Plants that Make Seeds

Transcription

1 Plants and Animals Plants that Make Seeds Scientists often classify, or group, plants by how they reproduce. When a plant reproduces, it makes more of the same kind of plant. One group of plants makes seeds that grow into new plants. Some plants, like pine trees, grow seeds inside cones. Other plants, like roses and daisies, grow seeds inside flowers. Parts of a Flower Most flowers have four main parts. The parts vary in shape and size. The stamen is the male part of the flower. Stamens make pollen. Sperm cells in pollen join with egg cells to make seeds. The pistil is the female part of the flower. Inside the pistil is an ovary where egg cells are made. Petals protect the parts of the flower that make seeds. The green parts below the petals are sepals. Sepals are the leaflike parts that cover and protect the flower bud before the flower opens.

2 Pollen and Seeds Pollen has to get from a stamen to a pistil for a seed to form. Animals often help move pollen. Flowers make a sweet liquid called nectar. Some animals eat nectar. Pollen from the stamen can stick to the animal s body and rub off on the next flower. The movement of pollen from stamen to pistil is called pollination. A pollen grain lands on a pistil. Then a thin tube grows down into the pistil. Sperm cells from pollen move down the tube to egg cells. A sperm and an egg join in a process called fertilization. Each fertilized egg inside the ovary becomes a seed. Seeds on the Move Suppose seeds from a tree fell to the ground. Many seeds would start to grow. But the tree takes up a lot of space. Many seeds might grow poorly or not at all. Seeds that are scattered far from a parent plant will grow better. Some plants have parts that help them scatter their seeds. Starting to Grow A seed has a small, young plant inside it. To start to grow, or germinate, a seed needs water, oxygen, and the right temperature.

3 Inherited Characteristics More than one hundred years ago, a monk noticed that his pea plants were not all alike. They had different traits, or characteristics. Characteristics are the qualities a living thing has. Some pea plants were tall. Others were short. Some seeds were green, and others were yellow. The pea plants were like their parents because of characteristics passed on to them. But plants do not always look exactly like their parent plants. Plants and animals inherit characteristics. In science, to inherit is for a living thing to receive characteristics from its parents. A fish, the flounder can change color to match its background. This is an inherited trait.

4 Environmental Characteristics Something in the environment can cause a living thing to change. An environment is everything that surrounds a living thing. Weather and food supply are parts of the environment. The environment can cause a plant or an animal to look different or grow in a different way. A flamingo is a bird that has white feathers. But many flamingos are pink or red. That is because of the foods they eat. The foods change the color of their feathers.

5 Animal Instincts Animals inherit characteristics from their parents. Some traits make them look like their parents. They also learn behaviors, or ways of acting, from their parents. They learn behaviors from other animals too. Physical traits and behaviors help them stay alive. Some young animals are born with instincts that help them meet their needs. An instinct is a behavior that is inherited. For example, young geese are born with the instinct to follow their parents. By staying close to them, the young birds are protected.

6 Instinctive Behavior Migration Migration is not learned. Geese live in Canada and the northern United States in spring and summer. They migrate to warmer places during winter. Protection The porcupine will protect itself by turning its back and raising its sharp quills at an enemy. Hibernation Some animals hibernate. Hibernation is a state of almost no activity when temperatures are cold. During hibernation marmots may wake up a few times to eat.

7 Learned Behavior Many animals learn by watching their parents or other animals. The behaviors they learn develop over time. For example, lion cubs learn to hunt by watching older lions. Lions pounce, or jump, on their prey. A lion cub learns how to pounce on prey by jumping on its mother s moving tail. Learning and Instinct Combined Some behaviors are partly instinct and partly learned. The white-crowned sparrow inherits the recognition a song. Only sparrows of its kind know that song. But it does not inherit the way to sing the song. It must learn that from other sparrows.

8 Plant Life Cycles All plants have life cycles. A life cycle is the various stages a living thing passes through as it grows, matures, and finally dies. Most plant life cycles start with seeds that grow into young plants and then adult plants. Those adult plants produce seeds. Then the cycle starts again. Life Cycle of a Nonflowering Plant The pond pine is a plant that forms seeds in cones. Pond pines grow along riverbanks. The tree has both male and female cones. Pollen from the male cone fertilizes the female cone. Seeds form. Heat from forest fires causes the cones to open. Then the seeds can spread. Falling seeds are carried by wind. The young tree grows into an adult tree. A new cycle begins. Life Cycle of a Flowering Plant The daylily forms seeds in its flowers. Daylilies are grown in gardens all over the United States. When a seed germinates, it takes in water and swells. The seed coat splits. The first root and the first stem push through the seed coat. The young plant, or seedling, has leaves that make food. The adult plant gets larger and grows flowers. Pollinated flowers have fertilized eggs that become seeds. Fruits grow around the seeds. Over time, the fruit and seeds fall from the parent plant. New seeds germinate. The cycle begins again.

9 Animal Life Cycles Animals also go through a life cycle. They are born, they grow, they reproduce, and someday they die. Some animals change more than others as they grow. A mammal baby, such as a lion cub, often looks like its parents. Some insects change form as they grow. Life Cycle of a Reptile The American alligator is a large reptile. Reptile babies often look like their parents. A mother alligator lays eggs and covers them. She stays close by. After about 65 days, the mother breaks open the nest to help the young hatch. Young alligators eat insects and small fish. As they grow they will eat bigger animals. At the age of six, alligators are adults and can reproduce.

10 Metamorphosis Some animals go through metamorphosis, or a change in form, as they grow. Insects go through either complete or incomplete metamorphosis. Complete Metamorphosis Insects that go through complete metamorphosis go through four stages. Each stage looks different from the others. Butterflies go through complete metamorphosis. For example, a female zebra longwing butterfly lays her eggs on or near a vine. The eggs hatch into caterpillars that eat and get bigger. Each caterpillar hangs upside down from a branch. Its skin splits and a chrysalis is left. After about a week, the chrysalis breaks open. The adult butterfly comes out. Incomplete Metamorphosis Insects that go through incomplete metamorphosis, such as cockroaches, go through three stages. When the cockroach hatches, it looks like a tiny adult. It molts, or sheds its outer covering, as it grows. An adult female roach lays about 20 eggs in an egg case. Each young roach hatches in about 48 days. It is called a nymph. It looks like its parents, but smaller. The nymph grows and molts many times until it is an adult.

11 Glossary characteristics environment fertilization germinate inherit instinct life cycle metamorphosis pollination the qualities a living thing has everything that surrounds a living thing the process in which a sperm cell and an egg cell join to start to grow to receive characteristics from one s parents a behavior that is inherited the various stages a living thing passes through as it grows, matures, and dies a change in form that some animals go through as they grow the movement of pollen from stamen to pistil