IB DP Biology- A4.1 Evolution and speciation - IB Style Questions For SL Paper 2 -New Syllabus

(a)

Evolution occurs through natural selection. Analogous structures can arise through convergent evolution, where organisms with different evolutionary origins develop similar structures or adaptations because they experience similar environmental conditions and selective pressures.

Similar functional requirements can therefore favour similar adaptations in unrelated organisms. The resulting structures have similar functions, even though they evolved from different ancestral structures.

For example, the streamlined, torpedo-shaped bodies of sharks and whales are adaptations for efficient swimming, but the structures evolved independently from different ancestors.

(b)

Plants growing in hot deserts have adaptations that reduce water loss and/or allow them to obtain and store water.

• Wide-spreading roots allow water to be collected from a large area.
• Deep roots allow plants to obtain water from greater depths or underground sources.
• Water-storage tissue in thick leaves or stems allows survival during long periods without rainfall.
• Few stomata reduce transpiration and therefore minimize water loss.
• A waxy cuticle reduces water loss from the surface of the plant.
• Stomata opening at night reduces transpiration because conditions are cooler and generally less dry.
• Leaves may be absent, narrow, or modified into spines/scales, reducing surface area and therefore reducing transpiration.
• Rolled leaves or hairs around stomata can retain humidity and decrease water loss.
• Pitted or sunken stomata reduce transpiration and water loss.
• Pleated stems can allow the stem to shrink and reswell while providing a structure for water storage.

These adaptations allow desert plants to obtain, store and conserve water under conditions of high temperature and limited rainfall.

(c)

Herbivores have a range of adaptations that allow them to obtain plant material and digest it efficiently.

• Piercing mouthparts or a stylet allow some herbivores to feed by sucking sap from plants.
• Chewing mouthparts and mandibles allow leaves, stems or wood to be eaten.
• Grinding teeth or ridged molars help break down tough plant material.
• Multiple stomachs can allow more effective digestion of plant material.
• A long caecum or intestine provides more opportunity for digestion and absorption.
• Some herbivores can detoxify plant toxins, allowing them to feed on plants containing defensive chemicals.
• Some herbivores produce or harbour cellulase-producing microorganisms, allowing cellulose to be digested.
• Some birds, such as hummingbirds, have a long beak or tongue adapted for extracting nectar.