Answer:
Controlled group does not receive the treatment. It used as a benchmark to measure how different tested subjects affected the result of the experiment.
For example, the famous experiment of whether plants grow faster with music in one room and without music in the other room. The plant in the no music room is the controlled group.
1) C
A population has to be isolated for speciation
2) D
Different species are incapable of reproducing with one another
3) D
When a population is contained, the recessive alleles can become dominant within the population
I'd say, ina general way, that the most imporant cells in defense against parasitic organisms are definitely white blood cels, the cells responsible for defeating antigens, pathogens and deseases.
Although these might be the most important ones in that specific task (defending against parasitic organisms), all the cells in the immune system, along with other non-cell things are important, since they all play a specific role indispensable in our immune system.
Hope it helped,
BioTeacher101
i BELEIVE THE ANSWER TO BE :C:
