Living things display certain characteristics that may be absent from material objects. MRS GREN is an acronym often used to help remember all the necessary features of living organisms: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition.


The first letter of MRS GREN stands for movement. Although some organisms are pretty much immobile they will always have some level of self-powered movement, be it their entire body or particular body parts. Movement is evolutionarily important for organisms because it improves the chances of catching food or avoiding capture for both predator and prey. Organisms that aren’t able to move freely will usually have strong defences against predation or prolific reproduction.


MRS GREN - SensitivityRespiration is the conversion of energy from carbohydrates and fats into energy that can be used by cells. In multi-cellular organisms, respiration is built around the breakdown of sugars with the use of oxygen. This produces carbon dioxide as a by-product. Some microorganisms, in areas where there is not very much oxygen, use other molecules, such as nitrates and iron, to help break down sugars.


Sensitivity refers to the way organisms respond to their environment. All organisms are able to sense changes in their environment and will respond accordingly. For example, barnacles will close their shells during low tide to prevent themselves from drying out, squid release ink when they feel threatened, and deer run away when they are startled by a noise.


MRS GREN is sometimes known as MRS C GREN to recognize the importance of how living things control their internal environment. All living things have an internal environment inside their body and inside their cells. This internal environment needs to be maintained within certain conditions. Control refers to the way organisms are able to preserve the environment inside of their cells and organs to a certain set of conditions. Maintaining the internal environment of an organism is known as homeostasis.


Growth is an irreversible change in mass. It is possible because respiration provides excess energy for organisms to use to grow. Excess energy can be used for the production of new cells and tissue which inevitably leads to the growth of an individual.


MRS GREN - ReproductionReproduction is the creation of a living thing from an existing organism. The simplest form of reproduction is the division of one cell into two. For large, multi-cellular organisms reproduction is more complicated than a single division of a cell.
Reproduction can occur sexually or asexually. Sexual reproduction requires two organisms. Asexual reproduction is where one organism produces a new organism entirely by themselves. In sexual reproduction, the genetic material from each parent is split in half and combined with the genetic material of the second parent. This creates a unique individual with a mix of genes from two parents.


All organisms produce wastes that need to be removed. Normal functions in cells and tissues of organisms produce waste such as urine and dead cells. If waste products stay inside an organism they can become toxic. All organisms, therefore, have methods for removing waste products from their body. Excretion is the term used to define the removal of waste products from an organism.


Nutrition is the final component of MRS GREN. In order for organisms to survive they require food for energy and nutrients. Energy and nutrients are essential for growth, survival and reproduction. Many living things, such as animals, acquire nutrients by eating other organisms. Other organisms, such as plants, get food and nutrients from their environment. Plants use energy from the sun to convert carbon dioxide in the atmosphere into sugars and their roots absorb water and nutrients from the soil.

Last edited: 5 October 2020

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