1.
The head of a phospholipid is __________.
Correct Answer
E. None of the above
Explanation
The head of a phospholipid is none of the above. Phospholipids have a hydrophilic head that is made up of a phosphate group and a glycerol molecule. This hydrophilic head is attracted to water and is located on the outer surface of the cell membrane. The hydrophobic tail, on the other hand, is made up of fatty acid chains and is repelled by water, therefore it is located on the inside of the cell membrane.
2.
A membrane is permeable to hydrogen but impermeable to sodium ions. Which molecule cannot move into the cell?
Correct Answer
B. Sodium ions
Explanation
Since the membrane is permeable to hydrogen but impermeable to sodium ions, it means that hydrogen can move freely across the membrane while sodium ions cannot. Therefore, the molecule that cannot move into the cell is sodium ions.
3.
Cell membranes are constructed mainly of ______.
Correct Answer
A. Phospholipids
Explanation
Cell membranes are primarily composed of phospholipids that make up two bilayers. Phospholipids have a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail, allowing them to form a double layer in which the hydrophilic heads face the watery environment both inside and outside the cell, while the hydrophobic tails are sandwiched in between. This arrangement provides a barrier that controls the movement of substances in and out of the cell. While proteins, cholesterol, glycoproteins, and transport proteins are also present in the cell membrane, they are not the primary components responsible for its construction.
4.
Which of these statements best describes the function of the cell membrane?
Correct Answer
B. It controls which substances enter and exit the cell.
Explanation
The cell membrane acts as a selectively permeable barrier, controlling the movement of substances in and out of the cell. It allows certain molecules to pass through while preventing others from entering or leaving. This regulation is essential for maintaining the cell's internal environment and ensuring proper functioning. Therefore, the statement "It controls which substances enter and exit the cell" accurately describes the function of the cell membrane.
5.
In the diagram below, what structure is labeled with the letter A?
Correct Answer
C. Protein
Explanation
The structure labeled with the letter A in the diagram is a protein. Proteins make up transporters (bridges) that regulate what can enter or exit the cell.
6.
What is the function of the carbohydrates in the cell membrane?
Correct Answer
B. Communication
Explanation
Carbohydrates in the cell membrane play a crucial role in communication. They act as recognition sites for cell-cell interactions and help in identifying and binding to specific molecules. This is important for various cellular processes such as immune response, cell signaling, and development. Carbohydrates on the cell surface also participate in cell adhesion, allowing cells to stick together and form tissues. Therefore, communication is the main function of carbohydrates in the cell membrane.
7.
The tail of a phospholipid is _________.
Correct Answer
E. None of the above
Explanation
The tail of a phospholipid is not made of carbohydrates, proteins, nucleic acids, or hydrophilic. The tail of a phospholipid is actually made of fatty acids (lipids), which are hydrophobic in nature.
8.
What is the function of proteins in cell membranes?
Correct Answer
A. Cellular transport
Explanation
Proteins in cell membranes play a crucial role in cellular transport. They act as channels and pumps, allowing specific molecules and ions to enter or exit the cell. These proteins also facilitate the movement of larger substances through the membrane via processes like endocytosis and exocytosis. Additionally, proteins in the cell membrane are involved in cell signaling and communication, helping to relay signals from the external environment to the inside of the cell. Therefore, the correct answer is cellular transport.
9.
This process stores energy for the cell in the form of sugar.
Correct Answer
C. Photosynthesis
Explanation
Photosynthesis is the correct answer because it is the process by which plants and some microorganisms convert sunlight, carbon dioxide, and water into glucose (sugar) and oxygen. The glucose produced during photosynthesis is then stored as energy for the cell to use later. This process takes place in the chloroplasts of plant cells and is essential for the survival of plants and the production of oxygen in the atmosphere.
10.
This process releases the energy stored as sugar.
Correct Answer
A. Cellular respiration
Explanation
Cellular respiration is the correct answer because it is the process by which cells convert glucose (sugar) into usable energy in the form of ATP. During cellular respiration, glucose is broken down in the presence of oxygen to produce carbon dioxide, water, and energy. This energy is stored in the form of ATP and is used by cells for various functions and activities. Therefore, cellular respiration is the process that releases the energy stored in sugar.
11.
This energy-rich molecule, produced by cellular respiration, is vital for the functioning of the cell.
Correct Answer
D. ATP
Explanation
ATP (adenosine triphosphate) is the correct answer because it is an energy-rich molecule that is produced by cellular respiration. It is often referred to as the "energy currency" of the cell because it is used to fuel various cellular processes and reactions. ATP provides the necessary energy for activities such as muscle contraction, active transport of molecules across cell membranes, and synthesis of macromolecules. Without ATP, the cell would not be able to perform its essential functions and would ultimately cease to function.