Cell: The Unit of Life MCQs

Schleiden studied plant cells and proposed that all plants are composed of cells, while Schwann extended this to animals, stating that all living organisms are made of cells. Their combined statements established the two main tenets of the cell theory. Hence the correct answer is Matthias Schleiden and Theodor Schwann.

Motility in bacteria requires a whip‑like appendage that can rotate to propel the cell.

Fimbriae and pili are short, hair‑like structures used for attachment and DNA transfer, not for movement.

The glycocalyx is a slime layer or capsule involved in protection and adherence, not locomotion.

Flagella are long, helical filaments that rotate like a propeller, providing the main mechanism for bacterial motility.

Hence the correct answer is Flagella.

Plasmodesmata are microscopic channels that traverse the cell walls of plant cells, linking their cytoplasm.

These channels allow movement of substances and signaling molecules directly between adjacent cells.

Thus the cytoplasmic connections through the cell wall are called plasmodesmata.

Inner mitochondrial membrane forms deep invaginations to increase surface area for oxidative phosphorylation.

These invaginations are called cristae, not to be confused with thylakoids of chloroplasts.

Thus the correct choice is Cristae.

Comma‑shaped bacteria are curved rods, not straight rods or spirals.

The term “Vibrio” is used for bacteria that are curved or comma‑like in appearance.

Bacillus refers to straight rods, Spirillum to helical coils, and Coccus to spherical cells.

Hence the correct answer is Vibrio.

Fungal cell walls are rigid structures that protect the cell and maintain shape.

The main polysaccharide in these walls is chitin, a polymer of N‑acetylglucosamine.

Cellulose is typical of plant walls, peptidoglycan of bacterial walls, and pectin of plant middle lamella.

Hence the cell wall of fungi is composed of chitin.

Mitochondria generate ATP through oxidative phosphorylation, providing energy for cellular activities.

The organelle’s inner membrane folds (cristae) increase surface area for the electron‑transport chain.

Thus they serve as the cell’s main energy‑producing unit, earning the name “Powerhouses of the cell”.

Ribosomes consist of a large and a small subunit that together form the site of protein synthesis. Each subunit is a complex of ribosomal RNA (rRNA) molecules that provide structural and catalytic functions, together with associated ribosomal proteins that stabilize the rRNA and assist in binding mRNA and tRNA. Hence the two subunits are made up of ribosomal RNA and proteins. Ribosomal RNA and proteins.

Cell theory states that all cells arise from pre‑existing cells; this concept was formulated by Rudolf Virchow in 1855.

He added the phrase “Omnis cellula e cellula” to the earlier ideas of Schleiden and Schwann, emphasizing that cells do not spontaneously generate.

Thus the correct answer is Rudolf Virchow.

The bacterial flagellum has a long external filament that acts as a propeller, a curved hook that connects the filament to the motor, and a basal body embedded in the cell envelope that functions as the rotary engine. These three structural components together enable bacterial motility. Hence the correct choice is filament, hook and basal body.

The outer nuclear membrane is continuous with a system of flattened sacs and tubules that extend throughout the cytoplasm.

These interconnected tubules and sacs form the endoplasmic reticulum, serving as a membrane network linked to the nucleus.

Thus the correct answer is Endoplasmic reticulum.

The citric acid cycle enzymes are soluble proteins that function in the mitochondrial matrix where acetyl‑CoA is generated.

Substrate‑level reactions of the cycle require the aqueous environment of the matrix for diffusion of NAD⁺, FAD and ADP.

Thus the cycle occurs in the mitochondrial matrix, not on membranes or in the intermembrane space.

Hooke examined thin sections of cork under a microscope and saw tiny box‑like compartments.

He described these compartments as “cells” because they resembled the small rooms (cells) in a monastery.

Thus the first observer who coined the term “cell” was Robert Hooke.

The plasma membrane is a dynamic bilayer of phospholipids with proteins interspersed, allowing lateral movement of its components. This description matches the model that depicts a fluid lipid bilayer with a mosaic of proteins. Hence the widely accepted model is the fluid mosaic model.

Rough ER is studded with particles that give it a granular appearance under the microscope.

These particles are ribosomes bound to the cytoplasmic side of the ER membrane.

Ribosomes synthesize proteins that enter the lumen of the ER, making the surface look “rough.”

Hence the correct answer is Ribosomes on its surface.

Plastids are membrane‑bound organelles that contain pigments or store substances, characteristic of photosynthetic eukaryotes.

Only plant cells and certain protists such as euglenoids possess these organelles; bacteria and animal cells lack them.

Thus the correct choice is Plant cells and euglenoids.

Observing pond water under a simple microscope, he noted moving, single‑celled organisms that reproduced independently.

These observations were the first documented descriptions of living, free‑standing cells.

Thus the scientist who first saw and described free‑living cells is Anton von Leeuwenhoek.

The fluid mosaic model describes the membrane lipids as a semi‑fluid layer where individual phospholipids can move sideways. Because the bilayer is not rigid, embedded proteins are not fixed in place. This lateral mobility permits proteins to diffuse within the plane of the membrane. Hence the correct answer is lateral movement of proteins within the bilayer.

Smooth ER lacks ribosomes, so it does not synthesize proteins.

It contains enzymes for fatty‑acid and phospholipid synthesis, the main components of cellular membranes.

Thus the major biosynthetic activity of smooth ER is lipid formation, matching the answer Lipids.

Leucoplasts are non‑pigmented (colourless) plastids found in roots, seeds and other non‑photosynthetic tissues.

They function mainly in storage of substances such as starch, oils or proteins, which are nutrients.

Since they lack chlorophyll and other pigments, they appear colourless, distinguishing them from chloroplasts and chromoplasts.

Therefore the colourless nutrient‑storing plastids are Leucoplasts.