IB MYP 4-5 Biology-Pathogens/parasites, predator/prey- Study Notes - New Syllabus
IB MYP 4-5 Biology-Pathogens/parasites, predator/prey- Study Notes – New syllabus
IB MYP 4-5 Biology-Pathogens/parasites, predator/prey- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Parasitism: Host-parasite relationships (tapeworms, fleas)
- Predation: Adaptations of predators and prey
- Disease transmission and vectors
- Population dynamics in predator-prey cycles
Interactions Between Organisms
What Are Biological Interactions?
In every ecosystem, organisms don’t live alone. They interact with one another – some interactions are helpful, others harmful.
These interactions influence species’ survival, reproduction, and population size. Here are three major types:
- Pathogens and parasites
- Parasitism (host-parasite)
- Predator-prey relationships
1. Pathogens and Parasites
Pathogen: A microorganism (like bacteria or viruses) that causes disease in another organism.
Parasite: An organism that lives on or inside another organism (host) and feeds off it, often causing harm.
2. Parasitism: Host-Parasite Relationships
Parasitism is a one-sided relationship where:
- Parasite benefits
- Host is harmed
Examples of Host-Parasite Relationships
| Parasite | Host | Effect on Host |
|---|---|---|
| Tapeworm | Humans/Animals | Steals nutrients from intestines |
| Fleas | Dogs, cats, humans | Bite and suck blood, cause itching |
| Plasmodium | Humans (blood) | Causes malaria |
| Lice | Humans | Live in hair, cause irritation |
| Dodder plant | Other plants | Steals water and nutrients |
3. Predator-Prey Relationships
Predation is when one organism (the predator) hunts and eats another (the prey).
Prey increase → predator increase
Prey decrease → predator decrease
Examples of Predator-Prey
| Predator | Prey |
|---|---|
| Lion | Zebra |
| Owl | Mouse |
| Shark | Fish |
| Eagle | Rabbit |
Parasite vs Predator – Key Differences
| Feature | Parasite | Predator |
|---|---|---|
| Kills host? | No – keeps it alive | Yes – kills prey to eat |
| Lives on/in host? | Yes | No |
| Feeding style | Slow, long-term | Quick, one-time |
| Example | Tapeworm in humans | Tiger eating a deer |
Ecosystems are full of interactions:
Pathogens cause disease
Parasites feed off hosts
Predators hunt prey
These relationships shape survival, evolution, and balance in the natural world.
Predation: Adaptations of Predators and Prey
What Is Predation?
Predation is a biological interaction where a predator hunts, kills, and eats another organism known as the prey.
It’s a survival-based relationship – predators need food, prey want to stay alive. Both evolve adaptations to improve their chances.
Adaptations in Predators
Predators are adapted for detecting, catching, and killing their prey with speed, power, and precision.
| Adaptation | How It Helps | Example |
|---|---|---|
| Sharp teeth/claws | Kill or tear flesh | Tigers, wolves |
| Forward-facing eyes | Good depth perception for aiming | Lions, eagles |
| Camouflage | Helps sneak up unnoticed | Leopards, crocodiles |
| Speed & agility | Chase and catch prey | Cheetahs |
| Venom or traps | Paralyze or kill quickly | Spiders, snakes |
| Night vision | Hunt in darkness | Owls, cats |
Adaptations in Prey
Prey evolve features that help them avoid detection, escape predators, or survive attacks.
| Adaptation | How It Helps | Example |
|---|---|---|
| Camouflage | Blends into surroundings | Leaf insects, deer |
| Warning colors | Warns of poison/bad taste | Frogs, butterflies |
| Mimicry | Looks like dangerous species | Snake mimicking cobra |
| Fast reflexes/speed | Escape quickly | Rabbits, gazelles |
| Eyes on side | Wide vision to detect threats | Birds, zebras |
| Herding/grouping | Safety in numbers | Fish schools, buffalo herds |
| Defensive structures | Protection against attack | Porcupine quills, turtle shells |
Arms Race in Nature
Predators and prey are locked in a continuous evolutionary battle – an arms race.
- If prey gets faster → predator must get faster
- If prey camouflages better → predator must improve detection
Example Pair: Predator vs Prey Adaptations
| Predator | Key Adaptation | Prey | Defense Adaptation |
|---|---|---|---|
| Owl | Silent flight, night vision | Mouse | Nocturnal, fast reflexes |
| Crocodile | Camouflage in water | Wildebeest | Group behavior |
| Eagle | Sharp vision and talons | Snake | Camouflage, fast strike |
Predation drives evolution – predators adapt to hunt, prey adapt to survive.
This back-and-forth shapes behaviors, physical traits, and entire ecosystems.
Disease Transmission and Vectors
What Is Disease Transmission?
Disease transmission is the way a disease-causing microbe (pathogen) spreads from one host to another. These pathogens include bacteria, viruses, fungi, and parasites.
Two Main Types of Transmission
1. Direct Transmission
No middle step – just person to person.
| Method | Example Diseases |
|---|---|
| Touch/skin contact | Athlete’s foot, warts |
| Body fluids | HIV, Hepatitis B |
| Droplets (coughs) | Flu, COVID-19, tuberculosis |
| Sexual contact | Gonorrhoea, chlamydia |
2. Indirect Transmission
The pathogen spreads via something else before reaching a host.
Indirect Way | Example Source | Disease Example |
|---|---|---|
| Contaminated water | Drinking dirty water | Cholera, typhoid |
| Contaminated food | Undercooked meat | Salmonella, food poisoning |
| Airborne particles | Dust in air | Measles, tuberculosis |
| Surfaces (fomites) | Phones, doorknobs | Norovirus, cold |
| Vectors (insects) | Mosquitoes, fleas, ticks | Malaria, dengue, plague |
What Are Vectors?
A vector is a living organism (usually an insect or animal) that carries and transmits a pathogen to another host – without getting the disease itself.
Examples of Disease Vectors
| Vector | Pathogen Carried | Disease Caused |
|---|---|---|
| Mosquito | Plasmodium (protist) | Malaria |
| Mosquito | Dengue virus | Dengue fever |
| Flea | Yersinia pestis (bacteria) | Bubonic plague |
| Tick | Borrelia bacteria | Lyme disease |
| Housefly | Multiple bacteria | Diarrheal diseases |
| Tsetse fly | Trypanosome parasite | Sleeping sickness |
– They are fast-moving and mobile
– One vector can infect many people
– They’re hard to control, especially in tropical climates
How to Prevent Transmission
| Method | What It Does |
|---|---|
| Handwashing | Removes contact-transmitted pathogens |
| Clean drinking water | Prevents waterborne illnesses |
| Vaccinations | Prepares immune system for defense |
| Insect repellents/nets | Protects from vector bites |
| Quarantine | Stops spread from infected individuals |
| Cooking food properly | Kills harmful microbes in food |
Case Study: Malaria
Vector: Female Anopheles mosquito
Transmission: Infected mosquito bites a healthy person, injecting the parasite into the blood
Prevention: Mosquito nets, sprays, draining stagnant water
Diseases can spread directly (like flu or HIV) or indirectly (via water, food, air, or vectors).
Vectors like mosquitoes and fleas are especially dangerous because they spread disease quickly and silently.
Prevention methods – like vaccines, nets, and clean water – are essential for public health.
Population Dynamics in Predator-Prey Cycles
What Is Population Dynamics?
Population dynamics is the study of how and why the number of individuals in a species changes over time in an ecosystem.
In predator-prey cycles, the sizes of predator and prey populations are closely linked – when one changes, the other responds.
Predator-Prey Relationship: How It Works
In ecosystems, predators rely on prey for food. If prey increases, predators eat more and survive/reproduce better. But if there are too many predators, prey gets overhunted, and both populations decline.
Typical Predator-Prey Cycle Pattern
- Prey population increases → More food for predators
- Predator population increases → More hunting, prey decreases
- Prey population drops → Less food, predator numbers drop
- Predator population drops → Prey can recover
The cycle continues in a wave-like rhythm over time.
Key Features of the Cycle
| Observation | Explanation |
|---|---|
| Prey numbers always rise first | More food = more predators later |
| Predator peak lags behind prey | It takes time for predator numbers to increase |
| When prey drops, predator also drops | Less food leads to predator death |
| Low predators allow prey to recover | Prey increase again → cycle restarts |
Real-World Example: Lynx and Snowshoe Hare
In Canada, snowshoe hares (prey) and lynxes (predators) show classic population cycles.
- Every ~10 years, their numbers rise and fall together
- Lynx population peaks shortly after hare population
Factors Affecting These Cycles
| Factor | Effect on Population Dynamics |
|---|---|
| Food availability | Less food = slower prey recovery |
| Disease | Can reduce predator or prey population |
| Human interference | Hunting, pollution, or habitat destruction can break natural cycles |
| Migration | Populations can shift locations, altering the cycle |
| Climate/Seasons | Affects birth rate, survival, and food supply |
Why This Matters in Biology
- Helps understand how ecosystems stay balanced
- Important for wildlife conservation and management
- Reveals how one species influences another
Predator and prey populations rise and fall in a repeating cycle.
Prey increase first, then predators. As prey decrease, predators also decline – allowing prey to recover.
This natural balance