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IB MYP 4-5 Biology-Receptors and Hormones- Study Notes

IB MYP 4-5 Biology-Receptors and Hormones- Study Notes - New Syllabus

IB MYP 4-5 Biology-Receptors and Hormones- Study Notes – New syllabus

IB MYP 4-5 Biology-Receptors and Hormones- Study Notes – IB MYP 4-5 Biology –  per latest IB MYP Biology Syllabus.

Key Concepts: 

  • Types of receptors (chemoreceptors, photoreceptors, etc.)
  • Endocrine system overview
  • Key hormones (insulin, adrenaline, auxins)
  • Comparison of nervous vs hormonal control

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

Receptors and Hormones

What Are Receptors?

Receptors are specialized cells or proteins that detect specific stimuli (like light, sound, pressure, or chemicals). They act like sensors that alert your body when something changes in the environment or inside the body.

Where Are Receptors Found?

  • In sense organs (eyes, ears, skin, nose, tongue)
  • Inside cells, especially hormone target cells

Each receptor is specific it responds to only one type of stimulus.

Types of Receptors and What They Detect

Type of ReceptorStimulus DetectedLocationExample
PhotoreceptorsLightRetina (eye)Detects light and color
ChemoreceptorsChemicalsNose, tongue, blood vesselsSmells, tastes, CO₂ levels
MechanoreceptorsTouch, pressure, soundSkin, ears, musclesVibrations, sound, textures
ThermoreceptorsTemperatureSkin, brainHot and cold sensing
Pain receptorsTissue damageThroughout bodyDetect injury or harm
BaroreceptorsBlood pressureArteries, heart wallsMaintain pressure balance

Photoreceptors                                                                                                      Thermoreceptors

                                        

Mechanoreceptors                                                                          Chemoreceptors     

                  

Receptors and the Nervous System

Receptors send electrical messages through sensory neurons to the CNS (brain or spinal cord), where the information is processed and a response is triggered.

Example: Touch something hot → Thermoreceptor activates → Signal to spinal cord → Reflex pulls hand away

Receptors and Hormones

What Are Hormones?

Hormones are chemical messengers made by endocrine glands. They travel through the bloodstream and act only on target cells with the right receptors.

Hormone + Receptor = Lock and Key Match
If the target cell lacks the receptor, the hormone has no effect.

Hormones and Their Target Receptors

HormoneTarget Receptor LocationEffect
InsulinLiver, muscle cellsLowers blood sugar
AdrenalineHeart, muscles, liverPrepares body for action
EstrogenUterus, ovaries, breast cellsControls female development
TestosteroneTestes, musclesControls male development

Why Are Receptors Important?

  • Detect environmental and internal changes
  • Trigger responses for homeostasis and safety
  • Allow hormones to act only where needed
  • Control mood, growth, movement, and reflexes

Endocrine System

What Is the Endocrine System?

The endocrine system is a network of glands that produce and release hormones chemical messengers that travel through the bloodstream to regulate body processes.

Unlike the fast electrical signals of the nervous system, the endocrine system works more slowly but produces long-lasting effects.

Main Functions of the Endocrine System

  • Controls growth and development
  • Regulates metabolism (energy use)
  • Manages mood, sleep, and stress
  • Controls reproduction and sexual traits
  • Maintains internal balance (homeostasis)

What Are Hormones?

  • Chemical messengers made by endocrine glands
  • Travel through the bloodstream
  • Act only on cells with the correct receptors

A small amount of hormone can cause big changes!

Main Endocrine Glands and Their Hormones

GlandHormone(s)Main Role
Pituitary glandGrowth hormone, ADHControls other glands, growth, water balance
Thyroid glandThyroxineRegulates metabolism
Adrenal glandsAdrenalinePrepares body for action (“fight or flight”)
PancreasInsulin, glucagonControls blood sugar levels
Ovaries (females)Estrogen, progesteroneFemale traits, menstrual cycle, pregnancy
Testes (males)TestosteroneMale traits, sperm production

How It Works – Hormone Pathway

  1. A stimulus triggers a gland
  2. The gland releases hormone into the bloodstream
  3. The hormone travels to a target organ
  4. Receptors detect the hormone
  5. The target cell responds (e.g., grow, store glucose, make protein)
Example – Blood Sugar Control:
After a meal → Pancreas releases insulin → Cells absorb glucose → Sugar level decreases
When hungry → Pancreas releases glucagon → Liver releases glucose → Sugar level increases

Nervous System vs Endocrine System

FeatureNervous SystemEndocrine System
Type of signalElectrical (nerve impulse)Chemical (hormone)
SpeedVery fastSlower
DurationShort-livedLong-lasting
PathwayNeuronsBloodstream
Main useQuick responses (e.g., reflexes)Long-term control (e.g., growth)
 

Key Hormones: Insulin, Adrenaline, Auxins

What Are Hormones Again?

  • Hormones are chemical messengers made by glands (animals) or tissues (plants)
  • They travel through blood (animals) or cell tissues (plants)
  • Only target cells with matching receptors are affected
  • They act slowly but have long-lasting effects

1. Insulin (Animal Hormone)

Made byPancreas
Target organLiver, muscle, and fat cells
Main roleLowers blood sugar by storing glucose
Released whenAfter meals, when blood sugar rises

How It Works: After a meal, glucose increases → pancreas releases insulin → insulin tells cells to store glucose → blood sugar drops to normal.

Lack of insulin causes diabetes.

2. Adrenaline (Animal Hormone)

The “emergency hormone”

Made byAdrenal glands (on kidneys)
Target organsHeart, lungs, liver, muscles
Main rolePrepares body for “fight or flight”
Released whenStressed, scared, or excited

Effects of Adrenaline:

  • Increases heart and breathing rate
  • Converts glycogen to glucose for energy
  • Dilates pupils
  • Prepares muscles for action

3. Auxins (Plant Hormone)

Made byTips of shoots and roots
Target areaCells just behind the tip
Main roleControls plant growth direction
Responds toLight, gravity, water
Phototropism: Auxins move to the shady side → those cells grow faster → plant bends toward light → better photosynthesis

Quick Recap Table

HormoneMade byMain FunctionType
InsulinPancreasLowers blood sugarAnimal
AdrenalineAdrenal glandsPrepares for actionAnimal
AuxinsShoot/root tipsDirects plant growthPlant
Summary:
Hormones are powerful messengers:
Insulin manages sugar,
Adrenaline helps in emergencies,
Auxins guide plant growth.
Together, they support balance, survival, and development in both animals and plants.

Nervous vs Hormonal Control

Why Do We Need Two Control Systems?

The body constantly responds to both internal and external changes. To do this effectively, it uses:

  • Nervous System – fast, electrical control
  • Endocrine System – slower, chemical control

Each system has its own way of sending messages and controlling body functions.

Nervous System: Quick Response Team

  • Sends electrical impulses through neurons
  • Works very quickly (milliseconds)
  • Controls muscles and reflexes
  • Short-lived responses
  • Involves the brain, spinal cord, and nerves
Example: Moving your hand away from a hot surface

Hormonal (Endocrine) System: Chemical Manager

  • Uses hormones that travel in the bloodstream
  • Slower response (seconds to hours)
  • Effects last longer
  • Controls growth, metabolism, and reproduction
  • Involves glands like pancreas, thyroid, adrenal
Example: Insulin controlling blood sugar after meals

Comparison Table: Nervous vs Hormonal Control

FeatureNervous SystemHormonal System (Endocrine)
Signal typeElectrical (nerve impulses)Chemical (hormones)
Speed of responseVery fast (milliseconds)Slow (seconds to hours)
Duration of responseShortLong-lasting
PathwayNeuronsBloodstream
Target areaSpecific (muscles/glands)Widespread (many organs)
Control typeVoluntary + InvoluntaryInvoluntary only
ExampleReflex actionBlood sugar control by insulin

Why Both Are Important

SituationSystem Involved
Escape from dangerNervous (reflexes) + Hormonal (adrenaline)
Balancing blood sugarHormonal (insulin & glucagon)
Reacting to noise or painNervous system
Controlling puberty and growthHormonal system
In “fight or flight”, both systems work together:
Nervous system reacts first, then adrenaline amplifies the response.
Summary:
The nervous system is your fast responder – quick and short-lived.
The hormonal system is slower but longer lasting.
Together, they keep your body balanced and ready to adapt to any situation.
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