Which organelle is responsible for providing a barrier allowing only certain things in and out of the cell?

Apart of an ecosystem that can restrict the growth of a population is referred to as

The bacteria inside a tube worm would be analogous to what organism in the ocean ecosystem near the waters surface? a. photosynthetic algae b. shrimp c. clown fish d. parasitic lamprey

Look at the photo of the leaf, which term best describes this leaf ? a-simple.b-parallel.c-lobed.d-tooth.