NEET Biology Cell The Unit of Life MCQs Set 34

Answer: (a) Discoid or oval

Explanation:
1. Chloroplasts of higher plants are lens-shaped, discoid or oval.
2. Spiral (Spirogyra) and cup-shaped (Chlamydomonas) chloroplasts are found in algae.

Teacher's Note:
1. Algae show a variety of chloroplast shapes.
2. Higher plants have a uniform discoid shape and many chloroplasts per cell.

Answer: (d) Ribosome

Explanation:
1. The nucleus, mitochondria and chloroplasts all contain DNA.
2. Ribosomes contain rRNA and protein only.

Teacher's Note:
1. Ribosomes are made of RNA and protein.
2. DNA is absent from all membrane-less organelles.

Answer: (a) Possess their own nucleic acid

Explanation:
1. They have their own circular DNA and 70S ribosomes and divide by fission like bacteria, which suggests that they arose from engulfed prokaryotes.
2. The other statements are false for them.

Teacher's Note:
1. Endosymbiotic theory explains the bacteria-like features of these organelles.
2. They reproduce, so "do not reproduce" is wrong.

Answer: (d) Oxidising enzymes (oxidases)

Explanation:
1. Peroxisomes contain oxidases and catalase, which produce and then break down hydrogen peroxide.
2. Hydrolytic enzymes belong to lysosomes.

Teacher's Note:
1. Peroxisomes are also called uricosomes.
2. Catalase converts hydrogen peroxide to water and oxygen.

Answer: (d) Ribosome

Explanation:
1. Mitochondria and chloroplasts divide by fission.
2. Ribosomes are made afresh from rRNA and proteins in the nucleolus and do not duplicate themselves.

Teacher's Note:
1. Ribosomes are assembled and not duplicated.
2. Only organelles with their own DNA divide.

Answer: (a) Plasma membrane

Explanation:
1. Microtubules, cilia and flagella are made of tubulin.
2. The plasma membrane is made of lipids and proteins other than tubulin.

Teacher's Note:
1. Microtubules are polymers of alpha and beta tubulin.
2. Actin forms microfilaments.

Answer: (d) Photorespiration and degradation of hydrogen peroxide

Explanation:
1. In green plant cells peroxisomes take part in the glycolate pathway of photorespiration.
2. In all cells they break down hydrogen peroxide with catalase.

Teacher's Note:
1. Peroxisomes also carry out beta oxidation of fatty acids.
2. They work together with chloroplasts and mitochondria in photorespiration.

Answer: (a) Glyoxysomes

Explanation:
1. Glyoxysomes are peroxisome-like microbodies in oil seeds that carry out the glyoxylate cycle.
2. They are described as highly specialised peroxisomes.

Teacher's Note:
1. Glyoxysomes are found in oil-rich seeds, yeast cells and guard cells.
2. They convert fat to carbohydrate.

Answer: (a) Centriole

Explanation:
1. The basal body at the base of a cilium or flagellum has the same 9+0 structure as a centriole and is formed from one.
2. So it is a centriole-derived structure.

Teacher's Note:
1. Centrioles form the basal bodies of cilia and flagella.
2. They also form the spindle poles in animal cells.

Answer: (a) Svedberg unit

Explanation:
1. S is the Svedberg unit, a measure of the sedimentation rate in a centrifuge.
2. It depends on size and shape, so 50S + 30S = 70S does not add up arithmetically.

Teacher's Note:
1. Eukaryotic ribosomes are 80S, made of 60S and 40S subunits.
2. S values are not additive.

Answer: (b) Chromoplast

Explanation:
1. Chromoplasts contain carotenoid pigments that give yellow, orange and red colours to fruits and flowers.
2. Chloroplasts are green, leucoplasts are colourless and etioplasts form in the dark.

Teacher's Note:
1. Carotenes and xanthophylls are fat-soluble pigments.
2. Chromoplasts are formed from chloroplasts when a fruit ripens.

Answer: (d) 9 + 0

Explanation:
1. A centriole has nine peripheral triplets of microtubules and no central tubules, which is called the 9+0 arrangement.
2. Cilia and flagella have the 9+2 arrangement.

Teacher's Note:
1. Centriole 9+0 with triplets, cilium 9+2 with doublets.
2. A cartwheel appearance is seen in a cross section.

Answer: (b) 9

Explanation:
1. A centriole has nine peripheral fibres, each of which is a triplet of microtubules.
2. They are joined to the central hub by radial spokes.

Teacher's Note:
1. Nine triplets give a total of 27 microtubules.
2. The count of fibres is nine, not the count of tubules.

Answer: (c) Ribosome

Explanation:
1. Ribosomes are about 15 nm by 25 nm and have no membrane.
2. They are the smallest organelles.

Teacher's Note:
1. Ribosomes are smaller than any membrane-bound organelle.
2. They are the protein factories of the cell.

Answer: (c) Stroma

Explanation:
1. The stroma is the colourless matrix containing enzymes for carbohydrate synthesis, DNA and ribosomes.
2. Thylakoids and grana bear chlorophyll.

Teacher's Note:
1. The stroma is the site of the dark reactions.
2. Stroma lamellae connect grana but they also bear pigment.

Answer: (a) Both are present in animal cells

Explanation:
1. Both organelles are found in eukaryotic plant cells and both have their own DNA.
2. Chloroplasts are absent from animal cells, so statement (a) is not common to both.

Teacher's Note:
1. Plant cells have both organelles, animal cells have only mitochondria.
2. Both have circular DNA and 70S ribosomes.

Answer: (a) Ribosome

Explanation:
1. Ribosomes are the sites where amino acids are assembled into proteins, so they are called the engine or protein factory of the cell.
2. The other organelles do not have this nickname.

Teacher's Note:
1. Ribosomes are the site of translation.
2. They are also called organelles within an organelle because they occur inside mitochondria and chloroplasts.

Answer: (b) RNA and protein

Explanation:
1. Ribosomes contain ribosomal RNA and about 80 different proteins in eukaryotes.
2. They have no DNA.

Teacher's Note:
1. Ribosomes are ribonucleoprotein particles.
2. They are not covered by a membrane.

Answer: (a) 9 + 2 arrangement of microtubules

Explanation:
1. Both are outgrowths of the cell with a core of nine doublets around two central microtubules.
2. They are found in many cells, not only in protozoa.

Teacher's Note:
1. The 9+2 pattern is called the axoneme.
2. Cilia are short and numerous, flagella are long and few.

Answer: (c) Ribosome and nucleolus

Explanation:
1. Ribosomes and the nucleolus are not surrounded by a membrane.
2. All the other organelles are enclosed by one or two unit membranes.

Teacher's Note:
1. The nucleolus is a dense region of rRNA and protein inside the nucleus.
2. Centrioles and cytoskeleton are other membrane-less structures.

Answer: (b) Secretion

Explanation:
1. The Golgi body modifies, packs and dispatches materials for secretion.
2. Respiration is in mitochondria and degradation is in lysosomes.

Teacher's Note:
1. Secretory cells have well-developed Golgi bodies.
2. The Golgi body is the middle man of the cell.

Answer: (a) 40S and 60S

Explanation:
1. The eukaryotic 80S ribosome has a small 40S subunit and a large 60S subunit.
2. The 30S and 50S subunits make the prokaryotic 70S ribosome.

Teacher's Note:
1. S values are not additive because they measure sedimentation.
2. Memorise the pairs 40S with 60S and 30S with 50S.

Answer: (b) Secondary constriction

Explanation:
1. The nucleolar organiser region lies at the secondary constriction of satellite-bearing chromosomes, where rRNA genes are located.
2. The primary constriction is the centromere.

Teacher's Note:
1. Secondary constriction = NOR = nucleolus formation.
2. The part beyond it is called the satellite.

Answer: (a) DNA, RNA, histones and non-histones

Explanation:
1. Chromosomes are made of chromatin: DNA, histone proteins, non-histone proteins and a little RNA.
2. Statement (a) is the most complete.

Teacher's Note:
1. Nucleosomes contain DNA wrapped around a histone octamer.
2. Non-histone proteins help in packing and gene regulation.

Answer: (d) RNA

Explanation:
1. DNA in the nucleus is transcribed into mRNA, which goes into the cytoplasm through nuclear pores and directs protein synthesis.
2. This is how the nucleus controls the cytoplasm.

Teacher's Note:
1. The nucleus sends messenger RNA rather than DNA.
2. Information flows from DNA to RNA to protein.

Answer: (c) Nucleus and cytoplasm

Explanation:
1. RNA is made in the nucleus and works in the cytoplasm, and it is also found in ribosomes, mitochondria and chloroplasts.
2. It is not restricted to one place.

Teacher's Note:
1. rRNA, tRNA and mRNA are all found in both nucleus and cytoplasm.
2. Only DNA is mostly confined to the nucleus and a few organelles.

Answer: (d) The secondary constriction

Explanation:
1. The nucleolus forms around the nucleolar organiser at the secondary constriction of specific chromosomes.
2. The primary constriction is the centromere.

Teacher's Note:
1. The nucleolus is the ribosome factory of the cell.
2. Chromosomes with a secondary constriction form it again after each division.

Answer: (a) On ribosomes present in the cytoplasm as well as in mitochondria

Explanation:
1. Free and ER-bound ribosomes in the cytoplasm make proteins, and mitochondria have their own ribosomes for some of their proteins.
2. Ribosomes of the nucleolus are only being assembled and do not synthesise proteins.

Teacher's Note:
1. Proteins are made on free ribosomes, ER ribosomes and mitochondrial ribosomes.
2. Animal cells have no plastids.