NEET Biology Cell The Unit of Life MCQs Set 33

Answer: (d) Proteins, phospholipids and some carbohydrates

Explanation:
1. Chemical analysis shows lipids (mainly phospholipids), proteins and a small amount of carbohydrate.
2. The carbohydrate is attached to lipids and proteins on the outer surface. Cellulose belongs to the cell wall, not the membrane.

Teacher's Note:
1. Proteins and lipids are the main components, and the carbohydrate part is small.
2. Always choose the option that lists all three components.

Answer: (d) Glycoprotein

Explanation:
1. Short sugar chains (oligosaccharides) are attached to proteins as glycoproteins and to lipids as glycolipids on the outer surface.
2. Hemicellulose and cellulose are cell wall materials and starch is a storage product.

Teacher's Note:
1. Glycoproteins and glycolipids make up the glycocalyx.
2. They are found only on the outer face, which makes the membrane asymmetric.

Answer: (b) Cell recognition

Explanation:
1. The sugar chains of glycoproteins and glycolipids on the outer surface act as identity markers.
2. Examples are recognition between sperm and egg during fertilisation and the blood group antigens.

Teacher's Note:
1. Cell recognition is the standard function of membrane carbohydrate.
2. Attachment to the cytoskeleton is done by proteins such as spectrin, not by sugars.

Answer: (b) Lipid

Explanation:
1. The lipids of the bilayer, rich in unsaturated fatty acids, are quasi-fluid, so proteins can move sideways in the membrane.
2. Carbohydrates are only attached on the outer surface and do not decide fluidity.

Teacher's Note:
1. Unsaturated tails make the bilayer more fluid, and cholesterol makes it more rigid.
2. Fluidity is measured as the ability of molecules to move within the bilayer.

Answer: (a) Primary cell wall

Explanation:
1. The primary wall is thin and elastic, forms in young cells and is capable of growth.
2. As the cell matures it becomes thinner and the secondary wall is laid down on its inner side.

Teacher's Note:
1. The secondary wall is laid inside the primary wall once growth stops.
2. Tertiary cell wall is not a standard layer.

Answer: (a) Selectively permeable

Explanation:
1. The membrane lets some substances pass easily and holds others back, depending on size, charge and solubility.
2. So it is selectively permeable.

Teacher's Note:
1. Do not confuse a living membrane with a purely semipermeable artificial membrane.
2. Selective permeability depends on carriers and channels in the membrane.

Answer: (b) Arrangement of proteins

Explanation:
1. Both models have a lipid bilayer.
2. Robertson's unit membrane put protein layers on both surfaces of the bilayer as a sandwich, whereas Singer and Nicolson placed protein molecules floating within and across the bilayer as a mosaic.

Teacher's Note:
1. The difference lies in the arrangement of proteins.
2. In the fluid mosaic model proteins are not continuous layers.

Answer: (c) Phospholipids form a bimolecular layer in the middle

Explanation:
1. The phospholipids form a bilayer with polar hydrophilic heads facing outward and non-polar hydrophobic tails inside.
2. Proteins are embedded in this bilayer and do not form a middle layer.

Teacher's Note:
1. Heads are polar and water loving, tails are non-polar and water hating.
2. The bilayer is the structural frame of the membrane.

Answer: (a) Proteins can also undergo flip-flop movements in the lipid bilayer

Explanation:
1. Lateral movement of proteins is common and some proteins stay in specific domains.
2. Flip-flop movement from one face to the other is very rare for proteins, because their polar parts cannot pass through the non-polar core, so statement (a) is incorrect.

Teacher's Note:
1. Lipids flip-flop slowly and proteins hardly at all.
2. This is why membrane asymmetry is maintained.

Answer: (d) Phosphoglycerides

Explanation:
1. Plant membranes have phosphoglycerides (phospholipids built on glycerol) as the main structural lipid.
2. Peptidoglycan belongs to bacterial walls and glycocalyx is the sugar coat.

Teacher's Note:
1. Phosphoglycerides are glycerol, two fatty acids and a phosphate-containing head.
2. They are the main lipid in nearly all membranes.

Answer: (b) Mitochondria

Explanation:
1. Mitochondria contain the enzymes of the Krebs cycle, electron transport and oxidative phosphorylation, as well as many others.
2. That gives them the largest number of enzymes among the organelles listed.

Teacher's Note:
1. Mitochondria are the enzyme-rich power house of the cell.
2. The lysosome has about 50 hydrolytic enzymes, which is fewer.

Answer: (a) Protein synthesis

Explanation:
1. Ribosomes sit on the surface of rough ER and make proteins to be secreted or sent to membranes.
2. Lipids and cholesterol are made on smooth ER.

Teacher's Note:
1. Rough ER = ribosomes = proteins, smooth ER = lipids and steroids.
2. Cell wall formation is done by Golgi vesicles and plasma membrane enzymes.

Answer: (b) Lysosome

Explanation:
1. Lysosomes contain about 50 acid hydrolases that digest proteins, lipids, carbohydrates and nucleic acids.
2. They are therefore called the digestive bags of the cell.

Teacher's Note:
1. Lysosomal enzymes work best at pH 5.
2. An active proton pump in the lysosomal membrane keeps the interior acidic.

Answer: (c) Mitochondria, chloroplast

Explanation:
1. Mitochondria and chloroplasts have their own circular double-stranded DNA and 70S ribosomes.
2. Peroxisomes, ribosomes, plasma membrane and dictyosomes (Golgi bodies) have no DNA.

Teacher's Note:
1. Organelles with DNA are the nucleus, mitochondria and plastids.
2. They are called semi-autonomous organelles.

Answer: (a) Mitochondria

Explanation:
1. Mitochondria have their own DNA and ribosomes and can make some of their proteins, but they still depend on nuclear genes for others.
2. So they are only semi-autonomous.

Teacher's Note:
1. The semi-autonomous organelles are mitochondria and chloroplasts.
2. Ribosomes and peroxisomes have no DNA.

Answer: (b) Tubules

Explanation:
1. Smooth ER consists mainly of branched tubules.
2. Rough ER is mostly flattened cisternae and vesicles.

Teacher's Note:
1. Smooth ER has tubules, rough ER has cisternae.
2. Smooth ER lacks ribosomes and ribophorins.

Answer: (b) Endoplasmic reticulum

Explanation:
1. The endoplasmic reticulum is a network of membranes that divides the cytoplasm into the luminal and extra-luminal compartments.
2. It is therefore called the system of membranes.

Teacher's Note:
1. The ER is continuous with the outer nuclear membrane.
2. It extends throughout the cytoplasm.

Answer: (a) pH 5

Explanation:
1. Lysosomal acid hydrolases work in an acidic medium of about pH 5.
2. The membrane proton pump keeps the lumen acidic.

Teacher's Note:
1. The enzymes would be harmless to the cell if they leaked because the cytosol is near pH 7.
2. This protects the cell from self-digestion.

Answer: (d) Mitochondria

Explanation:
1. Mitochondria contain the oxidative enzymes of the Krebs cycle and the respiratory chain.
2. The other three do not carry out oxidation on such a scale.

Teacher's Note:
1. Mitochondria are also called oxysomes when the enzyme particles are meant.
2. Peroxisomes have oxidases too but are not among the options.

Answer: (d) Packaging of materials for secretion

Explanation:
1. The Golgi apparatus receives materials from the ER, modifies them and packs them into vesicles.
2. The vesicles go to targets inside the cell or are secreted outside.

Teacher's Note:
1. The Golgi body is the packaging and dispatch centre.
2. It is also the site of lysosome formation.

Answer: (a) Mitochondria

Explanation:
1. Mitochondria contain the enzymes for the Krebs cycle and electron transport.
2. Chloroplasts perform photosynthesis, not respiration.

Teacher's Note:
1. Glycolysis takes place in the cytoplasm and the rest of aerobic respiration in mitochondria.
2. Mitochondria are the site of the complete oxidation of pyruvate.

Answer: (d) Lysosomes

Explanation:
1. GERL stands for Golgi-associated endoplasmic reticulum from which lysosomes arise.
2. The path is ER, then Golgi, then lysosome.

Teacher's Note:
1. GERL is a region next to the Golgi body that forms lysosomes.
2. It is not a separate organelle.

Answer: (c) Both endoplasmic reticulum and Golgi bodies

Explanation:
1. Lysosomal enzymes are made on the rough ER and then packaged by the Golgi body into vesicles that become lysosomes.
2. Both organelles therefore take part.

Teacher's Note:
1. Lysosomes form through the route ER, Golgi, lysosome.
2. Mitochondria are not part of the endomembrane system.

Answer: (b) Cisternae, tubules and vesicles

Explanation:
1. The Golgi complex has flattened disc-like cisternae, branched tubules and spherical vesicles.
2. Thylakoids and grana belong to chloroplasts.

Teacher's Note:
1. The three parts are cisternae, tubules and vesicles.
2. Some books add the Golgi vacuoles as a fourth part.

Answer: (d) Lysosomes

Explanation:
1. Lysosomes are bounded by one unit membrane.
2. Mitochondria and chloroplasts have two, and ribosomes have none.

Teacher's Note:
1. Single-membrane organelles are ER, Golgi, lysosomes, vacuoles and microbodies.
2. Double-membrane organelles are the nucleus, mitochondria and plastids.

Answer: (b) Mitochondria

Explanation:
1. Mitochondria are surrounded by an outer and an inner membrane.
2. Ribosomes and centrioles have no membrane and lysosomes have one.

Teacher's Note:
1. The nucleus, mitochondria and plastids have two membranes.
2. This fits their endosymbiotic origin.

Answer: (b) Smooth ER

Explanation:
1. Phospholipids, cholesterol and steroids are made on the smooth ER.
2. Rough ER is concerned with proteins.

Teacher's Note:
1. The smooth ER is also a site of detoxification.
2. It lacks ribosomes, so it is called agranular ER.

Answer: (a) Cytochrome P450

Explanation:
1. Cytochrome P450 enzymes in the smooth ER hydroxylate and detoxify drugs, toxins and steroids.
2. The others are electron carriers of respiration or photosynthesis.

Teacher's Note:
1. The liver has abundant smooth ER for this reason.
2. P450 makes the molecules more water-soluble so they can be excreted.

Answer: (a) Potato

Explanation:
1. Elaioplasts store oils and are abundant in coconut, groundnut and sunflower seeds.
2. Potato stores starch, so it has amyloplasts and no elaioplasts.

Teacher's Note:
1. Amyloplast stores starch, elaioplast stores oil, aleuroplast stores protein.
2. These are the three types of leucoplast.