B3.2.6 - Plant Hormones Flashcards
What is positive tropism?
When a part of a plant grows towards a stimulus
What is negative tropism?
When a part of a plant grows away from a stimulus
What does phototropism mean?
Growing towards light
Give an example of phototropism.
When a stem grows towards the light so a plant can photosynthesise for food
What does gravitropism mean?
It means growing in the same direction as gravity.
Give an example of gravitropism.
It is important for the roots to grow downwards as growing deeper into the soil provides more anchorage
Why is gravitropism important for germinating seeds?
When seeds are scattered they often land the wrong way up so gravitopism ensures the plant grows correctly
What is auxin?
A plant hormone that enables a plant to grow towards or away from a stimulus
Where is auxin made?
In the cells near the tips of plant shoots or roots
What does auxin stimulate?
For shoot cells to grow more but inhibits the growth of root cells
Why does the auxin response to a stimulus occur?
Because there is an uneven distribution of auxin
Why does a shoot bend towards light?
Because when light hits one side of the shoot tip, the auxin moves to the unlit side to increase the concentration of auxin. The cells respond by elongating which makes the unlit side longer and causes the shoot to bend towards the light
What happens when the light falls evenly on both sides of a shoot?
The level of auxin is evenly distributed and therefore all the cells in the tip grow at the same rate in a striaght line
Describe the role of auxins in gravitropism.
In the root and the shoot, the auxins gather on the lower side due to gravity. Therefore, the root grows more on the side with least auxin, making it bend and grow down towards the force of gravity, whilst the shoot does the complete opposite. Once both are grown the auxins are evenly spread again
