Cambridge IGCSE Biology

## Characteristics of living organisms Every living organism carries out seven processes, and something that does not do all of them is not alive in the ordinary sense. - **Movement** is an action by an organism, or by part of it, that changes its position or place. A plant does not usually change place, but its shoots and leaves move as they grow towards light. - **Respiration** is the set of reactions inside cells that split nutrient molecules apart and release the energy that metabolism needs. - **Sensitivity** is the ability to detect changes in the internal or external environment and respond to them. - **Growth** is a permanent increase in size and dry mass. Dry mass is used because fresh mass changes with the water content, which can go up and down without any real growth. - **Reproduction** is the set of processes that make more organisms of the same kind. - **Excretion** is the removal of the waste products of metabolism and of substances present in excess of what the body needs. - **Nutrition** is taking in materials that provide energy, growth and development. ## Species and naming Organisms are sorted into groups according to the features they share. The basic group is the **species**, a group of organisms that can reproduce with each other to produce fertile offspring. A horse and a donkey can breed, but their offspring (a mule) is sterile, so they are separate species. Scientists everywhere use the **binomial system**, which gives each species a two-part Latin…