This might be a stupid question, but, How does a seed "know" which direction the surface is?

Question

Or does it just grow in all directions and the side that reaches the surface is the one that becomes the "top."

Answer 1

Maybe it heads toward the warmth (or sun).

Answer 2

Geotropism: positve, negative, transversal.

Answer 3

the seed is attracted to the light since that's where it gets a lot of it's nutrients from. Since the light generally comes from the "top" it grows in that direction.

Answer 4

the plant will grow towards the surface where it is warm and there is sunlight (the plant is drawn to the sunlight)-- while the roots will remain down and in the cooler, moist soil

Answer 5

Gravity - it knows which direction is down and so it grows in the opposite direction.

Answer 6

gravity. Why do so many people think its light ???   Its gravity. Mother Nature is smart....................

Answer 7

If I remember my biology class correctly, the hormone that triggers root growth tends to settle in the lowest part of the seed due to gravity.  Here's another idea; also, this source states that scientists aren't sure on the exact mechanism:

Answer 8

light and heat.

when you put a seed into it it tries to reach the top of the soil because of the light.

its funny,because it kinda does "grow" in all direction, as in you can make the roots the plant and the plant the roots but turning it upside down (some plants)

but ya, heat and light.

Answer 9

They use a Co2/O2 & heat concentration gradient.  There is more Co2 towards the surface of the soil than deeper into it.  The air diffuses downward into the soil, the deeper you go, the soil is more dense and there is less Co2.  Therefore the germinating seed seeks out this gas source and grows towards it.

Answer 10

lol velvet, i think because seeds are never that deep in the ground, light can always reach it in some way, it can sense/feel this and grows 'towards the light!'

good q.

Answer 11

there are only theories concerning this. No one has ever proven exactly how a seed knows how to grow the way it does. A large majority of the scientific community believes it is probablt a combination of both gravity and sunlight. Check out the Statolith theory (plant perception) it explains the widest believed theory on this subject.

Answer 12

they did a show about that on tv, ill find the video but it will grow towards the light

http://www.youtube.com/watch?v=QYAeG0j-S...

Answer 13

Plants are affected by gravity, so they do know which way is up and which way is down. Plants also know that water is found down in the ground and sunlight is found up in the sky. All plants need water and sunlight. The roots of a plant will always grow down to find water and the stem will always grow up to find sunlight so the plant can produce food through photosynthesis.

Gravitropism [or geotropism] is a turning or growth movement by a plant or fungus in response to gravity. Charles Darwin was one of the first Europeans to document that roots show positive gravitropism and stems show negative gravitropism. That is, roots grow in the direction of gravitational pull (i.e., downward) and stems grow in the opposite direction (i.e., upwards). This behaviour can be easily demonstrated with a potted plant. When laid onto its side, the growing parts of the stem begin to display negative gravitropism, bending (biologists say, turning; see tropism) upwards. Herbaceous (non-woody) stems are capable of a small degree of actual bending, but most of the redirected movement occurs as a consequence of root or stem growth in a new direction.

The following also explains this phenomena.

Gravitropism in the root

If the root cap is removed, root growth ceases to respond to gravity. The root cap is vital for gravitropism since it contains cells with sensors called statoliths, which are amyloplasts packed with starch. Amyloplasts are a type of plastid similar to chloroplasts. Statoliths are dense organelles that settle to the lowest part of the root cap cells in response to a change in the gravity vector. This initiates differential cell expansion in the root elongation zone causing a reorientation of the root growth (see below). The location of the elongation zone is many cells above the root cap, so intercellular signal transduction must occur from the site of gravity perception, in the root cap, to the growth response in the elongation zone. As of 2002, the nature of this signal is an active area of research in plant biology.

Roots bend in response to gravity due to a regulated movement of the plant hormone auxin known as polar auxin transport. In roots, an increase in the concentration of auxin will inhibit cell expansion, therefore, the redistribution of auxin in the root can initiate differential growth in the elongation zone resulting in root curvature.

[edit] Gravitropism in the stem

A similar mechanism is known to occur in plant stems except that the shoot cells have a different dose response curve with respect to auxin. In shoots, increasing the local concentration of auxin promotes cell expansion; this is the opposite of root cells.

The differential sensitivity to auxin helps explain Darwin's original observation that stems and roots respond in the opposite way to the gravity vector. In both roots and stems auxin accumulates towards the gravity vector on the lower side. In roots, this results in the inhibition of cell expansion on the lower side and the concomitant curvature of the roots towards gravity (positive gravitropism). In stems, the auxin also accumulates on the lower side, however in this tissue it increases cell expansion and results in the shoot curving up (statolithic gravitropism).

Answer 14

the seed grows whichever way the light is which is the top!!

Answer 15

roots in plants respond to gravitational polls, which is why you can do experiments with young plants that demonstrates the roots' inclination towards the ground.

Answer 16

well as we as people grow UP it is only thought normal for plants and things to do the same, wouldn't you think? Plus it grows the way of air and openness (up)

Answer 17

No...it searches for sun and oxygen and nature tells it...that is up!!!

Answer 18

It naturally seeks out the sun light.

Answer 19

think of what plants need....of course the seed will get water underground, but it needs sunlight and air so where do you think it will grow towards

Answer 20

good question, I think it just knows. Kind of like a baby knows to cry or laugh when they're happy. It's not taught, they just "know"

Answer 21

usually you have to plnt it a certain way to grow upwards ,so no usually it doesnt but sometimes it will just follow sunlight as all plants will go towards sunlight to photosynthesisie in the daytime,and respire in the night.

Answer 22

It grows towards the light and the root of plant senses gravity and will grow downwards. You'll notice that plants always grow towards the direction of the sun or a light.

Why?

Roots will then grow 'root hairs' which absorb water from the earth. Plants need light for photosynthesis. Photosynthesis is the conversion of light energy into chemical energy. Greeek meaning photo (light) and synthesis (putting together).

Plants have a green pigment, chlorophyll, which absorbs sunlight and makes its energy available to the plant for photosynthesis.

Photosynthesis stores this energy in energy-rich molecules called carbohydrates.

While plants photosynthesis only during the day when the sun shines, plants and animals both respire 24 hours a day.

So to be able to survive - they need to know which end is up. LOL!

**Good question. It's along the lines to wondering how the ocean knows where to stop at the shoreline. Brings out the "that is amazing when you think about it".

Answer 23

Have you been smoking that Loco weed again?