Cell Biology and Biomolecules — Practice

Question 1

The statement 'all cells arise from pre-existing cells' was given by:
(a) Virchow (b) Schleiden (c) Schwann (d) Robert Hooke

Accepted Answer

(a) Virchow.

Rudolf Virchow added this idea (Omnis cellula-e cellula) to the cell theory proposed by Schleiden and Schwann.

Question 2

Which is absent in a prokaryotic cell?
(a) membrane-bound nucleus (b) ribosomes (c) cell membrane (d) DNA

Accepted Answer

(a) membrane-bound nucleus.

Prokaryotes have a nucleoid (naked DNA) but no true membrane-bound nucleus or membrane-bound organelles. They still have ribosomes (70S), a membrane and DNA.

Question 3

Mitochondria and chloroplasts are called semi-autonomous organelles because they:
(a) have their own DNA and 70S ribosomes (b) lack membranes (c) are found only in plants (d) do not divide

Accepted Answer

(a) have their own DNA and 70S ribosomes.

Both contain circular DNA and prokaryote-type 70S ribosomes, make some of their own proteins and divide independently — evidence for the endosymbiotic theory.

Question 4

The 'powerhouse of the cell' is the:
(a) mitochondrion (b) ribosome (c) lysosome (d) Golgi apparatus

Accepted Answer

(a) mitochondrion.

Mitochondria carry out aerobic respiration and produce ATP, the cell's energy currency — hence 'powerhouse of the cell'.

Question 5

Lysosomes are known as 'suicide bags' because they contain:
(a) hydrolytic (digestive) enzymes (b) chlorophyll (c) DNA (d) ribosomes

Accepted Answer

(a) hydrolytic (digestive) enzymes.

Lysosomes are membrane sacs of hydrolytic enzymes that digest cellular material and can break down the cell itself, earning the name 'suicide bags'.

Question 6

The axoneme of a cilium shows a microtubule arrangement of:
(a) 9 + 2 (b) 9 + 0 (c) 9 + 3 (d) 11 + 2

Accepted Answer

(a) 9 + 2.

Cilia and flagella have nine peripheral microtubule doublets surrounding a central pair (9 + 2). Centrioles are 9 + 0 (nine triplets, no central pair).

Question 7

The fluid-mosaic model of the plasma membrane was proposed by:
(a) Singer and Nicolson (b) Watson and Crick (c) Robert Brown (d) Camillo Golgi

Accepted Answer

(a) Singer and Nicolson.

Singer and Nicolson (1972) described the membrane as a fluid phospholipid bilayer with proteins embedded in a mosaic pattern.

Question 8

A plant cell placed in a hypertonic solution will undergo:
(a) plasmolysis (b) turgidity (c) bursting (d) no change

Accepted Answer

(a) plasmolysis.

In a hypertonic solution water leaves the cell by osmosis and the protoplast shrinks away from the wall — plasmolysis. A hypotonic solution would make it turgid.

Question 9

The most abundant protein in the animal world is:
(a) collagen (b) haemoglobin (c) insulin (d) keratin

Accepted Answer

(a) collagen.

Collagen, the main structural protein of connective tissue, is the most abundant protein in the animal kingdom.

Question 10

Enzyme activity falls sharply above its optimum temperature because the enzyme:
(a) denatures (b) dissolves (c) becomes acidic (d) gains a cofactor

Accepted Answer

(a) denatures.

Above the optimum temperature, heat unfolds the enzyme's tertiary structure (denaturation), destroying the active site so substrate can no longer bind.

Question 11

DNA replication takes place during which phase of the cell cycle?
(a) S phase (b) G₁ phase (c) M phase (d) G₂ phase

Accepted Answer

(a) S phase.

DNA is replicated (synthesised) during the S phase of interphase, doubling the DNA content before the cell enters mitosis.

Question 12

Sister chromatids separate and move to opposite poles during:
(a) anaphase (b) metaphase (c) prophase (d) telophase

Accepted Answer

(a) anaphase.

In anaphase the centromeres split and sister chromatids are pulled to opposite poles, ensuring each daughter cell gets an identical chromosome set.

Question 13

Crossing over between homologous chromosomes occurs during:
(a) prophase I (b) metaphase I (c) anaphase II (d) telophase I

Accepted Answer

(a) prophase I.

Crossing over — the exchange of segments between homologous chromosomes — occurs in the pachytene sub-stage of prophase I, generating genetic recombination.

Question 14

Meiosis of one diploid cell produces:
(a) four haploid cells (b) two diploid cells (c) two haploid cells (d) four diploid cells

Accepted Answer

(a) four haploid cells.

Meiosis involves one DNA replication followed by two divisions, giving four genetically different haploid cells — the basis of gamete formation.

Question 15

Which occurs in meiosis but NOT in mitosis?
(a) reduction of chromosome number (b) DNA replication (c) spindle formation (d) cytokinesis

Accepted Answer

(a) reduction of chromosome number.

Meiosis halves the chromosome number (2n → n) and includes crossing over; mitosis conserves the number (2n → 2n). Both involve DNA replication, spindle formation and cytokinesis.

Practice — Cell Biology and Biomolecules

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