NEET Biology Structural Organisation in Animals Important Questions Set 01

These Class 11 NEET Biology important questions on Structural Organisation in Animals give 45 questions with step-by-step answers, arranged as very short, short and long answer types, as asked in school and board examinations. They help NEET aspirants revise the definitions, structures, differences and key terms of the chapter.

Very Short Answer Type Questions

Question 1. Mention the location of setae in earthworm.
Answer: Setae are located in each body segment except the first, the last and clitellar segments.

Question 2. What is the location and significance of clitellum in earthworm?
Answer: In mature earthworm, segments 14–16 are covered by a prominent dark band of glandular tissue called clitellum which form cocoon.

Question 3. Which segment in earthworm bears female genital pore?
Answer: A single female genital pore is present in the mid-ventral line of 14th segment.

Question 4. Name the organs of sight in cockroach.
Answer: Compound eyes

Question 5. What is gonapophyses?
Answer: In cockroach, irregular chitinous plates are found in both male and female which surround genital pore in them. These plates are called gonapophyses and they help in copulation.

Question 6. Which glands of cockroach help in formation of ootheca?
Answer: Collaterial glands

Question 7. Name an intermediate stage of development in cockroach.
Answer: Nymph

Question 8. How many times moulting occur in Periplanata americana so that nymph grows to reach adult form?
Answer: Nymph undergoes moulting about 13 times to reach the adult form.

Question 9. Which kind of respiration takes place in frog, if it is inside water?
Answer: Cutaneous respiration

Question 10. Name the parts of ear in frog.
Answer: Middle ear and internal ear

Short Answer Type Questions

Question 11. What is metameric segmentation?
Answer: In earthworm, the body is externally and internally divided into segments with a serial repetition of at least some organ such type of segmentation is called metameric segmentation or metamerism.

Question 12. Explain sexual dimorphism with one example.
Answer: When the male and female individuals are distinguished externally, the phenomenon is called sexual dimorphism. It is present in frogs as well as in cockroach.

Question 13. What are spiracles? Name one animal in which they are present.
Answer: Spiracles are slit like openings present on body for the entry and exit of air. They are present in cockroach and play a vital role in respiration.

Question 14. Write a short note on malpighian tubules.
Answer: In cockroach, excretion and osmoregulation are brought about by malpighian tubules which are present at the junction of midgut and hindgut. The tubules are lined by glandular, cuboidal, brush-bordered cells that extract nitrogenous waste matter from the haemolymph and discharge it into the ileum as uric acid.

Question 15. Explain the process of respiration in earthworm.

Answer:

In earthworm, specialised respiratory organs are absent. The gaseous exchange takes place through general body surface. The body surface shows following adaptations for gaseous exchange to occur :

(i) It is kept moist by epidermal cells and coelomic fluid.

(ii) It is thin and richly supplied with blood. Gaseous exchange, i.e., intake of oxygen and giving out of CO₂ take place between blood capillaries of outer epidermis and surface film of moisture. The oxygen diffuses into the blood and combines with haemoglobin to form oxyhaemoglobin, which is carried to different tissues.

Question 16. Describe :
(a) Hibernation
(b) Camouflage
(c) Sexual dimorphism in frog

Answer:

(a) Hibernation : Frog is a cold-blooded or poikilothermous animal, i.e., the temperature of its body fluctuates with that of the environment. During adverse environmental conditions in winter or dry hot summer days, frogs are not seen. As they get burry in the soft damp bottom mud (i.e., deep burrow inside grounds) for protection. They become metabolically inactive and stop feeding, living only on the glycogen and fat stored in their bodies. Lung respiration is suspended and cutaneous respiration through damp skin alone is sufficient. This state of dormancy is called hibernation or "winter sleep" during winter.

(b) Camouflage : The frogs are capable of changing their colour, though gradually with the change in its surroundings and climatic conditions. They camouflage in order to hide themselves from enemies.

(c) Sexual dimorphism in frog :  Frogs exhibit sexual dimorphism, i.e., there are some differences in external characters by which male and female can be distinguished.  Male croak loudly as they have vocal sacs which are absent in females.  Males have swollen copulatory pads on inner fingers of forelimbs which are especially developed in breeding season for grasping the female during mating.

Question 17. Compare the composition of blood of cockroach and frog.
Answer: (a) Blood composition of cockroach :
(i) Blood or haemolymph : The haemolymph of cockroach consists of a clear colourless plasma rich in amino acids etc., and numerous different types of cells, called haemocytes. Some haemocytes transfer food material from blood to the tissues while others act as phagocytes in removing the metabolic wastes from tissues. Haemolymph is devoid of a respiratory pigment, and hence does not assist in respiration.
(ii) Haemocoel : The body cavity of the cockroach is filled with blood and that is why it is referred to as a haemocoel. The blood-filled spaces are known as sinuses.
(b) Blood composition of frog : Blood carries nutrients, gases and water to the respective sites in the body. Hence, it is the chief circulatory fluid of the body . It contains a clear liquid, called plasma, in which are suspended various types of free cells, called blood corpuscles.
(i) Plasma : It is largely water (90%) in which are dissolved mineral salts, absorbed foods (sugars, proteins), excretory wastes (urea), and other soluble substances.
(ii) Corpuscles : Three types of blood corpuscles are present in the plasma, viz., erythrocytes (RBCs
– red blood corpuscles), leucocytes (WBCs – white blood corpuscles) and thrombocytes – spindle cells or platelets. RBCs are nucleated, oval and biconvex and have haemoglobin (respiratory pigment). WBCs are amoeboid shaped and are protective in function. Thrombocytes or platelets are spindle-shaped and help in blood clotting.

Question 18. Write a short note on lymphatic system of frog.
Answer: Lymphatic system : Lymph flows through the lymphatic system. Lymph is without RBCs and contains few proteins. It is colourless. Lymph is constantly produced from filtering of blood through capillaries into intercellular spaces. Tissue fluid or lymph bathes the tissues and lubricates many of the internal organs. It functions as the middleman passing over food and oxygen to cells and waste materials to blood. Lymphatic system comprises lymph capillaries (closed at the tip), lymph channels or sinuses (spaces filled with lymph) and lymph nodes.

Question 19. Describe the economic importance of earthworm.
Answer: Economic importance of Earthworm :  Earthworms are simple, common place creatures of great economic importance to man.  They are certainly small, but directly or indirectly very useful to us.  They are well-known as "Friends of Farmers", because they make the soil loose and porous by their burrowing habit. Thus, the soil ploughed by their burrowing habit, provides quick aeration to plant roots and also help in penetration of the developing plant roots. Such soil provides quick aeration and absorption of water, thereby the roots of the plant can respire and penetrate easily with water. Earthworms increase soil fertility and also upturn soil continuously, i.e., they bring lower soil on the surface. Thus, they plough the land, and share the work of the farmers. The large soil particles are ground up into finer ones by the gizzard (a grinding organ of their alimentary canal). Thus, it provides more surface to the soil for water absorption.  Worm castings of the earthworms are of manurial value. The nitrogenous wastes, and other secretions of this worm increase the fertility of the soil. The process of increasing fertility of soil by earthworm is called Vermicomposting. They reduce both acidity and alkalinity of the soil, and thus create optimum conditions for plant growth.  They are also used as bait for catching the fishes all over the world.

Question 20. Write a short note on eye and ear of frogs.

Answer:

(a) Eye : There are two large eyes. Each eyeball is roughly spherical and lodged inside an orbit in the dorso- lateral side of head protected by eyelids. A nictating membrane is present over the eyes which protects them inside water and also enables frog to see under water. The wall of the eye ball mainly consists of three layers, i.e., outer fibrous coat (sclerotic), middle vascular coat (choroid) and inner nervous coat (retina).

Light rays coming from an object into eyes are refracted by internal eye layers and an image is obtained on the retina which is transmitted to brain.

(b) Ear : A pair of ears are attached to skull, posto-laterally in all vertebrates. They are statoacoustic organs as they help in both hearing and balancing of body.

(i) An ear of frog mainly consists of two parts – middle and internal ears.

(ii) There is no external ear in them and only tympanum (part of middle ear) is seen externally.

(iii) Middle ear : The cavity of middle ear is closed externally by the conspicuous eardrum or tympanic membrane which is a dark, flat, circular patch of skin behind eye. Middle ear cavity contains air and communicates with pharynx. With air present on both the sides of eardrum, it can vibrate without being damaged under the impact of striking sound waves.

(iv) Internal ear : It is lodged in the bony capsule which contains a watery fluid. This capsule lodges actual statoacoustic organ (hearing as well as balancing organ).

Question 21. Give an account of the mouth parts of cockroach.

Answer:

The mouth parts of cockroach consist of :

(i) Labrum : It is a broad, chitinous flap which forms anterior margin of mouth cavity (hence also known as upper lip).

(ii) Mandibles : These are two small structures. They work like jaws.

(iii) Maxillae : They lie beneath the mandible on either side on the head capsule. Both maxillae act as accessory jaws.

(iv) Labium (lower lip) : It is a single structure forming lower lip.

(v) Hypopharynx : A median flexible lobe acting as tongue.

Question 22. Explain digestive system of Periplaneta.

Answer:

(i) Cockroach (Periplaneta) is omnivorous, animal which usually feeds at night.

(ii) It searches food by the sweeping of antennae and taste it by maxillary and labial palps. It captures food by the help of fore legs, labrum and labium.

(iii) In the mouth, food mixes with salivary secretion and is pushed into pharynx with the help of labium.

(iv) Food now starts moving through alimentary canal by peristalsis.

(v) Food is stored in crop. And upon entering gizzard, food is subjected to further mastication by internal teeth worked upon by muscles.

(vi) In midgut, partly digested food is mixed with enzymatic secretions of hepatic caecae and midgut itself.

(vii) Epithelial cells of midgut are also absorptive, hence also they absorb digested food.

(viii) Undigested food is passed first into ileum and then into colon. In rectum, water is absorbed from it and faeces is eliminated to outside through anus.

Question 23. Give a brief account of
(a) Compound eyes of cockroach
(b) Sensory receptors of earthworm
Answer: (a) Compound eyes of cockroach : The most important sense organs in cockroach are a pair of large, sessile, compound eyes which are situated at the dorsal surface of the head. These eyes are black and kidney-shaped. Each eye consists of about 2,000 visual elements or units, called ommatidia (singular : ommatidium).  With the help of ommatidia, a cockroach can receive several images of an object. The image received by them is compound and made up of large number of separate images each of which is contributed by single ommatidium. Thus, the image seen by the whole eyes is made up of many dark and light spots of light, each contributed by one ommatidium. This kind of vision is known as mosaic vision with more sensitivity but less resolution, being common during night, hence called nocturnal vision. Compound eyes are specially adapted to perceive movements of objects.
(b) Sensory receptors of earthworm : Earthworms do not have special sense organs like eyes etc., but they have well-developed receptor cells which are quite simple in their structure. There are three types of receptors found :  Photoreceptors or light-sensitive organs : They are present on anterior end dorsal surface. They are present on dorsal surface of the body and they are numerous in anterior region. They enable worms to judge the intensity and duration of light.  Epidermal receptors or touch-sensitive organs : They are distributed all over epidermis but are more abundant on the lateral sides and ventral surface of the body. They are tactile (relating to touch) in function and also help worms to feel the vibrations in the ground.  Buccal receptors or taste receptors of chemoreceptors : They are specialised cells present in buccal chamber of earthworms. They are gustatory and olfactory (relating to taste and smell) and probably also respond to chemical stimuli.

Question 24. How many types of nephridia are present in Pheretima, discuss any two of them?
Answer: In Pheretima, on basis of the location in the body, there are three types of nephridia (any two). On basis of their location inside the body of Pheretima, there are three types of nephridia. They are :
(a) Pharyngeal nephridia : These nephridia occur as paired tufts in the 4th, 5th and 6th segments on each side of the alimentary canal in these segments. Each tuft consists of large number of nephridia which are abundantly supplied with blood vessels. They bear gland cells which can extract excess of water and nitrogenous wastes from the blood.
(b) Integumentary nephridia : These are attached to the inner surface of body wall in all segments, except the first-two. They are microscopic and their ducts open on the body surface independently.
(c) Septalth nephridia : They are present on both the sides of each intersegmental septum behind 15 segment. The ducts of these nephridia open into intestine in each segment.

Question 25. Write a short note on the types of respiration occurring in Rana tigrina.
Answer: Being amphibious in nature, the frog can utilise free oxygen and also oxygen dissolved in water. The adult frog, respires on land and in the water by two different ways. These are :
(1) Cutaneous respiration : The skin of frog provides an extensive surface for exchange of gases. It is thin richly supplied with blood and kept moist by the mucus and water. The cutaneous respiration is always carried out. It is practically the only mode of respiration when the frog is under water. Dissolved oxygen in the water is exchanged through the moist surface of the skin by diffusion.
(2) Pulmonary respiration : On land, the buccal cavity, skin and lungs all act as the respiratory organs. Breathing on land in atmospheric air with the help of lungs is called pulmonary respiration. It involves lungs and respiratory tract. The lungs are a pair of elongated, thin-walled, elastic, pink-coloured sacs present in the upper part of trunk region, i.e., thorax. The inner surface of each lung is divided by a series of partitions, the septa into many small cavities known as alveoli. Air enters into the buccal cavity through nostrils and then into lungs.

Question 26. Differentiate between the mesothoracic and metathoracic wings of cockroach.

Answer:

Mesothoracic wings Metathoracic wings
1. They are thick, leathery, opaque and dark 1. They are delicate, thin transparent and

2. They are not used for flight, but cover and 2. They are used for flight, but in the resting protectthemetathoracic wings. position,liefoldedbelowthetegmina.
3. They are larger than the second pair of 3. Movements are due to special muscles wings. attachedto wingbases.

Question 27. What is metamorphosis? Explain briefly metamorphosis in cockroach.
Answer: Metamorphosis : The process of transformation of larva into adult form through series of drastic changes is known as metamorphosis. In cockroaches, after fertilisation a female produces 9–10 oothecae, each containing 14–16 fertilised eggs. Thus, 14–16 young cockroaches (nymphs) develop in one ootheca. The nymph grows by moulting about 13 times to reach the adult forms. There is paurometabolous (gradual) metamorphosis.

Question 28. Explain the external features (morphology) of earthworm.
Answer: The external features (morphology) of earthworm :  Earthworms have long, narrow, cylindrical body.  Their body is divided into short and similar segments.  These similar segments are known as metameres. They are about 100 to 120 in number.  These metameres divide body both externally and internally, such type of segmentation is called metameric segmentation or metamerism.  These segments are separated from each other by distinct ring-like grooves or annuli.  The dorsal surface of their body is recognised by a dark median/mid-dorsal line, which is in fact a dorsal blood vessel beneath the skin.  Their ventral surface can be recognised by the presence of genital apertures (pores).  The earthworms do not possess a distinct head nor any specialised sense organs-like eyes or ears.  So, the anterior end of these worms consist of mouth and the prostomium.  Mouth is a crescentric aperture at the anterior end of first segment. This segment is known as peristomium (or buccal segment).  The dorsal edge of peristomium projects forward above the mouth, as a small fleshy lobe called prostomium which serves as covering for the mouth. It is used as a muscular probe in burrowing. It is also sensory in function.  Other external features of earthworm include – presence of clitellum, setae and various apertures.

Question 29. Compare the locomotory organs of earthworms and frogs.
Answer: (a) Locomotory organs of earthworm : Setae : Each body segment, except the first, the last and clitellar segments, bears a ring of tiny, curved, chitinous structures known as setae or chaetae. They are embedded in the epidermal pits known as setigerous sac, in the middle of each segment. These pits or sacs have special muscle to move the seta in or out and to bend it forward or backward. Hence, they help in locomotion.
(b) Locomotory organs of frog : It includes two pairs of limbs, i.e., fore limbs and hind limbs.
(i) Forelimbs :  They arise anteriorly from trunk just behind the head.  Each forelimbs consists of the upper arm, forearm, wrist and hand bearing four digits without web.  In male frog, the base of first inner finger is thickened especially in breeding season, forming the copulatory pad or nuptial pad for clasping the female.
(ii) Hindlimbs :  They are much elongated and powerful, arise close together posteriorly from trunk.  Hindlimbs are larger and muscular than forelimbs.  The hindlimbs end in five digits which are connected by broad thin webs of skin which assist in swimming.

Question 30. Explain how the digestion of food takes place in frogs.
Answer: Process of digestion : Frog feeds on insects, worms, molluscs etc. The prey is captured by rapid flicking action of prehensile and bilobed tongue and swallowed whole. It passes down the oesophagus to reach stomach. Here, digestion of food takes place by the action of HCl and gastric juices secreted from walls of the stomach. The liquefied semidigested acidic food is called chyme which passes down from stomach to the duodenum of small intestine. In duodenum, chyme is mixed with bile and pancreatic juices for further digestion to take place. Bile neutralises the acidity of chyme and emulsifies fat. Pancreatic juices contain various type of enzymes to digest carbohydrates and proteins. The digestion is completed in the intestine only. This completely digested food is absorbed by numerous finger-like folds in the inner wall of intestine (i.e., ileum). The undigested solid waste moves into the rectum (where water reabsorption occurs) and finally it passes out through cloaca.

Long Answer Type Questions

Question 31. Discuss structure of heart in frog.
Answer: Structure of heart in frog : Aortic trunks  Heart is a muscular structure which lies mid-ventrally inside the anterior trunk region. Left pre-caval Right pre-caval  It is reddish in colour and somewhat conical or triangular in shape. Left auricle Right auricle  It is enclosed within a thin, transparent, Sinus venosus two-layered sac called the pericardium. Pulmonary veins  It protects the heart from friction or Ventricle mechanical shocks. Post caval  It has a three-chambered structure, made of two anterior atria, right and left and a single posterior ventricle.  The heart of frog has two additional chambers – sinus venosus and truncus arteriosus (= conus arteriosum).  Sinus venosus is a thin-walled, triangular chamber attached dorsally to heart. It opens into the right larger atrium through an aperture. Truncus arteriosus : It arises anteriorly from the right ventral side of ventricle. It is a tubular chamber. The opening of ventricle into truncus arteriosus is guarded by three semilunar valves which prevent backflow of blood from truncus into ventricle.

Question 32. How development and metamorphosis take place in frog?
Answer: Development is indirect. Within two weeks fertilised eggs or zygote develop into free-swimming aquatic larvae called tadpoles. It is small, fish-like creature which hatches out from the egg after completing the development. The tadpole swims freely in the water feeding on planktonic food, i.e., herbivorous. Initially, the tadpole have external gills which become replaced by internal gills later after metamorphosis. Limbs appear gradually and tail shortens. Along with these changes, a few other significant changes, like quick growth and movement of the eyes to higher up the skull and formation of eyelids, formation of skin glands, thickening of the skin and development of an eardrum to lock the middle ear take place. These changes transform the tadpoles into a young adult frogs. These changes together constitute metamorphosis. The disappearance of the tail is somewhat later (occurs at higher thyroxine level) and after the tail has been reabsorbed the animals are ready to leave the water). After metamorphosis, young adults may leave the water and disperse into terrestrial habitats, or continue to live in the aquatic habitat as adults.

Question 33. Draw a well-labelled diagram of reproductive system of earthworm. Discuss female reproductive organs of earthworm.

Answer:

A well-labelled diagram should show these parts: 1; 2; 3; 4; 5; 6; 7; Spermathecae; 8; 9; Testis sac with testes; 10; Testis; 11; Spermiducal funnel; 12; Seminal vesicles; 13; Ovary; 14; Ovarian funnel; 15; Vasa deferentia; 16; Accessory glands; 17; Commonand prostatic spermatic duct; 18; Prostate gland; 19; 20.

Female reproductive organs of earthworm : They consist of following structures :

(1) Ovaries : There is a pair of whiteth minute masses of the ovaries attached to the posterior surface of the septum present between the 12 and 13th segments. They produce ova.
(2) Oviducts : They are two short tubes each lying immediately behind the respective ovary. The two ovarian tubes from backwards and converge toth meet in the body wall and open to outside by a female genital aperture on mid-ventral side of the 14 segment. The mature ova liberated by each ovary are received by the oviducts and pass ova outside through the female genital aperture.
(3) The ova produced by the ovaries are received by the oviducts and are finally passed outside into the cocoon through a female genital aperture. It is the cocoon where the fertilisation and development of the embryo takes place.

Question 34. Give details of male reproductive organs in adult frog with a labelled diagram.
Answer: Male reproductive system of frogs : It consists of two testes (attached to kidneys), several vasa efferentia and two urinogenital ducts Vasa (copulatory organs are lacking). efferentia
1. Testes : It is an elongated or ovoid light-yellow Fat bodies body attached to the antero-ventral surface of each kidney by a double fold of peritoneum, Testis called mesorchium. Each testis is a compact Kidney mass of much coiled seminiferous tubules, the epithelial lining of which produces Adrenal gland spermatozoa. Urino
2. Vasa efferentia : There are 10–12 very fine genital duct tubes connecting the testis to kidneys on Rectum each side. The vasa efferentia run transversely Cloaca through the mesorchium. They open into the Urinary bladder Cloacal aperture Bidder's canal. The sperm produced by testes are passed into Bidder's canal via vasa efferentia and then carried to the urinogenital duct.
3. Urinogenital duct : Ureter in male frog is both a urinary duct and a vas deferens (which carries sperms), hence it is called a urinogenital duct. Each kidney gives rise to muscular urinogenital duct at its outer border, which carries urine as well as sperms. Each urinogenital duct runs posteriorly, and before opening into cloaca. Cloaca is a common chamber which receives faecal matter, urine and sperms. All these products are passed out through cloacal aperture.

Question 35. Describe the different apertures present in the abdominal segment of cockroach.

Answer:

A well-labelled diagram should show these parts: VI; V; VII; VIII; IX; Anal cercus; 10th; X; Opening of tergum oothecal; Anal chamber; A cercus; B 10th tergum.

Abdomen : The posterior region of body is called abdomen. It is broader than thorax and dorso-ventrally flattened. Abdomen in both males and females consists of 10 segments (in adults while embryo has 11 segments). A typical abdominal segment is enclosed by four sclerites. A dorsal tergum, one ventral sternum and two lateral pleura are found.

Apertures : The abdomen bears the following apertures.
(i) Anus : It lies in the 10th abdominal segment just below the tergum. The waste matter is expelled out through it.
(ii) Genital aperture : In male, it lies below anus between the 10th tergumth andth9th sternum. Female genital aperture opens into the genital chamber which is formed by 7th, 8 and 9 sterna. In both the sexes, genital aperture is surrounded by gonapophyses.

Question 36. How fertilisation takes place in cockroach and what happens after it?

Answer:

(a) Copulation : During copulation, the male transfers its spermatozoa in the form of packets, called spermatophores, directly into the female genital pouch.

(b) Spermatophore formation : Spermatozoa produced by testes get stored in seminal vesicles of male. At the time of copulation, these pass into the ejaculatory duct where they get mixed with a nourishing fluid. A spermatophore consists of a central chamber which contains spermatozoa in a spermatic fluid.

(c) Ootheca formation and fertilisation : Eggs from each ovariole usually descend into genital pouch, where they become fertilised by sperms ejected simultaneously from spermatheca.

 Fertilised egg become surrounded by the secretion of collaterial glands, which hardens to form an egg case or ootheca. 16 eggs are arranged in two rows in one ootheca. On an average, about 9–10 ootheca are laid by the female cockroach. An ootheca is about 3/8″ (8 mm) long. It is a dark reddish to blackish brown capsule. The female cockroach carries the ootheca, protruding from tip of her abdomen, for several days, till it is deposited or dropped or glued to a suitable surface, usually in a crack or cervice of high relative humidity near a food resource. Each egg inside ootheca undergoes cleavage and finally results in the formation of nymphs. Freshly-hatched nymphs are delicate, transparent and almost colourless with black eyes. They possess nearly all adult characters but differ in size and colouration, in being sexually immature and without wings.  Metamorphosis : The nymph grows by moulting about 13 times to reach the adult form. This development includes; wings formation, growth of body size, colouration change (i.e., colour changes to dark brown or black) and development of genitalia etc. development of cockroach, i.e., Periplaneta americana is gradual metamorphosis, i.e., occurs through series of nymphal stages and is known as paurometabolous.

Question 37. Describe the alimentary canal with its various modification in earthworm.

Answer:

(a) Alimentary canal in Pheretima is a complete and straight tube running along the entire length, i.e., between first to last segment of the body.

(b) It consists of following parts :  Mouth : It is a terminal aperture in peristomium, overhung by prostomium.  Buccalst cavity : Mouth leadsrd into a thin-walled, small tube called buccal cavity. It extends from the 1 to the middle of the 3 segment.

 Pharynx : Buccal cavity is followed by the pharynxth which is a small, pear-shaped sac. It extends from the middle of third segment to the end of 4 segment.

 Oesophagusth: The pharynx leads into a small, narrow tubular structure. It extends from the 5th segment to 7 segment.

 Gizzard : Oesophagus is modified into a prominent, oval, hard and thick-walled muscular organ, the gizzard, in segments 8 and 9. Gizzard grinds the food i.e. the soil particles and decaying leaves etc., with the help of thick muscles and cuticle.  Stomachth : Gizzard is followed by a short narrow tubular stomach which extends from the 9th to the 14 segment. Its wall are highly vascular and glandular. In stomach, a chalky secretion of calciferous glands located in stomach wall, neutralises the humic acids present in humus, i.e., soil.  Intestine : The stomach leads into a wide thin-walled intestine which runs from the 15th segment to the last segment where it opens to the outside by means of anus. (It gives off a pair of small, conical lateral intestinal caeca in 26th segment.)

median fold of dorsal wall called typhlosole. This increases the effective area of absorption in the intestine.

 Anus : The alimentary canal opens to the exterior by a small-rounded aperture called the anus.

Question 38. Describe the nervous system of frogs in detail.

Answer:

The nervous system of frog is composed of three main sub-divisions :

1. Central nervous system comprising brain and spinal cord.

2. Peripheral nervous system including cranial and spinal nerves.

3. Autonomic nervous system : It comprises sympathetic and parasympathetic nervous system.

1. Central nervous system :

(1) Brain : It is enclosed in the cranial cavity of the skull called brain box. The brain is divisible into three parts :

(a) Forebrain : It comprises two olfactory lobes, two cerebral hemispheres and diencephalon.

(b) Midbrain : It consists of optic lobes and crura cerebri (thick bands of nerve fibres).

(c) Hindbrain : The posterior part of brain includes cerebellum and medulla oblongata.

(i) Cerebellum : It controls equilibrium and muscular coordination which are of little importance in frogs (so it is poorly developed in them).

(ii) Medulla oblongata : It is the last small conical part which is continuous with spinal cord. It controls involuntary functions such as heartbeat, metabolism, respiration etc.

(2) Spinal cord : The spinal cord extends posteriorly from medulla oblongata through foramen magnum and lies protected within neural canal of vertebral column. It is short, thick, cylindrical, somewhat flattened and white in colour. It is mainly concerned with the reflex actions.

2. Peripheral nervous system :

(1) Cranial nerves : There are 10 pairs of cranial nerves which originate from brain of frog.

(2) Spinal nerves : Frog has 10 pairs of spinal nerves, often reduced to only 9 pairs. Every spinal nerve on either side arises from spinal cord.

3. Autonomic nervous system : It is a system of nerve fibres and ganglia which controls and coordinates the involuntary activities of the visceral organs, such as secretion of digestive fluid, action of heart etc. This system is autonomic in the sense that it regulates such activities of the body in which the will power of the animal is not involved.

Question 39. Write the names of male and female reproductive organs found in frogs. Discuss in brief the process of fertilisation and post-fertilisation events in frogs.

Answer:

Frogs have well-organised male and female reproductive system. The male reproductive system consists :

With the onset of rainy season, frogs emerge out of aestivation and immediately start breeding. Male gather in shallow waters and starts croaking just to attract females for mating or copulation. The male mounts upon the back of female and grasps her firmly with the help of copulatory pads. Then, female deposits several hundred (2500 to 3000) ova or eggs through her cloaca into water. The male discharges sperms over eggs to fertilise them. Thus, fertilisation is external. The male now releases grip and leaves the female. Mass of eggs is embedded in a gelatinous material which on contact with water swells into a protective transparent jelly. Within two weeks fertilised eggs or zygotes develop into free-swimming aquatic larvae, called tadpoles, which undergo metamorphosis to become adult frog.

Question 40. Describe in brief :
(a) Exoskeleton of cockroach
(b) Blood vessels in earthworm

Answer:

(a) Exoskeleton of cockroach :  The entire body is covered externally by a non-living brown-coloured hard, jointed and chitinous exoskeleton composed of several plates called sclerites.  It is formed by the surface layer or cuticle of the body wall.  Exoskeleton for each segment consists of a dorsal tergum and a ventral sternum; these plates are joined to each other by a thin and flexible articular membrane known as arthrodial membrane.

(b) Blood vessels in earthworm : Lateral Lateral hearts oesophageal Dorsal vessel hearts 13 14 15 16 Commissural 5 6 7 8 9 10 11 12 4 vessel 3 2 1

Lateral oesophageal Ventral Anterior Subneural vessel vessel loops vessel  Blood flows in well-organised vessels which run all along the body of earthworm.  Some prominent blood vessels found in earthworm are : Dorsal blood vessel : It is the largest blood vessel of body running mid-dorsally above the alimentary canal, from one end of body to the other. It has valves which prevent the backflow of blood. It receives blood from various parts of earthworm through different connecting vessels.

Ventral blood vessel : It also extends from the one end to the other end of the body. It does not have any valves and flow of the blood is from anterior to the posterior end of the body. It is a main distributing blood vessel.

Question 41. Discuss in brief various reproductive organs found in female cockroach with its labelled diagram.

Answer:

A well-labelled diagram should show these parts: Ovary; Oviduct; Commonor oviduct vagina; Spermatheca; Collaterial glands; Genital chamber Genital; Vestibulum pouch; Gonapophyses.

Female reproductive system : It includes ovaries, oviducts and vagina, spermatheca, collaterial gland, genital pouch and external genitalia, all confined to abdomen.

(1) Ovaries : A pair of yellow-coloured ovaries lie in 2nd to 6th abdominal segments, one on either side of hindgut, and embedded in fat bodies. Each ovary consists of eight elongated, tapering and beaded blind tubes called ovarian tubules or ovarioles. Each ovariole contains a linear series of ova in various stages of development.

(2) Oviducts and vagina : Posteriorly, all the ovarioles ofthan ovary unite to form a short and wide lateral oviduct. The two lateral oviducts in their turn unite in 7 segment to form a very short median common oviduct. Its posterior wider part is called vagina which opens into large genital chamber or pouch by a vertical slit-like female genital pore.

(3) Spermatheca : A pair of spermatheca is present in the 6th segment which opens into the genital chamber. In a fertile female, spermatheca is found filled with spermatozoa, received during copulation from the male.

(4) Collaterial gland : A pair of branched accessory or collaterial glands lies behind and above the ovaries. Secretion of collaterial glands forms the hard egg – case or ootheca around groups of eggs.

(5) Genital pouch or chamber : It is locatedth at the hind-end of abdomen. In female cockroach, 7th sternum is large, boat-shaped and alongwith 8 and 9th sterna forms genital pouch. Genital pouch can be divided into two parts – smaller anterior part containing female gonopore and pores of spermatheca and collaterial glands is termed genital atrium, while its larger posterior part in which ootheca is formed is called vestibulum.

(6) External genitalia or ovipositor : There are three pairs of plate-like chitinous, gonapophyses present between female genital pore and anus. These form ovipositor valves which assist in copulation, and in laying eggs.

Question 42. Discuss in brief digestive system of frog.

Answer:

Digestive system of frog :  It consists of alimentary canal and digestive glands.  The alimentary canal is short because frogs are carnivores, and hence the length of intestine is reduced.  The alimentary canal is complete.  It is a long coiled tube extending between mouth and cloaca. It consists of the following parts :
(i) Mouth : Mouth is a wide anterior-most opening leading to a spacious buccal cavity that leads to the oesophagus through pharynx.

(ii) Oesophagus : Because of the absence of neck in frog the oesophagus is only a short tube. The oesophagus leads to the stomach.

(iii) Stomach : It lies on the left side in the body cavity. Its large broad anterior part is called cardiac stomach, while short narrow posterior part, the pyloric stomach. It also contains multicellular gastric glands which secrete the enzyme pepsinogen and unicellular oxyntic glands which secrete hydrochloric acid. Its posterior end opens into small intestine.

(iv) Small intestine : It is the longest part of the alimentary canal and is divisible into :

Duodenum : It receives bile from gall bladder and pancreatic juice from the pancreas through a common bile duct (i.e., hepatopancreatic duct).

Ileum : The internal lining of the ileum is also thrown into a large number of finger-like branched projections known as villi which increase the absorptive surface area.

Rectum : The ileum leads into a broad, thin-walled short but wider tube, known as rectum or large intestine. It opens outside by the cloaca.

(v) Digestive glands :

Liver : It is a reddish-brown, multilobed gland located close to the heart and lungs. Liver secretes a greenish alkaline fluid, the bile. The bile is transferred to the gall bladder for storage.

Pancreas : It is a branched flat elongated pale yellow gland. It secretes pancreatic juice containing several digestive enzymes.

Process of digestion

Frog feeds on insects, worms, molluscs etc. The prey is captured by rapid flicking action of prehensile and bilobed tongue and swallowed whole. It passes down the oesophagus to reach stomach. Here, digestion of food takes place by the action of HCl and gastric juices secreted from walls of the stomach. The liquefied semidigested acidic food is called chyme which passes down from stomach to the duodenum of small intestine. In duodenum, chyme is mixed with bile and pancreatic juices for further digestion to take place. Bile neutralises the acidity of chyme and emulsifies fat. Pancreatic juices contain various type of enzymes to digest carbohydrates and proteins. The digestion is completed in the intestine only. This completely digested food is absorbed by numerous finger-like folds in the inner wall of intestine (i.e., ileum). The undigested solid waste moves into the rectum (where water reabsorption occurs) and finally it passes out through cloaca.

Question 43. Describe the excretory structures in cockroach.

Answer:

It regulates the amounts of nitrogenous material, inorganic salts and water in blood or haemolymph. Excretory system includes the following :

(1) Malpighian tubules  These are attached to the alimentary canal at the extreme anterior end of hindgut.  These are fine, long, unbranched, yellowish and blind tubules lying freely in the haemolymph.  Each tubule is lined by glandular epithelium with a characteristic ciliated cells (i.e., brush-bordered cells).  Malpighian tubule has two functional parts : Glandular cells of secretory part extract nitrogenous wastes (mostly in the form of salts of uric acid) and water from haemolymph form in a solution called urine.

The urine flows towards the second absorptive part of tubule which reabsorbs certain salts and some water resulting in precipitation of uric acid. From malpighian tubules, uric acid moves into ileum by gentle waves, from there it passes to colon and rectum parts of hindgut and finally eliminated with faeces through anus.

Therefore, this insect is called uricotelic.

(2) Fat body : It consists of fat cells which lie below the body wall filling most of the space within the body which is not occupied by other internal organs. These cells accumulate, produce and store uric acid and urate granules throughout life.

(3) Nephrocytes : These are large colourless ovoid binucleate cells attached to the dorsal diaphragm in the body cavity. They are also found arranged on each side of the heart.

(4) Urecose glands : In some species, in males urecose glands are present on periphery of mushroom glands. The glands synthesize uric acid.

Question 44. Explain briefly the anatomy of digestive system found in cockroach with the help of labelled diagram.

Answer:

Digestive system : The cockroach has well-developed digestive system comprising the alimentary canal and associated digestive glands. Pharynx Salivary gland

Salivary reservoir

Oesophagus

Crop

Gizzard

Hepatic caeca

Mesentron or midgut

Malpighian tubules Rectum Ileum

Colon Alimentary canal : It consists of three parts :

(1) Foregut or stomodaeum

(2) Midgut or mesenteron

(3) Hindgut or proctodaeum

The foregut and the hindguts are formed by ectoderm and are lined by cuticle internally, while the midgut is developed from endoderm of the embryo and not lined by cuticle.

(1) Foregut : It comprises the mouth, pharynx, oesophagus, crop and gizzard.  Mouth : A narrow opening at the base of pre-oral cavity (i.e., space lying in front of the mouth to receive the food) which leads to pharynx and bounded by the mouth parts.  Pharynx : It is short tube-like structure which lies in the head region and leads into the oesophagus.  Oesophagus : It is a tubular thin-walled structure lying in the neck and continues into the crop. There are paired salivary glands lying one on each side of the oesophagus and crop. Their secretion is known as saliva which lubricates food and its digestive enzymes hydrolyse the starch of food.  Croprd: Thethoesophagus dilates to form a large, thin-walled, pear-shaped sac, which extends upto the 3 or 4 abdominal segment. It is the largest part of foregut where food is stored. It opens into the gizzard.  Gizzard or proventriculus : Crop leads into a small, cone-shaped, muscular and thick-walled chamber called the gizzard or proventriculus. It has an outer layer of thick circular muscles which are needed by the gizzard for grinding. It also bears thick inner layer of cuticle which produces/forms six highly chitinous plates called teeth (which are strong and sharp). They are also used for grinding the food.

(2) Midgut : It is a thin-walled somewhat coiled tube with almost uniform thickness. It is the only part of the alimentary canal which is not lined by the cuticle. From the junction of midgut and gizzard (i.e., foregut) arises six to eight finger-like structures called hepatic caecae. They are short, narrow, blindly ending hollow tubes which secrete digestive enzymes into midgut.

The junction of midgut and hindgut is marked by the presence of another ring of 100–150 yellow fine thread-like structures, the malpighian tubules. They help in removal of excretory products from haemolymph.

(3) Hindgut : It comprises of ileum, colon, rectum.  Ileum : The midgut continues into the ileum which is a narrow, short tube passing into the colon.  Colon : It is longer and wider and an irregular-shaped tubular structure. It leads into the rectum.  Rectum : It is terminal short thick-walled structure which opens outside through anus.

Question 45. (a) Discuss spermathecae in brief.
(b) Describe how direct development takes place in case of earthworm?
Answer: (a) Spermathecae : They are a pair of sacs of unequal size which are present in the 6th, 7th, 8th and 9th segments of earthworm and 6th abdominal segment of cockroach. The spermathecae in case of earthworms open to outside through spermathecal pores situated ventro-laterally in the successive grooves separating 6th, 7th, 8th and 9th segments, while in cockroach they open by a common duct into the genital chamber. Their primary function is to store the sperms received from another partner during copulation.
(b) Earthworms are hermaphrodite or bisexual or monoecious. The male sex organs mature earlier than the female, so cross-fertilization occurs which is accompanied by the copulation. The copulation takes place during night or in the early morning from July to October in rainy season. Two worms attach themselves with their ventral surfaces and become opposed to each other in opposite direction. During copulation, male genital papilla of one earthworm is inserted into the spermathecal pore of the other earthworm to transfer the sperms. After copulation, two worms separate. Now, the glandular cells of the clitellum secrete a fluid that forms a girdle around the clitellum. The girdle is filled with mature ova released through female genital pore. The worm wriggles backwards when the girdle passes over the spermathecal pores it receives the sperms stored in spermathecae and albuminous secretion of the epidermal gland cells of skin. Ultimately, the worm wriggles out completely and the girdle is therefore, left free in moist soil. Now, this structure is called cocoon. Fertilisation and development occur inside the cocoon. All the eggs in a cocoon may be fertilised but after about three weeks, each cocoon produces 2 to 20 worms with an average of four. Other eggs (zygotes) are used as food by developing embryos Development is direct (without larva).