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Food supply as a limiting Food supply as a limiting factorfactor
Chapter 37Chapter 37
Today’s lessonToday’s lesson
Understand the concept of natural Understand the concept of natural succession, land overuse, & deforestationsuccession, land overuse, & deforestation
Discuss the use of chemicals to increase Discuss the use of chemicals to increase food productionfood production
Discuss how selective plant breeding & Discuss how selective plant breeding & DNA technology has potential benefits for DNA technology has potential benefits for food productionfood production
Discuss the effects of food shortages on Discuss the effects of food shortages on the world’s populationthe world’s population
Natural SuccessionNatural Succession Bare rock colonised by a pioneer Bare rock colonised by a pioneer
community community - e.g lichen- e.g lichen Other species would follow Other species would follow - e.g moss, soil, plants, grasses- e.g moss, soil, plants, grasses Eventually a climax community Eventually a climax community
would form would form - e.g. deciduous trees- e.g. deciduous trees Human land use ensures that Human land use ensures that
vast natural forests are cleared vast natural forests are cleared for agriculture etc. for agriculture etc.
Natural succession very rare Natural succession very rare these daysthese days
Developing countries Developing countries Population increase leads to Population increase leads to
land overuse (soil fertility drops)land overuse (soil fertility drops) Demand for fertile land rises Demand for fertile land rises
dramaticallydramatically Forests cleared – prevents Forests cleared – prevents
natural successionnatural succession Causes Causes deforestationdeforestation – often – often
irreversibleirreversible Often cleared land used for cash Often cleared land used for cash
crops, not food (v risky)crops, not food (v risky) Often wood is needed for fuelOften wood is needed for fuel Use of Use of marginal landmarginal land can can
accelerate deforestationaccelerate deforestation
Use of chemicals to increase food Use of chemicals to increase food productionproduction
Monoculture – vast cultivation of one Monoculture – vast cultivation of one identical type of cropidentical type of crop
E.g. wheat, maize, rice, potatoesE.g. wheat, maize, rice, potatoes Fertilisers raise nutrient supply to soilFertilisers raise nutrient supply to soil Eliminate need for natural cycling of Eliminate need for natural cycling of
chemical nutrients chemical nutrients - by decay & nitrification- by decay & nitrification Supports continuous use of land for Supports continuous use of land for
growth of a cropgrowth of a crop DisadvantagesDisadvantages - Doesn’t substitute - Doesn’t substitute humushumus – poorer soil – poorer soil
aerationaeration - Nitrates can get washed into water - Nitrates can get washed into water
suppliessupplies - Eutrophication – makes a waterway - Eutrophication – makes a waterway
over-rich (algal blooms)over-rich (algal blooms)
Herbicides/PesticidesHerbicides/Pesticides HerbicidesHerbicides eliminate weeds which may eliminate weeds which may
compete with crops for nutrients etc.compete with crops for nutrients etc. Can be selective or non-selectiveCan be selective or non-selective In a monoculture, pests & parasites have In a monoculture, pests & parasites have
unlimited foodunlimited food InsecticidesInsecticides wipe out invertebrate pests wipe out invertebrate pests - e.g. nematode worms, slugs, insects- e.g. nematode worms, slugs, insects Without their use 25-45% of cereal crops Without their use 25-45% of cereal crops
could be lostcould be lost FungicidesFungicides kill fungi (e.g. mildew) kill fungi (e.g. mildew) Sprayed onto crop plants or grains Sprayed onto crop plants or grains
covered in spores covered in spores - require repeated applications- require repeated applications All pesticides must be All pesticides must be specificspecific, , short-livedshort-lived
& & safesafe Genetically engineered pesticides now Genetically engineered pesticides now
widely developedwidely developed
Selective plant breedingSelective plant breeding To produce food plants with desirable To produce food plants with desirable
characteristicscharacteristics E.g. higher yields, disease resistance, E.g. higher yields, disease resistance,
faster growth etcfaster growth etc Plants can be Plants can be inbredinbred (self-pollination) (self-pollination) Maintains uniformity in future generationsMaintains uniformity in future generations Can lead to inbreeding depressionCan lead to inbreeding depression Plants also can be Plants also can be outbredoutbred (cross- (cross-
pollination)pollination) Benefit – hybrid viguourBenefit – hybrid viguour Disadvantage – new strains not Disadvantage – new strains not
guaranteed to have desirable guaranteed to have desirable characteristicscharacteristics
These have led to a These have led to a Green RevolutionGreen Revolution Risks Risks – – if all plants are identical, could all suffer if all plants are identical, could all suffer
from one disease strainfrom one disease strain - require vast amounts of fertiliser (V. - require vast amounts of fertiliser (V.
costly)costly)
Genetic manipulationGenetic manipulation
Recombinant DNA technology Recombinant DNA technology allows DNA from one species to allows DNA from one species to be transferred to anotherbe transferred to another
E.g lectin transferred from pea E.g lectin transferred from pea to potato plantsto potato plants
Somatic fusion Somatic fusion allows non-sex allows non-sex cells from different species to be cells from different species to be fused togetherfused together
Can form a hybrid Can form a hybrid protoplastprotoplast This has a mixture of parental This has a mixture of parental
plant traitsplant traits E.g. potato leaf roll disease E.g. potato leaf roll disease
controlcontrol
Effects of food shortageEffects of food shortage FamineFamine – spell of food shortage – spell of food shortage Balanced diet – supply of proteins, Balanced diet – supply of proteins,
fats & carbs fats & carbs - min. of 9500kJ/day- min. of 9500kJ/day STARVATION:STARVATION: 1. Undernutrition1. Undernutrition – – failure to receive enough food failure to receive enough food - tissue death, emaciation, death- tissue death, emaciation, death 2. Malnutrition2. Malnutrition – – lack of a balanced dietlack of a balanced diet Leads to a deficiency disease e.g. Leads to a deficiency disease e.g.
kwashiorkor (lack of protein)kwashiorkor (lack of protein) World food distribution very uneven World food distribution very uneven
(40 million die every year)(40 million die every year) Food production exceeds population Food production exceeds population
growthgrowth Excess food often stored, rather than Excess food often stored, rather than
be shared to the needybe shared to the needy Overeating & irregular food chains Overeating & irregular food chains
prevalent in developed countriesprevalent in developed countries