Name the pioneer species on a bare rock. How do they help in establishing the next type of vegetation? Mention the type of climax community that will ultimately get established.

Lichens are called pioneer colonisers of bare rock. How can they help in to formation of soil ?

The gradual and predictable change in the species composition of a given area is called ecological succession. What do you understand with the pioneer and climax community in this context?

Define ecological succession. Mention the two types of succession in plants based on the nature of the habitat. What is a pioneer species?

(i) Bee sting leaves a chemical substances that causes pain and irrigation. Name the chemical substance. Identify the type of substance which may give relief on the sting area when applied on it. (ii) Mention the pH value below which tooth decay begins. How this fall below this value? Explain the ill effect of the acidic medium in the mouth. How can this be prevented?

Name any two factors on which the type of pioneer species if plant develops insecondary succession.

Describe how sodium and chlorine form sodium chloride. Name the type of bonding shown in the structure (At no. : Na=11, Cl=17) OR Show the formation of Nacl with the help of electron dot structure.