Key Idea: All organisms need food as a source of molecules that provide chemical energy and building materials.
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Plants make their own food in the form of sugar molecules from carbon dioxide molecules and water molecules. In the process of making sugar molecules, oxygen molecules are produced as well.

These items have been aligned to more than one key idea. To view the sub-ideas click on a key idea below.

  • All organisms need food as a source of molecules that provide chemical energy and building materials.

    Students are expected to know that:

    1. Food consists of carbon-containing molecules in which carbon atoms are linked to other carbon atoms.
    2. Carbon-containing molecules serve as the building materials that all organisms (including plants and animals) use for growth, repair, and replacement of body parts (such as leaves, stems, roots, bones, skin, muscles, and the cells that make up these structures) and provide the chemical energy needed to carry out life functions.
    3. If substances do not provide both chemical energy and building material, then they are not food for an organism.
    4. Chemical energy from carbon-containing molecules is the only form of energy that organisms can use for carrying out life functions.
    5. Carbohydrates (including simple sugars and starch), fats, and proteins are molecules that are food.
    6. Light is not food because it is not made of atoms and therefore cannot provide building material, and even though substances such as water, carbon dioxide, oxygen, and various minerals provide atoms for building materials for some types of organisms, they are not food because they do not contain carbon atoms that are linked to other carbon atoms and cannot be used as a source of chemical energy.

    Boundaries:

    1. The idea that there are other atoms besides carbon (mainly hydrogen and oxygen atoms) in carbon-containing molecules that are used as food is not part of this key idea.
    2. Students are not expected to know what chemical energy is other than it resides in the molecules of substances.
    3. Although students are expected to know that any molecule with carbon atoms linked to other carbon atoms could be food for organisms, they are not expected to know which of these other carbon-containing molecules are or are not food for any particular type of organism.
  • Plants make their own food in the form of sugar molecules from carbon dioxide molecules and water molecules. In the process of making sugar molecules, oxygen molecules are produced as well.

    Students are expected to know that:

    1. Unlike animals, plants do not take in food from their environment.
    2. Plants make their own food in the form of sugar molecules by means of a chemical reaction between carbon dioxide molecules and water molecules. Oxygen molecules are also a product of this reaction.
    3. The process of making sugar molecules involves linking together carbon atoms that come from molecules of carbon dioxide.
    4. The chemical reactions by which sugars are made takes place inside the plants. In most familiar land plants, the carbon dioxide molecules that are used come from the air that enters the plant primarily through its leaves, and that the water molecules that are used in the reaction enter the plant through its roots.

    Boundaries:

    1. Although there may be limited exceptions to the generalization that unlike animals, plants do not take in food from their environment, students are not expected to be aware of those exceptions.
    2. The items do not assess knowledge of any of the chemical structures or formulas of any of the reactants or products either of the overall chemical reaction or of any of the intermediate steps, such as light-dependent and light-independent reactions.
    3. The items do not assess exceptions to the expected knowledge: that some plants, such as cacti and some other desert plants do not take in carbon dioxide through their leaves but through their stems, that some plants, such as parasitic plants, do not make their own food and obtain some or all of their food by attaching to the stems or roots of other organisms, or that in addition to plants there are other types of organisms, such as many micro-organisms, that are able to make their own food.
    4. The items do not assess the idea that light is involved in the synthesis of sugars from carbon dioxide and water.
    5. The items do not use the terms producer, consumer, photosynthesis, organic, or inorganic.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number
Knowledge Being Assessed Grades
6–8
Grades
9–12
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ME112005

The carbon dioxide used by plants comes from the air.

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ME004012

A plant's food are the sugars that it makes--not minerals, water, or carbon dioxide.

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Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8
Grades
9–12

MEM130

Carbon dioxide is food for plants (AAAS Project 2061, n.d.).

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MEM121

Minerals are food for plants (Horizon, n.d.; Vaz et al., 1997).

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MEM119

Water is food for plants (Horizon, n.d.; Lee & Diong, 1999; Vaz et al., 1997, Wandersee, 1983).

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MEM017

Plants use oxygen during photosynthesis (Horizon Research; Wandersee, 1983).

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MEM015

Carbon dioxide is absorbed through the roots of plants (Simpson & Arnold, 1982).

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Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.