How Plants Live: Roots, Stems, Leaves and Flowers

Look at a flowering plant from its roots to its flowers. Each part does a job that helps the whole plant. A bean plant, an apple tree, and even grass are flowering plants.

Four parts, four main jobs

A part is a structure. Its job is its function. These words help you describe what you see.

The shape of each part helps it work. Thin roots reach between bits of soil. Wide leaves catch light. Flowers may have bright petals that bring insects close. Their colors help with seed making; they do more than look pretty.

Follow a sunflower

Picture a sunflower growing in damp soil. Follow what happens, one step at a time.

1. The roots take in water from the soil.
2. The stem carries that water up to the leaves.
3. The leaves use sunlight, water, and carbon dioxide from air to make sugar. Sugar is the plant’s food.
4. The stem carries food to growing parts, including roots and flowers.
5. The flower head later makes seeds.

The roots supply water to the leaves. The leaves supply food to the roots. These linked jobs make the plant a system: parts working together. If many roots are damaged, leaves can wilt. Even leaves high above the soil depend on those roots.

Big plants and small flowers

A tree has the same main parts. Its trunk is a thick, woody main stem. Branches are smaller stems. Oak trees make flowers, although their flowers are easy to miss.

Grass flowers are small too. A flowering plant does not need large, colorful petals. You may see its leaves long before it flowers.

Parts can also look different across plants. A carrot has a thick root. Grass has many thin roots. A cactus has a fat stem, while a tulip has a thin one. When you name a part, think about its job as well as its shape.

Roots usually grow below the ground. You may only see them when a seed sprouts or a plant is lifted. They help the plant in several ways.

Holding on and taking in water

Roots anchor a plant: they hold it firmly in place. A branching root spreads between bits of soil. That makes a plant harder to pull out or blow over.

Roots also take in water and nutrients. Nutrients are substances a plant needs in small amounts to grow well. They are dissolved in the water around roots. The roots take them in with the water.

Near a growing root’s tip are tiny root hairs. These reach into small spaces in the soil. More root surface touches water, so the root can take in more. On a sprouting radish, they can look like soft white fuzz.

Different root shapes

Tree roots do not all go straight down. Many spread sideways near the surface. Some reach farther than the tree’s branches.

A root can store food

A carrot stores extra food in its thick root. Later, the plant uses that food to grow flowers and seeds. A beet has a food store too.

Think about a dandelion whose leaves have been pulled off. Its long root may still be in the ground. Stored food in that root can help new leaves grow. The root both holds on and stores food.

That food was made by green parts of the plant. Roots do not eat soil. Water and nutrients from soil are useful, but they are different from the sugar a plant makes as food.

Roots need air too

Tiny spaces in soil usually hold some air. Roots need oxygen from that air. When soil stays soaking wet, water fills those spaces. Many roots then lack air and begin to rot.

If a plant droops, check its soil before adding water. Dry soil and soaking wet soil point to different problems. Damaged roots can leave the plant short of water even when the soil is wet.

A stem links roots with leaves and flowers. Its two main jobs are support and transport. Support means holding up. Transport means carrying things from place to place.

Holding parts where they can work

A stem lifts leaves into the light. It also holds flowers where insects or wind can reach them. A bean stem may bend, while a tree trunk stands stiffly upright. Both support the plant.

Soft, green stems stay firm partly because they are full of water. Woody stems contain stiff, strong wood. Their bark protects the outside.

Imagine a bean plant that has gone days without water. Its soft stem bends and its leaves hang down. The plant has wilted. After its dry soil is watered, the plant may stand upright again. Water has helped fill and firm its soft parts.

Carrying water and food

Many tiny tubes run through a stem. Picture a bundle of thin drinking straws. There is no single large water pipe in the center.

• Some tubes carry water and nutrients upward from the roots.
• Other tubes carry sugar from leaves to parts that need food.

Sugar can travel down to roots as well as toward growing flowers. Roots need food even though they cannot catch sunlight underground.

Follow a bean plant after rain. First, its roots take in water. Next, water moves up the stem to the leaves. The leaves use some water to make food. Food then travels to growing parts. The stem helps connect these jobs.

Stems that store

A cactus keeps water in its thick stem. Its green stem also makes food. This helps a cactus live through dry weeks.

A potato is a swollen stem that grows underground. It stores food. The small “eyes” are buds that can grow into shoots. Being underground does not make every plant part a root.

A tree’s trunk is also a stem. Its size and woody surface do not change its main jobs. Branches carry water toward leaves, while food travels from leaves to parts that need it.

A plant cannot go shopping for lunch. Its leaves make food: a kind of sugar. The plant uses sugar for energy and to build new parts.

What a leaf needs

To make food, a leaf needs sunlight, water, and carbon dioxide. Carbon dioxide is a gas in air. Water reaches the leaf from the roots through the stem.

Sunlight supplies energy. It is not the food itself. The food is the sugar made using that energy. Making food this way is called photosynthesis.

Leaves contain chlorophyll, a green substance that catches light. That is why many leaves look green. Red and purple leaves have chlorophyll too; other colors hide its green color.

While making food, leaves release oxygen. People and other animals need this gas to breathe. Plants also use oxygen in all their living parts.

A shape that helps

Many leaves are wide and flat. A broad surface catches more light. Lines called veins carry water into the leaf and sugar away.

Tiny holes, mostly underneath the leaf, let gases move in and out. Carbon dioxide enters. Water vapor can leave. These holes are far too small to see easily with your eyes.

Follow the food

A sunflower leaf uses light, water, and carbon dioxide to make sugar. Some sugar helps the leaf work. Some travels through the stem to growing roots or flowers. Extra food can be stored for later.

Carrots store food in roots. Potatoes store it in stems. Seeds hold food that feeds a tiny new plant before it has working leaves.

Light makes a difference

Suppose a board lies on grass for two weeks. Under the board, the grass turns pale yellow. The board blocked light, so the grass could not keep making food or chlorophyll. Remove the board and living grass can become green again.

Fertilizer cannot replace the missing light. It supplies nutrients, not sugar. Labels sometimes call fertilizer “plant food,” but plants still need to make their own food.

Leaves are the main food makers. Other green parts can make food too. A cactus has spines in place of ordinary leaves, and its green stem does the food making.

A plant’s shape gives you clues about how it lives. You can look closely, make a claim, and find evidence to test your idea.

Parts that help plants survive

Some parts protect a plant from being eaten. Sharp thorns or spines can put animals off. Stinging nettles have stinging hairs. Tough bark protects a woody stem.

A cactus has several parts suited to dry places. Its spines are changed leaves. They protect it and lose far less water than broad leaves. Its thick green stem stores water and makes food.

These parts help the cactus survive. Other parts help plants grow, react to light, or reproduce. Reproducing means making new living things of the same kind.

Plants do not plan their shapes. A plant does not decide to grow spines because it feels thirsty. Young plants inherit features from the plants that made their seeds.

Claim, evidence, reasoning

A scientific explanation connects three things:

1. A claim says what you think is true.
2. Evidence is what you observe or measure.
3. Reasoning explains how that evidence supports your claim.

Here is an example.

• Claim: “A cactus’s thick stem helps it survive dry weeks.”
• Evidence: “The stem holds water, and rain can be weeks apart.”
• Reasoning: “Stored water supplies the cactus between rains.”

The reasoning connects the feature with a need. Saying “It helps because it helps” would leave that connection unexplained.

Use a count as evidence

Suppose you watch two patches of the same flowers. One patch has its petals; the other has petals removed. Watch each for 10 minutes. In these sample results, bees make 12 visits to the first patch and 2 to the second.

There were 10 more visits to flowers with petals. That supports the claim that petals help attract bees. The reason matters: bees can carry pollen, helping flowers make seeds.

Choose evidence that fits your claim. Counting petals would tell you how many petals there are. Counting bee visits helps answer whether flowers attract bees. Measurements become useful evidence when you connect them to the job you are explaining.

Most water enters a plant through its roots. Some reaches leaves high above the ground. Follow the path to see how the parts connect.

One joined path

Water moves from soil to root hairs, roots, stem, and leaves. The tiny tubes in these parts join together. Leaf veins are part of this water path.

Water carries dissolved nutrients from roots. Some water is used for food making. It also keeps soft stems and leaves firm and helps cool leaves on hot days.

Most water that reaches leaves does not stay there. It becomes water vapor, which is water as a gas. The vapor leaves through tiny holes in the leaves. This water loss is called transpiration.

A pull from the leaves

Plants have no heart to pump water upward. As water leaves the leaves, it pulls more water up the tubes. Water sticks to itself, so the pull can pass along the water path.

Think of sipping through a straw. Your pull comes from the top. A plant’s pull comes from water escaping at its leaves. The plant is not sucking with a mouth; the comparison helps you picture the direction of the pull.

Even very tall trees move water this way. Coast redwoods can grow more than 100 meters tall, about 330 feet. Their roots and top leaves are linked by water tubes.

Catch water from a leaf

You can collect evidence of water loss. On a sunny day, choose dry leaves on a leafy branch. Put a dry, clear bag around the branch and tie its opening. Put another dry bag around a nearby stick of similar thickness.

After a while, look for drops. The leaf bag should collect more. Water vapor leaving the leaves turns back into drops on the bag. The stick bag helps you compare water from the air already inside each bag. Remove both bags when you finish.

Weather changes water loss

Hot, sunny, windy weather can make leaves lose water faster. More water is then drawn from the roots, and soil dries sooner. A plant may wilt when water leaves faster than roots can replace it.

Water the soil around roots. Spraying leaves does not replace the main water supply. If roots are badly damaged, the plant can wilt even in damp soil.

Clear water is hard to follow inside a plant. Food coloring makes its path easier to see. The dye travels with liquid water and stays behind when water leaves as vapor.

Set up your test

Gather fresh celery with leaves, a clear cup, food coloring, and a ruler. Ask an adult to do all cutting.

1. Write a prediction, such as “The color will reach the leaves.”
2. Put 200 milliliters of water and 10 drops of coloring in the cup.
3. Have the adult cut 1 centimeter from the stalk’s bottom.
4. Stand the fresh end in the water. Record the starting time.
5. Check after 1 hour, 4 hours, and 24 hours. Measure the color’s height from the cut end.

Record what actually happens. Here is a sample for a stalk 20 centimeters long.

Between the first two checks, the color rose 9 centimeters. That took 3 hours: an average of 3 centimeters each hour. An average spreads the total rise evenly across the time. The water may have moved faster during some hours.

Look inside

Color appears in leaf veins and along leaf edges. Have the adult cut across the stalk. Colored dots near its curved outer side show the ends of tiny water tubes. The whole stalk does not turn one solid color.

Celery’s long stalk is a leaf stalk, not its main stem. It still carries water through tiny tubes, so it helps you study water transport.

Make useful comparisons

Stand a third stalk in plain water. It stays its usual color, helping show where the dye caused a change.

To test whether leaves help, compare two same-length stalks. Keep leaves on one and remove them from the other. Keep their water, dye, place, and test time the same. In sample results after 4 hours, color rises 12 centimeters with leaves and 7 without. That is 5 centimeters higher with leaves. Leaves losing water help pull liquid upward.

A cut white carnation can show the path too. Its petals take on the dye’s color. If an adult splits its stem between two colored cups, different tubes can carry colors to different parts.

Say what you found

A useful conclusion is “Water moved upward through tiny tubes and reached the leaves.” The cut celery has no roots, so root uptake needs a different test. Dye shows the path; it is neither plant food nor something plants need.

Most plants need light, water, air, nutrients, warmth, and room to grow well. Each need helps in a different way. More of something is not always better.

Light, water, and air

Light supplies energy for food making. Without enough light, a plant may become pale, thin, and weak. Some bend toward the brightest spot.

Water helps make food, carries nutrients, and keeps soft parts firm. Too little can cause wilting. Too much can fill soil’s air spaces and harm roots.

Plants use two gases in air. Leaves use carbon dioxide to make food. All living parts, including roots, also use oxygen. Plants need access to air above and below the soil.

Nutrients, warmth, and room

Nutrients help build healthy new parts. Most plants take them from soil water. Compost and fertilizer add nutrients to soil. Too much fertilizer can damage plants.

Plants grow best within suitable temperatures. Cold often slows growth. Frost can kill tender beans and tomatoes. Very hot conditions can harm them too. “Warmth” means a suitable temperature, not the hottest place you can find.

Roots need space to spread. Leaves need space to reach light. Crowded plants compete for water, light, and nutrients. A gardener may remove some crowded carrot seedlings so the rest have room.

Is soil itself a need?

Soil gives roots support, water, and nutrients. Many plants grow well in it. But plants can grow without soil when those needs are met another way.

In hydroponic growing, roots receive water with nutrients mixed in. The plants still need air, light, suitable warmth, and support. Taking soil away does not take away those needs.

Read the clues

Imagine three pots on a shelf.

• One has dry soil and drooping leaves. Check its water supply.
• One has soaking wet soil and yellow leaves. Adding more water could harm its roots.
• One has pale, stretched growth toward a window. It needs more light.

Check the plant and its surroundings, change the likely problem, and watch. The amount needed depends on the kind of plant. A fern can grow in shade, while many garden flowers need much brighter light.

A habitat is the place where a living thing lives. How much light, water, and warmth it has helps decide what grows there. Soil and space matter too.

Parts suit places

A cactus stores water in its thick stem. That helps it through dry spells. A water lily roots in pond mud, while its leaves float in the light. A fern grows well in damp shade. Many mountain plants grow low, away from strong, cold winds.

Plants can react to their surroundings without walking away. A shoot grows toward light, while roots grow downward. Put a seedling by a window and watch its stem bend. Turn the pot, and new growth bends toward the window again.

Many trees change with the seasons. They drop leaves in fall and live on stored food through winter. New leaves grow in spring.

When conditions change

Dry spells, floods, frost, extreme heat, and deep shade can threaten plants. Salt, pollution, and trampling can harm them too. A growing plant stays rooted in its place; its seeds can travel elsewhere.

Picture a large tree falling in a forest. Light reaches ground that was shady. Seedlings there can grow faster, and plants that need bright light appear. Years later, new trees may shade the ground again. Changes in conditions change which plants grow well.

Look for a pattern outside

Choose a sunny patch and a shady patch. In each, mark a square 1 meter long on each side. Count plants of each kind. Note dampness, soil, and signs of trampling too.

Suppose your sample counts are 18 dandelions in sunshine and 3 in shade. That is 15 more in sunshine, or 6 times as many. A table or labeled drawing keeps the comparison clear.

Light may explain the pattern. But the sunny square may also have different soil or water. Fieldwork compares places as you find them, so several things can differ. Record those differences. To test light more closely, grow matching plants and change only their light supply.

A good plant test begins with a question you can answer by watching or measuring. “Do bean plants grow stronger in light?” can be tested. You can record leaf color and stem strength, as well as height.

Choose what changes

In a fair test, change one thing and keep everything else the same. You might change light, water, soil, temperature, or fertilizer. Changing several at once makes the cause unclear.

Write a prediction before you start. For example, “Plants in the window will have greener leaves.” Then plan your comparison.

Use several plants in each group. One seedling might grow oddly on its own. Three in each group help you see whether a result is shared.

Set up a light test

Start with six bean seedlings, each 3 centimeters tall. Put three in a sunny window and three in a dark closet. Keep their kind, pots, soil, and room temperature the same. Give each 50 milliliters of water every 2 days.

Measure from soil level to the highest tip on the same days. Count leaves, note their color, and record whether stems stand firmly. A table makes changes easier to compare.

Here are sample results after 14 days.

The middle heights are 15 and 21 centimeters. The closet plants are 6 centimeters taller. But height is only one clue. Their pale leaves and weak stems show unhealthy growth.

Explain the result

A dark-grown seedling uses stored food to stretch toward light. It cannot make new food in darkness. If left there, it weakens and dies.

A conclusion matching these results is “Bean plants need light to grow strong and green.” Saying “Darkness makes plants healthier” would ignore the color and strength results.

Record changes over time

One window plant might measure 3 centimeters on day 0, 9 on day 7, and 15 on day 14. It grew 6 centimeters in each week. A line graph can show this change; a bar chart can compare groups.

Keep checking for long enough to see growth. Results that differ from your prediction can help you form a better explanation.

A flower helps a plant make seeds. Look from its outside toward its center. Many flowers have sepals, petals, stamens, and a pistil.

Outer parts

Sepals protect the flower while it is a closed bud. They are often small and green. Petals are often bright and may attract animals that carry pollen.

Flowers vary. Some have large petals; some have none. A sunflower head is made of many tiny flowers packed together.

Where pollen comes from

A stamen is a flower’s male part. It has two main pieces:

• The filament is a thin stalk.
• The anther sits on it and makes pollen.

Pollen is a powder of tiny grains. Dusty yellow or orange marks on a tulip’s anthers are pollen. Pollen helps seeds form, but a pollen grain is not a seed.

Where seeds can form

The pistil is the female part. It has three main regions.

An ovule can grow into a seed after fertilization. The ovary surrounds the ovules. Do not mix up the larger ovary with the tiny ovules inside.

You may also hear the word carpel. A pistil is made of one carpel or several joined carpels. The words do not always name exactly the same structure.

Look through a tulip

With an adult handling the cutting, look inside a tulip. Work from the outside inward. You may count 6 colored parts that look like petals. Inside are 6 stamens with anthers. In the center is 1 pistil. That gives 13 visible parts, before counting the ovules inside its ovary.

Many flowers have stamens and a pistil together. Squash and corn have separate flowers for the male and female parts. So use the parts you can see; do not expect every flower to match the tulip.

Pollen travels to a stigma before seeds develop inside the ovary. It does not simply fall off an anther and grow into a new plant.

A bee visits a flower to feed. While it eats, it may help that flower make seeds. The flower and bee each gain something.

What pollination means

Pollination moves pollen from an anther to a stigma. The pollen must be from the same kind of plant. Apple pollen reaching a rose will not help the rose make seeds.

Some plants can use their own pollen. Many need pollen from another plant of the same kind. Most flowers need pollination before they can make seeds.

Follow a feeding bee

1. A bee lands on a flower to feed.
2. Its body brushes the anthers. Pollen sticks to its hairs.
3. It flies to another flower of the same kind.
4. Some pollen brushes onto the sticky stigma.

The bee is looking for food. It does not need to plan the pollen delivery. Many flowers provide nectar, a sweet liquid the bee drinks. Bees also collect pollen for food.

For example, a bee can carry pollen from an apple blossom to a blossom on another apple tree. The receiving flower can then develop seeds. Those seeds grow inside the apple.

Flowers help visitors find them

Bright petals and sweet smells attract animals. Some petals have lines leading toward nectar. Long, tube-shaped flowers suit visitors with long tongues or beaks.

Bees are only some of the pollinators, or animals that carry pollen. Butterflies, moths, flies, and beetles pollinate too. Some birds and bats also do this job. Pale, scented flowers opening at night can attract moths or bats.

Most flowering plants depend on animals for pollination. The animals gain food, while plants gain help moving pollen. Watch bees from a little way off, and leave them untouched.

Keep pollen and seeds separate

Pollination happens before seeds form. The moving grains are pollen. Later, seeds form and may travel away from the parent plant.

A bird carrying pollen while drinking nectar is helping with pollination. A bird eating a berry and later dropping its seeds is helping with seed dispersal. Both help plants, but they happen at different stages.

Not every flower needs a visiting animal. Grasses, corn, wheat, oak, birch, and hazel use wind to carry pollen. Their flowers have features that suit moving air.

Send and catch

Anthers often dangle outside wind-pollinated flowers. Moving air shakes pollen loose. The pollen is light and dry, so it travels in air easily.

Stigmas are often large and feathery. Sticking out into the wind helps them catch passing grains, like a net.

Wind does not aim at a flower. Most grains land elsewhere. Making huge amounts of pollen increases the chance that some reaches a suitable stigma.

Compare flower clues

These are useful clues when you meet an unfamiliar flower. Look for several clues together. A small green flower with dangling anthers and feathery stigmas is most likely wind-pollinated. A scented flower with nectar is more likely to attract animals.

Follow pollen on corn

At the top of a corn plant, tassels release pollen. Wind carries it toward silks on young ears. Each silk leads to one possible kernel. A silk that receives no pollen cannot develop its kernel.

This links shape with function. Exposed tassels release pollen into the air. Exposed silks can catch it. Missing pollination can leave gaps among the kernels.

Trees and floating pollen

Many wind-pollinated trees flower before or while new leaves open. Fewer leaves block the pollen’s path. Pine trees also use wind, but they make cones instead of flowers.

Light, floating pollen from grasses and trees often causes hay fever. Bright petals do not tell you how much pollen floats in air. The sticky pollen of many insect-pollinated flowers mostly stays on the flower or a visitor.

Pollen reaching a stigma starts a new part of the story. Seeds form inside the flower, and fruit grows around them.

After pollination

A grain on a suitable stigma grows a tiny tube. The tube goes down the style toward an ovule in the ovary. Material from the pollen travels down it and joins with an egg inside the ovule.

That joining is fertilization. Pollination moves pollen to the stigma. Fertilization happens afterward inside an ovule. They are different steps.

After fertilization, parts of the flower change.

Petals often dry and fall off. The flower has finished attracting visitors, while the fruit and seeds keep developing.

What is inside a seed?

A seed holds a tiny new plant and a store of food. A tough seed coat protects them. The food feeds the young plant while it starts to grow.

A bean is a seed. When a soaked bean is split, you can see its food store and tiny plant. The outer coat wraps around them.

Fruit is more than sweet food

In science, a fruit develops from a flower’s ovary and holds seeds. A cucumber, pepper, tomato, pea pod, or acorn counts. Sweetness is not the test.

Follow a cherry flower. First, a bee brings suitable pollen. After fertilization, the ovary swells. The petals fall. Later, a red cherry surrounds a hard stone with a seed inside.

Now look at a pea pod containing 6 peas. The pod is the fruit. Each pea is a seed that developed from an ovule. Six seeds mean six ovules grew into seeds. A tiny flat pea shows a place where a seed did not develop normally.

Fruits can hold one seed or many. A cherry usually holds one; a tomato can hold many. The number depends on the ovules and how many develop into seeds.

Seeds often grow best away from the parent plant. Nearby seedlings compete with it for light, water, nutrients, and room. Seed dispersal means spreading seeds away.

Wind and water

Light seeds can have parts that catch air. A dandelion has fluffy parachutes. A maple has winged fruits that spin as they fall. Poppy heads shake tiny seeds out through holes.

Water can carry floating fruits. A coconut’s thick husk helps protect the seed inside. The fruit can float to a new shore. Some pond and riverside plants have seeds that float too.

Animals give seeds a ride

Animals help in three main ways.

• Hooks on burrs catch on fur or clothing. Seeds later fall elsewhere.
• Animals eat fruit, and some swallowed seeds leave in droppings.
• Squirrels and jays bury acorns. Some forgotten ones sprout.

A seed’s shape helps you work out its likely route. Hooks suggest a ride on fur. A sweet, colorful fruit can attract animals that eat it. Fluff or wings suggest wind.

Never taste wild berries or seeds unless a trusted adult says they are safe. Food that suits a bird can make a person very sick.

Bursting and falling

Ripe jewelweed pods burst when brushed, flinging seeds away. Gorse and broom pods twist open as they dry and throw seeds.

Some fruits simply fall. An acorn may drop, roll, and later be carried by an animal. A seed can use more than one kind of journey.

Traveling helps, but not every seed grows

Picture a seed dropping under a leafy parent. It may land in deep shade beside many roots. Another seed travels to an open patch with damp soil. That second place may offer more light and room.

Travel does not guarantee success. Seeds can land on a dry path, be eaten, or end up too crowded. Plants make many seeds because many never become new plants. Seeds cannot steer toward a good spot. Wind, water, animals, or falling carry them wherever the journey leads.

A model is a simple way to show how something works. To model pollination, show pollen moving. To model dispersal, show seeds traveling.

Make a pollen carrier

Wrap a fuzzy pipe cleaner around a stick. It will act as a bee. Make two paper flowers. Put a little cocoa powder on the first flower to stand for pollen.

Touch the fuzzy bee to the powder, then to the second flower. Powder moves between them. The fuzzy surface acts like hairs that carry pollen. The second flower stands for the flower receiving it on a stigma.

Test a smooth straw too. Use the same powder and flower setup. In sample results from 5 visits each, the straw transfers powder once. The pipe cleaner transfers it 4 times. That is 3 more successful transfers, supporting the idea that hairs help carry pollen.

Give model seeds a ride

Pull an old fuzzy sock over your hand. Make 10 paper seeds with small hook-and-loop patches and 10 smooth paper seeds. Sweep the sock across each group in the same way.

Suppose 8 hooked seeds stick, compared with 1 smooth seed. That is 7 more with hooks. The sock acts like fur, and the patches act like hooks on burrs.

Test a wind seed

Fold a paper spinner with two wings. Crumple a same-sized piece of paper into a ball. Have an adult drop each from 2 meters in front of a fan. Repeat each drop three times.

The middle distances are 130 and 25 centimeters. The spinner travels 105 centimeters farther. Its wings catch moving air and slow its fall.

Change, test, improve

If you test wing size, keep paper, drop height, and fan the same. Repeat drops because one may be unusual. Change one feature, test again, and compare.

Explain both what the model shows and what it leaves out. A fuzzy stick shows pollen sticking to hairs. It does not show an animal visiting for food. A model’s action matters more than looking exactly like a bee or seed.

A seed holds a living young plant. It may rest until conditions suit growing. Germination is when the seed starts to grow, or sprout.

Get started

Most seeds need water, air, and suitable warmth to germinate. Many can sprout in darkness. Their stored food supports the first growth before leaves can make food.

Soil is not needed for that first start. A bean can sprout on a damp paper towel. It still needs air; a seed left under too much water may lack it.

Once green leaves open, the seedling needs light to keep making food. It also needs nutrients to keep growing well. A sprouting seed and a leafy plant are at different stages.

Watch a bean

Put a bean between a damp paper towel and a clear jar’s side. Keep it at about 20 to 25°C (68 to 77°F). Watch and draw changes over the next two weeks. The exact timing can vary.

1. Water enters and the bean swells.
2. Its seed coat splits.
3. A tiny root usually comes out first and grows downward.
4. A shoot grows upward.
5. Green leaves open and begin making food.

The young plant is a seedling. Some seeds rest through winter before sprouting. Others wait much longer for suitable conditions.

Follow the whole cycle

A flowering plant’s life cycle repeats across generations.

Seed → germination → seedling → adult plant → flowers → pollination → seed formation → seed dispersal.

A seed landing in suitable conditions can begin the cycle again. Flowers help keep a flowering plant’s kind going by making new seeds. An old plant does not turn back into a seed; its seeds begin the next generation.

Plants without flowers

Not every plant flowers. Pine and spruce are conifers. They make seeds in cones and use wind to carry pollen. Many of their seeds have small wings.

Ferns and mosses make spores instead of seeds. These tiny structures can grow into new plants. Flowers and seeds describe one important kind of life cycle, but they do not describe every plant.