A. the cells of their epidermis have no blood capillaries
B. they have well developed respiratory structures
C. their cylindrical shape gives high surface area to volume ratio
D. their surface area to volume ratio is very low
Correct Answer:
Option C – their cylindrical shape gives high surface area to volume ratio
Explanation
In simple organisms, such as cnidarians and flatworms, every cell in the body is close to the external environment.
Their cells are kept moist and gases diffuse quickly via direct diffusion. Flatworms are small, literally flat worms, which “breathe” through diffusion across the outer membrane.
Annelids have a closed circulatory system; the blood is entirely contained in vessels.
Annelids have no lungs, although many species have simple gills.
