INTRODUCTION

• Biology is the science of life forms and living processes.
• The living organisms interact with one another as well as with their physical and chemical environment.
• The term biology was introduced by G. R. Treviranus and Lamarck (1802).
• The living organisms occur almost in every habitat on earth.
• All living beings share certain unified and basic characteristics. These include organisation, energy utilization, regulation or homeostasis, growth, development, reproduction and adaptation.

LIFE

Living organisms show a great biodiversity and are classified into different kingdoms-Monera, Protista, Fungi, Plantae and Animalia. All of these share the following properties -

• They have definite organisation.
• They always have cellular nature so are either unicellular (e.g., Amoeba, Paramecium etc.) or multicellular (e.g., Hydra, man etc.).
• They show coordination between different parts of body to maintain homeostasis (constant internal environment) inside the body.
• They have the ability of movements and locomotion.
• They show metabolic functions in the presence of energy.
• They have the ability of growth and development.
• They have specific receptors (e.g., sense organs to receive external and internal stimuli) and specific effectors (e.g., muscles and glands to give specific response).
• They have regulatory mechanisms (e.g., nervous system and hormones in animals, and only hormones in plants) to maintain homeostasis inside the body.
• They show adaptations to their environment to increase their chances of survival.
• They show variations which help in speciation and evolution.
• They have capacity to reproduce for continuity of their race.
• They have definite life span (period from birth to death).
• They undergo ageing after adulthood and then natural death.