NEET Biology Cell The Unit of Life MCQs Set 30

Answer: (c) All cells arise from pre-existing cells

Explanation:
1. Schleiden and Schwann proposed that all plants and animals are made of cells.
2. Virchow added that new cells arise from pre-existing cells, and this completed the cell theory.
3. So the statement 'all cells arise from pre-existing cells' is the part that was added in the final cell theory.

Teacher's Note:
1. Virchow: Omnis cellula e cellula.
2. Observations about plant and animal cell structure are not part of the theory itself.

Answer: (a) prokaryotes

Explanation:
1. Mesosomes are infoldings of the plasma membrane seen in prokaryotic cells such as bacteria.
2. They help in cell wall formation, DNA replication and distribution to daughter cells, and increase the surface area for enzymes.

Teacher's Note:
1. Mesosomes are absent in eukaryotes.
2. Their respiratory enzymes resemble those of mitochondria.

Answer: (b) Primary wall, Secondary wall, Primary wall

Explanation:
1. The primary wall of a young cell is capable of growth.
2. As the cell matures the primary wall stops growing and a secondary wall is laid down on its inner side.

Teacher's Note:
1. Order from outside: middle lamella, primary wall, secondary wall.
2. Secondary wall gives mechanical strength.

Answer: (b) plasmodesmata and middle lamella respectively

Explanation:
1. Plasmodesmata are cytoplasmic channels that run through the walls and connect adjacent plant cells.
2. The middle lamella, a layer mainly of calcium pectate, cements neighbouring cells together.

Teacher's Note:
1. Desmosomes are cell junctions in animal tissues, not in plants.
2. Pectin is the main cementing material.

Answer: (d) It synthesises cell wall materials

Explanation:
1. The vacuole stores water, ions, sugars and waste products and helps in osmoregulation.
2. It does not synthesise cell wall materials; that is mainly a function of the Golgi apparatus and the plasma membrane.

Teacher's Note:
1. The tonoplast surrounds the vacuole.
2. In plant cells the vacuole can occupy up to 90 percent of the cell volume.

Answer: (d) Oxidation of carbohydrates

Explanation:
1. The endomembrane system (ER, Golgi, lysosomes and vacuoles) takes part in protein and enzyme synthesis and processing, and forms lysosomes.
2. Oxidation of carbohydrates (respiration) takes place in the mitochondria, which are not part of the endomembrane system.

Teacher's Note:
1. Mitochondria and chloroplasts are not part of the endomembrane system.
2. Peroxisomes are also excluded.

Answer: (b) protein synthesis

Explanation:
1. The nucleolus is the site of rRNA synthesis and ribosome assembly.
2. Cells making large amounts of protein need many ribosomes, so they have more than one nucleolus.

Teacher's Note:
1. Nucleoli are not membrane-bound.
2. The nucleolus is a spherical structure within the nucleus.

Answer: (a) Lysosome

Explanation:
1. Lysosomes contain hydrolytic enzymes that digest carbohydrates, proteins, lipids and nucleic acids inside the cell.

Teacher's Note:
1. Lysosomal enzymes work best at acidic pH.
2. They are called suicide bags because they can digest the cell itself.

Answer: (c) B and C

Explanation:
1. (A) is false: leucoplasts have no pigments.
2. (B) is true and (C) is true: the basal body has the same 9+0 triplet structure as a centriole.
3. (D) is false: eukaryotic cells also have 70S ribosomes in mitochondria and chloroplasts.
4. So only B and C are correct.

Teacher's Note:
1. Chromoplasts and chloroplasts have pigments, leucoplasts do not.
2. Organelles with their own DNA also have 70S ribosomes.

Answer: (c) A-ii, B-i, C-iv, D-iii

Explanation:
1. Thylakoids are flattened membranous sacs (ii).
2. Amyloplasts store starch (i).
3. Elaioplasts store oils and fats (iv).
4. Aleuroplasts store proteins (iii). So the match is A-ii, B-i, C-iv, D-iii.

Teacher's Note:
1. Leucoplasts store nutrients: amyloplasts (starch), elaioplasts (oils), aleuroplasts (proteins).
2. Thylakoids are inside chloroplasts.

Answer: (b) Glyoxysome

Explanation:
1. Glyoxysomes, found in germinating fatty seeds, contain the glyoxylate cycle enzymes that convert stored fat into carbohydrate.

Teacher's Note:
1. Glyoxysomes are a special type of peroxisome in plants.
2. Fat is first broken to fatty acids and then to acetyl-CoA.

Answer: (a) nucleolus

Explanation:
1. The nucleolus contains the genes for rRNA and is the site where rRNA is transcribed and ribosomal subunits are assembled.

Teacher's Note:
1. Ribosomal subunits leave the nucleus through the nuclear pores.
2. rRNA genes are present on several chromosomes.

Answer: (c) Lysosome - flattened membranous sac

Explanation:
1. Microtubules are protein (tubulin) structures, cristae are infoldings of the inner mitochondrial membrane and cisternae are the flattened sacs of the Golgi complex.
2. A lysosome is a single-membrane-bound vesicle with hydrolytic enzymes, not a flattened sac, so (3) is incorrect.

Teacher's Note:
1. Cisternae are the flattened, disc-shaped sacs stacked in the Golgi.
2. Lysosomes are vesicular structures formed by the Golgi.

Answer: (c) their functions are coordinated

Explanation:
1. These organelles are grouped together because their functions are coordinated: materials made in the ER are modified in the Golgi and sent to lysosomes and vacuoles.

Teacher's Note:
1. The endomembrane system is a functional concept, not a structural one.
2. Mitochondria, chloroplasts and peroxisomes are not included.