system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a seed "know" which way is down or up to grow?

Edit: I know it has to do with gravity. I'm asking the biological proccess that makes a seed know which way to go.
gpt
Plants can sense gravity due to special containers (organelles) that store starch in a plant cell. The starch is rather dense compared to the rest of the cell so that the container will be affected by gravity. The containers are entangled in a mesh (actin) which can sense the direction they are moving. Based on these signals a special hormone (auxin) is distributed in the shoot to indicate the growth direction.
This is only one of many possible mechanisms.