All questions of MCQ Corner for NEET Exam

Passive transport, also known as passive diffusion, is a process by which an ion or molecule passes through a cell wall via a concentration gradient, or from an area of high concentration to an area of low concentration. It’s like moving from the train to the platform of a subway station, or stepping out of a crowded room. Basically, passive transport gives an ion or molecule “room to breathe.”

Single membrane-bound: Some organelles are bounded by a single membrane. For example, vacuole, lysosome, Golgi Apparatus, Endoplasmic Reticulum etc. They are present only in a eukaryotic cell.

 An improved model of the structure of cell membrane was proposed by S.J. Singer and G.L. Nicolson (1972) widely accepted as fluid mosaic model.CORRECT OPTION IS B.

Carbohydrates are organic compounds synthesized in the chlorophyll containing cells of some bacteria,-algae and green plant cells, during photosynthesis. Certain photoautotrophic bacteria eg. Green sulphur bacteria and purple sulphur bacteria contain pigments like chlorobium chlorophyll and bacteriochlorophyll respectively that helps them in photosynthesis. During photosynthesis carbon dioxide is reduced into carbohydrates by water and oxygen is liberated. so option C ) is correct ( . __ .)

Lysosomes are spherical bodies, or vacuoles that are enclosed by a single membrane  (membrane- bound organelles). It contains different hydrolytic enzymes, such as proteases, lipases, and nucleases that are capable of breaking down all types of biological polymers (e.g., proteins, nucleic acids, carbohydrates, and lipids) that enter the cell or are no longer useful to the cell. So, the correct answer is 'Lysosome'.

It is consisted of a porphyrin head and a phytol tail. Porphyrin is a cyclic tetrapyrol structure, having a magnesium atom in the centre. Chlorophyll a methyl group (CH3) is attached to the third carbon in the porphyrin head.

In eukaryotes , there is a set of positively charged , basic proteins called history. Histones are organized to form a unit of eight molecules called Histones octamer. The negativity charged, DNA is wrapped around the positively charged histone octamer to form a structure called nucleosome . Nucleosome constitute the repeating unit of a structure in nucleus called chromatin.

Plastids have no role in mitotic division of a cell. They are only responsible for colors. Eg; Animal cells do not have plastids yet they can divide.

**Mitochondria and Cristae**

The correct answer is option B: Mitochondria. Cristae are indeed associated with mitochondria.

**Explanation**

Mitochondria are double-membrane-bound organelles found in most eukaryotic cells. They are often referred to as the "powerhouses" of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP), which is used as a source of chemical energy.

One important feature of mitochondria is their inner membrane, which is highly folded to form structures called cristae. Cristae are invaginations or inward folds of the inner mitochondrial membrane. These folds increase the surface area of the inner membrane, allowing for more space where ATP synthesis can occur.

**Function of Cristae**

The presence of cristae in mitochondria is crucial for their function. The inner membrane of the mitochondria contains the electron transport chain (ETC) complexes, which play a key role in generating ATP through aerobic respiration. The ETC complexes are responsible for transferring electrons from electron donors to electron acceptors, creating a proton gradient across the inner mitochondrial membrane. This proton gradient is then used to drive the synthesis of ATP.

The highly folded structure of cristae increases the surface area available for the ETC complexes and ATP synthase, which are embedded in the inner membrane. This allows for more efficient ATP production, as there is a higher concentration of these proteins in the cristae. The increased surface area also allows for more efficient electron transfer and proton pumping, further enhancing ATP synthesis.

**Summary**

Cristae are associated with mitochondria. They are invaginations or inward folds of the inner mitochondrial membrane. The presence of cristae increases the surface area of the inner membrane, allowing for more efficient ATP synthesis through the electron transport chain and ATP synthase.

RNA is located in the cytoplasm of a cell, where it will later be translated into proteins that the cell needs to keep preforming daily functions. it is present in nucleus also.

The correct answer is option 'A': Nucleoplasm condenses and group together to form chromosomes.

Explanation:
The nucleus is a membrane-bound organelle found in eukaryotic cells. It is often referred to as the control center of the cell because it houses the genetic material and is responsible for regulating various cellular activities.

Let's discuss each option one by one:

a) Nucleoplasm condenses and group together to form chromosomes:
This statement is incorrect. The nucleoplasm is the semi-fluid matrix present inside the nucleus. It contains various components such as chromatin, nucleolus, and soluble proteins. The chromatin consists of DNA, RNA, and proteins. During cell division, the chromatin undergoes condensation and forms chromosomes. Therefore, nucleoplasm does not condense to form chromosomes, rather it contains the chromatin which condenses.

b) Nucleus helps in reproduction and acts as the control centre of the cell:
This statement is correct. The nucleus contains the genetic material in the form of DNA. DNA carries the instructions for the synthesis of proteins and the regulation of cellular activities. The nucleus is involved in cell reproduction through processes like mitosis and meiosis. It also acts as the control center of the cell by regulating gene expression and cellular functions.

c) In plant cells, nucleus lies towards the periphery due to the large nucleus that occupies almost the entire region of the cell:
This statement is incorrect. In plant cells, the nucleus is typically located towards the center of the cell. It is surrounded by the cytoplasm and various organelles. The large central vacuole in plant cells occupies a significant portion of the cell's interior, but it does not displace the nucleus to the periphery.

d) Nucleus comprises of nuclear membrane, nuclear pores, nucleolus, nucleoplasm, and chromatin:
This statement is correct. The nucleus is enclosed by a nuclear membrane composed of two lipid bilayers. It has nuclear pores that allow the exchange of materials between the nucleus and the cytoplasm. The nucleolus is a prominent structure within the nucleus involved in the synthesis of ribosomes. The nucleoplasm is the semi-fluid matrix present inside the nucleus, as discussed earlier. Chromatin, consisting of DNA, RNA, and proteins, is also present in the nucleus.

Chromosomal Constrictions
Chromosomes are composed of DNA and proteins and can be visualized under a microscope during cell division. Sometimes, certain chromosomes exhibit non-staining constrictions at a constant location, which are known as satellites.

Explanation
- Satellite: These constrictions are called satellites because they appear as small, satellite-like structures attached to the main body of the chromosome.
- Location: Satellites are located at a specific region of the chromosome and are usually seen as small extensions from the main chromosomal body.
- Composition: Satellites consist of heterochromatin, which is densely packed DNA that does not undergo active transcription. This differentiates them from the rest of the chromosome.
- Function: The exact function of satellites is not fully understood, but they are thought to play a role in gene regulation, chromosomal stability, and centromere function.
- Identification: Satellites can be visualized using specific staining techniques during cytogenetic analysis, helping to identify specific chromosomes and genetic abnormalities.
Satellites are an interesting feature of chromosomes that provide valuable information about their structure and function. Further research is needed to fully understand the significance of these chromosomal constrictions.

Ribosome Synthesis Overview
Ribosomes are essential cellular structures responsible for protein synthesis. They are composed of ribosomal RNA (rRNA) and proteins, and their synthesis occurs in a specific region of the cell.
Location of Ribosome Synthesis
- Nucleolus: The primary site for ribosome synthesis is the nucleolus, a dense region within the nucleus. Here, rRNA is transcribed and combined with ribosomal proteins imported from the cytoplasm.
- Ribosomal Subunits: In the nucleolus, the rRNA molecules are processed and assembled with proteins to form the two ribosomal subunits: the small subunit and the large subunit. These subunits are crucial for the ribosome's function in translating mRNA into proteins.
Other Cell Structures
- Cytoplasm: While ribosomes do exist in the cytoplasm, they are not synthesized there. Instead, the cytoplasm is where ribosomal subunits come together to form functional ribosomes once they exit the nucleolus.
- Mitochondria and Golgi Complex: Mitochondria have their own ribosomes for synthesizing some of their proteins, but these ribosomes are distinct and originate from the cell's nucleus. The Golgi complex is involved in modifying and packaging proteins but does not synthesize ribosomes.
Conclusion
In summary, ribosomes are synthesized in the nucleolus, where rRNA and proteins combine to form ribosomal subunits. Once assembled, these subunits are transported to the cytoplasm, where they play a vital role in protein synthesis. Understanding this process is crucial for students preparing for examinations like NEET.

Chloroplast Structure
Chloroplasts are specialized organelles found in plant cells and some algae, playing a crucial role in photosynthesis. They contain several membranes and compartments that facilitate this process.
Thylakoids
- The correct answer is Thylakoids (option C).
- Thylakoids are membrane-bound structures within chloroplasts that are organized into stacks known as grana.
- Each thylakoid membrane is rich in chlorophyll, the pigment essential for capturing light energy.
Function of Thylakoids
- Thylakoids convert light energy into chemical energy during photosynthesis.
- The light-dependent reactions occur in the thylakoid membranes, where sunlight is absorbed by chlorophyll, leading to the production of ATP and NADPH.
- The thylakoid membranes also contain other pigments and proteins that assist in the photosynthetic process.
Other Membranes in Chloroplasts
- Cisternae: These are flattened membrane-bound compartments but are not related to chlorophyll.
- Cristae: These are foldings of the inner mitochondrial membrane, not found in chloroplasts.
- Tonoplast: This is the membrane surrounding the central vacuole in plant cells, distinct from thylakoids.
Conclusion
Understanding the role of thylakoids in chloroplasts is essential for grasping how plants convert sunlight into energy. Their structure and the presence of chlorophyll make them vital for the photosynthetic process.