Cell: The Unit of Life — Class 11 MCQs with Answers

Cell: The Unit of Life — important questions & MCQs with answers (Class 11 Biology)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   Cell theory was proposed by:

   ADarwinBMendelCSchleiden and SchwannDPasteur
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   Answer: Schleiden and Schwann

   Explanation: Schleiden and Schwann proposed cell theory in 1838-39; Virchow later added that cells arise only from pre-existing cells. Darwin and Mendel are famous biologists too, but they worked on evolution and heredity, not cell origin.

2. Q2 of 6Easy

   Powerhouse of the cell:

   ANucleusBMitochondriaCRibosomeDLysosome
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   Answer: Mitochondria

   Explanation: Mitochondria are the powerhouse because their inner membrane hosts oxidative phosphorylation, making most cellular ATP. Ribosomes make protein and lysosomes digest waste — neither one generates energy.

3. Q3 of 6Medium

   Modern cell theory does NOT include?

   AAll living organisms are made of cellsBCells arise from pre-existing cellsCCell is the basic unit of structure and functionDAll cells contain chloroplasts
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   Answer: All cells contain chloroplasts

   Explanation: Modern cell theory says all organisms are made of cells and cells arise from pre-existing cells — it says nothing about chloroplasts, which occur only in plant and algal cells, never in animal or fungal ones.

4. Q4 of 6Medium

   Prokaryotes lack:

   ARibosomesBDNACCell wallDMembrane-bound nucleus and organelles
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   Answer: Membrane-bound nucleus and organelles

   Explanation: Prokaryotes lack a nuclear envelope and membrane-bound organelles like mitochondria — their DNA sits free as a nucleoid. They still have DNA, a cell wall and 70S ribosomes, so those options are wrong picks.

5. Q5 of 6Hard

   Chloroplasts perform:

   ADigestionBRespirationCPhotosynthesisDExcretion
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   Answer: Photosynthesis

   Explanation: Chloroplasts trap light energy and fix CO2 into sugars during photosynthesis, using their thylakoid membranes. Respiration is the mitochondrion's job — the two are often swapped since both handle cell energy.

6. Q6 of 6Hard

   Assertion: Mycoplasmas can grow without a cell wall. Reason: Their plasma membrane is reinforced with sterols.

   AA true, R falseBBoth true; R doesn't explain ACBoth true; R explains ADA false, R true
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   Answer: Both true; R explains A

   Explanation: Mycoplasmas genuinely lack a cell wall yet survive because their plasma membrane is reinforced with sterols for extra rigidity — the reason directly explains the assertion, since sterols compensate for the wall's missing mechanical support.

Cell: The Unit of Life notes: key concepts (Class 11 Biology)

The cell is the structural and functional unit of all life. This chapter traces cell theory, contrasts small prokaryotic cells with compartmentalised eukaryotic cells, and details the fluid-mosaic membrane, the cell wall and each organelle whose division of labour keeps the cell alive and working.

Cell theory

Given by Schleiden and Schwann and extended by Virchow: all organisms are made of cells, cells are the basic unit of life, and cells arise only from pre-existing cells.

Prokaryotic cell

Lacks a true nucleus and membrane-bound organelles; DNA lies naked in the nucleoid, with mesosomes, 70S ribosomes and often a glycocalyx, plasmid and flagella.

Eukaryotic cell

Has a membrane-bound nucleus and organelles, an endomembrane system, a cytoskeleton and 80S ribosomes; found in protists, fungi, plants and animals.

Fluid-mosaic model

Singer and Nicolson's model: a lipid bilayer with proteins floating like a mosaic; phospholipids give fluidity, letting the membrane act as a selectively permeable barrier.

Membrane transport

Passive diffusion and osmosis need no energy and follow the gradient; active transport spends ATP to pump molecules against the concentration gradient.

Cell wall

A rigid, non-living outer layer of cellulose (plus hemicellulose and pectin) in plants; it gives shape, prevents bursting and enables cell-to-cell contact.

Endoplasmic reticulum

A network of tubules; rough ER studded with ribosomes synthesises and transports proteins, while smooth ER makes lipids and steroids and stores calcium.

Golgi apparatus

Stacked flattened cisternae that modify, package and dispatch proteins and lipids; its cis face receives material and the trans face ships secretory vesicles.

Mitochondria

Double-membraned power houses; the inner membrane folds into cristae bearing ATP synthase, and the matrix holds DNA and 70S ribosomes for aerobic respiration.

Plastids

Plant-only organelles; chloroplasts with thylakoid grana perform photosynthesis, chromoplasts store coloured pigments and leucoplasts store starch, oil or protein.

Ribosomes

Non-membranous granules of rRNA and protein that assemble amino acids into proteins; 70S in prokaryotes, mitochondria and plastids, 80S in eukaryotic cytoplasm.

Lysosomes

Membrane sacs of hydrolytic enzymes formed by the Golgi; they digest worn organelles and foreign matter, earning the name 'suicidal bags' of the cell.

Nucleus

Bounded by a porous double envelope, it holds chromatin (DNA plus histones) and a nucleolus that makes ribosomes; it directs cell activity and heredity.

Cytoskeleton, cilia & flagella

Microtubules, microfilaments and intermediate filaments give shape and movement; cilia and flagella share a 9+2 axoneme arising from basal bodies.