Test: Biology - 11 - NEET MCQ

Entamoeba causes dysentery, trypanosoma gambiense causes sleeping sickness and giardia is a known as Grand old man of intestine.... all these three are parasitic protozoan in option A elphidium, in option C euglena and in option D Volvox are odd one...

Protozoa and the Kingdom Protista
Protozoa are single-celled eukaryotic organisms that have traditionally been classified separately from animals. They are characterized by their ability to move independently and obtain nutrition through a variety of means, such as ingestion, absorption, or photosynthesis.
The classification of organisms into different kingdoms is based on their evolutionary relationships and shared characteristics. Protozoa have been included in the kingdom Protista, which is one of the five kingdoms of life, along with animals, plants, fungi, and bacteria.
Whittaker's Five Kingdom Classification
The classification of organisms into five kingdoms was proposed by Robert Whittaker in 1969. Whittaker's classification was based on several criteria, including cellular organization, mode of nutrition, and reproduction. He recognized that the traditional two-kingdom system of plants and animals was not sufficient to encompass the diversity of life on Earth.
Whittaker's five kingdoms are as follows:
1. Kingdom Monera: Consists of prokaryotic organisms, such as bacteria.
2. Kingdom Protista: Includes eukaryotic organisms that do not fit into the other kingdoms.
3. Kingdom Fungi: Comprises organisms that obtain nutrients through absorption.
4. Kingdom Plantae: Composed of multicellular, photosynthetic organisms.
5. Kingdom Animalia: Contains multicellular, heterotrophic organisms.
Inclusion of Protozoa in Kingdom Protista
Protozoa are included in the kingdom Protista because they possess certain characteristics that differentiate them from animals. These characteristics include:
1. Unicellularity: Protozoa are single-celled organisms, whereas animals are multicellular.
2. Lack of Tissue Differentiation: Protozoa do not possess specialized tissues or organs, unlike animals.
3. Modes of Nutrition: Protozoa exhibit a wide range of nutritional modes, including ingestion, absorption, and photosynthesis, which sets them apart from animals.
Conclusion
In summary, protozoa are separated from animals and included in the kingdom Protista by Robert Whittaker's five kingdom classification system. This classification is based on the recognition of their unicellular nature, lack of tissue differentiation, and diverse modes of nutrition. By placing protozoa in the kingdom Protista, Whittaker aimed to provide a comprehensive classification system that reflects the evolutionary relationships and characteristics of different organisms.

The less active or motionless food is ingested by Amoeba as follows:
A: Circumvallation:
- Circumvallation is the process in which the Amoeba surrounds the food particle with its body membrane.
- The food particle remains outside the Amoeba's body, trapped within a food vacuole.
- This method is used for larger or more solid food particles that cannot be engulfed directly.
B: Circumfluence:
- Circumfluence is the process in which the Amoeba creates a current of water to bring food particles towards it.
- The Amoeba extends its pseudopodia to create a flow of water around the food particles.
- The food particles are then swept towards the Amoeba's body and engulfed.
C: Import:
- Import is the process in which the Amoeba engulfs the food particle directly.
- The Amoeba forms pseudopodia around the food particle, enclosing it within its body.
- The food particle is then brought inside the Amoeba's body and enclosed in a food vacuole.
D: Invagination:
- Invagination is the process in which the Amoeba folds its cell membrane around the food particle.
- The food particle is trapped within a small pocket formed by the folding of the membrane.
- The pocket is pinched off to form a food vacuole containing the ingested food.
Answer: B - Circumfluence
- The less active or motionless food is ingested by Amoeba through circumfluence.
- Amoeba creates a current of water to bring the food particles towards it, using its pseudopodia.
- The food particles are swept towards the Amoeba's body and engulfed in this process.

Pernicious malaria is:
- Pernicious malaria is a severe and life-threatening form of malaria caused by the parasite Plasmodium falciparum.
- It is characterized by rapid onset and progression of symptoms, leading to complications and high mortality rates if left untreated.
- Pernicious malaria is more common in areas with high transmission rates of P. falciparum, such as sub-Saharan Africa.
- It can affect people of all ages, but children and pregnant women are particularly vulnerable to severe complications.
- Symptoms of pernicious malaria include high fever, chills, headache, nausea, vomiting, and muscle aches.
- Complications of pernicious malaria can include severe anemia, organ failure, cerebral malaria (infection of the brain), and respiratory distress.
- Prompt diagnosis and treatment with appropriate antimalarial medications are crucial to prevent complications and reduce mortality.
- Treatment typically involves a combination of antimalarial drugs, such as artemisinin-based combination therapy (ACT).
- Prevention strategies for pernicious malaria include the use of insecticide-treated bed nets, indoor residual spraying, and chemoprophylaxis for travelers to high-risk areas.

Amoeba cyst is Three layered
The amoeba cyst, which is the dormant stage of the amoeba, has a three-layered structure. Each layer serves a specific purpose and helps the cyst survive in unfavorable conditions.
The three layers of the amoeba cyst are:
1. Outer Layer: The outermost layer of the cyst is called the ectocyst. It is a protective covering that helps in shielding the cyst from external environmental factors such as temperature changes, chemicals, and desiccation. The ectocyst is made up of a tough proteinaceous material that provides structural support and prevents the cyst from collapsing.
2. Middle Layer: The middle layer is known as the mesocyst. It acts as a barrier and regulates the exchange of substances between the external environment and the innermost layer of the cyst. The mesocyst helps in maintaining osmotic balance and prevents the entry of harmful substances into the cyst.
3. Inner Layer: The innermost layer is called the endocyst. It surrounds the cytoplasm of the amoeba and protects it during the cyst stage. The endocyst is made up of a thin, flexible membrane that allows for the exchange of gases and nutrients. It also contains the nucleus and other essential organelles of the amoeba.
Overall, the three-layered structure of the amoeba cyst ensures its survival and enables it to withstand harsh conditions until favorable conditions for growth and reproduction are available.

Introduction:
Trypanosomiasis, also known as sleeping sickness, is a disease caused by the protozoan parasite Trypanosoma spp. It is primarily transmitted to humans and animals by the bite of infected tsetse flies.
Identification of the vector:
Among the given options, the vector responsible for transmitting Trypanosomiasis is Glossina palpalis (also known as the riverine tsetse fly).
Explanation:
Here is a detailed explanation of why Glossina palpalis is the correct answer:
1. Trypanosomiasis is mainly transmitted by tsetse flies, which are found in sub-Saharan Africa.
2. Glossina palpalis is a species of tsetse fly that is known to transmit Trypanosoma brucei gambiense, the parasite responsible for causing the chronic form of sleeping sickness in humans.
3. This species of tsetse fly is adapted to live near rivers and streams, making it commonly found in areas with suitable habitats.
4. Glossina palpalis feeds on the blood of humans and animals, and during its blood meal, it can transmit the Trypanosoma parasite from an infected host to a susceptible host.
5. The transmission of Trypanosoma spp. occurs through the saliva of the tsetse fly, which contains the infective form of the parasite.
Conclusion:
In conclusion, Trypanosomiasis, or sleeping sickness, is primarily transmitted by the Glossina palpalis tsetse fly. It is important to control and prevent the spread of this disease by implementing vector control measures and raising awareness about the risks associated with tsetse fly bites.

Metakelfin is used in the treatment of Malaria.
Explanation:
- Malaria is a parasitic infection caused by Plasmodium parasites transmitted by the bite of infected female Anopheles mosquitoes.
- Metakelfin, also known as Metakelfin hydrochloride, is a medication used in the treatment of malaria.
- It belongs to the class of antimalarial drugs called 4-aminoquinolines.
- Metakelfin works by interfering with the growth and reproduction of the parasites in the red blood cells, thereby helping to eliminate the infection.
- It is effective against various species of Plasmodium, including Plasmodium falciparum, which is the most deadly species responsible for severe malaria.
- Metakelfin is usually used in combination with other antimalarial drugs to prevent the development of drug resistance.
- The dosage and duration of treatment with Metakelfin depend on the severity of the infection, the type of malaria parasite, and the individual's age and weight.
- Side effects of Metakelfin may include gastrointestinal disturbances, skin reactions, and neurological symptoms in rare cases.
- It is important to take Metakelfin as prescribed by a healthcare professional and complete the full course of treatment to ensure the eradication of the malaria infection.

Spongilla belongs to class Demospongiae.
Detailed explanation:
Spongilla is a genus of freshwater sponges that belong to the phylum Porifera. The phylum Porifera is divided into three main classes: Hyalospongia, Demospongiae, and Hexctinellida.
Here's a detailed explanation of each class:
Hyalospongia:
- This class consists of glass sponges, which are characterized by their silica spicules.
- Glass sponges have a unique skeletal structure made up of intricate glass-like spicules.
Hexctinellida:
- This class consists of the deep-sea or glass sponges.
- Hexctinellida sponges have a skeleton made up of silica spicules, similar to Hyalospongia.
- They are known for their delicate and intricate structure.
Calearea:
- This class consists of calcareous sponges, which have a skeleton made up of calcium carbonate.
- Calcareous sponges are usually found in marine environments.
Demospongiae:
- This is the largest class of sponges, comprising over 90% of all sponge species.
- Demospongiae sponges have a skeleton made up of spongin fibers or silica spicules.
- They are found in a wide range of habitats, including freshwater and marine environments.
Based on the information provided, Spongilla belongs to the class Demospongiae.

Explanation:
The prosopyle is a structure in the canal system of sponges that allows water to flow between the incurrent (incoming) canal and the radial canal. Here is a detailed explanation of why the correct answer is option D:
1. Canal System in Sponges:
- Sponges have a unique water transport system called the canal system.
- The canal system consists of various channels and chambers through which water flows, allowing the sponge to filter nutrients and oxygen from the water.
2. Radial Canal:
- The radial canal is a larger channel that runs through the body of the sponge.
- It is responsible for distributing water throughout the sponge's body.
3. Incurrent Canal:
- The incurrent canal is the channel that brings water into the sponge.
- It is usually located on the periphery of the sponge's body.
4. Prosopyle:
- The prosopyle is a small opening or pore present in the canal system of sponges.
- It acts as a valve or gate that regulates the flow of water between different parts of the canal system.
5. Function of Prosopyle:
- The prosopyle permits water to flow from the incurrent canal to the radial canal.
- It allows water, along with suspended food particles and oxygen, to enter the radial canal for distribution throughout the sponge's body.
6. Answer Option D:
- Option D states that the prosopyle permits water to flow from the incurrent canal to the radial canal, which is the correct answer.
- This means that when water enters the sponge through the incurrent canal, it can pass through the prosopyle and reach the radial canal for further distribution.
In conclusion, the prosopyle in the canal system of sponges is responsible for allowing water to flow from the incurrent canal to the radial canal, and this is why the correct answer is option D.

Explanation:
The statement claims that sponges represent the dead end branch of the evolutionary tree. To understand why this is the case, we need to examine the characteristics unique to sponges.
Cellular level of organisation:
- Sponges are the only animals that exhibit a cellular level of organization.
- This means that their bodies are composed of individual cells that work together to perform various functions.
- Other animals have tissues, organs, and organ systems, which allows for a higher level of complexity and specialization.
Canal system:
- Sponges have a unique canal system that allows water to flow through their bodies.
- This system helps the sponge filter out small organisms and nutrients from the water.
- Other animals have a more advanced circulatory or respiratory system.
Choanocytes:
- Choanocytes are specialized cells found in sponges.
- They have a collar-like structure that helps them capture food particles from the water.
- Choanocytes are not found in any other animal group.
Sedentary:
- Sponges are typically sessile or sedentary organisms.
- They attach themselves to a substrate and do not move around like other animals.
- This lack of mobility limits their ability to adapt to changing environments or exploit new resources.
Based on these characteristics, it can be concluded that sponges represent a dead end branch in the evolutionary tree. They exhibit a lower level of complexity and specialization compared to other animal groups and have unique features that are not found in any other organisms.

Neuron of Hydra in relation to nerve impulse conduction:
The correct answer is B: Multidirectional.
Explanation:
The neuron of Hydra, a small aquatic animal, exhibits a unique characteristic in relation to nerve impulse conduction. Here is a detailed explanation of why the correct answer is B:
1. Unidirectional conduction:
- Unidirectional conduction refers to the transmission of nerve impulses in a single direction along the length of a neuron.
- In some organisms, such as mammals, nerve impulses travel in one direction only, from the dendrites to the axon terminals.
- However, in the case of Hydra, the nerve impulse conduction is not strictly unidirectional.
2. Multidirectional conduction:
- Hydra is a simple organism with a nerve net rather than a centralized nervous system.
- The nerve net consists of interconnected neurons that allow for multidirectional conduction of nerve impulses.
- Nerve impulses can travel in various directions within the nerve net, facilitating communication between different parts of the organism.
- This multidirectional conduction is essential for coordinating the activities of different regions of the Hydra's body.
3. Polarization:
- Polarization refers to the difference in electrical charge across the cell membrane of a neuron.
- While Hydra neurons do exhibit polarization, it is not a defining characteristic in relation to nerve impulse conduction.
- Polarization plays a role in the generation and propagation of nerve impulses but does not determine the direction of conduction.
4. Non-polarized conduction:
- Non-polarized conduction does not accurately describe the nerve impulse conduction in Hydra.
- All neurons, including those of Hydra, have a resting membrane potential and exhibit polarization.
- Non-polarized conduction implies a lack of electrical difference across the cell membrane, which is not the case in any functional neuron.
In conclusion, the neuron of Hydra exhibits multidirectional conduction of nerve impulses within its nerve net, making the correct answer B: Multidirectional.

Ingression involves in the formation of Stereogastrula.
Explanation:
Ingression is a process that occurs during embryonic development in certain organisms, particularly in the animal kingdom. It involves the movement of cells from the surface layer of the embryo into the interior, resulting in the formation of new tissue layers. Ingression plays a crucial role in the formation of various structures and organs during development.
During ingression, cells undergo morphological changes and detach from the surface layer of the embryo. These cells then migrate towards the interior, where they contribute to the formation of different tissue layers. One of the outcomes of ingression is the formation of a structure called the gastrula.
The gastrula is a stage in embryonic development characterized by the presence of three distinct germ layers - ectoderm, mesoderm, and endoderm. These germ layers give rise to different tissues and organs in the developing organism. The formation of the gastrula is a result of the ingression process.
Among the options given, the formation of Stereogastrula involves ingression. Stereogastrula is a stage in embryonic development characterized by the presence of both ectoderm and endoderm layers, but lacking the mesoderm layer. This stage is found in certain organisms, such as sea urchins.
Therefore, the correct answer is B: Stereogastrula.

Pennatula is a
- Answer: C. Actinozoan
Detailed explanation:
- Pennatula is a type of marine organism commonly known as a sea pen.
- Sea pens belong to the phylum Cnidaria, which includes animals such as jellyfish, corals, and sea anemones.
- Within the phylum Cnidaria, sea pens specifically belong to the class Anthozoa.
- Anthozoa is further divided into two subclasses: Hexacorallia and Octocorallia.
- Pennatula belongs to the subclass Octocorallia, along with other organisms such as soft corals and gorgonians.
- Octocorallia are characterized by their eight-branched tentacles and a central axis made of a flexible protein called gorgonin.
- Pennatula and other sea pens are sessile organisms, meaning they are attached to the ocean floor and do not move around freely.
- They are filter feeders, using their tentacles to capture small organisms and particles from the water.
- Pennatula is commonly found in deep-sea environments, where they form colonies and play important ecological roles in the marine ecosystem.
Key points:
- Pennatula is a type of sea pen.
- Sea pens belong to the phylum Cnidaria.
- Pennatula belongs to the class Anthozoa.
- Anthozoa is further divided into subclasses Hexacorallia and Octocorallia.
- Pennatula belongs to the subclass Octocorallia.
- Octocorallia are characterized by eight-branched tentacles and a central axis made of gorgonin.
- Pennatula is a sessile filter feeder found in deep-sea environments.

Protein and phenol and it's use in Portuguese war because hypnotoxin is affected central nervous system.

The member of platyhelminthes is:
A: Loa loa
- Loa loa is not a member of platyhelminthes. It is a parasitic nematode that causes loiasis in humans.
B: Wuchereria
- Wuchereria is also not a member of platyhelminthes. It is a parasitic filarial worm that causes lymphatic filariasis in humans.
C: Taenia
- Taenia is a member of platyhelminthes. It is a genus of parasitic tapeworms that infect the intestines of vertebrates, including humans. There are several species of Taenia, such as Taenia solium (pork tapeworm) and Taenia saginata (beef tapeworm), which can cause diseases in humans.
D: all of these
- The correct answer is D: all of these. Taenia is a member of platyhelminthes, and both Loa loa and Wuchereria are not members of this phylum.

Explanation:
Liverfluke:
Liverfluke is a parasitic flatworm that infects the liver and bile ducts of various mammals, including humans. It has a complex life cycle with multiple larval stages.
Larval stages:
1. Redia: Redia is the larval stage of liverfluke that develops from the miracidium. It is a sac-like structure with a mouth and digestive system. Redia reproduce asexually to produce more rediae or develop into cercariae.
2. Cercaria: Cercaria is the next larval stage of liverfluke that develops from redia. It is a free-swimming larva with a tail and is released from the snail intermediate host into water. Cercariae can infect the final host directly or encyst as metacercariae on vegetation.
3. Miracidium: Miracidium is the first larval stage of liverfluke. It hatches from the eggs shed in the host's feces and infects a specific species of snail intermediate host. Inside the snail, miracidium develops into sporocysts, which further produce rediae.
4. Dipinnaria: Dipinnaria is not a larval stage of liverfluke. It is a larval stage of some species of starfish and sea urchins.
Therefore, the correct answer is C: dipinnaria.

Explanation:
Metamerism refers to the division of the body into segments or repeated units. In addition to annelida (segmented worms) and arthropoda (arthropods), metamerism is also exhibited by cestoda (tapeworms).
Reasoning:
- Trematodes, also known as flukes, do not exhibit metamerism. They have a non-segmented body plan.
- Acanthocephala, commonly known as thorny-headed worms, also lack metamerism. They have a cylindrical body without distinct segments.
Conclusion:
Therefore, the correct answer is option B: cestoda.

The study of worms causing parasitic infestation in humans is helminthology.
Helminthology is the branch of biology that specifically deals with the study of worms, also known as helminths, that can cause parasitic infestations in humans. Here is a detailed explanation:
What are helminths?
- Helminths are a type of parasitic worms that can infect humans and cause various diseases and health problems.
- They include different types of worms such as roundworms, tapeworms, flukes, and hookworms.
What is helminthology?
- Helminthology is a specialized field of study within the broader discipline of parasitology that focuses specifically on the study of helminths.
- It involves the identification, classification, lifecycle, morphology, behavior, and pathology of helminths.
Why is helminthology important?
- Helminth infections are prevalent in many parts of the world, particularly in areas with poor sanitation and limited access to clean water.
- These infections can lead to significant health problems, including malnutrition, anemia, impaired cognitive development, organ damage, and even death.
- Understanding the biology and characteristics of helminths is crucial for developing effective prevention strategies, diagnostic methods, and treatment options.
Methods and techniques used in helminthology:
- Helminthology involves various laboratory techniques and methods to study helminths, including:
- Microscopic examination of helminth specimens to identify and classify different species.
- Molecular techniques such as DNA sequencing to determine genetic relationships among different helminth species.
- Experimental studies to investigate the lifecycle, behavior, and host-parasite interactions of helminths.
- Epidemiological studies to assess the prevalence, distribution, and risk factors associated with helminth infections.
In conclusion, helminthology is the field of study that focuses on the worms causing parasitic infestations in humans. It plays a vital role in understanding and combating helminth infections to improve human health.

Answer:
The cross section at the midpoint of the middle piece of a human sperm will show the following structures:
1. Centriole: This is a cylindrical structure found at the base of the middle piece of the sperm. It plays a crucial role in cell division and the formation of the sperm tail.
2. Mitochondria: These are the powerhouses of the cell and are responsible for producing energy in the form of ATP. In the middle piece of the sperm, mitochondria are present in abundance to provide the necessary energy for the sperm's motility.
3. Arrangement of microtubules: The middle piece of the sperm contains a 9+2 arrangement of microtubules. This refers to nine outer microtubule doublets surrounding a central pair of microtubules. This arrangement provides structural support and allows for the sliding of microtubules, which generates the whip-like movement of the sperm tail.
In summary, a cross section at the midpoint of the middle piece of a human sperm will show the presence of centriole, mitochondria, and a 9+2 arrangement of microtubules. Therefore, the correct answer is C: Mitochondria and 9 2 arrangement of microtubules.

The correct answer is D: Oviduct.
Explanation:
The Wolffian duct is a structure that forms the male reproductive system during embryonic development. It gives rise to several structures including the epididymis, vas deferens, and ejaculatory duct. However, it does not contribute to the formation of the oviduct, which is part of the female reproductive system.
Details:
Here are some key points to consider:
- The Wolffian duct is present in both males and females during early development.
- In males, the Wolffian duct develops into the epididymis, vas deferens, and ejaculatory duct.
- The epididymis is a coiled tube located on the surface of the testis, where sperm mature and are stored.
- The vas deferens is a muscular tube that transports sperm from the epididymis to the urethra during ejaculation.
- The ejaculatory duct is formed by the union of the vas deferens and the duct from the seminal vesicle. It passes through the prostate gland and empties into the urethra.
- In females, the Wolffian duct regresses and does not contribute to the formation of the oviduct.
- The oviduct, also known as the fallopian tube, is a tube that connects the ovary to the uterus. It is responsible for the transport of eggs and is the site of fertilization.
In summary, the oviduct is not formed by the Wolffian duct, while the epididymis, vas deferens, and ejaculatory duct are all derived from the Wolffian duct.

Acrosome of sperm contains:
- Hyaluronidase: This enzyme helps in breaking down the hyaluronic acid present in the outer layer of the egg, allowing the sperm to penetrate and fertilize it.
- Acrosin: This protease enzyme is involved in the breakdown of proteins in the zona pellucida, which is the protective layer surrounding the egg.
- Other enzymes: The acrosome also contains other enzymes such as neuraminidase and proacrosin, which aid in the fertilization process.
Correct Answer: A: Hyaluronidase and acrosin.

Explanation:
Gametes are specialized reproductive cells that are involved in sexual reproduction. They are responsible for transmitting genetic information from one generation to the next. In animals, gametes are formed through a process called gametogenesis, which occurs in the gonads (testes in males and ovaries in females).
Gamete Formation in Animals:
Gametes in animals are formed from epithelial tissue, specifically from cells known as germ cells. Germ cells are a type of stem cell that gives rise to gametes. Here is a detailed explanation of the process:
1. Germ Cell Migration: During early development, germ cells migrate from their place of origin to the developing gonads.
2. Meiosis: Once the germ cells reach the gonads, they undergo a specialized type of cell division called meiosis. Meiosis consists of two rounds of division, resulting in the formation of haploid gametes with half the number of chromosomes as the parent cell.
3. Spermatogenesis (in males): In males, the germ cells undergo spermatogenesis in the testes. This process involves several stages, including the production of spermatogonia (immature sperm) and their maturation into spermatozoa (mature sperm).
4. Oogenesis (in females): In females, the germ cells undergo oogenesis in the ovaries. This process also involves several stages, including the production of oogonia (immature eggs) and their maturation into ova (mature eggs).
5. Fertilization: Once the gametes are formed, they can be released from the gonads and are capable of fertilization. Fertilization occurs when a sperm cell combines with an egg cell, resulting in the formation of a zygote.
Therefore, the correct answer is D: Epithelial tissue. Gametes are formed from germ cells within the epithelial tissue of the gonads in animals.

Spermogenesis/spermateleosis is the formation of spermatzoa from:
Explanation:
Spermogenesis, also known as spermateleosis, is the process of spermatid maturation into spermatozoa. It occurs in the seminiferous tubules of the testes and involves several stages of development.
The correct answer is C: Spermatids. Spermatids are the immature male germ cells that undergo further changes to become mature spermatozoa.
Here is a detailed explanation of the different stages of spermogenesis:
1. Primary spermatocyte: This is the initial stage of spermogenesis. Primary spermatocytes are diploid cells that undergo meiosis I to produce two secondary spermatocytes.
2. Secondary spermatocyte: Secondary spermatocytes are haploid cells that result from meiosis I. They undergo meiosis II to produce four haploid spermatids.
3. Spermatids: Spermatids are haploid cells that are the immediate precursors to spermatozoa. They undergo a series of morphological changes, including the development of a head, tail, and flagellum, to become mature spermatozoa.
4. Geminal cells of testes: While geminal cells (also known as germ cells) are involved in the process of spermatogenesis, they are not directly responsible for the formation of spermatozoa. Geminal cells refer to the cells that give rise to spermatozoa, including spermatogonia, primary spermatocytes, and secondary spermatocytes.
In conclusion, spermogenesis/spermateleosis is the process of spermatid maturation into spermatozoa, with spermatids being the specific stage where this transformation occurs.

The head of mature mammalian sperm is made of:
- An acrosome: The acrosome is a cap-like structure located at the anterior end of the sperm head. It contains enzymes that are essential for the sperm to penetrate and fertilize the egg.
- Elongated nucleus covered by acrosome: The nucleus of the sperm is elongated and contains the genetic material. It is covered by the acrosome, which helps protect and prepare the genetic material for fertilization.
- Two centrioles and an axial filament: The sperm head contains two centrioles, which are involved in the formation of the microtubules that make up the sperm's tail. The axial filament, also known as the flagellum, is responsible for the sperm's motility and helps it move towards the egg.
- Nucleus, acrosome, cytoplasm, and mitochondrial sheath: The mature mammalian sperm head also contains the nucleus, which contains the genetic material, the acrosome, which helps with fertilization, the cytoplasm, which provides energy for the sperm's movement, and the mitochondrial sheath, which produces this energy.
Therefore, the correct answer is B: Elongated nucleus covered by acrosome.

Sugar fructose is present in the secretion of Seminal vesicles.
The seminal vesicles are a pair of glands located behind the bladder and connected to the ejaculatory ducts. They play a crucial role in the production of semen, which is a fluid that helps nourish and transport sperm.
Fructose is a type of sugar that provides energy for sperm cells. It is secreted by the seminal vesicles and forms a significant component of semen.
Here are some key points to remember:
- Seminal vesicles: These glands are responsible for producing a significant portion of semen and contribute to its overall composition.
- Fructose: The sugar fructose is present in the secretion of seminal vesicles.
- Energy for sperm: Fructose provides energy for sperm cells, allowing them to swim and fertilize an egg.
- Semen composition: In addition to fructose, semen also contains other substances such as proteins, enzymes, vitamins, and minerals that are essential for sperm function and survival.
In conclusion, sugar fructose is present in the secretion of seminal vesicles, which is an important component of semen.

In testis, the immature male germ cells (spermatogonia) produce sperms by spermatogenesis, that begins at puberty. The spermatogonia (sing. spermatogonium) present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers. Each spermatogonium is diploid and contains 46 chromosomes (in question this number is given as 40). Some of the spermatogonia called primary spermatocytes periodically undergo meiosis. A primary spermatocyte completes the first meiotic division (reduction division) leading to formation of two equal, haploid cells called secondary spermatocytes, which have only 23 chromosomes each (in question this number is given as 20). The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids (chromosome number 20). The spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis. After spermiogenesis, sperm heads become embedded in the sertoli cells, and are finally released from the seminiferous tubules by the process called spermiation.

Cryptorchidism is a condition of testes:
Explanation:
Cryptorchidism refers to the condition in which one or both testes fail to descend into the scrotal sacs. This condition is quite common in newborns and infants, but it typically resolves on its own within the first few months of life. However, if the testes do not descend by the age of 6 months, medical intervention may be required.
The detailed solution is as follows:
1. Definition:
- Cryptorchidism is a condition in which the testes, which are normally located in the scrotal sacs, fail to descend properly.
2. Symptoms:
- The absence of testes in the scrotal sacs is the primary symptom of cryptorchidism.
- Other symptoms may include an empty scrotal sac, smaller size of the scrotum, or a palpable lump in the groin area.
3. Causes:
- Cryptorchidism can have various causes, including hormonal imbalances, genetic factors, and anatomical abnormalities.
- Premature birth is also known to increase the risk of cryptorchidism.
4. Diagnosis:
- Cryptorchidism is usually diagnosed through physical examination.
- An ultrasound may be performed to locate the undescended testes.
5. Complications:
- If left untreated, cryptorchidism can lead to several complications, including infertility, testicular cancer, and an increased risk of testicular torsion.
6. Treatment:
- Treatment for cryptorchidism depends on the age of the patient and the severity of the condition.
- Hormone therapy may be prescribed to stimulate testicular descent.
- Surgical intervention, called orchidopexy, may be necessary if the testes do not descend on their own.
7. Prognosis:
- With early intervention, the prognosis for individuals with cryptorchidism is generally good.
- Successful treatment can help prevent complications and restore normal testicular function.

Testosterone production
Testosterone is a hormone that plays a crucial role in the development and maintenance of male reproductive tissues. It is primarily produced in the testes in males and in smaller amounts in the ovaries and adrenal glands in females. Specifically, testosterone is produced by Leydig cells in the testes.
Leydig cells
Leydig cells, also known as interstitial cells, are located in the testes and are responsible for the production of testosterone. These cells are found in the connective tissue surrounding the seminiferous tubules, which are the structures where sperm production occurs. Leydig cells are stimulated by luteinizing hormone (LH) from the pituitary gland to produce testosterone.
Function of testosterone
Testosterone has various important functions in the body, including:
1. Development of male sex organs: Testosterone is responsible for the development of the male reproductive organs, such as the penis and testes, during fetal development.
2. Secondary sexual characteristics: Testosterone promotes the development of secondary sexual characteristics in males, such as facial and body hair, deepening of the voice, and increased muscle mass.
3. Sperm production: Testosterone is essential for the production of sperm in the testes.
4. Libido and sexual function: Testosterone plays a role in maintaining a healthy sex drive and sexual function in males.
5. Bone and muscle health: Testosterone helps maintain bone density and muscle strength.
6. Mood and cognition: Testosterone has an impact on mood, cognitive function, and overall well-being.
In conclusion, testosterone is primarily produced by Leydig cells in the testes. These cells are stimulated by luteinizing hormone to produce testosterone, which plays a crucial role in various aspects of male reproductive health and development.

Adaptation of eye in dark occurs due to:
There are two types of photoreceptor cells in the retina of the eye - rods and cones. Rods are responsible for vision in dim light, while cones are responsible for color vision and visual acuity in bright light. The adaptation of the eye in the dark refers to the ability of the eye to adjust and function optimally in low-light conditions. This adaptation occurs due to the following reasons:
1. Repletion of visual pigment in rods:
- Rod cells contain a visual pigment called rhodopsin, which is responsible for detecting light in low-light conditions.
- In the dark, the concentration of rhodopsin increases in the rod cells, making them more sensitive to light.
- This repletion of visual pigment allows the rods to capture even small amounts of light and enhance our ability to see in the dark.
2. Depletion of visual pigment in cones:
- Cones contain a different visual pigment called photopsin, which is responsible for color vision and visual acuity in bright light.
- In the dark, the concentration of photopsin decreases in the cone cells, making them less sensitive to light.
- This depletion of visual pigment in cones reduces their ability to function effectively in low-light conditions, which is why we rely more on our rod cells for vision in the dark.
Therefore, the correct answer is D: Repletion of visual pigment in rods.

The helicotrema is the part of the cochlear labyrinth where the scala tympani and the scala vestibuli meet. It is the main component of the cochlear apex. The hair cells near this area best detect low frequency sounds.