Cell: The Unit of Life Chapter-Wise Test 13

Correct answer Carries: 4.

Wrong Answer Carries: -1.

Consider the following developments in cell biology:

P. Robert Brown described the nucleus.
Q. Camillo Golgi observed densely stained reticular structures near the nucleus.
R. George Palade observed ribosomes as dense particles under the electron microscope.
S. Singer and Nicolson proposed the fluid mosaic model.

Which sequence arranges these developments from earliest to latest?

S → P → Q → R
P → Q → R → S
Q → P → S → R
R → Q → P → S
2

Robert Brown described the nucleus in 1831, Camillo Golgi observed the Golgi structures in 1898, George Palade observed ribosomes in 1953, and Singer and Nicolson proposed the fluid mosaic model in 1972.

A bacterium possesses an outer loose sheath, a rigid layer that maintains shape and an innermost selectively permeable membrane that is structurally similar to a eukaryotic plasma membrane.

Which option correctly gives the order and collective role of these layers?

Plasma membrane → cell wall → glycocalyx; together they form the protein-synthesis system.
Cell wall → glycocalyx → plasma membrane; together they form the bacterial chromosome.
Glycocalyx → plasma membrane → cell wall; together they form the locomotory apparatus.
Glycocalyx → cell wall → plasma membrane; together they act as a protective unit.
4

The bacterial envelope consists of the outermost glycocalyx, followed by the cell wall and then the plasma membrane. Although the layers perform distinct functions, they operate together as a protective unit.

Two cells show the following features:

Cell X is relatively small, multiplies rapidly, contains naked genetic material and lacks membrane-bound organelles other than ribosomes.
Cell Y has an organised nucleus, extensive cytoplasmic compartmentalisation and complex cytoskeletal and locomotory structures.

Which conclusion is best supported?

X is prokaryotic, whereas Y is eukaryotic; protists, plants, animals and fungi possess cells of the Y type.
X is an animal cell, whereas Y is a bacterium with a nuclear envelope.
Both X and Y are prokaryotic because both contain ribosomes.
X is a chloroplast, whereas Y is a bacterial inclusion body.
1

Small size, rapid multiplication, naked DNA and absence of membrane-bound organelles identify X as prokaryotic. An organised nucleus and extensive compartmentalisation identify Y as eukaryotic. Eukaryotes include protists, plants, animals and fungi.

Cell A has a much higher level of physiological activity than Cell B. Their mitochondria are difficult to distinguish in unstained preparations, but both cells are then treated with the same suitable mitochondrial stain.

Which observation is most reasonable?

Cell B should contain more mitochondria because less active cells require more ATP.
Neither cell should show mitochondria because staining destroys double membranes.
Cell A is likely to reveal a greater number of mitochondria because mitochondrial number varies with physiological activity.
Both cells must show exactly the same mitochondrial number because all eukaryotic cells are structurally identical.
3

Mitochondria are not easily visible unless specifically stained. Their number varies according to the physiological activity of the cell, so the more active cell is likely to contain and reveal more mitochondria.

A green leaf cell contains approximately 20–40 double-membrane organelles. Each contains chlorophyll and carotenoid pigments and possesses thylakoids within a stroma.

Which inference best integrates these observations?

The cell is probably a mesophyll cell, and the organelles are chloroplasts that trap light energy for photosynthesis.
The cell is probably an animal cell, and the organelles are mitochondria performing intracellular digestion.
The cell is a bacterium, and the structures are inclusion bodies storing pigments.
The cell is a sieve-tube cell, and the structures are lysosomes containing chlorophyll.
1

Most chloroplasts of green plants occur in leaf mesophyll cells, where approximately 20–40 may occur per cell. Chloroplasts contain chlorophyll and carotenoids that trap light energy required for photosynthesis.

An animal-cell organelle contains two cylindrical structures positioned perpendicular to one another. They are surrounded by amorphous material, and each cylinder shows a cartwheel-like organisation.

Which interpretation is correct?

It is a Golgi complex surrounded by lysosomal material.
It is a centrosome whose centrioles are surrounded by amorphous pericentriolar material.
It is a nucleus whose chromosomes are surrounded by nucleoplasm.
It is a chloroplast whose grana are surrounded by stroma.
2

A centrosome usually contains two perpendicular cylindrical centrioles surrounded by amorphous pericentriolar material. Each centriole possesses a cartwheel-like organisation formed from peripheral triplets and radial spokes.

A double-membrane structure separates nuclear contents from the cytoplasm. Its outer membrane is continuous with the endoplasmic reticulum and bears ribosomes. At certain locations, its two membranes fuse to form passages.

Which conclusion correctly identifies the structure and the role of its passages?

It is a mitochondrion, and the passages release ATP into the nucleus.
It is a chloroplast, and the passages join neighbouring grana.
It is a vacuole, and the passages actively accumulate ions in the sap.
It is the nuclear envelope, and its pores permit movement of RNA and proteins between the nucleus and cytoplasm.
4

The nuclear envelope forms a barrier between the nucleus and cytoplasm. Its outer membrane is continuous with ER and may bear ribosomes. Fusion of its two membranes forms nuclear pores through which RNA and proteins move in both directions.

Consider the following statements about the number of nuclei in cells:

I. A cell normally contains one nucleus.
II. Variations in nuclear number are frequently observed.
III. Mature erythrocytes of many mammals and sieve-tube cells of vascular plants may lack a nucleus.

Which option correctly evaluates these statements?

Only statement I is correct.
Only statements I and II are correct.
Statements I, II and III are correct.
Only statement III is correct.
3

One nucleus per cell is the usual condition, but variations in nuclear number occur. Some specialised mature cells, including erythrocytes of many mammals and sieve-tube cells of vascular plants, lack a nucleus.

A treatment reduces the number of cristae in a mitochondrion but leaves its matrix, circular DNA and 70S ribosomes intact. Which cellular process would be most directly reduced?

Synthesis of ribosomal RNA inside the nucleolus
Oxidative phosphorylation and ATP generation associated with mitochondrial membrane activity
Formation of glycoproteins and glycolipids in Golgi cisternae
Accumulation of ions inside a plant vacuole by the tonoplast
2

Cristae increase the area of the inner mitochondrial membrane, which contains enzymes associated with mitochondrial activity. Reducing cristae would reduce the membrane area available for oxidative phosphorylation and ATP generation.

Scientists are attempting to determine the organisation of a cell membrane rather than merely observe the external outline of a cell. Which approach and conclusion are most appropriate?

Combine electron microscopy with biochemical studies of membranes such as those of erythrocytes; infer a phospholipid bilayer containing surface and buried proteins, cholesterol and carbohydrates.
Use only an unaided eye; infer that membranes consist entirely of cellulose.
Examine bacterial inclusion bodies; infer that every membrane is composed only of proteins.
Study chromosome arm length; infer the orientation of phospholipid heads and tails.
1

Detailed membrane structure became accessible with electron microscopy, while chemical and biochemical studies—especially of erythrocyte membranes—revealed lipids, proteins, cholesterol and carbohydrates. Together, these findings supported models of bilayer organisation and membrane proteins.

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