- Photosynthesis makes food for the plant
- A leaf performs photosynthesis / gas exchange
- Hence, a leaf makes food for the plant by performing photosynthesis

- A leaf makes food for the plant by performing photosynthesis
- Providing food is a kind of specific life process
- So, a leaf performs a specific life process of making food for the plants

- A leaf performs a specific life process of making food for the plants
- Organs perform specific life process in organisms
- So, a leaf in a plant is performing like an organ in organisms

Therefore, a leaf in a plant is performing like an organ in organisms
Question: Plants have cells, tissues, organs, and systems that allow them to function as complete organisms. Which parts of a plant function as an organ?
Context: - Photosynthesis makes food for the plant 
- Organs perform specific life process in organisms 
- Providing food is a kind of specific life process 
- A leaf performs photosynthesis / gas exchange