Metabolism – All biochemical reactions of processes taking place in the living organisms have two interwoven aspects, viz.
(i)Anabolism – Synthesis of complex organic molecules from simple molecules by the living organisms. It is the constructive or synthesis phase of metabolism, e.g. the formation of proteins from amino acids.
(ii)Catabolism (also Katabolism) – Break down of complex molecules into simpler molecules to release energy, i.e. breaking down of hydrocarbons into the simpler forms with the release of energy. Metabolism takes place in a controlled manner at body temperature. Enzymes act as bio-catalysts for the process. The energy released in such reactions is stored and used for growth and development. The elimination of waste products generated in the process is called excretion.
Respiration – A term with two distinct meanings, viz. breathing and the transport of oxygen and carbon dioxide to and from the cells known as external respiration. Internal respiration or cell respiration occurs within the cell and constitutes the chemical reactions from which an organism derives energy. Internal respiration using oxygen is termed aerobic while anaerobic respiration may occur in the absence of oxygen. Both plants and animal respire.
Animals need oxygen to release the energy present in their food and get rid of waste, i.e. carbon dioxide.
Skin breathing – carried out through the skin bi slow-moving animals.
Gills breathing – Fish possess gills which absorb oxygen from water flowing over them taken in through the mouth.
Tracheal breathing – system developed by insects which include network of tubes which take oxygen to all parts of the body.
Lung breathing – acquired by evolved animals.
Fertilisation – It is the union of two gametes or sex cells to produce a zygote or fertilised egg which grows into a new off-spring.
External and internal fertilisation
Fertilisation in frogs and toads is external, as it is in fishes, most water creatures and lower plants (e.g. Ferns). By this we mean, the male gamete swims across a watery surface to fertilise the female gamete or egg. The fertilised egg cell is then able to develop to an individual creature.
Fertilisation in mammals, birds, reptiles and insects is internal. That is to say, the sperms are shed directly into the female’s body where they fertilise the egg before these are laid as in birds and reptiles whereas in mammals the cell develops into an embryo within the female body.
Fertilisation in flowering plants – In higher plants it is a complex process involving pollen grains which are transferred to the egg-bearing organism by wind or insects. The process is called pollination in plants. On falling on a stigma each pollen grain of the right kind germinates and sends a pollen-tube containing a male reproductive cell down through the style and into an ovule where the male cell fuses with an egg cell which can develop into an embryo plant.
Transpiration – Evaporation of water from the stem and leaves of plants. It serves the purpose of cooling the leaves on hot days and protects delicate leaf tissue from drying up. It draws water up from the roots towards the leaves which give out excess water into the atmosphere.