IB DP Biology Adaptation to environment Study Notes
IB DP Biology Adaptation to environment Study Notes
IB DP Biology Adaptation to environment Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Biology syllabus with guiding questions of
- How are the adaptations and habitats of species related?
- What causes the similarities between ecosystems within a terrestrial biome?
Standard level and higher level: 3 hours
B4.1.1 – Habitat as the Place Where Organisms Live
🏞️ What is a Habitat?
A habitat is the natural place where a species, population, or community lives.
- Geographical location (e.g. desert, mountain, ocean)
- Physical features (e.g. temperature, water, soil type, altitude)
- Biological features (e.g. presence of predators, prey, vegetation)
🔍 Key Features of a Habitat
- Climate – Temperature, rainfall, wind patterns
- Soil and Water – Type of soil, availability of fresh/salt water
- Flora and Fauna – Plants and animals that share the habitat
- Light and Shelter – Sunlight exposure, hiding or nesting spots
🌱 Species Have Specific Habitat Needs
- Cactus: Lives in hot, dry deserts with sandy soil and very little water.
- Polar bear: Needs icy, cold Arctic regions with access to seals for food.
⚠️ Threats to Habitats
- Habitat loss – e.g. deforestation for agriculture
- Fragmentation – splitting a habitat into smaller parts by roads, buildings
- Pollution – makes the habitat unlivable
These lead to biodiversity loss and threaten species survival.
🌸 Example: Ranunculus glacialis (Glacier Buttercup)
| Feature | Description |
|---|---|
| Habitat | High-altitude alpine regions |
| Climate | Snow in winter, strong sunlight in summer |
| Soil | Acidic, well-drained |
| Adaptation | Survives extreme conditions with little competition |
A habitat is more than a physical space – it includes all environmental conditions necessary for a species to survive and reproduce. Protecting habitats is key to preserving biodiversity.
B4.1.2 – Adaptations of Organisms to the Abiotic Environment of Their Habitat
🧊 What Are Abiotic Factors?
Abiotic factors = Non-living parts of the environment
- Examples: Temperature, light, soil, water, salinity, pH, wind
These factors strongly influence:
- Where organisms can live
- How they survive and reproduce
🌾 Example 1: Grass Adapted to Sand Dunes
Sand dunes are dry, windy, nutrient-poor, and unstable habitats. Grasses like Ammophila arenaria (marram grass) show several key adaptations:
| Adaptation | Function |
|---|---|
| Rolled leaves | Reduce surface area → less water loss |
| Waxy cuticle | Prevents evaporation |
| Sunken stomata | Creates humid air pockets, reducing transpiration |
| Tough, flexible leaves | Resist sand abrasion and strong winds |
| Deep roots & rhizomes | Anchor the plant and absorb water from deep underground |
| Sclerenchyma cells | Provide structural support during drought |
| Carbohydrate accumulation | Increases osmotic potential for water uptake |
🌳 Example 2: Tree Adapted to Mangrove Swamps
Mangrove swamps are salty, waterlogged habitats. Trees like Rhizophora (Red Mangrove) are adapted to survive:
| Adaptation | Function |
|---|---|
| Salt glands in leaves | Excrete excess salt |
| Pneumatophores (aerial roots) | Allow gas exchange in low-oxygen soils |
| Thick waxy cuticle | Prevents water loss and salt entry |
| Vivipary (germination on parent) | Ensures seedling survival in salty water |
| Flexible stems and roots | Resist tidal forces and currents |
Organisms develop structural and physiological adaptations to survive the unique abiotic conditions of their habitats. Whether it’s conserving water in sand dunes or tolerating salt in mangroves, these traits ensure survival and reproduction in challenging environments.
B4.1.3 – Abiotic Variables Affecting Species Distribution
🧪 What Are Abiotic Variables?
Abiotic variables = Non-living environmental factors that affect where organisms can live.
- Temperature
- Water availability
- Sunlight
- Soil pH
- Salinity
- Altitude
- Wind
- Oxygen concentration (in water/air)
🌿 Effect on Plants
| Abiotic Variable | Effect on Plants |
|---|---|
| Light intensity | Affects photosynthesis → growth rate & flowering |
| Soil pH | Influences nutrient availability (e.g., blueberries need acidic soil) |
| Water availability | Determines whether a plant is xerophytic (dry habitat) or hydrophytic (wet habitat) |
| Temperature | Affects enzymatic activity and germination |
Example: Cacti grow in deserts due to their drought tolerance, while ferns thrive in damp forests.
🐾 Effect on Animals
| Abiotic Variable | Effect on Animals |
|---|---|
| Temperature | Affects metabolism (e.g., polar bears have thick fur and fat) |
| Water | Aquatic vs. terrestrial animals depend on water availability |
| Oxygen levels | Limits fish species in stagnant ponds |
| Light | Some animals are nocturnal or active only at certain light levels |
Example: Frogs are found in moist areas because their skin must stay wet for gas exchange.
🧬 Range of Tolerance
Each species survives best within a specific range of abiotic conditions.
Too much or too little of a factor can lead to:
- Stress
- Reduced reproduction
- Death
📈 Think of it as a bell curve – there’s a minimum, optimum, and maximum for each factor.
Species distribution is not random — it’s shaped by abiotic factors. Each organism survives only within a certain range of conditions. Adaptations allow them to cope, but outside their tolerance limits, they cannot survive or reproduce.
B4.1.4 – Range of Tolerance of a Limiting Factor
🧬 What Is the Range of Tolerance?
Every species has a range of tolerance for each abiotic factor.
It defines the range of conditions in which a species can:
- Survive
- Grow
- Reproduce
Shown as a bell-shaped curve:
- Minimum → survival is possible but stressful
- Optimum → ideal for growth and reproduction
- Maximum → survival possible, but no growth/reproduction
🚫 What’s a Limiting Factor?
A limiting factor is an abiotic variable that restricts the presence or performance of an organism when it’s outside its range of tolerance.
Examples:
- Temperature: limits crop growth in winter
- pH: affects soil microbial activity and plant health
- Light intensity: limits photosynthesis in dense forests
🌱 Field Skill: Using a Transect to Investigate Tolerance
Transect = A straight line or path across a habitat where you sample organisms and abiotic data at regular intervals.
What You Do:
- Lay out a transect line across a changing habitat (e.g., from a shaded forest into open grassland).
- At each point:
- Record species presence/abundance
- Measure abiotic factors (e.g., light, temp, pH using sensors or meters)
- Create a scatter graph or line chart to correlate species distribution with abiotic changes.
🌍 Where to Do This?
- In natural habitats (e.g., untouched woodland)
- Or semi-natural ones (e.g., old meadows, school fields with wild species)
🧪 Application of Skills
| Activity | Purpose |
|---|---|
| Use of sensors | Get accurate readings of abiotic variables |
| Sampling along transect | Track species changes across different conditions |
| Data analysis | Identify tolerance ranges for specific species |
Organisms only thrive within certain abiotic conditions. A limiting factor falling outside this range can reduce a species’ presence. Transect studies help us observe real-world patterns of tolerance and distribution.
B4.1.5 – Conditions Required for Coral Reef Formation
🏝️ What Are Coral Reefs?
Coral reefs are marine ecosystems built by colonies of tiny coral animals.
They rely on a symbiotic relationship with zooxanthellae – algae that live inside their tissues and perform photosynthesis.
🌊 Environmental Conditions Needed for Coral Reefs to Thrive
| Factor | Why It Matters |
|---|---|
| Water Depth | Reefs grow in shallow waters (0–50 m) so sunlight can reach the zooxanthellae for photosynthesis. |
| pH | Coral skeletons are made of calcium carbonate, which forms best in slightly alkaline conditions (pH 8.0–8.3). Ocean acidification lowers pH and threatens reef formation. |
| Salinity | Reefs need stable salt levels—between 32–42 ppt. Sudden changes (from freshwater runoff or evaporation) can stress or kill corals. |
| Water Clarity | Clear water allows sunlight to penetrate. Sediment, algae blooms, or pollution reduce clarity and limit photosynthesis. |
| Temperature | Coral reefs form in warm tropical waters, ideally between 23°C and 29°C. Temperatures above 30°C can cause coral bleaching. |
⚠️ Why Coral Reefs Are Vulnerable
Even small changes in one condition (like temperature or pH) can lead to coral stress, bleaching, or death.
Coral reefs are often referred to as “canaries in the coal mine” for climate change because they are so sensitive to environmental shifts.
🧠 Real-World Example: Great Barrier Reef (Australia)
- The largest coral reef system in the world.
- Currently threatened by rising sea temperatures, acidification, and pollution from agriculture and coastal development.
Coral reefs need warm, shallow, salty, clear, and slightly alkaline water to grow. They are one of the most biodiverse and sensitive ecosystems on Earth, making them highly vulnerable to climate change and pollution.
B4.1.6 – Abiotic Factors as the Determinants of Terrestrial Biome Distribution
🌱 What Is a Biome?
A biome is a large geographic region with a specific climate, and a distinct group of plants and animals adapted to it.
Terrestrial biomes include forests, deserts, tundras, grasslands, and more.
🌡️Key Abiotic Factors: Temperature & Precipitation
The two main factors that determine the type of terrestrial biome:
- Average annual temperature
- Average annual rainfall (precipitation)
📊 Biome Distribution Graph
Below is a general representation of how biomes distribute based on temperature and rainfall:
📌 One Climate = One Dominant Ecosystem
Each combination of temperature and precipitation tends to support one dominant biome type.
Example:
- A region with high rainfall and warm temperatures will almost always support a tropical rainforest.
- A cold, dry area will result in tundra, regardless of the continent.
🌍 Biome Examples by Climate
| Biome | Temperature | Rainfall | Example Location |
|---|---|---|---|
| Desert | Hot/Cold | Very Low | Sahara, Atacama |
| Tropical Rainforest | Hot | High | Amazon Basin |
| Grassland | Mild-Hot | Seasonal | North American Prairies |
| Boreal Forest | Cold | Moderate | Siberia, Canada |
| Tundra | Very Cold | Low | Arctic regions |
The type of terrestrial biome in any region is determined by the temperature and rainfall patterns. Each unique climate combination leads to the development of a specific ecosystem with organisms adapted to survive there.
B4.1.7 – Biomes as Groups of Ecosystems with Similar Communities Due to Similar Abiotic Conditions and Convergent Evolution
🌱 What Are Biomes?
Biomes are large-scale ecosystems defined by climate (temperature + precipitation) and dominant vegetation.
They consist of multiple ecosystems with similar abiotic conditions and communities of species that are adapted to those conditions.
🌍 Why Do Similar Biomes Have Similar Organisms?
Convergent Evolution
Distantly related species living in similar abiotic environments may evolve similar adaptations.
This is called convergent evolution – a process where unrelated organisms develop similar traits due to similar environmental pressures.
🪴 Example:
- Cactus (Americas) and Euphorbia (Africa) both:
- Have succulent stems to store water.
- Develop spines or thorns for protection and water conservation.
- Show reduced leaf surface area to minimize transpiration.
- Even though they are not closely related, they look and function similarly because they evolved under similar desert conditions.
Key Abiotic Conditions Across Major Biomes
| Biome | Climate | Typical Vegetation | Example Locations |
|---|---|---|---|
| Tropical Forest | Hot, high rainfall all year | Dense evergreen trees, vines | Amazon, Congo Basin, SE Asia |
| Temperate Forest | Mild temperatures, seasonal rainfall | Deciduous trees, shrubs | Europe, Eastern USA, China |
| Taiga (Boreal) | Cold, moderate precipitation (snow) | Coniferous trees (pine, spruce) | Canada, Russia |
| Grassland | Warm summers, dry seasons | Grasses, few trees | African savanna, US prairies |
| Tundra | Very cold, low precipitation | Mosses, lichens, dwarf shrubs | Arctic, Northern Canada |
| Hot Desert | Hot, very dry | Succulents (cacti), drought-tolerant shrubs | Sahara, Arabian Desert |
🔬 Same Pressures, Same Solutions
Even if biomes are on different continents, they often show similar adaptations:
- Burrowing animals in both deserts and tundras (to escape extreme temps)
- Thick fur or fat in cold climates (like wolves in taiga or polar bears in tundra)
- Fire-resistant bark in forests with seasonal fires (like eucalyptus in Australia and some pines in USA)
Biomes consist of ecosystems that share similar climates and thus support similar communities of organisms. Through convergent evolution, unrelated species evolve similar traits to cope with the same abiotic challenges, even on different continents.
B4.1.8 – Adaptations to Life in Hot Deserts and Tropical Rainforests
🔥 Life in Hot Deserts
Deserts have extreme heat, scarce water, and intense sunlight. Organisms must adapt to conserve water and avoid overheating.
Plant Example: Saguaro Cactus (Carnegiea gigantea)
- Water Storage: Thick, fleshy stem stores large amounts of water.
- Pleated Stem: Expands when water is available.
- Shallow, wide root system: Quickly absorbs rainfall over a large area.
- Waxy cuticle: Reduces water loss via evaporation.
- Spines (modified leaves): Reduce surface area and provide shade + defense.
- CAM Photosynthesis: Stomata open at night to reduce water loss.
Animal Example: Fennec Fox (Vulpes zerda)
- Large ears: Help release excess body heat.
- Nocturnal behavior: Avoids daytime heat.
- Light fur: Reflects sunlight; also provides camouflage.
- Thick fur on feet: Protects against hot sand.
- Burrowing: Lives in underground dens to stay cool.
🌴 Life in Tropical Rainforests
Rainforests have high rainfall, dense canopy, high biodiversity, and intense competition for light.
Plant Example: Meranti Tree (Shorea spp.)
- Very tall growth: Competes for sunlight above the canopy.
- Buttress roots: Support the tall tree in shallow, nutrient-poor soil.
- Drip-tip leaves: Allow rain to slide off easily, preventing fungal growth.
Animal Example: Red-Eyed Tree Frog (Agalychnis callidryas)
- Sticky pads: Help cling to leaves and branches in the canopy.
- Bright red eyes: Startle predators (a defense mechanism called deimatic behavior).
- Green body: Provides camouflage among leaves.
- Nocturnal activity: Avoids daytime predators and overheating.
In both deserts and rainforests, organisms have evolved specialized adaptations to survive in their environments. These include water conservation, temperature regulation, light competition, and camouflage. These adaptations reflect the influence of abiotic pressures like heat, water availability, and light intensity.