Homeostasis and Regulation

• 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— either internal environment or external environment.
• Properties of Homeostatic Mechanisms

  The system should have a receptor or sensor, an integrator, and an effector. Sometimes these parts may be molecules or chemical processes.
• Properties of Homeostatic Mechanisms

  The mechanism is negative feedback if it corrects the initial change. In other words, the response is in the opposite direction of the initial change in the environment.
• Properties of Homeostatic Mechanisms

  The mechanism is positive feedback if it makes the initial change more intense. In other words, the response is in the same direction as the initial change in the environment.
• Feedback Mechanisms in Plants

  Day: Stomata open

  Night: Stomata closed
• Homeostatic regulation of plants seeks to:

  1. Maintain an adequate uptake of water and nutrients from soil into leaves
• Homeostatic regulation of plants seeks to:

  2. Control stomatal opening so that water loss is minimized and carbon dioxide is maximized
• REGULATION IN PLANTS

  Plants must maintain:

  1. water balance
  2. oxygen balance
  3. carbon dioxide balance
  4. temperature balance
  5. nutrient balance
• Plant Ultrastructure: The Leaf

  Xylem

  • transports water and minerals from roots to leaves
• Plant Ultrastructure: The Leaf

  Chloroplasts

  • within mesophyll cells
• Plant Ultrastructure: The Leaf

  Phloem

  • transports food from leaves to rest of plant
• 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
• STEM TISSUES

  1. Dermal Tissues
  2. Ground Tissues
  3. Vascular Tissues
• Stem Tissues

  1. Dermal: Epidermis

  • covers and protects the plant
• Ground Tissues: Ray, cortex, pith

  • for photosynthesis
  • support
  • storage
• Vascular Tissues: Xylem, Phloem, Sclerenchyma fibers

  • transports water, minerals, and sugars to different parts
• STEM function

  • connects the roots to the leaves
• STEM Function

  • helping to transport absorbed water and minerals to different parts of the plant
• STEM Function

  • helps to transport the products of photosynthesis, namely sugars, from the leaves to the rest of the plant
• The primary function of root hair is water and nutrient acquisition.
• Root Hairs

  • These minute structures provide a large surface area for the active uptake of water and minerals.
• Some other roles of root hair include:

  • Anchor the plant to the ground.
• Some other roles of root hair include:

  • Interact with soil microorganisms, including bacteria and fungi.
• Some other roles of root hair include:

  • Directly involved in the formation of root nodules in legume plants.
• Some other roles of root hair include:

  • Secrete some acids, such as malic and citric acid, which solubilize minerals by changing their oxidation state, making the ions easier to absorb.