Senses

Human Senses

100

A person eats spicy food while having a blocked nose due to a cold. They complain that "everything tastes bland."

What sensory system is mainly responsible for this problem? Explain your reasoning.

Answer

The olfactory (smell) system is mainly responsible.

Reasoning:
Taste buds can still detect sweet, salty, sour, bitter and umami, but smell provides most of the flavour. A blocked nose prevents odour molecules from reaching olfactory receptors, making food seem bland.

200

Two students are studying.

• Student A notices smoke before hearing the fire alarm.
• Student B hears the alarm before noticing the smoke.

Did both students rely on exteroception? Which senses were involved?

Yes.

Both relied on exteroception because they responded to external stimuli.

• Student A → Smell (olfactory receptors)
• Student B → Hearing (auditory receptors)

300

If humans could enhance only one sense to twice its normal ability, which sense would produce the greatest overall improvement in quality of life?

Support your answer with at least three scientific reasons.

There is no single correct answer.

400

Two pedestrians are crossing a road.

• Person A is blind but has excellent hearing.
• Person B is deaf but has excellent vision.

Suddenly, an electric car approaches quietly from behind.

Who is more likely to detect the danger first? Justify your answer using sensory functions.

Person B (likely).

Because the car is almost silent, vision is more reliable for detecting movement than hearing in this situation. 

500

Imagine humans permanently lose only one sense.

Which loss would have the greatest impact on survival in modern society? Justify your answer.

There is no single correct answer.

Plant Responses

100

A plant kept beside a window grows sideways instead of straight upward.

State the type of tropism. Why is this actually beneficial?

The plant is showing positive phototropism.

Growing sideways helps it receive more sunlight for photosynthesis, increasing food production.

200

A seed is planted upside down. A week later, the roots grow downward while the shoot grows upward.

Which stimuli are each responding to?

Roots:

• Positive gravitropism
• Positive hydrotropism (if water is available)

Shoots:

• Positive phototropism
• Negative gravitropism

300

A vine wraps around a wooden pole instead of immediately growing toward nearby light.

Which tropism dominates and why?

Thigmotropism

Touching a support allows the plant to climb higher, where it can later access more sunlight.

400

A scientist waters only one side of a plant pot for several weeks.

Predict how the roots will grow.

Roots will be likely to grow toward the watered side due to positive hydrotropism, improving water absorption.

500

A scientist creates a mutant plant that:

• cannot detect light,
• cannot detect gravity,
• can still detect water and touch.

After three weeks, the plant is still alive.

Explain how this is possible. Which tropisms are allowing the plant to survive, and what limitations would it likely face in the long term?

The plant survives because hydrotropism directs roots toward water and thigmotropism helps it attach to supports if it is a climbing plant. However, without phototropism, shoots may not efficiently reach light for photosynthesis, and without gravitropism, roots and shoots may grow in disorganized directions. Over time, the plant would likely show poor growth, reduced photosynthesis, and lower chances of reproduction.

Receptors

100

Touching an ice cube and touching a needle both cause someone to pull their hand away.

Did the same receptor detect both stimuli?

No.

Ice → Thermoreceptors

Needle → Nociceptors

Different receptors detect different stimuli.

200

A person touches a very hot metal spoon while wearing thick insulated gloves.

Which receptors are least stimulated?

Thermoreceptors. The gloves reduce heat reaching the skin.

300

A gymnast closes her eyes but can still accurately touch her nose.

Which receptors make this possible?

Proprioceptors

They detect body position and movement.

400

A robot has cameras, microphones, and temperature sensors.

Which human receptors have engineers copied, and which important receptor type is still missing if it cannot feel pain?

Copied:

• Photoreceptors
• Mechanoreceptors
• Thermoreceptors

Missing:

• Nociceptors

500

Astronauts discover an invisible, odorless, tasteless poisonous gas.

Which human receptor type would be least useful for detecting it first? How would astronauts detect such gas?

Chemoreceptors

Humans cannot naturally detect many dangerous gases.

Scientists would need gas detectors.

Sensory Impairments

100

A patient correctly identifies sweet, salty, sour and bitter foods but says food has lost its flavour.

Which impairment is most likely?

Anosmia

Loss of smell greatly reduces flavour perception.

200

A student reads books perfectly but cannot recognize classmates standing across the playground.

Which condition explains this?

Myopia

Near vision is normal.

Distance vision is blurred.

300

Someone constantly feels insects crawling on their skin even though nothing is there.

Which sensory condition best explains this?

Tactile hallucinations

400

A musician develops a tumour affecting the vestibular nerve.

Besides hearing, which daily ability will likely become difficult?

Balance

The vestibular system contributes to balance.

500

A patient:

• cannot smell smoke,
• cannot detect gas leaks,
• but can still identify sweet and salty foods.

Which impairment explains all three symptoms?

Anosmia

Taste receptors function normally, but smell is lost.

Case Studies

100

A 42-year-old chef visits the hospital after recovering from a viral infection.

He reports:

• Food feels "boring."
• He can correctly identify sugar, salt and lemon juice.
• He accidentally burnt a pan because he did not notice the smoke until he saw it.
• His eyesight and hearing are completely normal.

Questions

1. Which sense is most likely impaired?
2. What evidence supports your diagnosis?
3. Which receptor type is most affected?
4. Would this problem affect exteroception or interoception?

Diagnosis:
Anosmia (loss of smell)

Evidence:

• Can still taste basic tastes.
• Cannot smell smoke.
• Food has lost flavour.

Receptors:
Chemoreceptors (olfactory receptors).

Type:
Exteroception

200

A patient enters the emergency room after being found wandering in a park.

Doctors observe:

• He cannot recognise the smell of smoke.
• He cannot feel that he has a fever.
• He can still see, hear and speak normally.
• He says,

"I don't feel thirsty, even though everyone tells me I'm dehydrated."

Questions

1. Which two sensory systems appear affected?
2. Which symptoms involve exteroception?
3. Which symptoms involve interoception?
4. Why could this become life-threatening?

Affected systems:

• Smell
• Interoception

Exteroception:
Cannot smell smoke.

Interoception:
Cannot detect thirst or fever.

Danger:
The patient cannot detect internal body needs or external dangers.

300

A botanist grows two identical bean plants.

Plant A grows near a window.

Plant B grows inside a rotating chamber where gravity is constantly changing.

After two weeks:

• Plant A bends sideways.
• Plant B has roots growing in random directions.

Questions

1. Which tropism explains Plant A?
2. Which tropism has been disrupted in Plant B?
3. Why would Plant B struggle to survive outdoors?

Plant A:
Phototropism

Plant B:
Gravitropism

Reason:
Roots cannot consistently grow downward, reducing water absorption.

400

A cook accidentally touches a hot frying pan.

She does not pull her hand away.

Five seconds later she notices severe burns.

Doctors discover the muscles and bones are perfectly healthy.

A cook accidentally touches a hot frying pan.

She does not pull her hand away.

Five seconds later she notices severe burns.

Doctors discover the muscles and bones are perfectly healthy.

Questions

1. Which receptors failed first?
2. Which nervous pathway was interrupted?
3. Why did the delayed response increase tissue damage? 
4. Which receptors failed first?
5. Which nervous pathway was interrupted?
6. Why did the delayed response increase tissue damage? 

Receptors:
Nociceptors and thermoreceptors

Pathway:
Stimulus → receptor → sensory neuron → brain/spinal cord → motor response

Reason:
Without immediate detection, the protective withdrawal response did not occur.

500

A patient arrives after an experimental drug trial.

Doctors discover:

• Eyes respond normally to light.
• Ears detect sound normally.
• Skin receptors respond to touch.
• However, the patient reports:
  • "I can't recognise anything I'm seeing."
  • "Voices sound like meaningless noise."
  • "I don't know whether this object is hot or cold."

MRI scans show that all sensory organs are healthy.

Questions

1. Where is the problem most likely located?
2. Why can receptors still function while perception fails?
3. Explain the difference between detecting a stimulus and interpreting a stimulus.

Location:
The brain (sensory processing/interpretation areas).

Reason:
Receptors only detect stimuli and convert them into electrical impulses. The brain gives those impulses meaning.

Difference:

• Detection = receptors receive the stimulus and generate nerve impulses.
• Interpretation = the brain processes those impulses into meaningful perceptions (e.g., recognising a face, understanding speech, identifying temperature).