What does the term motile mean?

Choice A rationale: Only use lower power magnification is incorrect because this does not solve the problem of the dark field of view, but rather avoids it. Using lower power magnification means that you will not be able to see the details of the specimen that you want to observe under the 40x objective lens. Lower power magnification also has a larger field of view and a lower resolution than higher power magnification.

Choice B rationale: Add more immersion oil is incorrect because immersion oil is only used for the highest magnification objective lens, which is the 100x oil immersion objective lens, not the 40x objective lens. Immersion oil is a type of oil that has the same refractive index as glass, which means that it bends light in the same way as glass. Immersion oil is applied between the slide and the lens to reduce the refraction of light and increase the clarity of the image.

Choice C rationale: Adjust the fine adjustment knob is incorrect because the fine adjustment knob is used to fine-tune the focus of the specimen, not the brightness of the field of view. The fine adjustment knob is a small knob that is located on the side of the microscope, next to the coarse adjustment knob. The fine adjustment knob is used to make small changes in the distance between the objective lens and the specimen, which improves the sharpness of the image.

Choice D rationale: Increase the light intensity is correct because the light intensity is the amount of light that reaches the specimen and the objective lens, which affects the brightness of the field of view. The light intensity can be adjusted by using the rheostat, which is a dial that is located on the base of the microscope, next to the light source. The rheostat can increase or decrease the voltage of the light source, which changes the brightness of the light. Increasing the light intensity can make the field of view brighter and easier to see.

Choice A rationale: The variant is a term used to describe a viral genome that may contain one or more mutations. It is not related to the difference in concentration between two areas. ³

Choice B rationale: The concentration gradient is the correct term for the difference in concentration between two areas. It is a measure of how steep the change in concentration is. ¹

Choice C rationale: Level gradient is not a term used in biology or chemistry. It may refer to the slope of a surface or a line, but not to the concentration of solutes in a solution.

Choice D rationale: The osmotic pressure is the minimum pressure required to prevent the flow of solvent molecules through a semipermeable membrane. It depends on the concentration of solute particles in the solution and is calculated with the formula π = iCRT. It is not the same as the concentration gradient, although it is related to it. ⁴

Choice E rationale: Turgid pressure is the force exerted by stored water against a cell wall. It is caused by the osmotic flow of water and occurs in plants, fungi, and bacteria. It is also called hydrostatic pressure and affects cell growth, movement, and dispersal. It is not the same as the concentration gradient, although it is influenced by it. ⁵