Crop PlantsCrop Plants

AS Biology Module 2AS Biology Module 2

J. Gilbert Feb ’04J. Gilbert Feb ’04

www.biologymad.com www.biologymad.com

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What factors are important to What factors are important to consider to produce a good consider to produce a good

harvest?harvest?• Light

• Water

• Temperature range

• Availability of inorganic ions i.e. nitrates, phosphates and potassium.

In this unit we will look at:In this unit we will look at:

• Producing a high crop yieldProducing 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

In this unit we will look at:In this unit we will look at:

• Problem with crop plantsProblem 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

Cereal CropsCereal 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

Cereal CropsCereal Crops

Rice(completed - 01/03/04)(completed - 01/03/04)

Maize(completed - 01/03/04)(completed - 01/03/04)

Sorghum

WheatWheat

Rice

• Grown manly in Asia – Swamp Plant• Main source of food for nearly half the world’s

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RiceRice

• 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

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Rice - AdaptationsRice - 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.

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Rice - AdaptationsRice - Adaptations

• When oxygen levels fall too low, the root cells respire anaerobically, producing ethanol (seedling only). – Ethanol is 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

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MaizeMaize

• Grown in central America and tropics where temperature and light intensity are high.

• Tropical plant

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MaizeMaize

• 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.

•It is grown as a staple food in much of Africa.

–Major draw back - deficient in the essential amino-acids tryptophan and lysine

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MaizeMaize

• 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.

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Maize - AdaptationsMaize - 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

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SorghumSorghum

• Grown in very hot (+35oC) regions of Africa and Central India

• Called a Xerophyte Plant (found in dry conditoins)

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SorghumSorghum• 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.

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Sorghum - AdaptationsSorghum - 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.

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Sorghum - AdaptationsSorghum - 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

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Sorghum - AdaptationsSorghum - 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.

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WheatWheat(not directly in the specification)(not directly in the specification)

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WheatWheat

• Is the world’s most widely-grown crop• Grown throughout the temperate regions of the

world – human (flour) and animal feed

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Wheat 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.

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SummarySummary

CropCrop Growth requirementsGrowth requirements AdaptationsAdaptations

WheatWheat Warm, frost free climate, fertile soil, drought intolerant

NA

MaizeMaize Adapted to a wide range of temperature climates and soils

C4 pathway, arial roots

RiceRice Tropical, paddy varieties are aquatic, drought intolerant

Arenchyma, tolerance to ethanol

SorghumSorghum Wide range of soils. Drought tolerant. Grown in regions too dry for maize

Dense roots, thick waxy cuticle, sunken stomata, motor cells,

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