Cell Structures and Functions
This organelle is known as the "powerhouse of the cell" because it produces ATP.
What is the mitochondrion?
As a cell increases in size, this ratio decreases, limiting its efficiency in exchange with the environment.
What is the surface area to volume ratio?
This model describes the structure of the plasma membrane as a mosaic of protein molecules in a fluid bilayer.
What is the fluid mosaic model?
Movement of molecules from high to low concentration without energy.
What is passive transport?
A solution with a lower solute concentration than the cell is described as this.
What is hypotonic?
Ribosomes can be found floating freely in the cytoplasm or attached to this organelle.
What is the rough endoplasmic reticulum?
Calculate the surface area to volume ratio of a cube-shaped cell with sides of 2 µm.
What is 3:1?
(SA = 24 µm², V = 8 µm³)
Phospholipids in the membrane have this type of head and tail, making the bilayer selectively permeable.
What are hydrophilic heads and hydrophobic tails?
Transport of large molecules into the cell via vesicles is called this.
What is endocytosis?
If a cell is placed in a hypertonic solution, it will do this.
What is shrink or undergo plasmolysis?
This organelle contains hydrolytic enzymes that break down macromolecules.
What is the lysosome?
According to this theory, mitochondria and chloroplasts originated from prokaryotic cells engulfed by an ancestral eukaryote.
What is the endosymbiotic theory?
Cholesterol in the plasma membrane helps to maintain this, especially at varying temperatures.
What is membrane fluidity?
Oxygen and carbon dioxide move freely across the plasma membrane without the help of transport proteins. What characteristic of these molecules allows them to diffuse directly through the lipid bilayer?
What is that they are small and nonpolar?
Calculate the water potential of a solution at 25°C with a solute potential of -1.2 MPa and a pressure potential of 0.5 MPa.
What is -0.7 MPa?
a. This interconnected system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles. It plays a critical role in the synthesis, modification, and transport of proteins and lipids within the cell.
b. Trace the pathway of a protein that is secreted from the cell, starting with the nucleus
a. endomembrane system
b. nucleus -> ribosome on rough ER ->transport via vesicles to the Golgi apparatus → modification and packaging in the Golgi → transport via vesicles to the plasma membrane → exocytosis.
Name 3 pieces of evidence supporting the endosymbiotic theory.
any three: circular DNA, double membrane, own mitochondria, mitochondria more similar to prokaryotic ones, etc...
Organisms living in cold environments often adjust the types of fatty acids in their phospholipid bilayers. Explain why an increase in this type of phospholipid fatty acid tail is advantageous in cold temperatures.
What is unsaturated fatty acid tail, as it prevent the membranes from packing too close together with the double bond kinks to prevent the membrane from solidifying.
Compare the ability of the following molecules to diffuse across a phospholipid bilayer without assistance: water, Na⁺, and glucose. Rank them from most permeable to least permeable and justify your ranking.
What is: water > glucose > Na⁺? Water is small and polar and can pass slowly through the membrane or via aquaporins; glucose is larger and polar, requiring transport proteins; Na⁺ is charged and cannot pass through the nonpolar membrane without a specific ion channel.
A cell with a solute potential of -0.8 MPa is placed in a solution with a solute potential of -1.0 MPa. Predict the net movement of water.
What is out of the cell?
Certain eukaryotic cells contain disproportionately high numbers of a specific organelle to support their specialized function. For example, muscle cells and sperm cells are packed with this organelle. Identify the organelle and explain how its abundance supports the specific energy demands of these specialized cells.
What is the mitochondrion? Its abundance provides the high levels of ATP required for muscle contraction in muscle cells and for flagellar movement in sperm cells, both of which are energy-intensive processes.
Two cells have the same volume, but different shapes: Cell A is spherical, and Cell B is long and cylindrical. Explain which cell is more efficient at exchanging materials with its environment and why, using the concept of surface area to volume ratio.
What is Cell B, the cylindrical cell? Because elongated or flattened shapes have a higher surface area relative to their volume compared to spheres, Cell B has a higher surface area to volume ratio, making it more efficient for diffusion and exchange of materials with the environment.
A mutation alters the primary structure of a transmembrane protein, replacing a hydrophilic region with hydrophobic amino acids in the center of the polypeptide. Predict how this change could affect the protein’s localization or function within the membrane, and explain your reasoning based on membrane structure and protein folding principles.
The altered protein may misfold or become embedded incorrectly in the membrane, potentially failing to span the bilayer or localizing entirely within the hydrophobic core? Because transmembrane proteins rely on hydrophilic and hydrophobic regions aligning with membrane polarity, changing a hydrophilic region to hydrophobic can disrupt proper insertion, folding, and function.
Glucose is a small molecule, but it cannot cross the plasma membrane by simple diffusion. Explain why, and identify how it typically enters the cell.
What is because glucose is polar and too large to pass through the hydrophobic interior of the membrane? It requires facilitated diffusion via a carrier protein.
A plant cell with a pressure potential of 0.3 MPa is placed in a solution at 25°C. The solution has a sucrose concentration of 0.5 M. Using the formula Ψs = –iCRT, calculate the solute potential of the solution and determine the net direction of water movement. (Assume i = 1, R = 0.0831 L·bar/mol·K, and T = 298 K).
What is: Ψs = –(1)(0.5 mol/L)(0.0831)(298) = –12.38 bar = –1.238 MPa?
Because the cell's total water potential (Ψ = Ψs + Ψp) is higher (depends on internal Ψs, assumed closer to 0), water will move out of the cell into the solution.