- Green plants provide food for consumers by performing photosynthesis
- Green plants are a kind of producer
- So, green plants provide food for consumers

- Green plants provide food for consumers
- Food is a source of energy for animals / plants
- So, producers provide energy for consumers

- A consumer is a kind of living thing
- Living things all require energy for survival
- Therefore, all consumers require energy for survival

- All consumers require energy for survival
- If something requires something else then that something else is important to that something
- Therefore, energy is important to consumers

- Producers provide energy for consumers
- Energy is important to consumers
- Hence, producers are important to consumers because they provide energy to consumers

- Organisms are a part of an ecosystem
- A consumer is a kind of organism
- So, consumers are a part of an ecosystem

- Consumers are a part of an ecosystem
- If something is important to a part of a thing then that something is important to that whole thing
- Hence, if something is important to consumers then that something is important to an ecosystem

- Producers are important to consumers because they provide energy to consumers
- If something is important to consumers then that something is important to an ecosystem
- Therefore, producers are important to an ecosystem because they provide energy to consumers

Hence, producers are important to an ecosystem because they provide energy to consumers
Question
The primary reason that plants are important for an ecosystem is because they

Context
- Organisms are a part of an ecosystem 
- A consumer is a kind of organism 
- Food is a source of energy for animals / plants 
- If something is important to a part of a thing then that something is important to that whole thing 
- Green plants provide food for consumers by performing photosynthesis 
- A consumer is a kind of living thing 
- Living things all require energy for survival 
- Green plants are a kind of producer 
- If something requires something else then that something else is important to that something