Botany: Starch Test and Leaf Structure

Starch Test (Iodine Test)

• Purpose: To detect the presence of starch, a product of photosynthesis.
• Procedure:
  • Boil leaf in water to kill cells and make walls permeable.
  • Immerse in iodine solution (iodine turns blue-black in presence of starch).
  • Rinse in cold water to soften.
  • Observe colour: blue-black indicates starch presence.
• Why steps are necessary:
  • Boiling kills the leaf and makes cell walls permeable.
  • Iodine stains starch blue-black for easy detection.

Leaf Structure

• External Structures:
  • Apex/Tip: Tip of the leaf.
  • Margin/Edge: Edge of the leaf.
  • Midrib/Main vein: Central vein.
  • Leaf blade: Sections of the leaf.
  • Veins (Vascular Bundles): Transport water/minerals (xylem), and sugars (phloem).
  • Stalk/Petiole: Bottom of the leaf.
• Internal Structures:
  • Upper epidermis: Single protective cell layer.
  • Palisade mesophyll: Tightly packed cells for photosynthesis.
  • Spongy mesophyll: Loosely packed cells for gas exchange (CO2, O2).
  • Xylem: Transports water and minerals.
  • Phloem: Transports sugars.
  • Stomata: Pores for gas exchange.
  • Guard cells: Control stomata opening/closing.

Circulatory System

• Blood Components:
  • Red blood cells (Erythrocytes): Carry oxygen (hemoglobin). 45% of blood.
  • White blood cells (Leukocytes): Fight infection. 1% of blood.
  • Platelets: Aid in clotting. <1% of blood.
  • Plasma: Liquid part, carries nutrients, hormones, and waste. 55% of blood.
• Circulatory System:
  • Double circulatory system: Two loops:
    • Pulmonary circulation: Heart to lungs (oxygenation).
    • Systemic circulation: Heart to body (oxygen delivery/waste removal).
• Heart Structure & Function:
  • Atria (Left & Right): Receive blood (right – body, left – lungs).
  • Ventricles (Left & Right): Pump blood (right – lungs, left – body).
  • Valves: Prevent backflow.
    • Tricuspid (Right atrium to Right ventricle)
    • Bicuspid/Mitral (Left atrium to Left ventricle)
    • Pulmonary (Right ventricle to pulmonary artery)
    • Aortic (Left ventricle to aorta)
• Veins & Arteries:
  • Veins: Carry blood to the heart (thin walls, valves).
  • Arteries: Carry blood away from the heart (thick, muscular walls).
• Diseases:
  • Stroke: Blocked blood flow to brain.
  • Anemia: Low red blood cells/hemoglobin.
  • Heart attack: Blocked blood flow to heart.
  • Leukemia: Cancer of the blood-forming tissues.

Large Intestine

• Structure:
  • Cecum: Junction between small and large intestine.
  • Colon: Main part, absorbs water/salts.
  • Rectum: Stores feces.
  • Anus: Excretion opening.
• Function: Absorbs water, salts, some vitamins. Houses bacteria for breaking down food & vitamin production.

Photosynthesis

• Process: Plant conversion of light to chemical energy (glucose).
• Word Equation: Carbon dioxide + Water → Light → Glucose + Oxygen
• Chemical Equation: 6CO₂ + 6H₂O → light → C₆H₁₂O₆ + 6O₂
• Key Points:
  • Occurs in chloroplasts (using chlorophyll).
  • Requires light, CO₂, and water.
  • Produces glucose & oxygen.

Blood Flow (Lungs & Heart)

• Deoxygenated blood enters the right atrium, then the right ventricle.
• Pushed to lungs via pulmonary artery.
• Oxygenated blood returns to left atrium via pulmonary veins.
• Then to left ventricle, pumped to body via aorta.

Air Passage (Respiratory System)

• Nose/Mouth → Trachea → Bronchi → Bronchioles → Alveoli (gas exchange).

This quiz covers the starch test, which detects the presence of starch using iodine, and the structure of leaves, including both external and internal features. Understand the importance of each step in the starch test and familiarize yourself with the components of leaf anatomy.