Chapter 8 : Plant Physiology

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Chapter Overview & SLOs

What is plant physiology? Chapter 8, "Plant Physiology," investigates how plants move essential substances, maintain internal balance, and adapt to diverse environments. This chapter answers fundamental questions about how plants transport water, minerals, and sugars while maintaining homeostasis. What are essential plant nutrients? You will learn about macronutrients and micronutrients required for plant growth: - Macronutrients (required in large amounts): Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S). Deficiency of Nitrogen or Magnesium leads to chlorosis (yellowing of leaves due to reduced chlorophyll production). - Micronutrients (required in trace amounts): Iron (Fe), Manganese (Mn), Boron (B), Zinc (Zn), Copper (Cu), Molybdenum (Mo), Chlorine (Cl). How do roots absorb water and minerals? You will study the internal structure of roots including: - Root hairs (increase surface area for absorption) - Epidermis, cortex, endodermis (with Casparian strip regulating mineral entry) - Xylem vessels (transport water upward) - Mechanisms of active transport (uses ATP to move minerals against concentration gradient) and passive transport (movement of water by osmosis). What is the TACT theory for water transport? The notes explain the TACT theory (Transpiration pull, Adhesion, Cohesion, and Tension) which drives the ascent of sap in xylem vessels: - Transpiration pull: Loss of water vapor from leaves creates suction - Adhesion: Water molecules stick to xylem vessel walls - Cohesion: Water molecules stick to each other (hydrogen bonding) - Tension: Creates a continuous negative pressure pulling water upward Why is transpiration called a necessary evil? You will analyze transpiration (loss of water vapor from plant surfaces): - Benefits: Cooling effect, creates transpiration pull for water and mineral transport, maintains cell turgidity - Costs: Causes water loss (up to 99% of absorbed water is lost), can lead to wilting in drought conditions - Factors affecting transpiration rate: Light intensity (stomata open in light), temperature (increases rate), humidity (decreases rate with high humidity), wind speed (increases rate), soil water availability How are sugars translocated in plants? You will learn about the pressure flow mechanism for sugar translocation in phloem: - Source to Sink Movement: Sugars produced in leaves (source) are transported to areas of growth or storage (roots, fruits, seeds - sink) - Role of companion cells: Load and unload sugars into sieve tubes using active transport - Pressure flow: High sugar concentration at source creates osmotic pressure gradient, causing water to enter and push sap toward sink How do plants exchange gases? The chapter covers gaseous exchange patterns in plants: - During Day: Photosynthesis exceeds respiration. CO2 is taken in (for photosynthesis), O2 is released as byproduct. Stomata open. - During Night: Only respiration occurs (no photosynthesis). O2 is taken in, CO2 is released. Most stomata closed. - Compensation Point: When rate of photosynthesis equals rate of respiration. No net gas exchange. Important for understanding plant growth requirements. How do plants adapt to different environments? You will explore osmotic adjustments and excretory strategies: - Hydrophytes (water plants): Large air spaces (aerenchyma) for buoyancy and gas exchange, reduced roots, thin cuticles. - Halophytes (salt-tolerant plants): Salt glands to excrete excess salt, succulence for water storage. - Xerophytes (desert plants): Thick cuticles, sunken stomata, reduced leaves, water storage tissue, deep root systems. - Excretory strategies: Leaf abscission (shedding leaves to remove waste products), root exudation (secretion of waste from roots), deposition of waste in bark and heartwood. These notes are strictly aligned with the Student Learning Outcomes (SLOs) for the FBISE 2026 annual examination.

• What are essential plant nutrients and how do roots absorb them? Describe the roles of essential plant nutrients including macronutrients (N, P, K, Ca, Mg, S) and micronutrients (Fe, Mn, B, Zn, Cu, Mo, Cl), and explain the structural adaptations of roots (root hairs, epidermis, endodermis, Casparian strip, xylem) for water and mineral absorption through active and passive transport.
• What is the TACT theory of water transport? Explain the TACT theory (Transpiration pull, Adhesion, Cohesion, Tension) for the ascent of sap in xylem vessels, and analyze the factors affecting the rate of transpiration including light intensity, temperature, humidity, wind speed, and soil water availability, including why transpiration is called a necessary evil.
• How are sugars transported in plants? Discuss the translocation of organic solutes via the pressure flow mechanism in phloem (source to sink movement), and describe the role of companion cells in loading and unloading sugars into sieve tubes.
• How do plants exchange gases and adapt to different environments? Compare the patterns of gaseous exchange in plants during day (photosynthesis dominant), night (respiration only), and at the compensation point (photosynthesis equals respiration), and describe osmotic adjustments and excretory adaptations in hydrophytes, halophytes, xerophytes, including leaf abscission and root exudation.

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