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Crop Plants

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Crop Plants AS Biology Module 2 J. Gilbert Feb 04 www.biologymad.com Menu What factors are important to consider to produce a good harvest? – PowerPoint PPT presentation

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Title: Crop Plants


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

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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 worlds
    population

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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

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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.

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10
Rice - 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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11
Maize
  • Grown in central America and tropics where
    temperature and light intensity are high.
  • Tropical plant

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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.

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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.

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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

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

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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.

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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.

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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

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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.

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20
Wheat(not directly in the specification)
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21
Wheat
  • Is the worlds most widely-grown crop
  • Grown throughout the temperate regions of the
    world human (flour) and animal feed

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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.

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23
Summary

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