How many types of elements together make up the xylem tissue? Name them.

How many types of elements together make xylem tissue? Name them.

How many types of Plant tissues are ?

(a) How many types of blood vessels are there in the human body ? Name them (b) Why does the heart need valves ?

How many types of crystal systems are there? Name them.

How many types of ecological pyramids are there in practice? Name them.