Plant Growth

 

Plants use hormones to control growth and responses to light/gravity.

 

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Positive means ‘in the direction of that thing’. So in gravitropism, positive refers to the same direction as gravity even though it makes the plant grow downwards.

 

The main growth hormone in plants is auxin. They accumulate on the shaded side of the plant and cause cell elongation/growth.

 

Phototropism  

1. Light hits one side  

2. Auxins move to shaded side  

3. Shaded side grows faster than non shaded side → plant bends toward light  

→ More photosynthesis

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If light is distributed evenly or not provided at all, the plant will grow up straight.

 

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Gravitropism  

• Roots grow down (positive) → anchor + water  

• Shoots grow up (negative) → light  

→ Works even in dark