Biology 171L: Laboratory Exercises in Diffusion, Osmosis, Enzymatic Activity, Pigment Analysis, and Cellular Respiration

Comprehensive vocabulary flashcards covering the experimental procedures, reagents, calculations, and concepts across Biology 171L laboratory exercises: Diffusion and Osmosis, Enzymatic Activity of Peroxidase, Analysis of Photosynthetic Pigments, and Cellular Respiration in Organisms.

Diffusion

The movement of molecules down a concentration gradient (from areas of high concentration to areas of low concentration) driven by constant, random molecular motion.

Semi-permeable Membrane

A physical barrier, such as cellulose dialysis tubing, that permits the passage of some molecules while restricting others based on molecular size relative to its pores.

Barium Chloride ($\text{BaCl}_2$) Test

An assay where barium ions ($\text{Ba}^{2+}$) react with sulfate ions ($\text{SO}_4^{2-}$) to form an insoluble white precipitate of barium sulfate ($\text{BaSO}_4$).

Silver Nitrate ($\text{AgNO}_3$) Test

An assay where silver ions react with chloride ions ($\text{Cl}^-$) to form a white and silver precipitate of silver chloride ($\text{AgCl}$).

Iodine Solution Test

A chemical assay used to detect the presence of starch, which yields a black reaction product upon contact.

Bradford's Reagent Test

A reagent assay used to test for proteins (such as albumin), reacting to yield a dark royal blue product.

Positive Control

A standard reaction setup that produces a known positive result, used as a visual comparison and to verify that the experimental reagents and procedures are functioning correctly.

Dialysis Tubing Pore Size Limit

The approximate cutoff range determined experimentally to be between $96\,\text{daltons}$ (permeable sulfate ions) and $40{,}000\,\text{daltons}$ (impermeable starch molecules).

Osmosis

The net flow of water across a semipermeable membrane from a less concentrated solution into a more concentrated solution when solute molecules are restricted from diffusing.

Isotonic Solution

A solution where the solute concentration is equal on both sides of the plasma membrane, resulting in no net gain or loss of water by the cell.

Hypotonic Solution

A solution containing a lower solute concentration than the inside of a cell, causing water to enter the cell by osmosis.

Hypertonic Solution

A solution containing a higher solute concentration than the inside of a cell, causing water to flow out of the cell by osmosis.

Turgor Pressure

The internal hydrostatic pressure exerted against the plant cell wall when the cytoplasm and central vacuole take up water under hypotonic conditions.

Crenation

The shrinking of a cell that occurs when it loses water via osmosis after being placed in a hypertonic solution.

Anthocyanin

A water-soluble purple pigment located within the central vacuole of plant cells like Elodea that becomes visible and concentrated when the cell loses water and shrinks.

Orange G

A low-molecular-weight dye ($452\,\text{Da}$) that diffuses faster and travels farther through a $2\%$ agar plate in one hour than higher-molecular-weight dyes.

Enzyme

A biological catalyst, almost always a protein, that accelerates chemical reaction rates by lowering the activation energy.

Peroxidase

A plant enzyme extracted from turnip tissue that catalyzes the reduction of hydrogen peroxide ($\text{H}_2\text{O}_2$) to water while concomitantly oxidizing guaiacol.

Guaiacol

A phenolic compound serving as an electron donor that starts reduced and colorless, turning into a brown oxidized product during the peroxidase-catalyzed reaction.

Tetraguaiacol

The brownish, oxidized tetramer formed from four guaiacol molecules that strongly absorbs light at a wavelength of $500\,\text{nm}$.

Denaturation

The unfolding of the native conformation of a protein into a random, inactive configuration caused by extreme thermal agitation (such as boiling) or extreme pH levels.

Optimal Temperature for Peroxidase

Approximately $30^\circ\text{C}$, the temperature at which the enzyme exhibited its highest rate of reaction based on $500\,\text{nm}$ absorbance readings over time.

Optimal pH for Peroxidase

Approximately $\text{pH } 5$, which produced the greatest increase in absorbance over time compared to buffers at $\text{pH } 3$, $\text{pH } 7$, or $\text{pH } 9$.

Pepsin

A protein-digesting enzyme found in the stomach that operates at an optimal acidic condition of approximately $\text{pH } 2$.

Spectrophotometer

An instrument designed to produce light at a specified wavelength, pass it through a solution in a cuvette, and measure the light transmitted or absorbed.

Absorbance ($A$)

A logarithmic measurement of the light absorbed by a solution, ranging from $0$ to $2.0$, calculated by the equation $\text{Absorbance} = -\log_{10}(T)$.

Transmission ($T$)

The fraction or percentage ($0\text{--}100\%$) of light at a set wavelength that passes completely through a solution in a cuvette, where $T = \frac{\%\text{ Transmission}}{100}$.

Spectrophotometer Blank

A standard reference solution containing all reaction components except the active substance under test, calibrated to read $100\%$ transmission and $0.000$ absorbance.

Tube #1 (Enzyme Blank)

A control tube containing homogenization buffer, $\text{pH } 5$ buffer, $\text{H}_2\text{O}_2$, and guaiacol, but omitting turnip extract to calibrate the spectrophotometer at $500\,\text{nm}$.

Solvent Extraction

The removal of a chemical compound from a mixture based on its preferential solubility in a specific fluid, such as extracting photosynthetic pigments from spinach using acetone.

Paper Chromatography

A technique separating mixtures on polar paper via capillary action as a solvent travels upward, partitioning molecules according to their relative solubilities and polarities.

7:1 Petroleum Ether:Acetone

The non-polar developing solvent system utilized in paper chromatography to separate photosynthetic plant pigments based on their polar functional groups.

$R_f$ Value

The retention factor relative to the solvent front, calculated as: $R_f = \frac{\text{Distance travelled by pigment (cm) from origin}}{\text{Distance travelled by solvent (cm) from origin}}$.

Chlorophyll b

An olive-green photosynthetic pigment containing $6$ polar groups that forms the slowest-migrating band near the origin with an $R_f$ of approximately $0.32$.

Chlorophyll a

A blue-green primary photosynthetic pigment containing $5$ polar groups that migrates above chlorophyll b, exhibiting an $R_f$ of approximately $0.39$.

Violaxanthin

A yellow accessory carotenoid pigment containing $2$ polar groups that migrates to an intermediate distance with an $R_f$ of approximately $0.45$.

Lutein

A yellow accessory carotenoid pigment containing $1$ polar group that migrates relatively high on the chromatogram with an $R_f$ of approximately $0.60$.

$\beta$-Carotene

A yellow-orange non-polar accessory pigment with $0$ polar groups that migrates furthest with the non-polar solvent front, yielding an $R_f$ of $1.0$.

Visible Light Spectrum

The electromagnetic radiation band detectable by human vision, ranging from $380\,\text{nm}$ to $750\,\text{nm}$ (violet to red).

Photosynthesis

A biochemical pathway summarized by the equation: $\text{Sunlight} + 6\text{ CO}_2 + 6\text{ H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{ O}_2$.

Aerobic Cellular Respiration

The metabolic pathway consuming oxygen to break down glucose and generate chemical energy, summarized by: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{ O}_2 \rightarrow 6\text{ CO}_2 + 6\text{ H}_2\text{O} + \text{ATP (energy)}$.

Carbonic Acid Dissociation

The chemical series occurring when released carbon dioxide dissolves in water: $\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3 \rightarrow \text{H}^+ + \text{HCO}_3^-$, causing acidification.

Phenolphthalein

A pH indicator dye that appears pink in basic alkaline solutions above $\text{pH } 8.5$ and turns clear when acidified below $\text{pH } 8.5$.

Reference Beaker

A control beaker filled with pink alkaline phenolphthalein held at room temperature, titrated with acid to establish the baseline amount of $H^+$ needed to clear the solution.

Burette Calibration Value

The determined volume per drop obtained by delivering $2.0\,\text{mL}$ of $0.005\,\text{M H}_2\text{SO}_4$ across $49\,\text{drops}$, yielding $0.041\,\text{mL/drop}$.

$$\mu\text{moles CO}_2\text{ per Drop}$$

The stoichiometric equivalent of carbon dioxide calculated from the burette delivery of $0.005\,\text{M H}_2\text{SO}_4$, equal to $0.205\,\mu\text{moles CO}_2\text{/drop}$.

Net Number of Drops

The number of drops of sulfuric acid added to clear the pea beaker subtracted from the total drops added to clear the reference beaker, representing net $\text{CO}_2$ respired.

Cellular Respiration Rate Unit

The standardized rate expressed as $\mu\text{moles CO}_2/\text{gram}/\text{hour}$, which normalizes respiration measurements across differing organism weights and incubation times.

Germinating Peas (Experimental Model)

Non-photosynthesizing plant tissues that obtain energy via the catabolism of stored lipids and carbohydrates, making them ideal for measuring $\text{CO}_2$ production without photosynthetic uptake.

Temperature Effect on Pea Respiration

The metabolic increase observed when peas were incubated at $30^\circ\text{C}$ ($8.96\,\mu\text{moles CO}_2/\text{g}/\text{hr}$) compared to $15^\circ\text{C}$ ($4.55\,\mu\text{moles CO}_2/\text{g}/\text{hr}$), driven by faster enzyme kinetics at warmer temperatures.