Download Homework Questions – Unit 1 – Biochemistry

Homework Questions – Unit 1 – Biochemistry
Section: The Cell Membrane
1. List 3 functions of the cell membrane.
 transport raw materials into the cell
 transport manufactured products and wastes out of the cell
 prevent the entry of unwanted matter into the cell
 prevent the escape of the matter needed to perform the cellular functions
2. Identify the component(s) of the cell membrane that give it a fluid consistency.
 Cholesterol – increases the fluidity (bendibility) of the membrane.
3. Why does the cell membrane require a fluid consistency?
 The cell membrane is considered to be a semi-permeable membrane, allowing
some biological molecules to pass through it.
 To allow movement, cell functioning.
4. Why does your body manufacture cholesterol even if you do not eat any food that contain
cholesterol?
 Your cells need cholesterol to increase fluidity of the membrane
Section: Through the Cell Membrane
1. Define diffusion using one specific example.
 Diffusion is the movement of molecules from an area of high concentration to an
area of low concentration.
 Eg. Perfume sprayed in a room
 Eg. Water moving in and out of a cell
2. Explain the concept of a concentration gradient, and use a simplified diagram to clarify your
explanation.
 The difference in concentrations between these regions is called the
concentration gradient.
3. Identify three different molecules that diffuse into cells.
 Water
 Amino Acids
 Glucose


Oxygen
Carbon dioxide
4. Distinguish between osmosis and diffusion.
 Diffusion is a spontaneous movement of particles from an area of high concentration to

an area of low concentration through a semi-permeable membrane. (ex. tea flavoring
moving from an area of high to low concentration in hot water.)
Osmosis is the spontaneous net movement of water across a semipermeable membrane
from a region of low solute concentration to a solution with a high solute concentration,
down a solute concentration gradient.
5. What is homeostasis? Why is homeostasis important to cells?
 The conditions inside every cell must remain nearly constant in order for it to
continue to function normally.
 This steady state inside a cell is called homeostasis.
 It is important to cells in order for them to function properly and do their jobs.
6. Diffusion allows for the effective movement of substances over short distances. How is this
important for the cell?
 Cells cannot be too large (surface area-volume ratio) or diffusion cannot occur properly
7. How is facilitated diffusion different from diffusion?
 Facilitated diffusion uses specific transport proteins to help or facilitate substances
passing through the cell membrane.
 Two types of facilitated diffusion proteins:
o Carrier proteins
o Channel proteins
8. Identify two distinguishing properties of molecules that determines what type of transporter
protein is used.
 Carrier protein – for medium-sized, uncharged molecules
 Channel proteins – for medium-sized, charged molecules
9. What would happen to a cell if its cell membrane were permeable rather than semipermeable?
 Permeable allows any particles/molecules through
 Semi-permeable allows certain molecules through
10. Explain why water pollution has such a profound effect on living organisms.
 Water diffuses into cells
Section: Bulk Membrane Transport
1. How does the structure of the cell membrane facilitate endocytosis/exocytosis?

Endocytosis is the process of the cell membrane engulfing a small amount of matter
from the extracellular fluid. Therefore the structure of the cell membrane folds inward,
and traps and encloses the matter so it is inside the cell.

Exocytosis is just the reverse of endocytosis. It takes the amount of matter thats
inside the cell and ejects it out. The structure of the cell membrane gets fused from a
vesicle (thus restoring membrane removed in endocytosis). The contents of the
outward-bound vesicle are secreted into the extracellular fluid.
2. Endocytosis involves the formation of vesicles to bring matter into the cell. Once inside, what
happens to this matter?

The vesicle floats through the cytoplasm and fuses with a lysosome, which will
digest the contents.
3. Compare and contrast endocytosis to active transport.
Endocytosis:
 The cell membrane folds inwards, trapping and enclosing some substance.
 Part of the membrane pinches off and surrounds the substance – forms an
organelle called a vesicle.
 The vesicle floats through the cytoplasm and fuses with a lysosome, which will
digest the contents.
a) Pinocytosis - called “cell drinking”; involves the intake of small particles.
b) Phagocytosis - called “cell eating”; involves the intake of one large molecule.
c) Receptor-assisted endocytosis - involves the intake of specific molecules that attach to
special proteins in the cell membrane that serve as receptors; these membrane
receptors are shaped so that they only one specific type of molecule will fit here (almost
like 2 pieces of a puzzle).
Active Transport
 Often, the cell must expend energy to transport substances from an area of low
concentration to an area of high concentration (think of pushing an object up a
hill).
 The process of moving substances against the concentration gradient is called
active transport.