Animals have to eat plants or other animals to get energy to live. Plants don’t have to eat to get energy. Instead, they capture energy from sunlight to make their own food, a process called photosynthesis. Generally, animals can’t photosynthesise, but in science there are exceptions to almost every rule. Sea slugs are definitely animals, but some species of sea slug can photosynthesise. Scientists had not been sure how much photosynthesis helps these sea slugs. But now, researchers report that sea slugs that can photosynthesise grow faster than those that can’t because of that extra food they make right inside their bodies.
Chloroplasts are the things inside plants that make them green, and they capture the energy from sunlight like solar panels. Certain species of sea slugs are green because they steal the chloroplasts or “solar panels” from the algae they eat. Sea slugs keep those chloroplasts in special storage areas in their body. This gives them a nice green camouflage. When we eat our green leafy vegetables, we don’t turn green because our digestive system breaks up the chloroplasts.
Besides making the sea slugs look like a leaf, the stored chloroplasts inside sea slugs can actually work like they do in leaves. Sea slugs can’t live by photosynthesis alone, but some scientists think it helps them survive when there is not a lot of food around. When there is plenty of food to eat, is there an advantage to photosynthesis? To answer this question, scientists fed the same species of sea slug two different algae diets. The sea slugs got working chloroplasts from one type of algae. From the other algae, the sea slugs could only get fragile chloroplasts that were damaged when they ate them.
The team learned that the slugs grew twice as fast when they had chloroplasts that could actually photosynthesise rather than the ones that were not working. Importantly, the sea slugs grew faster only when kept in light that they could use for photosynthesis, but not when kept in the dark. Too bad we couldn’t gain a little solar power from eating our green veggies.