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Plants (3037 words)

PlantsLife science
7th grade Jr high
Chapter 1
Plants are the basis of the food pyramid for all living things, even other plants. They have always been very important to people, not only for food, but also for clothing, weapons, tools, dyes, medicines, shelter and a great many other purposes.Both humans and animals benefit from plants. We eat many different types of plants such as fruits and vegetables. We also use plants for our herbs. Plants are also used to manufacture many different products such as shampoos, rubber, paper, and camera film. In some countries, fermented sugar cane is used instead of gasoline.

Animals use plants in many different ways also. They eat many fruits and other plants. Many animals use plants for shelter. Plants also provide animals with protection from predators. The destruction of different plants sometimes leads to animals becoming endangered or extinct.

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The basic structure of plants consists of roots, stem, leaves, flower and/or fruit or seeds. A flower is the part of the plant that makes the seeds. The main parts of a flower are the carpels and stamens. These parts are often found in the center of the flower. There are egg cells in the carpel and pollen cells in the stamen. All flowers have four basic parts: sepals, petals, carpels, and stamen. Different flowers have different numbers and shapes of these parts.

Most plants can be divided into one of two general categories: herbaceous or woody plants. Herbaceous plants have soft stems, while woody plants are tree-like. Herbaceous plants produce completely new stems each year. The approaching cold weather causes the new stems to die back to the ground.

Some herbaceous plants survive periods of cold by forming underground bulbs, or tubers used for food storage. Many herbaceous plants complete their life cycles within one growing season and the whole plant dies, even the roots. These annuals produce seeds that will form new plants the next year.

Land plants are divided into two groups based on whether they have vascular tissues or not. All nonvascular plants are placed in one division. There are nine divisions of vascular plants. These are divided based on whether they form seeds or not.

Division Bryophyta – nonvascular plants
Class – Musci – the mosses
Division Pterophyta – ferns, group of seedless plants
Division Coniferophyta – cone-forming seed plants
Division Anthophyta – fruit-forming seed plants
Class – Monocotyledonae
Class – Dicotyledonae
Chapter 2
Roots help to anchor a plant in the ground. They also absorb water and minerals from the soil, and store food. Plants generally conform to one of two root systems, a taproot system or a fibrous root system.

A taproot system, generally found in dicotyledons, is made up of a central, large root that is called the taproot. The taproot is larger in diameter than the lateral roots. Lateral roots, which come from the pericycle, branch off from the taproot, and then lateral roots, can branch off other lateral roots. Taproots generally grow more deeply into the soil than do fibrous roots.

Unlike the taproot system, the fibrous root system is made up of thin, stringy roots that all have about the same diameter. These roots branch several times and form a complex mat under the plant that binds to the upper soil layers. Fibrous roots can be found in monocots such as grasses.

Some plants, such as the tomato plant, can have a fibrous root system or a taproot system depending on how the plant was grown. If the plant is grown from a seed, the plant will grow from a taproot. When the plant is grown from cuttings, a fibrous root system will form.

Every root grows a mass of tiny hairs near its tip to absorb water from the soil. These tiny hairs are called root hairs, and they are made from cells. They take water to the main root. The main root brings the water to the main plant. The roots also help hold the plant in the ground.

The inside of a root has four different parts. The epidermis is the outside part. It is like our skin. It protects the inside parts of the root, like our skin protects us. Plants take in water from the soil through their roots. The water passes through the vascular rays until it reaches the center of the root, the stele. This is where the veins are located. The veins are called xylem. They carry the water and food through the plant. Between the epidermis and the stele is the fleshy cortex.

Land plants are divided into two groups based on whether they have vascular tissues or not. All nonvascular plants are placed in one division. There are nine divisions of vascular plants. These are divided based on whether they form seeds or not.

Chapter 3
Stems support the plant. They transport vitamins, minerals and water up and down inside the plant. They also serve as a storage area for plants.

There are several different types of stems such as, woody, herbaceous, stolons, rhizomes, and bulbs. These are described below.

Herbaceous, non-woody, plants have vascular tissues arranged in bundles. These vascular bundles are either scattered throughout the stem or found in a ring toward the edge of the stem. The stems of herbaceous plants remain upright because of the structure of the cells in the stem. The individual cells have rigid walls. Water in the cells helps retain their shape. During dry periods water can be drawn out of the cells. Without sufficient water pressure, the cells become limp and the plant droops or wilts. After a rainfall, the water pressure increases as the individual cells reabsorb the necessary water and swell up. An example of a herbaceous plant would be simple flower or plant such as a daisy.

In woody plants, the phloem is located in a ring near the stem while the xylem is located more to the inside. The stem also takes on different appearances depending on the season.Springwood cells occur when water is plentiful. This is when wide xylem cells with thin walls are produced. During dry weather, new xylem cells are smaller with thicker walls and it is called summerwood. These changes produce a visible difference in the appearance of the woody stem. Since one sequence of this occurs each year, the age of a tree can be closely estimated by counting the “rings.” Heartwood occurs when the xylem becomes clogged, it can no longer transport water and will take on a dark color. This can be seen in the center of most trees. Sapwood is the lighter-colored wood in a tree. Even if the cells are no longer living, they can still function to transport water. An example of a woody plant would be an oak tree.

Rhizomes are grown from thickened, underground stems. Iris plants are rhizomatous-type plants. They can get overcrowded after growing in the same spot for a long time. When they don’t have enough space, there are fewer blooms. After the flowers have bloomed, they need to be cut back to the remaining healthy leaves in order for it to come back the next year. Then they are replanted below the soil surface.

Stolens are aboveground stems that grow parallel to the soil surface. The strawberry plant reproduces itself asexually by stolons, which are known as runners. Runner plants develop from axillary buds on the crown of the mother plant under long-day photoperiodic conditions of summer. When the days become shorter, the strawberry ceases to make runners and develops flower buds for the following season. Soon after the daughter plant reaches the soil, it develops vigorous roots (peg roots) that anchor it to the soil. It can remain attached to the mother plant for a long time, but it usually is capable of living independently within three to four weeks. A single mother plant can produce up to 1000 daughter plants in a single season.

Bulbs are like “storage tanks”. They help a plant survive dormant periods when it is too cold or hot for it to flower, and they nourish the plant during the growing and flowering season. There are three major types of bulbs, including true bulbs, such as hyacinths, daffodils, and tulips. Iris plants also have bulbs. After the blooming season is over, bulbs can be left in the ground. Some will, in time, spread out from their planting position and form new bulbs. This is called “naturalizing.” After a few years, some of the bulbs need to be dug up and divided to prevent overcrowding.

Chapter 4
Leaves are specialized for capturing sunlight for photosynthesis. The blade of a leaf is attached to the stem by a stalklike petiole. A simple leaf has one blade and one petiole. In compound leaves, the blade is divided into leaflets on the same petiole.

Animals inhale oxygen and exhale carbon dioxide. Green plants are the only plants that produce oxygen and make food, which is called photosynthesis. Photosynthesis means “putting together with light.” This takes place in chloroplasts, which have chlorophyll in them. Chlorophyll absorbs the sunlight. From sunlight, green plants combine carbon dioxide and water to make sugar and oxygen. Green plants use sugar to make starch, fats and proteins. These are tiny pores called stomata. Stomata are plant spores, which enable gas exchanges to take, place, and water to vapor to be lost. This has the benefit of moving water up the plane in a process called transpiration. The pore and the guard cells make up a single stoma. There may be as many as 6 million per typical leaf. The area just inside the internal structure of the leaf and below the stoma is the air space, which brings carbon dioxide very close to the palisade parenchyma tissue. Oxygen and carbon dioxide enter and leave through the stomata. Plants also sleep at night by closing their stomata. They cannot make food at this time.

When green plants absorb solar energy, they convert it to chemical energy. This chemical energy aids in the growth and functions of the plant. When an organism eats the plant, it gets energy to carry out its processes. Without solar energy, plants could not grow, and life on earth would cease to exist.

Chlorophyll, found in plants, is used to trap solar energy. This solar energy is import for the separation of H atoms from H2O. When water splits, H2 is released and built into ATP and NADPH2. O2 is given off, as well, which aids in the respiration of living organisms. The ATP and NADPH2 produced in the light phase is ready to be used for the reduction of CO2 to form glucose in the dark phase.

The chemical equation for photosynthesis in green plants:
6CO2 + 12H2O =====? C6H12O6 + 6O2 + 6H20
Currently, fossil fuels are our main source of useable energy on earth, but they are rapidly being depleted and one day may be non-existent. It is estimated, though, that all green plants on earth, together, convert 1.44 X 10 (14) kg of C from CO2 to produce energy containing carbohydrates every year.

Plants that have little or no chlorophyll, about a tenth of all the world’s species, cannot manufacture their own food and must get it in some other way. One method is that used by the sapronphytes, mostly bacteria and fungi that feed on dead or decaying organisms or on dead parts of plants living nearby. The Indian pipe, one of the few flowering saprophytes, obtains all of its organic food and minerals by means of a mutually beneficial association with fungi growing underground. These surround its roots and supply it with the nutrients from digested forest litter.

These scavengers are the many parasitic plants that feed only on living organisms, deriving all or most of their food and water from green plants. Dodder, for example, with no true leaves or roots, winds sinuous threads around its host to supply itself with food. The deadly dodder, however, also has enemies of its own, at least two kinds of aphids afflict it, extending the chain of eat and be eaten from the plant to the animal kingdom.

Chapter 5
All life on Earth depends on plants to provide good, shelter, and oxygen for other living things. Plant reproduction is important to all other life on this planet. The first step in plant reproduction is called pollination. This occurs when pollen grains, the male germ cell of a plant, reach the stigma, the female reproductive part of the same species of plant. Depending on the plant species, a flower can produce male, female, or both structures. Pollination can also occur within the same flower.

Most flowering plants depend on animals to make the vital pollen-grain delivery. The remaining flowering plants rely on wind and sometimes splashing raindrops to ferry pollen, but this is a less precise method. Pollinating animals do the job for a reward: food, usually in the form of nectar.

The female reproductive part of a flower is receptive to pollen only at certain times of the year. Creatures like insects and birds, which move from flower to flower in search of food, are a fast and often guaranteed way for plants to distribute their pollen.

Both the male and the female reproductive parts of a plant are in the center of the flower. The male, pollen-producing part is called the anther, held up by a stalk called a filament. The entire male part is called a stamen. Teach pollen grain is unique to its species. The female reproductive part of a plant, the stigma, sits on top of a style, or stalk, which leads to an ovary at the base. The entire female plant mechanism is called a pistil.

A pollinator such as a bee, bird, bat, or butterfly searches for food in a plant. The plant has secreted nectar, and tucks it in its blossom. While crawling around the blossom looking for nectar, the pollinator rubs against the pollen, which becomes attached to different parts of the pollinator’s body. When the pollinator visits another blossom, it transfers the pollen grains from its body onto a strategically placed stigma. After it reaches the stigma, the pollen grain grows a tiny pollen tube down the style and into an egg-filled ovary. Eventually, the pollen and the egg form a seed. The flowers use this pollen to make seeds. Other flowers use their own pollen to make seeds.

A seed has everything it needs to produce new plants. No seed can grow with the fruit around it. A seed has to have enough water, good soil, and sunlight. Sometimes people plant them and other times the seeds get planted on their own. People also put seeds in gardens or fields and water and fertilize the seeds.

Birds help fruit seeds to spread by eating the fruit, the letting the pit or seed drop. Some seeds travel by sailing in the wind. Others float in the water to get to the land. Some seeds attach themselves to people or animals. Seeds can also grow in a flower and drop to the ground. When the seeds leaves the flower or whatever it was in, its called dissemination.

Chapter 6
Plants are divided up into four main groups; these are called mosses and liverworts, ferns, conifers and flowering plants. All plants and trees fall into one of these groups.

Ferns – Have proper roots and produce spores.

Mosses ; Liverworts – simple plants which do not have proper roots.

Conifers – trees with needle-shaped leaves and cones
Flowering Plants – have flowers which produce seeds
The Pterophyta is a group of seedless plants. These plants reproduce by forming spores. Examples of these plants would be the ferns, mosses, algaes, liverworts, and hornworts.

Ferns range in size from just a few inches to 25 meters in height. The leaves of a fern are known as fronds. Ferns are vascular plants that reproduce by forming spores. Spores form in sacs called sporangia on the underside of the fronds.

Mosses have structures that serve as roots and leaves, but no true roots and leaves. They produce sexually by forming spores. A single moss plant is a gametophyte. When moss reproduce, the sperm from one gametophyte fertilizes the egg of another, producing a zygote. A Sporophyte, a stalk-like structure with a capsule contains the spores that grow from the zygote. When released, the spores will grow into new gametophytes.

Liverworts and Hornworts
While people typically know what a moss is, few have even heard of liverworts and hornworts. These primitive plants function much like mosses and grow in the same places, often intertwined with each other. The liverworts take on one of two general forms, making them into two classes of liverworts: Jungermanniidea are leafy, like moss and marchantiopsidea are leaf-like.

Hornworts are very similar to liverworts but differ in the shape of the sporophyte generation. Instead of generating spores in a capsule atop a stalk, the hornwort generates spores inside a green horn-like stalk. When the spores mature the stalk splits, releasing the spores. Hornworts are grouped into a single class, anthocerotae.

Mosses, liverworts, and hornworts do not need to support the leaves and other parts of the body so they do not collapse. The do need to obtain water and minerals. They transport food, water, minerals, and other materials from one part of the body to another. They try to prevent excess water from going into the environment. Both sperm and egg cells together are needed for reproduction to occur.

A multicellular alga lacks the tubes that transport water and other materials through the bodies of land plants. They are divided into three groups – red, brown, and green algae. They all make their own food (autotrophs) with photosynthesis. Their life cycles, pigments, and stored food supplies are similar to land plants. They evolved about 450-500 million years ago.

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