many chromosomes
• C. enclosed inside a nuclear envelope
• D. a single circular DNA molecule lying in the nucleoid

Explanation: The bacterial chromosome is one circular DNA molecule condensed into a nucleoid region, with no membrane around it and no histone packaging. Histones and multiple linear chromosomes belong to eukaryotes.

44. Which structure is commonly present in bacteria but absent from animal cells?

• A. Plasmid
• B. Plasma membrane
• C. Ribosomes
• D. Cytoplasm

Explanation: Plasmids are small circular DNA molecules that carry extra genes, often for antibiotic resistance, and are widely used as vectors in genetic engineering. Animal cells share the plasma membrane, ribosomes and cytoplasm with bacteria, so only the plasmid separates them.

45. Mycoplasma differs from most other bacteria in that it

• A. contains no DNA
• B. possesses 80S ribosomes
• C. lacks a cell wall
• D. is multicellular

Explanation: Mycoplasma is the smallest known self-living organism and has no cell wall, which is why antibiotics that attack wall synthesis, such as penicillin, have no effect on it. It remains fully prokaryotic, with 70S ribosomes and a single circular chromosome.

46. The idea that mitochondria and chloroplasts descended from free living prokaryotes engulfed by ancestral cells is called the

• A. cell theory
• B. germ theory
• C. theory of biogenesis
• D. endosymbiotic theory

Explanation: The endosymbiotic theory is supported by the double membranes, circular DNA and 70S ribosomes of both organelles. Cell theory states that all organisms are made of cells, and germ theory links microbes to disease, so neither addresses organelle origins.

47. Antibiotics such as streptomycin kill bacteria without seriously harming human cells because they

• A. block transcription in the human nucleus
• B. dissolve the plasma membrane of bacteria only
• C. bind to 70S ribosomes and stop bacterial protein synthesis
• D. prevent DNA replication in both cell types equally

Explanation: Human cytoplasmic ribosomes are the larger 80S type, so drugs aimed at the bacterial 70S ribosome interfere selectively with the bacterium. This selectivity is the basis of safe chemotherapy, and it is why the ribosome difference matters clinically.

48. Which of the following organisms is prokaryotic?

• A. Amoeba
• B. Cyanobacterium
• C. Yeast
• D. Paramecium

Explanation: Cyanobacteria, once called blue green algae, are photosynthetic bacteria with no membrane-bound organelles. Yeast is a fungus, while Amoeba and Paramecium are protists, and all three of those are eukaryotes.

49. Smooth endoplasmic reticulum is especially abundant in liver cells because it is the site of

• A. detoxification of drugs and poisons
• B. synthesis of proteins for export
• C. production of most of the cell's ATP
• D. digestion of worn out organelles

Explanation: The smooth ER carries the enzymes that break down drugs, alcohol and metabolic poisons, which is why liver cells are rich in it. Protein export depends on rough ER, ATP on mitochondria, and digestion of organelles on lysosomes.

50. The acrosome of a spermatozoon, which contains enzymes that penetrate the egg's coverings, is formed by the

• A. Golgi apparatus
• B. ribosome
• C. mitochondrion
• D. smooth endoplasmic reticulum

Explanation: During sperm maturation, vesicles from the Golgi collect hydrolytic enzymes and fuse at the tip of the nucleus to form the acrosome. This is a standard example of the Golgi's packaging role, distinct from the mitochondria that supply energy for the tail.