Answer:
Open circulatory system:
Relies on the heart to keep blood flowing
Used in all vertebrates
Sorry thats all i know :)
Answer and Explanation:
It's a constrictive growth pyramid I think. They could die out in the future..
I can't remember the factors that have led to the growth
Answer:
C.
Explanation:
Food chains focus on one set of organisms and their predators/prey, while food webs show multiple for each. Hope this helps. :)
Because if we're simultaneously moving/manipulating two different variables it can be very hard to determine why one variable is changing and why the other is changing. While this can be done with more complicated experimental designs, it usually is the case that scientists will only manipulate one variable and not two different ones.
