Students who demonstrate understanding can: Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.
Clarification statement: Emphasis is on tracing movement of matter and flow of energy.
Assessment boundary: Assessment does not include the biochemical mechanisms of photosynthesis.
Official wording from the Next Generation Science Standards (NGSS Lead States, 2013). NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the NGSS were involved in the production of this page, and they do not endorse it. View on nextgenscience.org
Where does the mass of a giant tree come from? Most students guess the soil, yet the surprising answer is the air. During photosynthesis, plants, algae and many microorganisms take in carbon dioxide from the atmosphere and water from their surroundings and use energy from sunlight to rearrange those atoms into sugar. Oxygen is released as a by-product. The sugar becomes the raw material the plant uses to build roots, stems, leaves and wood, or it is stored for later.
Students construct an explanation that tracks two separate things. Matter (atoms) cycles: carbon atoms move from carbon dioxide in the air into plant sugars, then into animals that eat the plants, and back to the air when organisms respire or decompose. Energy flows: it arrives as sunlight, is stored in the chemical bonds of sugar, and is eventually released and lost as heat. Matter is recycled, but energy is not.
The biochemical steps of photosynthesis are outside this standard. What matters is the inputs, outputs and the role photosynthesis plays at the start of almost every food chain.
Soil supplies water and small amounts of minerals, but a plant's sugar, and most of its mass, is built from carbon dioxide in the air during photosynthesis.
Plants carry out cellular respiration all the time, day and night, to release energy from the sugar they made. Photosynthesis only happens when light is available.
Atoms are reused again and again, but energy that arrives as sunlight is eventually lost as heat. Ecosystems need a constant input of light energy.
For the plant, the useful product is sugar. Oxygen is released as a by-product, even though it matters a great deal to other organisms.
A willow seedling planted in 90 kg of dry soil was watered for five years. The tree gained about 74 kg, but the soil lost only about 0.06 kg. Explain where the tree's new mass came from.
Answer: The tree's mass came mostly from carbon dioxide and water combined into sugar by photosynthesis, using light energy; the soil supplied very little.
Begin with the question about where a tree's mass comes from and collect predictions before showing a classic soil-mass data set. Follow with a sealed jar or indicator investigation, such as aquatic plants in bromothymol blue, so students see carbon dioxide being used up in light.
Ask students to draw two kinds of arrows on the same diagram: one color for matter (carbon dioxide, water, sugar, oxygen) and another for energy (light, stored chemical energy, heat). Keeping the two separate is the heart of the standard.
Original questions written for this standard. Choose an option or type your answer, then press Check. Every question has a worked explanation.
Answer: A) Carbon dioxide
Carbon dioxide provides the carbon atoms that become part of the sugar made during photosynthesis.
Answer: D) Carbon dioxide from the air
The carbon in sugar and wood comes from carbon dioxide. Sunlight provides energy, not mass.
Answer: oxygen (also accepted: o2)
Photosynthesis releases oxygen into the air or water.
Answer: B) Light from the Sun
Light energy powers photosynthesis and is stored in the chemical energy of sugar.
Answer: A) Matter cycles, but energy flows through and is lost as heat
Atoms are reused, while energy enters as light and leaves as heat.
Answer: sugar (also accepted: glucose, sugars)
Sugar (glucose) is used to build new plant material and to release energy.
Support an argument that plants get the materials they need for growth chiefly from air and water.
A full lesson with slides, activities and an exit ticket on photosynthesis, matter and energy, pitched to grades 6-8 and editable in PowerPoint or Google Slides.
Make a lesson βA printable, differentiated worksheet on MS-LS1-6 with an answer key, ready in about a minute.
Make a worksheet βTurn photosynthesis, matter and energy into a quiz students answer online that marks itself, with a class summary for you.
Build a test βStudents should know the inputs and outputs, but the assessment boundary excludes the biochemical mechanisms of photosynthesis.
Photosynthesis brings matter and energy into food webs, which is developed further in MS-LS2-3.