lab for bio

Lab 4: Diffusion, Osmosis, and Membrane Permeability1. Osmosis

Osmosis is the movement of water across a selectively permeable membrane from an area of XX solute concentration to XX solute concentration.

Remember: Water moves toward the side with MORE solute.

2. Hypertonic, Hypotonic, and Isotonic

Hypotonic solution

XX solute outside the cell → water XX→ animal cells XX and may XX.

Hemolysis: XX of XX XX cells.

Hypertonic solution

More solute XX → water XX → animal cells XX (crenation).

Plant cells undergo XX, where the cell membrane pulls away from the cell wall.

Isotonic solution

XX effective solute concentrations → no XX XX movement → animal cells remain normal.

Plant cells: In a hypotonic solution, water enters, creating turgor pressure. The cell becomes turgid rather than bursting because of its cell wall.

3. Dialysis Bags and Osmosis

A dialysis membrane is XX XX. Small molecules and water can pass through, while large molecules such as starch generally cannot.

Your practice exam has a bag containing 10% salt placed in three different solutions.

Outside solution	Water movement	Bag mass
10% salt	No net movement	Same
2% salt	Into bag	Increases
30% salt	Out of bag	Decreases

Exam trick: The bag in 2% salt gains the most mass because XX moves into the bag.

4. Chemical Tests to Memorize

Reagent	Tests for	Positive result	Negative result
Iodine (Lugol's)	XX	XX-XX	XX-XX
Biuret	XX	XX	XX
Benedict's + heat	XX XX	XX/XX/XX	XX
Barium chloride	XX XX	XX XX	XX XX
Silver nitrate	XX XX	XX XX	XX X
Sudan IV	XX	XX/XX-stained lipid	XX distinct stained lipid layer

Membrane permeability: Focus on the molecule being tested, not the reagent used. XX and XX are generally too large to cross your dialysis membrane, while smaller solutes may pass depending on the membrane.

Lab 4: Diffusion, Osmosis, and Membrane Permeability1. Osmosis

Osmosis is the movement of water across a selectively permeable membrane from an area of lower solute concentration to higher solute concentration.

Remember: Water moves toward the side with MORE solute.

2. Hypertonic, Hypotonic, and Isotonic

Hypotonic solution

Less solute outside the cell → water enters → animal cells swell and may burst.

Hemolysis: Bursting of red blood cells.

Hypertonic solution

More solute outside → water leaves → animal cells shrink (crenation).

Plant cells undergo plasmolysis, where the cell membrane pulls away from the cell wall.

Isotonic solution

Equal effective solute concentrations → no net water movement → animal cells remain normal.

Plant cells: In a hypotonic solution, water enters, creating turgor pressure. The cell becomes turgid rather than bursting because of its cell wall.

3. Dialysis Bags and Osmosis

A dialysis membrane is selectively permeable. Small molecules and water can pass through, while large molecules such as starch generally cannot.

Your practice exam has a bag containing 10% salt placed in three different solutions.

Outside solution	Water movement	Bag mass
10% salt	No net movement	Same
2% salt	Into bag	Increases
30% salt	Out of bag	Decreases

Exam trick: The bag in 2% salt gains the most mass because water moves into the bag.

4. Chemical Tests to Memorize

Reagent	Tests for	Positive result	Negative result
Iodine (Lugol's)	Starch	Blue-black	Yellow-brown
Biuret	Protein	Purple	Blue
Benedict's + heat	Reducing sugars	Green/yellow/orange/red	Blue
Barium chloride	Sulfate ions	White precipitate	No precipitate
Silver nitrate	Chloride ions	White precipitate	No precipitate
Sudan IV	Lipids	Red/orange-stained lipid	No distinct stained lipid layer

Important corrections to your notes: Barium chloride tests for sulfate ions, not proteins. Sudan IV is a lipid stain, so a milky-white result is not the standard positive color.

Membrane permeability: Focus on the molecule being tested, not the reagent used. Starch and proteins are generally too large to cross your dialysis membrane, while smaller solutes may pass depending on the membrane.

Lab 5: Enzymes and Peroxidase1. What Is an Enzyme?

An enzyme is a XX XX that XX up chemical reactions by lowering activation energy.

• Substrate: Molecule an XX acts on.

• Product: Molecule XX by the XX,

• Active site: Region where the XX XX.

• Inhibitor: Substance that XX enzyme activity.

• Denaturation: Loss of XX XX and function, often caused by excessive heat or extreme pH.

2. Peroxidase Reaction

Peroxidase is an enzyme that helps break down XX XX (H₂O₂).

In your experiment, it catalyzes the oxidation of guaiacol.

2 Guaiacol + H₂O₂ → 2 oxidized guaiacol + 2 H₂O

Before

Colorless guaiacol

After

Reddish-brown product

The stronger or faster the reddish-brown color develops, the greater the XX XX under comparable conditions.

Your lab measures this using a spectrophotometer at 470 nm.

3. Factors Affecting Enzyme Activity

Factor	Effect on enzyme activity
More enzyme	XX reaction if enough XX is available
More substrate	XX reaction until enzymes become XX
Optimal pH	XX enzyme activity
Extreme pH	XX decreases
Increasing temperature	Speeds reaction until XX XX
Excessive heat/boiling	Denatures enzyme, XX activity
Hydroxylamine	Inhibits XX, XX activity

Hydroxylamine interferes with XX by binding to the iron in its heme group.

4. Enzyme Activity Calculations

Your lab measures how quickly absorbance increases.

Formula:

Rate = Change in XX÷ Change in XX

Example: Absorbance increases from 0.200 to 0.400 in 20 seconds.

Change = 0.400 − 0.200 = 0.200

Rate per minute = (0.200 ÷ 20) × 60 = 0.600 absorbance units/min

A steeper upward slope means greater enzyme activity.

5. Practice Exam Question: Which Tube Changes Color Most?

Tube	Guaiacol	Hydroxylamine	Expected result
1	No	No	Little or no color change
2	Yes	No	Strongest color change
3	Yes	Yes	Reduced color change

All three contain pea-root enzyme extract.

Answer: Tube 2, because it has guaiacol and active peroxidase without the inhibitor.

Remember for Lab 5: Peroxidase + guaiacol + H₂O₂ → reddish-brown color; hydroxylamine decreases the reaction.

Lab 5: Enzymes and Peroxidase1. What Is an Enzyme?

An enzyme is a biological catalyst that speeds up chemical reactions by lowering activation energy.

• Substrate: Molecule an enzyme acts on.

• Product: Molecule produced by the reaction.

• Active site: Region where the substrate binds.

• Inhibitor: Substance that decreases enzyme activity.

• Denaturation: Loss of enzyme structure and function, often caused by excessive heat or extreme pH.

2. Peroxidase Reaction

Peroxidase is an enzyme that helps break down hydrogen peroxide (H₂O₂).

In your experiment, it catalyzes the oxidation of guaiacol.

2 Guaiacol + H₂O₂ → 2 oxidized guaiacol + 2 H₂O

Before

Colorless guaiacol

After

Reddish-brown product

The stronger or faster the reddish-brown color develops, the greater the peroxidase activity under comparable conditions.

Your lab measures this using a spectrophotometer at 470 nm.

3. Factors Affecting Enzyme Activity

Factor	Effect on enzyme activity
More enzyme	Faster reaction if enough substrate is available
More substrate	Faster reaction until enzymes become saturated
Optimal pH	Highest enzyme activity
Extreme pH	Activity decreases
Increasing temperature	Speeds reaction until optimal temperature
Excessive heat/boiling	Denatures enzyme, decreasing activity
Hydroxylamine	Inhibits peroxidase, decreasing activity

Hydroxylamine interferes with peroxidase by binding to the iron in its heme group.

4. Enzyme Activity Calculations

Your lab measures how quickly absorbance increases.

Formula:

Rate = Change in absorbance ÷ Change in time

Example: Absorbance increases from 0.200 to 0.400 in 20 seconds.

Change = 0.400 − 0.200 = 0.200

Rate per minute = (0.200 ÷ 20) × 60 = 0.600 absorbance units/min

A steeper upward slope means greater enzyme activity.

5. Practice Exam Question: Which Tube Changes Color Most?

Tube	Guaiacol	Hydroxylamine	Expected result
1	No	No	Little or no color change
2	Yes	No	Strongest color change
3	Yes	Yes	Reduced color change

All three contain pea-root enzyme extract.

Answer: Tube 2, because it has guaiacol and active peroxidase without the inhibitor.

Remember for Lab 5: Peroxidase + guaiacol + H₂O₂ → reddish-brown color; hydroxylamine decreases the reaction.

Lab 6: Cellular Respiration and Fermentation1. Cellular Respiration

Cellular respiration breaks down XX to release energy and produce XX

Aerobic respiration requires oxygen.

Glucose + O₂ → CO₂ + H₂O + ATP

XX is the final electron acceptor in the electron transport chain.

Fermentation allows cells to continue producing ATP through glycolysis when oxygen is unavailable.

2. Alcoholic Fermentation in Yeast

Yeast can perform alcoholic fermentation.

Glucose → Glycolysis → Pyruvate

Ethanol + CO₂

Net 2 ATP per glucose from glycolysis

Remember: Yeast fermentation produces XX,XX, and XX.

The CO₂ is produced during the conversion of pyruvate into acetaldehyde, which is then converted into ethanol.

3. How Different Sugars Affect Yeast Respiration

Your lab tested yeast with glucose, fructose, sucrose, lactose, and water.

Sugar	Expected yeast activity
Glucose	XX
Fructose	XX
Sucrose	XX after breakdown
Lactose	Very XX for typical baker's yeast
Water	Very XX; no added sugar

Important: More CO₂ produced per minute generally indicates a higher XX of yeast respiration or fermentation under the conditions of the experiment.

Your lab used a CO₂ sensor to measure the gas produced. The slope of the CO₂-versus-time graph gives the rate in ppm/min.

4. Germinating vs. Non-Germinating Peas

Germinating peas are actively growing and require more ATP.

• Germinating peas: Higher cellular respiration rate and CO₂ production.

• Non-germinating peas: Generally lower respiration rate.

• Cold germinating peas: Slower respiration because cold temperatures reduce enzyme activity.

• Very high temperatures: Can reduce respiration by damaging enzymes.

Key point: Germinating peas at a suitable temperature generally respire faster than cold germinating or non-germinating peas

Lab 6: Cellular Respiration and Fermentation1. Cellular Respiration

Cellular respiration breaks down glucose to release energy and produce ATP.

Aerobic respiration requires oxygen.

Glucose + O₂ → CO₂ + H₂O + ATP

Oxygen is the final electron acceptor in the electron transport chain.

Fermentation allows cells to continue producing ATP through glycolysis when oxygen is unavailable.

2. Alcoholic Fermentation in Yeast

Yeast can perform alcoholic fermentation.

Glucose → Glycolysis → Pyruvate

Ethanol + CO₂

Net 2 ATP per glucose from glycolysis

Remember: Yeast fermentation produces ATP, CO₂, and ethanol.

The CO₂ is produced during the conversion of pyruvate into acetaldehyde, which is then converted into ethanol.

3. How Different Sugars Affect Yeast Respiration

Your lab tested yeast with glucose, fructose, sucrose, lactose, and water.

Sugar	Expected yeast activity
Glucose	High
Fructose	High
Sucrose	High after breakdown
Lactose	Very low for typical baker's yeast
Water	Very low; no added sugar

Important: More CO₂ produced per minute generally indicates a higher rate of yeast respiration or fermentation under the conditions of the experiment.

Your lab used a CO₂ sensor to measure the gas produced. The slope of the CO₂-versus-time graph gives the rate in ppm/min.

4. Germinating vs. Non-Germinating Peas

Germinating peas are actively growing and require more ATP.

• Germinating peas: Higher cellular respiration rate and CO₂ production.

• Non-germinating peas: Generally lower respiration rate.

• Cold germinating peas: Slower respiration because cold temperatures reduce enzyme activity.

• Very high temperatures: Can reduce respiration by damaging enzymes.

Key point: Germinating peas at a suitable temperature generally respire faster than cold germinating or non-germinating peas

Lab 7: Photosynthesis1. Photosynthetic Pigments

Pigments are molecules that absorb light energy.

Chlorophyll a is the main reaction-center pigment, while other pigments help capture additional light wavelengths.

Pigment	Color	Function
Chlorophyll a	XX-XX	XX photosynthetic pigment
Chlorophyll b	XX XX	XX pigment
Xanthophyll	XX	XX pigment
Beta-carotene	XX	XX pigment

Remember: Plants appear green because chlorophyll reflects much of the green light rather than absorbing it.

2. Absorption Spectrum vs. Action Spectrum

• Absorption spectrum: Shows which XX a pigment absorbs.

• Action spectrum: Shows how effective different XX are at driving photosynthesis.

Photosynthesis is generally most effective under blue/violet and red light and less effective under green light.

The two spectra are different because accessory pigments absorb additional wavelengths besides those absorbed by chlorophyll a.

3. Thin-Layer Chromatography (TLC)

Chromatography separates pigments based on their polarity and their attraction to the solvent and stationary phase.

In your lab, the solvent mixture was mostly nonpolar, and the TLC plate had a polar silica surface.

• More nonpolar pigments: Travel farther up the plate.

• More polar pigments: Stay closer to the starting line.

Approximate order from most polar to least polar:

Chlorophyll b → Chlorophyll a → Xanthophyll → Beta-carotene

Exact positions can vary with the solvent mixture and type of xanthophyll.

4. Calculating Rf Values

Rf = Distance traveled by xx / Distance traveled by xx

Example from your practice exam:

• Pigment travels 40 mm.

• Solvent travels 80 mm.

\[ Rf=\frac{40}{80}=\boxed{0.5} \]

Remember: Rf is generally between 0 and 1, and a pigment traveling farther has a larger Rf.

5. Hill Reaction and DCPIP

The Hill reaction demonstrates xx xxduring the light reactions using isolated chloroplasts.

DCPIP is an artificial electron acceptor used to track this process.

Oxidized DCPIP

xx

Reduced DCPIP

xx

When chloroplasts are exposed to light, electrons are transferred to DCPIP.

DCPIP gains electrons → reduced → blue becomes colorless.

This is especially important because your notes had the states reversed. The correct answer is oxidized = blue; reduced = colorless.

6. Effect of Light and Diuron

Diuron is an inhibitor of photosynthetic electron transport at Photosystem II.

Condition	Expected DCPIP result
Bright light + healthy chloroplasts	Blue fades xx
Darkness	Remains mostlyxx
Light + Diuron	Remains xx or fades much more xx
More intense light	Generally faster xx, until another factor limits it

The lab used a spectrophotometer at 600 nm to monitor DCPIP absorbance.

Remember: More electron transport → more DCPIP reduced → less blue color → lower absorbance.

Lab 7: Photosynthesis1. Photosynthetic Pigments

Pigments are molecules that absorb light energy.

Chlorophyll a is the main reaction-center pigment, while other pigments help capture additional light wavelengths.

Pigment	Color	Function
Chlorophyll a	Blue-green	Primary photosynthetic pigment
Chlorophyll b	Yellow-green	Accessory pigment
Xanthophyll	Yellow	Accessory pigment
Beta-carotene	Orange	Accessory pigment

Remember: Plants appear green because chlorophyll reflects much of the green light rather than absorbing it.

2. Absorption Spectrum vs. Action Spectrum

• Absorption spectrum: Shows which wavelengths a pigment absorbs.

• Action spectrum: Shows how effective different wavelengths are at driving photosynthesis.

Photosynthesis is generally most effective under blue/violet and red light and less effective under green light.

The two spectra are different because accessory pigments absorb additional wavelengths besides those absorbed by chlorophyll a.

3. Thin-Layer Chromatography (TLC)

Chromatography separates pigments based on their polarity and their attraction to the solvent and stationary phase.

In your lab, the solvent mixture was mostly nonpolar, and the TLC plate had a polar silica surface.

• More nonpolar pigments: Travel farther up the plate.

• More polar pigments: Stay closer to the starting line.

Approximate order from most polar to least polar:

Chlorophyll b → Chlorophyll a → Xanthophyll → Beta-carotene

Exact positions can vary with the solvent mixture and type of xanthophyll.

4. Calculating Rf Values

\[ Rf=\frac{\text{Distance traveled by pigment}}{\text{Distance traveled by solvent}} \]

Example from your practice exam:

• Pigment travels 40 mm.

• Solvent travels 80 mm.

\[ Rf=\frac{40}{80}=\boxed{0.5} \]

Remember: Rf is generally between 0 and 1, and a pigment traveling farther has a larger Rf.

5. Hill Reaction and DCPIP

The Hill reaction demonstrates electron transport during the light reactions using isolated chloroplasts.

DCPIP is an artificial electron acceptor used to track this process.

Oxidized DCPIP

Blue

Reduced DCPIP

Colorless

When chloroplasts are exposed to light, electrons are transferred to DCPIP.

DCPIP gains electrons → reduced → blue becomes colorless.

This is especially important because your notes had the states reversed. The correct answer is oxidized = blue; reduced = colorless.

6. Effect of Light and Diuron

Diuron is an inhibitor of photosynthetic electron transport at Photosystem II.

Condition	Expected DCPIP result
Bright light + healthy chloroplasts	Blue fades faster
Darkness	Remains mostly blue
Light + Diuron	Remains blue or fades much more slowly
More intense light	Generally faster reduction, until another factor limits it

The lab used a spectrophotometer at 600 nm to monitor DCPIP absorbance.

Remember: More electron transport → more DCPIP reduced → less blue color → lower absorbance.