Biology 12: Chapter 4- Review Worksheet Answer Key
Transport Across Plasma membrane
A. Plasma Membrane Structure and Function
1) Plasma membrane regulates passage of molecules into and out of cell
largely responsible for maintaining cellular homeostasis
2) Fluid mosaic model = plasma membrane made of phospholipid bilayer w/
protein molecules partially/wholly embedded. Fluid consistency, proteins
scattered in a mosaic pattern. Polar heads face outward b/c attracted to water.
3) The basic structure of the plasma membrane is determined by the lipid bilayer,
but the various functions of the membrane are carried out by the plasma
5)a) Phospholipids = abundant lipids, amphipathic, main fabric of PM, fluid bilayer
Membrane Proteins = also amphipathic, determine most of PM’s specific
b) Cholesterol = stiffens and strengthens PM, helps regulate its fluidity.
6) Peripheral = partially embedded in bilayer, held in place by cytoskeleton
Integral = mostly/fully embedded in bilayer, can move laterally, also held in place
by cytoskeleton filaments
7) Channel = proteins have a channel through which an ion or molecule can
simply move across the membrane.
Carrier = protein combines with substance and helps it move across membrane.
Receptors = each receptor has specific shape which allows particular molecule to
bind to it.
Enzymatic = carry out metabolic reactions
Cell recognition = facilitates adhesion between cells, reception of signal
molecules, cell-cell recognition, protects cell with “sugar coat” (glycocalyx).
8) Glycocalyx = carbohydrate chains of cell recognition proteins; protects cell,
facilitates adhesion between cells, reception of signal molecules, cell-cell
9) Small non-charged, lipid-soluble substance is easier to cross a PM because
10) PM = differentially permeable b/c it controls what enters and leaves
regardless of size.
Passive transport = diffusion, both simple and facilitated without ENERGY
Active transport = endocytosis , exocytosis with ENERGY
B. Diffusion and Osmosis
1) Diffusion = net movement of substance from region of high concentration to
region of low concentration. Example is dye and water molecules, dye is
dissolved in water, resulting in a coloured solution.
2) B/c lipid-soluble molecules such as alcohol and certain gases are small and
3) Water molecules pass through PM with relative ease b/c of osmosis. Low
[solute] to high [solute], and water molecules are relatively small.
4) Solute = substance that is dissolved in a solvent, forms a solution
Solvent = Fluid such as water that dissolves solutes.
5) Osmosis = diffusion of water through a selectively permeable membrane.
6a) Isotonic solution = [solute] and [water] both inside and outside of cell are
equal ∴no net gain or loss of water.
b) IV solutions are isotonic with human blood so that your RBCs don’t crenate or
7a) Hypotonic solution = solutions that cause cells to swell or even burst due to
an intake of water. Water will enter a cell.
b) Animal cells will expand and sometimes burst due to buildup of pressure.
c) Disrupted red blood cells = hemolysis
d) Plant cell encounters turgor pressure, expansion of cytoplasm b/c large central
vacuole gains water, and PM pushes against rigid cell wall. Plant cell does not
burst b/c CW doesn’t give way.
8) Hypotonic solution = turgor pressure. Maintains plant’s erect position.
9a) Hypertonic solution = higher [solute] than cell. Water will leave cell.
b) Animal cell will crenate or shrivel up.
c) Plant cell will lose water and shrink; PM pulls away from CW- plasmolysis.
C. Cell Transport
1) Carrier proteins needed in both facilitated and active transport.
2a) Facilitated diffusion = explains passage of non-lipid molecules’ across PM,
transportation of solute in either direction, following [ ] gradient.
b) Controlled by amount of [ ] on either side
3a) Active transport = ions/molecules move through PM, accumulating either
inside/outside of cell, goes against [ ] gradient
b) The sodium-potassium pump will create a high [ ] of Na+ ions outside the cell
and a high [ ] K+ ions inside the cell.
4) Malfunction in the chlorine channel causes cystic fibrosis.
5) Endocytosis = taking in macromolecules invagination
Exocytosis = secreting macromolecules
7) Regulated secretion= certain cells in pancreas make insulin and secrete into
blood by exocytosis. Vesicles only fuse with PM when insulin is needed to lower
9) Phagocytosis = “cell eating” specific, digested when fused with lysosome,
engulfed by particle being wrapped by pseudopodia. Eg WBC’s engulf worn-out
RBC’s and bacteria.
Pinocytosis = “cellular drinking’ unspecific, any solutes dissolved in fluid droplet
Receptor-mediated Endocytosis = extremely specific, uses receptor protein
shaped in specific way. Substances that bind to these sites called ligands =
vitamins, peptide hormones, lipoproteins. Receptors found in coated pit.
D. Completion and Short Answer Questions
1) Diffusion is the movement of molecules from an area of high [ ] to an area of
low [ ].
2) Osmosis is the movement of water across a differentially permeable
3) A cell is isotonic to a solution of 0.01% sugar. A [ ] that is hypertonic is greater
than 0.01%, whereas a [ ] that is hypotonic is less than 0.01%.
4) If an animal cell is place in a hypotonic solution, it would burst whereas an
animal cell placed in a hypertonic solution would crenate/shrink.
5) Turgor pressure is best exemplified by placing a plant cell in a hypotonic
6) Cells engaged in the process of actively transporting substances across the
membrane expend ATP.