iGCSE Biology (Triple) Edexcel

Characteristics of Living Organisms

• All living organisms can perform seven fundamental actions, summarised by the mnemonic MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition.
• Movement relates to the ability of an organism to change its position. This could be the entire organism, like a cheetah running, or just a part of it, such as the contraction of human muscles.
• Respiration is the process through which organisms convert food into energy. In humans and other animals, this primarily involves inhaling oxygen and exhaling carbon dioxide.
• Sensitivity or response to stimuli is an essential characteristic of living organisms. This might involve a plant bending towards sunlight or a human withdrawing a hand from a hot stove.
• Growth is a part of life for all organisms and occurs either through producing more cells (in multi-cellular organisms like humans) or by increasing cell size.
• Reproduction is the process where organisms produce offspring, either sexually or asexually. This allows for the continuation of species.
• Excretion is the biological process where waste products are removed from an organism. Examples include the exhalation of carbon dioxide in humans and the removal of urea in urine.
• Nutrition refers to the intake of food and drink necessary for energy, growth, and repair. This is obtained in multiple ways in different organisms–through photosynthesis in plants and consuming other organisms in animals.
• Cells are the basic building blocks of all living things. They consist of several parts, including a cell membrane, cytoplasm, and a nucleus in eukaryotic cells.
• Organisms can be categorised into different groups based on their structure and characteristics. These are known as the five kingdoms: Monera (bacteria), Protista (single-celled organisms with a nucleus), Fungi, Plantae, and Animalia.
• Among organisms, there exists vast biodiversity, leading to classification systems to accurately categorise the various species.
• The binomial system of naming species is universally used and consists of the genus name (uppercase) and species name (lowercase), both of which are italicised.