14 Plant Behavior-Mid

Plant Behavior FOCUS Question How do plants respond to the world around them?

The Life of a Plant You might think being a plant would be boring. You sprout out of the soil. Then you stay in one place your whole life. But there's much more to being a plant than just sprouting and standing still! Plants grow on every continent. They can live where it is hot or cold, wet or dry. To live in so many different places, plants must adapt to their habitat. Plants have parts that help them get water, air, and sunlight. These are physical adaptations. But plants also have behavioral adaptations. That's right. Plants behave, or act, in certain ways! They respond to light, heat, water, and touch.

Seeking Sunlight All plants need sunlight to stay alive. They use it to make their own food. But getting sunshine isn't always easy. In many forests, large trees create a canopy, or upper layer of leaves. This layer blocks light from reaching the plants below. As a result, those plants actively search for sunlight. Lianas (lee-AH-nuz) are vines found in tropical rainforests. They start life on the ground as small shrubs. But they soon begin to climb toward sunlight. A liana uses sticky hairs to attach to a tree. It also has special stems that grasp the tree as the vine grows. Over time, the vine winds all the way to the top.

Handling Heat Desert plants don't have to worry about finding sunlight. Instead, they must deal with extreme heat and dryness. For example, the leaves of the jojoba (huh-HO-buh) grow straight up and down. At midday, the Sun's rays shine straight down. The rays hit just the edges of the leaves, so the plant stays cooler But when the Sun is rising or setting, the weaker light hits the sides of the leaves. The plant needs this sunlight to make food. To conserve water on a hot day, cacti close their stomata. These tiny holes on the plant take in carbon dioxide. They also give off oxygen and water vapor. Cactus plants wait until the cooler nighttime to open their stomata As a result, they lose less moisture.

Spreading Pollen Arctic poppies live where it is very cold. These bright yellow flowers follow the warm sunlight throughout the day. The sunlight warms the centers of the flowers. This warmth attracts insects that pollinate (PAH-li-nate) the plant. This means they help the plant reproduce. The night-blooming cereus (SEER-ee-us) is a desert cactus. For most of the year, this plant looks like a dead bush. But for only a night or two in the summer, its large flowers open up. That's because the creatures that pollinate it are active at night. Sphinx moths and nectar-feeding bats help pollinate the flowers.

Waiting for Water Ephemerals (uh-FEM-er-uhls) are plants with short life cycles. They go from seeds to mature plants to new seeds in a very short time. The desert paintbrush is an ephemeral. This plant depends upon rare desert rains. Its seeds wait in the ground until there is enough water. They may sit in the soil for years. When it finally rains, the seeds sense the moisture and sprout. The young plants leap to life, growing quickly. The plants must flower and produce new seeds before the water runs out. The wind scatters the seeds across the desert floor. These new seeds will wait there until it is time to grow again.