USF BSC2010L Midterm

What is the scientific method?

A structured way to investigate a question using observations, a testable hypothesis, an experiment, data analysis, and conclusions.

What is a hypothesis?

A testable proposed explanation or prediction about the relationship between variables.

What does falsifiable mean?

A hypothesis is falsifiable if evidence could potentially show that it is wrong.

What is an independent variable?

The factor deliberately changed or manipulated by the experimenter.

What is a dependent variable?

The response that is measured to determine the effect of the independent variable.

What is a control variable?

A factor kept constant so it does not provide an alternative explanation for the results.

How is a Methods section different from a step-by-step procedure?

A Methods section explains how the experiment was performed clearly enough to understand or reproduce it, usually in past tense and paragraph form; it is not simply a numbered instruction list.

What belongs on the x-axis of a graph?

The independent variable.

What belongs on the y-axis of a graph?

The dependent variable.

What should a properly formatted graph include?

A descriptive title, labeled x- and y-axes, units where appropriate, an appropriate scale, and clearly displayed data.

What is percent error?

|experimental value − accepted value| ÷ accepted value × 100%.

What is percent change?

(final value − initial value) ÷ initial value × 100%.

How do you calculate a rate from a graph?

Rate = slope = change in y ÷ change in x (∆y/∆x).

What is maximum steady rate?

The steepest sustained linear rate in the data, found from the slope over that steady interval.

What is % w/v?

Percent weight/volume = grams of solute ÷ mL of final solution × 100. A 5% w/v solution contains 5 g solute per 100 mL solution.

1 meter equals how many millimeters and micrometers?

1 m = 1,000 mm = 1,000,000 µm.

1 liter equals how many milliliters?

1 L = 1,000 mL.

1 milliliter equals how many microliters?

1 mL = 1,000 µL.

1 gram equals how many milligrams?

1 g = 1,000 mg.

When should appropriate PPE be worn?

Whenever the procedure or hazard requires it; this can include goggles, gloves, and a lab coat depending on the material or procedure.

Why must hazardous waste go into designated containers?

Different hazards require specific disposal methods; improper disposal can expose people or the environment to dangerous materials.

What is plagiarism?

Presenting someone else's words, ideas, or work as your own without appropriate attribution.

What is a micropipette used for?

Accurately measuring and transferring very small liquid volumes, usually in microliters.

What is the typical P20 volume range?

About 2-20 µL.

What is the typical P200 volume range?

About 20-200 µL.

What is the typical P1000 volume range?

About 100-1000 µL.

What is the first stop on a micropipette used for?

Press to the first stop before aspirating and use the first stop for the measured dispensing stroke.

What is the second stop on a micropipette used for?

Blowout: pushing out the remaining liquid from the tip during dispensing.

What is the basic micropipette sequence?

Set a valid volume → attach tip → press to first stop → immerse tip → slowly release to aspirate → move to receiving vessel → press to first stop, then second stop to dispense → withdraw tip → release plunger → eject tip.

Why should you not set a micropipette outside its stated range?

It can produce inaccurate measurements and may damage the pipette.

What does a spectrophotometer measure?

How much light a sample absorbs or transmits at a selected wavelength.

What is absorbance?

A measure of how much light is absorbed by a sample.

What is a chromophore?

A molecule or part of a molecule that absorbs light at particular wavelengths.

Why do you blank a spectrophotometer?

To account for absorbance from the solvent, cuvette, and other background components so the measured absorbance mainly reflects the analyte.

When should a spectrophotometer be blanked?

Before measuring experimental samples and again when required after changing relevant measurement conditions such as wavelength or blank solution.

What is an absorption spectrum?

A graph showing how strongly a substance absorbs light across different wavelengths.

What is λmax?

The wavelength at which a substance has its maximum absorbance.

What is a standard curve?

A graph made from known concentrations and their measured responses, used to determine the concentration of an unknown.

How do you find an unknown concentration from y = mx + b?

Rearrange to x = (y − b) ÷ m, where y is the measured response.

What dilution equation should you know?

M1V1 = M2V2.

A 10 mL sample of 2.0 M solution is diluted to 50 mL. What is the final concentration?

C2 = (2.0 M × 10 mL) ÷ 50 mL = 0.40 M.

What is diffusion?

The net movement of particles from an area of higher concentration toward an area of lower concentration due to random molecular motion.

What does it mean to move down a concentration gradient?

To move from higher concentration toward lower concentration.

What is dynamic equilibrium?

Particles continue moving randomly, but there is no net change in concentration because movement in opposite directions balances.

How does increasing temperature generally affect diffusion?

It increases molecular motion and generally increases the rate of diffusion.

Why is surface-area-to-volume ratio important?

Exchange occurs across the surface while the cell's needs depend on its volume. As size increases, volume grows faster than surface area, making exchange less efficient.

How can organisms overcome surface-area-to-volume limitations?

Examples include remaining small, being thin/flattened, folding surfaces, branching structures, or using internal transport systems.

What is osmosis?

The diffusion of water across a selectively permeable membrane.

In osmosis, water tends to move toward which side?

Toward the side with the greater effective solute concentration (lower free-water concentration).

What is a hypotonic solution relative to a cell?

The solution has a lower effective solute concentration than the cell, so water tends to enter the cell.

What is a hypertonic solution relative to a cell?

The solution has a higher effective solute concentration than the cell, so water tends to leave the cell.

What is an isotonic solution?

A solution that has the same effective solute concentration as the cell.

What happens to an animal cell in a strongly hypotonic solution?

Water enters; the cell swells and may lyse because it lacks a rigid cell wall.

How do plant cells respond to hypotonic conditions?

Water enters, but the cell wall resists excessive expansion; the cell becomes turgid.

How can bacteria resist bursting in hypotonic environments?

Their cell wall helps resist osmotic swelling.

How can freshwater protists remove excess water?

Contractile vacuoles collect and expel excess water.

What does a positive percent change in mass in an osmosis experiment suggest?

The specimen gained water; net water movement was into it.

What does a negative percent change in mass suggest?

The specimen lost water; net water movement was out of it.

How can an egg's osmolarity be estimated from an osmosis graph?

Find the external solute concentration where percent change in mass is approximately 0%; that is the isotonic point and estimates the egg's internal osmolarity.

What is the function of the ocular lens?

The eyepiece you look through; it provides part of the microscope's total magnification.

What is the function of an objective lens?

Provides the main magnification and resolution near the specimen.

What is the stage in a microscope?

The platform that supports and positions the microscope slide.

What does the condenser do?

Focuses light onto the specimen.

What does the iris diaphragm do?

Controls the amount/angle of light reaching the specimen and affects contrast.

What is the coarse-focus knob used for?

Large focusing adjustments, generally at low power; avoid using it at high power where it can drive the objective into the slide.

What is the fine-focus knob used for?

Small, precise focus adjustments, especially at higher magnification.

How is total magnification calculated?

Ocular magnification × objective magnification.

If the ocular is 10× and objective is 40×, what is total magnification?

400×.

What is magnification?

How much larger the image appears than the actual specimen.

What is resolution?

The ability to distinguish two nearby points as separate; better resolution reveals finer detail.

What is contrast?

The visible difference between a specimen and its background or between structures within the specimen.

What is depth of field?

The thickness of the specimen that appears in focus at one time; it generally decreases as magnification increases.

What is refraction?

The bending of light as it passes between materials with different refractive indices.

Why is immersion oil used with the 100× objective?

Its refractive index reduces light bending/loss between the slide and objective, improving light collection and resolution.

What is a wet mount?

A specimen placed in a drop of liquid on a slide and covered with a coverslip for microscope viewing.

What equation relates field of view and magnification?

FOV1 × Mag1 = FOV2 × Mag2.

If FOV is 4.0 mm at 40×, what is FOV at 400×?

0.40 mm.

How can cell size be estimated using field of view?

Approximate cell size = field-of-view diameter ÷ number of cells that fit across that diameter.

What is the main difference between prokaryotic and eukaryotic cells?

Prokaryotes lack a membrane-bound nucleus and membrane-bound organelles; eukaryotes have them.

Do bacteria have a nucleus?

No. Their DNA is located in a nucleoid region.

What is a nucleus?

A membrane-bound organelle in eukaryotic cells that contains most of the cell's DNA.

What is a nucleoid?

The non-membrane-bound region of a prokaryotic cell containing its DNA.

What is a chloroplast?

A photosynthetic organelle in plants and algae containing chlorophyll and the internal membranes needed for photosynthesis.

What is a mitochondrion?

A eukaryotic organelle where major stages of aerobic cellular respiration occur.

What is the central vacuole?

A large plant-cell compartment involved in storage and maintaining turgor pressure.

What is the cell wall?

A rigid layer outside the plasma membrane that provides support and protection; its composition differs among groups.

What is a contractile vacuole?

An osmoregulatory organelle that collects and expels excess water, common in freshwater protists.

What are cilia?

Numerous short cellular projections that can propel a cell or move material along its surface.

What are pseudopodia?

Temporary cytoplasmic extensions used by cells such as amoebae for movement and engulfing material.

What does endosymbiotic theory explain?

The origin of mitochondria and chloroplasts from ancestral free-living bacteria that became permanent symbionts inside another cell.

What evidence supports endosymbiotic theory?

Mitochondria and chloroplasts have bacterial-like size, circular DNA, bacterial-type ribosomes, divide by a fission-like process, and have double membranes.

What is Elodea?

A freshwater aquatic plant; its cells are photosynthetic eukaryotic plant cells.

What are microscope ID clues for Elodea?

Rectangular/brick-like cells arranged in rows, obvious cell walls, many green chloroplasts, a large central vacuole, and sometimes visible cytoplasmic streaming.

What is Egeria densa?

A freshwater aquatic plant used to observe living photosynthetic plant cells and chloroplasts.

What are microscope ID clues for Egeria densa?

Long rectangular cells arranged in rows with rigid walls and many green chloroplasts. It can look extremely similar to Elodea.

What is Lactobacillus?

A prokaryotic bacterium: very small rod-shaped cells, often requiring high magnification/oil immersion; no visible nucleus or membrane-bound organelles.

What is Anabaena?

A photosynthetic prokaryotic cyanobacterium. Bead-like chains/filaments of rounded cells. Some specialized cells may look larger or different from ordinary vegetative cells.

What is Oscillatoria?

A photosynthetic prokaryotic cyanobacterium. Long, unbranched filaments made of many fairly uniform cells; looks more like a segmented thread than a bead necklace.

What is Amoeba Proteus?

A single-celled eukaryotic protest. Irregular, constantly changing shape with pseudopodia; may show vacuoles and flowing cytoplasm..

What is Paramecium caudatum?

A single-celled eukaryotic protist. Elongated/slipper-shaped cell covered in cilia; may show contractile vacuoles and internal structures.