notes-p2

Homeostasis and Response

Homeostasis (5.1)

  • Definition: Maintenance of a constant internal environment.

  • Importance: Ensures optimum conditions for enzyme action and cellular functions despite external changes.

  • Human Controls:

    • Blood glucose concentration

    • Body temperature

    • Water levels

  • Communication Systems: Nervous and hormonal systems detect and respond to changes.

Control Systems Components

  • Receptors: Cells detecting environmental stimuli.

  • Coordination Centres: Process information (e.g., brain, spinal cord, pancreas).

  • Effectors: Bring about responses to restore optimum conditions (e.g., muscles, glands).

The Human Nervous System (5.2)

Structure and Function (5.2.1)

  • Function: Reacts to surroundings and coordinates responses to stimuli.

  • Process:

    1. Receptor cells convert stimuli into electrical impulses.

    2. Sensory neurons carry impulses to the CNS.

    3. The CNS processes information and coordinates responses, sending impulses through motor neurons.

    4. Effectors execute the response (muscles contract, glands secrete).

  • Reflexes: Automatic responses occurring rapidly through a reflex arc preventing harm.

Reflex Arc Pathway

  1. Stimulus detected by receptors.

  2. Impulses travel along sensory neurons.

  3. Relay neuron in CNS processes the impulse.

  4. Motor neuron sends impulse to effector.

  5. Effector initiates response.

  • Examples: Adjusting pupil size in bright light, withdrawing hand from a hot surface.

Synapses

  • Definition: Gaps between neurons.

  • Impulse Transmission:

    • Chemical release triggers impulses in the next neuron.

Reaction Time

  • Measurement: Ruler drop test to measure how quickly one responds to a stimulus.

The Brain (5.2.2 - Biology Only)

  • Composed of interconnected neurons, controlling complex behaviors.

  • Regions and Functions:

    1. Cerebral Cortex: Consciousness, intelligence, memory, language.

    2. Cerebellum: Muscle movement control.

    3. Medulla: Unconscious actions (breathing, heart rate).

  • Challenges:

    • Complexity and delicacy.

    • Damage susceptibility.

    • Limitations of treatment interventions.

Mapping Brain Function

  1. Studying Brain Damage: Changes in behavior inform about impacted areas.

  2. Electrical Stimulation: Stimulating regions may elicit behavioral responses, identifying functions.

  3. MRI Scanning: Allows visualization of affected regions, identifying tumors or activity patterns.

The Eye (5.2.3 - Biology Only)

  • Function: Senses light intensity and color; adapts to focus on objects (accommodation).

  • Key Structures:

    1. Retina: Light-sensitive cells sending impulses to the brain.

    2. Optic Nerve: Transmits impulses from retina to brain.

    3. Sclera: Supportive outer layer.

    4. Cornea: Bends and focuses light onto retina.

    5. Iris: Controls pupil size based on light conditions.

    6. Ciliary Muscles & Suspensory Ligaments: Adjust lens shape for focusing.

Accommodation Process

  • Near Objects:

    • Ciliary muscles contract, suspensory ligaments loosen.

    • Lens becomes thicker and more curved.

  • Distant Objects:

    • Ciliary muscles relax, suspensory ligaments tighten.

    • Lens becomes thinner, light refracted less.

Eye Defects

  1. Myopia (short-sightedness): Lens too curved, distant objects blur.

  2. Hyperopia (long-sightedness): Lens too flat, unable to refract light sufficiently.

  • Treatments:

    • Glasses (concave/convex), contact lenses, laser surgery, lens replacement.

Control of Body Temperature (5.2.4 - Biology Only)

  • Thermoregulatory Centre: In the brain; monitors body temperature.

  • Normal Temperature: 37.5 degrees Celsius.

Responses to High Temperature

  • Sweating: Evaporation cools the body.

  • Vasodilation: Increases blood flow to skin, enhancing heat transfer.

Responses to Low Temperature

  • Sweating Stops.

  • Shivering: Muscle contractions generate heat.

  • Vasoconstriction: Reduces blood flow to surface, maintaining heat.

Hormonal Coordination in Humans (5.3)

Human Endocrine System (5.3.1)

  • Communication Systems: Nervous vs. Endocrine; hormones as messengers.

  • Glands:

    • Pituitary Gland: Master gland regulates other glands.

    • Pancreas: Secretes insulin for blood glucose control.

    • Thyroid: Regulates metabolic rate via thyroxine.

    • Adrenal Gland: Releases adrenaline for 'fight or flight'.

    • Ovaries/Testes: Produce sex hormones affecting reproductive health.

Control of Blood Glucose Concentration (5.3.2)

  • Pancreas Role: Monitors blood glucose via insulin and glucagon.

  • High Glucose: Insulin causes glucose uptake and glycogen storage.

  • Low Glucose: Glucagon stimulates glycogen breakdown to glucose.

  • Diabetes: Can be Type 1 (insulin deficient) or Type 2 (cells unresponsive).

Maintaining Water and Nitrogen Balance (5.3.3 - Biology Only)

Osmosis

  • Water movement based on concentration gradients influences cell function.

The Kidneys

  • Function: Maintenance of water/ion balance via filtration and reabsorption.

  • Waste Management:

    • Excretes water, ions, urea through urine.

Anti-Diuretic Hormone (ADH)

  • Role: Modulates water loss in urine by altering kidney tubule permeability.

Kidney Failure Treatments

  1. Dialysis: Artificial kidney function via membrane filtration.

  2. Transplant: Replacement with a healthy kidney from a donor.

Hormones in Human Reproduction (5.3.4)

Reproductive Hormones

  • Male: Testosterone; stimulates sperm production.

  • Female: Oestrogen; involved in menstrual cycle and secondary characteristics.

Menstrual Cycle Regulation

  • Key Hormones:

    1. FSH: Egg maturation in ovaries.

    2. Oestrogen: Uterine lining growth; inhibits FSH.

    3. LH: Triggers ovulation.

    4. Progesterone: Supports pregnancy by maintaining uterine lining.

Contraception (5.3.5)

Hormonal Methods

  • Contraceptive Pill: High oestrogen inhibits FSH; alters mucus and lining.

  • Patch/Implant/Injection: Releases hormones to prevent ovulation and thickens cervical mucus.

Non-Hormonal Methods

  • Chemical (spermicides), Barrier (condoms), IUDs, Sterilization.

Treating Infertility (5.3.6)

  • Fertility Drugs: Increase egg maturation likelihood.

  • IVF: Egg extraction, fertilization in a lab, and implantation.

Negative Feedback (5.3.7)

  • Role of Thyroxine: Regulates metabolism via negative feedback.

  • Adrenaline Effects: Increases heart rate, energy availability during stress.

Plant Hormones (5.4 - Biology Only)

Control and Coordination (5.4.1)

  • Auxin: Stimulates growth in response to light/gravity.

  • Phototropism & Gravitropism: Positive response towards light and gravity.

  • Research Methods: Experiments on light/gravity effects on plants.

Use of Plant Hormones (5.4.2)

  • Applications in Agriculture/Horticulture: Increased yield, desirable plant features.

  1. Weed Killers (Auxin): Selectively terminates broad-leaved plants.

  2. Rooting Powder: Cloning via auxins.

  3. Gibberellins: Enhancements in flowering, seed dormancy, and fruit size.