Plant Responses and Adaptations
Hormones Just like animals, plants rely on hormones to control growth and development, and responses to environmental stimuli Recall that hormones are chemical messengers that signal changes in an organism
The hormone Auxin Is a plant hormone that causes both phototropism and gravitropism This hormone also control when new branch appears
Phototropism Is the tendency for a plant to grow toward a light source Auxins stimulate cell elongation and are found in high concentration on shady side of plant stems and are produced at the apical meristem
Gravitropism Is the response of a plant to the force of gravity It causes roots to grow downward and stems upward, no matter the plant/seed orientation
Cytokinins Hormones Cause dormant seeds to sprout and stimulate the growth of new branches – Auxins inhibit new branching until plant is ready, but cytokinins actually cause the growth
Gibberellins Produce dramatic increases in size of a plant, particularly in the stems and fruit Also causes early and rapid growth of a plant
Ethylene Stimulates fruits to ripen (plants all naturally release this slowly due to auxin responses) Artificially used in commercial settings to ripen fruit that was picked un-ripened
Plant Responses Tropisms—are all responses to external stimuli – 1. Gravitropism – 2. Phototropism – 3.Thigmotropism The response of a plant to touch
Photoperiodism This is the response that plants have to periods of light and darkness – Short-day plants—flower when the days are short – Long-day plants—flower when the days are longer
Dormancy Is the period of time in which an organisms growth and activity dramatically decreases or stops As cold weather approaches, deciduous plants turn off photosynthesis and transport important nutrients that are in the leaves to the roots – This is why plant leaves turn yellow/red in the fall
Plant Adapations
Aquatic plants – Water environments are typically really low in oxygen – Typically have tissues with large air filled spaces through which oxygen can diffuse
Desert Plants Plants that live in the desert are called Xerophytes – Plants adaptations in the desert include extensive roots, reduced leaves, and thick stems that store water
Nutrition Specialists These are plants that have specialized features for obtaining nutrients Both 1.Carnivorous—eat other organisms for survival ie. the venus fly trap 2. Parasites—don’t run photosynthesis, harvest another plants nutrients.ie mistle toe
Epiphytes These are plants that grow directly on the bodies of other plants, they aren’t tied to soil Most get their water from rain capture
Chemical Defenses Many plants defend themselves against insects and other herbivores by manufacturing compounds that have harmful effects on these animals
Physical Defenses Plants also defend themselves by building structures on their bodies the prevents herbivores from eating them