Earth is home to hundreds of thousands of species of flowering plants. In recent studies, some scientists claim there may be as many as 400,000 different species.
Flowering plants share common parts. Observe a flowering plant, and you’re likely to see one or more flowers, a stem that supports the flowers, and leaves along the stem. If you were able to look beneath the ground, you would also likely see a root or root system. Tiny root hairs often branch off the roots.
As you continue reading, return to this page to refer to the diagram. Use its labels to help you remember the plant parts common to flowering plants.
After a seed is planted in the ground, the roots are the first part of the plant to develop. Roots anchor the plant in the ground. The plant will stay in that spot for its entire life.
The roots also absorb water and food from the soil and transport them to the stem. In some plants, food is stored in the roots. Most roots are covered with thread like structures called root hairs. These hairs increase the amount of food and water the plant can absorb from the soil.
Not all roots are the same. Some plants, such as grass, have a mass of roots that spread out wide and grow near the surface of the ground. Other plants, such as the dandelion and carrot, have one major root that grows deep into the ground. This deep root is called a tap-root.
Stems have two basic functions. They support the plant and they transport food and water throughout the plant. In some parts of the stem, water and nutrients travel up from the roots to the leaves. In other parts of the stem, food manufactured in the leaves moves down to the roots.
Tree trunks are stems that can grow quite tall and strong. Other stems are small and grow close to the ground. Some stems even grow underground. Onions and tulip bulbs are underground stems that also store food.
Leaves are green because so many of their cells contain chlorophyll, a green pigment, or colored substance, that enables light to be absorbed by the plant’s cells. It is in these cells, the chloroplasts, that food is made. Leaves also contain tiny openings, called stomates, that allow gases from the air to enter and exit the leaf. Both the chloroplasts and the stomates are essential to life on Earth.
Cacti, which grow in dry deserts, have leaves that are thin needles. This reduces loss of water through the leaves. The broad, flat leaves of some water-dwelling plants help the plants float.
Flowers are actually a specialized part of the stem. They are made of four different types of leaves called sepals, petals, stamens, and carpels.
Sepals enclose the flower bud. Petals have different colors and markings that attract specific insects, birds, and mammals. For example, some flowers have markings that guide insects to the center of a flower. Some flowers also produce fragrances to attract pollinators that have a better sense of smell than sight. Drawing organisms to flowers in this way is essential to plant reproduction. Reproduction is the process by which organisms generate new individuals of the same kind.
Stamens and carpels are reproductive structures. Stamens are the male parts of a plant and contain pollen. Carpels are the female parts of a plant and contain ovules, which can develop into seeds.
Flowers vary tremendously from plant to plant. Each type of flower may have a unique shape, color, markings, and fragrance. Flowers also may be simple or composite. Simple flowers, such as buttercups, are single flowers with many petals. Composite flowers, such as red clover and sunflowers, are made of clusters of many individual flowers, which may appear to be a single flower. Such flowers are sometimes called blooms. Because of their clustered arrangement, composite flowers produce many fruits. Each fruit carries seeds inside it.
Photosynthesis is the process that plants use to make food. The equation below will help you to understand it. It involves both sunlight and chlorophyll, the pigment that gives leaves their color.
|carbon dioxide + water + sunlight → sugar + oxygen|
|6CO2 + 6H2O + sunlight → C6H12O6 + 6O2|
As the Sun shines on a leaf, chlorophyll absorbs the Sun’s light energy. At the same time, water moves into the leaf from the stem and roots. Carbon dioxide, a gas from the air, enters the leaf through tiny holes.
Cell parts called chloroplasts perform the reactions of photosynthesis. Using the energy of sunlight, they combine carbon dioxide and water into glucose, a simple sugar. Oxygen is left over and is released into the air. Both plants and animals use that oxygen to break down food and release its energy, a process called respiration.
Reproduction in Flowering Plants
Most people notice and admire the petals of a flower. The petals, however, serve mainly to protect the plant’s reproductive structures. In the diagram of the flower, find the stamens that are just inside the petals. Stamens are the flower’s male reproductive structures. Tiny grains of pollen are produced on the tip of the stamens. Pollen is the male reproductive material of flowering plants. These pollen grains hold one half of the plant’s genetic information.
One or more carpels form the pistil. The pistil is the female reproductive structure of the flower. The pistil is covered with a sticky fluid. When a pollen grain lands on the top of the pistil, a tube grows down to the swollen base of the pistil. The base contains an egg cell, which holds the other half of the plant’s genetic information. The pollen grain travels down the tube and fertilizes the egg. Fertilization combines the genetic information from the male and the female cells.
If pollination, the process by which plants transfer reproductive materials from one plant to another, succeeds, the egg cell at the base of the pistil develops into a seed. The seed may develop into a fruit. The fruit falls to the ground or is eaten by a bird or an animal. Some seeds, such as dandelion seeds, simply blow away. If the seed lands in a place where it can root, it will grow into a young plant.
Bees are the pollinators for many types of plants. Bees are attracted to the bright colors and sweet smells of flowers. Bees also gather the flower’s nectar to make honey. As the bees explore the flower, they brush up against the stamens. The pollen sticks to the bees’ legs. When the bees enter the next flower, the pollen falls onto the pistil.
Other insects, birds, animals, the wind, and even rain can pollinate flowers. Some types of plants, such as cotton, pea, and tomato plants, can even pollinate themselves.