Cell - The Unit of Life

The primary function of Golgi apparatus is to package the materials made by endoplasmic reticulum and deliver it to intracellular targets and outside the cell, this statement is correct and the reason statement is also correct. Golgi apparatus remains in close association with endoplasmic reticulum. Here, assertion and reason statements both are correct but reason is not correctly explaining assertion.

The eukaryotic ribosomes are 80S and prokaryotic ribosomes are 70S type.

Each ribosome has two sub-units.

The two sub-units of 80 S ribosome are 60 S and 40 S while that of 70 S are 50 S and 30 S .

The correct answer is Mesosome (Option C).

Key points about mesosomes in prokaryotes:

They are infoldings of the plasma membrane.

They house enzymes and machinery for:

• Cell-wall synthesis

• DNA replication and segregation

• Respiratory processes (electron transport)

No other prokaryotic structure (cristae, ER or chromatophores) performs all three functions together.

The explanation of the terms in List-I is as follows:

Centromere: This is involved in cell division. It is a region on a chromosome where the spindle fibers attach during mitosis and meiosis.

Cilium: Responsible for cell movement. Cilia are hair-like structures that extend from the surface of many animal cells and move in a coordinated manner to propel the cell or move fluid past the cell.

Cristae: These are the finger-like structures found within mitochondria. They increase the surface area of the inner mitochondrial membrane, enhancing its ability to produce ATP through cellular respiration.

Cell membrane: It consists of a phospholipid bilayer. This membrane separates the interior of the cell from the external environment and regulates the passage of substances in and out of the cell.

By matching List-I with List-II, we can see:

A (Centromere) corresponds to II (Cell division).

B (Cilium) corresponds to III (Cell movement).

C (Cristae) corresponds to I (Mitochondrion), specifically the internal structure.

D (Cell membrane) corresponds to IV (Phospholipid Bilayer).

$\bullet$ Nucleus as a cell organelle was first described by Robert Brown as early as 1831.

$\bullet$ Later the material of the nucleus stained by the basic dyes was given the name chromatin by Flemming.

$\bullet$ Ribosomes are the granular structure first observed under the microscope as dense particle by George Palade.

$\bullet$ Camillo Golgi first observed densely stained reticular structure near the nucleus. It consist of many disc shaped sac or cisternae.

Hence, A-II, B-IV, C-III, D-I is correct.

The correct answer is Option C: Special structure formed by extension of plasma membrane.

Here's a detailed explanation:

Mesosomes are inward folds or invaginations of the plasma membrane in prokaryotic cells (bacteria and archaea). They are not present in all prokaryotes and are considered artifacts of chemical fixation used in electron microscopy. While they were once thought to be important for various cellular functions, they are now believed to be a result of the preparation process rather than a true cellular structure.

Let's look at why the other options are incorrect:

Option A: Membrane bound vesicular structure: While mesosomes are membrane-bound, they are not vesicular structures. Vesicles are small, membrane-enclosed sacs that transport materials within the cell. Mesosomes are more like extensions or folds of the plasma membrane.

Option B: Chain of many ribosomes attached to a single mRNA: This describes a polysome or polyribosome, which is a structure involved in protein synthesis.

Option D: Medium sized chromosome: Prokaryotes have a single, circular chromosome located in a region called the nucleoid. It's not a "medium-sized" chromosome in the same way eukaryotic cells have multiple, linear chromosomes.

In summary, mesosomes are an artifact of chemical fixation and are not considered true cellular structures. They are formed by extensions of the plasma membrane in prokaryotic cells.

The correct answer is Option D: A-III, B-IV, C-I, D-II

Here's a breakdown of why:

Histones (A) - Positively charged basic proteins (III)

Histones are proteins that are rich in basic amino acids (like lysine and arginine), giving them a positive charge. This positive charge allows them to bind tightly to the negatively charged DNA molecule.

Nucleosome (B) - DNA wrapped around histone octamer (IV)

A nucleosome is the fundamental unit of chromatin. It consists of a core of eight histone proteins (two each of H2A, H2B, H3, and H4) around which a segment of DNA is wrapped. This wrapping is what gives chromatin its "beads-on-a-string" appearance.

Euchromatin (C) - Loosely packed chromatin (I)

Euchromatin is a less condensed form of chromatin that is actively transcribed. It is more loosely packed, allowing access for transcription factors and other proteins involved in gene expression.

Heterochromatin (D) - Densely packed chromatin (II)

Heterochromatin is a highly condensed form of chromatin that is generally inactive in transcription. It is densely packed, making it difficult for transcription factors to access the DNA.

Therefore, the correct match is:

A - III

B - IV

C - I

D - II

The correct statement about the type of junction and their role in our body is Option B: Tight junctions help to stop substances from leaking across a tissue.

Let's break down why this is correct and why the other options are incorrect:

Tight junctions are indeed responsible for forming a seal between cells, preventing the passage of fluids and molecules between them. This is crucial for maintaining the integrity of tissues and organs. Imagine the lining of your stomach or intestines - tight junctions ensure that digestive juices and enzymes don't leak out and cause damage to surrounding tissues.

Here's why the other options are incorrect:

Option A: Adhering junctions facilitate the cells to communicate with each other.

This statement is incorrect. While adhering junctions do help in holding cells together, they are primarily involved in providing structural support and mechanical strength to tissues. Communication between cells is primarily facilitated by gap junctions, not adhering junctions.

Option C: Tight junctions help to perform cementing to keep neighbouring cells together.

This statement is partially correct, but incomplete. While tight junctions do play a role in holding cells together, their primary function is to form a barrier, preventing leaks. Adhering junctions are more specifically responsible for cementing cells together.

Option D: Gap junctions help to create gaps between the cells and tissues.

This statement is completely incorrect. Gap junctions actually form channels between cells, allowing for the direct passage of ions, small molecules, and even electrical signals. These channels are essential for cell-to-cell communication and coordination in various tissues like heart muscle and smooth muscle.

In summary, tight junctions act as barriers, adhering junctions provide structural support, and gap junctions enable communication between cells.

To solve this matching question, we need to correctly associate the items in List-I with the appropriate items in List-II based on their biological significance.

Here is the breakdown of the items:

1. F₁ Particles (A) - These are found in the mitochondria and are involved in ATP synthesis via oxidative phosphorylation.

2. Histones (B) - Histones are proteins that package and order DNA into structural units called nucleosomes, and they are crucial components of chromosomes.

3. Axoneme (C) - The axoneme is the central strand of a cilium or flagellum, typically comprising a complex of microtubules.

4. Cisternae (D) - These are flattened membrane disk structures that are a part of the Golgi apparatus and the endoplasmic reticulum.

Based on these associations, we can match:

• (A) F₁ Particles → (IV) Mitochondria
• (B) Histones → (I) Chromosomes
• (C) Axoneme → (II) Cilia
• (D) Cisternae → (III) Golgi apparatus

Therefore, the correct option is:

Option B: A-IV, B-I, C-II, D-III

The Golgi cisternae are concentrically arranged near the nucleus with distinct convex cis or the forming face and concave trans or the maturing face.

A number of proteins synthesised by ribosomes on the endoplasmic reticulum are modified in the cisternae of the Golgi apparatus before they are released from its trans face.

Hence the correct answer is option (D).

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:

$\text{A-III, B-II, C-IV, D-I}$.

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

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.

Both mitochondria and chloroplasts are double membrane bound cell organelles.

Transport of ions occurs across the inner membrane of mitochondria. The inner membrane of chloroplast is impermeable to ions and metabolites. Therefore, it is said that inner membrane of mitochondria is relatively more permeable to that of chloroplast.

The correct answer is :

Option C : Both Statement I and Statement II are correct.

Here's why :

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.

The Golgi apparatus, sometimes called the Golgi body or Golgi complex, plays a critical role in the processing and packaging of proteins and lipids following their synthesis in the endoplasmic reticulum. It also has a role in the formation of glycoproteins and glycolipids.

So, among the given statements :

(A) It is the important site of formation of glycoprotein and glycolipids - This statement is correct.

(B) It produces cellular energy in the form of ATP - This statement is incorrect. The mitochondria, not the Golgi apparatus, are responsible for the production of ATP.

(C) It modifies the protein synthesized by ribosomes on ER - This statement is correct. The Golgi apparatus modifies and packages proteins received from the ER.

(D) It facilitates the transport of ions - This statement is not generally correct. Ion transport is primarily facilitated by the plasma membrane and ion channels.

(E) It provides mechanical support - This statement is incorrect. While the Golgi apparatus does help maintain cellular structure to a degree, its main role is in processing and packaging substances, not providing mechanical support.

So the most appropriate answer from the options given would be Option B : (A) and (C) only.

In tissue culture experiments, leaf mesophyll cells are put in a culture medium to form callus. This phenomenon may be called as dedifferentiation.

Dedifferentiation is a phenomenon by which the living differentiated plant cells, that by now have lost the capacity to divide can regain the capacity of division under certain conditions.

The ribosome consists of structural RNAs and about 80 different proteins.

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.

The phenomenon where certain living differentiated cells regain or attain their ability to divide and form new cells is known as dedifferentiation.

Porins are huge pores in outer membrane of mitochondria.

Leg haemoglobin turns the nodules pink in colour.

H+ accumulation in lumen of thylakoid occurs during photosynthetic electron transport.

Respiration is an amphibolic pathway.

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.

In prokaryotes, ER is absent be it RER or SER.

The statement that is not correct is:

Option B: Lysosomes are formed by the process of packaging in the endoplasmic reticulum.

Lysosomes are indeed membrane-bound structures (Option A) that contain numerous hydrolytic enzymes (Option C) which are active under acidic conditions (Option D). However, lysosomes are not formed by the endoplasmic reticulum. Instead, they are formed from vesicles that bud off from the Golgi apparatus. The endoplasmic reticulum is involved in the synthesis of proteins, some of which are destined for lysosomes, but the actual formation and packaging of lysosomes occur at the Golgi apparatus.

The correct matching is:

Option C

(a) $ \to $ (iii), (b) $ \to $ (iv), (c) $ \to $ (i), (d) $ \to $ (ii)

Here's a detailed explanation of the match:

(a) Thylakoids $ \to $ (iii) Flat membranous sacs in stroma: Thylakoids are indeed the flattened, sac-like structures found within the stroma of chloroplasts. They are the sites of light-dependent reactions in photosynthesis.

(b) Cristae $ \to $ (iv) Infoldings in mitochondria: Cristae are the inward folds of the inner membrane of mitochondria. These folds increase the surface area, providing more space for the electron transport chain and ATP synthesis, crucial processes in cellular respiration.

(c) Cisternae $ \to $ (i) Disc-shaped sacs in Golgi apparatus: Cisternae are the flattened, stacked membrane-bound compartments that make up the Golgi apparatus. They play a role in modifying, sorting, and packaging proteins and lipids.

(d) Chromatin $ \to $ (ii) Condensed structure of DNA: Chromatin is the complex of DNA and proteins found in the nucleus of eukaryotic cells. It condenses during cell division to form visible chromosomes.