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IB MYP 4-5 Biology-Senses- Study Notes

IB MYP 4-5 Biology-Senses- Study Notes - New Syllabus

IB MYP 4-5 Biology-Senses- Study Notes – New syllabus

IB MYP 4-5 Biology-Senses- Study Notes – IB MYP 4-5 Biology –  per latest IB MYP Biology Syllabus.

Key Concepts: 

  • Human sensory organs (eyes, ears, skin, etc.)
  • Stimulus reception and response
  • Sensory adaptation

IB MYP 4-5 – Biology-Concise Summary Notes- All Topics

IB MYP 4-5 Biology Exam Questions MCQs and FRQs

Senses – Human Sensory Organs

What Are Senses?

Humans have five main senses that help detect changes in our surroundings. Each sense is linked to a special sensory organ that collects information and sends it to the brain for interpretation.

The 5 Main Sense Organs and Their Functions

1. Eyes – Sense of Sight (Vision)

  • Detect light, color, shape, and movement
  • The retina contains light-sensitive cells (rods and cones)
  • Signals are sent to the brain via the optic nerve
Helps us: see the world, recognize faces, avoid danger

2. Ears – Sense of Hearing and Balance

  • Detect sound vibrations through ear canal, eardrum, and inner ear
  • The cochlea helps us hear; the semicircular canals help with balance
Helps us: hear sounds, understand speech, stay balanced

3. Nose – Sense of Smell (Olfaction)

  • Smell receptors detect airborne chemicals
  • Signals sent via the olfactory nerve to the brain
Helps us: smell food, detect smoke, enjoy scents

4. Tongue – Sense of Taste

  • Taste buds detect 5 main tastes: sweet, salty, sour, bitter, and umami
  • Works closely with smell to enhance flavor
Helps us: enjoy food, detect spoiled or harmful substances

5. Skin – Sense of Touch

  • Largest sense organ with receptors for pressure, pain, temperature, and texture
  • Spread across the entire body
Helps us: feel touch, heat, cold, and danger signals (like pain)

Summary Table:

SenseOrganWhat It Detects
SightEyesLight, color, movement
HearingEarsSound and balance
SmellNoseAirborne chemicals (odors)
TasteTongueSweet, salty, sour, bitter, umami
TouchSkinPressure, pain, temperature

How Do Our Senses Work Together?

  • Sensory organs detect stimuli (light, sound, smell, etc.)
  • Nerves carry messages to the brain
  • The brain interprets the signals → we react, feel, and respond

Why Are Our Senses Important?

  • Keep us safe from danger (e.g., heat, smoke, sharp objects)
  • Allow enjoyment of life — music, food, textures, scenery
  • Help us communicate, explore, and learn about the world

Stimulus, Reception, and Response

What Is a Stimulus?

A stimulus is any change in the environment that can be detected by the body and causes a reaction.

  • External stimuli: light, sound, touch, pain, temperature
  • Internal stimuli: thirst, hunger, low sugar, body temperature
A stimulus is like a signal telling your body something has changed.

What Detects the Stimulus?

Receptors are special cells that detect stimuli. They are found in sense organs, and each type responds to a different kind of signal.

Sense OrganStimulus DetectedType of Receptor
EyesLightPhotoreceptors
EarsSound & balanceMechanoreceptors
SkinTouch, pain, pressureThermo/Mechanoreceptors
NoseChemicals (odors)Olfactory receptors
TongueTaste (chemicals)Taste receptors

The Stimulus-Response Pathway

The body responds to a stimulus in three main steps:

  1. Reception: Receptor detects the stimulus (e.g., eye detects light)
  2. Coordination: Signal sent to brain/spinal cord → processed and decision made
  3. Response: Effector (muscle/gland) acts (e.g., blink, sweat, move hand)
This is called the “Stimulus-Response Pathway”.

Example – Touching Something Hot

StepWhat Happens
StimulusHot object touches skin
ReceptorTemperature/pain receptor in skin detects heat
CoordinationSignal travels to spinal cord for quick decision
ResponseMuscle contracts — hand pulls away
This is a reflex action fast and automatic to protect you from danger.

Summary Table:

StepRoleExample
StimulusChange in environmentBright light
ReceptorDetects the changePhotoreceptor in eye
CoordinationSends and processes signalBrain or spinal cord
EffectorCarries out actionMuscles make you blink
ResponseFinal outcomeEye closes quickly

Why Is This Important?

  • Helps us react quickly to danger
  • Maintains internal balance (homeostasis)
  • Enables us to interact with the environment
  • Controls both voluntary and reflex actions
Stimulus → Receptor → Coordination → Effector → Response — this reflex pathway helps your body survive, respond, and stay in balance.

Sensory Adaptation

What is Sensory Adaptation?

Sensory adaptation is when your sense organs become less responsive to a constant or unchanging stimulus over time.

It’s your body’s way of saying: “This isn’t important anymore, so I’ll stop focusing on it.”

Examples:

SituationWhat Happens
Walk into a smelly roomSmell fades after a few minutes
Put on socksYou feel them at first, then forget
Background noise (fan, AC)You stop noticing the sound soon
Cold waterFeels warmer after a while

Why Does Sensory Adaptation Happen?

  • Your brain filters out unimportant information
  • It helps focus on new or changing stimuli
  • Prevents sensory overload
Only new, strong, or changing signals stay noticeable.

Which Senses Adapt?

SenseAdapts?Example
SmellYesStop noticing food or perfume smell
TouchYesClothes or watch feel invisible later
SightYesEyes adjust to dark or bright light
HearingYesIgnore ticking clock or traffic noise
TasteSlightlyStrong flavors feel weaker over time
PainNoPain stays to alert you — no adaptation

Is Sensory Adaptation Good or Bad?

  • Helpful: Avoids distraction, focuses brain on important changes
  • Risky: Might ignore ongoing dangers (like gas leak or loud machinery)

In Biology and Psychology

Sensory adaptation is a clear example of how the nervous system works:

  • Receptors reduce signals when a stimulus stays the same
  • The brain starts to ignore constant signals
It shows how stimulus → response can change with time!
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