NEET Biology Cell The Unit of Life MCQs Set 38

Answer: (a) Magnesium

Explanation:
1. Magnesium ions help to maintain the structure of ribosomes by holding the two subunits together.
2. Zinc, copper and molybdenum are not involved in ribosome structure.

Teacher's Note:
1. Mg2+ is required for the association of 50S and 30S subunits.
2. Low Mg2+ concentration dissociates ribosome subunits.

Answer: (d) Nucleolus

Explanation:
1. The nucleolus is a non-membranous region in the nucleus and the site for synthesis of rRNA, where ribosomal subunits are also assembled.
2. Golgi bodies and microbodies have no role in rRNA synthesis.

Teacher's Note:
1. Nucleolus is the ribosome factory.
2. It is large in cells that actively synthesise proteins.

Answer: (d) Golgi bodies 34

Explanation:
1. The Golgi apparatus is the important site of formation of glycoproteins and glycolipids, where sugar residues are added to proteins and lipids received from the ER.
2. Polysomes make protein, and peroxisomes carry out oxidation.

Teacher's Note:
1. Golgi bodies modify, package and sort products.
2. Glycosylation is an important function.

Answer: (c) These are involved in ingestion of food particles.

Explanation:
1. Inclusion bodies are non-membranous reserve materials such as starch granules, glycogen and gas vacuoles lying free in the cytoplasm.
2. They are not involved in ingestion of food particles.
3. The statement about ingestion is incorrect.

Teacher's Note:
1. Inclusion bodies are stored materials in prokaryotes and eukaryotes.
2. Food ingestion is done by phagocytosis in protozoans.

Answer: (b) Golgi complex

Explanation:
1. Secretory cells synthesise and export large quantities of substances, which are packaged in the Golgi complex, so the Golgi bodies are very numerous in them.

Teacher's Note:
1. Golgi complex is prominent in glandular cells.
2. It packages and secretes products.

Answer: (c) rRNA

Explanation:
1. The non-membranous nucleoplasmic structures in the nucleus are nucleoli, the sites of active rRNA synthesis.
2. Messenger and transfer RNAs are made elsewhere in the nucleoplasm.

Teacher's Note:
1. Nucleolus synthesises rRNA.
2. RNA polymerase I works there.

Answer: (b) Double stranded circular naked DNA

Explanation:
1. Organisms with only 70S ribosomes are prokaryotes.
2. Their genetic material is a circular, double-stranded, naked DNA in the nucleoid and not enclosed by a nuclear membrane.

Teacher's Note:
1. Prokaryotic DNA is naked and circular.
2. Eukaryotic DNA is linear and associated with histones.

Answer: (b) Passive transport requires a concentration gradient across a biological membrane whereas active transport requires energy to move solutes

Explanation:
1. Passive transport takes place along a concentration gradient and needs no energy, while active transport moves solutes against the gradient using energy, usually ATP.
2. Both can be selective, so the difference lies in the requirement of energy.

Teacher's Note:
1. Energy input is the key difference.
2. Facilitated diffusion is also a passive process.

Answer: (a) (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)

Explanation:
1. Golgi apparatus forms glycoproteins and glycolipids, lysosomes digest biomolecules, vacuoles trap waste and excretory products, and ribosomes synthesise protein.
2. The match is a-iii, b-iv, c-ii, d-i.

Teacher's Note:
1. Lysosomes are digestive bags with hydrolytic enzymes.
2. Vacuoles store water, wastes and pigments.

Answer: (c) Lysosomes and Vacuoles

Explanation:
1. Mitochondria, chloroplasts and the nucleus contain DNA.
2. Lysosomes and vacuoles are single-membrane organelles without their own DNA.

Teacher's Note:
1. Only the nucleus, mitochondria and plastids have DNA.
2. Single-membrane organelles do not.

Answer: (d) Lysosomes are formed by the process of packaging in the endoplasmic reticulum.

Explanation:
1. Lysosomes are membrane-bound vesicles with numerous hydrolytic enzymes active at acidic pH.
2. They are formed by packaging of enzymes in the Golgi apparatus, not in the endoplasmic reticulum.

Teacher's Note:
1. Lysosomal enzymes are synthesised on the rough ER and packaged by the Golgi apparatus.
2. Lysosomes are therefore called suicide bags.

Answer: (a) Rudolf Virchow

Explanation:
1. The statement omnis cellula-e cellula, meaning that new cells arise from pre-existing cells, was proposed by Rudolf Virchow.
2. Schleiden and Schwann gave the cell theory.

Teacher's Note:
1. Virchow modified the cell theory.
2. Schleiden was a botanist and Schwann a zoologist.

Answer: (b) Enzymes of electron transport are embedded in outer membrane.

Explanation:
1. The outer mitochondrial membrane is permeable to small molecules, the inner membrane is convoluted into cristae, and the matrix contains a circular DNA and 70S ribosomes.
2. The enzymes of the electron transport chain are embedded in the inner membrane, not in the outer one.

Teacher's Note:
1. ETS enzymes are located in the inner membrane.
2. ATP synthase particles lie on the cristae.

Answer: (a) Polysome

Explanation:
1. Many ribosomes attached to a single mRNA form a string called polysome or polyribosome, which synthesises several copies of the polypeptide simultaneously.

Teacher's Note:
1. Polysomes increase the efficiency of protein synthesis.
2. Each ribosome reads the mRNA in turn.

Answer: (d) Free ribosomes and RER

Explanation:
1. Nissl bodies, found in neurons, are made of free ribosomes and rough endoplasmic reticulum, and they synthesise proteins.

Teacher's Note:
1. Nissl granules indicate high protein synthesis in nerve cells.
2. They are absent from axons.

Answer: (d) Large central vacoules - Animal cells

Explanation:
1. Protists are eukaryotes, methanogens are prokaryotic archaebacteria, and gas vacuoles occur in cyanobacteria and in photosynthetic purple and green bacteria.
2. Large central vacuoles are characteristic of plant cells, not of animal cells, so the last pair is a mismatch.

Teacher's Note:
1. Mature plant cells have a large central vacuole bound by the tonoplast.
2. Animal cells have small vacuoles.