The Food Cycle And Food Chains (1963)

[Music] one of the first facts we learn in the study of biology is that food is necessary to the continual growth of all living things some of the chemicals in food provide energy for work and some chemicals are used for the growth and repair of the body cells a process by which food reaches any consumer may be described as a food chain this meat for example is a link in one such chain the meat came from a steer in order for the steer to develop it too needed food the food in this case was grass thus grass is another Link in this food chain which when put together might look like this grass is eaten by steer which is eaten by human let's trace a similar chain for the milk we drink for this particular food chain grass would again be a link grass is eaten by a cow which provides milk milk is consumed by a human a somewhat different chain might be traced to the honey in this jar the honey which we eat is produced by honey bees to produce this food which they also need to live and grow the bees collect nectar from flowering plants so we might represent this particular food chain as flowers honeybees human note that all three of these food chains share in common a plant link the link of green plants green plants are defined as those plants which manufacture their own food in this cross-section view the speeded up action shows how the root of green plants extend through the soil through these roots plants receive water minerals and nitrogen compounds from the soil these are chemical building blocks which the plants use to manufacture simple sugars and proteins plants take in air through narrow slits in the UND sides of their leaves carbon dioxide from the air is another important chemical used in the synthesis of food by green plants the energy to synthesize the chemical compounds into food comes from sunlight through photosynthesis photosynthesis takes place within specialized cells of the plants called chloroplasts which are seen moving about in this magnified view of a leaf section thus food is manufactured or synthesized by plants from nitrogen compounds s minerals and water in the soil and carbon dioxide from the air both nitrogen compounds and carbon dioxide are provided by waste products of animal life these chemicals are used by plants to make food some animals eat plants as food while certain animals eat other animals as food plant and animal wastes are returned to the soil and Air and then reused by plants to make food this is the concept upon which the term food cycle is based since green plants are the only living things that can synthesize food from chemical compounds in the soil and in the air all animal life must ultimately depend on green plants for nourishment thus green plants are almost always part of any food chain growing in this pool are a variety of green plants such plants are the basic diet of minnows the next Link in this particular food chain the minnows might then be eaten by larger fish some large fish are caught and eaten by large seabirds a pelican is a fish eater in addition to food chains in a water environment there are land environment food chains as well trees which are green plants provide food for many herbivores or plant eaters such as the squirrel here then we have two links in a food chain a squirrel eating a nut the fruit of a tree as in many food chains the next link may be formed by a carnivore or meat eater in this case a coyote eats the squirrel here's the beginning of a somewhat longer food chain a housefly eats watermelon one of the green plants a housefly is trapped and eaten by a spider the spider in turn becomes the source of food for the robin this Hawk a carnivore is part of another food chain here it is eating a mouse a link in a food chain that can be traced back to the mouse eating grains of corn which were produced by plants primarily through the synthesis of nitrogen compounds carbon dioxide and water remember though that this food chain like all the others we've seen could be made up of many other links for example the corn could have provided food for a human or an insect or a crow or the crow might eat the insect and a cat might eat either the crow or The Mouse and the hawk might eat the cat but no matter what the links in a particular food chain or the direction it takes most food chains involve green plants and enriched soil plants too require chemicals that might be called food even though these materials cannot be utilized as food by animal life but how are these needed materials returned to green plants so that they can make more food let's look again at this food chain we know that our bodies cannot utilize all the substances in the meat or other Foods we eat those substances in food which cannot be utilized for body energy or maintenance are later eliminated as waste these these waste products often processed into or used directly as fertilizers serve a vital function both processed and natural fertilizer contain nitrogen compounds when these compounds are returned to the soil they are used by green plants for the manufacture of food Natural Animal wastes or manure are rich in nitrogen compounds when these wastes are returned to the soil and the air we have gone on a Step Beyond the food chain green plants provided food for an animal this animal in turn became food for another animal when essential chemical compounds contained in animal wastes are returned to the soil to be used for making food by other green plants a food chain becomes part of a larger concept the food cycle this is the never ending cycle by which food materials are used again and again a food cycle is forever continued in nature as chemical compounds are also returned to the soil through the decay of animals and plants in Decay dead plants and animals are fed upon by microscopic plants bacteria bacteria such as these draw nourishment from dead organisms and red reduce them to simple chemical compounds these compounds including nitrogen compounds are subsequently released into the atmosphere and soil other bacteria which help replenish the soil with vital nitrogen compounds are found generally in legumes in nodules on the roots here seen under high magnification are nitrogen fixing bacteria in a root nodule besides nitrogen green plants also need carbon dioxide to synthesize food green plants take carbon dioxide directly from the air about them this gas too is a waste product of animal life including human life in breathing air oxygen is absorbed and carbon dioxide is eliminated so human beings and other animal life add to the supply of carbon dioxide which plants must have to make food we have seen that green plants are the beginning of any number of food chains and we have also seen that these chains produce wastes which in turn continue the food cycle the unending pattern of Life growth and Decay that makes possible the maintenance of all forms of life in the world in which we live [Applause] to