Astudent wants to answer the question “does adding calcium powder to soil make pea plants grow faster? ” she adds calcium powder to the soil of 12 plants and does not add it to the soil of a second group of 12 plants. she measures the growth of all of the plants in each group for a month.
which statement best summarizes the factors that need to be controlled in this experiment?
a. all plants should be the same age and health and be given equal amounts of water and sunlight.
b. all plants should be placed in separate, equal-sized pots on the same table, where they receive the same amount of sunlight.
c. all plants should be watered in the morning at the same time each day, and given the same amount of soil and sunlight.
d. all plants should be the same health and be given equal amounts of water, calcium, and sunlight.

On a backpacking trip, kenny hikes all day at a steady pace, covering 30 kilometers and burning 4000 calories. at the school track, janelle runs the 100-meter sprint in 13.5 seconds, burning 10 calories. afterward, janelle’s leg muscles are aching and she is breathing hard, while kenny maintains normal breathing all day, even though he burns 400 times more calories than janelle. which two statements offer the best explanation for this phenomenon? a. if the aerobic pathway—cellular respiration—cannot meet the energy demand, then the anaerobic pathway—lactic acid fermentation—starts up, resulting in lactic acid buildup and "oxygen debt." b. aerobic cellular respiration produces more energy, but its use is limited because of lactic acid buildup in the muscles and the resulting "oxygen debt." c. after about 90 seconds of intense exercise, the muscles become depleted of oxygen, and anaerobic respiration can no longer function to produce atp, resulting in "oxygen debt." d. the rate of energy demand determines how the muscles will obtain energy, either from cellular respiration or from lactic acid fermentation if not enough oxygen is present.