In which part of the circulatory system does the exchange of oxygen and carbon dioxide take place between blood and cells?
veins
arteries
capillaries

Mario performed an experiment to determine if photosynthesis was affected by the amount of light that a plant received. what could he have done to increase the validity of his data? reduce the number of plants. remove the 1 hour group. add a 0 hours control. measure the oxygen in liters

Melting glaciers is a serious threat to the environment what is the possible consequence of melting glaciers on polar bears?

Which scientific design has both practical limitations and limitations due to scale? studying the effect of bleach on the growth of mold spores exposing cultures of duckweed to different intensities of light observing the replication of dna molecules with a hand lens using colored marbles to model a cross between two colors of rabbits