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Sze201 Fundamentals Of Arthropod Biology Question Paper
Sze201 Fundamentals Of Arthropod Biology
Course:Fundamentals Of Arthropod Biology
Institution: University Of Nairobi question papers
Exam Year:2007
QUESTIONS
1. Show the morphological difference between the male reproductive system and the female reproductive system.
2. Meaning of spermatogenesis and oogenesis.
3. Write and describe in short the mating behaviour in the crayfish.
4. How many eggs does the female deposit annually and for how many years?
5. Explain the fertilization and hatching process.
6. How do crustaceans regenerate the lost parts?
7. What is the remarkable phenomenon in regeneration?
8. Meaning of Autotomy – write in short about autotomy.
9. How does locomotion affect walking and swimming behaviour?
10. Comment: the crayfish either in rest or in motion is in state of unstable equilibrium.
11. How many stimuli affecting the reaction of the crayfish?
MARKING SCHEME
1. Show the morphological difference between the male reproductive system and the female reproductive system.
MALE FEMALE
The male organs consist of vas deferens and testis The female organs consist of ovary and oviduct
The genital pore is located near the base of the 5th leg 3rd leg
2. Meaning of spermatogenesis and oogenesis.
Spermatogenesis- Formation of spermatozoa from primitive germ cells that have undergone two maturation divisions in the testis.
Oogenesis- formation of female gamete from primitive germ cells in the ovary.
3. Write and describe in short the mating behavior in the crayfish.
1st copulation- 4 months old: In first year of their life; September, October or November
2nd copulation- 17months old: End of 2nd summer
3rd copulation- end of 3rd summer
The male grabs female using cephalic appendage and turns her over to enable him t copulate in her. The sperm is transferred from male through vas deferens into the seminal receptacle of the female where they are stored during winter.
4. How many eggs does the female deposit annually and for how many years?
From 100 to over 600 greenish eggs are laid by a single female
5. Explain the fertilization and hatching process.
Fertilization: The female stores sperm forming a sperm plug. The eggs are fertilized on their way out over the opening of the seminal receptacle as they are penetrated by the spermatozoa. The fertilized eggs are then carefully attached to the swimmerets.
? Hatching: In hatching the egg capsule splits and the larva emerges head foremost. Soon the larva possesses strength enough to grasp the egg string with its claws. After about 18 hours the larva passes into a second stage through molting. In the second larval stage the young is supported immediately after casting off its covering by a thread extending from the new to the old telson. When the larva becomes strong enough, it grasps the old larval skin and the telson thread drops off. Duration of the second larval stage is almost six days. No telson thread is present after the molt, but the young is able at once to cling to the old cuticle. Within a week the third larvae become independent of the mother, from this time on they are growing rapidly and molting at least four more times during the first summer. The first winter no growth nor molts occur. There are 4-5 molts, the second summer, 3-4 in 3rd summer, and one or two in the fourth summer. The life of a single individual extends over a period of about three or more years.
6. How do crustaceans regenerate the lost parts?
The Crustaceans have the power of regenerating lost parts.
The second and third maxillipeds, the walking legs, the swimmerets and eyes have all been injured at various times and subsequently renewed the lost parts. The growth of regenerated tissue is more frequent and rapid in young individuals than in adults. The new structure is not always like that of the one removed. For example, when the annulus containing the sperm receptacle of an adult is extirpated, another is segmented, but, although this is as large as the adult, it is comparable in complexity to that of an early larval stage.
7. What is the remarkable phenomenon in regeneration? Heteromorphosis
A more remarkable phenomenon is the segmentation of an apparently functional (tactile) antennae like organ in place of a degenerate eye. In this case a nonfunctional organ which was replaced by a new part which differs from the part removed is termed heteromorphosis.
8. Meaning of Autotomy – write in short about autotomy.
Autotomy s the breakage of damaged limbs at predetermined breakage points during predation or injury.
If the chelae are injured, they are broken off by the crayfish at the breaking points. The other walking legs, if injured, may be thrown off at the free joint between the second and third segments. A new leg, as large as the one lost, develops from the end of the stump remaining. This breaking off of the legs at a definite point is known as autotomy.
The power of autotomy is of advantage to the crayfish, since the wound closes more quickly if the leg is lost at the breaking point.
9. How does locomotion affect walking and swimming behaviour?
Locomotion
? It is affected in two ways: walking and swimming.
? Crayfishes are able to walk in any direction, forward usually, also side wise, obliquely or backward.
? -In walking, the forth pair of legs are most effective and bear nearly all of the weight of the animal; the fifth pair serve as props and to push the body forward 2nd, 3rd pairs of legs are less efficient for walking.
? Swimming only when animal is frightened or shocked.
? In such a case the crayfish extends the abdomen, spreads out the uropods and telson and by sudden contractions of the bundles of flexor abdominal muscles, bends the abdomen and darts backwards.
? The swimming reaction is not voluntary but is almost reflex.
10. Comment: the crayfish either in rest or in motion is in state of unstable equilibrium.
The crayfish either at rest or in motion is in a state of unstable equilibrium, and must maintain its body in the normal position by its own efforts.
The force of gravity tend to turn the body over.
The statocysts are the organs of equilibration.
When placed on its back, the crayfish has difficulty in righting itself. Two methods of regaining its normal position are employed (1) raising itself on one side and allowing the body to tip over by the force of gravity. (2) contracting the flexor abdominal muscles which causes a quick backward flop, bringing the body right side up
11. How many stimuli affecting the reaction of the crayfish?
Reaction to stimuli
Contact: It has tactile receptors on all surface areas.
? Receptors are concentrated on extremities, ventral surface and mouth parts.
? The tactile hairs are plumed, and supplied by a single nerve.
Light: Light of various intensities cause the crayfish to retreat.
? Individuals prefer colored lights to white, having a special liking for red.
? Negative reaction to light plays an important role in the animal’s life, since they influence it to seek a dark place where it is concealed from its enemies.
Chemicals: the reaction to food are due in part to chemical use.
? All surfaces seem sensitive to chemicals.
? The anterior appendages are the most sensitive.
Habit formation: crayfishes are able to learn habits and to modify them. They learn by experience and modify behaviour depending upon their familiarity with the situation.
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