VCE BIOLOGY

www.drlakshmisharma.comDr Lakshmi Sharma

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Plants Responding to Environment

RESPONDING TO THE ENVIRONMENT

• Plants do not have specific receptors.

• Hormonal response to stimuli, slow.

How do Plants Respond to the Environment?

5 Minutes to Discuss & Answer in Pairs

How do plants respond to the environment

The environmental stimulus causes a sensitive cell to produce a particular hormone

StimuliTwo types of Stimuli:

ChemicalPhysical

Can you explain the difference between these stimuli ?

Types of Stimuli

Geotropism

Types of Stimuli

Geotropism

Reaction to gravity

Types of Stimuli

Geotropism

Reaction to gravity

Phototropism

Types of Stimuli

Geotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Types of Stimuli

Geotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Types of Stimuli

Geotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Types of Stimuli

Geotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Hydrotropism

Types of Stimuli

Geotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Hydrotropism

Reaction to moisture (water)

Types of StimuliGeotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Hydrotropism

Reaction to moisture gradient (water)

Thigmotropism

Types of StimuliGeotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Hydrotropism

Reaction to moisture gradient (water)

Thigmotropism

Types of StimuliGeotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Hydrotropism

Reaction to moisture gradient (water)

Thigmotropism

Reaction to touch

Types of StimuliGeotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Hydrotropism

Reaction to moisture gradient (water)

Thigmotropism

Reaction to touch

Thermotropism

Types of StimuliGeotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Hydrotropism

Reaction to moisture gradient (water)

Thigmotropism

Reaction to touch

Thermotropism

Reaction to temperature

Types of StimuliGeotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Hydrotropism

Reaction to moisture gradient (water)

Thigmotropism

Reaction to touch

Thermotropism

Reaction to temperature

Chemotropism

Types of StimuliGeotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Hydrotropism

Reaction to moisture gradient (water)

Thigmotropism

Reaction to touch

Thermotropism

Reaction to temperature

Chemotropism

Reaction to chemicals

Types of StimuliGeotropism

Reaction to gravity

Phototropism

Reaction to light and different wavelengths

Photoperiodism

Reaction to the length of light and dark periods

Hydrotropism

Reaction to moisture gradient (water)

Thigmotropism

Reaction to touch

Thermotropism

Reaction to temperature

Chemotropism

Reaction to chemicals

2 categories of stimuli; Chemical & PhysicalCan you assign?

SENSING LIGHT Some wavelengths effect plants development

Blue wavelength (350-500nm) causes growth

the pigment CAROTENE produces a hormone in response

Orange-red (620-670nm) induces flowering and stem elongation

Far red (710-750nm) inhibit, flowering and stem elongation

How would different light affect the same plant?

What do you notice ?

PHOTOPERIOD (day/night cycle) & FLOWERING

Short day plants require long nights to trigger flowering.Late summer, autumn or winter

Long day plants. Flower if nights are shorter. During summer or spring

Neutral plantsunaffected by day length

PLANT MOVEMENTS

Presence and absence of light.

At night plants fold up their leaves and flowers.

Solar - Leaves twist on their stalk in response to

light

Nodding & Contraction

Pea seedlings move side to side ethylene

thickens & bends shoot – push through the soil

Sleep Movements

Rapid Response

Carnivorous plants rely on rapid movements to trap

prey.

Venus Fly Trap Responds to the fly’s touch (stimulus) in

specialised leaves, snapping them shut.

Plants survive harsh winters and droughts

by:

Seed dormancy

Bud dormancy

Vernalisation

Seed Dormancy

Triggers:

Winter (Cold)

Ready to grow in spring

Desert plant seeds non-germination until water washes

away the seed development inhibitor (ABA)

Some Australian native plants need smoke to germinate

WA – Wreath Lechenaultia

BUD DORMANCY

Plants become dormant in autumn, ready for winter (due to ABA-env. change)

Stimulus: decreasing temperature

Response:

Nutrients retreat back into stems and roots

Loss of chlorophyll in leaves

VERNALISATION

Vernalisation:period of winter cold that stimulates

flowering

Δ Some seeds need it for germination.

e.g. snow gums.

Cold Induces flowering in bulbs e.g. Crocuses

Biennials – after second year require vernalisation

for flowering, e.g.sugar beet

HOPE YOU ENJOYED THE LESSON !

ANY QUESTIONS ???!