# Technologies and Disorders

> Disorders of hearing, vision and the kidneys, and the technologies that help, from hearing aids and cochlear implants to glasses, laser surgery and dialysis.

From HSC Biology on WhizzNotes, free study notes for NSW students: https://whizznotes.com/biology/technologies-and-disorders/. Updated 3 November 2026.
Year 11 and Year 12 boxes go deeper than the Year 10 text around them.

### Story time: A sound for the first time
In 1978 in Melbourne, a man named Rod Saunders, who had lost his hearing in a car accident, had a device placed inside his ear by a team led by Professor Graeme Clark. When the device was switched on, Rod heard sounds. Over time, he learned to understand speech again.

Graeme Clark's father had been deaf, and he had seen how hard life could be without hearing. His team's invention, the **cochlear implant**, has since helped more than a million people around the world to hear. It works by skipping the damaged part of the ear and talking directly to the nerve.

**In short:** Technologies help people with disorders of hearing, sight and the kidneys. Hearing aids and cochlear implants treat hearing loss, lenses and surgery correct sight problems, and dialysis or a kidney transplant replaces failed kidneys.

## Starting point: what you already know

- Sound is a wave of vibrations. Light refracts through lenses (Year 10 physics).
- The kidneys filter blood and control water balance (see Homeostasis).
- Disorders can be genetic, environmental or caused by ageing (see the previous chapter).

## Hearing

**How we hear.** Sound waves enter the **outer ear** and make the **eardrum** vibrate. Three tiny bones in the **middle ear** (hammer, anvil and stirrup) pass the vibrations to the **cochlea** in the **inner ear**. Inside the cochlea, fluid moves tiny **hair cells**, which send signals along the **auditory nerve** to the brain.

**Hearing loss.**

- **Conductive** loss: sound cannot reach the inner ear, from blocked ear canals, infections like glue ear, or damage to the eardrum or bones.
- **Sensorineural** loss: damage to the hair cells or the nerve, from loud noise, ageing or genetics. It is usually permanent.

Hearing loss from noise is common in Australia. Being near sounds above about 85 decibels for long periods (loud concerts, power tools, headphones turned up) damages hair cells.

| Technology | How it works | Best for | Limitations |
|---|---|---|---|
| **Hearing aid** | A microphone picks up sound, an amplifier makes it louder and a speaker sends it into the ear | Mild to moderate loss, when hair cells still work | Cannot help if hair cells are badly damaged. Background noise is also louder |
| **Bone conduction implant** | Sends vibrations through the skull bone straight to the cochlea | Conductive loss | Needs a working cochlea |
| **Cochlear implant** | An outside microphone and processor send signals to electrodes inside the cochlea, which stimulate the auditory nerve directly | Severe sensorineural loss | Needs surgery. Sound is different from natural hearing and takes time to learn |

## Vision

**How we see.** Light passes through the **cornea** and **lens**, which bend (refract) it to focus an image on the **retina** at the back of the eye. The retina has light-sensitive **rods** (dim light) and **cones** (colour). Signals travel along the **optic nerve** to the brain.

| Disorder | What happens | Technology |
|---|---|---|
| **Myopia** (short-sightedness) | Eyeball too long, so distant objects focus **in front of** the retina | **Concave** (diverging) lenses, or laser surgery to flatten the cornea |
| **Hyperopia** (long-sightedness) | Eyeball too short, so near objects focus **behind** the retina | **Convex** (converging) lenses |
| **Cataracts** | Lens becomes cloudy, often with age or UV exposure | Surgery replaces the lens with a plastic one. The Fred Hollows Foundation has done this for millions of people in low income countries |
| **Glaucoma** | Raised pressure in the eye damages the optic nerve | Eye drops, laser, surgery |

Myopia is rising fast among young people around the world. Spending more time **outdoors** in daylight in childhood lowers the risk.

## The kidneys

The kidneys filter about 180 litres of blood plasma a day through about a million tiny filters called **nephrons**. They remove **urea** and extra salts and water, and return useful substances like glucose to the blood.

**Kidney failure** can be caused by diabetes, high blood pressure, infection or genetic disease. Wastes then build up in the blood, which can be fatal.

| Technology | How it works | Limitations |
|---|---|---|
| **Haemodialysis** | Blood flows from an arm into a machine. On one side of a partially permeable membrane is the blood, and on the other is **dialysis fluid**. Urea and extra salts diffuse out of the blood into the fluid. The cleaned blood returns to the body | About 4 hours, 3 times a week. Tiring, and diet is restricted |
| **Peritoneal dialysis** | Dialysis fluid is put into the abdomen. The lining of the abdomen acts as the membrane | Can be done at home, but has an infection risk |
| **Kidney transplant** | A healthy kidney from a donor replaces the failed one | Donors are scarce. Patients need **immunosuppressant** drugs for life so their immune system does not reject it |

### Exam tip: Why the dialysis fluid has glucose in it
The dialysis fluid has the **same** glucose and useful salt concentrations as normal blood, but **no urea**. So urea diffuses out, but glucose does not, because there is no concentration gradient for it.

**Mind map**

```text
Technologies and disorders
  Hearing
    Conductive loss
    Sensorineural loss
    Hearing aid: louder
    Cochlear implant: stimulates nerve
  Vision
    Myopia: concave lens
    Hyperopia: convex lens
    Cataract: replace lens
    Glaucoma: pressure
  Kidneys
    Nephrons filter
    Dialysis: diffusion across membrane
    Transplant: needs immunosuppressants
```

### Year 11: Evaluating a technology
HSC questions often ask you to evaluate how well a technology helps a disorder. Use this structure:

1. Explain the **normal** function of the organ.
2. Explain what goes **wrong** in the disorder.
3. Explain **how** the technology works and which part of the problem it fixes.
4. Give its **effectiveness** and **limitations** (cost, access, surgery risk, how close to normal function it gets).

**Example.** Cochlear implants are very effective for severe sensorineural loss in young children, who can often learn spoken language if they receive the implant early. But they do not restore natural hearing, and there are debates within the Deaf community about cultural identity and the use of sign language.

**More eye problems.**
- **Presbyopia**: after about 45, the lens gets stiffer and cannot change shape enough to focus on close objects, so people need reading glasses (convex lenses).
- **Astigmatism**: the cornea is curved unevenly, so some parts of the image are blurred. Special (cylindrical) lenses or laser surgery correct it.
- **LASIK** uses a laser to reshape the cornea so light focuses on the retina.
- **Glaucoma** drops lower the fluid pressure, which slows further damage to the optic nerve (damage already done cannot be reversed).

**Matching the person to the technology.** A young sportsperson with myopia may suit contact lenses or LASIK instead of glasses. An older person with long sight and cataracts may need cataract surgery and then convex reading glasses.

**Loud music and high notes.** Hair cells near the start of the cochlea detect high pitches, and they are damaged first by loud noise.

**Bionic eyes and cochlear implants** both skip the damaged sense cells and use electrodes to send signals straight to the nerve.

### Year 12: Disorders across Australia
Health technologies are not shared equally. Aboriginal and Torres Strait Islander children have some of the highest rates of **otitis media** (middle ear infection) in the world, which causes conductive hearing loss and affects learning at school. Programs that run hearing checks in schools and communities, and treat infections early, have shown real gains.

Rates of kidney failure are also much higher in many remote communities, often linked to diabetes. **Purple House**, an Aboriginal-run organisation, set up dialysis in remote communities so patients can be treated on Country instead of moving hundreds of kilometres away from family. Good evaluations include **access** and **equity**, not just how a device works.

**Why the flows run opposite ways.** In dialysis, blood and fluid flow in **opposite directions** (countercurrent). The blood always meets fresher fluid with even less urea, so a concentration gradient is kept along the whole membrane and more urea diffuses out.

**Transplant or dialysis?** A transplant gives near-normal kidney function and freedom from the machine, but needs a donor, surgery and lifelong immunosuppressants (raising infection risk). Dialysis is available sooner but takes many hours a week.

## Quick summary

- Conductive hearing loss blocks sound reaching the inner ear. Sensorineural loss damages hair cells or the nerve.
- Hearing aids make sound louder. Cochlear implants stimulate the auditory nerve directly.
- Myopia is corrected with concave lenses, hyperopia with convex lenses. Cataracts are fixed by replacing the lens.
- The kidneys filter blood in nephrons. Dialysis removes urea by diffusion across a membrane. Transplants need immunosuppressant drugs.
- Evaluate a technology by its effectiveness, limitations, cost and access.

## Quiz

Try these questions from the chapter quiz.

1. Which part of the ear contains the hair cells that detect sound?
   - A. Eardrum
   - B. Middle ear bones
   - C. Cochlea
   - D. Outer ear
   - Answer: C. Cochlea. Hair cells are in the cochlea.

2. Who led the team that developed the cochlear implant in Australia?
   - A. Graeme Clark
   - B. Fred Hollows
   - C. Howard Florey
   - D. Ian Frazer
   - Answer: A. Graeme Clark. Professor Graeme Clark in Melbourne.

3. Hearing loss caused by damaged hair cells is
   - A. conductive
   - B. sensorineural
   - C. infectious
   - D. temporary
   - Answer: B. sensorineural. Damage to hair cells or the nerve is sensorineural.

The whole chapter quiz is on the page, for signed-in students: https://whizznotes.com/biology/technologies-and-disorders/#quiz