Cell Structure and Function Flashcards
The cell theory was developed over many years. What are its four basic concepts?
Cells are the building blocks of all plants and animals.
Cells are the smallest functioning units of life.
Cells are produced through the division of preexisting cells.
Each cell maintains homeostasis.
What is the study of cells?
Cytology
List the general functions of the plasma membrane.
Physical isolation. The plasma membrane is a physical barrier that separates the inside of the cell from the surrounding extracellular fluid. Conditions inside and outside the cell are very different. Those differences must be maintained to preserve homeostasis.
Regulation of exchange with the environment. The plasma membrane controls the entry of ions and nutrients, the elimination of wastes, and the release of secretions.
Sensitivity to the environment. The plasma membrane is the first part of the cell affected by changes in the extracellular fluid. It also contains a variety of molecules that act as receptors, enabling the cell to recognize and respond to specific molecules in its environment.
Structural support. Specialized connections between plasma membranes, or between membranes and materials outside the cell, give tissues a stable structure.
Which component of the plasma membrane is primarily responsible for forming a physical barrier between the cell’s internal and external environments?
The phospholipids in a plasma membrane lie in two distinct layers. For this reason, the plasma membrane is called a phospholipid bilayer. In each half of the bilayer, the phospholipids lie with their heads at the membrane surface and their tails on the inside. The heads are soluble in water, or hydrophilic. The tails are insoluble in water, or hydrophobic.
Which functional class of membrane proteins allows water and small ions to cross the plasma membrane?
Channel proteins allow water and small ions to cross the plasma membrane.
What is meant by “selectively permeable,” when referring to a plasma membrane?
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A selectively permeable membrane allows the passage of some substances while restricting the passage of others. It falls between two extremes: impermeable, which allows no substance to pass, and freely permeable, which permits the passage of any substance.
Define diffusion.
Diffusion is the passive molecular movement of a substance from an area of higher concentration to an area of lower concentration; diffusion proceeds until the concentration gradient is eliminated and equilibrium is reached.
How would a decrease in the concentration of oxygen in the lungs affect the diffusion of oxygen into the blood?
Diffusion is driven by a concentration gradient. The larger the concentration gradient, the faster the rate of diffusion; the smaller the concentration gradient, the slower the rate of diffusion. If the concentration of oxygen in the lungs were to decrease, the concentration gradient between oxygen in the lungs and oxygen in the blood would decrease (as long as the oxygen level of the blood remained constant). Thus, oxygen would diffuse into the blood more slowly.
Define osmosis.
Osmosis is the diffusion of water across a selectively permeable membrane from one solution to another solution. Movement occurs toward higher solute concentrations because that is where the concentration of water is lower.
Relative to a surrounding hypertonic solution, the cytosol of a red blood cell is
Relative to a surrounding hypertonic solution, the contents of a red blood cell are hypotonic; that is, the solute concentration within an RBC is less than that of the solution surrounding it.
What is the difference between active and passive transport processes?
Active transport processes require the expenditure of cellular energy in the form of the high-energy bonds of ATP molecules. Passive transport processes (diffusion, osmosis, and facilitated diffusion) result in the movement of ions and molecules across the plasma membrane without any energy expenditure by the cell.
During digestion, the concentration of hydrogen ions (H+) in the stomach rises to many times that within the cells lining the stomach, where H+ are produced. Is the type of transport process involved passive or active?
An active transport process must be involved because H+ must be transported from the cells lining the stomach, where H+ are less concentrated, to the interior of the stomach, where H+ are more concentrated—that is, against their concentration gradient.
When certain types of white blood cells encounter bacteria, they are able to engulf them and bring them into the cell. What is this process called?
This process is an example of phagocytosis.
Describe the difference between the cytoplasm and the cytosol.
Cytoplasm is the material between the plasma membrane and the nuclear membrane. Cytosol is the fluid portion of the cytoplasm.
Identify the membranous organelles and list their functions.
The membranous organelles (and their functions) include (1) endoplasmic reticulum = synthesis of secretory products, intracellular storage and transport; (2) rough ER = modification and packaging of newly synthesized proteins; (3) smooth ER = lipid and carbohydrate synthesis; (4) Golgi apparatus = storage, alteration, and packaging of secretory products and lysosomal enzymes; (5) lysosomes = intracellular removal of damaged organelles or pathogens; (6) mitochondria = production of 95 percent of the ATP required by the cell; (7) peroxisomes = neutralization of toxic compounds.
