What is haemocoel?

Draw the diagram of $Spirogyra$ and label the following parts:
$(a)$ Cell wall $(b)$ Pyrenoid $(c)$ Nucleus $(d)$ Chloroplast.

Which among the following have an open circulatory system?
$(i)$ Arthropoda
$(ii)$ Mollusca
$(iii)$ Annelida
$(iv)$ Coelenterata

The branch of biology which deals with the principles and practice of classification of plants and animals is

Classify organisms of kingdom $Protista$ on the following basis and give an example of each:
$(a)$ Based on structure for locomotion.
$(b)$ Based on mode of nutrition.

Explain by giving three reasons,how the work done by earlier scientists with respect to classification is helpful to the present generation.