Plant Nutrition - Photosynthesis and Leaf Structure

Introduction

• Focus on IGCSE Biology Chapter 6: Plant Nutrition
• Covers photosynthesis and leaf structure
• For extended students (core students have a simpler syllabus)

Photosynthesis

Equations of Photosynthesis

• Green Plants: Make glucose from carbon dioxide and water using light and chlorophyll
• Word Equation: Carbon dioxide + Water → Glucose + Oxygen
• Chemical Equation: Extended students need to know the balanced chemical equation

Roles of Reactants and Products

• Reactants:
  • Carbon dioxide diffuses into leaves through stomata
  • Water is absorbed by roots and travels up the xylem
• Products:
  • Glucose: Used in respiration and stored as starch/cellulose
  • Oxygen: Used in respiration

Overview of Photosynthesis

• Plants are autotrophs (self-feeding organisms)
• Use light to manufacture carbohydrates
• Chlorophyll: Green pigment in chloroplasts reflecting green light; absorbs light energy
• Glucose converted into: Starch, cellulose, sucrose, lipids, and amino acids

Minerals in Plants

• Plants need mineral ions like magnesium (makes chlorophyll) and nitrates (for amino acids)
• Absorption Process: Active transport

Investigating Photosynthesis

Need for Chlorophyll

• Boil leaves in ethanol to remove chlorophyll
• Use iodine to test for starch (turns blue-black)

Need for Carbon Dioxide

• Use sodium hydroxide to absorb CO2
• Test leaves for starch using iodine

Rate of Photosynthesis

• Hydrogen Carbonate Indicator: Measures CO2 concentration (PMROY - Purple, Magenta, Red, Orange, Yellow)

Limiting Factors of Photosynthesis

• Temperature: Control by enzymes; has an optimal point beyond which rate decreases
• Light Intensity: More light increases rate until other factors limit it
• Carbon Dioxide Concentration: More CO2 increases rate until other factors limit it

Graph Analysis

• Light intensity and CO2 graphs plateau due to other limiting factors like temperature
• Temperature graph reflects enzyme activity curve

Leaf Structure

Key Components

• Cuticle, upper/lower epidermis, palisade/spongy mesophyll cells, guard cells, stomata, xylem, and phloem

Functions

• Waxy Cuticle: Waterproof layer prevents water evaporation
• Upper Epidermis: Allows light to enter; thin and transparent
• Palisade Mesophyll: Contains chloroplasts for photosynthesis
• Spongy Mesophyll: Allows gas exchange
• Vascular Bundle: Xylem and phloem transport
• Stomata and Guard Cells: Control gas exchange

Adaptations for Photosynthesis

• Large surface area, thin structure, chlorophyll, network of veins, and efficient gas exchange through stomata

Conclusion

• End of chapter on Plant Nutrition; next topic: Human Nutrition
• Encouragement to ask questions for clarity