Limiting Factors Jigsaw - Sammons Sci
Background: The main factors affecting rate of photosynthesis are light intensity, temperature, water availability, and wind speed. In any given situation any one of these may become a limiting factor, in other words the factors that directly affects the rate at which photosynthesis can take place masking the effects of the other factors.Directions: Once you are assigned to an EXPERT group, you are to each read that section and that section only. Take notes for that section of notes. Share the notes you took with your EXPERT group and add anything new that you didn’t get that you feel is important. Go back to your HOME group and each of you will share what you have learned about that limiting factor. Take notes on the other three sections and then complete the worksheet. Expert Group 1: Sunlight The Principle of Limiting Factors says that the maximum obtainable rate of photosynthesis is limited by whichever basic resource of plant growth is in least supply. There are 4 limiting factors for photosynthesis: Sunlight, Temperature, Water Availability, and Wind Speed. Sunlight is a requirement of photosynthesis. The plant must absorb energy from sunlight to convert into energy in glucose. The more sunlight the plant has available to it and the higher the light intensity, the more the chlorophyll can absorb. Therefore as light intensity increases, the rate of photosynthesis increases. Gradually the rate falls off and at a certain light intensity the rate levels out and remains constant. At this point, carbon dioxide becomes the limiting factor- a plant cannot photosynthesize if there is insufficient carbon dioxide because carbon dioxide is a raw material for glucose synthesis. Additionally, at a very high light intensity the rate of photosynthesis slows down because the pigment chlorophyll is damaged by ultra-violet.The reason is that the plant only has so many chloroplasts in the leaf to absorb the sunlight at any given moment. To get the most sunlight possible, many plants spread out their leaves in such a way that each leaf maximizes the amount of light falling on them. The also spread them in a way that the lower leaves are not shaded by the ones above. Expert Group 2: TemperatureThe Principle of Limiting Factors says that the maximum obtainable rate of photosynthesis is limited by whichever basic resource of plant growth is in least supply. There are 4 limiting factors for photosynthesis: Sunlight, Temperature, Water Availability, and Wind Speed. Enzymes are necessary for the process of photosynthesis. Enzymes are proteins that speed up chemical reactions. The more enzymes available and the faster they move effects how fast a chemical reaction, such as photosynthesis, can occur. As the temperature increases, molecules (enzymes) move faster, causing molecules to collide more and have more reactions. Therefore, as temperature increases, the rate of photosynthesis increases. However, if the temperature rises above 40oC, the enzymes become denatured. When an enzyme becomes denatured, its structure breaks down and it doesn’t work properly. So, at higher temperatures, the rate of photosynthesis will drop because the enzymes are denatured. Not all plants have the same optimum temperature. Plants which grow in colder climates have an optimum rate of photosynthesis at lower temperatures. Greenhouses are used to capitalize on the effects of higher temperatures increasing the rate of photosynthesis. Plants from regions of warmer climates can successfully grow in colder regions by using greenhouses. Additionally, high temperatures increase the rate of transpiration, leading to the closure of the stomata. Closing the stomata can cause a build-up of oxygen from photosynthesis in the leaves – and this reduces the rate of photosynthesis.Expert Group 3: Water AvailabilityThe Principle of Limiting Factors says that the maximum obtainable rate of photosynthesis is limited by whichever basic resource of plant growth is in least supply. There are 4 limiting factors for photosynthesis: Sunlight, Temperature, Water Availability, and Wind Speed. Water is a reactant of photosynthesis and is necessary to make glucose in the photosynthesis reaction. As water levels increase, the rate of photosynthesis increases. With increased water, the stomata (pores on the underside of leaves) can stay open and gases are exchanged to keep photosynthesis going. When there is not enough water available to the plant, photosynthesis will slow and even stop because transpiration increases. Transpiration is the process by which moisture is carried through plants from roots to the stomata (small pores on the underside of leaves), where it changes to vapor and is released to the atmosphere. Transpiration is essentially evaporation of water from plant leaves. The stomata will eventually close and the exchange of gases stops. However, at certain water levels, the rate of photosynthesis levels out as other factors become limiting. Water level is affected by precipitation and humidity. The more precipitation falling in an environment, the more water there is in the ground for the plant to take up through their roots for photosynthesis. Humidity is a measure of water in the air. As humidity increases, the air becomes wetter, and less transpiration occurs through the open stomata. Expert Group 4: Wind SpeedThe Principle of Limiting Factors says that the maximum obtainable rate of photosynthesis is limited by whichever basic resource of plant growth is in least supply. There are 4 limiting factors for photosynthesis: Sunlight, Temperature, Water Availability, and Wind Speed. Moderate winds favor gas exchanges, but strong winds can cause excessive water loss through transpiration as well as lodging or toppling of plants. Transpiration is the process by which moisture is carried through plants from roots to the stomata (small pores on the underside of leaves), where it changes to vapor and is released to the atmosphere. Transpiration is essentially evaporation of water from plant leaves. When transpiration rate exceeds that of water absorption, partial or complete closure of the stomata may ensue which will restrict the diffusion of carbon dioxide into the leaves. As a result, there will be a decrease in the rate of photosynthesis, growth and yield.As wind speed increases, it dries out the air (reduces humidity). Therefore at high wind speeds, transpiration increases. If the leaf dries out too much, the stomata shut and photosynthesis slows or stops. As long as other factors are not limiting, slower winds will not affect humidity. So, the rate of photosynthesis will rise slightly at lower wind speeds and then slow and drop off as wind speed increases. Additionally wind carries oxygen away from the plant. Less wind, less evaporation, less water requirement. Wind may aid in pollination, interfere with farm operations such as spraying crops, and may blow away pests and diseases thus carry pests to or away from crop.For each factor, fill in the graph to show how that factor affects photosynthesis. SunlightTemperatureLight IntensityRate of PhotosynthesisLight IntensityRate of PhotosynthesisTemperatureRate of PhotosynthesisTemperatureRate of PhotosynthesisWaterWind SpeedWater AvailabilityRate of PhotosynthesisWater AvailabilityRate of PhotosynthesisWind SpeedRate of PhotosynthesisWind SpeedRate of PhotosynthesisFor each scenario, predict the effect on photosynthesis. Scenario 1: Sunlight becomes less direct in autumn. Affect: INCREASE, DECREASE, STAY THE SAME- Justification (complete sentences): ____________________________________________________________________________________________________________________________________________________________Scenario 2: Plant experiences severe drought. Affect: INCREASE, DECREASE, STAY THE SAME- Justification (complete sentences): ____________________________________________________________________________________________________________________________________________________________Scenario 3: Wind speed increases. Affect: INCREASE, DECREASE, STAY THE SAME- Justification (complete sentences): ____________________________________________________________________________________________________________________________________________________________Scenario 4: Temperature lowers from 30oC to 10oC. Affect: INCREASE, DECREASE, STAY THE SAME- Justification (complete sentences): ____________________________________________________________________________________________________________________________________________________________ ................
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