1 Apply Concepts Using a houseplant, a marker and a sunny windowsill, describe how you might measure the plant’s response to light

2 Review Summarize plant responses to seasonal changes

3 Explain Which type of plant- short or long day- is likely to bloom in the summer- explain

Design an Experiment Design a controlled experiment to find out how a garden store owner could determine what light conditions are needed for a particular flowering plant to bloom

CH 24 PLANT REPRODUCTION AND RESPONSE

24.1 Plant Hormones

Hormones

Chemical signals produced by living organisms that affect Growth, Activity, and Development of cells and tissues

Coordinate responses to the environment.

Hormone-producing cells in a mature flower release hormones that travel into flower buds and inhibit development.

Once the mature flower is done blooming, production of the inhibiting hormone will decline, and the flower bud can then begin its bloom.

Target cell Portion of an organism affected by a particular

hormone Hormone receptors

Where hormone molecules bind.

Hormones may affect roots differently than stems or flowers and the effects may change as receptors are added or removed

All depends on the receptors.

Why does grass bend toward light Darwins hypothesized that the tip produces a

substance that regulates cell growth.

Auxins

Stimulate cell elongation and the growth of new roots

Produced in the shoot apical meristem and transported to the rest of the plant.

Auxins and Cell Elongation

Light hits one side of the shoot Auxins collect in shaded part of shoot Stimulates cells on dark side to lengthen

Causes shoot to bend away from shaded side.

Auxins also regulate cell division in meristems Growth at lateral buds is inhibited by auxins Apical dominance

Lateral buds near the apex grow more slowly than those near the base of the plant

Due to more auxin at apex.

Cytokinins

Produce effects opposite of auxins Auxins stimulate new roots and inhibit growth of

new shoot tips Cytokinins stimulate growth of new shoot tips and

inhibit new roots Produced in growing roots and in developing fruits

and seeds.

Gibberellins

Promote germination of plants May cause dramatic increases in size, particularly

in stems and fruits Found in the meristems of shoots, roots, and seed

embryos.

Abscisic Acid

Inhibits cell division, thereby halting growth Stops seed growth when seed development is

complete Causes seed to go dormant

Interacts with gibberellins to control seed dormancy

Found in the terminal buds and seeds.

Ethylene

Stimulates fruits to ripen Released from fruit Causes plants to seal off and drop organs that are

no longer needed (flower petals).

Tropisms

Plant response to environmental stimuli such as light, gravity, and touch.

Phototropism

Tendency of a plant to grow toward a light source

Changes in the concentration of auxins.

Gravitropism

Response of a plant to gravity

Auxins migrate to the lower sides of horizontal roots and stems.

Thigmotropism

Response of a plant to touch Vines and climbing plants wrap

around objects Grape vines have tendrils that

emerge from leaf base that wrap around objects.

Rapid Movements

Mimosa will fold in leaves when touched Osmotic pressure

Venus flytrap Insect triggers sensory cells on the inside of the leaf,

send electric signals, leaf snaps shut due to osmotic pressure and cell wall expansion.

Photoperiod

Plant response to the relative lengths of light and darkness

Major factor in the timing of seasonal activities such as flowering and growth

Due to phytochrome pigment.

Winter Dormancy

Phytochrome regulates the changes that prepare plants for winter dormancy

Deciduous plants Turn off photosynthetic pathways Transport materials from leaves to roots Seal off leaves from the rest of the plant.

Leaf Loss

Phytochrome absorbs less light as days shorten Auxin production drops Ethylene increases Chlorophyll breaks down Carotenoids (yellow and orange) become visible Anthocyanin (red) are made.

Meristems produce thick, waxy scales that form a protective layer around new leaf buds

Xylem and phloem tissues pump themselves full of ions and organic compounds Prevents tree’s sap from freezing.

Carrot cells were grown in varying auxin concentrations1. At what auxin concentration are the stems stimulated to grow the most2. How is the growth of the roots affected by the auxin concentration at which

stems grow the most3. If you were a carrot farmer, what concentration of

auxin should you apply to your fields to produce the largest carrots