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Living organisms (Mrs Gren)

There are seven things living organisms need to do to survive. The acronym MRS GREN can assist you with what these are. Let's explore this!

In this course, we look at understanding cells, what’s inside them and what they do.

Cells are the basic building blocks of all life forms including human tissue, plants, and even bacteria!
All living organisms are made up of cells. Let’s define a living organism:
An organism is an individual form of life that is capable of growing and reproducing, and has one or more cells. Animals, plants and bacterium are all organisms.

There are seven things that living organisms have to do to survive on earth. One way of remembering those seven things is by using the acronym MRS GREN.

Watch the short video above introducing MRS GREN, then come back here to read a fuller explanation below.


Movement All living things can move, even plants. For example organisms may: walk, blink, swallow, follow the sun and catch food.
Respiration All organisms use a process called cellular respiration, a complicated series of steps that converts the food eaten to produce energy for all life processes. In many organisms, oxygen is required to produce energy ATP (Adenosine triphosphate). All living organisms release energy from food at a cellular level.
Sensitivity All living organisms can detect and respond to environmental changes using their sensory receptors. Receptors can detect changes in temperature, pH, oxygen, and carbon dioxide levels.
Growth All living organisms can grow.
Reproduction All living things can make more living things of the same type (species). Reproduction can be sexual, where two individuals combine their genetic information (mating) to produce offspring that are different from one another and different from each parent. Asexual reproduction only needs one individual and does not require sexual activity, which is quicker but produces offspring that are identical clones of the adult.
Excretion All organisms remove the waste products of digestion and cellular respiration by excretion. Waste products include urea, water, solid organic matter, and carbon dioxide. Build up of these waste products can make an organism very ill. Most organisms have separate systems for removing the different types of waste, except birds who combine solid organic matter and uric acid in the same excrement.
Nutrition All living organisms ingest (eat) food and use it. Food provides organisms with the energy to build and repair cells and to power the body processes that keep the organism alive. Food also provides the nutrients, vitamins, minerals, fats, and water that organisms require to function correctly.

Let’s investigate different types of organisms next.

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The Basis of Life: Understanding Human Cells

Created by
FutureLearn - Learning For Life

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