Science 9 Biology - Cell Structure and Microscopy Vocabulary

Cell Structure

• Cell Definition: The smallest living part and building block of life.

Eukaryotic Cells

• Definition: Cells containing DNA within a nucleus.

• Key Feature: Presence of a nucleus.

Organelles in Eukaryotic Cells

• Nucleus:

  • Function: Controls all cell activities.

• Cytoplasm:

  • Function: Site of most chemical reactions.

• Cell Membrane:

  • Function: Controls substance movement in and out of the cell.

• Mitochondria:

  • Function: Site of aerobic respiration, releasing energy for the cell.

• Ribosomes:

  • Function: Site of protein synthesis.

Plant Cells

• Cell Wall:

  • Substance: Made of cellulose.

  • Function: Strengthens the cell and provides support.

• Chloroplasts:

  • Function: Contain chlorophyll to absorb light for photosynthesis.

• Permanent Vacuole:

  • Function: Stores cell sap and helps maintain cell rigidity.

Differences Between Animal and Plant Cells

• Plant cells have chloroplasts, a permanent vacuole, and a cellulose cell wall. Animal cells lack these.

Prokaryotic Cells

• Key Feature: Lack a nucleus; genetic material exists in the cytoplasm.

• Example: Bacteria.

• Cell Wall: Present in prokaryotes, but not made of cellulose.

• Slime Capsule: Some bacteria have an extra layer on top of the cell walls called a slime capsule.

• DNA: Circular DNA; may contain extra small DNA rings called plasmids.

• Flagella: Used for movement.

Difference Between Prokaryotic and Eukaryotic DNA

• Prokaryotic DNA is circular, while eukaryotic DNA is linear.

Differences Between Animal Cells and Bacteria

• Animal cells lack a cell wall and plasmids and have linear DNA, while bacteria have a cell wall, plasmids, and circular DNA.

Similarities Between Plant Cells and Bacterial Cells

• Both have cell walls (made of different materials).

Microscopy

Magnification

• Equation: Image Size = Actual Size \times Magnification

• Total Magnification Calculation: Eyepiece lens \times Objective lens magnifying power

• Unit Conversion: 5mm = 5000µm

Types of Microscopes

• Light Microscope:

  • Uses visible light to detect and magnify small objects.

  • Specimens must be thin and usually stained.

• Electron Microscope:

  • Has higher magnification and resolving power than light microscopes.

  • Uses a beam of electrons.

  • Images appear black and grey, sometimes in 3D.

  • Cannot be used with live specimens.

Using a Light Microscope

• Start with the lowest power objective lens (x4).

• Use the coarse focus knob for initial focusing at low power.

• Use the fine focus knob for detailed focusing.

• Do not use the coarse focus knob during high power magnification to avoid breaking the slide.

Electron Microscopy

• Increased understanding of organelles due to greater magnification and resolution.

Key Microscopy Terms

• Coarse Focus: Knob that moves the stage up and down in large increments for initial focusing.

• Electron Microscope: Microscope using electron beams; provides high magnification and resolution.

• Eyepiece Lens: Lens at the top of the microscope, usually with 10x magnification.

• Focus: Adjusting the distance between the specimen and objective lens for clarity.

• Light Microscope: Microscope using visible light for magnification.

• Magnification: The power of an instrument to enlarge an image.

• Objective Lens: Lenses used for specimen visualization (e.g., 4X, 25X, 50X, 100X).

• Stage: Platform where the specimen is placed for viewing.

Calculating Magnification with a Scale Bar

1. Measure the scale bar image in mm.

2. Convert to µm (multiply by 1000).

3. Magnification = \frac{Scale bar length in image (in \mu m)}{Actual scale bar length (written on the scale bar)}

Units of Measurement for Objects

• Large objects: Metres (m)

• Small objects: Centimetres (cm) or millimetres (mm)

• Tiny objects: Micrometres (µm) or nanometres (nm)

Practical Microscopy

Slide Preparation

1. Place a drop of water on the microscope slide.

2. Peel off a thin layer of epidermal tissue.

3. Use forceps to place the tissue on the slide.

4. Add 2 drops of iodine solution (wear goggles as it is an irritant).

5. Carefully lower the coverslip using a mounted needle.

6. Soak any excess liquid with paper.

Viewing the Slide

1. Place the slide on the stage.

2. Use the lowest power objective lens.

3. Turn the coarse adjustment knob to change the distance between the objective lens and slide.

4. Turn the fine adjustment knob to bring the cells into focus.

Rules for Biological Diagrams

1. Use a sharp pencil.

2. Use continuous lines.

3. Draw label lines with a ruler and pencil.

4. Never cross label lines.

5. Always include the magnification.

Magnification Formula Reminder

• magnification = \frac{size \space of \space image}{actual \space size \space of \space object}