Where do the electrons needed by photosystem ii come from?.

How many trophic levels are there in the following food chain? phytoplankton - shrimp - perch - pike - osprey

Select the correct answer from each drop-down menu. in an experiment, dr. travis examined the effects of calcium intake on osteoporosis, a condition that causes an increased risk of bone fractures. the amount of calcium is variable. the risk of bone fractures .

Which of the following was not a major animal on land during the carboniferous period? amphibians insects both a and b none of the above