Tomato plants, like all plants, get their energy from sunlight through the process of photosynthesis. Here's how it works:

1. Sunlight: The plant's leaves contain a green pigment called chlorophyll. Chlorophyll absorbs sunlight, specifically the red and blue wavelengths.

2. Carbon Dioxide: The plant takes in carbon dioxide from the air through tiny pores on its leaves called stomata.

3. Water: The plant absorbs water and nutrients from the soil through its roots.

4. Photosynthesis: Inside the leaves, the plant uses the absorbed sunlight, carbon dioxide, and water to produce glucose (sugar). Glucose is the plant's primary source of energy.

5. Oxygen: As a byproduct of photosynthesis, the plant releases oxygen back into the atmosphere.

So, in simple terms, tomato plants use sunlight to convert carbon dioxide and water into glucose, which they use as energy to grow, produce fruit, and perform other essential functions.