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 Hormone receptors 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 Venus flytrap 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 concentrations 1. At what auxin concentration are the stems stimulated to grow the most 2. How is the growth of the roots affected by the auxin concentration at which stems grow the most 3. If you were a carrot farmer, what concentration of auxin should you apply to your fields to produce the largest carrots