Detailed Notes

AQA Biology GCSE Topic 5: Homeostasis and Response

Page 1

• Overview of the topic covered, relevant for both separate science and double award students.

Page 2: Homeostasis

Definition

• Homeostasis is the maintenance of a constant internal environment.

• Mechanisms are in place to maintain optimum conditions despite changes.

• Important for enzyme action and all cell functions.

Key Features of Homeostasis

• **Controls specific factors: **

  • Blood glucose concentration

  • Body temperature

  • Water levels

• Communication systems:

  • Nervous and hormonal communication involved in automatic control systems.

Components of Control Systems

1. Receptors:

   • Cells that detect stimuli (changes in the environment).

2. Coordination Centres:

   • Process information received from receptors (e.g., brain, spinal cord, pancreas).

3. Effectors:

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

Page 3: The Human Nervous System

Structure and Function

• The nervous system reacts to surroundings and coordinates actions in response to stimuli.

• Steps in response:

  1. Receptor cells convert a stimulus into an electrical impulse.

  2. Impulse travels along sensory neurons to the CNS.

  3. Information is processed; appropriate response coordinated.

  4. Electrical impulse sent along motor neurons to effectors.

• Reflex responses:

  • Automatic; prevent injury by using a reflex arc (impulse does not pass through conscious areas of the brain).

Reflex Arc Sequence

1. Stimulus detected by receptors.

2. Impulse sent along a sensory neuron.

3. In CNS, impulse passes to a relay neuron.

4. Impulse sent along a motor neuron.

5. Impulse reaches effector for response (e.g., pupil response, hand withdrawal from heat).

Page 4: Synapses and Brain

Synapses

• Gaps between two neurons.

  • Chemical released into synapse at end of first neuron.

  • Chemical diffuses, triggers impulse in second neuron.

The Brain (For Biology Only)

• Made of connected neurons, controls complex behavior.

• Key components:

  1. Cerebral Cortex:

     • Controls consciousness, intelligence, memory, language.

  2. Cerebellum:

     • Coordinates fine muscle movements.

  3. Medulla:

     • Controls unconscious actions (breathing, heart rate).

Challenges in Brain Study

• Complexity and delicacy

• Difficulty in understanding functions of specific areas

• Drugs often can't penetrate brain membranes.

Page 5: Investigating Brain Function

Methods of Brain Mapping

1. Study of Brain Damage:

   • Observing effects of damage in certain areas.

2. Electrical Stimulation:

   • Pushing electrodes into brain to invoke and study responses.

3. MRI Scanning:

   • Imaging to identify tumor locations or active regions during tasks.

The Eye (For Biology Only)

• Contains receptors sensitive to light and color, enabling accommodation and dim light adjustment.

• Key components:

  1. Retina:

     • Layer of light-sensitive cells.

  2. Optic Nerve:

     • Carries impulses to the brain.

  3. Sclera:

     • White outer layer, supports eye structure.

  4. Cornea:

     • Curved surface focusing light onto retina.

  5. Iris:

     • Controls pupil size in response to light.

  6. Ciliary Muscles and Suspensory Ligaments:

     • Adjust lens shape for focusing.

Page 6: Eye Defects & Treatments

Common Eye Defects

1. Myopia (Short-Sightedness):

   • Lens too curved, distant objects blur.

2. Hyperopia (Long-Sightedness):

   • Lens too flat, can't refract light enough.

Treatment Options

• Spectacles (concave for myopia, convex for hyperopia).

• Contact lenses.

• Laser eye surgery (cornea reshaping).

• Replacement lens surgery for hyperopia.

Page 7: Control of Body Temperature (For Biology Only)

Thermoregulation

• Monitored by thermoregulatory centre in the brain.

  • Has receptors:

    • Monitor blood temperature.

    • Receive signals from skin receptors.

Responses to Temperature Changes

• If Too High:

  • Sweat production increases (evaporative cooling).

  • Vasodilation brings blood closer to skin.

• If Too Low:

  • Stops sweating.

  • Rapid muscle contractions (shivering) generate heat.

  • Hair stands up (insulation).

  • Vasoconstriction conserves heat.

Page 8: Hormonal Coordination in Humans

Endocrine System Overview

• Two communication systems: Nervous and Endocrine.

• Endocrine system uses hormones as chemical messengers from glands directly into the bloodstream.

Key Endocrine Glands & Their Functions

• Pituitary Gland:

  • The master gland; stimulates other glands.

• Pancreas:

  • Produces insulin; controls blood glucose levels.

• Thyroid:

  • Produces thyroxine; regulates metabolism.

• Adrenal Gland:

  • Produces adrenaline; "fight or flight" response.

• Ovary:

  • Produces estrogen; menstrual cycle regulation.

• Testes:

  • Produces testosterone; sperm production and male characteristics.

Page 9: Blood Glucose Control

Glucose Regulation Importance

• Controlled by the pancreas; vital for respiration.

• After carbohydrate consumption, blood glucose increases.

Response to High Glucose Levels

• Pancreas secretes insulin.

• Insulin actions:

  • Enables glucose entry into muscle cells.

  • Converts excess glucose to glycogen (storage).

Response to Low Glucose Levels

• Pancreas releases glucagon:

  • Converts glycogen back to glucose for bloodstream entry.

Page 10: Diabetes

Types

1. Type 1 Diabetes:

   • Insulin production is insufficient.

   • Requires insulin injections and carbohydrate management.

2. Type 2 Diabetes:

   • Body cells resist insulin.

   • Manage through diet , weight control, exercise, and medication.

Page 11: Maintaining Water Balance

Osmosis Overview

• Water moves from high concentration to low concentration (osmosis).

• Blood water concentration changes affect cell function.

Role of Kidneys

• Filters blood to create urine, maintaining water and substance balance.

  • Water, Ions, and Urea are processed:

    • Water can leave through lungs and skin.

    • Ions taken from food; regulated by kidneys.

    • Urea is formed from amino acid breakdown (toxic ammonia converted to urea).

Page 12: Anti-Diuretic Hormone (ADH)

• ADH regulates water retention by kidneys.

  • Released by the pituitary gland in response to blood concentration.

  • Affects kidney tubule permeability, influencing urine concentration.

Kidney Failure Treatments

1. Dialysis:

   • Artificially filters blood, requires frequent sessions.

2. Kidney Transplant:

   • Surgical replacement with a healthy kidney, issues include potential rejection.

Page 13: Hormonal Reproductive Changes

Hormones and Puberty

• Male hormone: Testosterone, stimulates sperm production.

• Female hormone: Oestrogen, controls cycles and physical changes.

Menstrual Cycle Overview

• Involves hormonal regulation through four key hormones:

  1. FSH:

     • Matures an egg, stimulates oestrogen production.

  2. Oestrogen:

     • Stimulates uterine growth, inhibits FSH.

  3. LH:

     • Triggers ovulation.

  4. Progesterone:

     • Maintains uterine lining and regulates reproductive hormones.

Page 14: Contraception Methods

Hormonal Contraception

• Contraceptive Pill:

  • Contains oestrogen and progesterone; prevents ovulation.

• Contraceptive Patch & Implant:

  • Releases hormones to prevent egg release and thickens cervical mucus.

• Injection:

  • Similar effects as implants, but temporary.

Page 15: Non-Hormonal Contraception

Methods

• Chemical (spermicides), barrier (condoms), intrauterine devices (copper).

• Surgical methods involve permanent solutions (tubal ligation, vasectomy).

Page 16: Hormones and Infertility Treatment

Fertility Drugs and IVF

• Fertility drugs (FSH and LH) increase chances of pregnancy.

• IVF involves egg extraction, fertilization outside the body, and reimplantation.

Page 17: Negative Feedback Mechanisms

Overview

• Regulates levels of hormones like thyroxine and adrenaline via negative feedback loops to maintain homeostasis.