Biology Questions

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1.What organ is characteristic of mollusks?
The muscular foot is the most characteristic feature admittedly many have shells i.e. bivalve mollusks and gastropods but not the cephalopods i.e. squid and octopus. All have a mantle, which in the case of the first two groups secrete the shell. And all have a visceral mass.
But the main characteristic is the muscular foot.
Molluscs are a very diverse group of animals, and include snails, squid, octopi, calms and oysters. Therefore, they contain members that are very mobile and predatory, and others, which are sessile and filter feeders. However, all have three main body groups. These are the visceral mass, which contains the organs, the foot, which is a large muscle, and the mantle, an outer covering. The mantle is also responsible for secreting the shell for those molluscs, which have one.
There are seven classes to the molluscs, most of which are exemplified by observing the anatomy of a bivalve, but the cephalopods are a very unique class, and must be considered separately.

http://www.es.ucl.ac.uk/schools/Glossary/molluscs.htm
http://www.austmus.gov.au/invertebrates/mal/index.htm
http://www.earthlife.net/inverts/mollusca.html

2. What is the chief advantage that the eye of a dragonfly has over the eye of a hawk?
Insect eyes are made up of composite lenses and as such are fantastic at detecting movement, not only this but in comparison to the hawks eyes they are set in a position on the head that gives them a wide field of vision.
The ability to see polarized light is another interesting concept as this is thought to be essential to explain the extraordinary navigational ability of insects
http://news.bbc.co.uk/1/hi/sci/tech/4946452.stm
http://polarization.com/eyes/eyes.html

http://entomology.unl.edu/ent801/vision.html
http://www.branta.connectfree.co.uk/dragonfly.htm
http://www.greenworldtrust.org.uk/

3.Although amphibians were the first animals to move onto dry land, they were still dependent on water for reproduction and lor respiration. What evolutionary adaptations allowed reptiles to become the first "true" land vertebrates?
The evolutionary adaptations are:
The development of shelled eggs
Internal fertilization
Behavioural adaptations include some parental care
Developed efficient lungs and ...