The answer is Cellulose. It does not provide calories/energy. The human digestive tract cannot break it down, so it is indigestible in humans.
Plant cell needs cell wall whereas animal cell do not because the plants need rigid structure so that they can grow up and out . All cells have cell membranes, and the membranes are flexible. So animal cells can have various shapes, but plant cells only have the shapes of their cell walls.
No . it has no life due to the cell theory .
the tiny blood vessels surrounding the alveoli are called capillaries.
the capillaries have thin walls and are connected to the larger blood vessels ( veins) and they bring oxygen to the heart threw oxygenated blood.
