Kaley is trying to determine how music affects the growth of plants. she hypothesizes that classical music will cause a plant to grow at a higher rate than no music or rap music. she grows nine tomato plants in similar lighting, temperature, and soil. three are exposed to classical music 24 hours a day, three are exposed to rap music 24 hours a day, and three are grown in complete silence. kaley measures the growth of the plants every day and finds that the plants all seem to have the same rate of growth. what is missing from kaley's scientific investigation?

As the description in the question shows, Kaley is taking careful and regular measurements. Hence, her experimental method is correct.

Kaley has also developed a hypothesis and the experiment she conducted is also valid hence there is no problem in these steps.

There is no mistake being done by her in depicting the results of the experiment.

Hence, the only thing which we can say is missing from the experiment is the past researches which scientists might have made on this topic.

Explanation:

the leaf is an organ of a typical plant, and the main functions are to complete photosynthesis and allow the plant to exchange gas, just like how we have the respiratory system. leaves have the stomata, which collects maintains co2 and o2 levels. this is necessary for cell metabolism. the leaf also collects sunlight using chloroplasts. succinctly, leaves own a pivotal role in sustaining plant life.

the answer is na (sodium)