Responses in Plants

Suppose you and your family take a camping trip. Your father is trying to build a fire, and he asks you to collect some sticks for a fire. While you are searching, you encounter a huge bear. What is your immediate reaction? Run! This is a result of external stimulus. An external stimulus is a stimulus that comes from outside an organism and causes a reaction. When you see the bear, your brain immediately recognizes danger. Your brain triggers the “flight mode” option, so that you can flee danger immediately.There are internal stimuli as well as external. And internal stimulus is a stimulus that comes from inside an organism. An example of this is instinct. Instinct is a natural reaction to a stimulus that is automatic instead of taught. In plants, this is known as a tropism. Based on the context, stimulus refers to _. outside reactions of your body the temperature of the body food that gives you energy a thing or event that causes a reaction A tropism is a growth response between plants and an external stimulus. What kind of stimulus could this be? Examples are weather, touch, time, gravity, or light. There are two basic responses, positive and negative. A positive response is indicated by a plant's growth toward the stimulus. A negative response is when it grows away from the stimulus. Two examples of tropism are gravitropism and phototropism. Gravitropism is a plant's growth response to gravity. Roots grow down in the ground to absorb water for a plant, and its stems and leaves grow upward above the ground to absorb light. If a plant were to lose its upright position, it might not be able to gain required nourishment. When this occurs, a plant will begin to bend so that it is upright once again. Phototropism is a plant’s response to a light stimulus. If a light source is blocked, a plant will change its growth in order to receive more light. When the plant bends, it allows a larger amount of light to hit the leaves surface. The leaves are then able to absorb this light to begin conducting photosynthesis for food. A houseplant is placed on a window sill that gets direct, bright sunlight every afternoon. The plant starts to grow toward the window. What kind of response is this? a negative response a learned behavior phototropism gravitropism Two other examples of tropism are thigmotropism and hydrotropism. Thigmotropism is a plant’s response to being touched. In many cases, a plant will grow straight until it comes into contact with something, such as a tree branch. Then, the plant will curl around the object for support. Roots, however, will grow away from rocks and other objects in the soil that get in their way. Hydrotropism is a plant’s growth response to water. Water is needed for growth and for plants to undergo photosynthesis. Roots will grow towards water, and stems and leaves will grow away from water. Interestingly, the hydro, or water, effect is stronger than the gravity effect, so if water is above the roots...the roots will actually grow upwards! Our environment is constantly changing. Plants would not be able to produce their own food without the ability to change to the environment. Tropisms allow the plants to constantly adapt! A Venus flytrap is a plant that gets its nutrients not only from photosynthesis, but also from eating insects. An insect lands on the Venus flytrap’s mouth and the mouth closes. This is an example of _. a negative response a learned behavior hydrotropism thigmotropism Which response is similar to an animal drinking when it gets thirsty? a plant making sugar in photosynthesis a plant wilting when it's soil dries out a plant growing toward light a plant's stem growing upward Which is the best summary of the passage? An external stimulus comes from outside the organism. Animals respond to stimuli through instinct and learned behaviors. Stimuli triggers responses in organisms that allow them to change along with the environment. Phototropism is a plant’s response to light and gravitropism is a plant’s response to grow upward against gravity. Plants have tropisms and can change to environments; animals do not have tropisms and cannot change to environments. What controls responses in plants? hormones neurons electrical impulses weather Plants respond to stimuli such as water, sunlight and gravity in order to perform what function? anaerobic respiration photosynthesis chemosynthesis thigmotropism