what necessary interactions are required for activation of helper T cells and what necessary interactions are required for activation of cytotoxic T cells

Astudent observes a star from two positions of earth in its orbit, in summer and winter, and measures the change in the position of the star. which of these can be best calculated by this method?

This is the diveristy of ecosystems natural communites and habits it is the variety of ways that species interact with each other and their environment

Which of the following is the best definition for the process of photosynthesis? a.) plants digest sugars to make energy. b.) plants use oxygen and glucose to make carbon dioxide. c.) plants use sunlight and carbon dioxide to make sugars. d.) plants use sunlight to make chlorophyll and chloroplasts.