Past Entrance Papers

Hint

(b) Tight junction helps to stop the leakage of the substances across a tissue and Gap junction are channels that physically connect neighbouring cells, mediating the rapid exchange of small molecules or ions.

Adheringjunction They are cell-cell junction complexes that make an important contribution to embryogenesis and tissue homeostasis.

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(c) is incorrect and can be corrected as Intercalated discs are not found in smooth muscles these are found in cardiac muscles.
Smooth muscle cells are spindle-shaped, have a single nucleus, and do not show striations. These involuntary muscles are found on the walls of internal organs such as blood vessels.

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(b) Cuboidal epithelium with brush border of microvilli is found in the proximal convoluted tubule of nephron (PCT).

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(a) Goblet cells of the alimentary canal are modified from columnar epithelial cells, which secrete mucus.
These cells are found in the lining of organs like the intestine and respiratory tract.

These secretes mucin (glycoprotein) and maintains the layer of mucus. As each cell secretes mucin for mucous production it is called a unicellular mucous gland.

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(d) Tight junctions provide a barrier that prevents leakage of fluid across epithelial cells. Adherens junctions aid to cement adjacent cells to form a sheet.

Gap junctions provide cytoplasmic channels to facilitate communication between adjacent cells.

Synaptic junctions help in the transmission of information through chemicals.

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(c) In humans, ciliated epithelial cells are present in the bronchioles and Fallopian tube. In bronchioles, these cells help in the movement of mucus, and in the Fallopian tube, these are required to move the egg towards the uterus.
On the other hand, salivary and pancreatic ducts are lined by simple cuboidal epithelium. The bile duct is lined by simple columnar epithelium and the Eustachian tube is lined by columnar epithelium having ciliated cells.

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(c) The correct route for transport of sperms in male frog is

Testes \(\rightarrow\) Vasa efferentia \(\rightarrow\) Kidney \(\rightarrow\) Bidder’s canal \(\rightarrow\) Urinogenital duct \(\rightarrow\) Cloaca.

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(c) Frog’s heart is myogenic, i.e., the heartbeat originates from the muscles of the heart. Hence, it is autorythmic. The wave of contraction originates from the sinus venosus and spreads to the wall of the sinus venosus and both auricles. This compels the heart to beat. Due to this reason, the frog’s heart will continue to beat as long as it gets supply of ATP.

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(a) Smooth muscle fibres are elongated and spindle-shaped (fusiform). Each fibre contains a single oval nucleus surrounded by cytoplasm (sarcoplasm). In cytoplasm, myofibrils are arranged longitudinally. These fibres lack striations and sarcolemma, however, are enclosed by the plasma membrane.

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(a)

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(d) Most cells in animal tissues (with the exception of a few terminally differentiated cells such as skeletal muscle cells and blood cells) are in communication with their adjoining cells via gap junctions. At the place where the gap junction is present, membranes of two adjacent cells are separated by a uniform narrow gap of about \(2-4 \mathrm{~nm}\). The gap is spanned by channel-forming proteins called connexins, which allow inorganic ions and other small water-soluble molecules to pass directly from the cytoplasm of one cell to the cytoplasm of other cells.

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(a) Arthrodial membrane is a tough, flexible cuticle that joins the skeletal elements of cockroach and other arthropods. It connects the terga, pleura, and sterna of cockroach body.

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(c) Areolar tissue is the most widely distributed loose connective tissue in the body. Tendon is a type of dense connective tissue, adipose tissue is a fat-storing loose connective tissue and cartilage is a specialised connective tissue.

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(c) The proximal convoluted tubule, which is the longest part of the renal tubule has simple tall cuboidal epithelium, with a brush border (microvilli). The epithelial cells in the distal convoluted tubule are cuboidal, with very few microvilli. The inner lining of salivary ducts has stratified columnar epithelia. A stratified squamous non-keratinized epithelium lines the oral surface. Bronchioles are lined by simple cuboidal epithelium.

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(d) Locomotion (performed by limbs) in humans depends on the movements of muscle fibres. Skeletal muscles are attached to the bones by tendons and help in the movement of the parts of the skeleton. These muscles are under the control of the conscious mind and are called voluntary muscles. Under the microscope, these muscles show transverse stripes and hence are designated as striated muscles.

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(b) Human erythrocytes are enucleated, and discoidal while in frogs erythrocytes are large, oval, and biconvex nucleated cells. Erythrocytes are the carriers of haemoglobin.

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(a) A macrophage is a type of white blood cell derived from monocytes and is responsible for detecting, engulfing, and destroying pathogens and apoptotic cells. They do this by the process called phagocytosis. Fibroblasts are large, flat cells with many branching processes. They secrete collagen fibers. Collagen fibers are unbranched, wavy, and arranged in bundles. They contain a proteinous substance called collagen. Mast cells contain heparin and histamine granules in their cytoplasm. Heparin prevents the clotting of blood and histamine carry out vasodilation.

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(d) Cartilage is a semi-rigid supportive or skeletal connective tissue in which the matrix is solid and made of mucoprotein or proteoglycan called chondrin. It is of four types -hyaline, fibrous, calcified, and elastic. Yellow elastic fibrocartilage is found in the pinna and external auditory canal of the ear, Eustachian tubes, epiglottis, and tip of the nose. Its matrix contains numerous yellow fibres which form a network by uniting with one another. Due to the presence of yellow fibres, the cartilage becomes more flexible. Hence, it provides flexibility to these organs.

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(a) Intestine is lined by glandular epithelium which is secretory in function. The glands found in the intestine are exocrine and may be unicellular or multicellular. When unicellular glands secrete mucus, they are called mucus cells or goblet cells and are common in the columnar epithelium of intestine. When unicellular glands secrete a clear watery fluid, they are called serous cells which are also present in intestinal glands. On the other hand, multicellular glands consist of a duct and secretory portion, both formed of epithelial cells. They are further of two types: tubular and saccular. In tubular glands, the secretory portion is tube-like for example, Crypts of Lieberkuhn (a type of simple straight tubular glands found in the intestine) and Brunner’s gland (a type of simple branched tubular glands found in the intestine).

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(c) Human erythrocytes are enucleated, and discoidal while in frogs erythrocytes are large, oval, and biconvex nucleated cells. Erythrocytes are the carriers of haemoglobin.

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(b) Simple squamous epithelium is composed of large flat cells whose edges fit closely together like the tiles on a floor, hence it is also called pavement epithelium. The nuclei of the cells are flattened and often lie at the centre of the cells and cause bulgings of cells surface. The epithelium lines the blood vessels, lymph vessels, heart, terminal bronchioles, alveoli of the lungs, walls of the Bowman’s capsules, and descending limbs of the loop of Henle. In the blood vessels and heart, it is called the endothelium.

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(b) Cartilage is avascular, as the blood vessels innervate only perichondrium through which nutrition diffuses into cartilage cells. The cornea is also avascular.

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(c) Smooth muscles are called as involuntary muscles as the action of these muscles is controlled by the autonomic nervous system i.e. not under the control of the animal’s will. Iris of the eyes consists of smooth involuntary muscles. The abdominal wall also has smooth muscles. The biceps of the upper arm is made of skeletal muscles while the heart wall consists of cardiac muscles.

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(b) The inner surface of bronchioles and Fallopian tubes possess ciliated epithelium. In the respiratory tract, cilia help to push mucus towards the pharynx. In the Fallopian tube, the cilia help to move an egg towards the uterus.

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(b) Epithelial tissues consist of variously shaped cells closely arranged in one or more layers. The cells are held together by intercellular junctions like tight, adhering, and gap junctions.

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(c) Yellow elastic fibrocartilage, a type of skeletal tissue, is found in the pinna, Eustachian tubes, epiglottis, and tip of the nose. It is a type of cartilage and due to the presence of yellow fibres, it becomes more flexible.

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(d) Neuron (nerve cell) is one of the basic functional units of the nervous system. The neuron is a cell specialized to transmit electrical nerve impulse and so carry information from one part of the body to another. Each neuron has an enlarged portion, the cell body (perikaryon), containing the nucleus; from the body extend several processes (dendrites) through which impulses enter from their branches. A longer process, the nerve fibre, extends outward and carries impulses away from the cell body. This is normally unbranched except at the nerve ending. The point of contact of one neuron with another is known as a synapse.

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(d) From the given four options cell junctions come across most frequently in the preparation of ciliated epithelium. A cell junction is a structure within a tissue of a multicellular organism. Cell junctions are especially abundant in epithelial tissues. They consist of protein complexes and provide contact between neighbouring cells, between a cell and the extracellular matrix, or they built up the paracellular barrier of epithelia and control the paracellular transport. Ciliated epithelium is a region of epithelium consisting of columnar or cuboidal cells bearing hairlike appendages that are capable of beating rapidly. Ciliated epithelium performs the function of moving particles or fluid over the epithelial surface

in such structures as the trachea, bronchial tubes, and nasal cavities. It often occurs in the vicinity of mucus-secreting goblet cells.

The other three (thrombocytes, tendon, and hyaline cartilage) belong to connective tissue. Connective tissue is widely distributed and has many functions including support, packing, defense, and repair. Thrombocytes or platelets aid the formation of blood clots by releasing various protein substances. Tendon attaches a muscle to a bone and hyaline cartilage consists largely of glycosaminoglycan, giving a shiny glass-like appearance and gives flexibility and support at the joints.

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(c) Areolar tissue is a loose connective tissue comprised of a semifluid ground substance containing several kinds of loosely arranged fibres. Its function is to attach the skin to the underlying tissues, to fill the spaces between various organs and thus hold them in place, and surround and supports the blood vessels. Tendons connect muscles with bone while ligaments connect bone with bone.

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(d) Mast cells are granulated wandering cells that are found in connective tissue. Their granules contain histamine which is a vasodilator. It causes running nose, sneezing, and itching; and narrows the airways in the lungs. Haemoglobin and myoglobin are the pigments present in the blood and muscles respectively.

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(b) Neurons are least likely to be replaced by new cells as they have the least regeneration power. Osteocytes are bone-forming cells. Liver cells and the Malpighian layer of the skin have regeneration power.

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(b) Mast cells are the large cells with densely granular cytoplasm that is found in connective tissues. Their granules contain histamine which is a vasodilator, heparin which is an anticoagulant, and serotonin which acts as a mediator of inflammation and allergic reactions. Vasopressin is a hormone secreted by the posterior pituitary gland. Calcitonin is a hormone secreted by the thyroid gland. Melanin is a pigment produced by specialized epidermal cells called melanocytes. Relaxin is a hormone produced by the corpus luteum and placenta during the terminal stages of pregnancy.

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(b) In areolar tissue, there is more intercellular space, so the largest quantity of extracellular material is present in this tissue. It contains all cell types and fibres of connective tissue. There is a thin layer of extracellular fluid in stratified epithelium whereas striated muscle is attached with tendons and there is very less amount of extracellular fluid in the myelinated nerve fibre.

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(a) Collagen is an insoluble fibrous protein found extensively in the connective tissue of skin, tendons, and bone. Collagen accounts for over \(30 \%\) of the total body protein of mammals. Globular proteins have compact rounded molecules and are usually water-soluble. Lipid is a diverse group of organic compounds, that are insoluble in water but soluble in organic solvents. Carbohydrates are compounds of carbon, hydrogen, and oxygen.

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(a) Melanin is produced by specialized epidermal cells called melanophores (or melanocytes). Their dispersion in these cells is controlled by melanocyte-stimulating hormone and melatonin. Melanin, a pigment present in the skin, protects it from the harmful effects of UV rays. People living in the tropics have more melanin in their skin which is an adaptation to protect themselves from harmful UV rays. Melanin cannot protect from infrared rays and X-rays.

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(c) Nerve cells are the highly excitable cells, specialized for impulse conduction. They originate from the neural plate of embryonic ectoderm and serve as structural and functional units of nervous tissue.

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(a) Proteoglycans consist of polysaccharide attached with a protein chondroitin. It is present in cartilage as well as in extracellular material. Ossein is a protein present in the matrix of bone. Casein is a milk protein.

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(b) Simple epithelium consists of a single layer of cells resting on a basement membrane. This makes a definite layer.

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(a) Sweat is secreted by sweat glands of the skin and helps in regulating body temperature. Saliva is secreted by salivary glands and helps in digestion (carbohydrate digestion). Sebum is the waxy secretion secreted by sebaceous glands. Sebum is a fatty mildly antiseptic material that protects, lubricates, and waterproofs the skin and hair and helps prevent desiccation. The humerus is the long bone of the upper arm. It articulates with the scapula at the glenoid cavity and with the ulna and radius at the elbow.

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(c) Ligament occurs in the form of cords in a modified yellow elastic fibrous tissue and connects bone with a bone. Modified white fibrous tissue is present in the tendons.

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(b) White fibrous tissue has two forms: cords and sheets. The white fibres run parallel to form cords, called tendons. Tendon attaches a muscle to a bone. It consists of collagen fibres and are therefore inelastic. They ensure that the force exerted by muscular contraction is transmitted to the relevant part of the body to be moved. Yellow elastic tissue also has two forms: cords and sheets. Here, cords are called ligaments. Adipose tissue is a fat-storing loose connective tissue. Areolar tissue is the most widely distributed connective tissue in the body.

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(b) Mast cells are found in the matrix of areolar connective tissue and secrete histamine (vasodilator), serotonin (vasoconstrictor), and heparin (anticoagulant). These take part in allergic reactions and also help in body defense. Fibroblasts and histiocytes are also found in the matrix of areolar tissue. Fibroblasts secrete ground substance while histiocytes engulf the microbes, foreign particles, and damaged cells. Lymphocytes are the type of leucocytes present in blood and secrete antibodies.

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(c) Chondrin is a protein present in the matrix of cartilage. It forms a constituent of a compound called chondrin sulphate. Chondrin sulphate consists of proteoglycans, that is protein chains bonded to long chains of disaccharide hyaluronic acid. Matrix of bone is made up of a protein called ossein.

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(a) Basement membrane (basal lamina) is a thin sheet of fibrous proteins that underlies and supports the cells of an epithelium, separating this from the underlying tissue. Basement membranes are components of the extracellular matrix (= the viscous watery fluid that surrounds cells in animal tissue) and help to regulate the passage of materials between epithelial cells and adjacent blood vessels. Each consists of a framework of collagen fibrils within which are glycosaminoglycans (mucopolysaccharides) and laminins, which are proteins that bind the basement membrane to neighbouring cells via cell adhesion molecules.

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(a) Stratum germinativum (also stratum basale or basal cell layer) is the layer of keratinocytes that lies at the base of the epidermis immediately above the dermis. It consists of a single layer of tall, simple columnar epithelial cells lying on a basement membrane. These cells undergo rapid cell division, and mitosis to replenish the regular loss of skin by shedding from the surface. About \(25 \%\) of the cells are melanocytes, which produce melanin which provides pigmentation for skin and hair.

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(a) Fronto-parietals are a pair of long, broad, flattened, and membranous bones. They are united along the mid-dorsal line and form the whole roof of the cranium. In larval frog, each fronto-parietal occurs into separate frontal and parietal parts, but in the adult frog, they become fused to form a single frontoparietal. The entire floor of the cranium is covered and strengthened by a large parasphenoid bone.

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(b) In adult frog, gills disappear and their skeletal framework is also reduced to form hyoid apparatus. It lies below the tongue in the floor of the mouth and provides the surface of attachment to the tongue.
Pterygoid contributes to the postero-ventral margin of the orbit of its side. Palatine connects the anterior side of the cranium with the middle of the maxilla. Parasphenoid forms the floor of the cranium.

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(c) The bony partition between the tympanic cavity (cavity of the middle ear) and auditory capsule (internal ear) is perforated by a small window-like oval aperture, the fenestra ovalis, which remains closed by a membrane and a cartilaginous nodule, the stapedial plate.

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(d) Mesonephros kidney is present in both the adult as well as the embryo of the frog. A mesonephros develops from the middle part of the intermediate mesoderm, posterior to each pronephros soon after its degeneration.

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(d) An epithelial tissue that has thin flat cells, arranged edge to edge so as to appear like closely packed tiles is known as the pseudostratified epithelium. It covers moist surfaces where there is little wear and tears by friction such as the inner lining of cheeks.

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(a) Each hair is present in a tubular pit called hair follicle which is made up by sinking of the epidermis. Living cells are present only at the base of hair i. e. in hair papilla, the rest of the hair is dead and is divisible into the outer cuticle, middle cortex, and inner medulla.

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(a) Bone is an unusual tissue in that it is continually being reconstructed. The osteoblasts secrete bone matrix, whereas the large, much-branched, motile, lysosome-rich, multinucleate cells, called osteoclasts, destroy bone matrix. The twin process of resorption and reconstruction enables a particular bone to remodel its structure to meet any change in the mechanical requirements of the animal during its development.

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(d) Mucus helps frogs in forming moist skin as skin is its respiratory organ.

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(a) The smooth muscle consists of long, narrow unbranched spindle-shaped fibres. Each fibre contains a single oval nucleus in its thick middle part. The cross-striations are absent so that the fibres look smooth, hence the name nonstriated. Its contraction is not under the control of the animal, therefore, also called involuntary muscle.

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(a) In male cockroach, \(9^{\text {th }}\) sternum bears a pair of short, unjointed thread-like anal styles which are absent in females. Anal cerci and antennae are present in both male and female cockroaches.

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(a) Mast cells are the large cells with densely granular cytoplasm that is found in connective tissues. Their granules contain histamine which is a vasodilator, heparin which is an anticoagulant, and serotonin which acts as a mediator o inflammation and allergic reactions. Vasopressin is a hormone secreted by the posterior pituitary gland. Calcitonin is a hormone secreted by the thyroid gland. Melanin is a pigment produced by specialized epidermal cells called melanocytes. Relaxin is a hormone produced by the corpus luteum and placenta during the terminal stages of pregnancy.

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(b) Red pigment of vertebrate blood is haemoglobin. Haemoglobin is a conjugated protein. It consists of a basic protein globin joined to a nonprotein group heme, hence the name haemoglobin. Heme is an iron-porphyrin ring. A mammalian haemoglobin molecule is a complex of 4 heme molecules joined with 4 globin molecules.

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(d) Squamous epithelium is formed of thin discoidal and polygonal cells that fit like tiles on a floor so is also called pavement epithelium. It is found in the walls of blood vessels, in the alveoli of the lung for the exchange of gas, and in Bowman’s capsule of nephron for ultrafiltration.

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(b) Simple epithelium is a tissue made of a single layer of compactly arranged cells all of which rest over a noncellular basement membrane.

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(c) The chief component of the ground substance of cartilage is chondromuco protein which is formed of chondriotin sulphate, keratin sulphate, and hyaluronic acid.

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(a) The wall of blood vessels (arteries & veins) are made up of mainly 3 layers – the outermost tunica externa has a loose connective tissue, collagen fibres, lymph vessels, and the middle tunica media has circular smooth muscle fibres, some elastic fibres and the innermost tunica interna is a single-layered endothelium of polyhedral squamous cells.

If the arteries reach organs they form arterioles which are thinner and mainly consist of smooth muscles and when they subdivide in the tissues they make capillaries. The wall of capillaries are very thin (usually less than one micron) and have numerous minute pores and are made up of only endothelium. Exchange of material takes place between blood and tissue fluid across the endothelial membrane of capillaries through active diffusion.

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(c) Thigh muscles are skeletal muscles that are striated and voluntary.

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(d) Voluntary muscles – under control of our will. Involuntary muscles – Not under the control of our will. Muscles of the urethra also remain under voluntary control after infancy.

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(a) is the right answer.

(A) Dry skin causes ceased cutaneous respiration

(B) Three-chambered heart
(C) Frog never becomes uricotelic
(D) External fertilization occurs in water

Hint

(b)