Mystery object 4 was a leaf.
Find out about plant pigments and photosynthesis below.
Generally plants make most of their food in their leaves. They do this by photosynthesis and it happens in chloroplasts. Chloroplasts contain a green substance (a plant pigment) called chlorophyll. It is the chlorophyll that absorbs the light energy that is needed in photosynthesis.
The word equation below summarises what happens in photosynthesis.
carbon dioxide + water ----> sugar + oxygen
note- the reaction needs light energy to take place.
There are other plant pigments (accessory pigments) that are used by some plants in photosynthesis such as the carotenoids are usually red, orange, or yellow and the phycobilins.