All questions of Biology: Topic-wise Test for NEET Exam

Hemoglobin is a tetramer that possesses a quaternary structure containing multiple folded polypeptide structures (tertiary structures). A tertiary protein will commonly contain a single polypeptide chain with one or more secondary structures.

Some roots, called adventitious roots, arise from an organ other than the root—usually a stem, sometimes a leaf. They are especially numerous on underground stems, such as rhizomes, corms, and tubers, and make it possible to vegetatively propagate many plants from stem or leaf cuttings.

All cells are surrounded by a plasma membrane. The membrane is composed of a phospholipid bilayer arranged back-to-back. The membrane is also covered in places with cholesterol molecules and proteins. The plasma membrane is selectively permeable and regulates which molecules are allowed to enter and exit the cell.

Gerl ---> golgi complexes, endoplasmic reticulum, lysosomes.....so your Ans is lysosomes ....

Water is absorbed by the roots of plants through a process called osmosis. The root system of a plant is responsible for absorbing water and nutrients from the soil, and distributing them throughout the plant. The process of water absorption by the roots is a complex one that involves several structures and mechanisms. Let us discuss them in detail.

Root Hairs:
Root hairs are elongated, thin-walled cells that are found on the surface of the root. They are responsible for the absorption of water and minerals from the soil. Root hairs greatly increase the surface area of the root, allowing for more efficient absorption of water and nutrients. They are constantly being replaced as they are sloughed off, and new ones are produced.

Root Cap:
The root cap is a structure located at the tip of the root. It is a protective layer that covers the delicate meristem cells at the apex of the root. The root cap releases a slimy substance that helps lubricate the soil around the root, making it easier for the root to penetrate the soil. The root cap also senses gravity and directs the root downward into the soil.

Root:
The root itself is an important structure for water absorption. The innermost layer of cells in the root, called the endodermis, is responsible for controlling the movement of water and nutrients into the plant. The endodermis acts as a barrier, allowing only certain molecules to pass through. This is important for preventing harmful substances from entering the plant.

Root Apex:
The root apex is the growing tip of the root. It is the site of cell division and growth in the root. As the root grows, it pushes through the soil, absorbing water and nutrients along the way. The root apex is constantly producing new cells, which eventually differentiate into the various types of cells that make up the root.

In conclusion, water is absorbed by the root hairs, root cap, root, and root apex of plants. Each of these structures plays an important role in the process of water absorption, allowing plants to grow and thrive in a variety of environments.

It is not a complete question or statement. Please provide more information.

Function of Atrial Natriuretic Factor (ANF)

ANF is a hormone that is released from the heart in response to increases in blood volume and blood pressure. Its main function is to regulate fluid and electrolyte balance in the body. The functions of ANF include:

Inhibits the release of renin from JGA

ANF inhibits the release of renin from the juxtaglomerular apparatus (JGA) in the kidney. Renin is an enzyme that plays a role in the renin-angiotensin-aldosterone system (RAAS), which regulates blood pressure and fluid balance in the body. By inhibiting renin release, ANF reduces the activity of the RAAS and promotes salt and water excretion by the kidneys.

Stimulates salt loss in urine

ANF promotes salt and water excretion by the kidneys by increasing the glomerular filtration rate (GFR) and inhibiting the reabsorption of sodium and water in the kidney tubules. This leads to increased urine output and reduced blood volume and blood pressure.

Inhibits sodium reabsorption from collecting duct

ANF inhibits the reabsorption of sodium and water in the collecting duct of the kidney. This leads to increased urine output and reduced blood volume and blood pressure.

Does not stimulate aldosterone secretion

Aldosterone is a hormone that is produced by the adrenal gland and plays a role in the RAAS. It promotes the reabsorption of sodium and water in the kidney tubules and increases blood volume and blood pressure. ANF does not stimulate aldosterone secretion; rather, it inhibits the activity of the RAAS and promotes salt and water excretion by the kidneys.

In conclusion, ANF is a hormone that plays an important role in regulating fluid and electrolyte balance in the body. It inhibits the release of renin from JGA, stimulates salt loss in urine, and inhibits sodium reabsorption from the collecting duct. However, it does not stimulate aldosterone secretion.

Explanation:

The sound of the heartbeat is produced by the closure of heart valves. The heart valves are responsible for ensuring that blood flows only in one direction. The sound of the heart is divided into two sounds. The first sound is a low-frequency, long-duration sound, and the second sound is a high-frequency, short-duration sound.

The first sound of the heartbeat is heard when the bicuspid and tricuspid valves close. These valves are located between the atria and ventricles. The closure of these valves causes the first sound of the heartbeat.

The second sound of the heartbeat is heard when the semilunar valves close. These valves are located between the ventricles and the great arteries. The closure of these valves causes the second sound of the heartbeat.

Therefore, the correct answer is option B - the first sound of the heartbeat is produced by the closing of the bicuspid and tricuspid valves.

Ans d also

Telophase I, is followed by an interphase, called interkinesis, similar to the mitotic interphase. During interkinesis the chromatin is partially uncoiled; however, there is no replication of the genetic material, because each chromosome already consists of two chromatids.

The crt opt is D. Cuz during metaphase, all the chromosomes lined up on the metaphase plate and further proceeding anaphase. So it is easy to count them at that stage by counting the number of functional centromere. Bcoz the number of chromosomes = count the number of functional centromere.

Transformation of membrane is the function of golgi complex.

Re-polarization in Excitable Cells

In excitable cells, such as neurons and muscle cells, action potentials are generated and transmitted. These action potentials are caused by the movement of ions across the cell membrane.

During an action potential, the cell membrane becomes depolarized as sodium ions enter the cell. This depolarization causes the cell to become more positive, which then triggers the opening of voltage-gated potassium channels.

Re-polarization

Re-polarization is the process by which the cell membrane returns to its resting potential after an action potential has occurred. This process is closely associated with the efflux of potassium ions from the cell.

K Efflux

Efflux means the outward flow. During re-polarization, the voltage-gated potassium channels that opened during depolarization allow K+ ions to flow out of the cell, which causes the membrane potential to become more negative.

As more potassium ions leave the cell, the membrane potential becomes more negative, and the cell returns to its resting state. This process of re-polarization allows the cell to generate another action potential if needed.

Conclusion

In conclusion, re-polarization in excitable cells is closely associated with the efflux of potassium ions from the cell. This process allows the cell to return to its resting potential and generate another action potential if needed.

Order of Phases in Meiosis

Leptotene

- This is the first stage of meiosis.
- During leptotene, chromosomes start to condense and become visible under a microscope.
- The chromosomes appear as thin threads, and homologous chromosomes start pairing up.

Zygotene

- In this stage, homologous chromosomes start to pair up completely.
- This process is called synapsis, and it results in the formation of bivalents or tetrads.
- The chromosomes continue to condense, and the paired chromosomes become visible as thicker threads.

Pachytene

- During pachytene, the chromosomes become even more condensed and shorten.
- Crossing over occurs between the paired homologous chromosomes and results in the exchange of genetic material between them.
- This exchange of genetic material increases genetic diversity.

Diplotene

- In this stage, the homologous chromosomes start to separate, but they are still linked at points called chiasmata where crossing over occurred.
- The chromosomes start to uncoil and become visible as thinner threads again.
- The nuclear envelope also starts to reform around each set of chromosomes.

Diakinesis

- This is the final stage of meiosis I.
- The chromosomes continue to condense and become visible as distinct structures.
- The nuclear envelope breaks down completely, and the spindle fibers start to attach to the chromosomes in preparation for their separation.

Correct Order of Phases in Meiosis

The correct order of phases in meiosis is:

Leptotene → Zygotene → Pachytene → Diplotene → Diakinesis

Option B is the correct answer as it presents the phases in the correct order.

A cofactor is a non-protein molecule that carries out chemical reactions that cannot be performed by the standard 20 amino acids. Cofactors can be either inorganic molecules (metals) or small organic molecules (coenzymes). .Holoenzyme- An apoenzyme together with its cofactor.

Centrioles are present in plant cells but absent in animal cells:
Plant cells and animal cells have some distinct differences in their structures and organelles. One of the key differences is the presence of centrioles.

Centrioles in Animal Cells:
- Centrioles are cylindrical structures composed of microtubules that are found in animal cells.
- They are involved in organizing the microtubules during cell division, helping in the formation of the spindle fibers.

Absence of Centrioles in Plant Cells:
- Plant cells do not have centrioles in their cytoplasm. Instead, they have microtubule-organizing centers (MTOCs) that perform similar functions to centrioles.
- The MTOCs help in organizing the microtubules during cell division in plant cells.

Function of Centrioles:
- Centrioles play a crucial role in cell division, especially in animal cells where they are involved in the formation of the mitotic spindle.
- The absence of centrioles in plant cells does not affect their ability to undergo cell division as they have alternative structures that serve a similar purpose.

Conclusion:
In summary, centrioles are present in animal cells but absent in plant cells. This difference is important in understanding the unique characteristics of these two types of cells.

Assertion (A) Explained
Monocotyledonous plants, commonly known as monocots, exhibit a unique root system.
- The primary root in these plants is indeed short-lived.
- It is typically replaced by a fibrous root system that consists of numerous roots emerging from the base of the stem.
This characteristic is a fundamental aspect of monocot structure.
Reason (R) Explained
The fibrous root system is crucial for the survival and growth of monocots.
- This type of root system allows monocots to develop a vast network of roots.
- Such an extensive system enhances their ability to absorb water and nutrients effectively.
The fibrous roots spread out horizontally and are closer to the soil surface, making them efficient in capturing moisture and nutrients from the top layers of soil.
Relationship between A and R
- Both the assertion and reason are true statements.
- The reason (R) serves as an explanation for the assertion (A) since the fibrous root system is a direct consequence of the short-lived primary root in monocots.
In summary, the primary root of monocots is transient, and the subsequent development of a fibrous root system supports their adaptation and efficiency in resource acquisition. Thus, the correct answer is option 'A': Both A and R are true, and R is the correct explanation of A.

- Smallest free-living organism
PPLOs, or pleuropneumonia-like organisms, are the smallest free-living organisms known. PPLOs are a type of bacteria that lack a cell wall and are classified as mycoplasmas. They are typically found in soil, water, and the respiratory tracts of animals.
- Bacteria, Viroids, and Viruses
Bacteria are larger and more complex than PPLOs, with a cell wall and organelles. Viroids are even smaller than bacteria and consist of only a short strand of RNA without a protein coat. Viruses are even smaller than viroids and can only replicate inside host cells.
- Comparison
When comparing the size of these organisms, PPLOs are considered the smallest free-living organisms due to their lack of a cell wall and minimal cellular structure. Bacteria, viroids, and viruses are all smaller than typical cells but are not considered free-living organisms in the same way that PPLOs are.
In conclusion, PPLOs are the smallest free-living organisms known, making them unique in their size and structure compared to bacteria, viroids, and viruses.

Understanding the Bilobed Nature of Anther
The bilobed structure of an anther is a significant feature in the reproductive system of flowering plants.
Key Factors Contributing to Bilobed Structure
- The distinct bilobed nature is primarily due to the microsporanguia, which are the pollen sacs located within the anther.
- Each lobe of the anther contains two microsporangia, which are responsible for producing pollen grains.
- The arrangement allows for efficient pollen production and distribution during the pollination process.
Microsporangia's Role
- Microsporangia develop within the lobes, leading to the characteristic shape of the anther.
- As these structures mature, they facilitate the release of pollen grains, which are crucial for fertilization.
Other Layers' Influence
- While the tapetum layer and epidermis play essential roles in supporting the anther's function, they do not directly contribute to its bilobed appearance.
- The tapetum assists in nourishing the developing pollen grains, and the epidermis provides protection, but the lobular structure is solely due to the arrangement of microsporangia.
Conclusion
In summary, the bilobed nature of an anther is distinctly observed in a transverse section because of the presence of microsporangia. This structural feature is essential for effective pollen development and dispersal, emphasizing the microsporangiua's critical role in the anther's anatomy and function.

Understanding Physiological Barriers to Microorganisms
The human body has several mechanisms to prevent the entry of microorganisms, and the correct answer to the question is indeed "C) Tears." Here’s a detailed explanation:
Tears as a Physiological Barrier
- Role of Tears: Tears are not just for keeping the eyes moist; they play a crucial role in protecting the eyes from pathogens.
- Antimicrobial Properties: Tears contain lysozyme, an enzyme that breaks down bacterial cell walls, effectively killing bacteria.
- Flushing Effect: The act of tearing helps wash away debris and microorganisms from the surface of the eye.
- pH and Salt Content: The natural pH and saline content in tears create an inhospitable environment for many harmful microorganisms.
Why Other Options are Less Effective
- Monocytes:
- These are immune cells that respond to infections, but they act after a pathogen has entered the body. They are not a physical barrier.
- Epithelium of Urogenital Tract:
- While it does provide some level of protection, it is primarily a structural barrier rather than a physiological one. It does not actively neutralize pathogens like tears do.
- Skin:
- The skin is a significant physical barrier to microorganisms, but it does not have the same physiological properties as tears in actively combating pathogens.
Conclusion
In conclusion, while all listed options contribute to the overall defense against pathogens, tears are uniquely effective due to their direct physiological role in safeguarding the eyes from microbial invasion.