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
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 Receptor | Stimulus Detected | Location | Example |
---|---|---|---|
Photoreceptors | Light | Retina (eye) | Detects light and color |
Chemoreceptors | Chemicals | Nose, tongue, blood vessels | Smells, tastes, CO₂ levels |
Mechanoreceptors | Touch, pressure, sound | Skin, ears, muscles | Vibrations, sound, textures |
Thermoreceptors | Temperature | Skin, brain | Hot and cold sensing |
Pain receptors | Tissue damage | Throughout body | Detect injury or harm |
Baroreceptors | Blood pressure | Arteries, heart walls | Maintain 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.
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.
If the target cell lacks the receptor, the hormone has no effect.
Hormones and Their Target Receptors
Hormone | Target Receptor Location | Effect |
---|---|---|
Insulin | Liver, muscle cells | Lowers blood sugar |
Adrenaline | Heart, muscles, liver | Prepares body for action |
Estrogen | Uterus, ovaries, breast cells | Controls female development |
Testosterone | Testes, muscles | Controls 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
Gland | Hormone(s) | Main Role |
---|---|---|
Pituitary gland | Growth hormone, ADH | Controls other glands, growth, water balance |
Thyroid gland | Thyroxine | Regulates metabolism |
Adrenal glands | Adrenaline | Prepares body for action (“fight or flight”) |
Pancreas | Insulin, glucagon | Controls blood sugar levels |
Ovaries (females) | Estrogen, progesterone | Female traits, menstrual cycle, pregnancy |
Testes (males) | Testosterone | Male traits, sperm production |
How It Works – Hormone Pathway
- A stimulus triggers a gland
- The gland releases hormone into the bloodstream
- The hormone travels to a target organ
- Receptors detect the hormone
- The target cell responds (e.g., grow, store glucose, make protein)
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
Feature | Nervous System | Endocrine System |
---|---|---|
Type of signal | Electrical (nerve impulse) | Chemical (hormone) |
Speed | Very fast | Slower |
Duration | Short-lived | Long-lasting |
Pathway | Neurons | Bloodstream |
Main use | Quick 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 by | Pancreas |
Target organ | Liver, muscle, and fat cells |
Main role | Lowers blood sugar by storing glucose |
Released when | After 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.
2. Adrenaline (Animal Hormone)
The “emergency hormone”
Made by | Adrenal glands (on kidneys) |
Target organs | Heart, lungs, liver, muscles |
Main role | Prepares body for “fight or flight” |
Released when | Stressed, 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 by | Tips of shoots and roots |
Target area | Cells just behind the tip |
Main role | Controls plant growth direction |
Responds to | Light, gravity, water |
Quick Recap Table
Hormone | Made by | Main Function | Type |
---|---|---|---|
Insulin | Pancreas | Lowers blood sugar | Animal |
Adrenaline | Adrenal glands | Prepares for action | Animal |
Auxins | Shoot/root tips | Directs plant growth | Plant |
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
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
Comparison Table: Nervous vs Hormonal Control
Feature | Nervous System | Hormonal System (Endocrine) |
---|---|---|
Signal type | Electrical (nerve impulses) | Chemical (hormones) |
Speed of response | Very fast (milliseconds) | Slow (seconds to hours) |
Duration of response | Short | Long-lasting |
Pathway | Neurons | Bloodstream |
Target area | Specific (muscles/glands) | Widespread (many organs) |
Control type | Voluntary + Involuntary | Involuntary only |
Example | Reflex action | Blood sugar control by insulin |
Why Both Are Important
Situation | System Involved |
---|---|
Escape from danger | Nervous (reflexes) + Hormonal (adrenaline) |
Balancing blood sugar | Hormonal (insulin & glucagon) |
Reacting to noise or pain | Nervous system |
Controlling puberty and growth | Hormonal system |
Nervous system reacts first, then adrenaline amplifies the response.
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.