18.104.22.168 Cycles & Energy Flow
Use words and equations to differentiate between the processes of photosynthesis and respiration in terms of energy flow, beginning reactants and end products.
Explain how matter and energy is transformed and transferred among organisms in an ecosystem, and how energy is dissipated as heat into the environment.
MN Standard in Lay Terms
Matter and energy are finite in our ecosystems and are constantly being transformed and passed from one system to another. This is done as they chemically change forms and recombine. Ultimately, however, energy is lost as heat to the environment and is no longer in a form that is useful to organisms.
All matter is recycled and passed through the ecosystem as they are used and their chemical form is changed. Energy is transformed until it is finally lost as heat. This is done through the processes of photosynthesis and respiration.
MN Standard Benchmarks
22.214.171.124.1 Use words and equations to differentiate between the processes of photosynthesis and respiration in terms of energy flow, beginning reactants and end products.
126.96.36.199.2 Explain how matter and energy in an ecosystem is transformed and transferred among organisms, and how energy is dissipated as heat into the environment.
"The cartoon, from this site can be download and used free of charge by individual teachers/educators." because of the various restrictions this site has for use of it's cartoons. The only free use they grant is a one time download for individual teachers.
Plant cells contain chloroplast, the site of photosynthesis. Plants and many microorganisms use solar energy to combine molecules of carbon dioxide and water into complex, energy rich organic compounds and release osygen to the environment. The process of photosynthesis provides a vital connection between the sun and the energy needs of living systems. (pg 184)
The atoms and molecules on the earth cycle among the living and nonliving on the earth cycle among the living and nonliving components of the biosphere. (pg 186)
Energy flows through ecosystems in one direction, from photosynthetic organisms to herbivores to carnivores and decomposers. ( pg 186)
The energy for life primarily derives from the sun. Plant capture energy by asboring light and using it to form strong (covalent) chemical bonds between the atoms of carbon containing organic molecules. these molecules can be used to assemble larger molecules with biological activity ( including proteins, DNA sugars and fats). In addition, the energy stored in bonds between the atoms (chemical energy) can be used as sources of energy for life processes. Pg 186
- AAAS Atlas:
See Benchmarks below.
Plants alter the earth's atmosphere by removing carbon dioxide from it, using the carbon to make sugars and releasing oxygen. This process is responsible for the oxygen content of air. (pg 74)
Benchmark 5E/3 The chemical elements that make up the molecules of living things pass through food webs and are combined and recombined in different ways. At each link in a food web, some energy is stored in newly made structures but much is dissipated into the environment as heat. Continual input of energy from sunlight keeps the process going. pg 121
Framework for K-12 Science Education
The process of photosynthesis converts light energy to stored chemical energy by converting carbon dioxide plus water into sugars plus released oxygen. The sugar molecules thus formed contain carbon, hydrogen, and oxygen; their hydrocarbon backbones are used to make amino acids and other carbon-based molecules that can be assembled into larger molecules (such as proteins or DNA), used for example to form new cells. As matter and energy flow through different organizational levels of living systems, chemical elements are recombined in different ways to form different products. As a result of these chemical reactions, energy is transferred from one system of interacting molecules to another. For example, aerobic (in the presence of oxygen) cellular respiration is a chemical process in which the bonds of food molecules and oxygen molecules are broken and new compounds are formed that can transport energy to muscles. Anaerobic (without oxygen) cellular respiration follows a different and less efficient chemical pathway to provide energy in cells. Cellular respiration also releases the energy needed to maintain body temperature despite ongoing energy loss to the surrounding environment. Matter and energy are conserved in each change. This is true of all biological systems, from individual cells to ecosystems. 12LS1.C
Photosynthesis and cellular respiration (including anaerobic processes) provide most of the energy for life processes. Plants or algae form the lowest level of the food web. At each link upward in a food web,
only a small fraction of the matter consumed at the lower level is transferred upward, to produce growth and release energy in cellular respiration at the higher level. Given this inefficiency, there are generally fewer organisms at higher levels of a food web, and there is a limit to the number of organisms that an ecosystem can sustain.
The chemical elements that make up the molecules of organisms pass through food webs and into and out of the atmosphere and soil and are combined and recombined in different ways. At each link in an ecosystem, matter and energy are conserved; some matter reacts to release energy for life functions, some matter is stored in newly made structures, and much is discarded. Competition among species is ultimately competition for the matter and energy needed for life.
Photosynthesis and cellular respiration are important components of the car- bon cycle, in which carbon is exchanged between the biosphere, atmosphere, oceans, and geosphere through chemical, physical, geological, and biological processes. 12LS2.B
Common Core Standards
Math standards can be easily incorporated into this topic.
Math 188.8.131.52 Make reasonable estimates and judgments about the accuracy of values resulting from calculations involving measurements.
Students may look at energy levels and the percent that is transferred to the next level in a food chain.
Math 184.108.40.206. Design simple experiments and explain the impact of sampling methods, bias and the phrasing of questions asked during data collection.
This standard can be addressed with all data collection methods. Statistical analysis and Graphing can be done
Common Core Language Arts: Students can write a laboratory report in the proper form and using their knowledge of technical writing skills. Common core standards addressed:
RST.9-10.1. Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.
RST.9-10.2. Determine the central ideas or conclusions of a text; trace the text's explanation or depiction of a complex process, phenomenon, or concept; provide an accurate summary of the text.
RST.9-10.3. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.
- Plants produce oxygen for our benefit.
- Sunlight is a food. Glucose is not made from sunlight, rather it is made of carbon dioxide and water. The sunlight just provides the energy required to make the bonds.
- Many students know that water is absorbed through a plants roots, but they assume that water is the primary growth material for the plant. Other studies show that students often think minerals are food for the plant or that they directly contribute to photosynthesis (Driver, et al. 1994)
- Energy accumulates in an ecosystem so that a top predator has all the energy from the organisms below it.
- Some students believe matter is conserved during decay , but do not know where it goes (Leach et al., 1992 - Atlas Vol II pg 32). See this page. Matter is conserved during decay - it is recycled.
After studying both photosynthesis and respiration, students are asked to make connections between the two processes. They are given aquatic plants (Elodea) and pond snails (representing animals) and bromothymol blue. Bromothymol blue is an indirect indicator for the presence of carbon dioxide.
Groups of students were given a different hypothesis to test about the connection between plants and animals (photosynthesis and respiration). Examples included: plants give off carbon dioxide in the light or in the dark. animals gives off carbon dioxide plants use carbon dioxide that animals give off.
The students determine how they would set up the experiment and let it sit overnight in either the light or dark. Some of the hypothesis are easier to test than others which allows for differentiation of student abilities and interests. (See NSE standard 220.127.116.11.2)
This project can be expanded by giving students dissolved oxygen kits, and materials to inhibit light like screens, black paper etc. Students can grow algae under a variety of conditions of light intensity and determine the dissolved oxygen in the system using relatively simple chemical tests - This demonstrates that the more light given to the system, the stronger the algae growth and consequently, the greater the amount of oxygen in the water. (See Vernier probes for dissolved oxygen)
Suggested Labs and Activities
18.104.22.168.1 Elicit student thinking by showing a time lapsed video of a seed growing into a plant. Have the students draw an annotated drawing to the question, "How did the seed change into a seedling and finally into a plant?" Have students write paragraph explaining their drawing.
22.214.171.124.1 Students mass out three batches of seeds weighing 1.5 g. Students decide on various experimental treatments to the seeds and predict will add the most biomass. (i.e seed on moist paper towels in the light, in the dark, dry paper towel in the light, etc). after one week, they mass the seeds again. (also applies to NSE 126.96.36.199 and 188.8.131.52)
184.108.40.206.1 Floating Leaf disk lab -Leaf disks float, normally. When the air spaces are infiltrated with solution the overall density of the leaf disk increases and the disk sinks. The infiltration solution includes a small amount of Sodium bicarbonate. Bicarbonate ion serves as the carbon source for photosynthesis. As photosynthesis proceeds oxygen is released into the interior of the leaf which changes the buoyancy--causing the disks to rise. Since cellular respiration is taking place at the same time, consuming oxygen, the rate that the disks rise is an indirect measurement of the net rate of photosynthesis.
By adding the same nutrients to algae cultures, eutrophication can be simulated and experimented with. Dissolved oxygen levels can be taken to show that increased levels of nitrogen and phosphorous lead to increased plant growth (increase in oxygen) with decreased oxygen when the plants over-crowd, block out light and start to die. (Great example for NSE 220.127.116.11) This could be expanded through experimentation with various algae and their usefulness as bioremediators.
18.104.22.168.2 Energy Bucket Game
Students are each given a roll in a food chain of varying lengths. The first food chain consists of a producer only, the second has a producer and a primary consumer, the third has a producer, primary and secondary consumer. Students line up in the food chain between the energy source (a five gallon bucket of water) and the collecting source (bucket at the end of the chain). Students are each given a plastic cup with at least 4 holes punched into the bottom of it. The pass the water from the source to the collecting bucket from person to person down the chain with the producer counting the number of times the cup was filled at the source. At the end of the game (when the source is finally empty and the students are slightly damp) they measure the amount of water in the end buckets in relation to the amount taken from the source. Students will quickly see that the longer the food chain the less energy (water) is collected at the end. This leads to a discussion of the ten percent rule and the trophic levels in food chains.
Annotated drawing (Koba & Tweed. Hard to Teach Biology Concepts NSTA Press pg 82)- Drawing uses the right brain to visualize and solve problems and allows thinking in a visual language. Drawing can be used to assess science concept knowledge, observational skill,s and ability to reason. They also allow students to explore their own understanding about a concept. Annotated drawings require students to select, organize and integrate ideas.
Concept cartoons - gives different responses. Students must choose the one they think is the most correct. In other situations, students may say "I don't know". But with concept cartoons, there is examples of answers. So students are more comfortable with choosing one response. But they have to defend their choice making them "dig deeper" into their thinking.
Science notebooks are good place for students to record their thinking /drawings for formative assessments. They can go back and review and revise their drawings as they change their thinking.
Concept maps connecting photosynthesis and respiration. Group Concept maps are powerful in the learning process.
Inquiry labs where students ask their own question, design an experiment testing different variables on photosynthesis. (22.214.171.124.1 cross reference)
List, group, label strategy - students place pictures into groups and then explain why they place them in the grouping. Example: all pictures are part of a food chain, all pictures are biomes, etc. - put in food chains/energy
Snail & Elodea lab (see vignette)
- photosynthesis - process used by plants and other autotrophs to capture light energy and use it to power chemical reactions that converts carbon dioxide and water into oxygen and carbohydrates such as sugars and starches
- respiration- process that releases energy from food in the presence of oxygen.
- glucose - traditional energy storage molecule - a sugar that when broken down into carbon dioxide energy is released which can be used by organisms.
- carbon dioxide - The molecule that is left after glucose is broken down in respiration or is used to make glucose in photosynthesis
- water - a product of cellular respiration and a requirement for photosynthesis in the process of assembly glucose.
- oxygen - a product of photosynthesis and a requirement of respiration in the break down of glucose.
- ATP - Adenosine triphosphate. A molecule used by cells to store and release energy.
- Equation for Photosynthesis: Carbon dioxide + water + energy (form is Sunlight) --> Glucose + oxygen
- Equation for Respiration: Oxygen + glucose --> Carbon dioxide + water + energy (form is ATP)
- Producer - organisms that make their own food through photosynthesis.
- Consumer (primary, secondary, tertiary) - organisms that rely on others organisms for their energy and food supply
- Decomposers - organisms that break down and obtain energy from dead organisms
- Food Chain -a series of steps in which organisms transfer energy by eating and being eaten.
- Food Web - a complex series of food chains based on the fact that most organisms eat more than one kind of food.
- Autotroph - An organism that is able to capture energy from sunlight or chemicals and use it to produce its own food.
- Heterotroph - Organisms that obtain food by consuming other living things.
- Energy pyramid - Shows the relative amount of energy contained in each trophic level of a given food chain or food web.
- Trophic level - Each step in a food chain or food web.
Includes actvities such as Exploring Photosynthesis with Fast Plants: This activity for middle, high school or post-secondary students is an engaging aboratory investigation, which can be used to explore and gather evidence for the products of photosynthesis (and cellular respiration). Many resources here.
This topic crosses over well with many social studies topics including geography and human society. The ability to do do photosynthesis and the production of food resources has great influence on societal needs and values.
Agriculture and Environmental Science - Most farming practices rely heavily on the processes of photosynthesis and respiration. Topics such as eutrophication, nitrogen fixation, fossil fuel acquisition all rely on nutrient cycling and are connected intimately to these standards.
Assessment of Students
Formative - 126.96.36.199.1 Show a picture of a tree and ask " Where does a Plant's Mass Come From?
ANSWER:The mass comes from carbon dioxide that was transformed into sugar through photosynthesis. The mass contributed from carbon dioxide is much greater than the mass from water. One molecule of carbon is 44 atomic mass units andn water is 18 atomic mass units.
Summative: 188.8.131.52.1 Suppose you water a potted plant and place it by a window in a transparent, airtight jar. Predict how the rate of photosynthesis might be affected over the next few days. What might happen if the plant was left there for several weeks. Explain.
Answer: As the plant depletes it carbon dioxide supply, the rate of photosynthesis will decrease. Over several weeks the plant will die as it is not able to obtain energy.
184.108.40.206.1 Summative Concept map - showing the connections between photosynthesis and respiration
Answer: The glucose formed in photosynthesis is the reactant broken down in glycolysis (the first step of respiration). Carbon Dioxide is released in respiration is taken in plant leaves and used for photosynthesis and the oxygen released in photosynthesis is usedAnswer: Energy flows in in forming ATP in respiration.
Students discuss what happens to the stored energy in grass as organisms eat one another in a food chain relationship of a fox, snake and grasshopper?
Answer: Most of the energy ended up in the grasshopper. As one organism is consumed by another the total amount of energy from that food passed from one level to the next is generally
220.127.116.11.2Summative - Compare the flow of energy and the flow of matter in an ecosystem
ANSWER: one direction from the producers to the top level consumers wit on 10% of the available energy going to the next trophic level.
Assessment of Teachers
1. What is the definition of food? How is this related to energy? Explain which of the following would qualify as food; sunlight, sugar, carbon dioxide, minerals, fertilizer, soil, water, leaves, oxygen, chlorophyll, vitamins, protein, fat. Explain why some of these qualify as food and others do not.
Possible Answer: Food by definition is a chemical that when consumed by an organism released chemical energy in a form usable by the organism. Sugar, Protein and Fat qualify as a food.
2. Experts have identified photosynthesis as a hard to teach topic. What are the barriers to effectively teaching this topic to students?
Possible Answer: Photosynthesis is a relatively abstract concept involving a working knowledge of chemistry and physics. Photosynthesis can be learned at a variety of levels from superficial to very deep.
3. The first law of thermodynamics states that neither matter nor energy can be created or destroyed. How does this apply to photosynthesis and respiration?
Possible Answer: The earth's system is an open system with constant energy input from the sun. As chemical bonds in the sun are broken and formed chemical energy is released in the form of light energy. This light energy is captured by the chlorophyll molecules as electrons are excited and a water molecule is split. The energy in these electrons is used to make ATP. The energy in the ATP molecule is transferred to the bonds between the carbon atoms (from carbon dioxide) as they are joined to make glucose. The energy is still stored in the molecular bonds until they are transferred to the organism in order to do work. Ultimately the energy is lost as heat. Atoms can also be traced from carbon dioxide and water to glucose and oxygen. No atom is created and no atom is lost. They are merely used over and over again.
Struggling and At-Risk
Hands on activities related to relevant occurences in the student's life are particularly effective. One good example would be the construction of a calorimeter using a coffee can. Students can test various food products and look for the energy content. Taking this into the realm of fossil fuels and measuring the energy content of these verses biofuels can also be quite applicable.
Annotated drawing - students can explain their drawing when they may not know the correct terms. The use of pictures may be helpful.
Students can search the Internet for amazing facts on ATP
Students can research and explain Von Helmonts famous experiment on "Where does the mass of a plant/tree come from?" or Pristley's experiment "Purifies" ari
Students can explore and explain the "endosymbiotic theory" proposed by Lynn Margulis. What evidence do we have that mitochondria and chloroplasts have descended from bacteria? Debate the theory, siting both pros and cons. How can mitochondria and chloroplasts be used to study the lineage of organisms? (This would connect to standards 9.4.3)
Students can explore the cycles of matter and energy as it related to their own cultural situation and those of others. Some examples may include energy uses involving both food sources and fuels. It may also be interesting to look at the plant species and life cycles in different parts of the world and relate them to production of food (example - deciduous trees in temperate zones, palm trees at the equator). This is excellent for all students but if multicultural students can talk about their "homeland" it will introduce a quality of ownership for the knowledge.
Annotated drawing - require students to select, organize and integrate ideas.
This allows students to explain their thinking when writing may be difficult.
Paper models or molecular models of carbon dioxide, water, oxygen and sugar can be manipulated through the process of photosynthesis and respiration. This helps to make an abstract concept much more concrete and help in understanding for all students but especially those with learning disabilities.
Students working in groups sharing their annotated cartoons. Students discussing/deciding on a variable to test in seed germination or oxygen production in photosynthesis. Students will be conducting experiments, collection data, analyzing data and drawing conclusions.
Parents can share some of their concerns in gardening. Amount of light in plant choice, soil type, time in blooming and others. Students and parents may design a garden together.