1. This Exercise focuses on how to develop a working knowledge of the Microscope and its
use.
Students should identify the different parts of the Microscope.
Material:
Compound Microscope, Clean Microscope Slides, Cover Slips, Lens papers, Sharp razor blades, Medicine droppers, Scissors, Distilled water, Xylene
Introduction:
Since an unaided eye cannot detect anything smaller than 0.1 mm in diameter, cells, tissues, and many small organisms are beyond our visual capability, so we need equipment to magnify objects that are too small to be seen with the unaided eye.
There are several types of microscopes, but the only one used in this laboratory is the compound light microscope. The compound microscope (sometimes called the student microscope or light microscope); these microscopes are known as compound microscopes because there are two magnifying lenses in the microscope. One magnifying lens is in the ocular or eyepiece, which further magnifies the image formed by the objective lens, and one is in the objective. Each contributes to the magnification of the object on the stage.
The total magnification of any set of lenses is determined by multiplying the magnification of the objective by the magnification of the ocular. The nose piece rotates the magnification of the microscope. Generally compound microscope magnifies from 40 x to 100 x. A binocular compound microscope.
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| Compound Microscope |
Parts of a microscope:
The compound microscope is a delicate instrument composed of many parts that are accurately fitted together.
1. Ocular of the eyepiece lens.
The ocular lens is the lens you look through; it is inserted at the top of the body tube. If your microscope has one ocular, it is a monocular microscope; if it has two, it is a binocular microscope. Its magnification is written on it.
2. Body tube
The body tube is the optical housing for the objective lenses.
3. Objective lenses.
The objective lenses are a set of three to four lenses mounted on a rotating turret at the bottom of the body tube. The four objective lenses of your microscope and their magnifications are: scanning lens, 4X; low power lens, 10X; high power lens, 40-45X; oil immersion lens, 100X. The magnification of the objective lens is written on the lens.
Note: except for the oil immersion lens, all the objective lens is used dry. The magnification of the oil immersion lens requires using the lens with special immersion oil for proper resolution.
4. Stage
The horizontal surface on which the slide is placed is called the stage. It may be equipped with simple clips for holding the slide in place or with a mechanical stage, a geared device for precisely moving the slide. Two knobs, either on top of or under the stage, move the mechanical stage.
5. Condenser lens.
The condenser lens system, located immediately under the stage, contains a system of lenses that focuses light on your specimen. The condenser may be raised or lowered using the condenser knob. An older microscope may have a concave mirror instead.
6. Iris diaphragm.
The iris diaphragm is located below the condenser or immediately below the stage in microscopes without a condenser. It functions in regulating the light intensity passing through to the stage. More light is required at higher magnification.
7. Light source
The light source has an (ON/Off) switch & may have adjustable lamp intensities & color filters.
8. Base
Base – also called the supporting stand- rests on the bench. 9. Body Arm The body arm is used when carrying the instrument.
10. Nose piece
The nosepiece is the mounting for the objective lenses, which rotates to bring the desired objective into position.
11. Coarse adjustment
The coarse adjustment knob is a large knob located at either side of the microscope, which functions in controlling the distance between the objectives and the stage. Use the coarse adjustment only with the scanning (4X) & low-power (10X) objectives. Why? So coarse adjustment is used for rapid focusing of the specimen until the specimen is roughly in focus & then left alone, in which the fine adjustment knob controls precise focusing of the object.
12. Fine adjustment.
Fine adjustment is a small knob located on either side of the microscope. This is used for the control of the object and precise focusing. You should use just the fine adjustment knob with the higher magnification objective lenses, because using the coarse adjustment knob with the higher objective lenses may damage the lens &/or the slide you are observing.
Magnification:
Compound microscopes consist of a two-lens system: the objective lens, which magnifies & projects a “virtual image” into the body tube, and the ocular lens, which magnifies the image further and projects the enlarged image into the eye. The total magnification of a microscope is the product of the magnification of the objective and the ocular. If the objective lens has a magnification of 5X and the ocular 12X, then the image produced by these two lenses is 60 times larger than the specimen.
Microscope safety cautions:
1. Always carry the microscope in an upright position using both hands.
2. Keep the microscope away from the edge of the table.
3. Always examine a slide first with the low-or medium-power objective; never use the high–power objective to view thick specimens.
4. Remove slide only after low-power objective has been rotated into viewing position, never when high–power objective is in position.
5. Keep the stage dry at all times. A wet stage will prevent the slide from being accurately positioned.
6. When returning your microscope to its proper place in the cabinet, always:
• Remove the slide from the mechanical stage.
• Clean all lens surfaces and the stage.
• Rotate the nosepiece so that the scanning lens is in place.
2.Stages of Mitosis in Onion Root Tip
| Stage | Key Features | What You’ll See |
|---|
| Prophase | Chromosomes condense, and the spindle forms | Dark, thread-like structures |
| Metaphase | Chromosomes align at the equator | Straight line of chromosomes |
| Anaphase | Sister chromatids separate | Chromatids pulled to opposite poles |
| Telophase | Nuclear envelope reforms | Two distinct nuclei forming |
| Cytokinesis | Cytoplasm divides | Two daughter cells are visible |
🧪 Lab Preparation
Material required:
Onion root tips, HCl, acetocarmine, spirit lamp, test tube, forceps, needle, microscope.
Collect onion root tips (2–3 mm).
Treat with HCl to soften tissue.
Stain with acetocarmine or aceto-orcein by heating the root tips for two minutes in a clean test tube.
Place on the slide, add fresh acetocarmine and a cover slip, then gently squash.
Observe under a compound microscope.
3.To observe meiosis in plants
The most common and effective method is to study anther cells from flowering plants, such as onions or lilies. These cells undergo meiosis during pollen formation, making them ideal for microscopic examination.
Material required:
Anthers of onion flower, slides, microscope, cover-slips, acetocarmine, HCL, forceps, test tube, and needles.
🔍 Best SpecimenOnion or lily flower anthers: contain pollen mother cells undergoing meiosis.
🧪 Lab Procedure
Collect flower buds at the right stage (not fully opened).
Fix the tissue in a solution like Carnoy’s fixative (ethanol + acetic acid).
Hydrolyze with dilute HCl to soften cells.
Stain with acetocarmine or aceto-orcein to visualize chromosomes.
Squash the anther on a slide under a cover slip.
Observe under a compound microscope.
| Meiosis Stage | Key Features | Observations |
|---|
| Prophase I | Chromosomes condense, crossing over | Thick threads, pairing visible |
| Metaphase I | Homologous pairs align | Chromosomes are in pairs at the equator |
| Anaphase I | Homologs separate | Chromosomes move to the poles |
| Telophase I | Two nuclei form | Cell begins to divide |
| Meiosis II | Similar to mitosis | Sister chromatids separate |
| End Result | Four haploid cells |
|
4. To study the desert biome(Thar Desert)
The Thar Desert biome is a remarkable arid ecosystem in northwestern India and eastern Pakistan. Despite its harsh climate—extreme heat, sandy soil, and scarce rainfall—it supports a surprising diversity of hardy plant species adapted to drought and high sunlight.
🌵 Key Features of the Thar Desert Biome
Climate: Hot summers, cold winters, <25 cm rainfall annually.
Soil: Sandy, poor in organic matter, but supports xerophytes.
Adaptations: Deep roots, reduced leaves, thorns, water storage tissues, short life cycles (ephemeral plants).
🌿 Plant Species in the Thar DesertHere are some notable plants found in this biome:| Plant Name | Scientific Name | Adaptation |
|---|
| Khejri tree | Prosopis cineraria | Deep roots, drought-resistant, important for fodder |
| Babool/Acacia | Acacia senegal | Thorny, small leaves to reduce transpiration |
| Caper bush | Capparis decidua | Leafless, photosynthesis through stems |
| Neem | Azadirachta indica | Medicinal uses, drought-tolerant |
| Mesquite | Prosopis juliflora | Invasive, survives extreme aridity |
| Calligonum | Calligonum polygonoides | Shrubby, adapted to sand dunes |
| Jujube/Ber | Ziziphus mauritiana | Produces edible fruit, survives poor soil |
| Desert Teak | Tecomella undulata | Valuable timber tree |
| Milk Hedge | Euphorbia caducifolia | Succulent stems store water |
| Apple of Sodom | Calotropis procera | Toxic plant, thrives in sandy soil |
Many grasses and small herbs also appear briefly after monsoon rains, completing their life cycle quickly before the soil dries out.
Ecological Importance
Provides fodder and fuelwood for desert communities.Prevents soil erosion with deep root systems.Supports traditional medicine and cultural practices.
5. To study the pond ecosystem
A pond ecosystem has the following featuresStill water (unlike rivers or streams).
High biodiversity in a small area.
Zonation: different organisms live in distinct zones (surface, middle, bottom
Key Components of a Pond Ecosystem:
Abiotic Factor
Sunlight penetration
Sunlight easily penetrates ponds, until it is very deep and turbid. Depth up to 1-2 m is called the euphotic zone, where sunlight is available, and photosynthetic plants are present
pH,
pH of the pond is neutral to slightly basic
Dissolved oxygen
Dissolved oxygen decreases with an increase in organic impurities. An increase in temperature decreases dissolved oxygen.
Biotic Factors:
Soil and sediment composition
| Group | Examples |
|---|
| Producers | Algae, phytoplankton, aquatic plants |
| Consumers | Fish, frogs, insects, snails |
| Decomposers | Bacteria, fungi |
How to Study a Pond Biome
Field Study
Visit a local pond and observe flora and fauna.
Use nets and jars to collect samples of plankton and insects.
Measure water quality (pH, temperature, turbidity).
Record species diversity and behavior.
Lab Study
Examine microscopic organisms under a microscope.
Analyze food chains and nutrient cycles.
Study adaptations of pond organisms.
Ecological Roles
Nutrient cycling: decomposition and recycling of organic matter.
Habitat: supports amphibians, insects, birds, and aquatic plants.
Water purification: natural filtration through plants and microbes.
different zones of the pond and plant types present there
A pond ecosystem is divided into
distinct zones, each supporting specific plant types adapted to light, depth, and nutrient availability. - Here’s a clear breakdown: Zones of a Pond and Plant Types
| Zone | Characteristics | Plant Types Present |
|---|
| Littoral Zone (near shore) | Shallow, lots of sunlight, nutrient-rich | Rooted plants like cattails, bulrushes, water lilies, lotus, and reeds |
| Limnetic Zone (open water surface) | Well-lit, away from shore, supports photosynthesis | Floating plants like duckweed, phytoplankton, and algae |
| Profundal Zone (deep water) | Dark, little to no sunlight, low oxygen | Few plants, mainly decomposers like bacteria and fungi |
| Benthic Zone (bottom sediments) | Muddy, nutrient-rich, home to decomposers | Rooted plants with long stems (if shallow), plus microbes and fungi |
- 🌿 Plant Categories in Ponds
- Submerged plants: Grow entirely underwater (e.g., hydrilla, pondweed).
- Phytoplankton: Microscopic producers floating in water, the base of the food chain.
- Floating plants: Rest on the water surface, roots may dangle freely (e.g., duckweed, water hyacinth).
- Emergent plants: Grow in shallow water, roots in soil, stems/leaves above surface (e.g., cattails, reeds).
- Water temperature
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