Final answer:
The heights of tomato plants in a normal distribution can be affected by genetic factors, controlled watering, environmental influences, and sunlight exposure, among other variables.
Step-by-step explanation:
The heights of tomato plants that were all planted on the same day and vary in a normal distribution could be influenced by a variety of factors. Some of these factors include genetic mutations, the amount of water the plants receive, environmental factors such as soil quality and pests, exposure to sunlight, and controlled variables like plant food. Experiments like Gary's aim to control certain factors, such as ensuring all plants are in the same size and type of pot, receive the same amount of water, and are planted in the same type of soil, to test the effects of specific variables like sunlight exposure. However, even with these controls, there can be unaccounted-for variables such as individual plant variation, soil temperature differences, water loss due to evaporation, and the effect of insects, which may contribute to the differences in plant growth as observed in a normal distribution pattern.