LESSON 9: PLANT AND ANIMAL ORGAN SYSTEMS AND THEIR FUNCTIONS

• Homeostasis


  The relatively stable state inside the body of an animal.
• Examples of internal conditions maintained homeostatically

  • Level of blood glucose
  • Body temperature
  • Blood calcium level
• Set point


  The specific value of some aspect of the body or its cells that the body's systems will usually attempt to go back to
• Stimulus


  A change in the internal or external environment that is detected by a receptor
• Response


  The adjustment of the system's activities so the value moves back toward the set point
• Adjust ernal and extemal changes in order toaintain this steady state. Animal organs and organ systems

  Animal organs and organ systems
• physiologic processes that result in negative feedback relationships.

  Homeostasis
• goal of homeostasis is the maintenance of equilibrium around a specific value of some aspect of the body or its cells called a set point.
• While there are normal fluctuations from the set point, the body's systems will usually attempt to go back to his point.
• A change in the internal or external environment is called a stimulus and is detected by a receptor;
• if the body ecomes too warm, adjustments are made to cool the animal. If glucose levels in the blood rise after a meal, adjustments are made to lower them and to get the nutrient into tissues that need it or to store it for later use.
• active regulation of osmotic pressure to maintain the balance of water and electrolytes in an organism.


  Osmoregulation
• needed to perform biochemical reactions and preserve homeostasis.


  Control of osmotic pressure
• movement of solvent molecules through a semipermeable membrane into an area that has a higher solute concentration.


  Osmosis
• Osmotic pressure is the external pressure needed to prevent the solvent from crossing the membrane.
• Osmotic pressure depends on the concentration of solute particles.
• In an rganism, the solvent is water and the solute particles are mainly dissolved salts and other ions,
• larger molecules (proteins and polysaccharides) and nonpolar or hydrophobic molecules (dissolved gases, lipids) don't cross a semipermeable membrane
• To maintain the water and electrolyte balance, organisms excrete excess water, solute molecules, and wastes.
• Two major types of osmoregulation are osmoconformers and osmoregulators.
• Osmoconformers use active or passive processes to match their internal osmolarity to that of the environment.
• commonly seen in marine invertebrates, which have the same internal osmotic pressure inside their cells as the outside water


  Osmoconformers
• control internal osmotic pressure so that conditions are maintained within a tightly-regulated range. 


  Osmoregulators
• Many animals are osmoregulators, including vertebrates (like humans).
• When osmolarity increases around bacteria, they may use transport mechanisms to absorb electrolytes or small organic molecules.
• The osmotic stress activates genes in certain bacteria that lead to the synthesis of osmoprotectant molecules.
• Protists use contractile vacuoles to fransport ammonia and other excretory wastes from the cytoplasm to the cell membrane, where the vacuole opens to the environment.
• Osmotic pressure forces water into the cytoplasm, while diffusion and active transport control the flow of water and electrolytes.
• Higher plants use the stomata on the underside of leaves to control water loss.
• Plant cells rely on vacuoles to regulate cytoplasm osmolarity.
• Plants that live in hydrated soil (mesophytes) easily compensate for water loss from by absorbingmore water
• The leaves and stem of the plants may be protected from excessive water loss by a waxy outer coating called the cuticle.
• Plants that live in dry habitats (xerophytes) store water in vacuoles, have thick cuticles, and may have structural modifications (i.e., needle-shaped leaves, protected stomata) to protect against water loss.
• Plants that live in salty vironments (halophytes) have to regulate not only water intake/loss but also the effect on osmotic pressure by salt.
• Some species store salts in their roots so the low water potential will draw the solvent in via osmosis.
• Salt may be excreted onto leaves to trap water molecules for absorption by leaf cells.
• Plants that live in water or damp environments (hydrophytes) can absorb water across their entire surface.
• Animals utilize an excretory system to control the amount of water that is lost to the environment and maintain osmotic pressure.
• Protein metabolism also generates waste molecules which could disrupt osmotic pressure.
• The organs that are responsible for osmoregulation depend on the species.