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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Life Processes and Functions
All living organisms, from the tiniest bacteria to the largest blue whale, share certain characteristics that make them 'alive'. These characteristics are shown through the life processes they perform. Understanding these processes helps us determine what is living and what is not.
Key Definitions:
Scientists use the acronym MRS GREN to remember the seven processes that all living things carry out. Let's explore each one:
Living organisms can move parts of their body or their whole body. This movement may be obvious like animals running or swimming, or less noticeable like plants growing towards light.
Examples:
All living things release energy from food molecules. This process is called respiration. It's not the same as breathing, though breathing is part of respiration in many animals.
Types:
Living organisms can detect and respond to changes in their environment. This ability is crucial for survival.
Examples:
Living things increase in size and complexity throughout their lives. Growth happens when cells divide and get bigger.
Key points:
Living organisms can make more of their own kind. This ensures the survival of the species even if individuals die.
Types:
Living things remove waste products made inside their bodies. These wastes could be harmful if they build up.
Examples:
Living organisms take in and use food substances to provide energy, for growth and to repair damaged cells.
Types:
These seven processes don't work in isolation. They're interconnected and support each other to maintain life:
Nutrition provides materials that respiration converts to energy. This energy powers movement, growth and other processes.
Respiration produces waste (CO₂) that must be removed through excretion. Nutrition creates waste products that also need excreting.
Sensitivity helps organisms find food (nutrition), avoid dangers and find mates (reproduction).
Sometimes it can be tricky to determine if something is alive. For example, seeds and dormant bacteria may not seem to be performing all life processes, but they have the potential to do so under the right conditions.
Let's compare how we can tell if something is living by checking for life processes:
| Object | Movement | Respiration | Sensitivity | Growth | Reproduction | Excretion | Nutrition | Living? |
|---|---|---|---|---|---|---|---|---|
| Dog | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | Yes |
| Tree | ✓ (slow) | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | Yes |
| Robot toy | ✓ | ✗ | ✓ (sensors) | ✗ | ✗ | ✗ | ✗ (uses battery) | No |
| Fire | ✓ | ✗ | ✗ | ✓ (spreads) | ✗ | ✓ (smoke) | ✓ (fuel) | No |
As you can see, only living things perform all seven life processes. Non-living things might show some characteristics that look similar to life processes, but they don't perform all of them.
Tardigrades (water bears) are microscopic animals that can enter a state called cryptobiosis when conditions are harsh. In this state:
This raises an interesting question: are they living when in this state? Scientists consider them alive because they maintain the potential to resume all life processes when conditions improve.
While all living things perform the same seven life processes, they may do so in different ways:
These different adaptations help organisms survive in their specific environments while still performing all the necessary life processes.
Understanding the seven life processes helps us:
Remember MRS GREN to identify the seven processes that make something alive: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition. If something performs all these functions (or has the potential to), it's alive!
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