Cell membranes are said to be selectively permeable. which statement best explains what selectively
permeable means?
(1) the cell membrane prevents any harmful substance from entering the cell.
(2) the cell membrane lets certain substances enter the cell and keeps certain substances out of the cell.
(3) the cell membrane allows only large molecules to diffuse into the cell.
(4) the cell membrane has pores that let only water and glucose into the cell and carbon dioxide out

The correct answer is option 2, that is, the cell membrane lets certain substances enter the cell and keeps certain substances out of the cell.

All the cells are surrounded by a cell membrane. The cells membrane is selectively permeable, that is, it allows only some of the ions or molecules to pass through them by assistance of active or passive transport. For example, the molecules of water can passes passively through small pores on the membrane.  

producers: apple trees, potatoes, carrots, grains, acorns, cabbage, grass, corn, lettuce

consumers: deer, mice, rabbits, chickens, squirrels, horses, worms, cows

predators: eagles, frogs, wolves, owls