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Rooting powder

Rooting powder makes stem cuttings quickly develop roots. Rooting powder contains growth hormones.

Controlling fruit ripening

Some hormones slow the ripening of fruits and others speed it up. These hormones and their inhibitors are useful for delaying ripening during transport or when fruit is displayed in shops

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Weedkillers

Selective weedkillers kill some plants but not others. This can be useful for getting rid of dandelions in a lawn without killing the grass, or getting rid of thistles in a field without killing the wheat plants. The selective weedkiller contains growth hormone that causes the weeds to grow too quickly. The weedkiller is absorbed in larger quantities by the weeds than the beneficial plants

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Auxin is produced in the tip of growing shoots.

If the tips are removed from growing shoots they cannot produce auxin, so phototropism cannot occur.

If the tips are covered, light cannot break down the auxin, so phototropism cannot then occur either

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Controlling the direction of growth

Auxin is a plant hormone responsible for controlling the direction of growth of root tips and stem tips in response to different stimuli including light and gravity.

Auxin is made at the tips of stems and roots. It's moved in solution to older parts of the stem and root where it changes the elasticity of the cells. More elastic cells absorb more water and grow longer, causing bending in the stem or root. It's thought that light and gravity can interfere with the transport of auxin causing it to be unevenly distributed.

You may have noticed that a houseplant grows towards the window and turns its leaves towards the light. It does this because light coming from the window side of the plant destroys the auxin in that side of the stem. So growth on that side slows down.

On the shaded side of the plant there is more auxin. So growth on this side speeds up. The result is that the shoots and leaves are turned towards the light for photosynthesis.

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Rooting powder contains growth hormones to make stem cuttings quickly develop roots.

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Plant hormones - Test

1.

What is a tropism?

Growth of a plant in response to a stimulus

The energy at each stage of a food chain

A hallucinogenic drug

2.

What does auxin do?

Control the amount of water a plant takes up

Control the amount of photosynthesis that takes place

Control the direction of growth in a plant

3.

What is geotropism?

A response to the light

A response to gravity

A response to the moon

4.

Which if the following is not a use of plant hormones?

Weedkiller

Rooting powder

Controlling diabetes

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http://www.youtube.com/watch?v=pi3P3uJOsN4

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http://www.youtube.com/watch?v=9UvlqAVCoqY

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The direction of plant growth

Plants need light and water for photosynthesis. They have developed responses called tropisms to help make sure they grow towards sources of light and water.

Positive phototropism in plant stems

There are different types of tropisms:

positive tropism – towards the stimulus

negative tropism – away from the stimulus

phototropism – growth in response to the direction of light

geotropism – growth in response to the direction of gravity

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Geotropisms

Auxins are also involved geotropisms. In a root placed horizontally, the bottom side contains more auxin than the top side. This makes the bottom side grow less than the top side, causing the root to bend in the direction of the force of gravity.

In a shoot placed horizontally, the bottom side contains more auxin than the top side. This makes the bottom side grow more than the top side, causing the shoot to bend and grow against the force of gravity

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http://www.youtube.com/watch?v=sQK3Yr4Sc_k

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Rooting powder

Rooting powder makes stem cuttings quickly develop roots. Rooting powder contains growth hormones

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http://leavingbio.net/plant%20responses.htm

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The Regulation of Growth

Plants’ growth is controlled by many
factors. Some of the factors are environmental and climatic while others come
from within the plants themselves.

External Environmental Factors

Some external factors that
regulate the growth of plants are light intensity, day length, gravity, and temperature.

Light- Light, obviously affects
the plants ability to grow because light is needed for photosynthesis. Through
photosynthesis the plant makes its energy carrying molecules. It is also needed
for the production of chlorophyll.

Day Length- Day length causes the plants to flower. Many other roles of day
length are being studied such as fruit and seed germination, dormancy, and leaf
loss.

Gravity- Gravity causes roots to grow down toward the soil and roots to grow
up away from the source of gravity.

Temperature- Temperature affects the rate of enzyme reaction. Higher
temperature, to a point, is best for plant growth while low temperatures are
needed for some plants to flower.

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In a shoot, the shaded side contains more auxin. This means that the shaded side grows longer, causing the shoot to bend towards the light.

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Control in plants - Test

1.

Shoots are:

positively phototropic and positively gravitropic .yes/no

negatively phototropic but positively gravitropic.yes/no

positively phototropic but negatively gravitropic.yes/no

2.

Roots are:

negatively phototropic and negatively gravitropic.yes/no

negatively phototropic but positively gravitropic.yes/no

positively phototropic but negatively gravitropic.yes/no

3.

Which statement about auxins is correct?

They move through the plant in solution.yes/no

They are involved in responses to light only.yes/no

They are involved in responses to gravity only.yes/no

4.

A phototropism involves a response to:

light yes/no

gravity yes/no

temperature yes/no

5.

Where is auxin made in a plant?

In the growing tip of a shoot or root yes/no

In the older part of a shoot or root yes/no

All plant cells can make auxins yes/no

6.

Which side of a shoot contains more auxin?

The shaded side yes/no

The side in the light yes/no

Both sides contain the same amount of auxin yes/no

7.

When a root bends in the direction of the force of gravity:

the top side grows more than the bottom side yes/no

the bottom side grows more than the top side yes/no

the top and bottom sides grow at the same rate yes/no

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Summary of the different types of tropism

Part of plant

Light stimulus

Gravity stimulus

shoot | positive phototropism (grows towards the light) | negative gravitropism (grows against the force of gravity)
root | negative phototropism (grows away from the light) | positive gravitropism (grows in the direction of the force of gravity)

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http://www.youtube.com/watch?v=HdwIcIkSoBY