Question

1. Briefly describe how respiration occurs in sharks. What structure, which allows a bony fish to respire without moving, do they lack ?

2. Mushrooms undergo the fusion of nuclei (karyogamy) in specialized regions of the fruiting body called _________________.

Answer 1

Q1) In sharks gills help in the process of respiration, there are 5-7 pairs of gill arches in them, each having a gill slit. In sharks operculum is absent which covers the gills acting as a lid, in case of bony fishes they are present. In case of sharks they have spiracles found behind the eye, which helps them in taking water inside.

Sharks use gill slits to oxygenate their blood, when they move forward water enters inside their mouth and crosses over their gills, this is called “Ram ventilation”. From the mouth, water enters the gill chambers and goes out by the gill slits. When shark is resting, it pumps water over it’s gills, gill rackers are present perpendicular to the gill arches, they support the secondary bars which direct the water flow. Sharks have low blood pressure, so continuous swimming helps in muscular contractions required for circulation of blood.

Deoxygenated blood goes to the S-shaped two chambered heart. Blood gets pumped from ventral aorta to afferent brachial arteries, when blood reaches gills they get oxygenated by water, then blood goes to dorsal aorta and other parts of body by efferent brachial artery. When blood gets deoxygenated they return by post cardinal vein into posterior cardinal sinus and then to ventricle of heart.

Depending on the speed of movement of shark in water this process becomes more efficient. In sharks the direction of blood flow is always opposite to the flow of water or water current. It helps in passing of maximum oxygen from water to blood this process is called “counter current flow”. Ample amount of oxygen in blood of shark helps it in it’s swift movement and in performing other works, Movement also helps in breathing and in buoyancy or floating of it.

Bony fish have a swim bladder which helps them to attend neutral buoyancy by exchanging gases with the blood vessels. But in case of Sharks it is absent, the lighter cartilaginous skeleton, hydrodynamic body plan and the low density oils in their large livers helps them in floating.

Q2) Mushroom undergoes the fusion of nuclei (karyogamy) in specialized regions of the fruiting body called _______?

Answer- Basidium is the place where karyogamy takes place.

Explanation- In mushrooms there is a long dikaryon stage before karyogamy, in basidiomycetes the sexual organs are absent, dikaryon is the mycelium which produces basidiocarp. The terminal cells develop into basidia or basidium where they undergoes karyogamy to form zygote.