Lab Practial 1

COMPLETE STUDY GUIDE General Biology Lab Practical I

1. SCIENTIFIC METHOD (FOUNDATION KNOWLEDGE)

Purpose of Science Experiments:

• Scientists design experiments to examine cause and effect relationships.

Variables:

• Independent Variable:

  • Definition: The variable that is deliberately changed by the scientist.
  • Role: It is considered the cause in the experiment.
  • Graphing: Typically plotted on the X-axis.
  • Example: Amount of fertilizer applied to plants.

• Dependent Variable:

  • Definition: The variable measured to assess the impact of the independent variable.
  • Role: It reflects the effect caused by the independent variable.
  • Graphing: Usually represented on the Y-axis.
  • Example: Height of plants.

• Controlled Variables (Constants):

  • Definition: Factors kept consistent across all experimental groups to ensure fairness.
  • Examples:
  • Same soil
  • Same light
  • Same temperature

Groups:

• Experimental Group:

  • Definition: The group subjected to the treatment being tested.
  • Example: Plants receiving fertilizer.

• Control Group:

  • Definition: The group not exposed to the treatment; serves as a comparison.
  • Example: Plants not receiving fertilizer.

Steps of the Scientific Method:

• Although listing them exactly isn't mandatory, comprehension of the process is crucial:
  1. Observation
  2. Question
  3. Hypothesis
  4. Experiment
  5. Collect data
  6. Analyze results
  7. Draw conclusions

2. METRIC SYSTEM & MEASUREMENTS (Exercise 1)

Importance of the Metric System:

• The metric system is utilized in biology as it is based on powers of 10.

Basic Units:

• Measurement Units:
  • Length: meter (m)
  • Mass: gram (g)
  • Volume: liter (L)

Metric Prefixes You Must Know:

Important Conversion:

• 1 mm = 1000 µm (microns)

3. SURFACE AREA & VOLUME

Significance in Biology:

• Cells must interact with their environment to exchange materials.

Volume:

• Definition: Amount of space within an object.
• Formula:$Volume = length imes width imes height$
  • Units: cm³

Surface Area:

• Definition: Total area of all sides of an object.
• Formula:$SA = 2(lw) + 2(lh) + 2(wh)$
  • Units: cm²

Surface Area to Volume Ratio:

• Ratio Formula:
  $SA:V = \frac{surface : area}{volume}$
• Important Concept: As the size of a cell increases, the SA:V ratio decreases, leading to less efficient material exchange in larger cells.

4. DENSITY

Definition:

• Density is a measure of how tightly packed matter is.
• Formula:$Density = \frac{mass}{volume}$
  • Units: g/mL or g/cm³

Important Relationship:

• 1 mL = 1 cm³

Floating vs Sinking:

• Water density = 1 g/mL
• If density is:
  • Greater than 1 → Object sinks
  • Less than 1 → Object floats

5. WATER DISPLACEMENT

Purpose: Used to measure the volume of irregular objects.

Steps:

1. Fill a graduated cylinder with water.
2. Record the initial volume.
3. Slowly add the object to the water.
4. Record the new volume.

• Volume of Object Formula:
  $Volume : of : object = Final - Initial$

6. TRIPLE BEAM BALANCE

Purpose: Used to measure mass in grams.

Procedure:

1. Move riders to zero position.
2. Place object on the pan.
3. Adjust riders until the balance is achieved.
4. Sum the values on the scale.

7. COMPOUND MICROSCOPE

Important Parts and Usage:

• Familiarity with microscope parts is essential. Parts include:
  1. Ocular lens (eyepiece)
  2. Diopter ring
  3. Arm
  4. Coarse adjustment
  5. Fine adjustment
  6. Power switch
  7. Brightness control
  8. Base
  9. Revolving nosepiece
  10. Objective lenses
  11. Stage
  12. Mechanical stage control
  13. Condenser
  14. Light source

Magnification Formula:

• Total Magnification:
  $Total : Magnification = Ocular imes Objective$
• Example: 10x ocular × 40x objective = 400x total magnification.

Objective Lenses Common Objectives:

Working Distance:

• Definition: The distance between the lens and the specimen.
• Important Rule: Higher magnification corresponds to a smaller working distance.

Field of View:

• Definition: The area visible through the microscope.
• Important Rule: Higher magnification results in a smaller field of view.

Letter "e" Experiment:

• Under the microscope, the letter appears:
  • Upside down
  • Reversed
• Explanation: This occurs due to the use of convex lenses in the microscope.

Carrying the Microscope:

Important Guidelines:

• Always use one hand on the arm and one hand on the base.

Storing the Microscope:

Steps:

1. Remove slide.
2. Clean lenses.
3. Set the objective to 4x.
4. Lower stage.
5. Wrap the cord.

8. FIELD OF VIEW CALCULATIONS

Formula:
$M<em>1 imes D</em>1 = M<em>2 imes D</em>2$

• Example from Review:
  • 4x objective yields a 5 mm field of view.
  • To calculate the 40x field of view:
    $(4)(5) = (40)(D)$
• Solving gives:
  $D = 0.5 \, mm$

Estimating Cell Size:

Formula:
$Cell : size = \frac{DFV}{number : of : cells}$

• Example: As shown in the lab review images.

9. WET MOUNT PREPARATION

Steps for Preparation:

1. Place a drop of water on the slide.
2. Add the specimen.
3. Lower the coverslip at an angle to avoid air bubbles.

10. STAINING CELLS

• Purpose: Stains increase visibility of cellular structures.
• Examples from Lab:
  • Cheek cells stained with methylene blue.
  • Onion cells stained with iodine (IKI).
• Effect: Staining enhances visibility of structures like the nucleus.

11. ORGANIC CHEMISTRY BASICS (Exercise 2)

Important Elements in Biology (CHNOPS):

• C: Carbon - Backbone of organic molecules.
• H: Hydrogen - Important for bonding.
• N: Nitrogen - Found in proteins and DNA.
• O: Oxygen - Essential for respiration.
• P: Phosphorus - Component of ATP and DNA.
• S: Sulfur - Integral part of proteins.

Functional Groups:

• Key groups recognized include:

  • Hydroxyl:
  • Structure: –OH
  • Carbonyl:
  • Structure: C=O
  • Carboxyl:
  • Structure: –COOH
  • Amino:
  • Structure: –NH₂
  • Phosphate:
  • Structure: –PO₄
  • Sulfhydryl:
  • Structure: –SH

• Role: These groups dictate the function of organic molecules.

12. ACIDS, BASES, AND pH

pH Scale:

• Ranges from 0 to 14.
• Types:
  • Acid: pH < 7
  • Neutral: pH = 7
  • Base: pH > 7

Hydrogen Ions:

• Acids: High concentration of H⁺ ions.
• Bases: Low concentration of H⁺ ions.

Buffers:

• Definition: Substances that resist changes in pH.
• Mechanism: They absorb excess H⁺ and OH⁻ ions.
• Effect: Buffered solutions need more acid or base to change pH compared to unbuffered solutions.

pH Indicator Used:

• Bogen's Universal Indicator:
  • Color Changes:
  • Acid: Red/orange
  • Base: Blue/purple

13. DILUTION FORMULA

Formula:
$C<em>1 V</em>1 = C<em>2 V</em>2$

• Variables:
  • C = concentration
  • V = volume
• Used in the preparation of diluted solutions.

14. SPECTROPHOTOMETER

Purpose: Measures the transmittance of light.

Important Steps:

1. Set the wavelength.
2. Zero the machine.
3. Insert the blank for calibration.
4. Adjust to 100% transmission.
5. Insert the sample.

Relationship Explanation:

• As dye concentration increases, light transmission decreases.
• Therefore, high concentration results in low percentage transmittance.

15. STANDARD CURVE

Definition: A graph relating dye concentration to light transmission.

• Independent Variable: Concentration of the dye.
• Dependent Variable: % transmittance of light.
• Purpose: Used to determine concentrations in unknown samples.

16. BIOCHEMICAL TESTS (Exercise 3)

Four Reagents You Must Know:

1. Benedict's Test:
   • Tests for: Reducing sugars.
   • Positive Result: Color change from blue to green to orange to brick red.
   • Negative Result: Remains blue.
2. IKI Test (Iodine):
   • Tests for: Starch.
   • Positive Result: Dark blue/black.
   • Negative Result: Yellow/brown.
3. Biuret Test:
   • Tests for: Proteins.
   • Positive Result: Purple/violet.
   • Negative Result: Stays blue.
4. Sudan IV:
   • Tests for: Lipids.
   • Positive Result: Red/orange staining.
   • Negative Result: No color change.

17. STARCH HYDROLYSIS

• Definition: Hydrolysis is the process of breaking down larger molecules into smaller constituents.
• Example of Process:
  • Starch → Glucose
  • Before hydrolysis, IKI test shows a positive result (presence of starch).
  • After hydrolysis, Benedict's test shows a positive result (presence of sugars).

18. OSMOSIS & DIFFUSION (Exercise 5)

Diffusion:

• Definition: Movement of molecules from an area of high concentration to an area of low concentration.
• Energy Requirement: No energy is required for diffusion.

Osmosis:

• Definition: Diffusion of water across a semipermeable membrane.

Tonicity:

• Terms:
  • Hypotonic: Lower solute concentration outside. Water moves into the cell.
  • Hypertonic: Higher solute concentration outside. Water exits the cell.
  • Isotonic: Equal concentrations of solute inside and outside.

19. DIALYSIS BAG EXPERIMENT

Purpose: The dialysis tubing simulates a cell membrane and is selectively permeable.

• Molecule Size: Small molecules can pass through while larger molecules cannot.

Percent Mass Change Formula:

$Percent : Mass : Change = \frac{Final - Initial}{Initial} imes 100$

20. ELODEA CELLS

• In Fresh Water (Hypotonic): Cells become turgid (increased pressure against the cell wall).
• In Salt Solution (Hypertonic): Cells become plasmolyzed (plasma membrane separates from cell wall).

Cytoplasmic Streaming:

• Definition: Movement of cytoplasm within plant cells, also referred to as cyclosis.
• Key Structures:
  • Green structures such as chloroplasts.

21. YEAST TRANSPORT EXPERIMENT

Dye Used:

• Compound: Congo Red.
• Live Yeast: Actively pumps the dye out of the cells; cells appear clear.
• Dead Yeast: Cannot pump the dye out; cells appear red.

22. PROTOZOANS (Microscope Identification)

Protozoans You Must Recognize:

1. Paramecium:
   • Movement: Cilia
   • Shape: Oval/slipper shaped.
2. Euglena:
   • Movement: Flagellum
   • Contains: Chloroplasts.
3. Amoeba:
   • Movement: Pseudopodia
   • Shape: Irregular.

23. CONTRACTILE VACUOLE

• Location: Found in protozoa.
• Function: Removes excess water to prevent cells from bursting in hypotonic environments.

24. DICHOTOMOUS KEYS

• Purpose: Tools used to identify organisms through a series of two-choice questions.
• Example:
  • Question: Does the organism have wings?
  • Yes: Proceed to step 3
  • No: Go to step 4