31 Years NEET Previous Year Questions: Cell: The Unit of Life Free MCQ

•  The Golgi apparatus is an essential component of the cellular endomembrane system responsible for modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles.
• The endoplasmic reticulum (ER) is involved in the synthesis of proteins (rough ER) and lipids (smooth ER).
• The Golgi apparatus receives materials from the ER, processes them, and then directs them to their appropriate destinations within or outside the cell.

Assertion (A): The primary function of the Golgi apparatus is to package the materials made by the endoplasmic reticulum and deliver it to intracellular targets and outside the cell:

• This statement is true. The Golgi apparatus processes and packages proteins and lipids synthesized in the ER and sends them to various destinations.
• The golgi apparatus principally performs the function of packaging materials, to be delivered either to the intra-cellular targets or secreted outside the cell.

Reason (R): Vesicles containing materials made by the endoplasmic reticulum fuse with the cis face of the Golgi apparatus, and they are modified and released from the trans face of the Golgi apparatus:

• This statement is true and provides the correct explanation for the Assertion.
• The Golgi apparatus has a cis face (receiving side) and a trans face (shipping side).
• Vesicles from the ER fuse with the cis face, and the materials within these vesicles are modified, sorted, and packaged as they move through the Golgi to be released from the trans face.
• That's why Golgi apparatus remains in close association with the endoplasmic reticlum.

Therefore, both A and R are true, and R correctly explains A, making the correct answer option C).

• Reductionist Biology is an approach in biology that seeks to understand complex biological systems by breaking them down into their simpler constituent parts. It involves studying the physical and chemical processes underlying the functioning of living organisms.
• This physico-chemical approach to study and understand living organisms is called ‘Reductionist Biology’.  The concepts and techniques of physics and chemistry are applied to understand biology.
• For example, the structure of DNA, the role of enzymes in metabolic pathways, and the biophysical properties of cell membranes are all studied using this approach.

Statement A: "The eukaryotic ribosomes are 80S and prokaryotic ribosomes are 70S" is correct.

• In eukaryotic cells, ribosomes have a sedimentation rate of 80S (indicating their size and density), while in prokaryotic cells, ribosomes are smaller with a sedimentation rate of 70S.

Statement B: "Each ribosome has two sub-units" is correct.

• Both prokaryotic and eukaryotic ribosomes consist of two subunits: a larger subunit and a smaller subunit.

Statement C: "The two sub-units of 80S ribosome are 60S and 40S while that of 70S are 50S and 30S" is correct.

• The eukaryotic 80S ribosome is composed of a larger 60S subunit and a smaller 40S subunit.
• The prokaryotic 70S ribosome consists of a larger 50S subunit and a smaller 30S subunit.

Statement D: "The two sub-units of 80S ribosome are 60S and 20S and that of 70S are 50S and 20S" is incorrect.

• This statement incorrectly mentions the smaller subunit as 20S, which is not accurate for either eukaryotic or prokaryotic ribosomes.

Statement E: "The two sub-units of 80S are 60S and 30S and that of 70S are 50S and 30S" is incorrect.

• This statement incorrectly mentions the smaller subunit of the 80S ribosome as 30S instead of 40S.

•  Mesosome is an infolding of the plasma membrane found in prokaryotic cells, especially in bacteria.
• Mesosomes are invaginations of the plasma membrane.
• These extensions are in the form of vesicles, tubules and lamellae. They help in cell wall formation, DNA replication and distribution to daughter cells.
• They also help in respiration, secretion processes, to increase the surface area of the plasma membrane and enzymatic content.

Other Options:

• Chromatophores: These are membranous structures found in photosynthetic prokaryotes like cyanobacteria. Their primary role is in photosynthesis.
• Cristae: Cristae are folds of the inner mitochondrial membrane found in eukaryotic cells. They are involved in oxidative phosphorylation and ATP production. 
• Endoplasmic Reticulum: The endoplasmic reticulum is an organelle exclusive to eukaryotic cells and is involved in protein and lipid synthesis. Prokaryotic cells do not have this organelle.

• Centromere (A-II): The centromere is a region of the chromosome where the microtubules of the spindle attach during cell division, specifically during mitosis and meiosis.
• Cilium (B-III): Cilia are hair-like structures on the surface of the cell, primarily involved in cell movement. They can move fluid over the cell surface or contribute to locomotion of the cell itself.
• Cristae (C-I): Cristae are the folds of the inner mitochondrial membrane, and they increase the surface area for chemical reactions to occur, including those involved in the synthesis of ATP during cellular respiration.
• Cell membrane (D-IV): The cell membrane is a phospholipid bilayer that provides a barrier which separates the interior of the cell from the outside environment while regulating the passage of materials into and out of the cell.

Let's analyze each item in List I and the correct match in List II.

Nucleolus (A) is primarily known as the site where ribosomal RNA (rRNA) is synthesized and where initial ribosome assembly occurs. Thus, it matches perfectly with III. Site of active ribosomal RNA synthesis.
Centriole (B) is a cylindrical cellular structure composed of microtubules and is best known for its role in facilitating cell division, especially in the formation of the spindle apparatus. Its structure is often described as being like a cartwheel, which makes it accurately matched with II. Organization like the cartwheel.

Leucoplasts (C) are a type of non-pigmented plastid found in plant cells, primarily involved in the storage of important nutrients such as starch, oils, and proteins. Hence, the appropriate pair is IV. For storing nutrients.

Golgi apparatus (D) functions in the sorting, modifying, and packaging of macromolecules for cell secretion or for use within the cell. It includes the synthesis of glycolipids among its activities. Consequently, the correct match is I. Site of formation of glycolipid.

With these correlations, the correct matches are:

• A - III,
• B - II,
• C - IV,
• D - I

Therefore, the correct option is Option A: A-III, B-II, C-IV, D-I.

Chloroplasts are organelles found in the cells of plants and of some other organisms that carry out photosynthesis. They contain their own genetic material, separated from the DNA found in the nucleus of the cell. The DNA in chloroplasts has a distinct structure and form.

The DNA within chloroplasts is mostly:

• Circular: The DNA forms a closed loop, similar to the DNA found in bacteria. This similarity supports the endosymbiotic theory, which proposes that chloroplasts originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells.
• Double-stranded: Like most DNA, the DNA in chloroplasts is made up of two complementary strands that wind around each other to form a double helix.
  Based on this information, the correct answer to your query about the form of DNA present in chloroplasts is: Option B: Circular, double stranded

Statement I is correct because both mitochondria and chloroplasts are double membrane-bound organelles.
Statement II is also correct because the inner mitochondrial membrane is highly selective (less permeable), whereas the inner membrane of chloroplast is comparatively more permeable due to transport proteins.

The correct matching between List I and List II can be understood by knowing the respective functions or structural components of the mentioned items:

• Axoneme: This is the core of cilia or flagella, consisting of microtubules arranged in a characteristic pattern. This hence matches with II 'Cilia and flagella'.
• Cartwheel pattern: The term 'cartwheel structure' is specifically associated with the central hub of the centriole's microtubule triplet arrangements in cellular structures. Therefore, this matches with I 'Centriole'.
• Crista: Cristae are the internal membranes of mitochondria that are folded into ridges, involved in the mitochondrial energy generation. Therefore, C matches with IV 'Mitochondria'.
• Satellite: In a cellular context, satellites typically refer to certain types of secondary structures or appendages associated with nucleic acids, hence best matching with III 'Chromosome'.

Thus, matching the correct items gives us: A-II, B-I, C-IV, D-III.
This corresponds to Option D.

Mesosomes are invaginations of the plasma membrane in prokaryotic cells, specifically bacteria. They play a crucial role in cell wall formation, DNA replication, and distribution to daughter cells. Other options are not directly involved in cell wall formation:
1. Ribosomes: These are the sites of protein synthesis but do not play a role in cell wall formation.
3. Golgi Apparatus: This organelle is involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles, not in bacteria.
4. Centrosomes: These are involved in organizing microtubules during cell division in eukaryotic cells, not in bacteria.

Here’s the matching of the components:

• A. Cilia: III. Axoneme - Cilia have a core structure called the axoneme, which is essential for their movement.
• B. Endoplasmic Reticulum: IV. Ribosomes - The rough ER is studded with ribosomes, which are the sites of protein synthesis.
• C. Mitochondria: II. Cristae - The inner membrane of mitochondria is folded into structures called cristae, which increase the surface area for ATP production.
• D. Kinetochore: I. Spindle fibres - The kinetochore is a protein structure on chromatids where the spindle fibers attach during cell division.

The Golgi cisternae are concentrically arranged near the nucleus with distinct convex cis or the forming  face and concave trans or the maturing face. The cis and the trans faces of the organelle are entirely different, but interconnected.

• (a) A-II, B-IV, C-III, D-I: This is the correct option. Fleming is associated with the discovery of the cell nucleus (IV), Robert Brown with the nucleus (IV), George Palade with ribosomes (III), and Camillo Golgi with the Golgi apparatus (I).
• (b) A-II, B-III, C-I, D-IV: This is incorrect as it misassigns the contributions of these scientists.
• (c) A-I, B-II, C-III, D-IV: This is incorrect as it misassigns the contributions of these scientists.
• (d) A-IV, B-II, C-III, D-I: This is incorrect as it misassigns the contributions of these scientists.

(a) Membrane bound vesicular structure: This option is incorrect as mesosomes are not simply vesicular structures; they are extensions of the plasma membrane.
(b) Chain of many ribosomes attached to a single mRNA: This describes a polysome, not a mesosome, making this option incorrect.
(c) Special structure formed by the extension of plasma membrane: This is correct. Mesosomes are invaginations of the plasma membrane in prokaryotic cells, believed to be involved in cell division and DNA replication.
(d) Medium sized chromosome: This option is incorrect as mesosomes are not chromosomes; they are membrane structures.

• A. Metacentric chromosome: Matches with II. Middle centromere forming two equal arms of chromosome. This is correct as metacentric chromosomes have centromeres located in the middle.
• B. Sub-metacentric chromosome: Matches with III. Centromere is slightly away from the middle chromosome resulting in two unequal arms. This is correct as sub-metacentric chromosomes have centromeres that are not centrally located.
• C. Acrocentric chromosome: Matches with IV. Centromere is situated close to its end forming one extremely short and one very long arm. This is accurate as acrocentric chromosomes have a centromere near one end.
• D. Telocentric chromosome: Matches with I. Chromosome has a terminal centromere. This is correct as telocentric chromosomes have their centromere at one end.

• A. F1 Particles: Matches with IV. Mitochondria. F1 particles are associated with ATP synthesis in mitochondria.
• B. Histones: Matches with I. Chromosomes. Histones are proteins that package and order DNA into structural units called nucleosomes, which make up chromosomes.
• C. Axoneme: Matches with II. Cilia. The axoneme is the structural basis of cilia and flagella, consisting of microtubules.
• D. Cisternae: Matches with III. Golgi apparatus. Cisternae are the flattened membrane-bound compartments that make up the Golgi apparatus.

Statement I is true because the Golgi apparatus has concentrically arranged cisternae near the nucleus with a convex cis (forming) face and a concave trans (maturing) face.
Statement II is false because although proteins are modified in the Golgi cisternae, they are released from the trans face, not the cis face.

The endomembrane system in a cell includes:
- The nuclear envelope
- The endoplasmic reticulum (ER)
- The Golgi apparatus (Golgi complex)
- Lysosomes
- Vesicles
- The plasma membrane
This system is involved in the modification, packaging, and transport of proteins and lipids.
Mitochondria and chloroplasts are not part of the endomembrane system. They are both organelles with their own separate membranes, and they have their own DNA. They are thought to have originated from a symbiotic relationship with prokaryotic cells, a theory known as endosymbiosis.
Peroxisomes, although they are membrane-bound organelles involved in many metabolic reactions, are also not considered part of the endomembrane system because they do not communicate with the other endomembrane organelles and are not involved in protein sorting or lipid synthesis like the other components of the endomembrane system.

An elaborate network of filamentous proteinaceous structures consisting of microtubules, microfilaments and intermediate filaments present in cytoplasm is collectively referred to as the cytoskeleton. It is involved in many functions such as mechanical support, motility, maintenance of the shape of the cell.

Statement I: In bacteria, the mesosomes are indeed formed by the extensions of the plasma membrane into the cytoplasm. They are typically observed as invaginations of the plasma membrane.
Statement II: Mesosomes in bacteria are thought to assist in several cellular processes including DNA replication, distribution of DNA during cell division, respiration, and cell wall formation. Hence, this statement is also correct.

(A) and (C) are correct. (B), (D) and (E) are incorrect. 

A. Statement A is correct. Glycoproteins and glycolipids are formed by addition of carbohydrate groups to proteins and
lipids, respectively. Golgi is the site of this glycosylation process. 

B. Statement B is incorrect. ATP production primarily occurs in the mitochondria, not the Golgi apparatus. 

C. Statement C is correct. Golgi body modifies the proteins synthesised by ribosomes on the endoplasmic reticulum (ER). The Golgi apparatus receives proteins synthesised on the ribosomes of the ER and modifies them. This modification includes processes, like adding sugar moieties, cleaving signal peptides, and folding the proteins into their functional conformation.

D. Statement D is incorrect. While the Golgi apparatus is involved in intracellular transport, it does not primarily facilitate the transport of ions. It mainly deals with the transport and sorting of proteins and lipids.

E. Statement E is incorrect. The Golgi apparatus does not provide mechanical support. The cytoskeleton, which is composed of proteins such as microtubules and microfilaments, is responsible for providing structural support to the cell.

Substances that have a hydrophilic moiety find it difficult to pass through the plasma membrane; thus, their movement has to be facilitated.

• Sol. Lysosomes contain hydrolytic enzymes which become active at acidic pH.
• If pH in lysosomes is increased to alkaline or basic then hydrolytic enzymes will become inactive.

Presence of membranous organelles is an exclusive property of eukaryotic cells. Endoplasmic reticulum is an example of membranous organelles, so, it will always be found in eukaryotic cells only and never in the prokaryotes. This is true for SER and RER both. 

• When the centromere is situated in the middle of two equal arms of chromosomes, the chromosome is called Metacentric.
• When the centromere is present slightly away from the middle, it is called sub-metacentric chromosome.
• When the centromere is present very close to one end of the chromosome, it is known acrocentric chromosome.
• When the centromere is present at terminal position, chromosome is refers as telocentric.

Topic in NCERT: Types of chromosomes based on the position of centromere

Line in NCERT: "the metacentric chromosome has middle centromere forming two equal arms of the chromosome."

• Proteins and lipids are formed in the endoplasmic reticulum and some of them are modified to form glycoproteins and glycolipids in the Golgi apparatus.
• Enlarged image of Endoplasmic reticulum and golgi apparatus (relation). Only golgi bodies given here.

Hence, the correct option is A