How do multicellular organisms respond to changes in their environment?

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One way multicellular organisms respond to changes in the environment is by behavioral adaptations. 

An example of this is in a desert ecosystem. Many organisms will seek shelter during the day and hunt during the nighttime when it is cooler. This helps to conserve water in their bodies and assist with thermoregulation. This way, they won't overheat during the daytime.

Another example of a behavioral adaptation is when a reptile basks in the sun on a rock to warm its body temperature. In the early morning hours, reptiles can be sluggish because they are ectothermic and gain heat energy from their environment. Basking is a behavior that allows them to respond to changes in temperature.

Migratory patterns followed by birds are also behavioral adaptations to insure they get to their breeding grounds for mating purposes, or to get to an area with more food and better climate during cold winter months.

Evolution plays a huge role in behaviors that animals do which enable them to survive in a changing environment. These behaviors are considered to be adaptations which help them win the struggle for existence and may be passed down if they are advantageous.

Plants are multicellular organisms that can also respond to changes in the environment. The term tropism has to do with plants growing in the direction of an environmental trigger or stimulus. This trigger can be water, light, gravity, etc.

In phototropism, plants will grow toward a source of light. Light is a stimulus which plants cannot see, however, their survival depends on growing toward the light so that they can carry out photosynthesis.

A plant hormone known as auxin stimulates cell elongation in plants. If the sun's rays are at an angle, there will be a greater concentration of auxin on the dark side of the stem. This auxin stimulates cell elongation on the dark side of the stem. The effect of these longer cells is that the plant bends over in the direction of the light source. 

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A stimulus is a change in an environment. A response is what an organism does as a result of a stimulus. Organisms respond to stimuli in order to maintain homeostasis. For example, an organism moves into the shade in order to keep cool on a hot day. Another example is when an organism sweats on a hot  day in order to maintain normal body temperature. 

An organism's response to stimuli is controlled by the nervous system. The nervous system is made of the brain, spinal cord, and neurons (nerve cells). The stimulus is picked up by receptors, which send a signal to sensory neurons. The sensory neurons send the signal to the central nervous system, which is made of the brain and spinal cord. The central nervous system then processes the information and relays it to the correct motor neurons. The motor neurons send the signal to motor neurons, which are connected to effectors. Effectors include muscles and glands. The effectors produce an appropriate response to the stimulus in order to maintain homeostasis within the organism. 

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Multicellular organisms adapt to changes in their environment and cope with the changes that way. Multicellular organisms are those that are made up of more than one cell (as the name suggests), unlike unicellular organisms such as bacteria. Human beings, plants, animals (such as cats, dogs, etc.) are examples of multicellular organisms. These organisms will adapt to environmental changes, such as thick fur for animals to counter cold and production of toxic chemicals to counter insects or pests in plants, etc. Many of these adaptations may be faster than the other and some may take place over a few generations. Human beings are an exception to these rules. We use technology to counter the environmental changes. For example, we wear warmer clothes and use heating to counter drop in temperature, while we switch on the air conditioning to counter increase in temperature, etc. We respond much faster to environmental changes than other multicellular organisms.

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