Do not write on the question paper, do not turn in the question paper. Put your answers on a new paper. Unless told otherwise.

Transcription

1 APES Unit 2 Packet Due Sept 10 at the beginning of class Instructions for all homework and labs: Put your name and date on top right corner of all your papers. Put the name of the problem or lab at the top of your paper to identify what you are doing. Do not write on the question paper, do not turn in the question paper. Put your answers on a new paper. Unless told otherwise. Your work may be written clearly in ink on lined paper or printed on plain paper. Print using Times New Roman, 12 font; 1 inch margins all around. Answers must be in complete sentences. Graphs must be properly labeled and have a legend. Independent variable goes on the x-axis, dependent goes on the y-axis. Graphs can be hand drawn or printed. You do not get credit for fancy, just for clearly written and drawn work. Grammar and spelling mistakes hurt your grade. Not too many words. Short and to the point gets better grades. Read Strunk and White, see it in the library.

2 POSITIVE AND NEGATIVE FEEDBACK MECHANISMS Feedback mechanisms either change a system to a new state or return it to its original state. NEGATIVE FEEDBACK MECHANISMS- push a system back to its original equilibrium position. Example: Imagine you are out walking in the country. As you walk, the sun rises higher in the sky and the air temperature increases. Your body senses that your internal temperature is rising above 37 0 C and you start to sweat, which reduces your body temperature by evaporating water from your skin, returning your temperature to normal. POSITIVE FEEDBACK MECHANISMS push a system to a new state of equilibrium. Example: Imagine you are lost on a high snowy mountain. When your body senses that it is cooling below 37 0 C, various mechanisms such as shivering help to raise your internal temperature again, but if these are insufficient to restore normal body temperature, your metabolic processes start to slow down, as, like most chemical reactions, they happen more slowly at lower temperatures. As a result you become lethargic and sleepy and move around less and less, allowing your body to cool even further. Unless you are rescued at this point, your body will reach a new equilibrium you will die of hypothermia. Both natural and human systems are influenced by feedback mechanisms. Generally, we wish to preserve the environment in its original state, so negative feedback is usually helpful and positive feedback is usually undesirable. However there are other situations where change is needed and positive feedback is advantageous. For example, if students enjoy their Environmental Systems lessons, they want to learn more, so attend classes regularly and complete assignments. Consequently they move to a new equilibrium of being better educated about the environment. On the following page there are a number of examples of how both positive and negative feedback mechanisms might operate in the physical environment. No-one can be sure which of these effects is likely to be most influential, and consequently we cannot know whether or not the Earth will manage to regulate its temperature, despite human interference with many natural processes.

3 1. Label each of the following examples as either positive or negative feedback. 2. Draw diagrams of one example of positive feedback and one example of negative feedback using the examples given, to show how feedback affects a system. Include feedback loops on your diagrams. Examples of possible positive and negative feedback in physical systems 3. As carbon dioxide levels in the atmosphere rise: Temperature of Earth rises As Earth warms: the rate of photosynthesis in plants increases more carbon dioxide is therefore removed from the atmosphere by plants, reducing the greenhouse effect and reducing global temperatures 4. As Earth warms: Ice cover melts, exposing soil or water Planetary albedo decreases More energy is absorbed by Earth s surface Global temperature rises More ice melts 5. As Earth warms, upper layers of permafrost melt, producing waterlogged soil above frozen ground: Methane gas is released in anoxic environment Greenhouse effect is enhanced Earth warms, melting more permafrost 6. As Earth warms, increased evaporation: Produces more clouds Clouds increase albedo, reflecting more light away from Earth Temperature falls Rates of evaporation fall

4 ENERGY FROM YEAST CELLS All living things require energy from food to carry but their life functions. This energy is released by the breakdown of energy-rich compounds such as sugar during respiration. The breakdown of sugar produces waste products. The presence of these waste products provides evidence of the breakdown of sugar. In this investigation, you will use the presence of these waste products to determine if fermentation has taken place. OBJECTIVE: To detect the products of fermentation using bromthymol blue as an indicator. MATERIALS: beaker 2 Erlenmeyer flasks (125 ml) 2 rubber stoppers assembled with tubing 1 teaspoon of yeast 2 teaspoon of sugar 30. ml of bromthymol blue (BTB) PROCEDURE: 1. Put the sugar in a beaker and add 30 m1 of warm water to the beaker. Stir well. Add - the yeast to the sugar solution and stir well. Pour into an Erlenmeyer flask 2.Put the bromthymol blue into the other flask. 3.Set up the fermentation apparatus as shown in the diagram 4. Make observations every 5 minutes for about minutes. Note reactions going on in the flask with yeast and sugar. Note color changes in the BTB flask. If your reaction seems to be going slowly,the flask with the yeast may be placed in a beaker of warm water. 5.Your teacher will set up a control for comparison. What should be left out of the control setup? OBSERVATIONS When you. take your apparatus apart, describe the smell of the yeast solution. Create a chart and record the flask appearance for 40 minutes. QUESTIONS AND CONCLUSIONS: 1. Why were you instructed to add warm water, not hot water, to the yeast culture? 2. Why is a two-hole stopper used in the flask containing the indicator? 3. For what substance is bromthymol blue an indicator? 4. Write the chemical equation that explains this reaction. 5. Alcoholic fermentation is the process that causes bread dough to rise. Explain how this happens. 6. Describe a method that could be used to turn the BTB back to its original blue color.

5 Grass Decomposition Lab Background: Saprotrophs, also known as decomposers, are essential in ecosystems. They feed off dead, organic matter in the soil. During this process, they release nutrients back into the soil for the primary producers (plants) to use. The main decomposers in soil are fungi and bacteria. Purpose: In this lab, students will observe the relationship between moisture level and plant (grass) decomposition. In addition, a comparison will be made between aerobic and anaerobic decomposition. Hypothesis: Create one (what do you think you will see?) Example: If the grass receives oxygen, then the weight will... Materials: -10 small, clear plastic cups with covers-distilled water -Freshly cut lawn grass -Graduated cylinder -Digital Balances Procedure: 1. 1) Place 2 grams of grass in each of the 10 plastic cups. Make sure to remove all small rocks, leaves, and twigs before massing the grass. 2. 2) Take2emptycups.Add0mLofwatertoeachcup.Labelthecupshowinghowmuchwater is in the cup and put your group name on it. Take 2 more empty cups. Add 4 ml of water to each cup. Label the cup again. Continue this procedure with 3 more sets of cups. Add 8 ml, 16 ml, and 64 ml of water to each set of cups. Do not forget to label the cup. 3. 3) Take a pin and punch 4 very small holes in just one of each of the following containers: 0 ml, 4 ml, 8 ml, 16 ml, and 64 ml. Now you have 2 sets of plastic decomposition cups, one with holes (aerobic) and one without holes (anaerobic). 4. 4) Take each cup and weigh it. Create a data table to record the weights of all containers for three days. Record the starting, pre-decomposition weights. 5. 5) Place all the cups together in the same area so as not to introduce extra variables such as temperature and light. 6. 6) Each day weigh the cups with the digital balances and record the data in your table. 7. 7) Draw 2 graphs, one of aerobic and the other of an aerobic decomposition.the x-axis should be the time in days and the y-axis should be the weight of the cups in grams. Begin with the initial mass. Conclusion: Detail what you observed. Was your hypothesis correct? Why or why not?