What Do Plants Need to Grow? - 2nd Grade Science

SECTION 1

What's Happening?

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🔍 LOOK AT THIS!

Cup A was put near a sunny window and got water every day. Cup B was put inside a dark closet and never got water.

After two weeks, your teacher took both cups out. Cup A had a tall, green plant growing! But Cup B had… nothing. The seed just sat in the dry dirt.

Two plant cups. Cup A has a tall green plant. Cup B has no plant growing.

Why did the plant in Cup A grow, but the seed in Cup B did not?

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💭 THINKING QUESTIONS

What was different about Cup A and Cup B?
What do you think plants need to grow big and strong?

SECTION 2

What Scientists Know

Plants are living things. Just like you need food, water, and a place to sleep, plants need certain things to grow. Scientists call these things needs.

When we observe (that means watch carefully) plants growing, we can figure out exactly what they need. Let's look at the most important things.

Water 💧

Plants drink water through their roots under the soil. Water helps the plant carry food inside its body. Without water, a plant dries up and cannot grow.

Light ☀️

Plants use light from the sun to make their own food! That is why most plants have green leaves. The leaves catch sunlight. Without light, a plant cannot make food.

The Right Space 🌍

Plants need a place to grow. Most plants grow in soil. Some plants grow in water. They also need enough room so they are not too crowded.

SECTION 3

Let's Try It!

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🌱 LET'S INVESTIGATE!

You will need: 4 small cups, soil, bean seeds, water, a sunny window, a dark closet.

Worked example

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Step 1

Fill all 4 cups with soil. Push one bean seed into each cup.
2
Step 2

Cup 1: Put it in the sun. Water it every day. Cup 2: Put it in the sun. Do NOT water it. Cup 3: Put it in a dark closet. Water it every day. Cup 4: Put it in a dark closet. Do NOT water it.
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Step 3

Every day for two weeks, look at each cup. Draw a picture of what you see. Write down how tall the plant is (or if nothing is growing).
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Step 4

After two weeks, put all your drawings and notes together. Compare (that means look at what is the same and what is different) all four cups.

When you compare your cups, you are doing what real scientists do! Scientists collect observations (notes and drawings about what they see) and then compare them to figure out answers.

Diagram showing 4 cups in different conditions: Cup 1 with sun and water, Cup 2 with sun but no water, Cup 3 in dark with water, Cup 4 in dark with no water.

SECTION 4

What We Discovered

When we compare all four cups, we can see something important. The plant that got water AND light grew the best. It was tall and green!

The cups that were missing something did not grow well. Cup 2 had light but no water. It barely grew. Cup 3 had water but no light. It grew a little, but it was pale and weak. Cup 4 had nothing — and it did not grow at all.

This tells us that plants need both water and light. Not just one — both! When we collect our observations (our drawings and notes) and compare them, we can see what made the difference.

CUP	WHAT IT GOT	WHAT HAPPENED
Cup 1	☀️ Light + 💧 Water	Grew tall and green!
Cup 2	☀️ Light only	Barely grew, dried out
Cup 3	💧 Water only	Weak and pale
Cup 4	Nothing	Did not grow

SECTION 5

See the Pattern!

Did you notice something? Every time a plant had what it needed, it grew. Every time it was missing something, it did not grow well. That is a pattern!

A pattern means something happens the same way again and again. Scientists love to find patterns because patterns help us understand the world.

This pattern is about cause and effect. A cause is what makes something happen. An effect is what happens because of it.

CAUSE (WHAT WE DO)	EFFECT (WHAT HAPPENS)
Give a plant water and light	The plant grows tall and green 🌱
Do NOT give a plant water	The plant dries up and does not grow 😟
Water a flower garden	The flowers bloom and grow pretty 🌸
Forget to water a flower garden	The flowers droop and turn brown 🥀

See? The same pattern shows up everywhere! When living things get what they need, they grow. When they do not, they struggle. This pattern works for plants in a cup, plants in a garden, and even plants in a big forest!

SECTION 6

Plants in the Real World

People use what we know about plants every day! Farmers grow food for us. They make sure their plants get plenty of water and sunlight.

Have you ever seen a greenhouse? A greenhouse is a big glass building where people grow plants. The glass lets sunlight in. People also make sure the plants get water. Greenhouses help people grow plants even in the winter!

At home, if you have a plant on a windowsill, you are using the same science. You put it near the window for light and give it water so it stays healthy.

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🌿 TRY THIS AT HOME!

SECTION 7

Key Vocabulary

Observe — To watch something very carefully and notice details.
Compare — To look at two or more things and find what is the same and what is different.
Growth — When a living thing gets bigger and taller over time.
Needs — Things a living thing must have to survive and grow, like water and light.
Pattern — Something that happens the same way again and again.

SECTION 8

Practice: Show What You Know!

Question 1: Beginner

Maya planted two bean seeds in pots with the same soil. She put Pot A by a sunny window and Pot B in a dark closet. After two weeks, the plant in Pot A was tall and green. The plant in Pot B was short and yellow. What can Maya learn from comparing these two plants?

A. Plants need light to grow well.
B. Plants grow better in dark places.
C. Bean seeds do not need soil to grow.
D. The pot by the window was a bigger pot.

Show answer

The correct answer is A. The only difference between the two pots was the amount of light. The plant with light grew tall and green, while the plant without light was short and yellow. This shows plants need light to grow well. B is wrong because the plant in the dark closet did worse, not better. C is wrong because both plants had soil, so this experiment didn't test whether soil was needed. D is wrong because Maya used the same kind of pots—the only thing she changed was the light.

Question 2: Intermediate

Carlos is growing three sunflower plants. He waters Plant 1 every day, Plant 2 once a week, and Plant 3 never gets water. After three weeks, he measures them. Plant 1 is the tallest, Plant 2 is medium, and Plant 3 has wilted and turned brown. What is the BEST way for Carlos to record his observations?

A. Draw a picture of only the tallest plant.
B. Make a chart that shows the height and health of all three plants each week.
C. Write down that sunflowers are his favorite flower.
D. Only measure the plants at the very end of the experiment.

Show answer

The correct answer is B. A chart that tracks the height and health of all three plants each week helps Carlos compare growth over time and see patterns. A is wrong because recording only one plant doesn't let him compare how different amounts of water affected growth. C is wrong because writing about a favorite flower is an opinion, not a scientific observation. D is wrong because measuring only at the end means Carlos misses how the plants changed over time, which makes it harder to compare their growth.

Question 3: Intermediate

A class planted radish seeds in four cups. All cups got the same water and light. Cup 1 had rich garden soil, Cup 2 had sand, Cup 3 had rocks, and Cup 4 had cotton balls. After ten days, the radish in Cup 1 grew the most. What does this observation help the class figure out?

A. Radish plants do not need water.
B. The type of material a plant grows in can affect how well it grows.
C. Light does not matter for plant growth.
D. All plants grow the same no matter where they are planted.

Show answer

The correct answer is B. Since water and light were kept the same, the only thing that changed was what the seeds were planted in. The plant in rich garden soil grew the most, showing that the growing material matters. A is wrong because all cups received the same water, so this experiment didn't test whether water was needed. C is wrong because all cups received the same light, so this experiment didn't test light either. D is wrong because the observations clearly showed different growth in different materials—the plants did NOT all grow the same.

Question 4: Advanced

Priya grew two tomato plants in the same sunny spot with the same soil. She gave Plant A warm water and Plant B ice-cold water. After four weeks, both plants were about the same height. Priya's friend says, "Your experiment didn't work because the plants are the same!" What should Priya say?

A. She should agree and throw her data away.
B. She should say her observations show that water temperature did not seem to change how these plants grew, and that is still a useful result.
C. She should change her measurements so the plants look different.
D. She should decide that tomato plants do not need any water at all.

Show answer

The correct answer is B. When scientists compare observations and find no difference, that is still important information. Priya's data shows that water temperature did not seem to affect how her tomato plants grew. A is wrong because throwing data away is not what scientists do—all observations matter. C is wrong because changing measurements to get a different result is dishonest and not how science works. D is wrong because both plants DID get water, so this experiment did not test whether plants need water; it tested whether water temperature matters.

SECTION 9

What's Next?

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🔮 WHAT'S NEXT?