B4.1Theme B — Form and function
Adaptation to environment — IB Biology HL Revision Notes & Topical Questions
5 min read 10 parts Lesson 10 of 14 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
B4.1 Adaptation to environment — IB BIOLOGY HL notes: Explain how abiotic factors limit species distribution and how organisms are adapted to habitats, coral reefs and biomes.Habitat = the place where an organism lives, containing many species that form a community.It is describe…
- Low oxygen
- Range of tolerance
- Extreme species
- Interaction
- Limiting factor
- Measuring abiotic factors
Part 1 of 8Habitats and abiotic factors
Habitat
Habitat the place where an organism lives, containing many species that form a community.
- It is described by location (for example polar habitats) and ecosystem type (for example grassland).
Abiotic factors
Abiotic factors non-living factors in a habitat.
- Light intensity and wavelength.
- Temperature.
- Water turbidity (cloudiness).
- Humidity.
- Soil or water pH.
- Soil or water salinity.
- Soil composition.
- Oxygen or carbon dioxide concentration.
| Abiotic factor | Effect on organisms |
|---|---|
| Light intensity | Plants need light for photosynthesis |
| Temperature | Affects the rate of enzyme-controlled reactions |
| Water availability | Required by all organisms |
| Soil pH and minerals | Different plants need different pH and nutrient levels |
| Wind speed | High speeds increase water loss by evaporation from leaves |
| Carbon dioxide | Needed by plants for photosynthesis |
| Oxygen | Needed for aerobic respiration |
Part 2 of 8Marram grass: a xerophyte
Habitat
- Habitat sand dunes with low water availability, high salinity and low nutrient levels.
Challenge
- Challenge dry air gives a steep concentration gradient so water evaporates quickly, and soil water is hard to replace.
Adaptations that raise humidity round the leaf and cut water loss
- Rolled leaves reduce exposure to wind and trap water vapour.
- Stomata sunk in pits trap water vapour.
- Tiny hairs on the inner leaf surface trap water vapour.
- A thick waxy cuticle reduces evaporation.
Part 3 of 8Mangroves
Habitat
- Habitat tropical coastal swamps often submerged in sea water, with high salinity, low fresh water and low oxygen.
Challenges
- Submerged root cells cannot take in oxygen for respiration.
- Fresh water is scarce.
- Sea water has a higher solute concentration than root cells, so roots risk losing water by osmosis.
Low oxygen
- Low oxygen aerial roots take in oxygen above the water.
- Red mangroves have prop roots that also give stability, and their underwater networks shelter marine animals.
- Black mangroves have pneumatophores that grow vertically up out of waterlogged soil.
Salt and fresh water
- Red mangrove root cells exclude salt from the water transport system, so they take up fresh water and avoid osmotic water loss.
- Black mangroves take in salt water and excrete excess salt through salt glands in the leaves.
Part 4 of 8Range of tolerance and distribution
Range of tolerance
Range of tolerance the range of an abiotic factor within which a species can survive, with an optimum inside it.
- Mangroves grow best at 3–27 ppt salinity, survive in fresh water and tolerate up to 75 ppt.
- Outside the range the species is absent, and population size is zero beyond the critical minimum or maximum.
Extreme species
- Extreme species they have a wide tolerance and an unusual optimum, such as marram grass with a low water optimum.
- They do well where competition is low but poorly in moderate environments where average species compete.
Interaction
- Interaction abiotic factors interact to decide distribution.
Limiting factor
Limiting factor any biotic or abiotic factor that restricts growth, and it decides distribution.
Part 5 of 8Investigating distribution with transects
Sampling
- Sampling measurements from a small, representative area estimate the whole, which saves time.
Transect
Transect a line (with a tape measure) along an environmental gradient to measure abundance and distribution.
| Type | Method |
|---|---|
| Continuous line | Record every species touching the tape |
| Interrupted line | Record species touching the line at regular intervals, such as every metre |
| Continuous belt | Place quadrats end to end along the line |
| Interrupted belt | Place quadrats at regular intervals along the line |
- Measuring abiotic factors
- measure only relevant factors at each sample site.
| Factor | Method |
|---|---|
| Air temperature | Thermometer |
| Rainfall | Rain gauge |
| Humidity | Hygrometer, an electronic device measuring water vapour |
| Dissolved oxygen | Electronic oxygen sensor |
| Water turbidity | Turbidity meter, or a Secchi disc lowered until it disappears |
| Light intensity | Electronic light meter |
| Landscape relief | Contour lines on a map or GPS |
| Site aspect | Compass |
| Slope | Clinometer |
| Soil or water pH | Indicator solution |
| Soil water content | Mass difference between a soil sample and the same sample dried |
Kite diagram
- Kite diagram it shows distribution along the transect (x-axis) and abundance by the width of each kite, with extra sections for abiotic factors such as height or soil pH.
Study design
- Study design studies can be in natural or semi-natural habitats and should use sensors for abiotic factors.
Part 6 of 8Coral reefs
Coral
- Coral a symbiosis of a coral polyp and zooxanthellae algae (photosynthesis products).
- (shelter and protection)
Reef formation
- Reef formation some polyps secrete calcium carbonate, and deposits from thousands of individuals build a reef.
Distribution
- Distribution reef-building corals live in the tropics and subtropics because they have a narrow tolerance for several factors.
| Abiotic factor | Effect on reefs |
|---|---|
| Water depth | Corals grow only in shallow water where enough light reaches the algae |
| pH | Calcium carbonate dissolves at low pH, and H+ ions bind carbonate ions, so less is available; CO2 from fossil fuels lowers ocean pH |
| Salinity | Needs 32–42 ppt, and freshwater run-off reduces it |
| Water clarity | Light must penetrate, and sediment and pollution reduce clarity |
| Temperature | Tolerance is about 20–28 °C and growth is best above 23 °C; warming makes polyps expel algae, causing bleaching |
Part 7 of 8Biomes
Biome
Biome a large community of plants and animals that develops because of environmental factors, usually named after its dominant vegetation.
- Examples are temperate and tropical rainforest, temperate deciduous forest, boreal forest (taiga), grassland, tundra and desert.
Distribution
- Distribution average temperature and rainfall decide the biome in a region, and similar regions contain the same biome.
Climograph
- Climograph a graph of mean annual rainfall against temperature that predicts the biome.
- At 200 cm rainfall and 25 °C a tropical seasonal forest develops.
- At 300 cm and 15 °C a temperate rainforest develops.
- At 100 cm and 0 °C taiga develops.
- Boundaries are gradual, soil type and grazing also matter, and the axes can be swapped, so read labels carefully.
Convergent evolution
- Convergent evolution similar abiotic factors give similar selection pressures, so unrelated species in equivalent biomes develop similar features.
- Cacti in the Americas and euphorbias in Africa both have spines and succulent stems but are not close relatives.
| Biome | Climate | Community features |
|---|---|---|
| Tropical forest | 2000–10 000 mm rain, 20–25 °C | Layers (canopy, understorey), high productivity, nutrient-poor soil, very high biodiversity |
| Temperate forest | 750–1500 mm rain, seasonal temperatures | Dominant deciduous trees, productive part of the year, high biodiversity, fertile soil from leaf fall |
| Taiga | 300–900 mm, heavy snow, −40 to 20 °C | Evergreen conifers, short growing season, low productivity, few species |
| Grassland | 500–950 mm, dry and wet seasons, −20 to 30 °C | Grasses dominate, low productivity, grazers and few top predators |
| Tundra | 150–250 mm, −50 to 18 °C | Too little water, light and warmth for trees, low productivity, hibernating or migrating animals |
| Hot desert | Under 250 mm, up to 49 °C by day and 0 °C by night | Very low productivity, few well-adapted species |
Part 8 of 8Adaptations to hot deserts and rainforests
Adaptation
Adaptation a trait that increases survival in a specific environment, produced by natural selection.
Saguaro cactus (Carnegiea gigantea)
- A thick waxy cuticle reduces evaporation.
- Spines in place of leaves reduce the surface area for water loss and reduce grazing.
- Stem cells expand to store water.
- A deep tap root reaches deep water and shallow roots absorb rainfall quickly.
Kangaroo rat (Dipodomys)
- It stays in underground burrows during the day to avoid heat.
- It obtains water from its diet and makes highly concentrated urine, so it can go without drinking.
Kapok tree (Ceiba pentandra)
- Rapid growth lets it reach the canopy and light before competitors.
- Wide buttress roots give stability during rapid growth.
Orchid mantis (Hymenopus coronatus)
- The female resembles an orchid flower and attracts pollinating insects that become prey, which is aggressive mimicry.
- The smaller, plainer male is camouflaged among stems and branches.
Key terms
| Term | Meaning |
|---|---|
| Abiotic factor | a non-living part of the environment such as temperature or pH. |
| Range of tolerance | the range of an abiotic factor within which a species survives. |
| Limiting factor | a factor that restricts the growth or distribution of a species. |
| Transect | a line along an environmental gradient used to sample abundance. |
| Xerophyte | a plant adapted to dry conditions. |
| Biome | a large community of organisms shaped by climate, named after its dominant vegetation. |
| Climograph | a graph of rainfall against temperature showing which biome develops. |
| Coral bleaching | loss of the algae from coral polyps due to high temperature. |
| Mimicry | an adaptation in which an organism resembles another object or organism. |
Avoid these mistakes
1
Abiotic factors include other organisms — they are non-living, while biotic factors are living.
2
Species can live anywhere with some of their needs met — outside the range of tolerance for any factor they are absent.
3
Similar desert plants are close relatives — similar features arise by convergent evolution.
4
Climographs give sharp biome boundaries — biomes shift gradually and other factors also act.
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