C4 plants like maize and sugarcane have adaptations that allow them to more efficiently fix carbon. These include bundle sheath cells that compartmentalize RuBisCO from oxygen, and mesophyll cells that fix carbon dioxide before it reaches the bundle sheath cells. Sorghum is adapted to arid environments through traits like a dense root system, waxy leaves that reduce evaporation, and leaves that can roll inward to hide stomata when water is scarce. Rice is adapted to grow with submerged roots through large air spaces that provide oxygen to roots, shallow roots with access to surface water, and the ability to undergo anaerobic respiration in roots.

1. Crop adaptations
• Adaptations of the leaves in C4 plants (e.g.
sugarcane and maize):
– In photorespiration, enzyme Rubisco acts as
catalyst for combination of O2 with RuBP
instead of CO2
– Results in overall intake of O2 and output of
CO2 and means that less RuBP is available for
CO2 fixation
– Tropical grasses have a leaf structure which
allows them to avoid photorespiration
ALBIO9700/2006JK

2. ALBIO9700/2006JK

3. • Structural features of the leaves which
distinguish C4 plants:
– Groups of cells around vascular bundle (bundle
sheath cells) – contain RuBP and Rubisco but no
contact with air (low concentrations of O2)
– Mesophyll cells around bundle sheath cells – no air
spaces between them, ensuring no O2 reaches the
bundle sheath cells
– Mesophyll cells contain an enzyme (PEP
carboxylase) – catalyses combination of CO2 with a
compound called phosphoenolpyruvate (PEP) –
formation of oxaloacetate
– Oxaloacetate converted to malate – passed on to the
bundle sheath cells – CO2 removed and combined
with RuBP – Calvin cycle ALBIO9700/2006JK

4. Corn leaf t.s. showing bundle
sheaths
ALBIO9700/2006JK

5. How sorghum is adapted to survive in
arid environments
• Fifth most important cereal crop that’s able to grow in
areas of low water supply and shows xerophyte
characteristics:
– Dense root system – widespread and deep – efficient uptake of
water
– Leaves covered with thick, waxy cuticle – reduces evaporation
– Specialised motor cells (bulliform cells) on upper-side of leaves
and strengthening tissue (sclerenchyma) below vascular bundles
– cause leaf to roll inward when water is in short supply (hiding
stomata). Build up of water vapour – reducing diffusion of water
vapour from leaves
– Number of stomata is low and air spaces inside leaf are small –
found away from vascular tissue
– C4 plant – can continue photosynthesis even when very hot and
sunny as long as there is sufficient water
ALBIO9700/2006JK

6. Sorghum
ALBIO9700/2006JK

8. How rice is adapted to grow with
its roots submerged in water
• ‘Swamp plants’
• Partly submerged in paddy fields – fields
flooded, ploughed and young rice plants
planted in mud
• O2 levels in mud fall rapidly (used by
bacteria in mud) and remain very low in
flooded paddy fields since O2 can only
diffuse slowly through water
ALBIO9700/2006JK

9. ALBIO9700/2006JK

10. • Rice plants adaptations which allow then
to grow in conditions of low O2 availability:
– Stems and leaves possess very large air
spaces – allow O2 to get through to the roots
from the air
– Roots are very shallow – allows them some
access to the higher levels of O2 in the surface
water
– Roots able to respire anaerobically –
production of alcohol (usually toxic). Rice root
cells show an unusually high tolerance to
alcohol – able to produce high levels of the
enzyme alcohol dehydrogenase
ALBIO9700/2006JK

11. Rice leaf t.s.
ALBIO9700/2006JK