Biology: Topic-wise Test- 3 - NEET MCQ

Observation of the Actual Living Cell
Answer: B. Anton van Leeuwenhoek
Detailed
Anton van Leeuwenhoek was the first to observe actual living cells. Here is a detailed explanation of his observations:
1. Anton van Leeuwenhoek:
- Anton van Leeuwenhoek was a Dutch scientist who is known as the father of microbiology.
- He was the first person to observe and describe microorganisms, including bacteria and protozoa.
- Using a simple microscope that he designed and built himself, he made numerous observations of various microscopic organisms.
2. Microscope Invention:
- Leeuwenhoek's microscope was a single-lens magnifying glass capable of achieving high magnification.
- It consisted of a tiny glass bead mounted on a metal plate with a pointed needle sticking out from it.
- By carefully grinding the glass bead, he was able to create a spherical lens that could magnify objects up to 270 times.
3. Observations of Cells:
- Leeuwenhoek made his observations by placing various samples under his microscope.
- He examined samples from pond water, saliva, blood, and many other sources.
- Through these observations, he discovered and described various microbial organisms, which he referred to as "animalcules."
4. Animalcules:
- Leeuwenhoek observed and described a wide range of animalcules, including bacteria, protozoa, and other microscopic organisms.
- He provided detailed drawings and accurate descriptions of their shapes, movements, and structures.
- These observations helped establish the existence of microorganisms and laid the foundation for the field of microbiology.
5. Significance:
- Leeuwenhoek's observations of actual living cells revolutionized the understanding of the microscopic world.
- His discoveries challenged the prevailing belief in spontaneous generation and paved the way for further investigation into the nature of life.
- His microscope design and observations set the stage for future advancements in microscopy and the study of cells.
In conclusion, Anton van Leeuwenhoek was the first to observe actual living cells using his self-designed microscope. His observations and descriptions of microorganisms greatly contributed to the field of microbiology and our understanding of the microscopic world.

Studies on the correlation between cell structure and function:
Introduction:
Studies in biology aim to understand the relationship between the structure and function of living organisms. In the case of cells, scientists have conducted extensive research to determine how the structure of cells influences their various functions.
Branch of Biology:
The branch of biology that specifically focuses on the study of cells, their structure, and their functions is known as Cell Biology.
Explanation:
Cell Biology encompasses a wide range of studies that investigate the structure and function of cells. It involves observing and analyzing various aspects of cells, such as their organelles, membranes, and genetic material, to gain insights into their functions and behaviors.
Key points:
- Cell Biology is a branch of biology that focuses on the structure and function of cells.
- It involves studying the different components of cells, including organelles, membranes, and genetic material.
- By analyzing the structure of cells, scientists can gain insights into their specific functions and processes.
- Cell Biology plays a crucial role in understanding various life processes, such as cell division, metabolism, and communication.
- It also helps in studying diseases and developing treatments by identifying abnormalities in cell structure and function.
Conclusion:
In conclusion, the branch of Biology that studies the correlation between the structure of cells and their functions is Cell Biology. This field of study plays a crucial role in understanding the complex processes occurring within cells and provides valuable insights into various life processes and diseases.

Explanation:
To obtain the highest resolution, it is important to consider the wavelength of light. The resolution is determined by the ability to distinguish two closely spaced objects as separate entities.
Shorter wavelength:
- Light with the shortest wavelength (A) will provide the highest resolution.
- This is because shorter wavelengths allow for smaller details to be resolved.
- The shorter the wavelength, the smaller the details that can be distinguished.
Other options:
- Light with PAR wavelength (B) refers to Photosynthetically Active Radiation, which is important for plant growth and photosynthesis, but it is not directly related to resolution.
- Light with 600 to 700 nm wavelength (C) falls within the visible spectrum and is commonly used in photography, but it may not provide the highest resolution compared to shorter wavelengths.
- UV radiation (D) has a shorter wavelength than visible light, but it can be harmful to the human eye and is not typically used for obtaining the highest resolution.
Therefore, the correct answer is A: light of the shortest wavelength.

Objective: To determine the maximum numerical aperture of an oil immersion objective.
Given:
- Option A: 1.4
- Option B: 1.350
- Option C: 200 nm
- Option D: 450 nm
Approach:
To determine the maximum numerical aperture, we need to understand the concept of numerical aperture and its significance in oil immersion objectives.
Numerical Aperture (NA):
Numerical aperture is a measure of the light-gathering ability of an objective lens. It is defined as the sine of the half-angle of the maximum cone of light that can enter the objective lens. In other words, it determines the resolving power and light-gathering capacity of the lens.
Oil Immersion Objective:
An oil immersion objective is a type of objective lens used in microscopy that requires the use of a special immersion oil to improve image quality and resolution. The oil has a refractive index similar to that of the glass slide and the lens, reducing the light loss and increasing the numerical aperture.
Maximum Numerical Aperture:
The maximum numerical aperture of an oil immersion objective is determined by the design and quality of the lens. It represents the highest possible value of numerical aperture that can be achieved with the objective.

Comparing the given options, we can determine that the correct answer is option A: 1.4. Here's why:
- Option A: 1.4
- Option B: 1.350
- Option C: 200 nm
- Option D: 450 nm
The maximum numerical aperture of an oil immersion objective is typically around 1.4. This value represents the highest light-gathering capacity and resolving power achievable with this type of objective. Therefore, option A is the correct answer.
Conclusion:
The maximum numerical aperture of most oil immersion objectives is 1.4. This value determines the light-gathering capacity and resolving power of the objective lens.

Closest Relative of Electron Microscope:
The closest relative of an electron microscope is the scanning probe microscope.
Explanation:
- The electron microscope and the scanning probe microscope are both types of microscopy techniques used to observe objects at a very small scale.
- Both microscopes use a probe to scan the surface of the sample and generate an image.
- The main difference between the two is the type of probe used.
- In an electron microscope, a beam of electrons is used as the probe, while in a scanning probe microscope, a physical probe is used.
- The scanning probe microscope can provide high-resolution images and can also measure properties such as surface roughness, conductivity, and magnetic fields.
- The scanning tunneling microscope (STM) and the atomic force microscope (AFM) are two common types of scanning probe microscopes.
- The STM uses a sharp probe to measure the tunneling current between the probe and the sample surface, while the AFM uses a small cantilever with a probe tip to measure the forces between the probe and the sample.
- Both the STM and AFM are considered to be close relatives of the electron microscope as they share the same principle of scanning a probe over the sample surface.
- Therefore, the correct answer is option A: Scanning probe microscope.

Explanation:
Normal Clinical Centrifuge:
A normal clinical centrifuge is a motorized instrument used in laboratories to separate substances of different densities by spinning them at high speeds.
Rotational Speed:
The rotational speed of a centrifuge is measured in revolutions per minute (rpm) and indicates how fast the rotor rotates.
Options:
The given options for the maximum rotational speed of the normal clinical centrifuge are:
A) 50000 rpm
B) 800 rpm
C) 100000 rpm
D) 5000 rpm

To determine the correct answer, we need to compare the given options with the maximum rotational speed of a normal clinical centrifuge.
Comparing Options:
A) 50000 rpm: This option indicates a high rotational speed, which may be possible for specialized centrifuges but not for a normal clinical centrifuge.
B) 800 rpm: This option indicates a relatively low rotational speed, which is not suitable for efficient separation of substances.
C) 100000 rpm: This option indicates an extremely high rotational speed, which is unlikely for a normal clinical centrifuge.
D) 5000 rpm: This option indicates a moderate rotational speed, which is more suitable for a normal clinical centrifuge.
Conclusion:
Based on the comparison, option D (5000 rpm) is the most reasonable and accurate answer as it represents a rotational speed that is suitable for a normal clinical centrifuge.

Enzymes used to join bits of DNA:

DNA ligase:

- DNA ligase is the enzyme responsible for joining or sealing the gaps between the fragments of DNA.
- It catalyzes the formation of phosphodiester bonds between the sugar-phosphate backbone of DNA strands.
- DNA ligase plays a crucial role in DNA replication, repair, and recombination processes.

DNA polymerase:

- DNA polymerase is primarily responsible for synthesizing new DNA strands by adding nucleotides to the growing chain.
- While DNA polymerase is not directly involved in joining bits of DNA, it is required for the replication of DNA and the synthesis of Okazaki fragments during lagging strand synthesis.

Primase:

- Primase is an enzyme that synthesizes short RNA primers needed for DNA replication.
- It catalyzes the synthesis of RNA primers that provide the starting point for DNA polymerase to bind and initiate DNA synthesis.
- Although primase is involved in DNA replication, it is not directly responsible for joining fragments of DNA.

Endonuclease:

- Endonuclease is an enzyme that cleaves DNA by breaking phosphodiester bonds.
- While endonucleases are involved in DNA repair processes, they are not specifically used to join bits of DNA.

Therefore, the correct enzyme used to join bits of DNA is DNA ligase.

Chromatography used for separation of Antibody, cellular enzyme, and m-RNA is Affinity chromatography.
Affinity chromatography is a type of chromatographic technique that separates molecules based on their specific interactions with a ligand immobilized on a solid support. In this technique, the target molecule selectively binds to the ligand, allowing for its purification and separation from other components in the sample. Here is a detailed explanation of how affinity chromatography is used for the separation of antibody, cellular enzyme, and m-RNA:
Principle:
Affinity chromatography utilizes the principle of specific affinity between a target molecule and a ligand. The ligand is immobilized onto a solid matrix, such as agarose beads or a chromatography column, creating an affinity column.
Procedure:
1. Preparation of the affinity column:
- The ligand is immobilized onto the solid matrix through covalent bonding or physical adsorption.
- The column is then equilibrated with a buffer solution to maintain optimal conditions for binding and separation.
2. Sample application:
- The sample containing the mixture of proteins, enzymes, and m-RNA is loaded onto the affinity column.
- The target molecule, such as the antibody, cellular enzyme, or m-RNA, selectively binds to the ligand on the column.
3. Washing:
- Unbound molecules are washed away using a wash buffer, which helps remove impurities and nonspecifically bound components.
- This step ensures the purification and separation of the target molecule from other contaminants.
4. Elution:
- The target molecule is eluted from the column using an elution buffer.
- The elution buffer disrupts the specific binding between the target molecule and the ligand, allowing the target molecule to be collected separately.
5. Analysis and further processing:
- The eluted fractions containing the purified target molecule are collected and analyzed for their purity and concentration.
- Depending on the downstream applications, the purified target molecule can be further processed or used directly.
Advantages of affinity chromatography:
- High selectivity: Affinity chromatography allows for the isolation of specific target molecules based on their affinity to the ligand.
- High purity: The technique provides high purification levels, resulting in highly pure target molecules.
- Mild conditions: Affinity chromatography can be performed under mild conditions, preserving the biological activity of the target molecule.
Conclusion:
Affinity chromatography is a powerful technique used for the separation and purification of specific target molecules, such as antibodies, cellular enzymes, and m-RNA. It offers high selectivity, purity, and mild conditions, making it a valuable tool in various fields, including biochemistry, biotechnology, and pharmaceutical research.

PAGE- term most suitable to
A: Chromatography
- Chromatography is a technique used to separate and analyze mixtures of different compounds.
- It involves the separation of the components based on their differential movement through a stationary phase and a mobile phase.
- The stationary phase can be a solid or a liquid, while the mobile phase is typically a liquid or a gas.
- Chromatography is used in various fields, including chemistry, biology, and biochemistry, for tasks such as drug analysis, environmental monitoring, and protein purification.
B: Centrifugation
- Centrifugation is a technique used to separate particles or substances based on their density and size.
- It involves spinning a sample at high speeds to create a centrifugal force, which causes the particles to separate based on their sedimentation rate.
- Centrifugation is commonly used in laboratories for tasks such as separating cells from a suspension, isolating subcellular components, and purifying proteins.
- It is also used in various industries, including pharmaceuticals, biotechnology, and food processing.
C: Microscopy
- Microscopy is a technique used to visualize and study objects or samples that cannot be seen with the naked eye.
- It involves the use of microscopes, which can magnify and resolve images at a higher resolution than the human eye.
- Microscopy is used in various scientific fields, including biology, chemistry, medicine, and materials science.
- It allows researchers to study the structure, composition, and behavior of microscopic objects, such as cells, tissues, nanoparticles, and crystals.
D: Electrophoresis
- Electrophoresis is a technique used to separate and analyze charged particles, such as proteins, nucleic acids, and small molecules.
- It involves applying an electric field to a gel or a capillary tube containing the sample, causing the charged particles to migrate towards the opposite electrode based on their charge and size.
- Electrophoresis is commonly used in molecular biology and biochemistry for tasks such as DNA sequencing, protein analysis, and genotyping.
- It can provide valuable information about the size, charge, and abundance of the separated molecules.
Overall, while all the techniques mentioned (chromatography, centrifugation, microscopy, and electrophoresis) are important in scientific research, in this context, the term "PAGE" is most suitable for electrophoresis.

Explanation:
Definition of stem cells:
- Stem cells are a type of cells that have the ability to differentiate into different cell types and self-renew.
- They are found in various tissues of the body and play a crucial role in growth, development, and repair.
Types of stem cells:
There are different types of stem cells based on their potential and origin. In the context of the given question, the correct answer is d. Totipotent cell. However, it is important to mention the other types of stem cells as well.
1. Totipotent cells:
- These are the most potent type of stem cells.
- They have the ability to differentiate into any cell type, including both embryonic and extraembryonic cells.
- They can give rise to an entire organism, including the placenta and other supporting tissues.
2. Pluripotent cells:
- These stem cells are derived from the inner cell mass of the blastocyst (an early-stage embryo).
- They can differentiate into any cell type of the body, but not the extraembryonic cells.
- Examples include embryonic stem cells and induced pluripotent stem cells.
3. Multipotent cells:
- These stem cells can differentiate into a limited number of cell types.
- They are found in specific tissues of the body, such as bone marrow, blood, and skin.
- Examples include hematopoietic stem cells and mesenchymal stem cells.
4. Unipotent cells:
- These stem cells have the ability to differentiate into only one specific cell type.
- They are usually found in adult tissues and play a role in tissue repair and regeneration.
- Examples include muscle satellite cells and basal cells of the skin.
Stem cells used in medical sciences:
- Stem cells, especially pluripotent and multipotent cells, are extensively used in medical sciences for various purposes.
- They have the potential to be used in regenerative medicine, tissue engineering, and disease modeling.
- Stem cell-based therapies are being explored for the treatment of diseases such as cancer, heart disease, diabetes, and neurodegenerative disorders.
- These therapies aim to replace damaged or dysfunctional cells/tissues with healthy functional ones derived from stem cells.
In conclusion, stem cells are undifferentiated cells that have the ability to differentiate into different cell types and self-renew. The correct answer to the given question is d. Totipotent cell, which refers to the most potent type of stem cells that can differentiate into any cell type, including both embryonic and extraembryonic cells.

Pllp mean protein lipid lipid protein which is structure of plasma membrane.

Acidic condition in lysosome maintained by:
A: Pumping proton into the interior of lysosome
- Lysosomes are membrane-bound organelles found in eukaryotic cells that contain digestive enzymes.
- The interior of lysosomes is maintained at an acidic pH, typically around pH 4.5-5.0.
- The maintenance of this acidic environment is crucial for the proper functioning of lysosomal enzymes.
- Protons (H+) are actively pumped into the interior of lysosomes by a protein called V-ATPase (Vacuolar-type H+-ATPase).
- V-ATPase uses energy from ATP hydrolysis to pump protons across the lysosomal membrane, creating an acidic environment inside the lysosome.
Why is pumping proton into the interior of lysosome important?
- The acidic pH inside lysosomes is essential for the optimal activity of lysosomal enzymes.
- Many lysosomal enzymes require an acidic pH for their activation and proper functioning.
- The acidic environment also helps to maintain the stability of the lysosomal membrane and prevents leakage of enzymes into the cytoplasm.
Other options:
B: Pumping proton out to the interior of lysosome
- Pumping protons out of the lysosome would result in an alkaline environment, which is not suitable for the activity of lysosomal enzymes.
C: Pumping proton acidic enzyme the interior of lysosome
- This option does not make sense as it does not explain how the acidic condition is maintained in the lysosome.
D: Pumping proton electromagnetic current into lysosome
- This option is not valid as there is no such thing as "pumping proton electromagnetic current" into lysosomes.
Therefore, the correct answer is A: Pumping proton into the interior of lysosome.

Antimycin-D and the State of Mitochondria
Introduction:
When a person takes Antimycin-D, it affects the state of mitochondria. In this response, we will discuss the different states of mitochondria and explain why the answer is B: Orthodox state.
States of Mitochondria:
There are several states in which mitochondria can exist. Let's explore each one:
1. Condensed state:
- Mitochondria in a condensed state refers to their compacted and tightly packed form.
- This state is typically associated with cellular stress or damage.
- Condensed mitochondria are often observed in cells undergoing apoptosis, a programmed cell death process.
2. Orthodox state:
- The orthodox state of mitochondria is the normal and functional state.
- In this state, mitochondria maintain their structural integrity and perform their essential functions.
- They produce ATP (adenosine triphosphate), which is the cell's main energy source, through oxidative phosphorylation.
3. Fractioned state:
- The fractioned state of mitochondria refers to when they are fragmented into smaller, discrete units.
- Mitochondrial fragmentation can occur in response to various cellular signals and stressors.
- This state is often associated with cellular processes such as mitosis, differentiation, and apoptosis.
4. Clump with chloroplast:
- Chloroplasts are organelles found in plants and some other organisms that carry out photosynthesis.
- Mitochondria and chloroplasts are distinct organelles with different functions.
- It is uncommon for mitochondria to clump with chloroplasts, as they have different roles within the cell.
Explanation:
Now that we have discussed the different states of mitochondria, let's explain why the answer is B: Orthodox state.
- Antimycin-D is an antibiotic that inhibits the electron transport chain in mitochondria.
- By disrupting this process, Antimycin-D affects ATP production in mitochondria.
- However, the orthodox state refers to the normal and functional state of mitochondria.
- While Antimycin-D may disrupt ATP production, it does not directly alter the structural integrity of mitochondria.
- Therefore, the mitochondria of a person taking Antimycin-D would still be in the orthodox state, albeit with impaired ATP production.
In conclusion, when a person takes Antimycin-D, the state of their mitochondria remains in the orthodox state, even though ATP production is affected.

Q, C, G, R banding is used in
Animal karyotyping
- Q, C, G, R banding techniques are commonly used in animal karyotyping.
- Animal karyotyping involves the analysis and visualization of chromosomes in an organism's cells.
- Chromosomes are stained with specific dyes to produce characteristic banding patterns, which can help identify structural abnormalities or rearrangements.
- Q, C, G, R banding techniques involve different staining methods that result in distinct banding patterns on the chromosomes.
- These banding patterns can be used to identify individual chromosomes, determine their size and shape, and detect any abnormalities.
Plant karyotyping
- Q, C, G, R banding techniques are not commonly used in plant karyotyping.
- Plant karyotyping often relies on other staining techniques such as Giemsa staining or fluorochrome staining.
- These techniques produce different banding patterns compared to Q, C, G, R banding.
- Plant chromosomes have different structural characteristics and banding patterns compared to animal chromosomes.
Both 1 and 2 (C)
- Q, C, G, R banding techniques are used in animal karyotyping.
- These techniques are not commonly used in plant karyotyping.
- Therefore, the correct answer is both 1 and 2.
Only in FISH (D)
- Q, C, G, R banding techniques are not exclusively used in fluorescence in situ hybridization (FISH).
- FISH is a different technique that involves the use of fluorescent probes to detect specific DNA sequences on chromosomes.
- Q, C, G, R banding techniques are used to visualize the overall structure of the chromosomes, while FISH is used for more specific gene or DNA sequence detection.
Therefore, the correct answer is B. Animal karyotyping.

Histogram term suitable to

A: Banding 

B: FISH

C: McFISH 

D: Flow cytometry

Answer: D
Explanation:
Flow cytometry is a technique used to analyze and measure various physical and chemical characteristics of cells or particles. A histogram is a graphical representation of the distribution of a set of data. In the context of flow cytometry, a histogram is commonly used to display the frequency or count of cells or particles with respect to a specific parameter, such as size, fluorescence intensity, or DNA content. Therefore, the term "histogram" is most suitable for flow cytometry because it is frequently used to visualize and analyze data in this field.
Here is a detailed explanation of why the other options are not suitable:
A: Banding refers to a technique used in cytogenetics to stain and visualize specific regions of chromosomes. Although banding patterns can be represented graphically, the term "histogram" is not commonly associated with banding.
B: FISH (Fluorescence In Situ Hybridization) is a molecular technique used to detect and localize the presence or absence of specific DNA sequences on chromosomes. While FISH data can be analyzed and visualized using various methods, the term "histogram" is not typically used in the context of FISH.
C: McFISH (Multiplex Fluorescence In Situ Hybridization) is a technique that combines multiple FISH probes to simultaneously detect multiple DNA sequences on chromosomes. Similar to FISH, the term "histogram" is not commonly used to describe the visualization or analysis of McFISH data.
Therefore, out of the given options, the term "histogram" is most suitable for flow cytometry as it is frequently used to represent and analyze data in this field.

Formation of new centriole:
To understand the formation of a new centriole, let's break down the process and the different stages involved:
1. Interphase:
During interphase, the cell undergoes normal growth and metabolic activities. The centrioles are duplicated in preparation for cell division.
2. S Phase:
The S phase is a specific stage within interphase where DNA replication occurs. This is an essential step for the formation of new centrioles.
3. Centriole Duplication:
Once the cell enters the S phase, centriole duplication begins. This process involves the following steps:
- Procentriole Formation:
- Within the centrosome, a small cylindrical structure called a procentriole starts to form adjacent to each existing centriole.
- Procentrioles consist of microtubules that are organized in a nine-fold symmetry pattern.
- Elongation:
- The procentrioles elongate by adding more microtubules to their structure.
- This elongation is facilitated by the assembly of tubulin proteins.
- Maturation:
- The procentrioles mature into new centrioles.
- They acquire their characteristic structure, consisting of nine microtubule triplets arranged in a cylindrical shape.
4. M Phase:
The M phase is the phase of cell division, which includes mitosis and cytokinesis. During this phase, the duplicated centrioles play a crucial role in the formation of the mitotic spindle.
Answer:
Based on the given options, the correct answer is B. S Phase. The formation of new centrioles occurs during the S phase of the cell cycle, specifically during the process of centriole duplication.
Note: The images provided in options A and C are not directly related to the formation of new centrioles and are not relevant to the question. Option D (M phase) is incorrect as the formation of new centrioles occurs before the M phase during interphase.

The stage between the telophase of the first meiotic division and the prophase of the second meiotic division is known as:

• Intrameiotic interphase

Explanation:

The process of meiosis involves two rounds of cell division, resulting in the formation of four daughter cells with half the number of chromosomes as the parent cell. The stages of meiosis are divided into meiosis I and meiosis II. The stage between the telophase of the first meiotic division and the prophase of the second meiotic division is called intrameiotic interphase. Here's a breakdown of the meiotic stages:

1. Meiosis I:
   
   
   
   • Prophase I: This is the longest phase of meiosis, and it can be further divided into five sub-stages: leptotene, zygotene, pachytene, diplotene, and diakinesis.
   
   
   • Metaphase I: Homologous chromosomes align at the metaphase plate.
   
   
   • Anaphase I: Homologous chromosomes separate and move to opposite poles.
   
   
   • Telophase I: Chromosomes reach the poles, and nuclear membranes may reform.
   
   
   • Cytokinesis I: The cytoplasm divides, resulting in two daughter cells.
   
   
   
   


2. Intrameiotic Interphase: This is a brief interphase between meiosis I and meiosis II, where the chromosomes partially uncoil and the nuclear envelope may reform.


3. Meiosis II:
   
   
   
   • Prophase II: Chromosomes condense, and the nuclear envelope breaks down.
   
   
   • Metaphase II: Chromosomes align at the metaphase plate.
   
   
   • Anaphase II: Sister chromatids separate and move to opposite poles.
   
   
   • Telophase II: Chromosomes reach the poles, and nuclear envelopes reform.
   
   
   • Cytokinesis II: The cytoplasm divides, resulting in a total of four daughter cells.
   
   
   
   

Therefore, the correct answer is C. Intrameiotic interphase.

Recombination nodule appears at:
- Zygotene: Recombination nodules do not appear at zygotene. During zygotene, homologous chromosomes begin to pair up and exchange genetic material in a process called synapsis.
- Pachytene: Recombination nodules appear at pachytene. This is the stage of meiosis where crossing-over occurs between homologous chromosomes. Recombination nodules are protein aggregates that facilitate the exchange of genetic material between non-sister chromatids.
- Diplotene: Recombination nodules do not appear at diplotene. During diplotene, the paired homologous chromosomes begin to separate but remain connected at points called chiasmata.
- Diakinesis: Recombination nodules do not appear at diakinesis. This is the final stage of prophase I where the chromosomes condense further and the nuclear envelope breaks down.
Therefore, based on the given options, the correct answer is Pachytene where recombination nodules appear.

Cytokinesis in animal cells actually occurs through the centripetal type.
Here is a detailed explanation:
Centrifugal Type:
- This type of cytokinesis occurs in plant cells, not animal cells.
- During centrifugal cytokinesis, a cell plate forms at the center of the cell and extends towards the periphery, dividing the cytoplasm and forming two daughter cells.
- This process is facilitated by the formation of a new cell wall.
Centripetal Type:
- In animal cells, cytokinesis occurs through the centripetal type.
- During centripetal cytokinesis, a contractile ring made of actin and myosin filaments forms at the equator of the cell.
- The contractile ring contracts, causing the cell membrane to pinch inward and eventually separate the cytoplasm into two daughter cells.
- This process is also called cleavage furrow formation.
Peripheral Type:
- Peripheral type cytokinesis does not exist. It is not a valid type of cytokinesis in animal cells.
Synapsis:
- Synapsis is a term used in genetics to describe the pairing of homologous chromosomes during meiosis. It is not related to cytokinesis.
Therefore, the correct answer is B: Centripetal type.

Homologous Chromosome Pairing
Homologous chromosome pairing is a crucial step in the process of meiosis, which is a type of cell division that produces gametes (sex cells). This pairing allows for the exchange of genetic material between homologous chromosomes, leading to genetic diversity in offspring. When two homologous chromosomes start pairing, it occurs in a specific manner. Let's explore the different options and identify the correct one.
A: Pro-terminal pairing
- In pro-terminal pairing, the pairing of homologous chromosomes starts at the terminal ends.
- This means that the chromosomes begin pairing at the tips and gradually progress towards the centromere, which is the region that holds the sister chromatids together.
- Pro-terminal pairing is an essential step in meiosis and ensures proper alignment and exchange of genetic material between homologous chromosomes.
B: Procentric pairing
- Procentric pairing is not the correct term for the process described in the question.
- This term does not accurately describe the process of homologous chromosome pairing.
C: Random pairing
- Random pairing is also not the correct term for the process described in the question.
- Random pairing would imply that the pairing of homologous chromosomes occurs in a random and haphazard manner, which is not the case.
D: Intermediate pairing
- Intermediate pairing is not the correct term for the process described in the question.
- This term does not accurately describe the process of homologous chromosome pairing.
Therefore, the correct answer is A: Pro-terminal pairing. This accurately describes the process of homologous chromosome pairing, where the pairing starts at the terminal ends and progresses towards the centromere.

True replication of DNA is possible due to:
- Complementary base pairing rule: The two strands of DNA are held together by complementary base pairing. Adenine (A) always pairs with Thymine (T), and Guanine (G) always pairs with Cytosine (C). This rule allows for the accurate replication of DNA by ensuring that each strand serves as a template for the synthesis of a new complementary strand.
- Hydrogen bonding: Hydrogen bonds form between the complementary bases in DNA. These bonds are relatively weak, allowing the DNA strands to separate during replication. The hydrogen bonds also facilitate the accurate pairing of the complementary bases during replication.
- Phosphate backbone: The DNA molecule has a sugar-phosphate backbone, with the phosphate groups linking the sugar molecules. This backbone provides stability and structural support to the DNA molecule during replication.
- Enzymes: Various enzymes, such as DNA polymerases, helicases, and ligases, are involved in the process of DNA replication. These enzymes help in unwinding the DNA strands, synthesizing new strands, and joining the fragments together.
- Semi-conservative replication: DNA replication follows a semi-conservative model, where each newly synthesized double-stranded DNA molecule consists of one original (parental) strand and one newly synthesized (daughter) strand. This ensures the accurate transfer of genetic information from one generation to the next.
In conclusion, true replication of DNA is possible due to the complementary base pairing rule, hydrogen bonding, the phosphate backbone, enzymes, and the semi-conservative replication model. These factors work together to ensure the accurate and faithful replication of DNA during cell division.

Mitotic Division:
- Mitosis is a type of cell division that occurs in somatic cells, including cancer cells.
- It involves the replication of the cell's DNA and the subsequent division of the cell into two identical daughter cells.
- This process allows for growth, tissue repair, and the production of new cells in the body.
- In cancer cells, mitotic division is often uncontrolled and leads to the formation of tumors.
Meiotic Division:
- Meiosis is a type of cell division that occurs in reproductive cells, specifically in the formation of gametes (sperm and eggs).
- It involves two rounds of division, resulting in the production of four non-identical daughter cells.
- Meiotic division is not typically observed in cancer cells, as cancer is characterized by abnormal cell growth and division.
Amitotic Division:
- Amitosis, also known as direct cell division or binary fission, is a type of cell division that occurs in some single-celled organisms.
- It involves the splitting of the cell into two daughter cells without the involvement of a mitotic spindle or the replication of DNA.
- Amitotic division is not typically observed in cancer cells.
Binary Fission:
- Binary fission is a type of cell division that occurs in prokaryotic organisms, such as bacteria.
- It involves the replication of the bacterial DNA and the subsequent division of the cell into two identical daughter cells.
- Binary fission is not typically observed in cancer cells, as cancer primarily affects eukaryotic cells.
Therefore, the correct answer is A: mitotic Division, as cancer cells exhibit uncontrolled mitotic division, leading to the formation of tumors.

Cell wall consists of:
- Galacturonic acid: It is a component of pectin, a complex carbohydrate found in the cell wall of plants. It provides structural support and helps in cell adhesion.
- Expansion Protein: These proteins are involved in the expansion and growth of the cell wall. They regulate the deposition and rearrangement of cell wall components, allowing the cell to expand and elongate.
- Calcium and magnesium pectate: These are cross-linking compounds that help to strengthen the cell wall by forming bonds between pectin molecules. They contribute to the rigidity and stability of the cell wall structure.
Explanation:
- The cell wall is a rigid outer layer that surrounds the plasma membrane of plant cells, fungi, and some bacteria. It provides support, protection, and shape to the cell.
- The main component of the plant cell wall is cellulose, a complex carbohydrate made up of glucose molecules. However, the cell wall also contains other components such as pectin, proteins, and cross-linking compounds.
- Pectin, which contains galacturonic acid, is a major component of the cell wall matrix. It helps to regulate cell adhesion and acts as a barrier against pathogens.
- Expansion proteins are involved in the growth and expansion of the cell wall. They control the deposition and arrangement of cell wall components, allowing the cell to elongate and grow.
- Calcium and magnesium pectate are cross-linking compounds that strengthen the cell wall structure. They form bonds between pectin molecules, contributing to the rigidity and stability of the cell wall.
In conclusion, the cell wall consists of galacturonic acid, expansion proteins, and calcium and magnesium pectate. These components work together to provide support, protection, and structural integrity to the cell.

Explanation:
Innermost layer in plants:
- There is an innermost layer in some plants that is rarely present.
- This layer is relatively thin and lacks cellulose microfibers.
Cytoplasmic bridges:
- The cytoplasmic bridges are present between adjacent cells.
- These bridges allow for communication and transport of materials between cells.
Name of the cytoplasmic bridges:
- The cytoplasmic bridges present between adjacent cells are called plasmodesmata.
Options:
A: Plasmodesmata - This is the correct answer as plasmodesmata are the cytoplasmic bridges present between adjacent cells.
B: Desmotubules - This is not the correct answer as desmotubules are structures that connect the endoplasmic reticulum of adjacent cells.
C: Symplasm - This is not the correct answer as symplasm refers to the interconnected cytoplasmic continuum of plant cells.
D: Apoplasm - This is not the correct answer as apoplasm refers to the interconnected extracellular spaces in plants.
Therefore, the correct answer is A: Plasmodesmata. Plasmodesmata are the cytoplasmic bridges present between adjacent cells in plants.

Microtubules diameter nearly:
The correct answer is C: 25 nm.
Explanation:
Microtubules are tiny cylindrical structures found in cells that play a crucial role in various cellular processes. They are composed of tubulin protein subunits and have a characteristic diameter.
Here are the details about the options given:
- Option A: 7 nm - This diameter is too small for microtubules. It is more suitable for describing the size of actin filaments.
- Option B: 8-10 nm - This diameter is also too small for microtubules. It is closer to the size of intermediate filaments.
- Option C: 25 nm - This is the correct answer. Microtubules have a diameter of approximately 25 nm. They are larger than actin filaments and intermediate filaments.
- Option D: 2.5 nm - This diameter is much smaller than microtubules. It is closer to the size of a single tubulin protein subunit.
In summary, microtubules have a diameter of approximately 25 nm, which is the correct answer.

Detoxification of Drugs carried out by SER
The detoxification of drugs is an important process in the body to eliminate toxins and foreign substances. The smooth endoplasmic reticulum (SER) is responsible for carrying out this detoxification process. Here's a detailed explanation of how SER detoxifies drugs:
1. Structure and Function of SER:
- The smooth endoplasmic reticulum is a network of membrane-bound tubules and vesicles within the cell.
- It lacks ribosomes on its surface, distinguishing it from the rough endoplasmic reticulum (RER).
- SER is involved in various functions, including lipid metabolism, calcium storage, and detoxification of drugs and toxins.
2. Role in Drug Detoxification:
- SER contains enzymes known as cytochrome P450 enzymes (CYP enzymes) that play a crucial role in drug metabolism.
- These enzymes are responsible for the breakdown of drugs and toxins, making them more water-soluble and easier to eliminate from the body.
- Drug detoxification by SER involves several metabolic reactions, such as oxidation, reduction, and hydrolysis.
3. Oxidation Reactions:
- CYP enzymes in SER oxidize drugs by adding oxygen molecules, resulting in the formation of metabolites.
- Oxidation reactions make drugs more polar and facilitate their excretion.
4. Reduction Reactions:
- SER also carries out reduction reactions, where drugs are chemically modified by the addition of electrons.
- Reduction reactions are essential for the detoxification of drugs that are highly reactive or toxic.
5. Hydrolysis Reactions:
- SER enzymes can break down drugs through hydrolysis, where water molecules are added to break chemical bonds.
- Hydrolysis reactions result in the formation of metabolites that are less toxic and easier to eliminate.
6. Importance of SER in Drug Detoxification:
- The detoxification process carried out by SER is crucial for preventing the accumulation of drugs and toxins in the body.
- Without the detoxification process, drugs would remain in the system for a longer duration, leading to potential adverse effects.
In conclusion, the smooth endoplasmic reticulum (SER) plays a vital role in the detoxification of drugs. Its enzymes, such as cytochrome P450, facilitate the breakdown and modification of drugs, making them more water-soluble and easier to eliminate from the body. This detoxification process is essential for maintaining overall health and preventing the accumulation of harmful substances.

The Important function of Golgi apparatus is to:
1. Packing:
- The Golgi apparatus plays a crucial role in the packaging and sorting of molecules.
- It receives proteins and lipids from the endoplasmic reticulum (ER) and modifies them by adding sugars, lipids, or phosphate groups.
- These modified molecules are then packaged into vesicles for transportation to their destination within or outside the cell.
- The Golgi apparatus also helps in the formation of lysosomes, which are responsible for the degradation of cellular waste.
2. Secretion:
- The Golgi apparatus is involved in the secretion of various substances from the cell.
- After the molecules are processed and packaged in the Golgi apparatus, they are transported to the plasma membrane or other organelles for secretion.
- The Golgi apparatus is responsible for the production of various secretory vesicles, such as insulin vesicles in pancreatic cells or neurotransmitter vesicles in nerve cells.
Therefore, the Golgi apparatus performs both the functions of packing and secretion.