ESSENTIAL BIOLOGY 02: CELLS
24. Draw and label a simplified (2D) diagram of the plasma membrane.
Include: phospholipid bilayer, integral and peripheral proteins, glycoproteins and
cholesterol.
Peripheral protein –
here a glycoprotein
Phospholipid
bilayer
Integral protein
cholesterol
25. What are the functions of these plasma membrane components?
a. glycoproteins - they play a role in recognition of like cells (same for glycolipids). They
also are important for immune response, hormone binding site.
b. cholesterol – regulate membrane fluidity and membrane stability. Cholesterol
molecules are present in animal cells membrane and reduces flexibility. They allow
effective membrane function at a wide range of temperatures. (in plant cells this is
done with unsaturated fatty acids.)
ESSENTIAL BIOLOGY 02: CELLS
26. Match the following membrane proteins with their functions:
Channel/ carrier proteins
used in cell surface reactions
Protein pumps
binding cells together
Receptor proteins
communication between cells
Enzymes
passive transport across the membrane
Adhesion proteins
active transport across the membrane
Neurotransmitter receptors
hormone binding and recognition
27. Draw a single phospholipid molecule. Label the hydrophobic and hydrophilic sections.
Hydrophilic head
Hydrophobic tail
head
28. Explain how hydrophobic and hydrophilic properties of the phospholipid bilayer allow a
membrane to maintain its structure.
The hydrophobic and hydrophilic regions cause the phospholipids to always align as a bilayer if
there is water present and there is a large amount of phospholipid molecules. The hydrophobic
tails of the phospholipid molecules always tend to attract to each other and away from the
water. The tendency of water to form hydrogen bonds, to the hydrophilic heads, will maintain
the whole structure.
29. Define diffusion. Diffusion is the passive movement of particles, from a region of higher
concentration to a region of lower concentration, as a result of the random movement of
particles.
Define osmosis. Osmosis is the passive movement of water molecules from a region of lower
solute concentration to a region of higher solute concentration, across a partially permeable
membrane.
ESSENTIAL BIOLOGY 02: CELLS
30. In the table below, tick the conditions required for each type of transport to occur.
Concentration
gradient
Selectively
permeable
membrane.
Membrane
proteins
Simple diffusion

Osmosis


Facilitated
diffusion





Active transport
ATP (source of
energy)

31. State four ways to maximize the rate of diffusion of a substance across a membrane.
a. maintain a high concentration gradient by addition of particles on the high
concentration side
b. maintain a high concentration gradient by removaln of particles from the low
concentration side
c. increase the temperature
d. many passages for the diffusion e.g. channels for facilitated diffusion.
32. Explain what is happening in this diagram:
ESSENTIAL BIOLOGY 02: CELLS
Water may diffuse through the selectively permeable membrane, but the red particles are to
large to pass. The concentration gradient result in a net diffusion of water molecules into the
part with higher solute concentration until the solutions on each sides are as good as equal.
The larger hydrostatic pressure from the right part is also a part in balancing the osmotic
pressure from the more concentrated solution.
33. In the space below, draw a diagram of a plant cell before and after plasmolysis.
Explain how osmosis causes plasmolysis.
If a plant cell is placed in an environment of higher solute concentration or suffer from desiccation, it
will loose water by osmosis. When the water leaves the cytoplasm, the cytoplasm will shrink and the cell
membrane loosens from the cell wall. The plant cell will not have enough plasma to keep the turgid
shape of the cell and it will wilt.
ESSENTIAL BIOLOGY 02: CELLS
34. In the space below, draw a simple, annotated diagram showing how a protein pump is used
in active transport of molecules across a plasma membrane. Use the Na+/K+ pump as an
example.
or
ESSENTIAL BIOLOGY 02: CELLS
35. What is a macromolecule? Give one example of a macromolecule produced in the cell.
A macromolecule is composed of many smaller molecules. One example is proteins that is
composed of many amino acids.
36. Complete and annotate the diagram below to show the process of vesicle transport of a
protein molecule through a eukaryote cell. Begin with protein synthesis in the Rough ER and
finish with exocytosis though the plasma membrane. Label all organelles shown.
Vesicles from R.E.R. to Golgi
apparatus with protein
Nucleus with
DNA and RNA
transcription
Vesicles from Golgi apparatus to
plasma membrane for exocytosis
Rough Endoplasmic
Reticulum with protein
synthesis and packing into
vesicles for transport to
Golgi apparatus.
Golgi apparatus
for mixing and packing
for export
Plasma membrane
37. Differentiate between exocytosis and endocytosis.
Exocytosis means that a vesicle from Golgi apparatus is united with the plasma membrane and
the content empted on the outside of the cell.
Endocytosis means that content from the outside of the cell is taken in. It is done by a
depression in the plasma membrane that finally forms a vesicle that is taken into the cytoplasm
of the cell.
ESSENTIAL BIOLOGY 02: CELLS
38. Describe how the plasma membrane breaks and reforms during exocytosis and endocytosis.
How does the fluidity of the membrane allow this?
The fluidity of the plasma membrane allows it to change shape and the phospholipid molecules
may change their attractions to other phospholipids and thus form depressions and vesicles.
If the membrane had been rigid, this could not have been done.