If the water concentration inside a cell is higher than the water concentration outside the cell, water flows out of the cell. This method of molecular transport is called
osmosis.
Cell membranes (plasma membranes) help organisms maintain homeostasis by controlling what substances may enter or leave cells. Some substances can cross a cell membrane through passive transport, while other substances can only cross a cell membrane through active transport. What is the difference between active and passive cellular transport?
A.
Active transport is the only form of transport that requires the use of protein carriers.
B.
Active transport requires the cell to form vesicles, while passive transport is done through osmosis.
C.
Active transport requires the cell to expend energy, while passive transport does not.
D.
Passive transport is the only form of transport that requires the use of protein carriers.
C. Active transport requires the cell to expend energy, while passive transport does not.
The sodium-potassium pump, shown below, is a mechanism that allows cells to move sodium ions out of the cell and potassium ions into the cell, against a concentration gradient (i.e., from a low concentration to a high concentration).
Picture of sodium pump
This mechanism maintains the correct concentrations of sodium and potassium ions inside of a nerve cell. Although this pump uses energy, it is necessary to maintain these conditions so nerve impulses can be transmitted properly.
Which of the following statements does this information best support?
A.
Energy is generated during most of the processes that occur in living organisms.
B.
Living organisms have processes and structures that help them maintain homeostasis.
C.
Evolution has increased the number of non-essential processes in living organisms.
D.
Organisms that are living today use more energy than their ancestors.
B. Living organisms have processes and structures that help them maintain homeostasis.
In carrying out normal activities, cells use oxygen and produce carbon dioxide. The concentration of oxygen is higher in the blood than inside the cell, so oxygen moves into the cell. Similarly, carbon dioxide moves out of the cell into the blood because the concentration of carbon dioxide inside the cell is greater than the concentration outside the cell.
How do the small molecules of oxygen and carbon dioxide move through the cell membrane?
A.
active transport by carrier proteins
B.
passive transport by diffusion
C.
passive transport by osmosis
D.
active transport by endocytosis