Free printable SSAT practice test for Grade 4

In many parts of the United States, fall turns the trees into a painting. Green leaves become yellow, orange, and red, and then they drift to the ground. Where do those bright colors come from?

Most of the year, leaves are green because they are full of a substance called chlorophyll. Chlorophyll helps a tree make food from sunlight, water, and air. A leaf is a little food factory, and chlorophyll is the worker that runs it.

But chlorophyll is not the only color in a leaf. Yellow and orange colors are there all summer long. We just cannot see them, because there is so much green covering them up.

As fall arrives, the days grow shorter and the nights grow cooler. The tree begins to get ready for winter. It slowly stops making chlorophyll. As the green fades away, the yellow and orange that were hiding underneath finally show through.

Red is different. Some trees, such as certain maples, make new red coloring in the fall, especially when the days are sunny and the nights are cool. That is why a sunny, crisp autumn often has the brightest reds.

Finally, the tree seals off each leaf where it joins the branch. With no water coming in, the leaf dries out and falls. The tree rests through the winter, and in spring, new green leaves begin the cycle again.

A honeybee that finds a field full of flowers has a problem. The hive may be far away, and thousands of other bees need to know where the food is. Bees cannot talk, and they cannot draw a map. So how does one bee tell the others where to go?

The answer is a dance. When a worker bee returns to the hive, she moves across the honeycomb in a special pattern called the waggle dance. She walks forward in a straight line while shaking her body from side to side. Then she circles back and does it again, over and over.

Every part of the dance carries information. The direction of the straight walk tells the other bees which way to fly, compared with the position of the sun. If the bee walks straight up the honeycomb, the flowers are in the same direction as the sun. If she walks a little to the right, the flowers are a little to the right of the sun.

The length of the waggle tells how far away the flowers are. A short waggle means the food is close. A long waggle means the bees will need to fly a longer way.

Other worker bees crowd around the dancer and follow her movements. They also smell the flowers' scent on her body. Then they fly out of the hive, ready to find the field on their own.

Scientists who study bees were amazed when they first figured out this dance. It showed that even a tiny insect can share exact, useful information with the rest of its group.

When winter comes, food becomes hard to find. Plants stop growing, insects disappear, and snow covers the ground. Some animals fly or walk to warmer places. Others stay put and do something remarkable: they hibernate.

Hibernation is much deeper than an ordinary night's sleep. A hibernating animal's body slows almost to a stop. Its heart beats much more slowly, and it breathes only now and then. Its body temperature drops, sometimes close to the temperature of the air in its den.

The woodchuck, also called the groundhog, is a famous hibernator. In the fall, it eats as much as it can and grows fat. Then it curls up in an underground burrow. During hibernation, its heart may beat only a few times a minute, and it lives on the fat it stored.

Many bats hibernate too. They hang upside down in caves, where the temperature stays cool but does not freeze. If people disturb them, the bats may wake up, and waking uses up energy they need to survive the winter.

Why does slowing down help? An active body burns a lot of energy, like a car with its engine running. By slowing everything down, a hibernating animal uses so little energy that its stored fat can last for months.

When spring returns and food appears again, the animal warms up, wakes, and goes back to its busy life.