(i) Antibiotics: The chemical substances which are produced by a micro¬organism, can stop growth of or kill another micro-organism. e.g., Pencillin. 

(ii) Antiseptics—These are chemical substances which destroy some bacteria and prevent the growth of others. Antiseptics are used locally in contact of body tissues because they are mild and are harmless to the tissues they work upon. Examples of antiseptics—Tincture, benzoic acid, boric acid, hydrogen peroxide, dettol and mercurochrome. 

(iii) Hormones: According to Selye (1948), “Hormones are the physiological organic compounds produced by certain cells for the sole purpose of directing theractivities to distant parts of the same origins.” A hormone is defined as “a chemical messenger secreted by an endocrine gland which reaches its destination by the blood stream and which has the power of influencing the activity of other distant target organs.” 

(iv) Diffusion: It is the process of movement of molecules of a substance (solid, liquid or gas) from the region of their higher concentration to the region of their lower concentration through the concentration gradient. 

Or 

Diffusion may be defined as the process of random movement of molecules of a substance from a region of higher concentration to a region of lower concentration. 

(v) Destarched plant: The plant which has no starch in the leaves and the leaf remains yellowish brown when the leaf is tested for photosynthesis with iodine solution