In most investigations, researchers try to gather information from subjects of varying age, gender, fitness, and stature. Why did the researcher chose all the participants in this study with similar characteristics?
Select one:
O a. The age, weight, gender, and fitness are manipulated variables that must be kept constant to evaluate the effect on heat production in the
muscle.
O b. The age, weight, gender, and fitness are manipulated variables that must be changed to evaluate the amount of heat produced by the
quadricep muscle.
O c. The age, weight, gender, and fitness are controlled variables to ensure that the measured heat production is due to muscle activation rather
than the fitness level of the participant.
O d. The age, weight, gender, and fitness of the individuals are the responding variables in this experiment.
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cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!

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when it is at an intermediate population density