Characteristics of living organisms

Movement: an action by an organism or part of organism causing a change of position, place or aspect

Respiration: the chemical reactions that break down nutrient molecules in living cells to release energy

Sensitivity: the ability to detect or sense changes in the environment (stimuli) and to make responses

Growth: a permanent increase in size and dry mass by an increase in cell number or cell size or both

Reproduction: the process that make more of the same kind of organism

Excretion: removal from organisms of toxic materials, the waste products of metabolism (chemical reactions in cells including respiration) and substances in excess of requirements

Nutrition: taking in of nutrients which are organic substances and mineral ions, containing raw materials or energy for growth and tissue repair, absorbing and assimilating them

Key definitions

  • Movement is an action by organism causing a change of position or place
  • Respiration describes the chemical reactions in cells that break down nutrient molecules and release energy
  • Sensitivity is the ability to detect and respond to changes in the environment
  • Growth is a permanent increase in size
  • Reproduction is the processes that make more of the same kind of organisms. Single-celled organisms and bacteria may simply keep dividing into two Multicellular plants and animals may reproduce sexually or asexually
  • Excretion is the removal from organisms of toxic materials and substances in excess of requirements
  • Nutrition is the taking in of materials for energy growth and development

The 7 characteristics that distinguish living things from non-living objects are: Nutrition, Excretion, Respiration, Sensitivity, Reproduction, Growth and Movement.

7 characteristics of living organisms

1.NutritionTake in

Absorb

Assimilate


Nutrients
Organic substances
Mineral ions
containing raw materials/energy
for: Growth + Tissue repair
Plants
make their
own food
Photo-
synthesis
H2O CO2 Light
2.ExcretionRemovalToxic Materials
Waste Products
of metabolism
Substance in Excess

By chemical reactions
in cells (respiration….)
3.RespirationBreakdownFood in cellsRelease Energy
4.SensitivitySense
Respond
Changes in the environment (Stimuli)
5.ReproductionProduceOffspringPrevent extinction of species
6.GrowthIncreaseSize
Mass
of an organism
By increasing
cell number
and/or cell size
7.MovementChangePosition
or Place
of an organism
or part of an organism
Ex: Parts of plants move very slowly to obtain more light for photosynthesis

Common misconceptions

  • Don’t confuse respiration with breathing.
  • Don’t use faeces or defecation as an example of excretion (faeces is indigested food-it has not been formed through metabolic processes).
  • Some non-living things, such as a car, may appear to show some of the characteristics – but not all of them.

Key definitions

If you are studying the extended syllabus you need to learn more detailed definitions of some of the characteristics of living things.

  • Movement is an action by an organism or part of an organism causing a change of position or place. Most single-celled creatures and animals move about as a whole. Fungi and plants may make movements with parts of their bodies.
  • Respiration describes the chemical reactions in cells that break down nutrient molecules and release energy for metabolism. Most organism need oxygen for this.
  • Sensitivity is the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses.
  • Growth is a permanent increase in size and dry mass by an increase in cell number or cell size or both. Even bacteria and single-celled creatures show an increase in size. Multicellular organisms increase the numbers of cells in their bodies, become more complicated and change their shape as well as increasing in size.
  • Excretion is the removal from organisms of the waste products of metabolism (chemical reactions in cells including respiration), toxic materials and substances in excess of requirements. Respiration and other chemical changes in the cells produce waste products such as carbon dioxide. Living organisms expel these substances from their bodies in various ways.
  • Nutrition is the taking in of materials for energy, growth and development. Plants require, light, carbon dioxide, water and ions. Animals need organic compounds and ions and usually need water. Organisms can take in the materials they need as as solid food, as animals do, or they can digest them first and then absorb them like fungi do, or they can build them up for themselves, like plants do. Animals, using ready-made organic molecules as their food source, are called heterotrophs and form the consumer levels of food chains. Photosynthesis plants are called autotrophs and are usually the first organisms in food chains.

Characteristics of living organisms

You know that a horse is alive, but a steel girder is not. However, it is not always so obvious whether something is alive or not – is a dried-out seed or a virus particle living or non-living ? To try to answer questions like this, biologists use a list of characteristics that living organisms show.

Living organisms:

  • Respire
  • Show irritability (sensitivity to their environment) and movement
  • Nourish themselves
  • Grow and develop
  • Excrete
  • Reproduce

The coming pages gives more details of the characteristics of life as well as the characteristics in the ‘ringer’ list, living things have a complex organisation that is not found in the non-living world. A snowflake or a crystal of quartz is an organised collection of identical molecules, but even the simplest living cell contains many different complex substances arranged in very specific structures.

Living things also show variations – the offspring are often different from one another and from their parents. This is important in adaptation to the environment and in the process of evolution.

How the characteristics of life depend on each other

Each of the characteristics of life is linked to the others – for example, organisms can only grow if they are nourished. As they take nourishment from their environment, they may also produce waste materials which they must then excrete. To respond to the environment they must organise their cells and tissues to carry out actions. Because of the random nature of reproduction, they are likely to show variation from generation to generation.

Depending on energy

The organisation in living things and their ability to carry out their life processes depends on a supply of energy. Many biologists today define life as a set of processes that result from the organisation of matter and which depend on the expenditure of energy.

In this chapter we shall see:

  • how energy is liberated from food molecules and trapped in a usable form
  • how molecules are organised into the structure of living organisms
  • how living organisms use energy to drive their life processes

Respiration: the chemical reactions – that break down nutrient molecules in living cells to release energy. The form of respiration that releases the most energy uses oxygen. Many organisms have gaseous exchange systems that supply their cells with oxygen from their environment.

Irritability (or sensitivity): the – ability to detect changes in the environment (i.e. stimuli) and to respond to them. These responses often involve movement (an action by an organism or part of an organism causing a change of position or place).

Nutrition: the taking in of nutrients – (food) which are organic molecules and mineral ions, providing raw materials or energy for growth, tissue repair and reproduction. Plants make their foods using the process of photosynthesis, whilst animals obtain their foods ‘ready-made’ by eating them.

Growth and development: the – processes by which an organism changes in size and in form. For example, as a young animal increases in size (as it grows), the relative sizes of its body parts change (it develops). Growth is a permanent increase in size and dry mass, and results from an increase in cell number or cell size or both.

Excretion: removal from organisms – of toxic materials, the waste products of metabolism and substances in excess of requirements.

Reproduction: the processes that make more of the same kind of organisms – new individuals. An organism may simply split into two or reproduction may be a more complex process involving fertilisation. Reproduction makes new organisms of the same species as the parents. This depends on a set of chemical plans (the genetic information) contained within each living organism.