Plant Adaptations and Tropisms

Adapt or Die! Plants dominate the surface of the Earth. There are not many areas where you can’t find at least a few plants. Given that the Earth has a vast array of different environments, each with its own characteristics and challenges, it would make sense that plants either adapt to the areas they live in or die trying. Remember, unlike the animals, once a plant is in place, it is not going anywhere!

Desert Plants To save water… Leaves are small – needles – so to minimize water loss. Thick cuticle to keep water inside. Stems are modified to store water. Roots are extensive to maximize water absorption. Seeds germinate quickly in short rainy season.

Wet Plants Plants that live in swamps or wetlands must: Float leaves and stems to surface for gas exchange. Oxygen is needed for cellular respiration (making ATP). Hollow stems can move oxygen downward for use in parts below the water-line. Plants also limit water intake in various ways so cells do not swell and rupture the cell walls.

Fire! Fire! Fire! Fires happen and they kill some plants in the forest. But, fires can also be a good thing… It removes old and dead trees that take up room that new growth would like to use. The ashes enrich the soil and can make acidic soils a little less acidic. Some seeds, while in the ground, require a lot of heat to germinate. When they final punch through the surface, the competition for soil and nutrients is gone!

Cold Plants Cold areas have tough temperatures, tough soils and they tend to have short growing seasons. To overcome this a plant may… Lose the leaves – too much energy needed to keep them and they will only weigh you down in the snow. Rely on needles – less surface area to gather ice and they minimize water loss. Undergo a very short reproductive and growing season.

TROPISMS

Tropisms A tropism is a plant growth response to an external/environmental stimulus. (Basically, a change in plant growth because of something around it.) There are positive tropisms in which the plant grows toward a stimulus and negative tropisms in which the plant grows away from the stimulus.

Phototropism A phototropism is a plants bending and growth of its stem toward the sunlight. (Photo = Light) Photosynthesis is needed so get your leaves up and at the sun. Roots show a negative response to light. Auxins help the plant bend toward or away from the sun.

Gravitropism A gravitropism is a plants growth response to gravity. Stems show a negative response while roots show a positive response to gravity. Helps in seed orientation when planted. Also known as geotropism.

Thigmotropism Thigmotropisms are plant growth responses to touch. Leaner plants will often use the stronger plants around it to gain height without growing the thick stem/trunk.

Chemotropism & Hydrotropism Chemotropisms are plant growth patterns directed by chemicals in the environment. Think of what fertilizers do to plants – they fluorish. Acids or toxins added to soil by industry can alter plant growth dramatically. A hydrotropism is a plants growth toward water. This is a great example of a positive tropism.

That’s All I Got…