Human Reproduction — BIOLOGY STD 12 Science — Question

What are the periods in Palaeozoic era and name the plant group that appeared in each of them?

Define a climax community. How does a sere differ from a seral community?

In an aquarium two herbivorous species of fish are living together and feeding on phytoplanktons. As per the Gause’s Principle, one of the species is to be eliminated in due course of time, but both are surviving well in the aquarium. Give possible reasons.

Identify A, B, C, D, E and F in the table given below:

S. No.	Component-I	Component-II	Chemical linkage bonding the two components	Product
(i)	A	B	C	Nucleotide
(ii)	Nucleotide	D	E	Nucleotide
(iii)	Nucleotide	Nucleotide	F	Dinucleotide

How are the following used in biotechnology?

1. Plasmid DNA
2. Recognition sequence
3. Gel electrophoresis

1. Name the respective forms in which the malarial parasite gains entry into

1. Human body
2. Body of female Anopheles

2. Name the hosts where the sexual and the asexual reproductions of malarial parasite occur respectively.
3. Name the toxin responsible for the appearance of symptoms of malaria in humans. Why do these symptoms occur periodically?

Taking ABO blood group as an example, explain the phenomenon of multiple allele and co-dominance.

A student on a school trip started sneezing and wheezing soon after reaching the hill station for no explained reasons. But, on return to the plains the symptoms disappeared. What is such a response called? How does the body produce it?

Explain giving one example, how co-extinction is one of the cause of biodiversity loss? List the other three causes also.