Cell Membrane and Transport Review

Which of the following is NOT a major part of the cell membrane?

• proteins

• nucleic acids

• carbohydrates

• phospholipids

Answer explanation

Nucleic acids, such as DNA and RNA, are not major components of the cell membrane. The membrane primarily consists of phospholipids, proteins, and carbohydrates, which play key roles in its structure and function.

1. What structure is the arrow pointing to in the image below?

• cholesterol

• protein

• phospholipid

• glucose

Answer explanation

The arrow points to a phospholipid, which is a key component of cell membranes. Phospholipids have a hydrophilic head and hydrophobic tails, distinguishing them from cholesterol, proteins, and glucose.

The cell membrane maintains ___________ by controlling what enters and leaves cells.

• homeostasis

• temperature

• structure

• reproduction

Answer explanation

The cell membrane regulates the movement of substances, which is essential for maintaining homeostasis, or the stable internal environment of the cell. This ensures that cells function properly.

1. What is the function of cholesterol in the cell membrane? 

• 1. It forms the lipid bilayer.

• 1. It works in cell identification.

• 1. It allows certain molecules to pass through.

• 1. It helps maintain the fluidity of the membrane.

Answer explanation

Cholesterol is crucial for maintaining the fluidity of the cell membrane. It prevents the fatty acid chains of phospholipids from packing too closely together, ensuring the membrane remains flexible and functional.

1. Some molecules pass through the cell membrane easily whereas other molecules cannot. What is the name of this property of the cell membrane? 

• 1. impermeable 

• semipermeable

• permeable

Answer explanation

The cell membrane is described as semipermeable because it allows certain molecules to pass through while restricting others. This selective permeability is crucial for maintaining homeostasis in the cell.

1. Which of these statements is true about active transport? 

• 1. It moves molecules from high concentration to low concentration.

• 1. It requires energy to occur.

• 1. It includes processes like simple and facilitated diffusion.

• 1. It goes down the concentration gradient.

Answer explanation

Active transport requires energy because it moves molecules against their concentration gradient, from low to high concentration, unlike diffusion which occurs naturally down the gradient.

1. Oxygen and carbon dioxide move into and out of the cell using _______. 

• 1. exocytosis

• 1. protein pumps

• 1. diffusion 

• 1. osmosis 

Answer explanation

Oxygen and carbon dioxide move into and out of the cell using diffusion, which is the process of molecules moving from an area of higher concentration to an area of lower concentration, allowing these gases to pass freely across the cell membrane.

1. A molecule moves into the cell using a channel protein. The molecule has moved from a higher concentration to a lower concentration. What type of transport is this? 

• 1. osmosis

• 1. facilitated diffusion

• 1. protein pump

• exocytosis

Answer explanation

The molecule moves from a higher to a lower concentration through a channel protein, which is characteristic of facilitated diffusion. This process does not require energy and relies on specific transport proteins.

1. A cell transports a very large molecule into the cell using energy. What type of transport is this? 

• 1. protein pump

• 1. diffusion

• 1. facilitated diffusion

• 1. endocytosis 

Answer explanation

The correct answer is endocytosis, as it involves the cell using energy to transport large molecules into itself. This process differs from diffusion and facilitated diffusion, which do not require energy.

1. What type of transport is pictured below? 

• 1. facilitated diffusion

• exocytosis

• osmosis

• 1. protein pump 

Answer explanation

Exocytosis is the process where cells expel materials in vesicles. This is distinct from facilitated diffusion, osmosis, and protein pumps, which involve the movement of substances across membranes without vesicle formation.