How Does Energy Enter and Move Through Living Systems?
- Every organism needs a constant supply of energy to survive.
- Most usable biological energy comes from the sun.
- Plants capture sunlight and convert it into chemical energy stored in glucose.
- Because plants start the movement of energy into living systems, they are known as producers.
- Without producers capturing this energy, ecosystems would not have a long-term energy supply.
Definition
Chemical energy
Energy stored inside the bonds of molecules such as glucose. Organisms release this energy during respiration.
Definition
Producer
An organism that makes its own food using an external energy source, usually sunlight.
How Do Plants Capture and Store Energy?
- Plants absorb light through chlorophyll in their leaves.
- They convert this light energy into chemical energy by making glucose.
- The energy stored in glucose becomes the starting point for all energy transfer in ecosystems.
- Plants use some of this energy for growth, reproduction, and repair.
Note
More on this process in the "photosynthesis" sub-topic 8 articles down.
Why Is Stored Chemical Energy Important?
- Chemical energy in glucose is stable, meaning it does not disappear immediately like sunlight.
- It is transportable, allowing plants to move energy to different parts of the organism.
- Other organisms can access this energy when they eat plant material.
- This makes plant biomass the main energy source that supports consumers.
Definition
Biomass
Living material that contains stored chemical energy.
How Does Energy Move Beyond Plants?
- Energy transfers when one organism consumes another.
- The chemical energy stored in plant biomass moves into the consumer.
- The consumer uses some of this energy for movement, growth, repair, and maintaining body conditions.
- Only a portion becomes stored in the consumer’s own biomass.
- This partial transfer continues each time one organism feeds on another.
Example
- Energy enters a grass blade from sunlight.
- That energy becomes available to any organism that eats the grass.
Why Does Less Energy Become Available at Each Step?
- Although the detailed structure of feeding relationships is covered later under "Food chains and webs:, the key idea here is simple:
- Organisms must use some energy to stay alive.
- Movement, temperature control, repair, and basic cell activity all require energy.
- Energy used this way does not remain stored in biomass.
- As a result, only part of the energy eaten by an organism becomes available to whatever eats it next.
Definition
Consumer
An organism that obtains energy by eating other organisms.
Analogy
- Energy transfer works like handing over a container that leaks slightly.
- Each time it changes hands, a bit is lost.
Why Must Energy Continuously Enter Ecosystems?
- Energy can't cycle in ecosystems.
- Once energy is released as heat, living organisms can't use it again.
- Ecosystems therefore require a constant input of new energy.
- Sunlight provides this input and keeps the system functioning over time.
Definition
Conservation of energy
Energy cannot be created or destroyed. It can only be converted from one form to another.
Self review
- Why do ecosystems rely on sunlight as their long-term energy source
- How do plants convert sunlight into a form that other organisms can use
- Why does each energy transfer pass on only part of the energy received
- Why must new energy continuously enter ecosystems rather than cycling indefinitely?
