25–1 Hormones and Plant Growth Section 25-1 25–1 Hormones and Plant Growth A. Patterns of Plant Growth - meristems are the source of plant growth. Plants never stop growing. Plant Hormones - are chemical substances that controls a plant’s patterns of growth and development, and the plant’s responses to environmental conditions The four main hormones are Auxins Cytokinins Gibberellins Ethylene

Figure 25-2 Hormone Action on Plants Section 25-1 Hormone Action in Plants   -Plant hormones are chemical substances that control patterns of development as well as plant responses to the environment. - Hormones are produced in one part of the plant to control another part of the plant. The cells affected by a hormone must have a hormone receptor

25–1 Hormones and Plant Growth - Continued Section Outline Section 25-1 25–1 Hormones and Plant Growth - Continued C. Auxins - are produced in the apical meristem and are transported downward into the rest of the plant. They stimulate cell elongation. D. Cytokinins - stimulate cell division and the growth of lateral buds, and cause dormant seed to sprout E. Gibberellins - produce dramatic increase in size, particularly in stems and fruit F. Ethylene - stimulates fruit to ripen

Figure 25–3 Auxins and Phototropism Section 25-1 High concentration of auxin Low concentration of auxin Control Tip removed Opaque cap Clear cap Opaque shied over base

Figure 25–5 Apical Dominance Section 25-1 Apical meristem Lateral buds Auxins produced in the apical meristem inhibit the growth of lateral buds. Apical meristem removed Without the inhibiting effect of auxins from the apicial meristem, lateral buds produce many branches.

25–2 Plant Responses Section Outline A. Tropisms - A plant’s ability to respond to external stimuli. Gravitropism - a plants response to the force of gravity. Controlled by auxins Phototropism - the tendency of a plant to grow toward a source of light. Auxins stimulate the elongation of stem cells on the dark side to elongate and the plant bends toward the light Thigmotropism - a plants response to touch. Vines and climbing plants like grapes have tendrils that wrap tightly around objects they encounter B. Rapid Responses - movement occurs from rapid changes in osmotic pressure. An example of a rapid change is the closing of a Venus fly trap leaf to capture a insect.

Tropisms

25–2 Plant Responses - continued Section Outline Section 25-2 25–2 Plant Responses - continued C. Photoperiodism - is responsible for the timing of seasonal activities such as flowering and growth. D. Winter Dormancy - as cold weather approaches, deciduous plants turn off photosynthetic pathways, transport materials from leaves to roots, and seal leaves off from the rest of the plant. 1. Leaf Abscission - photosynthesis stops and the green pigments are destroyed revealing the other colors that were there all along. Most water and available nutrients are removed from the leaf, and an abscission layer forms at the base of the leaf. 2. Overwintering of Meristems - produce thick waxy scales over the new leaf buds for the next spring. Xylem and phloem tissues pump themselves full of ions and organic compounds to act as an antifreeze during the cold winter.

Photoperiodism and Flowering Section 25-2 Short-Day Plant Long-Day Plant Midnight Noon Long Day Midnight Noon Short Day Midnight Noon Interrupted Night

25–3 Plant Adaptations Section Outline A. Aquatic Plants - to take in sufficient oxygen, many aquatic plants have tissues with large air filled spaces through which oxygen can diffuse. Other adaptations include seeds that float and quick growth following germination to allow the shoot to reach the surface of the water. B. Salt-Tolerant Plants - take in more salt than the plant can use to allow the roots to still absorb water by osmosis. The roots have adapted to tolerate the salt conditions that would destroy most plants. Excess salt is pumped out of the plant onto the leaves where it is washed away by the rain. C. Desert Plants - adaptations to a desert climate include extensive roots, reduces leaves, and thick stems that can store water. The spines on a cactus are actually modified leaves. Many seeds of desert plants can remain dormant for years.

Plant Adaptations

25–3 Plant Adaptations - continued Section Outline Section 25-3 25–3 Plant Adaptations - continued D. Nutritional Specialists - have specialized features for obtaining nutrients. 1. Carnivorous Plants - many live in bogs where there is little or no nitrogen present in the soil. Plants that live in these type of ecosystems have specialized leaves to capture and digest insects for a source of nitrogen. Ex) Venus fly trap and picture plant 2. Parasites - plants that extract water and nutrients directly from a host plant. E. Epiphytes - plants that are not rooted in the soil but instead grow directly on the bodies of other plants. Epiphytes are not parasites they gather their own moisture and produce their own food. F. Chemical Defenses - many plants defend themselves against insect attack by manufacturing compounds that have powerful affects on animals

Compare/Contrast Table Section 25-3 Comparing Carnivorous Plants, Epiphytes, and Parasites Characteristics Environment Method of obtaining nutrients Examples Carnivorous Plants bog leaves that trap and digest insects pitcher plant, sundew, Venus’ flytrap Epiphytes host plant gather moisture from rainfall and produce their own food Spanish moss, orchid Parasites host plant extract moisture and nutrients from host plant dodder, mistletoe

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