Question

Jaws first occurred in which group of fishes?

ostracoderms

sharks

placoderms

ray-finned fishes

If a mollusk had a lung, where in the body would it be located?

		visceral mass
		mantle
		foot
		radula

Which characteristic allows reptiles to thrive in deserts?

		the larval form, which can go dormant when water is unavailable
		the large number of prey and a limited number of predators available in deserts
		a cartilaginous skeleton that provides needed flexibility for locomotion on sand
		keratin-infused scales that reduce water loss and dehydration

Answer 1

1. Jaws first occured in Placoderms

Placoderms were among the first jawed fish and their jaws evolved from the first of their gill arches. Placoderms were a class of fish, heavily armoured ,which first appeared during the Silurian about 430 million years ago.

2.If a mollusk had a lung in the body would it be located in Mantle.

The respiration in molluscs take place through gills which are called ctenidia. They absorb oxygen from water and transfer it to the blood stream. They also receive carbon dioxide from the blood and release it into the surrounding water. The gills are located in the water-filled mantle cavity.

The mantle is a special organ in molluscs which is in form of a soft tissue layer that is formed from folds of the dorsal body wall. It lies beneath the shell and has several critical functions.It contains gills used for respiration and water is pumped into the mantle cavity to allow the gills to absorb oxygen.

3. The characteristic allows reptiles to thrive in deserts is keratin infused scales that reduced water loss and dehydration.

The scaly and impervious skin of reptiles prevents the loss of water by decreasing the rate of evaporation.The faeces contain uric acid which which much less soluble in water allowing them to retain more liquids. Most desert reptiles extract the water they need from their food and some drink water from the dew.