Grade by Grade
B. Life Systems · Growth and Changes in Plants

How Plants Adapt and React to Their Environment

B2.4 A1.2About 35 minutes
Learning goals
  • I can describe features that help different plants survive in their environment.
  • I can describe how plants react to light, water, gravity, touch and the seasons.
  • I can explain how Ontario plants react to changes from summer to winter.
  • I can investigate how a plant reacts to light.

Words to know

environment
Everything around a living thing: air, water, soil, weather, light and other living things.
adaptation
A feature a living thing has that helps it survive in its environment, like a cactus's spines.
react
To respond to a change. A plant reacts when it bends toward light.
deciduous
Trees that lose all their leaves in the fall, like maples and oaks.
evergreen
Trees that stay green all year, like pines and spruces.
dormant
Resting, not growing, waiting for better conditions (like trees in winter).

Remember from Grade 2

In Grade 2 you learned that animals have adaptations, like thick fur or webbed feet, that help them survive in their habitats. Plants have adaptations too! And even though plants cannot walk or run, they can react to changes around them.

Two ways plants handle their environment

  1. Adapt: Plants have features that suit the place where they live. A cactus in the desert has a thick stem that stores water. That feature took a very long time to develop and is part of every cactus.
  2. React: A plant can respond to a change during its own life. If you move a plant so the light comes from one side, its stem slowly bends toward the light.
A tall saguaro cactus with two raised arms standing in a dry desert with shrubs and mountains behind it.
A cactus has a thick stem that stores water and spines instead of wide leaves. These adaptations help it survive in a hot, dry desert. AI-generated image
PlantWhere it livesAdaptationHow it helps
cactushot, dry desertthick stem that stores water; spines instead of leavessaves water; spines keep animals from eating it
water lilyponds and lakesbig flat leaves with air spaces that floatleaves stay at the top of the water to catch sunlight
pine and sprucecold foreststhin, waxy needles; spruces have a cone shapelose little water in winter; snow slides off the branches
Arctic plants (like Arctic willow)the cold, windy Arctic tundragrow very low and close to the groundstay out of the cold wind and stay warmer
pitcher plantbogs with poor soilleaves shaped like cups that trap insectsgets nutrients from insects that it cannot get from the soil
dandelionlawns and fieldsdeep taproot; fluffy seedssurvives dry weather and mowing; seeds spread far
Plant adaptations for different environments.

How plants react

Plants react to many things around them:

  • Light: stems and leaves bend toward light. Young sunflower plants turn to follow the Sun across the sky.
  • Gravity: roots always grow down and stems grow up, even if the seed was planted upside down!
  • Water: roots grow toward damp soil. When the soil is dry, leaves wilt (droop) to save water.
  • Day and night: some flowers, like dandelions and tulips, close at night or on cold, cloudy days, and open in the sunshine.
  • Touch: a plant called the sensitive plant folds its leaves in seconds when you touch it.
  • Fire: jack pine cones are sealed shut with sticky resin. The heat of a forest fire opens them and lets the seeds out, so new trees grow after the fire.
windowThe stem bendstoward the light.
A plant on a windowsill. The stem bends toward the light coming in the window.
planted right way upplanted upside downshootrootshootrootseedupdown
Plants react to gravity. Even when a seed is planted upside down, its root turns to grow down and its shoot turns to grow up.

Ontario plants and the seasons

In Ontario the seasons change a lot. Plants react to these changes:

  • Fall: days get shorter and colder. Deciduous trees like maples, oaks and birches lose their leaves. In winter the ground is frozen, so the roots cannot get water. Dropping leaves helps the tree save water.
  • Winter: trees are dormant (resting). Their buds have tough scales to protect them. Evergreens like pines and spruces keep their waxy needles. Many smaller plants die back, but their roots or seeds survive under the snow.
  • Spring: days get longer and warmer. Buds open, sap flows in maple trees, and seeds germinate. Forest flowers like the trillium bloom early, before the trees grow their leaves and shade the forest floor.
  • Summer: plants grow quickly in the long, warm days. If there is a drought, some leaves wilt or turn brown.
Worked example

Let's tell adapt from react

Sort these into adaptation (a feature the plant always has) or reaction (a response to a change):

  1. A cactus has spines.
  2. A dandelion closes at night.
  3. A water lily has floating leaves.
  4. A house plant bends toward the window.
  1. Ask: Is it a feature the plant always has? Or is it something the plant does when something changes?
  2. 1. Spines are always there: adaptation.
  3. 2. Closing happens when it gets dark: reaction.
  4. 3. Floating leaves are always there: adaptation.
  5. 4. Bending happens because the light comes from one side: reaction.

Adaptations: 1 and 3. Reactions: 2 and 4.

Worked example

Let's explain a winter tree

Why does a sugar maple lose its leaves in the fall, while a white pine keeps its needles?

  1. In winter, the ground is frozen, so roots cannot get much water.
  2. Big, flat maple leaves lose a lot of water into the air. If the maple kept them, it would dry out. So it drops its leaves and rests (goes dormant).
  3. Pine needles are thin and waxy, so they lose very little water. The pine can keep them all winter.

The maple reacts to fall by dropping leaves to save water. The pine is adapted with waxy needles, so it can keep them.

Just for fun

Why are young sunflowers always so cheerful?

Because they keep turning to look on the bright side!

Hands-on activity

The plant that follows the light

You need: a potted plant that grows quickly (a bean seedling is perfect), a sunny window, a pencil and paper.

Part 1: Bending toward light

  1. Put the plant on the windowsill. Draw it carefully.
  2. Leave it for 3 days. Do not turn the pot. Draw it again. Which way does the stem bend?
  3. Turn the pot halfway around (so the bent side faces into the room). Predict what will happen. Check and draw again in 2 or 3 days.

Part 2: The light maze (challenge)

  1. A grown-up helps cut a hole in one end of a shoebox. Tape 2 pieces of cardboard inside as walls, each with a gap, to make a maze.
  2. Put a sprouted bean in a small pot at the other end. Close the lid and set the hole toward a window.
  3. Open the lid every 2 days to water and observe. Does the plant find its way to the light?

What to look for: the stem bends toward the light, and turns back toward the light after you turn the pot. In the maze, the stem grows around the walls toward the hole.

Safety: A grown-up does all cutting.

Your turn

1

What is the difference between a plant adapting and a plant reacting?

2

Which way do roots grow? Which way do stems grow?

3

How does a cactus survive in the desert?

4

Why do maple trees drop their leaves in fall?

5

What do dandelion flowers do at night?

6

What does it mean that a tree is dormant in winter?

7

How do jack pine trees react to a forest fire?

More practice: warm-up

1

Is a pine tree deciduous or evergreen?

2

Is a maple tree deciduous or evergreen?

3

What do leaves do when the soil is very dry?

4

What does a plant on a windowsill bend toward?

5

Name a plant that lives in water.

More practice: on your own

1

Why do Arctic plants grow low and close to the ground?

2

A pitcher plant traps insects. Why does it need to?

3

Why do trilliums bloom in early spring?

4

Ben planted a bean upside down. Will the root grow up? Explain.

5

Is a water lily's floating leaf an adaptation or a reaction? Explain.

Challenge

1

You turn a plant around on a windowsill so its bent stem points into the room. What will happen over the next few days? Why?

2

A big spruce grows in a place with lots of heavy snow. Explain how its shape and needles help it survive.

3

A garden had no rain for 2 weeks. The bean plants' leaves were drooping in the afternoon but stood up again in the morning. Explain what was happening.

Check your understanding

Quiz

1.

Which is an adaptation of a cactus?

2.

A plant on a windowsill bends toward the window. This is a...

3.

Which way do roots grow when a seed sprouts?

4.

Why do deciduous trees drop their leaves in fall?

5.

Which tree is an evergreen?

6.

Why do Arctic plants grow low to the ground?

For parents and teachers

Big idea (B2.4): Plants have adaptations (features that suit their environment) and also react to changes during their lives: they grow toward light, roots grow down with gravity and toward water, flowers open and close, leaves wilt, deciduous trees drop leaves and go dormant, and jack pine cones open with fire. The windowsill and maze activities practise observing and predicting (A1.2).

Accuracy notes: Only young sunflowers track the Sun; mature flower heads mostly face east. The sensitive plant (Mimosa pudica) is a house plant, not an Ontario wild plant. Pitcher plants grow wild in Ontario bogs.

Common difficulties:

  • Mixing up adapt and react. Use the question: "Is it always there, or does it happen because something changed?"
  • Thinking evergreens never lose needles. They do drop old needles a few at a time, just never all at once.

How to help: Notice reactions together: tulips closing at dusk, leaves wilting on a hot afternoon, house plants leaning toward windows. In fall, compare a maple and a spruce on the same street.