Photosynthesis

• Botany is the scientific study of plants, covering their physiology, structure, genetics, ecology, distribution, classification, and economic importance
• Plant physiology studies plant life processes and how plants function

Photosynthesis

• Photosynthesis converts light energy into chemical energy
• Light energy converts water and carbon dioxide into glucose and oxygen during photosynthesis
• Chlorophyll, a pigment in chloroplasts, absorbs light energy to drive photosynthesis
• The equation for photosynthesis is: 6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2
• The two main stages of photosynthesis are the light-dependent reactions and the light-independent reactions (Calvin cycle)
• Light-dependent reactions occur in the thylakoid membranes of chloroplasts
• Water is oxidized during the light-dependent reactions, releasing oxygen, protons, and electrons
• ATP and NADPH are produced during the light-dependent reactions, storing energy for use in the Calvin cycle
• The Calvin cycle occurs in the stroma of chloroplasts
• Carbon dioxide is fixed, reduced, and converted into glucose using ATP and NADPH during the Calvin cycle
• RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the initial carbon fixation step in the Calvin cycle
• C4 and CAM plants have adaptations to minimize photorespiration in hot and dry environments
• C4 plants spatially separate carbon fixation and the Calvin cycle into different cells (mesophyll and bundle sheath cells)
• CAM plants temporally separate carbon fixation and the Calvin cycle, performing these processes at different times of the day (night and day)

Respiration

• Plant respiration breaks down glucose to release energy for cellular activities
• Respiration consumes oxygen and releases carbon dioxide and water
• The equation for respiration is: C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy (ATP)
• The three main stages of respiration are glycolysis, the Krebs cycle (citric acid cycle), and the electron transport chain
• Glycolysis occurs in the cytoplasm and breaks down glucose into pyruvate, producing a small amount of ATP and NADH
• The Krebs cycle occurs in the mitochondrial matrix and oxidizes pyruvate, producing ATP, NADH, and FADH2
• The electron transport chain occurs in the inner mitochondrial membrane and uses electrons from NADH and FADH2 to produce a large amount of ATP through oxidative phosphorylation

Water Transport

• Water is essential for plant life, serving as a solvent, transport medium, and reactant in various biochemical processes
• Water moves through plants via the xylem, a vascular tissue composed of dead cells
• Transpiration is the process by which water evaporates from plant leaves, creating a tension that pulls water up the xylem
• Cohesion is the attraction between water molecules, while adhesion is the attraction between water molecules and the xylem walls
• The cohesion-tension theory explains how water is transported from the roots to the leaves against gravity
• Root pressure can also contribute to water movement, especially in smaller plants
• Guttation is the exudation of water droplets from plant leaves due to root pressure

Nutrient Transport

• Plants require essential nutrients for growth and development
• Macronutrients are needed in larger quantities, while micronutrients are needed in smaller quantities
• Essential macronutrients include nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur
• Essential micronutrients include iron, manganese, zinc, copper, boron, molybdenum, and chlorine
• Nutrients are absorbed from the soil through the roots
• The phloem is the vascular tissue that transports sugars and other organic compounds throughout the plant
• Translocation is the movement of sugars from sources (e.g., leaves) to sinks (e.g., roots, fruits)
• The pressure-flow hypothesis explains how sugars are transported in the phloem
• Sugars are actively loaded into the phloem at the source, creating a high concentration of solutes
• Water enters the phloem due to the high solute concentration, increasing the pressure
• The pressure gradient drives the flow of sugars to the sink, where sugars are unloaded

Plant Hormones

• Plant hormones are chemical messengers that regulate plant growth, development, and responses to the environment
• Auxins promote cell elongation, apical dominance, and root formation
• Cytokinins promote cell division and delay senescence
• Gibberellins promote stem elongation, seed germination, and flowering
• Abscisic acid (ABA) promotes dormancy, stomatal closure, and stress tolerance
• Ethylene promotes fruit ripening, senescence, and abscission
• Brassinosteroids promote cell elongation, vascular development, and stress responses
• Jasmonates regulate plant defense responses and development
• Plant hormones often interact with each other to regulate plant processes

Growth and Development

• Plant growth is the irreversible increase in size or mass
• Plant development is the series of changes that a plant undergoes throughout its life cycle
• Primary growth involves the elongation of stems and roots
• Apical meristems are located at the tips of stems and roots and are responsible for primary growth
• Secondary growth involves the increase in stem and root thickness
• Lateral meristems (vascular cambium and cork cambium) are responsible for secondary growth
• The vascular cambium produces secondary xylem (wood) and secondary phloem
• The cork cambium produces the periderm (bark)
• Plant life cycles can be annual (completing their life cycle in one year), biennial (completing their life cycle in two years), or perennial (living for more than two years)
• Environmental factors such as light, temperature, and water availability influence plant growth and development

Plant Responses to the Environment

• Plants respond to various environmental stimuli, including light, gravity, touch, and stress
• Phototropism is the growth response to light
• Gravitropism is the growth response to gravity
• Thigmotropism is the growth response to touch
• Plants can respond to stress caused by drought, salinity, temperature extremes, and pathogen attacks
• Plants have various defense mechanisms to protect themselves from herbivores and pathogens, including physical barriers (e.g., thorns, thick cuticles) and chemical defenses (e.g., toxins, repellents)
• Systemic acquired resistance (SAR) is a plant defense mechanism that provides long-lasting protection against a wide range of pathogens