1. Plant-Water Relations: Osmosis and Transpiration
This section explores how plants absorb, transport, and lose water—a vital requirement for all biochemical activities.
A. Potato Osmoscope
A simple experiment to demonstrate Osmosis (Endosmosis). A cavity is made in a potato tuber, filled with concentrated sugar solution, and placed in a beaker of water.
- Observation: The level of sugar solution inside the potato rises.
- Conclusion: Water moves from the beaker (high water potential) to the cavity (low water potential) through the potato tissues acting as a semi-permeable membrane.
B. Ganong’s Potometer
Used to measure the rate of transpiration by tracking the movement of an air bubble in a graduated tube.
- Principle: It assumes that the volume of water absorbed by the shoot is equal to the volume of water transpired.
2. Metabolism: Photosynthesis and Respiration
A. Photosynthesis (Oxygen Evolution)
Using the inverted funnel experiment with an aquatic plant like Hydrilla.
- Process: When exposed to sunlight, bubbles are observed escaping the plant and collecting in the test tube.
- Test: The collected gas supports combustion (glowing splinter test), proving it is Oxygen.
B. Respiratory Quotient (RQ)
The ratio of the volume of CO2 evolved to the volume of O2 consumed during respiration.
RQ = (Volume of CO2 evolved) / (Volume of O2 consumed)
3. Economic Botany: Useful Plants and Products
Applied botany involves identifying plants used in daily life for food, medicine, and industry.
- Cereals: Rice (Oryza sativa) and Wheat (Triticum aestivum). Part used: Caryopsis (Grains).
- Pulses: Gram (Cicer arietinum) and Pea (Pisum sativum). Part used: Seeds.
- Spices: Ginger (Zingiber officinale) and Turmeric (Curcuma longa). Part used: Rhizome.
- Beverages: Tea (Camellia sinensis). Part used: Leaves.
- Medicinal: Neem (Azadirachta indica). Parts used: Leaves, Bark, Seeds.
4. Plant Pathology: Common Local Diseases
Basic identification of diseases through visible symptoms on host plants.
- Citrus Canker: Caused by Xanthomonas citri. Symptoms: Corky, brown lesions on leaves, stems, and fruits.
- Late Blight of Potato: Caused by Phytophthora infestans. Symptoms: Water-soaked dark brown spots on leaves and rotting of tubers.
- Rust of Wheat: Caused by Puccinia graminis tritici. Symptoms: Reddish-brown elongated pustules on stems and leaf sheaths.
5. Exam Focus: Practical Tips & Viva Prep
Practical Tip: In the Hydrilla experiment, adding a pinch of Sodium Bicarbonate (NaHCO3) provides extra CO2, which speeds up the rate of photosynthesis and makes oxygen bubbles easier to count!
Viva Questions
- Why is the RQ of fats less than 1? Because fats are oxygen-poor and require more external oxygen for complete oxidation compared to the amount of CO2 they release.
- What is the active ingredient in Tea? Caffeine and Polyphenols.
- Define Plasmolysis. The shrinkage of the protoplast from the cell wall due to the exit of water when placed in a hypertonic solution.
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