Only small, uncharged molecules that are nonpolar can cross the cell membrane via diffusion. For example, oxygen molecules can easily diffuse across the cell membrane. Ions like potassium and sodium can cross the cell membrane through other mechanisms, such as active transport or through ion channels, but they cannot cross via the mechanism of diffusion.

Cholesterol is a major component of the plasma membrane fluidity. If we add more of this molecule to a cell membrane in normal conditions, we would hinder the movement of other lipids and essentially cause them to be more compressed. This compression would lead to a decrease in the fluidity of the membrane.

Peripheral proteins are located either on the inside or outside of the cell, but do not pass all the way through. Glycoproteins are located on the outside of the cell membrane. Mitochondria are located within the cell and make ATP. Golgi apparatus is also located within the cell, thus does not function for transport through the membrane. Integral proteins act as carrier proteins and allow substances to pass through the cell membrane from the inside to the outside of the cell (or outside to the inside).

Active transport is when a particle moves against its concentration gradient through a selective membrane with the aid of energy. Moving down its concentration gradient and from a high to low concentration is simple diffusion. The movement of water down its concentration gradient is osmosis and moving a particle or ion through a protein is facilitated transport. These are all examples of passive transport. 

Glucose need a channel protein to pass through the membrane because it is too large. Substances that pass through the membrane via simple diffusion need to be relatively small and not charged. Carbon dioxide and oxygen gas are both small nonpolar molecules that can easily diffuse through the plasma membrane. 

Only two choices are correct, facilitative diffusion and active transport because they both need carrier proteins for transport across the cell membrane. Simple diffusion does not require carrier proteins.

Nonpolar molecules can pass through the plasma membrane with relative ease. Even larger nonpolar molecules, such as steroid hormones, can pass through the plasma membrane easily. Passing through the membrane without the need for assisting proteins is known as passive diffusion.

Facilitated diffusion involves the use of membrane channel proteins to allow molecules to pass (example: potassium leak channels). Active transport requires the metabolism of ATP to pump a molecule against its concentration gradient (example: sodium-potassium pump). Secondary active transport uses ATP to generate an electrochemical gradient, then uses the gradient to transport molecules and perform work (example: ATPase).

Actin is what makes up microfilaments. Chitin is indeed in cell walls of fungi. Cellulose is the main ingredient to plant cell walls and peptidoglycan are found in the cell walls of cyanobacteria and bacteria. Also, cellulose is made of polysaccharides, therefore, this is also an incorrect answer because it is a component of the cell wall.

The fluid mosaic model says that proteins can extend all the way through the phospholipid bilayer of the membrane. There are peripherial, integral, and transitional proteins. Therefore, these proteins are various sizes and lengths. 

Lipids can diffuse freely across the cell membrane, because the cell membrane is made up of lipids. Ions will not be able to pass through the hydrophobic section of the membrane, because it is polar. Chloride is an ion. Water is polar and also won't be able to pass through the hydrophobic section of the membrane. Sucrose is too big to freely diffuse into the cell.