Visualisation of animal and plant cells Under Microscope

What are animal and plant cells?

Animal and plant cells serve as the building blocks of life for animals and plants, respectively. Both are eukaryotic cells, meaning they contain a true nucleus and specialized organelles, but they also display significant structural and functional differences.

Animal Cells

Animal cells are generally smaller and have a flexible, irregular shape. The key components of an animal cell include:

• Cell Membrane: This semipermeable membrane surrounds the cell, regulating the movement of substances in and out of the cell.
• Nucleus: Located centrally, the nucleus holds genetic material (DNA) and controls cellular activities such as growth, reproduction, and gene expression.
• Cytoplasm: This gel-like substance fills the cell, providing a medium for organelles to operate and for metabolic reactions to occur.
• Mitochondria: Often referred to as the cell’s “powerhouse,” mitochondria generate energy in the form of ATP through cellular respiration.
• Ribosomes: These small structures are the sites of protein synthesis and are found freely in the cytoplasm or attached to the endoplasmic reticulum.
• Lysosomes: Containing digestive enzymes, lysosomes break down waste materials and cellular debris, maintaining cellular cleanliness.

The primary functions of animal cells include providing structural support, facilitating movement, absorbing nutrients, converting nutrients into energy, and synthesizing proteins essential for cellular activities.

Plant Cells

Plant cells tend to be larger and have a defined, regular shape. They possess unique structures that differentiate them from animal cells, such as:

• Cell Wall: Composed mainly of cellulose, this rigid outer layer provides structural support, protection, and shape to the cell.
• Chloroplasts: These organelles enable photosynthesis, allowing plants to convert sunlight, water, and carbon dioxide into glucose and oxygen.
• Central Vacuole: A large vacuole occupies much of the cell’s volume, storing water, nutrients, and waste products while maintaining internal pressure for cell stability.
• Plastids: These structures are involved in storage and the synthesis of compounds necessary for plant functions.

In terms of function, plant cells are specialized for photosynthesis, food storage, structural support through the cell wall, and nutrient and waste management via the central vacuole.

Key Differences Between Animal and Plant Cells

These structural differences enable animal and plant cells to perform specialized functions necessary for the survival of each type of organism.

Materials Required for Visualizing Animal and Plant Cells

To effectively visualize the structures of animal and plant cells under a microscope, specific materials and tools are essential. These items not only facilitate the preparation of samples but also ensure clear and detailed observation of cell components. Here’s a comprehensive list and explanation of the materials needed for this purpose:

• Microscope: This is the primary tool for viewing cells, offering the necessary magnification to observe cellular structures in detail.
• Slides and Cover Slips: Slides provide a platform to hold the sample, while cover slips protect it and create a flat surface for clear observation under the microscope.
• Stains (Methylene Blue, Giemsa, and Safranin): These stains highlight different cell structures, enhancing contrast and making various organelles more visible. Methylene blue is often used for animal cells, while safranin and Giemsa are frequently applied to plant cells.
• Onion and Balsam Leaf: These serve as sample sources; onion cells are commonly used to observe plant cell structure, while balsam leaves allow for additional observation of leaf cell details.
• Glycerin: Glycerin is applied to prepared slides to prevent them from drying out, preserving the cell’s appearance for an extended period.
• Pasteur Pipettes or Droppers: Used to handle and transfer small amounts of liquid, such as water or stain, onto the slide without disturbing the sample.
• Filter Paper and Blotting Paper: These papers absorb excess stain or liquid on the slide, ensuring a clean sample for observation.
• Brushes (No. 6): Brushes help carefully position delicate samples on slides without causing damage, useful for handling soft plant tissues.
• Scalpel or Blade: These are used to carefully slice samples, such as an onion peel, into thin layers suitable for microscope viewing.
• Toothpick: A toothpick is used to gently scrape cells from surfaces, especially helpful for animal cell samples, such as cheek cells.
• Dissecting Needles: These allow for precise positioning and manipulation of the sample on the slide.
• Forceps: Useful for handling samples and small materials, such as cover slips, without direct contact.
• Ethanol (70%): Ethanol sterilizes tools, ensuring that samples remain uncontaminated and providing a clean working environment.
• Sterilized Needles: These may be required to obtain small tissue samples or to separate individual cells for clear observation.

Procedure for Visualizing Animal and Plant Cells

To effectively observe and understand the structural characteristics of animal and plant cells, temporary mounts of various cell samples such as human buccal cells, blood cells, onion epidermal cells, and balsam leaf cells can be prepared. Follow the step-by-step protocols below for each sample type to ensure accurate preparation and optimal visualization under a microscope.

• Human Buccal Epithelial Cells
  1. Rinse your mouth thoroughly with water to ensure a clean sample.
  2. Using the broad end of a clean toothpick, gently scrape the inside of your cheek, discarding the initial scraping.
  3. Scrape again and carefully spread the cells onto a clean slide.
  4. Add a drop of 0.9% NaCl (physiological saline) followed by a drop of methylene blue stain using a Pasteur pipette.
  5. After 2-3 minutes, remove any excess stain and saline with the edge of filter paper.
  6. Mount the cells by adding a drop of glycerin and carefully placing a cover slip on top.
  7. Gently press the cover slip with the back of a brush to evenly spread the cells.
  8. Observe the slide under the microscope to visualize cell details.
• Human Blood Cells
  1. Clean a microscope slide with 70% ethanol, allowing it to dry completely without touching the cleaned surface.
  2. Sterilize the middle or ring finger with 70% alcohol and let it dry.
  3. Prick the ball of the finger with a sterile blood lancet, wiping away the first drop of blood.
  4. Use a clean slide or capillary tube to collect a small drop of blood.
  5. Position a clean spreader slide at a 45° angle to the blood drop on the specimen slide, allowing the blood to spread along the edge.
  6. Swiftly and smoothly push the spreader slide forward to create an even smear.
  7. Air-dry the blood smear for approximately 10 minutes.
  8. Apply 5-6 drops of Giemsa stain, letting it sit for 2-3 minutes.
  9. Rinse the slide by dipping it in distilled water for 1-2 minutes, then allow it to dry.
  10. Examine the dried smear under a microscope, identifying different types of blood cells.
• Onion Epidermal Cells
  1. Cut an onion bulb into quarters and separate the thick layers, noting the delicate membrane on each inner surface.
  2. Carefully strip a thin membrane layer from the concave side of the leaf with a scalpel or blade.
  3. Place this membrane layer on a clean slide, cutting it into small sections for viewing.
  4. Add a drop of water to prevent the tissue from drying out, then add a drop of methylene blue stain with a dropper.
  5. Leave the stain on for 2-3 minutes, then gently remove any excess stain with filter paper.
  6. Add a drop of glycerin to mount the sample, and carefully place a cover slip to avoid air bubbles.
  7. Gently press the cover slip with a brush to spread the cells evenly.
  8. Observe the stained cells under the microscope to examine cellular structures.
• Balsam (Impatiens Balsamina) Leaf Epidermal Cells
  1. Pick a fresh balsam leaf and fold it gently.
  2. Tear the lower side of the leaf along the fold, observing a colorless border along the edge.
  3. Using forceps, carefully pull off the thin transparent layer from the lower epidermis and place it in distilled water on a watch glass.
  4. Transfer the epidermal layer to another watch glass containing safranin solution using a brush.
  5. Let the peel stain for about 1 minute, then transfer it to a watch glass with distilled water to remove excess stain.
  6. Move the peel onto a clean slide with a brush, then add 1-2 drops of glycerin to mount it.
  7. Carefully place a cover slip over the peel with a sterilized needle, blotting any excess glycerin.
  8. Examine the mounted peel under the microscope to view the stained cellular structures.

Observations and Results

Through microscopic examination, distinct features of animal and plant cells can be observed in prepared mounts. These observations highlight the diversity in cell structures and provide insights into cellular morphology and function.

• Human Buccal Epithelial Cells
  • Cells appear as large, irregularly shaped structures surrounded by a thin cell membrane.
  • Each cell displays a prominent, darkly stained blue nucleus located centrally, which is readily visible due to the methylene blue stain that binds to negatively charged biomolecules such as DNA and RNA.
  • The cytoplasm is faintly stained, creating a contrast with the darker nucleus.
  • Other cellular organelles are not clearly identifiable in these cells under basic staining techniques.
• Human Blood Cells
  • Red Blood Cells (RBCs): RBCs appear as biconcave, spherical cells that lack a nucleus. They are abundant, with typical concentrations of 4.4–6.0 million cells per microliter of blood, and exhibit a pink hue due to Giemsa staining. RBCs have a lifespan of approximately 120 days.
  • White Blood Cells (WBCs): Various types of WBCs, or leukocytes, are visible, each identifiable by unique nuclear shapes and staining characteristics.
    • Lymphocytes: Characterized by a deep blue, round or slightly indented nucleus, lymphocytes are typically present at levels of 1,500–4,000 cells per microliter. These cells can persist for many years in the bloodstream.
    • Basophils: Stained deep purple, basophils have a difficult-to-distinguish, two-lobed nucleus. Their presence is relatively rare, with levels between 0–150 cells per microliter.
    • Eosinophils: Identifiable by their bright red, two-lobed nucleus, eosinophils have short lifespans, ranging from minutes to hours, and are generally present in concentrations of 0–700 cells per microliter.
    • Neutrophils: With reddish-brown, lobed nuclei, neutrophils are the most abundant WBC type, at 1,800–7,300 cells per microliter, and have a lifespan of minutes to days.
  • Platelets: Small, anucleate cell fragments with violet to purple staining, platelets are always present in circulation, with concentrations of 150,000–500,000 per microliter, and play a vital role in blood clotting.
• Onion Epidermal Cells
  • The onion epidermal layer consists of rectangular cells arranged in a single layer, appearing uniform in shape and size.
  • Each cell contains a large central vacuole occupying most of the cell’s volume, pushing the nucleus to one side.
  • Cells are outlined by a distinct cell wall, giving structure and protection to the tissue.
  • Due to the wet mount preparation, the vacuole and cytoplasm are visible, with the vacuole occupying a significant part of the cell interior.
• Balsam Leaf Epidermal Cells
  • The balsam leaf epidermis consists of uniseriate layers of closely packed cells, each with a well-defined cell wall, nucleus, and cytoplasm.
  • The epidermal layer has interruptions called stomata, openings crucial for gas exchange.
  • Each stoma is surrounded by a pair of bean-shaped guard cells, which regulate the opening and closing of the stomata.

Precautions

Ensuring accurate and clear visualization of cells requires careful attention to detail during slide preparation. Following these precautions helps prevent errors, protects sample integrity, and optimizes microscope examination.

• Maintain Cleanliness of Slides and Coverslips
  • Both slides and coverslips must be clean and free from dust, fingerprints, or any other residues. Contaminants can obscure cell structures, making it challenging to observe finer details.
• Central Placement of Specimens and Fluids
  • Position the specimen and any mounting fluid in the center of the slide to ensure even distribution and clear visualization. This arrangement allows for optimal observation under the microscope without unnecessary edge interference.
• Control the Amount of Mounting Fluid
  • Use an appropriate amount of fluid on the slide. Excessive fluid causes the coverslip and specimen to shift, leading to unstable views. Conversely, using too little fluid increases the risk of trapping air bubbles, which can obscure cell structures and make analysis difficult.
• Remove Excess Mounting Fluids
  • Any excess fluid around the edges of the coverslip should be carefully blotted using the edge of a blotting or filter paper. This step ensures a stable coverslip position and prevents fluid from seeping out.
• Place the Coverslip Gently
  • Gently place the coverslip to avoid trapping air bubbles, which can obscure parts of the sample and interfere with clear visualization. A slow, angled placement often helps in minimizing bubble formation.
• Prevent Drying of the Specimen
  • Ensure that the specimen remains hydrated throughout observation, as drying can distort cellular structures. Place the slide in a moist petri dish if necessary, and consider sealing the coverslip edges to preserve moisture.