Class 11 Biology Notes Chapter 1 (Chapter 1) – Lab Manual (English) Book

Detailed Notes with MCQs of the essentials from the first chapter of your Biology Lab Manual. These practical skills and foundational knowledge are crucial, not just for your class assessments, but often form the basis for questions in various government exams where Biology is a component.

Chapter 1: Essential Laboratory Techniques & Microscopy

This chapter introduces you to the basic tools and techniques you'll use throughout your biology practical sessions. Mastery here is fundamental.

1. The Compound Microscope: Your Window to the Microscopic World

• Principle: It uses a combination of two lens systems (eyepiece and objective lens) to achieve high magnification of minute objects. Light passes through the specimen, then through the objective lens (which forms a magnified real image), and finally through the eyepiece lens (which forms a further magnified virtual image).
• Key Parts and Functions:
  • Base: Provides stable support.
  • Pillar/Arm: Connects the base to the body tube; used for carrying the microscope.
  • Stage: Flat platform where the slide with the specimen is placed. It has an aperture (hole) to allow light to pass through.
  • Stage Clips: Hold the slide firmly in place on the stage.
  • Diaphragm (Iris Diaphragm): Located below the stage, controls the amount of light reaching the specimen. Adjusting it helps control contrast and brightness.
  • Condenser: Lens system below the stage that focuses light onto the specimen.
  • Mirror/Light Source: Reflects ambient light (mirror) or provides illumination (electric lamp) through the condenser and specimen. One side of the mirror is plane (for strong light), the other concave (for weak light).
  • Body Tube: Holds the eyepiece at the top and the revolving nosepiece at the bottom.
  • Revolving Nosepiece: Rotating disc holding multiple objective lenses of different magnifications (e.g., 10X, 40X/45X, 100X - oil immersion).
  • Objective Lenses: Lenses closer to the specimen, providing initial magnification. Common powers are Low Power (10X) and High Power (40X or 45X).
  • Eyepiece (Ocular Lens): Lens closer to the observer's eye, providing further magnification (typically 10X or 15X).
  • Coarse Adjustment Knob: Larger knob for rapid, approximate focusing (used mainly with low power objective).
  • Fine Adjustment Knob: Smaller knob for precise, sharp focusing (used with both low and high power, essential for high power).
• Magnification:
  • Total Magnification = Magnification of Eyepiece Lens × Magnification of Objective Lens Used
  • Example: If eyepiece is 10X and objective is 40X, Total Magnification = 10 × 40 = 400X.
• Resolving Power: The ability of a microscope to distinguish between two closely situated points as separate entities. Higher resolving power means clearer images.
• Handling and Care:
  • Always carry with both hands (one under the base, one holding the arm).
  • Clean lenses only with lens paper.
  • Start focusing with the low power objective first.
  • Use only the fine adjustment knob when focusing under high power.
  • Never allow the objective lens to touch the slide.
  • After use, clean, turn the nosepiece to the lowest power objective, lower the stage (or raise the body tube), cover the microscope.

2. Preparation of Temporary Mounts

This is a fundamental skill for observing fresh specimens.

• General Steps:
  1. Clean Slide: Ensure the glass slide and coverslip are clean and dry.
  2. Mounting Medium: Place a drop of appropriate liquid (usually water or glycerin) in the center of the slide. Glycerin prevents rapid drying.
  3. Specimen Placement: Place the thin specimen material (e.g., onion peel, cheek scraping) in the drop of liquid.
  4. Staining (if necessary): Add a drop of appropriate stain (e.g., Methylene Blue for animal cells, Safranin for plant cells) and wait briefly. Remove excess stain carefully with blotting paper. Stains enhance visibility of cell structures.
  5. Coverslip Placement: Hold the coverslip at a 45° angle to the slide, touching one edge of the liquid drop. Gently lower it using a needle to avoid trapping air bubbles.
  6. Remove Excess Fluid: Use blotting paper to absorb any excess liquid around the coverslip.
• Example: Onion Peel Mount:
  • Material: Thin epidermal layer from the concave side of an onion scale leaf.
  • Stain: Safranin (stains cell walls and nucleus pink/red) or Methylene Blue.
  • Observation: Shows rectangular plant cells, prominent cell wall, large central vacuole (pushes nucleus to periphery), distinct nucleus, cytoplasm.
• Example: Human Cheek Cell Mount:
  • Material: Scraping from the inner lining of the cheek using a clean toothpick/spatula.
  • Stain: Methylene Blue (stains nucleus and cytoplasm blue).
  • Observation: Shows irregular-shaped animal cells, distinct cell membrane (no cell wall), centrally located nucleus, granular cytoplasm.

3. Common Stains and Reagents:

• Safranin: Stains lignified tissues, nuclei, chromosomes (Red/Pink). Commonly used for plant tissues.
• Methylene Blue: Basic stain, stains nuclei, cytoplasm, bacteria (Blue). Commonly used for animal cells and bacteria.
• Iodine Solution: Stains starch (Blue-Black), nuclei (Brown). Used for testing starch and observing plant cells.
• Glycerin: Used as a mounting medium. It's viscous, prevents the specimen from drying out quickly, and has a refractive index close to glass, improving clarity.

4. Biological Drawings:

• Use a sharp pencil on unruled white paper.
• Drawings should be large, clear, and in the center of the page.
• Do not shade; use stippling (dots) or lines if necessary to indicate thickness or texture.
• Label parts accurately using horizontal lines, all on one side (preferably the right). Lines should not cross each other.
• Write a clear title for the drawing below it.
• Mention the magnification observed (e.g., Observed under 400X).

5. Laboratory Safety:

• Handle glassware carefully. Report any breakage immediately.
• Handle chemicals with caution. Avoid direct contact; use spatulas or droppers. Never taste or smell chemicals directly.
• Keep your workspace tidy.
• Wash hands before and after experiments.
• Know the location of safety equipment (fire extinguisher, first-aid kit).
• Dispose of biological waste and chemicals as instructed.

Multiple Choice Questions (MCQs):

1. While observing a specimen under a compound microscope, if the eyepiece lens is 10X and the objective lens used is 45X, the total magnification achieved is:
   a) 10X
   b) 45X
   c) 55X
   d) 450X

2. Which part of the compound microscope controls the amount of light reaching the specimen?
   a) Condenser
   b) Diaphragm
   c) Objective Lens
   d) Mirror

3. When preparing a temporary mount of onion peel, which stain is commonly used to make the nucleus and cell wall more visible?
   a) Iodine Solution
   b) Methylene Blue
   c) Safranin
   d) Eosin

4. To prevent the temporary mount from drying out quickly, a drop of ________ is often used as the mounting medium.
   a) Alcohol
   b) Acetone
   c) Glycerin
   d) Formalin

5. Which part of the microscope is used for precise and sharp focusing, especially under high power?
   a) Coarse Adjustment Knob
   b) Fine Adjustment Knob
   c) Revolving Nosepiece
   d) Stage Clips

6. When observing human cheek cells under a microscope, which structure is NOT typically visible?
   a) Cell Membrane
   b) Nucleus
   c) Cytoplasm
   d) Cell Wall

7. What is the primary purpose of using a stain like Methylene Blue in preparing a temporary mount?
   a) To kill the cells
   b) To enhance the contrast and visibility of cellular components
   c) To preserve the specimen
   d) To measure the size of the cells

8. Which of the following is a correct rule for making biological drawings?
   a) Use a blue pen for labelling.
   b) Shade the diagram to make it look realistic.
   c) Label parts using horizontal lines, preferably on the right side.
   d) Draw small diagrams to save space.

9. The ability of a microscope to distinguish between two very close points as separate is known as its:
   a) Magnification Power
   b) Illumination Power
   c) Focusing Power
   d) Resolving Power

10. When placing the coverslip on a slide for a temporary mount, it should be lowered gently at an angle primarily to:
    a) Prevent the specimen from moving
    b) Avoid trapping air bubbles
    c) Ensure the stain spreads evenly
    d) Prevent the coverslip from breaking

Answer Key:

1. d) 450X
2. b) Diaphragm
3. c) Safranin
4. c) Glycerin
5. b) Fine Adjustment Knob
6. d) Cell Wall
7. b) To enhance the contrast and visibility of cellular components
8. c) Label parts using horizontal lines, preferably on the right side.
9. d) Resolving Power
10. b) Avoid trapping air bubbles

Study these notes carefully. Understanding these basics is key to performing well in practical exams and tackling related questions in competitive exams. Good luck!