Photosynthesis
Aligned to HS-LS1-5 — Next Generation Science Standards.
What this lesson teaches
In chloroplasts, plants capture light energy and use it to combine carbon dioxide and water into glucose, releasing oxygen. The light energy becomes chemical energy stored in the bonds of sugar.
Worked examples
Example 1
A leaf in sunlight takes in carbon dioxide through its stomata and water from its roots; chlorophyll captures light to build glucose, and oxygen bubbles off as a byproduct.
Example 2
Photosynthesis runs in two stages: light reactions capture energy, and the Calvin cycle uses it to fix carbon — the second stage needs no light directly.
Example 3
The oxygen released comes from the water, not the carbon dioxide. Isotope labelling settled that in the 1940s.
Practice questions
- Identify the reactants and products of photosynthesis and where in the cell it occurs.
- Draw arrows showing how light energy ends up stored in a glucose molecule.
- Explain where the mass of a large tree mostly comes from, using photosynthesis as evidence.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Fotosíntesis
En los cloroplastos, las plantas capturan energía luminosa y la usan para combinar dióxido de carbono y agua en glucosa, liberando oxígeno. La energía luminosa se convierte en energía química almacenada en los enlaces del azúcar.
Ejemplo 1: Una hoja bajo el sol toma dióxido de carbono por sus estomas y agua de sus raíces; la clorofila captura la luz para formar glucosa, y el oxígeno se libera como subproducto.
Ejemplo 2: La fotosíntesis ocurre en dos etapas: las reacciones luminosas capturan energía y el ciclo de Calvin la usa para fijar carbono — la segunda etapa no necesita luz directa.
Ejemplo 3: El oxígeno liberado viene del agua, no del dióxido de carbono. El marcaje con isótopos lo resolvió en los años cuarenta.
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