AAAS Conference on Developing Textbooks That Promote Science Literacy
February 27-March 2,
American Association for the Advancement of Science
Student-Focused Curriculum Materials Development: The “Food For Plants” Story
Kathleen J. Roth
Michigan State University
February 25, 2001
Content Organization And Background For The Food For Plants Unit
Content Organization and Background for This Unit
Central Question: How do plants get their food? What is food for plants?
The desired student response to the central question at the end of the unit:
This is how plants make their food inside themselves. They take in carbon dioxide (from the air) through the holes in their leaves, and water through their roots. The carbon dioxide and water travel inside the plant to cells in the leaf. The leaf is made up of many cells, and some of these cells are the places where the plant makes food. These cells need the water and carbon dioxide and also sunlight to make the food. Sunlight provides the energy for this chemical reaction. Chlorophyll is the green pigment in leaf cells that can catch the sun’s light and use it for changing carbon dioxide and water into energy-containing food. This is the only substance that can catch light energy and use it to change light energy into energy stored in food. Humans cannot make their own food because we do not have things that plants have such as chlorophyll. The carbon dioxide and water are transformed into a totally new substance that contains energy -- it is food in the form of sugar.
Because a totally new substance is made, this process is an example of a chemical change. This chemical change that happens inside plants is called photosynthesis. It is a very complicated process and scientists still do not completely understand it.
After the food is made in the leaf cells, it has to travel all over the plant to feed all the cells in the plant. The whole plant is made up of cells and each cell needs food to live. So food travels through the veins in the plant to all the cells. Sometimes a plant makes more food than it can use right away. So it stores food in what we call fruits and vegetables (like the carrot, potato, apple).
Food also gets stored in the seeds. Then when the seed falls off the plant and lands in a good spot where it gets water, the embryo inside the seed can start to grow using food stored in the seed's cotyledon. That food came from photosynthesis done by the mother plant! When the embryo has used all the food up in the cotyledon, it has to start making its own food (photosynthesis). A seed can start to grow in the dark because it can use food stored in the cotyledon, but it needs light to stay alive so that it can make its food.
Objectives and Main Ideas: Matching to Standards and Benchmarks
Food For Plants Unit: Objectives
- Describe the functions of seed parts.
- Identify examples and non examples of food as energy-containing material.
- Describe the process of food production, food storage, and food use in plants.
- Describe evidence that plants make and store food.
- Identify energy and matter changes during the food making process in plants.
- Use models to represent processes in the plant that you cannot see.
- Know that hypotheses are valuable even if they turn out not to be true, if they lead to fruitful investigations (Benchmarks, 6-8)
- Develop descriptions, explanations, predictions, and models using evidence. (NSES, 5-8)
- Think critically and logically to make the relationships between evidence and explanations. (NSES, 5-8)
- Trace all food energy back to plants and photosynthesis, categorizing plants as producers and animals as consumers.
Food For Plants Unit: Main ideas
National Science Education Standards:
- Plants are producers - they make their own food. (5-8, p. 158).
- Food provides energy and nutrients for growth and development. (5-8, p. 168)
- All animals, including humans, are consumers, which obtain food by eating other organisms. (5-8, p. 158)
- Plants use solar energy to combine carbon dioxide and water into complex, energy rich compounds. This process of photosynthesis provides a vital connection between the sun and energy needs of living systems. (9-12, p. 184)
- The energy for life primarily derives from the sun. Plants capture energy by absorbing light and using it to form energy-rich food. (9-12, p. 186)
- Evidence consists of observations and data on which to base scientific explanations. (p. 117)
- Models are tentative schemes or structures that correspond to real objects, events, or classes of events, and that have explanatory power. Models help scientists and engineers understand how things work. Models take many forms. (p. 117)
- Scientific explanations incorporate existing scientific knowledge and new evidence from observations, experiments, or models into internally consistent, logical statements (p. 117).
- Different terms, such as hypothesis and theory, are used to describe different types of scientific explanation (p. 117).
- It is normal for scientists to differ with one another about the interpretation of the evidence or theory being considered. Ideally, scientists acknowledge such conflict and work towards finding evidence that will resolve their disagreement. (5-8, p. 171).
Benchmarks for Science Literacy
- Food provides the fuel and building material for all organisms. Plants use energy from the light to make sugars from carbon dioxide and water. This food can be used immediately or stored for later use. Organisms that eat plants break down the plant structures to produce the materials and energy they need to survive. (6-8, p. 120)
- Some source of energy is needed for all organisms to stay alive and grow. (3-5, p. 119)
- Almost all food energy come originally from sunlight. (6-8, p. 120)
- Energy appears in different forms. (6-8, p. 85)
- Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe them directly. (6-8, p. 269)
- Scientists’ explanations about what happens in the world come partly from what they observe, partly from what they think. Sometimes scientists have different explanations for the same set of observations. That usually leads to their making more observations to resolve the differences. (3-5, p. 11)
- Scientists do not pay much attention to claims about how something they know about works unless the claims are backed up with evidence that can be confirmed and with a logical argument. (3-5, p. 11)
- Graphs, diagrams, sketches, maps, and stories can be used to represent objects, events, and processes in the real world, although such representations can never be exact in every detail.