The Cell in Its Environment
Fill in the blank to complete each statement.
1. Water diffusing through a semipermeable membrane is called ___________________.
2. ___________________ occurs when a cell engulfs large food particles.
3. The cell membrane is built of a double layer of ___________________.
4. Facilitated diffusion moves large molecules through ___________________
.
5. The ___________________ controls the materials that move into
and out of a cell.
6. The ___________________ use energy to pick up specific
molecules and carry them across the cell membrane.
Write the letter that best describes the type of transport on the line at the left.
7. _____​ Glucose enters a liver cell through a
protein channel.
A diffusion
B facilitated diffusion
C osmosis
D active transport
9.​ ​_____​A nerve cell uses energy to pump
sodium out of its cytoplasm into a
sodium-rich environment.
A diffusion
B facilitated diffusion
C osmosis
D active transport
8. _____​ Oxygen moves into a contracting
heart muscle cell.
A diffusion
B facilitated diffusion
C osmosis
D active transport
10. _____​ ​Water moves out of the skin cells of a
person swimming in a freshwater pond.
A diffusion
B facilitated diffusion
C osmosis
D active transport
Read the passage and study the diagram. Then use a separate sheet of paper to answer
the questions that follow.
Facilitated Diffusion
Some molecules are unable to pass through
the cell membrane even though they are
moving from an area of higher concentration
to an area of lower concentration. To pass
through the cell membrane, these molecules
must be facilitated, or helped, by a carrier
protein in the cell membrane. The passenger
molecule attaches to the carrier protein.
The carrier protein moves the passenger
molecule through the cell membrane and
releases it inside the cell. The process can
carry substances both into and out of cells,
as shown in the diagram, and it requires no
cellular energy.
1. Why isn’t cellular energy required for
the passenger molecule to be carried
across the cell membrane by the
carrier protein?
2. Why do the passenger molecules
need to be helped by the carrier
protein?
3. If the substance entering the cell was in higher concentration inside
the cell than outside the cell, what type of transport would be
required? Explain your answer.
4. What is the difference between facilitated diffusion with the help
of a carrier protein and active transport with the help of a transport
protein?
5. Assume a person has defective carrier proteins for a given substance.
Explain what effect this would have on the person’s cells.