PLANT PHYSIO

• Oxygen is colorless, odorless, and tasteless
• Oxygen


  • It plays a critical role in respiration, which is the energy-producing chemistry that drives the metabolisms of most living organisms
  • Oxygen production occurs during light reaction on the initial phase of photosynthesis which takes place in the photosystem within the chloroplast

  
• Light


  • Can be described as both an electromagnetic wave and photons (light particle) which carry an electromagnetic force
  • It always travels in a straight line unless it encounters an obstacle
  • Corresponds to certain wavelengths, with the longest being red light
  • The shorter the wavelength, the higher the energy

  
• Free radicals


  • Also known as Reactive Oxygen Species
  • Atoms or molecules with unpaired electrons, making them highly reactive
  • In plants, they arise from environmental factors and physiological processes
  • Their instability leads to cellular damage, disrupting delicate balance within plant tissues
  • Plants developed a defensive mechanism against its harmful effects through the function of antioxidants
• Photosynthesis


  • The process by which plants transform light energy into chemical energy
  • Requires light absorption by chlorophyll and the subsequent transfer of energy

  
• Chlorophyll


  • Green pigment in chloroplasts that absorbs light energy needed for photosynthesis
  • Absorbs light mainly in the blue and red parts of the spectrum, boosting its energy level
  • Absorbed light excites electrons within chlorophyll, initiating rapid energy transfer

  
• Photosystem II


  • Absorbs light primarily at around 680 nm (red light), driving the photolysis of water to release oxygen and protons while generating ATP through an electron transport chain

  
• Photosystem I


  • Absorbs light at around 700 nm (far-red light) and uses electrons from PS II to reduce NADP⁺ to NADPH, which is critical for the Calvin cycle

  
• Photosynthetic Unit


  Functional and structural arrangement of pigments, proteins, and other molecules within the thylakoid membrane that work together to absorb light energy and convert it into chemical energy (ATP and NADPH)

  
• Production of ATP and NADPH and Photosynthetic Phosphorylation

  1. Light Absorption in PSII

  2. ATP Synthesis (Chemiosmosis)

  3. NADPH Formation

  
• 1. Scheme


  • Fundamental model that explains the electron transport chain and photophosphorylation processes during photosynthesis
  • Occurring in the thylakoid membranes of chloroplasts

  
• 1. Scheme


  1. Light Absorption: Light energy is absorbed by photosystems PSII and PSI, exciting electrons

  2. Electron Transport: Excited electrons flow through an electron transport chain from PSII to PSI, releasing energy that pumps protons into the thylakoid lumen, creating a proton gradient

  3. ATP and NADPH Production: The proton gradient drives ATP synthesis via photophosphorylation, and energized electrons from PSI reduce NADP+ to NADPH, providing energy carriers for the Calvin cycle

  
• Primary electron acceptors


  Molecules that receive high-energy electrons during biochemical reactions. In photosynthesis, chlorophyll and other pigment molecules serve as primary electron acceptors
• Primary electron donors


  Molecules that donate electrons during biochemical reactions. In photosynthesis, water (H2O) serves as the primary electron donor
• Photophosphorylation


  Occurs in the thylakoid membrane of chloroplasts which utilizes light energy to generate ATP

  
• Oxidative Phosphorylation


  Occurs in the inner mitochondrial membrane and uses energy released from electron transfer along the electron transport chain to generate ATP
• Calvin Cycle


  1. Carbon fixation

  2. Reduction

  3. Regeneration
• • Three turns of the Calvin cycle are needed to make one G3P molecule that can exit the cycle and go towards making glucose
  • Two G3Ps to build a six-carbon glucose molecule
  • It would take six turns of the cycle to produce one molecule of glucose
• Types of plants based on carbon dioxide fixation

  • C3 plants
  • C4 plants
  • CAM plants
• External factors affecting photosynthesis

  • Light Intensity: Higher light intensity generally increases the rate of photosynthesis
  • Temperature: Photosynthesis rates typically increase with temperature up to an optimal range
  • Water: Sufficient water is crucial for maintaining turgor pressure in plant cells

  
• Internal factors affecting photosynthesis

  • Chlorophyll: Changes in chlorophyll content can affect the plant's ability to capture light energy
  • Enzyme Activity: Factors affecting enzyme activity, such as pH and temperature, can impact photosynthesis
  • Plant Age and Health: Factors such as plant age, health, and physiological status (e.g., flowering, dormancy) can influence photosynthetic rates

  
• Sieve tube members


  • Elongated cells joined end to end, with partially broken down end walls and sieve tube plates containing holes for solute passage
  • Facilitates flow of dissolved solutes like sucrose and amino acids in the phloem
• Companion cells


  • Connected to sieve tube members via plasmodesmata
  • Facilitate cytoplasmic continuity
• Mechanism of phloem transport

  1. Initiation of Transport: Sugars and organic substances are actively transported into companion cells and sieve elements of phloem, mainly in leaves, through plasmodesmata. Accumulation of substances leads to water influx into sieve elements via osmosis, raising turgor pressure.

  2. Flow of Fluid: Fluid containing sugars is pushed up and down the phloem. Cortex cells in stem and root remove sugars, consuming or converting them into starch, reducing osmotic pressure.

  3. Maintenance of Flow: Decrease in osmotic pressure ensures pure water remains in phloem, facilitating continued substance movement.

  4. Osmotic Pressure Requirement: Osmotic pressure in leaf phloem fluid must exceed that in the phloem of receiving tissues for efficient transport.