Plant Growth and Responses

22.5 Plant Hormones and Responses

KEY CONCEPT

Plant hormones guide plant growth and development.

22.5 Plant Hormones and Responses

• Plant hormones are chemical messengers.

– produced in one part of an organism
– stimulates or suppressesactivity in another part

22.5 Plant Hormones and Responses

– ending seeddormancy
– Stimulates germination,

shoot growth, and
flowering

• GIBBERELLINS are plant hormones that produce dramatic

increases in size.

22.5 Plant Hormones and Responses

– some fruits picked before

they are ripe

– sprayed with ethylene to

ripen when reach
destination

• Ethylene causes the ripening of fruits.

22.5 Plant Hormones and Responses

• Auxins are involved in the lengthening plant cells in the

apical meristem or root tip.

– stimulates growth of primary stem

22.5 Plant Hormones and Responses

– final stage in celldivision
– involved in growth of side branches

• Cytokinins stimulate cytokinesis.

22.5 Plant Hormones and Responses

A tropism is the movement of plant in response
to an environmental stimulus.

Plants can respond to light, touch, gravity, and seasonal
changes.

22.5 Plant Hormones and Responses

Phototropism is the
tendency of a plant to
grow towardlight.

– auxins build up on

shaded side of
stem

– cells on shaded

side lengthen

– causes stem to

bend toward light

22.5 Plant Hormones and Responses

Positive Thigmotropism:
climbingplants and vines
Tendrils emerge and wrap
around anything they touch.

Thigmotropism is a plant’s response to touch.

Negative Thigmotropism:
roots grow around obstacles.

22.5 Plant Hormones and Responses

– Some plants close when

touched. (mimosa)

– Some responses allow

plants to capturefood.
(venus fly trap)

• Some plants have rapid responses not involving growth.

22.5 Plant Hormones and Responses

– positive gravitropism is roots growing downward
– negative gravitropism is shoots growing upward

Gravitropism is a plant’s growth or turning in response
to gravity.

22.5 Plant Hormones and Responses

– shorter daylight triggers some plants to flower
– longerdaylight triggers leaves to change color.

Photoperiodism is a response to seasonal changes in
daylength.

22.5 Plant Hormones and Responses

Hydrotropism (positive) is a response to grow towards
water.

Multiple Choice

A plant's movement in response to any stimulus

• dormancy

• tropism

• hibernation

• pollination

Multiple Choice

Which hormone promotes seed germination?

• abscisic acid

• ethylene

• gibberellin

• auxin

Multiple Choice

Where is auxin formed

• Tip of stem and root

• Leaves

• Embryo

• All

Multiple Choice

Auxins are responsible for _____________ of a plant

• Colour change

• Watering

• Phototropism

• Growth

Multiple Choice

Stimulates cell division and

lateral growth/side branches

• auxin

• cytokinins

• gibberellin

• ethylene

Multiple Choice

Which plant hormone casues ripening and is natrually produced by plants?

• auxin

• gibberellin

• ethylene

• cytokinin

Multiple Choice

What is the role of auxin that causes a plant to bend towards light?

• The concentration of auxin in the plant increases when there is light.

• Auxin causes uniform growth on every stem.

• Auxin causes cells that are on the dark side to grow faster.

• Auxin causes the increase in the number of plant cells.

Multiple Choice

My banana has become black and soft. This is because of

• Auxins

• Cytokinins

• Ethylene

• Gibberellins

Multiple Choice

A plant's response to touch

• thigmotropism

• geotropism

• hydrotropism

• dormancy

Multiple Choice

The movement of roots toward the ground or the movement of stems away from the ground

• hydrotropism

• geotropism

• thigmotropism

• phototropism

Multiple Choice

What is the stimulus in this example?

• Internal

• Light

• Touch

• Temperature

Multiple Choice

A plant growing in response to a greenhouse light.

• Geotropism

• Phototropism

• Thigmotropism

• Hydrotropism

Multiple Choice

Venus Flytrap flower reacts to a bug.

• Thermotropism

• Negative Geotropism

• Thigmotropism

• Hydrotropism

Multiple Choice

Sunflowers turning towards the sun.

• Hydrotropism

• Phototropism

• Thigmotropism

• Geotropism

Multiple Choice

If a plant experiences a gravitropism, then it will do what?

• Grow toward or away from light. 

• Grow away from light. 

• Grow toward light.

• Grow in response to gravity. 

Multiple Choice

What type of tropism response to gravity?

• Hydrotropism

• Phototropism

• Thigmotropism

• Gravitropism

Multiple Choice

A change in an organism’s external environment that causes a response from the organism.

• External Stimuli

• Internal Stimuli

• Energy Transformation

• Turgor Pressure

Multiple Choice

A change in an organism’s internal environment that causes a response from the organism.

• External Stimuli

• Internal Stimuli

• Energy Transformation

• Turgor Pressure

Multiple Choice

The growth (or response) of a plant towards or away from TOUCH.

• Phototropism

• Geotropism

• Thigmotropism

• Hydrotropism

Multiple Choice

An organism’s ability to maintain steady internal conditions when outside conditions change, also called maintaining balance.

• Homeostasis

• Hormones

• Hydrotropism

• Homer

Multiple Choice

In plant cells, the force, exerted by the flow of water, within the cell that pushes the plasma membrane against the cell wall. This force gives plants structure and helps them stand up and not wilt.

• External Stimuli

• Internal Stimuli

• Energy Transformation

• Turgor Pressure

Multiple Choice

Why do plants develop tropisms (which help them maintain homeostasis and stay alive)?

• Plants need food and water to live. They grow towards sources of food in the soil in order to eat.

• Plants depend on people to keep them alive and well. Tropisms are designed to help people understand why plants only respond when people water them and keep them in the sunlight.

• 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.

• Tropisms are not important for plant growth and homeostasis. The correct answer is not shown here.

Multiple Choice

The movements in a plant in response to light

• phototropism

• geotropism

• hydrotropism

• thigmotropism