biology

• Homeostasis


  The regulation of the internal environment of an organism to maintain stable conditions necessary for the survival of cells and the organism
• Importance of homeostasis


  • An organism's internal environment must be regulated so that important life processes such as growth, tissue repair and reproduction can be carried out
  • If changes in the internal environment are out of the tolerance levels for too long, it will cause body systems to malfunction, which can result in illness or death
• How homeostasis is maintained


  1. Stimulus

  2. Receptor

  3. Control centre

  4. Effector

  5. Response
• Stimulus


  A change in the internal or external environment going outside of the 'set point'
• Receptor


  Specialised cells that detect a change in the environment and send a message to the control centre
• Control centre


  Normally the hypothalamus or pituitary gland (brain) that transmits a message via nerves and/or hormones to the effector
• Effector


  A muscle, gland or organ that receives the message from control centre and coordinates a response
• Response


  A change that occurs a counteract the origins stimulus
• Feedback systems


  • Negative and positive feedback systems
  • Most biological feedback involve negative feedback
• Examples of homeostatic regulation


  • Temperature regulation (thermoregulation)
  • Osmoregulation (water balanced)
  • Blood glucose regulation
• Body temperature regulation

  • Mammals and bored generate their own body heat through internal chemical reactions (endotherms)
  • Other animals reply on external sources for their body heat (ectotherms)
  • The set point for human body temperature is 37°C
  • 80% of the energy we get from cellular respiration is used to maintain core body temperature
• Thermoregulation - physiological responses


  1. Body temperature below 37°: Vasoconstriction, Shivering, piloerection, Increased metabolism

  2. Body temperature above 37°: Vasodilation, Sweat
• Osmoregulation


  Involves maintaining water balance (and solute balance)
• Human body requires approximately 3L of water per day
• Importance of water balance


  • Affects blood solute concentrations, blood volume and this blood pressure
  • Biochemical reactions occur in an aqueous environment
• Osmoregulation - physiological responses


  1. High osmolality (low water content in blood): Detected by hypothalamus osmoreceptors, Message sent to the pituitary gland which released the hormone ADH, ADH acts on the kidney to put more water back into the bloodstream, Urine becomes more concentrated

  2. Low osmolality (high water content in blood): Detected by hypothalamus osmoreceptors, Message sent to the pituitary gland to stop release hormone ADH, Urine becomes more dilute
• Negative feedback system - osmoregulation


  1. Stimulus: Increased osmolality of blood (high solute concentration)

  2. Receptor: Osmoreceptors (hypothalamus)

  3. Control centre: (hypothalamus)

  4. Effector: Pituitary gland (brain)

  5. Release: ADH release
• Blood glucose level (BGL)


  The concentration of glucose in the blood
• BGL is regulated within 3.5 - 8 mmol/L
• Glucose


  Converted into useable energy (ATP) via cellular respiration by cells in the body
• Excess glucose


  Stored in the body as glycogen in liver and muscle cells, and when the glycogen - storing capacity of the body is full, excess glucose is stored as fat
• Blood glucose regulation - physiological response


  1. High BGL (after eating a meal) are detected by receptors in the pancreas, Specialised cells in the pancreas (beta cells) release the hormone insulin into the bloodstream, Insulin helps glucose enter cells, Excess glucose is converted to glycogen and stored in the liver or muscles, BGL returns to normal

  2. Low BGL (after exercise or in the middle of the night) are detected by receptors in the pancreas, Specialised cells in the pancreas (alpha cells) release the hormone glycogen in the bloodstream, Glucagon causes liver or muscle cells to convert glycogen back to glucose and release it into the bloodstream, BGL returns to normal
• Specialisation and organisation of plant cells into tissues for specific functions in vascular plants


  Intake, movement and loss of water
• Specialisation and organisation of animal cells into tissues, organs and systems with specific functions


  Digestive, endocrine and excretory
• Regulation of body temperature, blood glucose and water balance in animals by homeostatic mechanisms

  1. Stimulus-response models

  2. Feedback loops

  3. Associated organ structures
• Malfunctions in homeostatic mechanisms: type 1 diabetes, hypoglycaemia, hyperthyroidism
• Palisade mesophyll cells


  Contain chloroplasts which contain chlorophyll for capturing light energy and are the site of photosynthesis
• Xylem


  To carry water from the roots to the leaves
• Phloem


  To carry sugars made in photosynthesis to other parts of the plant
• Stomata


  To allow CO2 (input of photosynthesis) and O2 (output of photosynthesis) to enter and exit the leaf
• Transpiration


  Water is drawn up through the plant (via the xylem) from the roots to the leaves. At the leaves, water vapour is lost via open stomata (during gas exchange).
• Increased air flow


  Water vapour lost faster
• Increased temperature


  Water vapour lost faster
• Increased humidity


  Transpiration rate decreases (lower concentration gradient)
• Factors that affect the rate of photosynthesis

  • Temperature
  • Light
  • Concentration of reactants
• Excretory system


  To remove waste products from the bloodstream (e.g. urea)
• Regulation of water balance

  Low water concentration (or high solute concentration) in blood is detected by osmoreceptors in the hypothalamus which sends a message to the pituitary gland to release ADH hormone. ADH acts on the kidney to put more water back into the blood stream (increase reabsorption of water) which will increase water concentration.
• Homeostasis


  The maintenance of a relatively stable internal environment, within narrow limits, despite changes in the external environment
• Positive feedback loops amplify the stimulus/change in a system
• Negative feedback loops reverse/counteract the stimulus/change in a system, returning the system back to its 'setpoint' (original state)