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