Name two egg-laying mammals.

Hard calcium carbonate structures are used as a skeleton by

Name an organism sensitive to $SO_{2}$ in air.

On the basis of the following features,identify the group and give one example of each:
$(i)$ Presence of notochord at some stage of life.
$(ii)$ Unicellular,microscopic,and eukaryotic.
$(iii)$ Seeds are enclosed in fruits.

$A$ plant specimen was found without differentiated roots.
$(a)$ Which plant structure helps in attaching this plant to the substratum?
$(b)$ To which group would you classify this plant?
$(c)$ Which plant could it be?

Write the names of a few thallophytes. Draw a labelled diagram of Spirogyra.