When a seed germinates, how does it knows which direction is up?
In: 90
Gravity, this is why trees on ledges emerge going up to the sky instead of out of the ground perpendicularly. Seeds have internal mechanisms to determine which way gravity is pulling it and grow in the opposite direction
Gravity – plants are incredible. It’s fascinating watching how they grow, especially how they respond to light once they’ve sprouted.
The initial gut reaction is to say gravity… And for the most part on earth this is kind of correct, but it is not the whole story.
There is a good explanation from NASA on actual testing, it is partially gravity, it is partially light gradient, it is partially a nutrient gradient…
[From NASA ](https://youtu.be/9MfWARdoF-o)
Plant cells produce dense starch structures inside themselves, which are pulled toward the bottom of the cell by gravity. This causes a plant hormone called auxin to be released — in root cells, this is in the direction of gravity; in shoots it’s the other way. Auxin then tells the plant cells which way to grow more in order to curve towards or away from gravity.
https://en.wikipedia.org/wiki/Amyloplast
There’s tons of different methods plants use , and it’s really hard to say which one is the most used
But here’s a few them an small eli5 of each
1. Water gradients/nutrient gradients. So I want you to think of a coffee filter with coffee grounds on it , when you pass that hot water through it you get coffee come out the bottom since the water dissolved and carried some of the stuff with it down , well as water gets more saturated with stuff less can dissolve into it , this means that a small gradient will form of more nutrients as you go deeper , seeds can use that gradient to determine which direct water is flowing in to send their roots which is often down but also how you get roots that grow along surfaces as well
2. Gravity. As much as seeds are pretty solid , just like you and me they have some little bit of movement as they grow , some of these bits that grow are denser then the others so essentially settle near the bottom from gravity which can usually signal where the root should shoot out
3. Heat. The vast majority of seeds are designed to be on the surface or barely covered after being dispersed , usually it’s during a time when the air is generally much warmer then the ground so even when submerged the top layer are warmer then the lower ones so by using temperature they can tell what side is likely the surface , some seeds even need heat to germinate since it’s part of how they tell it’s time to grow
4. Light . This one is the most basic and easy to understand , plants use light to make food and will grow towards it , they often will shoot roots in the opposite direction.
Gravity. This is why growing plants in Space is a bitch and why we use things like a centrifuge to simulate gravity
Latest Answers