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.
Light Microscopes
Use light and lenses to magnify specimens.
Allow viewing of individual cells and large subcellular structures like nuclei.
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 can be calculated using the formula:
magnification=real sizeimage size$$ \text{magnification} = \frac{\text{image size}}{\text{real size}} $$
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: image size=magnification×real size$$ \text{image size} = \text{magnification} \times \text{real size} $$
Calculation: image size=100×50=5000 μm=5 mm$$ \text{image size} = 100 \times 50 = 5000 \text{ μm} = 5 \text{ mm} $$
Useful for handling very small or large numbers.
Example: 0.0025 mm can be expressed as 2.5×10−3 mm$$ 2.5 \times 10^{-3} \text{ mm} $$
Moving the decimal point determines the power of 10 based on direction.
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.
Sperm Cells
Specialized for reproduction.
Features: Long tail for swimming, streamlined head, high mitochondria count for energy, enzymes to penetrate egg membrane.
Nerve Cells
Responsible for rapid signaling.
Features: Long with branched connections for network formation.
Muscle Cells
Specialized for contraction.
Features: Long with numerous mitochondria for energy.
Root Hair Cells
Absorb water and minerals.
Features: Hair-like projections increase surface area for absorption.
Phloem and Xylem Cells
Transport substances.
Features: Long strategic arrangement and few subcellular structures for efficient transport.
Add a drop of water to a clean microscope slide.
Obtain a specimen (e.g. onion epidermis).
Place the specimen in the water using tweezers.
Add a drop of iodine solution to stain the specimen.
Carefully place a cover slip on top to avoid air bubbles.
Clip the slide onto the microscope stage.
Start with the lowest-powered objective lens.
Use the coarse adjustment knob to focus on the slide.
Refine focus using the fine adjustment knob.
For higher magnification, switch objective lenses and refocus.
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 house genetic material (DNA) within the nucleus.
Each chromosome carries genes that determine traits, and humans have two copies of each chromosome.
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.
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.
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.
Stem cell research raises ethical concerns, particularly regarding the use of embryos.
Some advocate for alternative sources of stem cells to avoid ethical dilemmas.
Light Microscopes
Electron Microscopes
Sperm Cells
Nerve Cells
Muscle Cells
Root Hair Cells
Phloem and Xylem Cells