1. Which type of macromolecule stores energy and provides thermal insulation for the body? *

A. lipid
B. protein
C. nucleic acid
B. carbohydrate

2. Which structural feature of the cell membrane allows molecules such as oxygen and carbon dioxide to diffuse into and out of the cell? *

A. The cell membrane contains proteins molecules.
B. The cell membrane contains cholesterol molecules.
C. The cell membrane is made up of two layers of phospholipids.
D. The cell membrane is anchored to the cytoplasm by the cytoskeleton.

Lipids are among the four biomolecules, others being nucleic acids, carbohydrates, and proteins.
Lipids contain hydrocarbons and make up the building blocks of structure and function in living cells. Lipids includes; fats, oils, waxes and certain vitamins.
Lipid can be used for energy storage in the form of fat in animals. Additionally, lipids can be used as heat insulation as fat or adipose tissue under the skin reduces heat loss.

B. The cell membrane contains cholesterol molecules.

The structure of the lipid bi-layer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by simple diffusion.
Carbon dioxide and oxygen are molecules that can move across the lipid bi-layer without the help from membrane proteins or integral proteins. They are non-polar molecules and thus can easily pass through the hydrophobic interior of a membrane.