Microscopy

Importance of Microscopes

• Microscopes are crucial for biology as they allow us to see objects not visible to the naked eye.
• Microscopy techniques have evolved with technological advancements, improving our understanding of cells.

Types of Microscopes

1. Light Microscopes

   • Use light and lenses to magnify specimens.
   • Allow viewing of individual cells and large subcellular structures like nuclei.

2. Electron Microscopes

   • Use electrons instead of light, resulting in much higher magnification and resolution.
   • Enable visualization of smaller structures, such as ribosomes and internal mitochondria and chloroplasts.
   • Resolution: Ability to distinguish between two points; higher resolution yields sharper images.

Magnification Formula

• Magnification can be calculated using the formula:
  \text{magnification} = \frac{\text{image size}}{\text{real size}}
• Rearranging the formula allows for finding real size or image size.
• Ensure consistency in units when using the formula.
• Example Calculation:
  • Specimen width: 50 μm, Magnification: 100
  • Rearranged formula: \text{image size} = \text{magnification} \times \text{real size}
  • Calculation: \text{image size} = 100 \times 50 = 5000 \text{ μm} = 5 \text{ mm}

Working with Standard Form

• Useful for handling very small or large numbers.
• Example: 0.0025 mm can be expressed as 2.5 \times 10^{-3} \text{ mm}
• Moving the decimal point determines the power of 10 based on direction.

Cell Differentiation and Specialisation

Differentiation Process

• Differentiation is when a cell transforms to become specialized for its specific function.
• Most differentiation occurs during organism development, with many animal cells losing this ability early.
• Plant cells retain the ability to differentiate throughout life.

Types of Specialized Cells

1. Sperm Cells

   • Specialized for reproduction.
   • Features: Long tail for swimming, streamlined head, high mitochondria count for energy, enzymes to penetrate egg membrane.

2. Nerve Cells

   • Responsible for rapid signaling.
   • Features: Long with branched connections for network formation.

3. Muscle Cells

   • Specialized for contraction.
   • Features: Long with numerous mitochondria for energy.

4. Root Hair Cells

   • Absorb water and minerals.
   • Features: Hair-like projections increase surface area for absorption.

5. Phloem and Xylem Cells

   • Transport substances.
   • Features: Long strategic arrangement and few subcellular structures for efficient transport.

Practical Microscopy

Preparing a Slide

1. Add a drop of water to a clean microscope slide.
2. Obtain a specimen (e.g. onion epidermis).
3. Place the specimen in the water using tweezers.
4. Add a drop of iodine solution to stain the specimen.
5. Carefully place a cover slip on top to avoid air bubbles.

Using a Light Microscope

1. Clip the slide onto the microscope stage.
2. Start with the lowest-powered objective lens.
3. Use the coarse adjustment knob to focus on the slide.
4. Refine focus using the fine adjustment knob.
5. For higher magnification, switch objective lenses and refocus.

Drawing Observations

• Use a sharp pencil to draw what you see, with clear lines and no shading.
• Ensure the drawing occupies half the space and includes proportional subcellular structures.
• Title the drawing and note the magnification used.

Chromosomes and Mitosis

Chromosomes Overview

• Chromosomes house genetic material (DNA) within the nucleus.
• Each chromosome carries genes that determine traits, and humans have two copies of each chromosome.

The Cell Cycle

• Cells divide to create new cells through the cell cycle, consisting of growth and mitosis stages.
• Mitosis produces two identical daughter cells with the same chromosome number as the parent cell.
• Key stages include:
  • Interphase: DNA is spread out; the cell grows and duplicates its DNA.
  • Mitosis: Chromosomes align and are pulled apart into two new nuclei.

Stem Cells

Stem Cell Definition

• Undifferentiated cells (stem cells) can divide and become specialized.
• Found in embryos with potential to differentiate into any cell type.
• Adult stem cells are more limited, typically found in bone marrow, producing specific cell types like blood cells.

Medical Applications

• Stem cells can replace faulty cells in patients, such as blood cells or insulin-producing cells.
• Therapeutic cloning can create stem cells with the same genetic information as the patient to avoid rejection.

Ethical and Practical Considerations

• Stem cell research raises ethical concerns, particularly regarding the use of embryos.
• Some advocate for alternative sources of stem cells to avoid ethical dilemmas.