8 Marks Question

1. Describe the reproductive system of periplaneta and draw neat and labeled diagrams of it?
A: Reproductive System of Periplaneta:
Periplaneta is dioecious/unisexual. Female, males having short and broad abdomen, presence of brood pouch and absence of anal styles.
 

1. Male Reproductive System:
i) Testes: One pair, elongated and lobed structures, lying one on each lateral side in the 4^th to 6^th abdominal segments. They are embedded in the fat bodies. From the posterior end of each testis, there starts a thin duct, the vas deferens. The two vas deferens run backwards and inwards to open into a wide median duct, the ductus ejaculatorius in the 7^th segment. A charecteristic mushroom shaped gland is present in the 6th and 7^th abdominal segments which functions as an accessory reproductive gland. The gland consists of two types of tubules (1) long slender tubules, the utriculi majores/peripheral tubules. (2) short tubules, the utriculi breviores. Secretion of utriculi majores forms the sperma tophore while that of utriculi breviores nourishes the sperms. These tubules open into the anterior part of the ejaculatory duct.
      The seminal vesicles are present on the ventral surface of the ejaculatory duct. These sacs store the sperms in the form of bundles called spermatophores. The ejaculatory duct is a musculer tube that extends posteriorly and open into the gonopore/ the male genital pore on the ventral phallomere.

     The duct of phallic/ conglobate gland also opens near the gonopore. Its function is still not known. Surrounding the male genital opening there are three chitinous and asymmetrical structures called phallic organs/ gonapophyses/ phallomeres which helps in copulation. These are the male external genitalia. The term phallow refers to penis. The left phallomere bears a pseudopenis and titillator.
 

2. Female Reproductive System: It has a pair
of ovaries a pair of oviducts, vagina, spermatheca, spermathecal papilla and colleterial glands.
i) Ovaries: A pair of large ovaries lies laterally in 2nd to 6th abdominal segments. They are light yellow in colour surrounded by fat bodies. Each ovary consists of 8 tubules called ovarian tubules/ovarioles. Each ovarioledu consists of a tapering anterior filament called germarium and a posterior wider vitellarium.
     The germanium contains various stages of developing ova and the vitellarium contains mature ova with yolk. The tapering ends of the ovarioles of each ovary unite to form a single thread which attaches to the dorsal body wall. The ovarioles at their posterior end unite to form a short wide oviduct. The oviducts unite to form a very short median vagina. The vertical opening of the vagina is called female genital pore. It opens into a large genital pouch on the 8th sternum. A spermotheca/ receptaculum seminis consisting of a left sac like and a right filamentous caecum is present in the 6th segment which opens by a median aperture on a small spermathecal papilla in the dorsal wall of the genital pouch on the 9th sternum. In a fertile female, the spermatheca contains spermatophores, received during copulation.
     A pair of branched colleterial glands is present behind the ovaries. These glands open in to the genital pouch separately, just above the spermathecal aperture. Secretion of the 2 collaterial glands forms a hard egg case called ootheca around the eggs.
 

     Genital/ brood pouch is formed by 7^th, 8^th and 9^th abdominal sterna. The sternum of the 7^th segment is boat shaped and forms the floor and side walls of the genital pouch. The sterna of the 8^th & 9^th segments, which are tucked into the 7^th segment, constitute the anterior wall and the roof of the genital pouch respectively. The genital pouch has 2 chambers the anterior gynatrium/ genital chamber and posterior vestibulum/ oothecal chamber.
     3 pairs of plate like chitinous structures called gonapophyses are present around the female genital aperture. These gonapophyses guide the ova into oothecal chamber acting as ovipositors these are the female external genitalia, which help in copulation also.

4 Marks Questions
 

1. What is summer stratification? Explain.
A: During summer in temperature lakes, the density of the surface water decreases because of increase in its temperature (21-25°C). This ‘upper more warm water layer’ of a lake is called epilimnion. Below the epilimnion there is a zone in which the temperature decreases at the rate of 1°C per meter in depth and it is called thermocline / metalimnion. The bottom layer is the hypolimnion where water is relatively cool. Stagnant and with low O₂ content (due to absence of photosynthetic activity).

      During autumn (also called fall), the epilimnion cools down and the surface water becomes heavy when the temperature is 4°C and sinks to the bottom of the lake. Overturns bring about ‘uniform temperature’ in lakes during that period. This circulation during the autumn is known as the fall/ autumn. The upper O₂ rich water reaches the hypolimnion and the nutrient rich bottom water comes to the surface. Thus there is uniform distribution of nutrients and O₂ in the lake.
 

2. What are the deleterious effects of depletion of ozone in the stratosphere?
A: The depletion of ozone is particularly marked over the Antarctic region. This has resulted in the formation of a large area of thinned ozone larger, commonly called as the ''Ozone hole''.
UV radiation with wavelengths shorter than that of UV-B, are almost completely absorbed by earth's atmosphere, provided that the ozone layer is intact. But UV-B damages DNA and may induce mutations. It causes ageing of skin, damage to skin cells and various types of skin cancers. In human eye, cornea absorbs UV-B radiation and a high dose of UV-B causes inflammation of cornea, called snow blindness, cataract etc. Such exposure permanently damage the cornea.
 

3. How do marine animals adopt to hypertonic sea water?
A: Sea water is high in salt content compared to that of the body fluids. So, the marine animals continuously tend to lose water from their bodies by exosmosis and face the problem of dehydration. To overcome the problem of water loss, marine fishes have glomegular kidneys with less number of nephrons. Such Kidneys minimize the loss of water through urine. To compensate water loss the marine fish drink more water and along with this water, salts are added to the body fluids and disturb the internal equilibrium. To maintain salt balance (salt homeostasis) in the body, they have salt secreting chloride cells in their gills. Marine birds like sea gulls and penguins eliminate salts in the form of salty heat drips through their nostrils. In turtles the ducts of chloride secreting glands open near the eyes. Some cartilaginous fishes retain urea and Tri Methyleamine Oxide (TMO) in their blood to keep the body heat isotonic to the sea water and avoid dehydration of the body due to exosmosis.

4. l Draw a labelled diagram of ommatidium?   (4M)

2 Marks Questions

1. Why is the head in cockroach called hypognathous?
A: The Cockroach head lies hanging almost at right angles to the body with the posterior wider part upwards and the mouth parts directed down wards.
 

2. What is intima?
A: They are an outer basement membrane, a middle one cell thick epthelium and an inner layer of cuticle called 'intima'
 

3. What is storage excretion?
A: Fat body is a lobed white structure. Urate cells present in these bodies are associated with excretion in a way. These cells absorb and store uric acid throughout the life. This is called storage excretion.