Structural Organisation in Animals Test - 93

Due to the closed circulatory system, blood is confined to the heart and blood vessels. Contractions keep circulating in one direction. Smaller blood vessels supply the gut, nerve cord, and the body wall. Blood glands are present on the 4th,5th and 6th segments. They produce blood cells and haemoglobin which is dissolved in blood plasma. Blood cells are phagocytic in nature. 

A. Correct option is (C)
B. Explanation for the correct option

• In cockroach, the flow of haemolymph is heart → head→ perivisceral sinus → pericardial sinus → ostia → heart.
• The heart in a cockroach is neurogenic. Haemocoel (body cavity) is a perivisceral cavity filled with colourless blood (hemolymph).
• When alary muscle contract the dorsal diaphragm became flat and pericardial increases.
• Blood from the perivisceral sinus enter into pericardial sinus through a pore of dorsal diaphragm become dome-shaped and blood from pericardial sinus is forced into the heart through valvular ostia then the heart and aorta contract peristaltically.
• Blood flow from the posterior end to the anterior end in heart and flow into head sinus through the aorta. 

Cockroaches use their mandibles, or jaws, to bite and chew their food. The foregut opens into a crop, where undigested food is temporarily stored. From the crop, the food enters the gizzard. The gizzard is a muscular stomach with sharp teeth-like structures that grinds the food into smaller pieces.

Integumentary nephridia: Integumentary nephridia are smallest nephridia of Pheretima. So they are also called as micro nephridia. They lie scattered on the entire internal surface of the body wall except in the first two segments. They are V shaped structures and hang out in the coelom. The number ranges from 200-250 in each segment, except in the clitellar segments. In the clitellar segments they are ten times more than the usual number.

1. Each myofibril has alternate light and dark bands due to the presence of contractile proteins actin and myosin.
2. Z line is present in the center of each I band but not A band. So, this option is incorrect.
3. As shown in the diagram, A and I bands are arranged alternatively throughout the length of the myofibril.
4. The functional unit of muscle contraction is the sarcomere which shortens and lengthens during muscle contraction and relaxation. 
   
5. The central part of the thick filament which is not overlapped by the thin filament is H zone and not the M line (Refer Diagram).

So, the correct option is '1, 3 and 4 alone are correct'.

The wall of the tracheae is made of three layers. They are an outer basement membrane, a middle one cell thick epithelium and an inner layer of cuticle called intima. The intima is produced into spiral thickenings called taenidia. The taenidia keep the tracheae always open and prevent it from collapsing.

• This is an example of a simple reflex that is involved with the spinal cord as this action gets completed without the information reaching the brain. So, there is no involvement of the brain. 
• When the leg of the frog is pinched, the stimulus is received by receptors on the skin that set up a sensory impulse. 
• This impulse is carried to the spinal cord that transforms the sensory impulse into a motor impulse. 
• This impulse is then transmitted to the leg muscles. 
• Simple reflex is the spontaneous automatic mechanical response to a stimulus without animals' will. 

So, the correct option is (D).