General Physiology

• Homeostasis


  A process by which a biological system maintains stability while adjusting to its changing environment
• Properties of Homeostatic Mechanisms

  • The mechanism should be triggered by some change in the environment/stimulus
  • The system should have a receptor or sensor, an integrator, and an effector
  • The mechanism is negative feedback if it corrects the initial change
  • The mechanism is positive feedback if it makes the initial change more intense
• What homeostatic regulation in plants seeks to maintain

  • Water balance
  • Oxygen balance
  • Carbon dioxide balance
  • Temperature balance
  • Nutrient balance
• Leaf epidermis

  Protects the internal structure of the leaf, continuous with the stem epidermis
• Stem


  Connects the roots to the leaves, helps transport absorbed water and minerals, and transports photosynthesis products
• Root hairs


  • Main function is water and nutrient acquisition
  • Other functions include anchoring the plant, interacting with soil microorganisms, and secreting acids to solubilize minerals
• Plants are fairly tolerant of changes in the solute concentration of the extracellular fluid providing the solute concentration is hypotonic to the solute concentration inside their cells
• If the solute concentration of the extracellular fluid is hypertonic to the solute concentration of cytoplasm, water diffuses out of the cytoplasm, resulting in plasmolysis (shrinkage of the cytoplasm) and potentially cell death
• Stomata


  Pores in the leaf epidermis bounded by two highly specialised guard cells
• Guard cells


  • They are joined at their ends in pairs
  • Their cell walls are thicker on the side nearest to the stomatal pore
  • Bands of inelastic cellulose fibres run around each cell
• Stomatal movement


  1. Water flows into the guard cells by osmosis, increasing their turgor and causing them to expand and draw away from each other, opening the pore

  2. Potassium ions move out of the guard cells, water moves out, the cells shrink in size and the stoma closes
• Photosynthesis plants' ability to manufacture their own food
• Photosynthesis


  The process of producing carbohydrates from carbon dioxide, water and sunlight, with oxygen as a byproduct
• Photosynthesis occurs only in the mesophyll layers of plant leaves and/or in mesophyll cells in the stem
• Chloroplasts are incredibly small, with 400,000 chloroplasts in a square millimeter
• Chlorophyll


  The pigment found in chloroplasts that is responsible for trapping light energy from the sun
• If any of the ingredients for photosynthesis — light, water and carbon dioxide — is lacking, photosynthesis stops. If any factor is absent for a long period of time, a plant will die
• Homeostatic regulation of plants seeks to:

  1.Maintain an adequate uptake of water and nutrients from soil into leaves

  2.Control stomatal opening so that water loss is minimized and carbon dioxide is maximized
• Xylem transports water in a upward manner
• Phloem transports sugars downward
• LEAF FUNCTION:

  •to produce food for the plant by photosynthesis

  •Chlorophyll, the substance that gives plants their characteristic green color, absorbs light energy

  •The internal structure of the leaf is protected by the leaf epidermis, which is continuous with the stem epidermis
• REGULATION IN HIGH TEMPERATURES

  EXPOSURE TO HEAT CAUSES THE STOMATA OPEN, LEADING TO TRANSPIRATION, DECREASING INTERNAL TEMPERATURE BY EVAPORATIVE COOLING BUT RUN RISK OF DEHYDRATION
• REGULATION IN COLD STRESS:

  the water inside it expands as it turns to ice. This can cause the cell membrane to rupture and lead to cell death. Plants respond to cold temperatures by activating metabolic pathways that protect their cells from cold and freezing conditions.
• HEAT STRESS

  CHANGE IN PHENOLOGY
• HEAT AND COLD STRESS

  Increase in oxidative stress (ROS)
• HEAT and COLD STRESS

  • reduction in antioxidant enzyme activities
  • reduced grain growth and yield
• HEAT STRESS

  • decreased photosynthesis
  • reduced stomatal conductance and CO2 fixation
  • damaged photosynthetic pigment
  • Poor cell enlargement
• HEAT AND COLD STRESS

  • Inhibition seed germination
  • Changes in sensing and signaling
• HEAT STRESS

  • loss turgor
  • reduction in biomass
  • reduction in carbohydrate metabolism
  • reduction in production of secondary metabolites
• HEAT STRESS

  • dehydration
  • changes in expression of heat stress gene related
  • changes in +/- regulator gene expression
• COLD STRESS

  • decrease membrane stability
  • metabolism retarded
  • higher electrolyte leakage
  • Ion leakage or altered homeostasis
• COLD STRESS

  • protein disintegration
  • chlorophyll degradation
  • protoplast volume shrinkage
  • leaves chlorosis and wilting
• COLD STRESS

  • physiological and cellular perturbations
  • cellular dehydration and forming intracellular ice crystals
• COLD STRESS

  • reduced root branching and root surface area
  • reduced water and nutrient uptake
  • changes in expression of cold stress gene related
• REGULATING STOMATA

  • Stomal movement is the result of changes in the turgor of the guard cells.If water flows into the guard cells by osmosis, their turgor increases and they expand. The relatively inelastic inner wall makes them bend and draw away from each other. nThis opens the pore.
• STOMATAL OPENING

  1.Potassium ions move into the vacuoles.

  2.Water moves into the vacuoles, following   potassium ions.

  3.The guard cells expand.

  4.The stoma opens.
• STOMATAL CLOSING

  1.Potassium ions move out of the vacuole and   out of the cells.

  2.Water moves out of the vacuoles, following   potassium ions.

  3.The guard cells shrink in size.

  4.The stoma closes.
• Photosynthates = product of photosynthesis
• REGULATION OF FOOD

  •After producing carbohydrates, a plant either uses them as energy, stores them or builds them into complex energy compounds such as oils and proteins. The plant uses them when light is limited, or transports them to its roots or developing fruits.
• •Often chloroplasts are arranged perpendicular to incoming sun rays so they can absorb maximum sunlight.