How Green Plants Make And Use Food (Rev. 1984)

[Music] life on our planet forms a complex pattern each life form depending on others for its [Music] existence animal life is part of a food chain that begins with green plants many animals get their food directly from plants and the plant eaters may become food for other [Music] animals there are a few plants that are capable of using animals for food but most plants must get their food in some other way it might seem logical to suppose that plants get their food from the soil that idea can be tested by observation and experiment if you take a bean seed and cut it open you'll notice that the new plant the embryo is only a small part of the seed surrounding the embryo are two seed leaves called calans they contain stored food mostly starch that can be used when the seed sprouts and the new plant begins to grow we'll use timelapse photography to compress several days into a few [Music] seconds by the time a plant has developed green leaves the stored food has been used up this means that a growing plant must develop another source of food and perhaps that food or at least part of it does come from the soil timelapse photography shows that a plant growing in dry soil will become wilted and without water it will eventually die so in order to live and grow a plant needs water absorbed by the roots from the soil but it's likely that soil provides more than just water take a sample of rich soil and pour distilled water through [Music] it then boil away the water when the water evaporates it leaves a residue of mineral salts which came from the soil minerals dissolved in water can absorbed by plant [Music] roots when we add fertilizer to soil we're adding minerals that can be absorbed by growing plants fertilizer is sometimes called plant food and it's true that a plant needs minerals but food is more than just minerals and plant food must be more than what a plant can absorb from the soil a growing plant receives other things from its surroundings things which somehow combine to provide food for the plant put a plant under a bell jar and pump the air out of the jar without air the plant will wither and eventually it will die so plants also need air in order to live and light is also important two bean plants almost identical at first but the one on the right is receiving more light than the other in time-lapse photography notice the difference in the growth of the two [Music] plants green plants are adapted to grow toward light watch what happens when one light bulb is turned off this is time-lapse photography [Music] again so a green plant needs light as well as air water and minerals to see how this is related to food we need to take a closer look at the structure of a plant plants are made up of thousands of living cells there are several different types of cells most of them arranged in layers to form tissues some of these tissues serve as tubes that carry liquids through the plant the innermost layers of tissue are called xylem most of the cells here are dead and Hollow water and dissolved minerals enter through the roots and move upward in the Asylum tubes through the stem and into the leaves most of the water reaching the leaves is given off into the air but some water is used in a chemical reaction that also requires air and light the surface of a leaf has many small openings called stomata air passes through the stomata into air Chambers located just below the surface air and water are used as raw materials for a chemical reaction that takes place in certain specialized plant cells large numbers of these specialized cells are found in a leaf inside these cells are small bodies called chloroplasts the chloroplasts contain chlorophyll the pigment that gives a plant its green color in a green leaf molecules of carbon dioxide from the air move to the chloroplasts from the xylm tubes molecules of water also move to the chloroplasts the chloroplasts absorb light energy and this energy is used in a complex chemical reaction that converts carbon dioxide and water molecules to molecules of sugar releasing leftover oxygen into the air the reaction is called photosynthesis by means of this process green plants have produced the oxygen in the atmosphere that is essential to life and the simple sugar produced by photosynthesis is a basic raw material for the more complex forms of food that are used by animals as well as by the plants themselves the process of photosynthesis can be shown in a simplified chemical equation energy from sunlight is used to convert molecules of carbon dioxide and water and form molecules of simple sugar as well as oxygen which is released into the air in a leaf the sugar produced by photosynthesis moves to another set of tubes called the flam tubes a layer of living tissue next to the xylem the sugar is carried in the flm tubes to every part of the plant molecules of sugar are absorbed abbed by all the living cells of the plant some of the sugar is used directly to supply energy for growth this action has been speeded up by time-lapse [Music] photography [Music] the release of energy in a plant cell involves a chemical reaction that uses up oxygen and releases carbon dioxide just as it does in an animal cell but plants produce much more oxygen by photosynthesis than they use in providing for their energy needs plant cells also use sugar as raw material for other types of food the cells themselves are made of various types of protein which are produced in a plant by chemical reactions that combine simple sugar with minerals absorbed from the soil this process supplies the proteins needed for growth as cells become larger and eventually divide to produce new cells we're using time-lapse photography once [Music] again plant cells also produce starch from simple sugar starch is a concentrated form of food that is stored in various parts of a plant for later use so green plants don't take in food as animals do beginning with the process of photosynthesis green plants produce the food that nourishes the plants themselves and eventually all of the other forms of life on the earth including [Music] ourselves [Music] for