1. Ch. 8 Cells & Their Environment

2. Section 8.1 – Cell Membrane
1. What is homeostasis, and what is the main way that the cell membrane helps maintain homeostasis?
- the maintenance of stable internal conditions in a changing environment.
- by controlling the movement of substances across the cell membrane.
2. List three other functions of the cell membrane.
Provides structural support to the cytoplasm, recognizes foreign
material, communicates with other cells.
3. The _____ _____ is made of a double layer of phospholipids.
The double layer of phospholipids is called a(n) _____ _____.
- cell membrane
- lipid bilayer
4. The lipid bilayer forms because there
is _____ both inside and _____ of the cell.
- water
- outside
5. The phosphate _____ of a phospholipid
is polar. It is _____ _____ water.
- head
- attracted to

3. 6. The long fatty acid _____ of a phospholipid are nonpolar.
They are _____ _____ water.
tails
repelled by
7. The lipid bilayer forms a barrier, preventing
most molecules from passing through it. Only
molecules that are _____ in size and _____
can pass through the lipid bilayer.
small
nonpolar
8. Ions, which are _____ particles, and _____ molecules
are repelled by the nonpolar interior of the lipid bilayer.
charged
polar
9. The cell membrane includes various kinds of _____. Some face the inside of the cell. Some face the _____ of the cell. Others span the entire width of the _____ _____.
proteins
outside
cell membrane

4. Pair-Share
Take 3 minutes to explain why water requires a channel to get through the cell membrane.
Use the following terms in doing so:
Cell membrane
Lipid bilayer
Hydrophobic
Polar
Nonpolar

5. 10. What are proteins made of?
- amino acids
11. Why do proteins stay within the lipid bilayer of the cell membrane?
Nonpolar parts of the protein are attracted to the interior of the lipid bilayer while also repelled by water on either side of the membrane.
12. List the four types of proteins found in a cell membrane.
cell-surface markers
receptor proteins
enzymes
transport proteins

6. 13. Cell Surface Marker - identifies the cell type
Example: markers on red blood cells that denote blood type

7. 14. Receptor protein
recognizes and binds to substances outside the cell, enabling the cell to sense its environment
Example: HIV virus infecting human
white blood cells

9. 15. Enzyme
- helps with chemical reactions inside the cell

10. 16. Transport protein
- Helps substances move across the cell membrane

11. Use your notes to identify each of the following cell membrane proteins.3. 1. 2. 4.

12. Section 8.2 – Cell Transport
1. What is the purpose of cell transport? What is
the difference between active transport and
passive transport?
Cell transport is the movement of substances
across a cell membrane.
Active transport requires energy to move a
substance while passive transport does not.
2. What is equilibrium?
When a space is filled evenly with molecules
or particles.
3. What is diffusion? Why is diffusion an example
of passive transport?
The movement of substances from an area of high
concentration to an area of low concentration,
down the concentration gradient.

13. 4. simple diffusion
b. small, nonpolar molecules passing directly
through the cell membrane
5. facilitated diffusion with channel proteins
c. an ion, sugar, or amino acid moving through
a specific pore, based on the size and charge of
the moving substance
6. facilitated diffusion with carrier proteins
a. a substance binds to a protein, which changes
shape; both move together across the cell
membrane, where the substance is released

14. Osmosis 7. What is osmosis, and why is it important in cells?
- The movement of water across a membrane from an area of high concentration to an area of low concentration.
8. Explain how water moves across a cell membrane.
- Water moves through specific channel proteins.

15. 9. water moves into the cell
c. The solution a cell is in is hypotonic, meaning that it has a lower solute concentration than the cytoplasm does.
10. a state of ongoing equilibrium occurs
b. The solution a cell is in is isotonic, meaning that it has the same solute. concentration as the cytoplasm does
11. water moves out of the cell
a. The solution a cell is in is hypertonic,
meaning that it has a higher solute
concentration than the cytoplasm does

16. Active Transport
12. The transport of a substance across the cell membrane against its concentration gradient is called _____ _____.
- active transport
13. The energy needed for active transport is usually supplied by _____.
- ATP
14. What is the sodium-potassium pump? Describe how it works.

17. Endocytosis
15. Explain why proteins and polysaccharides cannot be transported across a cell membrane by carrier proteins. How do these substances cross the cell membrane?
- they are too large, they use vesicles
16. What is endocytosis? Describe how it works.
- The cell membrane forms a pouch around the substance to be imported which then pinches off into a vesicle.

18. Exocytosis 17. What is exocytosis? Describe how it works.
- A vesicle containing large molecules fuses with the cell membrane and expels its contents outside of the cell.
18. What are some circumstances in which cells use exocytosis?
Export proteins, release waste, remove bacteria

19. Label each of the following types of movement across a cell membrane.D. C.

20. Section 8.3 – Cell Communication
1. What is the main way cells communicate and coordinate activities?
- By sending chemical signals
2. What is a target cell?
- Cells that have specific proteins that recognize and respond to signals.

21. 3. How might neighboring cells communicate?
By direct contact between their cell membranes.
4. What is an environmental signal?
Give an example.
A signal that originates outside of
the body.
- An example of this would be light.

22. 6. What is a binding site, and why does it have a specific shape?
5. Cells are constantly bombarded by signals. How are they able to respond to only the few signals important to their cell function?
- It recognizes and responds to only a few that are important to its function.
6. What is a binding site, and why
does it have a specific shape?
A binding site is where a receptor
protein only binds to signals that
match the specific shape of its
binding site. It has a specific
shape so that it only reacts to
specific signals.

23. 7. Summarize the three responses cells generally have to a specific signal.
Permeability change: transport protein may open or close in response to a signal.
Enzyme activation: enzymes are activated inside the cell which then trigger specific chemical reactions.
Second messenger: a signal molecule is formed within the cell which then causes changes inside the cell.

24. 8. signal
d. carries information from one cell or cells to other cells
9. receptor protein
b. binds to a specific signal molecule,
causing a cell to respond
10. enzyme
c. speeds up a specific chemical
reaction in the cell
11. second messenger
a. forms in response to information
from outside a cell and acts as an
information carrier within a cell,
causing changes in the cytoplasm
or the nucleus