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By the end of this topic, students will be able to:
Microscopy is the use of microscopes to visualize and study small structures and cells. There are two main types of microscopes: light microscopes and electron microscopes. Light microscopes use visible light to produce an image, while electron microscopes use a beam of electrons to produce a highly magnified image. The resolution of a microscope is its ability to distinguish between two closely spaced points, and is limited by the wavelength of the light or electrons used.
Prokaryotes are a group of cells that lack a true nucleus and other membrane-bound organelles. They are typically small, ranging from 0.5 to 5.0 ?m in diameter, and have a simple structure consisting of a cell wall, a plasma membrane, and genetic material in the form of a single circular chromosome. Prokaryotes are found in a wide range of environments and include bacteria and archaea.
Eukaryotes are a group of cells that have a true nucleus and other membrane-bound organelles. They are typically larger than prokaryotes, ranging from 10 to 100 ?m in diameter, and have a complex structure consisting of a cell wall, a plasma membrane, and genetic material in the form of a true nucleus. Eukaryotes include plants, animals, fungi, and protists.
Organelles are specialized structures within eukaryotic cells that perform specific functions. Some common organelles include:
A biologist uses a light microscope to study the structure of a plant cell. The microscope has a magnification of 400x and a resolution of 0.2 ?m. If the biologist observes a cell wall that is 1.0 ?m thick, what is the minimum distance between two closely spaced points that the biologist can distinguish?
Solution: To find the minimum distance, we need to divide the resolution by the magnification. Minimum distance = resolution / magnification = 0.2 ?m / 400x = 0.0005 ?m.
A bacterium has a cell wall that is composed of a single layer of peptidoglycan. If the bacterium has a diameter of 2.0 ?m, what is the surface area of the cell wall?
Solution: To find the surface area, we need to use the formula for the surface area of a sphere: A = 4?r^2, where r is the radius of the sphere. The radius of the bacterium is half its diameter, so r = 1.0 ?m. Surface area = 4?(1.0 ?m)^2 = 12.57 ?m^2.
A plant cell has a chloroplast that is responsible for photosynthesis. If the chloroplast has a surface area of 100 ?m^2 and a volume of 50 ?m^3, what is the thickness of the chloroplast?
Solution: To find the thickness, we need to use the formula for the volume of a sphere: V = (4/3)?r^3, where r is the radius of the sphere. We can rearrange this formula to solve for r: r = (3V / 4?)^(1/3). Plugging in the values, we get r = (3(50 ?m^3) / 4?)^(1/3) = 1.0 ?m. The thickness of the chloroplast is twice the radius, so thickness = 2r = 2.0 ?m.
What is the primary difference between a light microscope and an electron microscope?
A) Light microscopes use visible light, while electron microscopes use ultraviolet light. B) Light microscopes have a higher magnification than electron microscopes. C) Light microscopes use a beam of electrons, while electron microscopes use visible light. D) Light microscopes have a lower resolution than electron microscopes.
Correct answer: D) Light microscopes have a lower resolution than electron microscopes.
Why the distractors fail: A) Ultraviolet light is not used in electron microscopes. B) Electron microscopes typically have higher magnification than light microscopes. C) Electron microscopes use a beam of electrons, while light microscopes use visible light.
What is the primary function of the cell wall in prokaryotic cells?
A) To regulate the movement of ions across the plasma membrane. B) To provide structural support and maintain the cell's shape. C) To synthesize proteins and other biomolecules. D) To regulate the cell's metabolism.
Correct answer: B) To provide structural support and maintain the cell's shape.
Why the distractors fail: A) The cell wall does not regulate ion movement. C) Protein synthesis occurs in the cytoplasm, not the cell wall. D) Metabolic regulation occurs in the cytoplasm, not the cell wall.
What is the primary function of the mitochondria in eukaryotic cells?
A) To synthesize proteins and other biomolecules. B) To regulate the cell's metabolism. C) To generate energy for the cell through cellular respiration. D) To regulate the movement of ions across the plasma membrane.
Correct answer: C) To generate energy for the cell through cellular respiration.
Why the distractors fail: A) Protein synthesis occurs in the cytoplasm, not the mitochondria. B) Metabolic regulation occurs in the cytoplasm, not the mitochondria. D) Ion movement is regulated by the plasma membrane, not the mitochondria.
What is the primary function of the endoplasmic reticulum in eukaryotic cells?
A) To synthesize proteins and other biomolecules. B) To regulate the cell's metabolism. C) To transport proteins and other biomolecules within the cell. D) To regulate the movement of ions across the plasma membrane.
Correct answer: C) To transport proteins and other biomolecules within the cell.
Why the distractors fail: A) Protein synthesis occurs in the cytoplasm, not the endoplasmic reticulum. B) Metabolic regulation occurs in the cytoplasm, not the endoplasmic reticulum. D) Ion movement is regulated by the plasma membrane, not the endoplasmic reticulum.
What is the significance of the cell wall in eukaryotic cells?
A) It provides structural support and maintains the cell's shape. B) It regulates the movement of ions across the plasma membrane. C) It synthesizes proteins and other biomolecules. D) It regulates the cell's metabolism.
Correct answer: A) It provides structural support and maintains the cell's shape.
Why the distractors fail: B) Ion movement is regulated by the plasma membrane, not the cell wall. C) Protein synthesis occurs in the cytoplasm, not the cell wall. D) Metabolic regulation occurs in the cytoplasm, not the cell wall.
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