Plant Responses and Adaptations

Plant Responses and Adaptations Chapter 25: Biology II

Plant Hormones • Chemical substances that control: • A plant’s patterns of growth and development • A plant’s responses to environmental conditions • Target Cell: cell affected by a particular hormone

Auxins • Stimulate cell elongation • Produced in the apical meristem • Transported downward into the rest of the plant • Responsible for: phototropism and gravitropism

Auxins: Phototropism • Tendency of plants to grow toward a source of light

Auxins: Gravitropism • Tendency of a plant to grow in a direction in response to the force of gravity

Auxins • Lateral Bud: meristematic area on the side of a stem that gives rise to side branches • Apical Dominance: phenomenon in which the closer a bud is to the stem’s tip, the more its growth is inhibited • Herbicide: auxin-like weed killers; compound that is toxic to plants

Cytokinins • Plant hormones that are produced in growing roots and in developing fruits and seeds • Stimulate cell division and the growth of lateral buds • Cause dormant seeds to sprout

Gibberellins • Growth-promoting substance produced by plants • Causes dramatic increases in size, particularly in stems and fruits • Produced by seed tissue • Responsible for the rapid early growth of many plants

Ethylene • Plant hormone that stimulates fruits to ripen • Released in small amounts as a response to auxins • Commercial products can use this to control the ripening process; treated with synthetic ethylene

Tropisms • The response of plants to environmental stimuli • Gravitropism • Phototropism • Thigmotropism

Thigmotropism • Response of plants to touch • Examples: • A plant that is touched regularly may be stunted in its growth-sometimes quite dramatically • Vines and climbing plants-tips wrap around objects

Rapid Responses • Some responses do not involve growth; they are not tropisms • Examples: • Mimosa pudica: the “sensitive plant” • The Venus flytrap

Photoperiodism • Responsible for the timing of seasonal activities such as flowering and growth • Phytochrome: plant pigment responsible for photoperiodism

Short-Day Plants • Plants that flower when daylight is short • Also called “long-night plants”

Long-Day Plants • Plants that flower when days are long • Also called “short-night plants”

Winter Dormancy • Period of time during which a plant embryo is alive but not growing • As cold weather approaches, deciduous plants: • Turn off photosynthetic pathways • Transport materials from leaves to roots • Seal leaves off from the rest of the plant

Abscission Layer • Layer of cells at the petiole that seals off a leaf from the vascular system

Aquatic Plants • To take in sufficient oxygen, many aquatic plants have tissues with large air-filled spaces through which oxygen can diffuse

Salt-Tolerant Plants • Leaves have specialized cells that pump salt out of the plant tissues and onto the leaf surfaces • Example: mangroves

Desert Plants • Also called: xerophytes • Extensive roots • Reduced leaves • Thick stems that can store water

Nutritional Specialists • Plants that have specialized features for obtaining nutrients • Carnivorous plants: obtain nutrients from digested prey • Parasites: plants that extract water and nutrients directly from a host plant • The dodder plant Cuscuta

Epiphytes • Plants that grow directly on the bodies of other plants • Gather their own moisture and produce their own food, unlike parasitic plants • Spanish moss-not a moss, but a bromeliad!

Chemical Defenses • Many plants defend themselves against insect attack by manufacturing compounds that have powerful effects on animals

Plant Responses and Adaptations