- - AGRICULTURE CORE CURRICULUM - - (CLF7000) Advanced Core Cluster: PLANT AND SOIL SCIENCE (CLF7300) Unit Title: PHOTOSYNTHESIS AND RESPIRATION ____________________________________________________________________________ (CLF7301) Topic: PHOTOSYNTHESIS Time Taught in Year(s) AND RESPIRATION 8 hours 3 and 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome #: (E-1) - Compare and contrast the processes of photosynthesis and respiration. (E-2) - Write the balanced formulas for both photosynthesis and respiration. (E-4) - Discuss how energy is acquired through photosynthesis and released through respiration. (E-3) - List the requirements for photosynthesis and explain what function each requirement performs (i.e., light, heat, CO2, water, and chlorophyll). (E-4) - List the foods derived from products of photosynthesis (i.e., starch, carbohydrates, sugars, fats). Special Materials and Equipment: None References: Hartman, Flocker, and Kofranek. PLANT SCIENCE, GROWTH DEVELOPMENT AND UTILIZATION OF CULTIVATED PLANTS. Evaluation: Quiz by instructor TOPIC PRESENTATION: PHOTOSYNTHESIS AND RESPIRATION A. All living things require energy for growth and movement. 1. Growth refers to an increase in size. a. As the body grows, it may also increase in dry weight. 2. Growth results from expansion of cells. a. Cells usually divide at intervals as they expand. 3. To expand and divide, cells must manufacture building materials and move them into suitable positions. Cells must spend energy to perform these tasks. B. Cells get energy by breaking down food molecules. 1. Carbohydrates (sugars, starch, etc.) and fats are the chief foods that are used for energy. But cells can also break down proteins and other substances for energy. C. To release the energy stored in foods, nearly all cells depend on the process called respiration. 1. In respiration, foods are broken down in a long series of chemical reactions that release energy a little at a time. 2. The overall process is called oxidation because atoms from the food molecules become bound to atoms of oxygen from the air. 3. Carbohydrates are the main foods used in respiration. a. Carbohydrates include sugars and larger molecules made by linking sugars into chains called polysaccharides. b. There are many kinds of sugars. Examples are glucose, fructose, and galactose. c. Sucrose (table sugar) consists of glucose linked to fructose. Sucrose circulates throughout the body of most plants, serving as a mobile energy source. Glucose and galactose combine to make lactose, or milk sugar. d. Starch consists of many glucose molecules linked together. e. Before starch and sucrose can be used in respiration, cells must break these chains down to release the individual sugar molecules. 4. In respiration, cells convert sugar and O2 into carbon dioxide (CO2) and water. a. If the sugar is glucose, its formula is C6H12O6; and the overall process of respiration is: C6H12O6 + 6O2 ------> 6CO2 + 6H2O + energy (glucose + oxygen ------> carbon dioxide + water + energy) b. This is the same overall process that occurs in combustion (fire), except that cells conduct the process in small steps that conserve energy in chemical forms instead of releasing all the energy as heat and light. 5. The rate of respiration is influenced by moisture, temperature, oxygen concentration, the general health of the body, and the stage of development of the body (growing bodies use more energy than mature ones). D. Plants manufacture their own food by the process called photosynthesis. 1. In photosynthesis, sunlight or artificial lights provide energy that is used to make sugar and oxygen from carbon dioxide and water: 6CO2 + 6H2O + light energy ------> C6H12O6 + 6O2 a. Thousands of calories of energy are required for each gram of CO2 changed into carbohydrate. b. The initial products of photosynthesis are simple carbohydrates, but these serve as building blocks for a wide variety of more complex materials including polysaccharides, proteins, and fats. 2. In terms of materials that are used and produced, photosynthesis is the opposite of respiration. a. You can see this by comparing the equations. b. When studied in detail, however, the two processes proceed by quite different steps. E. Photosynthesis is important for nearly all living things. 1. Photosynthesis only occurs in plants, some bacteria, and algae (primitive aquatic life forms such as kelps and green pond scum). 2. Animals, fungi, and most microbes cannot perform photosynthesis. However, they get their energy from foods that are produced by photosynthetic forms of life. 3. Thus, either directly or indirectly, nearly all life on Earth depends on photosynthesis for its energy supply. 4. Plants are cultivated for the complex molecules they synthesize. Carbohydrates, proteins, and fats are the major constituents of food, fiber, and wood. F. Most photosynthesis occurs in leaves, and the anatomy of the plant has many features that promote efficient photosynthesis. 1. The flat shape of the leaf helps to capture light and carbon dioxide. 2. A waxy cuticle covers the leaf and limits the loss of water to the air. 3. The leaf has many small pores (stomata) that allow carbon dioxide to enter the leaf. Each stoma can be opened and closed by a pair of guard cells. By opening the pore only when CO2 is needed, the guard cells keep the loss of water to a minimum. 4. Photosynthesis heats the leaf, and the loss of water through stomata cool the leaf in the same way that sweating cools a human. 5. Stiff veins keep the leaf blade extended, like the ribs of an umbrella. 6. The veins also serve as a circulatory system. a. Some cells in the veins make up a tissue called xylem that carries water and minerals. b. Other cells in the veins make up a tissue called phloem that carries sugar (in a water solution) out of the leaf. 7. Between the veins are many green cells that perform photosynthesis. 8. Other plant parts (young stems and even roots) may also perform photosynthesis. G. Within each green cell, functional units called chloroplasts carry out photosynthesis. 1. A leaf cell may contain as many as 200 football-shaped chloroplasts. 2. Each chloroplast has all the machinery needed to trap light and make sugar and oxygen. 3. A chloroplast has an envelope made of two thin layers of material called membranes. The envelope encloses a fluid, where additional membranes occur. 4. The chloroplast's inner membranes capture light energy and convert it to chemical energy. a. These membranes, called thylakoids, contain pigments that absorb light. 1) The chief pigments are chlorophylls, which give the leaf its green color. 2) Accessory pigments, such as the carotenoids, absorb light and pass its energy to chlorophyll. Carotenoids are the yellow, orange, and red pigments of autumn leaves and many fruits. b. In a complex series of events, thylakoids use the trapped energy to remove hydrogen atoms from water. This releases the oxygen of water, forming O2. 1) This process is the source of the oxygen in the air. Thus, photosynthesis replenishes the atmosphere while respiration depletes it. c. Thylakoids release hydrogen in a form that can be used to build sugars from carbon dioxide. 5. Sugars are made in the fluid part of the chloroplast, using carbon dioxide that comes from the environment, plus the energy and hydrogen that comes from the inner membranes. H. Several factors influence the amount of photosynthesis a leaf will perform. 1. Vigorous photosynthesis requires red and blue light, because these are the chief colors that chlorophyll absorbs. a. Sunlight contains all colors of light in adequate amounts, but artificial light and the shade cast by plants may be deficient in some colors. This can lead to spindly plants. 2. Within limits, the rate of photosynthesis can be increased by exposure to light of greater intensity (brightness). At very high intensities, however, additional light may give no further increases in photosynthesis because other factors (chiefly carbon dioxide and water) become limiting. 3. Photosynthetic production is proportional to the length of the day. 4. Temperature may also affect photosynthesis. a. For many temperate-zone plants, photosynthesis may double for each 18 degrees Fahrenheit increase in temperature. b. This is only true if light is intense enough to be non-limiting. At lower light intensities, temperature may have little effect. c. Extremely high temperatures may slow photosynthesis by causing stomata to close, reducing the supply of carbon dioxide. 5. Adequate CO2 supplies are needed for rapid photosynthesis. a. CO2 makes up about 0.03 percent of the atmosphere. Thus, at high light intensities, photosynthesis may be limited by the low amount of CO2 available. b. High CO2 concentrations are damaging to plants, but moderate artificial increases (for instance, to 0.05 percent) may speed photosynthesis. This is only practical in greenhouses and other enclosed spaces. 6. Water stress reduces photosynthesis. a. When transpiration rates are higher than water intake rates, plants wilt. b. When plants wilt there is a dramatic drop in photosynthesis, because stomata close, and the exchange of CO2 and O2 is restricted. c. Excessive soil moisture around the roots of a plant may cause an anaerobic condition (lack of O2) that reduces root respiration. This decreases photosynthesis in the leaves (why?). I. The main differences between photosynthesis and respiration can be reviewed in the following chart: Photosynthesis Respiration ---------------------------------------------------------------------------- Absorbs C02 Forms C02 Forms 02 Uses 02 Makes sugar Destroys sugar (& other substances) Increases weight Decreases weight Only in green cells In all living cells Only in light At all times (In both light and darkness) ---------------------------------------------------------------------------- __________________________________________________________ ACTIVITY: 1. Grow a number of plants: a. Remove different proportions of leaves. b. Completely remove leaves of some. c. Observe and discuss the differences in growth. 2. Cover all or a portion of the leaves of a fast growing plant such as Coleus. a. Students can make designs or draw their initials on leaves with light proof tape or foil. b. Place plants in light for several days. c. Pick the individual treated leaves and run an iodine starch test on them. NOTE: The dark stained areas will indicate photosynthetic activity (starch accumulation) __________________________________________________________ 7/24/90 sg #%&C