How Do Plants Respond to Their Environment? · survive, grow, and reproduce. Vines like the ones on...

Lesson 4How Do Plants Respond to Their Environment?

© Teachers’ Curriculum Institute62 Lesson 4 How Do Plants Respond to Their Environment?

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Think of what you already know about plants and why they gravitate toward the direction of the sun. Write questions you have.

Discuss: Have you ever been in a forest and seen a tree leaning a certain direction? What are some reasons the tree could be leaning?

Observe this phenomenon: Plants move their leaves toward the sun.

Grow a plant so that it is only receiving light from one direction. Observe the direction the leaves and stems grow.

Try It!

63© Teachers’ Curriculum Institute Lesson 4 How Do Plants Respond to Their Environment?

I N V E S T I G A T I O N

Observing Phenomena

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Setting Up and Reviewing Plant ResponsesTo prepare for the game, let’s create a simple model of a plant—using your body!

Attach the following plant structures to yourself. Use tape or a hole punch and string to:• attach the pieces of brown yarn to your legs/feet. These will be

your roots.• attach the green construction paper to your waist. This will be

your stem.• attach the leaves to your hands.

64 © Teachers’ Curriculum InstituteLesson 4 How Do Plants Respond to Their Environment?


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We’re about to play the “Plant Says” game. It is similar to “Simon Says.”

In this game, you will make movements with your body that model how a plant might respond to its environment.



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Playing “Plant Says”To play “Plant Says”:• Your teacher will call out “Plant Says” and point to a picture of

an environmental stimulus. Then, you must respond as the plant would (using the motions listed below).

• However, if the teacher calls out an environmental stimulus without saying “Plant Says,” you must not respond. (Freeze in place.)

• If you respond incorrectly, you will be eliminated and asked to sit down. The last plant standing wins the game!

“Plant Says” Responses

“Light source” = hands up to lights

“Gravity” = sit down

“Water source” = stomp your feet

“Touch” = twisting and moving arms

“Insect” = clap hands together

“Short days” = drop arms to floor

“Long days” = stretch arms up



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Describing How Plants RespondDraw a diagram of a plant. Label these structures on your diagram: roots, stems, and leaves. For each structure, explain one way that structure responds to the environment.



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Vocabulary

My Science Concepts

Match the word to its definition.

Word Bank

response stimulus gravity

1. A force that pulls objects down toward the

center of Earth.

2. What an organism does when it senses a

stimulus in the environment.

3. Anything in the environment that makes an

organism act in a certain way.

Reflect on your understanding. Draw an X along each line.

You modeled and mimicked a plant and some of its structures. Although the model was helpful to learn plant responses to stimuli, plants would not think about their responses like you had to do. Plants also typically have more roots and leaves than you had in the model.

still learning know it

Plant structures respond to their environment. Most plants can sense where the sun is and grow toward it so they can absorb more sunlight and make more food. Roots respond to gravity by growing down into the soil, and some can grow toward water sources. Some plants respond to touch by growing along a fence or snapping shut when an insect lands on it.

still learning know it



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1. Stems and Leaves Respond to Light

Imagine you put a plant on a sunny windowsill. After a few days, where are the plant’s stems and leaves pointing? They probably point toward the sunlight coming in through the window.

Stems and leaves are structures that usually grow upward and toward light. A plant must grow toward the light because it needs light to make food. For example, in a rainforest where there are many tree branches overhead, very little light reaches the forest floor. That means that plants that grow on the ground do not get very much light and cannot make very much food. So, many plants sprout in the soil and then grow long stems called vines that cling to the bark of trees. The vines grow up, climbing the tree trunk to reach the light. Once the vines reach the light, they start growing sideways, spreading out their leaves to absorb the light and make as much food as possible.

Light is a stimulus for a plant. A stimulus is anything in the environment that makes an organism act in a certain way. Whatever the organism does when it senses the stimulus is called a response. Plants respond to light by turning their stems and leaves toward it. This response helps the plant gather the energy it needs to survive, grow, and reproduce.

Vines like the ones on the side of this house grow upward, toward the sun. Many plants have stems that grow toward the sun.

69Lesson 4 How Do Plants Respond to Their Environment?© Teachers’ Curriculum Institute

T E X T W I T H N O T E S

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Suppose you just put these plants on your windowsill. Which direction do you think their leaves would turn to face? Why do you think that? Use these terms in your answer: sunlight, stimulus, and response.



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2. Roots Respond to Gravity and Water

Suppose you have a plant growing in a pot of soil. The stem and leaves are growing straight up and the roots are growing straight down. How does a sprouting seed grow its stem up and its roots down?

When a seed sprouts, the new root grows down into the soil in the same direction as gravity pulls. Gravity is a force that pulls objects down. In this case, gravity is a stimulus that makes a plant’s roots grow downward. This response of the growing roots holds the seed in the soil so it does not wash away.

The stem of a sprouting plant grows upward toward the surface. In this case, the stimulus is still gravity, but the response of the plant’s stem is to grow in the opposite direction of gravity, unlike the roots. As the stem approaches the soil’s surface, it can respond to the stimulus of light as well, growing toward it.

Once a new plant grows roots down into the soil, how do you think it finds water? The presence of water is also a stimulus that plants respond to. Many roots are able to respond to water by growing toward a water source. If a pond or stream is nearby, the roots will grow toward the water. This helps the plant find enough water to grow.

As an acorn sprouts, its roots grow downward, in the direction gravity pulls. Many plants respond to the stimulus of gravity in this way.



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Suppose that there is water near this plant. Do you think the water would affect how the plant’s roots grow? How so? Use these terms in your answer: roots, stimulus, respond, and water.



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3. Leaves and Stems Respond to Touch

You have read that vines in a rainforest grow up along tree trunks to reach more light. But how does the vine know where the tree is?

The vine cannot see the tree, but it can feel it. Many plants can respond to the stimulus of touch. When the stem of a vine touches an object such as a tree trunk, a wall, or a fence, it grows and coils around the object. This response supports the vine and helps it climb toward sunlight so it can make more food.

Many climbing plants have structures that help them find and cling to objects. Coil-like structures, called tendrils, bend and turn until they touch an object. Then the plant grows toward the object and grows around or along it. For example, you may have seen grape vines that are twisted around a fence.

Some plants respond to touch by trapping insects. For example, Venus flytraps have leaves covered with tiny hairs. When an insect touches those hairs, the leaves close very fast, and the plant can digest the insect to get extra nutrients. That reaction happens very fast, and requires many different structures all working together. As soon as the hairs feel a fly, they cause the leaves to close around the fly. When the leaves close around the fly, they start to produce substances that digest the insect.

A Venus flytrap leaf responds to the touches of an insect by snapping shut. The plant digests the insect to get nutrients.

These are vine tendrils. They grow until they touch something like a chain-link fence, and then they wrap around it for support.



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Some plant responses to touch are very fast. The sensitive plant in this image has responded to being touched by closing some of its leaves. Can you think of any reasons it might close its leaves so quickly?



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4. Plants Respond to Seasons

How do you know what season it is? You might look at a calendar or check the weather report. But a plant cannot do those things. How do you think a plant senses what season it is?

Plants can respond to the temperature changes from season to season. Winter days have fewer hours of daylight than summer days. So, the ground and air are colder in winter than in summer. When there is more light in spring, the weather is warmer. Many plants grow flowers. It is important for many kinds of plants to produce flowers in spring. Many plants grow their flowers even before they grow new leaves. This means that the flowers are on bare branches, and insects can see them more clearly, making pollination easier.

During fall, many plants respond to the decreasing number of daylight hours. Their response is to stop making chlorophyll in their leaves. When the plants stop making chlorophyll, their leaves change color. Soon, the leaves fall off the plant. Not having leaves in cold weather prevents water loss in a plant. Branches without leaves are also less likely to break when they are covered by heavy snow.

These are Japanese cherry trees. They grow pink flowers in the spring before they grow any leaves. They grow flowers in response to the amount of daylight in day.



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Describe what happens to this tree over the seasons. Use these terms in your answer: stimulus, respond, and daylight.



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Show What You Know

Write a claim that answers the lesson question: How do plants respond to their environment? Then, explain at least two pieces of evidence that support your claim.

Claim:

Evidence:

Hint: Think about your

experience during the

game. Look at your

notes and diagram.

Hint: Include the term

structure(s) in your

claim.


C H E C K F O R U N D E R S T A N D I N G

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Making Sense of the Phenomenon

Claim

Evidence

Reasoning

Use your findings from the investigation to answer this question:

Why do many plants change the way they grow based on where the sun is?

Go back to page 4 and fill out the unit checkpoint for this lesson.

Let’s revisit the phenomenon: Plants move their

leaves toward the sun.

Think about:• What structures are responding to stimuli?• How does this help the plant survive?


C H E C K F O R U N D E R S T A N D I N G

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N O T E S

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