Answer:
Because each subject in an experiment has to have equal conditions to ensure the most accurate results. And water temperature is known to impact plant growth. An experiment using different water temperatures is a terribly inaccurate experiment.
Temperate Rainforest and Tropical Rainforest
The best answer to fill in the blank is "multilayered membrane."
There are actually two planets referred to as gas giants which are Jupiter and Saturn. These two planets are made of mostly helium and hydrogen which makes them gas giants, while Uranus and Neptune have more ice and rock substances, so they are not considered gas giants.