Unit 2 Test Makeup Part 1 (Study Guide)
Water's Role: Explain how the polarity of a water molecule contributes to its ability to act as the universal solvent and facilitate life processes.
The water molecule contributes to its ability to act as the universal solvent and facilitate life processes because its partially negative oxygen and partially positive hydrogen ends attract and dissolve other polar molecules and ionic compounds.
Surface Area to Volume Ratio: Why does a cell's necessity to maintain a large surface area-to-volume ratio restrict the maximum size a cell can achieve?
A cell’s necessity to maintain a large surface area-to-volume ratio restricts the maximum size a cell can achieve because volume increases faster than surface area as a cell grows, making it harder to efficiently exchange nutrients and waste
Prokaryotic vs. Eukaryotic: Identify two major structural differences between prokaryotic and eukaryotic cells, other than the presence of a nucleus.
Two major structural differences between prokaryotic and eukaryotic cells other than the presence of a nucleus are the presence of membrane-bound organelles in eukaryotes and the distinct organization of their genetic material. (Eukaryotes have membrane-bound organelles like mitochondria and endoplasmic reticulum, while prokaryotes do not & eukaryotic DNA is linear and organized into multiple chromosomes, whereas prokaryotic DNA is typically a single)
Endosymbiotic Theory: Describe two pieces of evidence that support the Endosymbiotic Theory for the origin of mitochondria and chloroplasts.
Two pieces of evidence that support the Endosymbiotic theory for the origin of mitochondria and chloroplast is the presence of their own circular DNA and ribosomes and the double membrane structure surrounding both mitochondria and chloroplasts.
Ribosomes and ER: Compare the function and location of free ribosomes versus ribosomes bound to the Rough Endoplasmic Reticulum (RER).
Free ribosomes in the cytoplasm synthesize proteins within the cell, while ribosomes bound to the rough endoplasmic reticulum (RER) produce proteins destined for secretion, insertion into membranes, or delivery to other organelles.
Endomembrane System Path: Trace the path of a protein that is destined for secretion outside the cell, beginning with its synthesis on the RER.
First a secreted proten is synthesized on the rough endoplasmic reticulum (RER) then transported via vehicles to the golgi apparatus for modification and sorting.
Golgi Apparatus: Explain the main functions of the Golgi apparatus (or Golgi complex) in modifying and sorting proteins.
The golgi apparatus modifies, sorts and packages proteins. It carries out post-translational modifications such as glycosylation and phosphorylation. It also sorts proteins based on their destinations, and packages them into vesicles for transport o the cell membrane, lysosomes, or secretion outside the cell.
Lysosomes: Describe the primary function of a lysosome and explain why its contents are typically acidic.
The primary function of a lysome is to act as a cell’s waste disposal and recycling center. This is why its contents are typically acidic, because it is used to provide the optimal environment for their digestive enzymes.
Phospholipid Bilayer: Explain how the amphipathic nature of phospholipids leads to the formation of the lipid bilayer in an aqueous environment.
The amphipathic nature of phospholipids leads to the formation of the lipid bilayer in an aqueous environment due to the hydrophilic heads being oriented towards the water on both inside and outside of the cell, while chydrophobic tails tuck inward to avoid water, creating a stable double-layered membrane that acts aas a barrier between aqueous compartments.
Fluid Mosaic Model: What does the term "fluid mosaic" refer to in the context of the plasma membrane structure?
The term “fluid mosaic” refers to in the context of the plasma membrane structure a mosaic of various molecules embedded in a fluid lipid bilayer that allows for lateral movement.
Membrane Cholesterol: Describe the dual role of cholesterol in the animal cell membrane at different temperatures.
Cholesterol in animal cell membranes at different temperate acts as a regular of membrane fluidity, stabilizing the cell membrane at both high and low temperatures (high -> reduces fluidity by restricting movement of phospholipids; low -? Prevents membrane from solidifying by disrupting tight packing of phospholipids)
Selective Permeability: Explain why the plasma membrane is selectively permeable, and provide an example of a molecule that passes easily and one that does not.
The plasma membrane is selectively permeable because it is made of a phospholipid bilayer that repels charged and large molecules, but allows small, nonpolar molecules to pass through via diffusion
-> Ex. Oxygen can pass though, however glucose requires specific transport protein to cross the membrane.
Passive Transport: Distinguish between simple diffusion and facilitated diffusion, noting the role of membrane proteins in one but not the other.
Simple diffusion moves small nonpolar molecules directly through the cell membrane’s lipid bilayer, while facilitated diffusion uses specific membrane proteins (Channels or carriers) to transport larger, polar or charged molecules across the membrane.
Tonicity (Animal Cells): A red blood cell is placed in a hypotonic solution. Describe the net movement of water and the resulting effect on the cell.
The net movement of water and the resulting effect on the cell is that water moves into the cell through osmosis, due to the solution habing a lower solute concentration then the cell’s interior. This influx of water causes the cell to swell, and if the process continues, leads to it bursting or lysing.
Water Potential: Define water potential and explain how the addition of solutes affects the overall value of the water potential of a solution.
Water solution is a measure of the free energy of water per unit volume, indicating its tendency to move from one area to another. The addition of solutes to a solution lowers its water potential, maing it more negative because the solutes attract water molecules, reducing their free energy and ability to move.
Turgor Pressure (Plant Cells): Explain how the cell wall contributes to maintaining turgor pressure in a plant cell placed in a hypotonic environment.
In a hypotonic environment, water enters the cell by osmosis. The rigid cell wall resists swelling, creating turgor pressure that balances the water influx and keeps the cell firm and turgid.
Active Transport: Give one example of a primary active transport mechanism and explain why it requires an input of energy (ATP).
One example of a primary active transport mechanism is the sodium potassium pump, which uses ATP to move ions against concentration gradients. This requires energy because it pumps ions from a region of low concentration to that of a higher concentration.
Sodium-Potassium Pump: Briefly describe the key transport function of the Na+/K+ pump and state the specific direction (in or out) that each ion is moved.
The Na+/K+ pump uses ATP to activity transport ions across the cell membrane. It moves 3 Na + ions out of the cell, and 2 k+ ions in, helping maintain membrane potential and ion balance.
Cotransport: Explain how cotransport (secondary active transport) uses the concentration gradient established by a primary active transport pump to move a second substance against its own gradient.
Contransport uses energy stored in an ion’s concentration gradient created by a primary active transport pump, to drive another substance against it’s own gradient. As the ion moves down its gradient through a cortransporter, it provides energy to move the second molecule up its gradient.
Bulk Transport: Compare and contrast exocytosis and endocytosis as methods of moving materials across the plasma membrane.
Exocytosis and endocytosis are both forms of bulk transport that move large materials across the plasma membrane, but in opposite directions:
-> Exocytosis moves materials out of the cell by fusing vesicles with the plasma membrane to release their contents.
-> Endocytosis moves materials into the cell by forming vesicles from the plasma membrane that enclose external substances.
Both processes require energy (ATP) and involve vesicle formation and membrane remodeling.
Free Response Question (FRQ)
The Movement of Water Across Cell Membranes
An experiment was conducted to investigate the water potential of potato cells. Cubes of equal size and mass were cut from a potato and placed into six different beakers containing sucrose solutions of varying molarities (0.0 M to 0.6 M). After 24 hours, the potato cubes were removed from the solutions, blotted dry, and their final masses were recorded. The results are plotted on the graph below.
Table 1: Percent Change in Potato Mass After 24 Hours
Define the term osmosis in biological terms.
Osmosis is the movement of water molecules through a selectively permeable membrane from an area of high water concentration (low solute) to an area of low water concentration (high solute)
Determine the molar concentration of the sucrose solution that is isotonic to the potato cell cytoplasm. Justify your answer using the data table and/or graph.
The molar concentration of the sucrose solution is about 0.25 M. Percent change crosses zero between 0.2 M and 0.3 M, so the isotonic concentration (no net mass change) is about half way.
If the potato cube from the 0.6 M sucrose solution was transferred immediately to the 0.0 M (distilled water) solution, predict the direction of the net movement of water and the resulting effect on the cell's volume.
Water moves into the potato cells, and the cells gain water and swell, increasing in volume.
Describe the structure of the plasma membrane that enables it to be selectively permeable, including the selective movement of water molecules (osmosis).
The plasma membrane is a phospholipid bilayer with embedded proteins, making it selectively permeable. Small nonpolar molecules pass freely, while transport proteins control specific substances. Aquaporins let water move by osmosis, from low to high solute concentrations.