Biologus

Any time the class can be started if the students are prepared

The biological process by which new individual organisms are produced from the older ones is called Reproduction. Generally, two forms of reproduction i.e. asexual (vegetative) and sexual (gametic) are known. In asexual reproduction, an organism can reproduce without the involvement of another organism while in sexual reproduction an offspring is produced from a pre existing  organism only when another organism is involved.  

A chemical substance may well be defined as “any material with a definite chemical composition” which is unique to itself in terms of atomic structure and reactivity. It can either be a pure chemical element or a pure chemical compound. A chemical compound is a chemical substance that is composed of a particular set of atoms or ions. Two or more elements ( pure) combined into one substance through a chemical reaction form a chemical compound (often called as substance). All compounds are substances, but not all substances are compounds.

Poriferans are animals that have numerous pores (i.e., pori) on their body. Generally we know them as Sponges. They may be either  marine or freshwater animals. They have a body fixed witha a substratum like rock, wood etc. Examples- Sycon, Glass-rope sponge, Hexactenellida etc . Food enters through numerous body pores (ostia) and  undigested matterexits through the single big axial pore (osculum)

Coelenterates are animals which have a body cavity as their digestive system (coel- body cavity or coelom; enteron- gut). These animals have numerous cnidoblast cells (spine cells) on their body. These animals are also called Cnidarians (cnidi-spines or thorns). Examples- Hydra, Obelia, Aurelia etc. Food enters through mouth (also called Hypostome) and undigested matter exits through it also.