Crop Plants

1. Crop Plants AS Biology Module 2 J. Gilbert Feb ’04 www.biologymad.com Menu

2. What factors are important to consider to produce a good harvest? • Light • Water • Temperature range • Availability of inorganic ions i.e. nitrates, phosphates and potassium.

3. In this unit we will look at: • Producing a high crop yield • Cereal plants have adaptations that allow them to grow in different environment conditions • Farmers have found ways of altering habitats e.g. fertilisers, greenhouses and pesticides

4. In this unit we will look at: • Problem with crop plants • After harvesting, the inorganic ions are removed from the soil. • Farmers need to maintain high yield: • Use of Fertilisers • Not enough fertiliser – yield will be poor • Too much fertiliser – waste of money and pollution of nearby lakes and rivers

5. Cereal Crops • Account for over 50% of all human energy and protein needs • Occupy two-thirds of cultivated land • Cereal grains contain a very low proportion of water • All the plants have adaptations that enable them to survive and grow well in particular environmental conditions

6. Cereal Crops Rice (completed - 01/03/04) Maize (completed - 01/03/04) Sorghum Wheat

7. Rice • Grown manly in Asia – Swamp Plant • Main source of food for nearly half the world’s population Menu

8. Rice • Minimum temp. 20oC • Grown partly submerged in paddy fields • Fields are flooded and then ploughed • Young rice plants are planted in the rich mud • Oxygen concentration of this mud falls rapidly Menu

9. Rice - Adaptations • The stem has large air spaces (hollow arenchyma) running the length of the stem. • Allows oxygen to penetrate through to the roots which are submerged in water. • The roots are also very shallow • allowing access to oxygen that diffuses into the surface layer of the waterlogged soil. Menu

10. Rice - Adaptations • When oxygen levels fall too low, the root cells respire anaerobically, producing ethanol (seedling only). • Ethanolis normally toxic to cells, but the root cells of rice have an unusually high tolerance to it • they have large levels of the enzyme alcohol dehydrogenase in their cells Menu

11. Maize • Grown in central America and tropics where temperature and light intensity are high. • Tropical plant Menu

12. Maize • It is grown as a staple food in much of Africa. • Major draw back - deficient in the essential amino-acids tryptophan and lysine • This causes children after weaning (i.e. about 4-7 years old) to become ill. Their livers greatly enlarge in an attempt to synthesise the missing amino-acids and they suffer from Kwashiorkor. • Note that these children are not ‘starving’ – they may have plenty of calories in their diet – but they are malnourished. Menu

13. Maize • High temperatures increase the rate of transpiration, leading to the closure of the stomata. • Closing the stomata can cause a build up of oxygen from photosynthesis in the leaves – this can reduce the photosynthetic yield. • If plants are grown close together, then there will be competition for carbon dioxide. Menu

14. Maize - Adaptations • Slightly different biochemical pathway for photosynthesis. • Called the C4 pathway • The plant can fix carbon dioxide at low levels as a four-carbon molecule. • This allows photosynthesis to continue at high rates • The roots are shallow, so maize has small aerial roots at the base of the stem • Increases ability to withstand buffeting winds Menu

15. Sorghum • Grown in very hot (+35oC) regions of Africa and Central India • Called a Xerophyte Plant(found in dry conditoins) Menu

16. Sorghum • Is the fifth commonly grown cereal in the world and is another tropical C4 cereal, like Maize • In the drier regions of Africa and Central India it is often a staple food, being made into a tasteless porridge, but in the rest of the world it is used as animal feed or as a source of oil and fibre. Menu

17. Sorghum - Adaptations • adapted to hot, arid, low-soil nutrient conditions • Can withstand high temperatures by synthesising special ‘heat-shock’ proteins very rapidly when the temperature rises. Menu

18. Sorghum - Adaptations • A dense root system • efficient at extracting water from the soil (both wide and deep). • Thick waxy cuticle • prevents evaporative water loss through the leaf surface • Motor cells on the underside of the leaf • causes the leaf to roll inwards in dry conditions. • This traps moist air in the rolled leaf and reduces water loss Menu

19. Sorghum - Adaptations • Small number of sunken stomata • fewer openings out of which water vapour can diffuse (transpiration). • Sunken so that water vapour builds up near the opening, reducing water potential gradient, slowing diffusion. Menu Menu Menu

20. Wheat(not directly in the specification) Menu

21. Wheat • Is the world’s most widely-grown crop • Grown throughout the temperate regions of the world – human (flour) and animal feed Menu

22. Wheat • Bread wheat (drum wheat) • Heard wheat • High protein (gluten) content – enables dough to stretch when rising, also excellent for making pasta! • Winter wheat • Soft wheat • Low gluten content and is good for making cakes and biscuits. Menu

23. Summary Menu