B4.1 Adaptation to Environments

Define habitat

The natural place where an organism, species, population, or community lives

What elements make up a habitat?

1) Geographical location - The physical area

2) Physical conditions (e.g. temperature, light, soil, water availability) 

Describe the role of abiotic factors in an environment

Abiotic factors are non-living aspects of an environment that influence:

• Where organisms can live

• How they survive & reproduce 

[CS] Lyme grass in sand dunes - describe their background & adaptation [7]

• Sand dunes are dry, windy, & nutrient-poor habitats

• Grasses, like lyme grass, have key adaptations to survive in such conditions

Adaptation	Function
Rolled leaves with stomata	Reduce surface area  → less water loss from strong winds
Waxy cuticle	Acts as hydrophobic surface on leaves & stems  → prevents evaporation
Sunken stomata	Creates air pockets that traps humidity → reducing transpiration
Deep roots & rhizomes	Anchors plant in soil & absorbs water from deep underground
Tough schlerenchyma cells	Provide structural support during droughts → prevents wilting

[CS] Mangrove trees in swamps - describe their background & adaptation [7]

• Coastal swamps have waterlogged, salty, & anoxic 

• Mangrove trees have the following adaptations:

Adaptation	Function
Salt glands	Excrete excess salt
Pneumatophores (aerial roots)	Allows gas exchange (absorb O2) in low-oxygen soils
Thick waxy cuticle	Prevents water loss & soil entry
Vivipary (germination on parent)	Ensures seedling survival in salty water
Stable & flexible root network	Stable (e.g. stilt & buttress roots) - broaden tree base to anchor tree in soft mud  Flexible - resist tidal forces & currents

Explain the effects of abiotic factors on plants & animals [5×2]

Abiotic variable	Effect on plants	Effect on animals
Light intensity	Affects photosynthesis → growth rate of plants	Affects behaviour (nocturnal/only active at certain levels)
Water availability	Determines whether a plant is xerophytic (adapt to dry environment) or hydrophytic (adapt to aquatic environment)	Affects osmoregulation (hydration, excretion) & adaptations for water retention
Temperature	Affects enzymatic activity & germination	Affects metabolism & enzyme function
pH	Of soil - Influences nutrient availability & enzyme activity in roots	Of water - Affects aquatic animals & enzyme function
Salinity	Separates aquatic species (freshwater, brackish, marine) depending on survival requirements  Affects water potential in plant tissues/osmoregulation in animals

What is a range of tolerance?

Definition: The optimal range of abiotic conditions in which each species thrive best

• Too much or too little of a factor can cause stress, reduced reproduction, or death

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 coral tissues)

  • Coral provides shelter & nutrients

  • Zooxanthellae perform photosynthesis which supplies sugar to the coral

Describe the conditions required for coral reef survival & consequence if unmet [5×2]

Coral reefs are highly sensitive to changes & require specific environmental conditions:  

Factor	Significance	Consequence if unmet
Water depth	Reefs grow in shallow waters (0-50m) where sunlight can reach zooxanthellae for photosynthesis	Deep waters → sunlight cannot reach, limits zooxanthellae photosynthesis
pH	Coral skeletons are made of calcium carbonate, which forms best under slightly alkaline conditions (pH 8-8.3)	Ocean acidification lowers pH → threatens formation
Salinity	Stable salt levels (32-42 ppt) required for osmoregulation	Sudden changes (freshwater runoff/evaporation) → stress/kill corals
Water clarity	Clear water allows sunlight to penetrate	Sediment, algae blooms, pollution → reduce clarity & limit photosynthesis
Temperature	Coral reefs form in warm tropical waters (23-29°C)	Above 30°C → coral bleaching

Define biome

Large groups of ecosystems sharing similar abiotic factors

What are the two main factors that determine type of terrestrial biome?

1) Average annual temperature

2) Average annual rainfall

Explain why different biomes have similar communities [2]

• Different biomes have organisms with similar adaptations due to common selection pressures (abiotic conditions) 

• Hence, they develop analogous structures via convergent evolution

Describe the climate conditions of major biomes [6×4]

Biome	Temperature	Precipitation	Light intensity
Tropical Forest	High, no cold season	High rainfall	High
Temperate Forest	Moderate (summers warm, winter cold)	Medium to high rainfall	Moderate
Taiga (Boreal Forest)	Low w/ short summers	Medium to high rainfall	Low to medium
Grassland	Medium to high in summer Medium to low in winter	Low rainfall	Medium to high
Hot Desert	High daytime, low nighttime	Low rainfall	High
Tundra	Very low w/ short summer	Low to medium (mostly snow)	Low

[Example] Hot desert plant adaptation - Saguaro cactus (Carnegiea gigantea) [6]

Adaptation	Function
Wide-spreading roots	Collect water from a wider area
Tap roots	Collect water from deep in the subsoil
Thick, fleshy stems	Composed of tissue for voluminous water storage
Pleated stems	Water regulation - expands in rain for absorption & shrinks in droughts to limit water loss
Spines	Lower surface area = less transpiration
CAM photosynthesis	Stomata open at night to reduce water loss

[Example] Hot desert animal adaptation - Fennec fox (Vulpes zerda) [5]

Adaptation	Function
Large ears	Radiate excess body heat → keep body temperature down
Nocturnal behaviour	Avoids daytime heat
Light fur	Reflects sunlight, provides camouflage
Thick fur on feet	Protects against hot sand
Burrowing	Lives in underground dens to stay cool

[Example] Tropical rainforest plant adaptation - Yellow meranti (Shorea faguetiana)

Adaptation	Function
Grows over 80 metres tall	Away from competition → reaching full sunlight
Buttress roots	Anchors tree in shallow soil
Smooth trunk	Sheds rainwater rapidly to limit mould
Drip-tip leaves
Leaf enzymes function up to 35°C	Prevent denaturing under high temperatures

[Example] Tropical rainforest animal adaptation - Spider monkey (Ateles geoffroyi)

Adaptation	Function
Long arms & legs	Climbing & reaching for fruit on high trees
Hook-like thumbless hands	Grasp branches & lianas, pick fruit
Prehensile tail	Acts as a fifth limb for gripping & balance
Highly developed larynx	Communication with group across dense canopy