Ch37: Food as a limiting Factor Higher Human Biology

1. Ch37: Food as a limiting Factor Higher Human Biology

2. How does land like this… …turn into this?

3. Image source: spectrum.troy.edu Image source: www.racerocks.com Image source: www.countrysideinfo.co.uk Primary Succession Colonisation of a previously uninhabited area e.g. lichens on bare rock. The lichens make acids that breakdown the rock This allows mosses to become established. Over many years the rock disintegrates & dead plants accumulate making a layer of soil.

4. Soil fertility increases Infertile soil Succession Pioneer species Climax community e.g. Oak woodland

5. Cause of succession • Succession occurs because each community acts on and modifies its habitat. • After a short time of stability the community makes the habitat less favourable for itself & a more favourable community succeeds it. • Each stage makes the soil more fertile. As growing conditions improve larger grasses and shrubs choke and shade out smaller plants. These are then replaced by small trees and eventually the climax community. Try the activity: Scholar Unit 3, Table 10.1: Increasing complexity in succession http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=3aa25eb0-80da-ba3f-3012-a9fa8a329c7f

6. Climax Community As succession proceeds Greatest diversity of animal species & most complex food webs. Varies from climate to climate • Soil becomes more fertile • Soil becomes deeper • Height of vegetation increases • Biomass of vegetation increases Image source: www.wyco-rpc.net

7. Image source: www.wiltshirewildlife.org Effect of Land use on Natural Succession 400 years ago Britain was completely covered in Oak Woodland Vast areas cleared for agriculture & human settlements Now Halt on the process of natural succession

8. More agricultural land needed to support population Human population increasing Land overused & soil fertility drops Land used for cash crops & cattle ranches More land needed so trees deforested Developing Countries

9. Cocoa Coffee Cash Crops Instead of using deforested land to grow basic food for locals, most of the land is used to grow cash crops By selling these to rich countries, they try to earn the money needed to support their fragile economy. e.g.

10. Growing Cash Crops – A Risky Business If the price of the cash crop drops, the poor country is left in debt and short of food for local people. Country borrows from international banks to buy food, seed & fertiliser, so gets into more debt More forests cleared to grow food and cash crops

11. Fossil fuels Nuclear power Fuel Sources Developed Countries Developing Countries Wood  encourages more deforestation Animal dung Crop stubble  leads to a lack of natural fertiliser & reduces soil fertility

12. Wheat Maize Rice Potatoes Increased food production Monoculture • A monoculture is a large cultivated population of one crop species. • needed to support the increasing human population • forests cleared to make space for crops • usually all plants are genetically identical • very susceptible to pests/disease e.g.

13. Increased food production: Fertilisers Advances in agriculture due to the use of chemicals, has supported the increasing human population. Harvesting crops causes the Carbon and Nitrogen cycle to become unbalanced because most of the dead plant material is removed. So nutrients don’t get released back into the soil and the soil becomes less fertile. Adding fertilisers (Nitrates, Phosphates and Potassium) increases the nutrient level of soil. Promotes growth of a particular crop

14. Pesticides Increase in food supply Herbicides Fertilisers Increased food production: Chemicals Increase in Crop Yields In developed countries… Use of fertilisers have eliminated the need for crop rotation as the same piece of land can be continuously used for the same crop.

15. Leached fertilisers or sewage effluent running into water can become over-rich in nutrients (e.g. nitrate) leading to eutrophication (rapid growth of algae, drop in oxygen) Disadvantages of using fertilisers • Soil structure & humus content not maintained • Excess nitrates can be washed (leached) by rain, into rivers, which can affect drinking water quality

16. Herbicides • Crop plants compete with weeds for: • water • light • mineral nutrients • space • Herbicides (weedkillers) - control unwanted weeds. • 2 types: • Selective • Non-selective - …..

17. Selective Herbicides Plants with broadleaves (e.g. dandelion) absorb a lot, but plants with narrow leaves (e.g. grasses) don’t, so this often used on lawns. Herbicides cause the plant to grow rapidly, using up its food reserves, then it dies of starvation. View the animation: Scholar Unit 3, Figure 4.15: Use of IAA as a selective weedkiller http://courses.interactiveuniversity.net/vle/scholar/session.controller?action=viewContent&contentGUID=c55d4bc9-c029-987d-d6ab-a0701c9431b6

18. Non-Selective Herbicides These herbicides have a destructive but short-lived effect on all green plants, so are used to clear an area of plants completely e.g. before sowing crops.

19. Growth fails Pesticides • Pests reduce crop yield by: • Feeding directly on part used as food • Attack roots • Attack leaves Pests also effect the animals that depend on that plant whose populations will decrease. Insecticides Fungicides

20. Fungicides • Used to kill fungi • Sprayed • before fungal attack • OR • to kill fungal spores – that absorb chemical when germinate then die • Rain washes fungicide off • Needs to be applied often • New leaves are vulnerable because they aren’t protected

21. Importance of Pesticides • Reduced loss of crops due to pests & disease • Increased food production • Allows production of high quality crops • Good pesticides should be: • Specific • Act quickly / Short-lived • Safe • Should breakdown in environment becoming • harmless Scientists are now trying to genetically engineer pesticides.

22. Selective breeding Selective breeding is repeated selection of individuals possessing desirable characteristics to be used as parents for the next generation. Such selection also prevents plants lacking the desirable characteristics from breeding. Most plants that are eaten by humans have been selectively bred from wild species. There are 2 methods…..

23. Selective breeding • Inbreeding • Cross closely related members of the same species • In plants: self-pollination • maintains uniformity in future generations • can result in reduced vigour (inbreeding depression)

24. Selective breeding • Outbreeding • Crossing unrelated members of the same species • In plants: cross-pollination • can result in hybrid vigour (better than it’s parents) • can’t be depended on to produce good offspring • process needs to be repeated for each generation

25. Images source: http://en.wikipedia.org Selective breeding in plants • Selective breeding in plants (e.g. wheat, barley, potatoes, tomato) has produced: • higher yields • resistance to disease • fruit with better flavour • Several varieties have been developed through selective breeding of the cabbage plant.

26. Green Revolution New varieties have formed due to selective breeding (e.g. drought resistant wheat) so food production has increased. But genetically uniform crops are more susceptible to disease – have no natural resistance, So to save them pesticides must be applied rapidly. These are often high yielding, rapid-response strains which can be harvested 2-3 times per year, but only with massive use of fertilisers. Cost of fertiliser leads to debt for many farmers in developing countries!

27. Genetic Engineering Genetic engineering is the transfer of one or more genes from one organism to another. Genetic engineering allows the genes of completely unrelated organisms to be combined into one organism. This allows a new variety to be produced in just one generation. This scientific process is still very controversial and has prompted much debate due to the moral and ethical issues that surround it.

28. Genetic Engineering Terminology Genome - the single set of haploid chromosomes typical of a species. Recombinant DNA technology = genetic engineering Transgenic – an organism whose genes have been altered by genetic engineering

29. Somatic Fusion • The somatic (body) cells of 2 different plant species have their walls removed using the enzyme cellulase. • These cells, now called protoplasts, are then subjected to an electric current and fuse. • The new hybrid formed is then induced to form a cell wall and divide into a mass of undifferentiated cells. • A hormone then induces the callus to develop into a hybrid of the 2 different plants.

30. Somatic Fusion Sexual incompatibility prevents many species from interbreeding successfully, but scientists can overcome this using somatic fusion. Somatic cells = body cells Protoplasts = cells with their cell wall removed Cellulase = enzyme that breaks down cell walls Callus = a group of undifferentiated (unspecialised) cells. View the animation: Scholar Unit 2, Producing plant hybrids by somatic fusion, Fig 7.13: http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=2f0602b8-0992-f0f4-f203-75a4d069e8df

31. Resistance to the potato leaf roll virus Tuber-bearing fruit Image source: www.bbc.co.uk Image source:draf.bretagne.agriculture.gouv.fr Somatic Fusion Example Potato: A new variety of potato plant, produced by somatic fusion, has:

32. Effects of Food Shortage • Famine • many deaths due to lack of food • applies to animals as well as humans

33. Undernutrition (lack of food) deficiency diseases more susceptible to disease e.g. kwashiokor (lack of protein) Malnutrition (unbalanced diet) Effects of Food Shortage Starvation

34. Unequal Distribution of Food Developed countries produce surplus food which is stored for future use. Keeps the price high, too expensive for developing countries

35. …populations become helpless & need to depend on emergency aid for survival. Sometimes adequate food supplies exist but there is unequal distribution locally. Starvation Unequal Distribution of Food The global unequal distribution of food leads to….

36. Overeating & Long Food Chains Diet developed countries Vs Diet developing countries • 1.5x kilojoules • 2x protein • 5 x more protein from animals Grain can support many people directly but if the same quantity is fed to livestock it will support far fewer people because energy is lost at each stage of the food chain. If less meat is eaten in developed countries, more food would be available for people in developing countries.