Growth of Organisms

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Yield Noun

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[yeeld]

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Yield

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The amount of an agricultural product, like a crop, that is produced or provided from a specific area.

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Example: A plant uses sunlight, water, and carbon dioxide in a process that yields glucose (food) and oxygen (a byproduct).

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Drought Noun

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[drowt]

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Drought

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A prolonged period of abnormally low rainfall, which results in a significant shortage of available water in a region.

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Example: This image shows the effects of a drought: the ground is cracked and dry, and the trees have died from a lack of water.

Front

Urushiol Noun

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[uh-roo-shee-ol]

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Urushiol

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An oily organic allergen found in plants like poison ivy that causes an irritating and allergic rash upon contact.

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Example: This image shows a poison ivy plant, the natural source of urushiol, an oily chemical that causes an itchy rash upon contact.

Front

Stimulus Noun

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[stim-yuh-luhs]

Back

Stimulus

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A detectable change in the internal or external environment that evokes a specific functional reaction in an organ or tissue.

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Example: The sharp spine of the cactus is a stimulus that causes a response: the girl feels pain and pulls her finger away.

Front

Tropism Noun

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[troh-piz-uhm]

Back

Tropism

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The turning or directed growth of a plant or other organism in a particular direction in response to an external stimulus.

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Example: This image shows geotropism, a plant's response to gravity. The roots grow down with gravity (positive), while the stem grows up against it (negative).

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Phototropism Noun

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[foh-toh-troh-piz-uhm]

Back

Phototropism

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The orientation or growth of a plant or other organism in response to a light source, either towards or away.

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Example: This image shows a plant bending its stem to grow towards a light source, which is an example of positive phototropism.

Front

Heliotropism Noun

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[hee-lee-o-troh-piz-uhm]

Back

Heliotropism

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The directional growth or movement of a plant's parts in response to the daily movement of the sun across the sky.

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Example: This image shows a sunflower bending toward the sun. A diagram shows hormones (auxins) moving to the shaded side of the stem, causing it to bend.

Front

Gravitropism Noun

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[grav-i-troh-piz-uhm]

Back

Gravitropism

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A coordinated process of differential growth by a plant or other organism in response to the force of gravity.

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Example: This image shows how a plant responds to gravity: the roots grow downward (positive gravitropism) and the stem grows upward (negative gravitropism).

Front

Thigmotropism Noun

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[thig-mo-troh-piz-uhm]

Back

Thigmotropism

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The turning, bending, or directional growth of a plant or other organism in response to a physical touch stimulus.

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Example: This image shows a plant's tendril coiling around a metal support, which is a growth response to touch called thigmotropism.

Front

Hormones Noun

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[hor-mohnz]

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Hormones

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Signaling molecules in multicellular organisms that are sent to distant organs to regulate physiology, growth, and overall behavior.

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Example: Endocrine cells release hormones, which travel through the bloodstream to act on specific target cells with matching receptors.