Biology science projects can include vegetation as the subject of the study. Plant flower or vegetable seeds under a variety of controlled conditions and measure growth rate, for example. Another project could be what is called the "Double Color Flower" study. Split a white flower stem in half and put one end of the stem in a glass of plain water. Put the other half of the stem into a glass of water with red food coloring. The results are almost immediate as you see that one half of the flower will turn red while the other half remains white.
Using ants as a subject could steer students toward any number of scenarios, including the eating preference of ants. For example, do ants prefer sugar or aspartame? Over a predetermined period of time, offer ants two sources of water: one with sugar and one with aspartame and record results. Students might substitute food for water and record the results visually or with a camera.
Caterpillar larvae may be purchased, or perhaps in your area it is abundant enough that you may carefully remove a leaf and place it in a container to use as a project subject. An example experiment would require two sets of larvae in two separate containers, which should be kept in different environments that will affect caterpillar growth, such as warmth, direct sunlight and so forth. Have students record the parameters and the difference in growth between the two subjects.
Having access to neighbors' pets could help students do a study on overweight pets. Or solicit help from a local veterinary clinic for additional pets to add to your classroom work. Students will need to record the pets' weight, eating habits and levels of physical activity.