Plant Physiology PDF

# Plant Physiology ## Main Topics 1. Structure 2. Photosynthesis 3. Respiration 4. Nutrition 5. Water Relations 6. Nativity and Solutions 7. Transport ## The Cell and Membrane - **Cell Membrane** is semipermeable. - **Types of Membranes** - **Impermeable Membranes** - Do not al...

# Plant Physiology ## Main Topics 1. Structure 2. Photosynthesis 3. Respiration 4. Nutrition 5. Water Relations 6. Nativity and Solutions 7. Transport ## The Cell and Membrane - **Cell Membrane** is semipermeable. - **Types of Membranes** - **Impermeable Membranes** - Do not allow anything to pass through. - **Permeable Membranes** - Allow anything to pass through. - **Semipermeable Membranes** - Allow certain substances to pass through and block others. - **Factors That Affect Permeability** - Size of molecules: Smaller molecules usually pass through easier. - Charge of the molecules: Most molecules pass through the membrane easier if they are neutral. - The membrane's structure: Lipid-soluble molecules generally pass through more easily than water-soluble molecules. - **Passive Transport** - **Diffusion**: Movement of molecules from a region of higher to lower concentration. - **Facilitated Diffusion**: Movement of molecules across a membrane with the help of a carrier protein. - **Active Transport** - Movement of molecules across a membrane against a concentration gradient, requiring energy. - **Types of Active Transport** - **Proton Pumps**: Moves protons across the membrane to create a proton gradient. - **Ion Pumps**: Moves ions across the membrane to maintain ion balance. - **Osmosis** - Movement of water from areas of high water potential to low water potential across a semipermeable membrane. - **Water Potential** (Ψ) - The measure of the free energy of water in a system. - Water potential can be described by the formula: Ψ = Ψs + Ψp - Ψs is the solute potential: How many solutes are dissolved in the water. - Ψp is the pressure potential: The effect of physical pressure on the water. - **Factors that affect Water Potential** - Solute Concentration: A higher solute concentration results in a lower water potential. - Pressure Potential: An increase in pressure results in an increase in the water potential. ## Imbibition - The process of absorbing water and swelling up from the surrounding, which generates imbibition pressure. - **Importance of Imbibition** : - Water absorption by seeds : Helps in germination. - Water absorption by roots : Helps in root growth. - Water absorption by stems : Helps in stem growth. ## Water Movement in Plants - **Water Potential Gradient** - The difference in water potential between two points. - **Factors that influence water movement:** - **Transpiration**: The process of water evaporating from the leaves, generating a negative pressure in the xylem. - **Capillary Action**: The ability of water to climb up narrow tubes, such as the xylem, due to surface tension. - **Root Pressure**: The pressure generated by roots pushing water up the xylem. - **Steps of Water Movement in Plants:** 1. Water enters the roots through root hairs. 2. Water moves through the cortex and endodermis. 3. Water enters the xylem vessels in the root. 4. Water moves up the stem through the xylem vessels. 5. Water is transported to the leaves and evaporates from the stomata. ## Water in the Soil - **Types of Soil Water**: - **Gravitational Water**: Water that is held loosely in soil, drains freely down due to gravity. - **Capillary Water**: Water that is held more tightly within soil, and is available to plants for absorption, the water is held in the smaller pore spaces. - **Hygroscopic Water**: Water that is held tightly to soil particles, and is not available to plants. - **Soil Water Potential**: The negative pressure of water held in soil particles due to the cohesive and adhesive forces of the soil particles. - **Field Capacity**: The amount of water held in the soil after excess gravitational water has drained. - **Permanent Wilting Point**: The amount of water held in the soil when plants can no longer extract water, resulting in wilting. - **Factors affecting soil water potential**: - **Soil Texture**: The size of the soil particles. - **Soil Structure**: The arrangement of soil particles. - **Soil Organic Matter**: The amount of decomposed plant and animal material in the soil. - **Temperature**: Higher temperatures can increase evaporation rates and lower soil water potential. ## Transpiration - The process of water loss from the plant. - **Importance of Transpiration:** - **Water Movement:** Creates a negative pressure in the xylem, pulling water up from the roots. - **Temperature Regulation:** Cools plants by removing excess heat. - **Nutrient Transport:** * Helps transport dissolved nutrients to the leaves. - **Types of Transpiration**: - **Stomatal Transpiration**: Most of the transpiration occurs through stomata. - **Cuticular Transpiration**: Water loss through the cuticle. - **Lenticular Transpiration**: Transpiration through lenticels on the bark. ## Factors Affecting Transpiration - **Light Intensity**: Higher light intensity increases stomatal opening and transpiration. - **Temperature**: Higher temperatures increase evaporation rate and transpiration. - **Humidity**: Lower humidity increases evaporation rate and transpiration. - **Wind**: Wind increases the rate of transpiration by removing the layer of humid air around the leaves. ## Important Notes - **Cohesion** refers to the attraction between water molecules. - **Adhesion** refers to the attraction of water molecules to other surfaces. - **Capillary action** is the movement of water in a narrow tube due to cohesion and adhesion. - **Guttation** is a phenomenon where water drops form on the edges of leaves in humid conditions, due to root pressure. - **Wilting** occurs when the water potential of the plant cells falls below the soil water potential causing the cells to lose turgor. - **Osmosis** is important for regulating water potential within plant cells. - **Plant cells** have cell walls that provide strength and support. - **Root hairs** are extensions of the root epidermis and increase the surface area for water absorption from the soil. - **Xylem** is a vascular tissue that transports water and dissolved minerals from the roots to the rest of the plant.