3.E: Cell Structure and Function (Exercises)
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3.1: How Cells Are Studied
In multicellular organisms, several cells of one particular kind interconnect with each other and perform shared functions to form tissues (for example, muscle tissue, connective tissue, and nervous tissue), several tissues combine to form an organ (for example, stomach, heart, or brain), and several organs make up an organ system (such as the digestive system, circulatory system, or nervous system). Several systems functioning together form an organism (such as an elephant, for example).
Multiple Choice
When viewing a specimen through a light microscope, scientists use _________ to distinguish the individual components of cells.
A. a beam of electrons
B. radioactive isotopes
C. special stains
D. high temperatures
- Answer
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C
The ___________ is the basic unit of life.
A. organism
B. cell
C. tissue
D. organ
- Answer
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B
Free Response
What are the advantages and disadvantages of light, transmission, and scanning electron microscopes?
- Answer
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The advantages of light microscopes are that they are easily obtained, and the light beam does not kill the cells. However, typical light microscopes are somewhat limited in the amount of detail that they can reveal. Electron microscopes are ideal because you can view intricate details, but they are bulky and costly, and preparation for the microscopic examination kills the specimen. Transmission electron microscopes are designed to examine the internal structures of a cell, whereas a scanning electron microscope only allows visualization of the surface of a structure.
3.2: Comparing Prokaryotic and Eukaryotic Cells
Cells fall into one of two broad categories: prokaryotic and eukaryotic. The predominantly single-celled organisms of the domains Bacteria and Archaea are classified as prokaryotes (pro- = before; -karyon- = nucleus). Animal cells, plant cells, fungi, and protists are eukaryotes (eu- = true).
Multiple Choice
Which of these do all prokaryotes and eukaryotes share?
A. nuclear envelope
B. cell walls
C. organelles
D. plasma membrane
- Answer
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D
A typical prokaryotic cell __________________ compared to a eukaryotic cell.
A. is smaller in size by a factor of 100
B. is similar in size
C. is smaller in size by a factor of one million
D. is larger in size by a factor of 10
- Answer
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A
Free Response
Describe the structures that are characteristic of a prokaryote cell.
- Answer
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Prokaryotic cells are surrounded by a plasma membrane and have DNA, cytoplasm, and ribosomes, like eukaryotic cells. They also have cell walls and may have a cell capsule. Prokaryotes have a single large chromosome that is not surrounded by a nuclear membrane. Prokaryotes may have flagella or motility, pili for conjugation, and fimbriae for adhesion to surfaces.
3.3: Eukaryotic Cells
At this point, it should be clear that eukaryotic cells have a more complex structure than do prokaryotic cells. Organelles allow for various functions to occur in the cell at the same time. Before discussing the functions of organelles within a eukaryotic cell, let us first examine two important components of the cell: the plasma membrane and the cytoplasm.
Multiple Choice
Which of the following is found both in eukaryotic and prokaryotic cells?
A. nucleus
B. mitochondrion
C. vacuole
D. ribosome
- Answer
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D
Which of the following is not a component of the endomembrane system?
A. mitochondrion
B. Golgi apparatus
C. endoplasmic reticulum
D. lysosome
- Answer
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A
Free Response
In the context of cell biology, what do we mean by form follows function? What are at least two examples of this concept?
- Answer
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“Form follows function” refers to the idea that the function of a body part dictates the form of that body part. As an example, organisms like birds or fish that fly or swim quickly through the air or water have streamlined bodies that reduce drag. At the level of the cell, in tissues involved in secretory functions, such as the salivary glands, the cells have abundant Golgi.
3.4: The Cell Membrane
The plasma membrane is referred to as the fluid mosaic model and is composed of a bilayer of phospholipids, with their hydrophobic, fatty acid tails in contact with each other. The landscape of the membrane is studded with proteins, some of which span the membrane. Some of these proteins serve to transport materials into or out of the cell. Carbohydrates are attached to some of the proteins and lipids on the outward-facing surface of the membrane. These function to identify other cells.
Multiple Choice
Which plasma membrane component can be either found on its surface or embedded in the membrane structure?
A. protein
B. cholesterol
C. carbohydrate
D. phospholipid
- Answer
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A
The tails of the phospholipids of the plasma membrane are composed of _____ and are _______?
A. phosphate groups; hydrophobic
B. fatty acid groups; hydrophilic
C. phosphate groups; hydrophilic
D. fatty acid groups; hydrophobic
- Answer
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D
Free Response
Why is it advantageous for the cell membrane to be fluid in nature?
- Answer
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The fluidity of the cell membrane is necessary for the operation of some enzymes and transport mechanisms within the membrane.
3.5: Passive Transport
The most direct forms of membrane transport are passive. Passive transport is a naturally occurring phenomenon and does not require the cell to expend energy to accomplish the movement. In passive transport, substances move from an area of higher concentration to an area of lower concentration in a process called diffusion. A physical space in which there is a different concentration of a single substance is said to have a concentration gradient.
Multiple Choice
Water moves via osmosis _________.
A. throughout the cytoplasm
B. from an area with a high concentration of other solutes to a lower one
C. from an area with a low concentration of solutes to an area with a higher one
D. from an area with a low concentration of water to one of higher concentration
- Answer
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C
The principal force driving movement in diffusion is __________.
A. temperature
B. particle size
C. concentration gradient
D. membrane surface area
- Answer
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C
Free Response
Why does osmosis occur?
- Answer
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Water moves through a semipermeable membrane in osmosis because there is a concentration gradient across the membrane of solute and solvent. The solute cannot effectively move to balance the concentration on both sides of the membrane, so water moves to achieve this balance.
3.6: Active Transport
Active transport mechanisms require the use of the cell’s energy, usually in the form of adenosine triphosphate (ATP). If a substance must move into the cell against its concentration gradient, that is, if the concentration of the substance inside the cell must be greater than its concentration in the extracellular fluid, the cell must use energy to move the substance. Some active transport mechanisms move small-molecular weight material, such as ions, through the membrane.
Multiple Choice
Active transport must function continuously because __________.
A. plasma membranes wear out
B. cells must be in constant motion
C. facilitated transport opposes active transport
D. diffusion is constantly moving the solutes in the other direction
- Answer
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D
Free Response
Where does the cell get energy for active transport processes?
- Answer
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The cell harvests energy from ATP produced by its own metabolism to power active transport processes, such as pumps.