Back to topics

Where does the wood in a growing tree come from?

A tree can gain a great deal of wood without removing the same mass of soil from beneath it. Photosynthesis brings carbon from atmospheric carbon dioxide into sugars that help build the plant. Water and mineral nutrients still have their own essential roles.

3–5 min

Questions you could explore

  • Why would measuring a tree's fresh mass give a different answer from measuring its dry mass?
  • How could a mass balance separate carbon arriving from the air from water and minerals entering through roots?

Start reading

Ready to try your ideas aloud?

Your topic carries over. Record up to 2½ minutes, depending on your plan.

Nature and biology

How does a honey bee dance give directions?

A returning honey bee can communicate about food without leading every other bee to it. The direction and duration of its waggle dance carry information that other bees can use beyond the dark hive.

3–5 min

How does a honey bee dance give directions?

Nature and biology3–5 minA returning honey bee can communicate about food without leading every other bee to it. The direction and duration of its waggle dance carry information that other bees can use beyond the dark hive.

Nature and biology

How can an octopus change color so quickly?

An octopus can alter the appearance of its skin far faster than a new coat of pigment could grow. Tiny structures already in the skin control what becomes visible, with pigment and reflected light playing different roles.

5–7 min

How can an octopus change color so quickly?

Nature and biology5–7 minAn octopus can alter the appearance of its skin far faster than a new coat of pigment could grow. Tiny structures already in the skin control what becomes visible, with pigment and reflected light playing different roles.

Nature and biology

Finding prey through returning echoes

An echolocating bat uses the delay and character of returning sound to follow a target. Its calls can change as it approaches prey, connecting the sound it sends with the information it needs next.

3–5 min

Finding prey through returning echoes

Nature and biology3–5 minAn echolocating bat uses the delay and character of returning sound to follow a target. Its calls can change as it approaches prey, connecting the sound it sends with the information it needs next.

Where does the wood in a growing tree come from? | Speech Topic | speaking.app