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