What is bilateral symmetry?

State reasons for the following:
$(a)$ Mammals have mammary glands.
$(b)$ Annelids have a true body cavity.
$(c)$ Fish possess gills.

Fungi are heterotrophic eukaryotic organisms and have a cell wall made of chitin. Name five cell organelles that are present in the fungal cell. Also,state two structural differences between a plant cell and a fungal cell. Which life form occurs due to the association of cells of fungi and algae?

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.

Why are bats not placed in birds?

Justify giving one reason: crocodiles have a four-chambered heart,but are still classified as reptiles.