RowQ
The Vault
RowQ
The Vault
CBSE Class 11 Biology · 10 questions · 24 marks
A single cell can do everything an amoeba needs, but a cockroach or a frog runs on division of labour — cells specialise, group into tissues, and tissues combine into organs. This chapter opens with the four fundamental animal tissues and then applies them to two thoroughly studied examples, the earthworm and the cockroach, along with the frog. Learning the digestive and reproductive layout of these animals gives you a template you will reuse throughout human physiology.
The excretory structures found at the junction of the midgut and hindgut of a cockroach are the:
Answer
Malpighian tubules are correct — about 100 to 150 fine yellow tubules at this junction absorb nitrogenous waste from the haemolymph and pass it as uric acid into the gut; the hepatic caeca at the other end of the midgut are digestive, not excretory.
Cardiac muscle is distinguished from skeletal muscle by the presence of:
Answer
Intercalated discs between branching fibres is correct — these communication junctions let the impulse spread so the heart contracts as a unit; both cardiac and skeletal muscle are striated, but only skeletal muscle is under voluntary control.
In the earthworm, the internal median fold of the dorsal wall of the intestine that increases the surface for absorption is the:
Answer
Typhlosole is correct — this longitudinal ridge projects into the intestinal lumen and greatly increases the absorptive area, while the clitellum is a glandular band that secretes the cocoon.
Tissue in which cells are joined by junctions that seal the space between them and prevent substances from leaking across is showing:
Answer
Tight junctions are correct — they stop material from passing between adjacent cells, whereas adhering junctions merely cement cells together and gap junctions actually allow ions and small molecules to move from one cell to the next.
Assertion (A): A cockroach can survive for several days after its head is removed. Reason (R): The nervous system of a cockroach is spread along a ventral nerve cord bearing segmental ganglia rather than being concentrated in the head alone.
Answer
Both A and R are true and R is the correct explanation of A — because the segmental ganglia can continue to control the muscles of their own segments independently, basic activity continues without the brain, and the insect eventually dies of starvation rather than immediate nervous failure.
Distinguish between a tendon and a ligament with respect to structure and function.
Answer
A tendon is a dense regular connective tissue made almost entirely of tightly packed parallel collagen fibres; it is very strong but has little elasticity, and it attaches a skeletal muscle to a bone so that the force of contraction is transmitted to the skeleton. A ligament is also a dense regular connective tissue but contains a large proportion of elastic fibres along with collagen, so it has considerable strength together with elasticity; it connects one bone to another at a joint and holds the joint together while allowing controlled movement.
Trace the path of food through the alimentary canal of the earthworm and state the function of the gizzard and the intestinal caeca.
Answer
Food, which is soil containing organic matter, is taken in at the mouth situated under the prostomium and passes into the buccal cavity, then the muscular pharynx, then the narrow oesophagus, then into the muscular gizzard, and from there into the stomach, then the long intestine, and finally out through the anus at the last segment. The gizzard has thick muscular walls that grind the soil and decaying leaf material into fine particles, so that the digestive enzymes can act on a much larger surface. A pair of short conical intestinal caeca arises from the intestine in about the twenty-sixth segment and secretes digestive enzymes that help break down the food as it passes along.
Classify epithelial tissue, describing the structure, location and function of each type.
Answer
Epithelial tissue covers the outer surfaces of the body and lines its cavities and tubes; its cells are compactly packed with very little intercellular material and always rest on a basement membrane. It is divided into simple epithelium, made of a single layer of cells, and compound epithelium, made of two or more layers. Simple squamous epithelium consists of a single layer of flat cells with irregular boundaries fitted together like tiles; it is found in the walls of blood vessels and in the alveoli of the lungs, where its extreme thinness allows rapid diffusion of gases and fluids across the boundary. Simple cuboidal epithelium consists of a single layer of cube-shaped cells and lines the ducts of glands and the tubular parts of the nephrons in the kidney, where it carries out secretion and absorption; in the proximal tubule the free surface bears microvilli forming a brush border that increases absorptive area. Simple columnar epithelium is made of a single layer of tall cells with the nucleus at the base and lines the stomach and intestine, where it both secretes and absorbs. When columnar or cuboidal cells bear cilia on their free surface they form ciliated epithelium, which lines the bronchioles and the fallopian tubes and moves mucus or the ovum in one specific direction. Some columnar or cuboidal cells become specialised for secretion and form glandular epithelium, which is unicellular as in the goblet cells of the gut, or multicellular as in the salivary glands; glands releasing their product through a duct are exocrine and those releasing hormones directly into the blood are endocrine. Compound epithelium has many layers of cells and therefore does not take part much in absorption or secretion; its function is protection against mechanical stress and chemical damage, and it is found in the dry surface of the skin, the moist lining of the buccal cavity and the pharynx, and the inner lining of the ducts of salivary glands.
Describe the digestive, circulatory and excretory arrangements of the cockroach.
Answer
The alimentary canal of the cockroach lies in the body cavity and is divided into three regions. The foregut begins at the mouth, which opens into a short pharynx leading to a narrow oesophagus; this widens into a thin-walled sac called the crop where food is stored, and the crop is followed by the gizzard or proventriculus, whose inner wall carries six highly chitinous plates called teeth that grind the food finely. The mouth parts, consisting of labrum, a pair of mandibles, a pair of maxillae and a labium, together with the hypopharynx acting as a tongue, chew the food before it enters, and the saliva from the salivary glands moistens it. At the junction of foregut and midgut there is a ring of six to eight blind tubules called hepatic or gastric caeca that secrete digestive juice. The midgut is the main site of digestion and absorption. At the junction of midgut and hindgut arise about one hundred to one hundred and fifty fine yellow filaments, the Malpighian tubules; these remove nitrogenous waste from the surrounding haemolymph and pass it into the gut, so the cockroach is uricotelic and excretes waste largely as uric acid. The hindgut is broader and comprises the ileum, colon and rectum, the rectum opening to the exterior through the anus; some fat body cells, nephrocytes and the cuticle also assist in storing or removing waste. The circulatory system is of the open type. Blood vessels are poorly developed and open into large spaces called sinuses, in which the colourless blood or haemolymph bathes the organs directly; the haemolymph consists of plasma and free haemocytes. The heart is a long muscular tube lying along the mid-dorsal line of the thorax and abdomen and is divided into thirteen chambers, each with a pair of slit-like openings called ostia through which blood enters. Waves of contraction pass forward along the heart and drive the blood towards the head, from where it returns through the sinuses. Since the haemolymph carries no respiratory pigment, gases are not transported by the blood at all; instead the cockroach breathes through a network of fine air tubes called tracheae that open at ten pairs of spiracles guarded by sphincters, and the finest branches, the tracheoles, deliver oxygen directly to the tissues.
A student examining prepared slides records the following. Slide 1: a single layer of very flat cells lining a thin air sac. Slide 2: cells with a large fat droplet pushing the nucleus to one side, packed under the skin. Slide 3: branching muscle fibres with faint cross bands and dark lines where the ends of fibres meet. Slide 4: a fluid tissue with a straw-coloured matrix and no fibres. (a) Name the tissue on Slide 1 and explain how its structure suits the location. (b) Identify the tissue on Slide 2 and state its two main functions. (c) Name the tissue on Slide 3, the dark lines described, and where in the body it occurs. (d) Why is the tissue on Slide 4 classified as connective tissue despite being liquid?
Answer
(a) Slide 1 shows simple squamous epithelium. Its cells are extremely thin and form a single layer, so the diffusion distance across the wall is minimal and oxygen and carbon dioxide can pass rapidly between the air in the sac and the blood. (b) Slide 2 shows adipose tissue, a type of loose connective tissue. It stores fat as a long-term energy reserve, and the layer it forms beneath the skin acts as insulation against heat loss and as a cushion protecting the organs. (c) Slide 3 shows cardiac muscle. The dark lines where the ends of the fibres meet are intercalated discs, which are communication junctions allowing the impulse to spread quickly from fibre to fibre. This tissue occurs only in the wall of the heart. (d) Blood is classified as connective tissue because it consists of cells suspended in an abundant intercellular matrix, which in this case is the fluid plasma rather than a solid or fibrous ground substance, and because it performs the connective-tissue role of linking and supplying every part of the body by transporting gases, nutrients, hormones and wastes between them.
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