Ecosystems — BIOLOGY STD 12 Science — Question

Differentiate between the two cells enclosed in a mature male gametophyte of an angiosperm.

In what form is tobacco used? Describe the side effects caused by this. ###Smoking paves the way for the consumption of strong drugs. What does this mean? Explain.

Which property of DNA double helix led Watson and Crick to hypothesis semiconservative mode of DNA replication? Explain

Explain how the inflow of large amount nutrients like phosphates and nitrates into the water body drastically affect the aquatic life there. Name the phenomenon responsible.
OR
'Fish mortality increases with the influx of nutrients in a freshwater body.' Write two reasons. How will the influx of nutrients affect the BOD level of this water body?

OR
How is it that the mortality rate of fish increases downstream from the point of sewage discharge into a water body? Explain.

What is self-incompatibility?

How can you say the lobefin fish were the ancestors of amphibian?

Explain mechanism of sex determination in birds.

Draw well labelled diagram of T.S. of Testis.

Some organisms suspend their metabolic activities to survive in unfavourable conditions. Explain with the help of any four examples.

List the specific symptoms of amoebiasis. Name the causative organism.