First Look; Background Information

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Youth Education Programof San Francisco Botanical Garden Society

A First Look at Plants

Background Information

AN INTRODUCTION TO THE PARTS OF FLOWERING PLANTSOur lives are intricately bound with the plants around us. They provide us with essentials for

survival like oxygen, medicine, clothing, and shelter and with tools and materials to make our

lives more comfortable and beautiful.

Plants are basically small factories that produce food from simple raw materials. And since they

alone are able to produce their own food, they are the basis for the food chains that support all

other living organisms on our planet.

There is fantastic variety in plant shapes and structures, as plants have adapted themselves in

clever ways to survive. Yet all flower and seed bearing plants share certain characteristics in theirbasic parts and the ways those parts function.

Each part of a plant has a specialized function, whether it controls the growth of the plant,

produces the food, or ensures survival through reproduction. Very basically, there are three major

organs in flowering plants: roots, shoots, and flowers. Roots and shoots are the vegetative

organs, providing a structure for growth and the factory for food production. Flowers are the

reproductive organ, forming the seeds to perpetuate the species. Here is a closer look at the basic

parts of flowering plants and their functions.

ROOTSAs part of the plants food-producing factory, the roots are specialists in charge of supplying the

minerals and nutrients needed for growth and the water needed to transport these substances to

the rest of the plant.

Roots serve three important functions:

- They absorb water and minerals from the soil- They anchor the plant to the soil.- They store excess food for later use.

At the very tip of each root is a tough protective cap that helps the root to push its way down into thesoil. This protective cover is constantly being replaced as it is worn away, and often the cap has a

slippery coating to help ease it through the soil. Just behind this root tip is the root meristem, and it is

from this section that the roots actually grow and develop.

The outer cells of the root form the skin of the root, called the epidermis. From the epidermis

grow the root hairs, delicate projections that absorb water and nutrients from the soil. New root

hairs are constantly growing as the root tip pushes its way deeper into the soil.


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While the function of roots remains the same, there is a great deal of variety in the way plants

have adapted their roots to perform their jobs. Here are some examples of specialized root

systems:

- Aerial roots develop on vining and epiphytic plants to anchor the plant and absorb moisturefrom the air. (orchids)

- Adventitious roots can grow from other parts of the plant like leaves or stems. (willow,tomato)

- Prop roots develop from the plant stems to help support a plant that is especially tall or wide.(corn, mangrove)

SHOOT SYSTEMThe shoot system of the plant consists of two parts that develop together: stems and leaves.

Stems The stem of a plant is the major support system for the leaves and flowers of the plant.The stem functions in four important ways:

- It supports the plant above ground.- It acts as a pipeline, conducting water and minerals up from the roots and passing food from

the leaves down to the roots.

- It stores water and excess foods.- It provides a framework for supporting leaves.Inside the stem is a complex system of ducts made up of specialized cells that run from the roots

up to all the growing parts of the plant. Most stems grow above the ground, but many plants

have developed specialized stems:

- Corns, tubers, rhizomes are all enlarged, underground stems that can store food and waterfor the plant. (potato, onion)

- Runners, stolons, rootstocks are specialized stems which grow near the surface of the soil andproduce new plantlets. (strawberry)

- Tendrils, thorns are outgrowths of stems. (pea, thistle)Leaves Leaves come in a fantastic variety of shapes, sizes, and patterns, but their basicfunction is the same to manufacture food for the plant through a process called photosynthesis.

In each leaf are chloroplast cells which contain a green pigment (chlorophyll) that captures and

stores the suns energy. With this energy the leaf combines two ingredients: water, which is

brought up from roots, and carbon dioxide from the air, which enters the leaf through tiny pores

on its underside called stomata. Hydrogen from the water and carbon dioxide from the air form

sugar for the plants food. The leftover oxygen atoms are released into the atmosphere as a by-

product of this process.


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The variety in leaf size, shape, and texture and the arrangement of leaves on a stem are all

adaptations that allow plants to hold or release water and to regulate the amount of sunlight

needed to make photosynthesis most efficient. There are numerous adaptations in leaves. For

example, silvery leaves reflect heat and light, succulent leaves store water, broad leaves capturesunlight, hairs, spikes, or toxins in leaves repel predators, and pointed leaves allow excess water

to drip off. Leaves may be smooth, scaly, hairy, fuzzy, waxy, or even covered with powders. Leaf

edges may be smooth, serrated, lobed, or toothed. Each plant has its own distinct characteristics

which can help to identify it.

Most leaves have two parts: the blade the thin, flat, broad part where photosynthesis occurs

and the petiole the narrow stalk that connects the blade to the stem. Here are some other

characteristics of leaves:

Leaf Form = the overall shape of the leaf:Simple The leaf is one broad piece which connects directly to the stem or twig.

Compound The leaves have blades divided into many separate leaflets connected to a

leafstalk.

Leaf Veins = the intricate system of veins in leaves are the ducts that carry water and mineralsinto the leaf and move the manufactured food sugars out. There are three common patterns:

Palmate Veins branch out from the leaf base into a webbed pattern like a hand with the

fingers spread.

Pinnate Veins branch out from each side of one middle axis, like a feather.

Parallel Veins all run in the same direction without intersecting.

Flowers More than half of the worlds plants are flower-bearing plants, called angiosperms.While there is tremendous variety in the size, color and shape of flowers, they all have the same

function to produce the seeds which will insure the growth of new plants and the survival of the

species.

The shape of flowers varies tremendously among flowering plants. Some flowers are highlydeveloped, showy advertisements designed to attract pollinators, while other flowers are fairly

plain. But almost all flowers have the same basic structure and characteristics.


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Here are some basic parts of a flower:

receptacle The enlarged end of a stem to which the flower parts are attached.

sepals Modified leaves, the outer circle of floral parts. Sometimes they are colorful, but

most often they are green. Together, the sepals are called a calyx.

petals The inner circle of floral parts, usually the showiest part of the flower. They may

be separate or fused together into tubular, cupped or bell shapes. Together the petals are called

the corolla.

stamens The male organ of the flower. It produces the male sperm cells needed to

fertilize the plants egg cells. The stamen is made up of two parts, a long slender stalk called the

filament, and a large tip, called the anther. The anther produces the powdery pollen which

contains the sperm cells. There are usually many stamens in a flower.

pistil The female organ of the flower. It produces the seeds for the plant. The pistil is

made up of three parts. At its base is the ovary, which contains the egg cells that will develop into

seeds. A small stalk, the style, grows up out of the ovary. At the top of the style is a sticky or

feathery surface for gathering pollen, called the stigma. There is usually only one pistil in a

flower.


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A complete flower has all the flower parts described above. Most, but not all flowering plants

bear perfect flowers, which contain both the male and female reproductive parts needed for

fertilization, the stamens and pistils. Some plants bear male and female parts in separate flowers.

When pollination occurs, pollen from the anther reaches the stigma at the top of the pistil. The

pollen grain sends a tiny tube down the style into the ovary and the sperm cells fertilize the egg

cells. Once fertilized, the egg cells begin to grow into a protective container for the seeds called a

fruit. The fruits may also help to disperse the seeds away from the parent plant. With the dispersal

and germination of the seeds, the life cycle of the plant begins again.

Seeds For all flowering plants the life cycle begins with the germination of a seed. Technically,a seed is the fertilized, ripened ovule of a flower. It is a complete, tiny plant in a dormant or

resting stage, waiting for favorable conditions to sprout and grow. While seeds vary dramatically

in size, shape, and coloring, each contains the parts that will become the roots, stem, and leaves

of a plant, as well as food that will nourish the infant plant until it can manufacture its own food.

There are three basic parts to a seed:

embryo Tiny plant contained within the seed. It is made up of the first leaves, the shoot

system that will become the stem, and the root tip that will develop into the complex root system.

seed coat (testa) The outer layer of the seed that keeps the embryo from drying out and

that protects it from the cold and from being destroyed by animals or disease. Hand lenses are a

good tool for revealing the details that distinguish each seeds distinctive coat. A seed coat can be

a slender, almost paper-thin covering, or it can be such a tough outer layer that it requires an

animals digestive juices or a fire to break it down.

food (endosperm) The inner layer surrounding the embryo and containing the starches,

oils, and protein that the young plant will use when it first sprouts until it can produce its own

food.

Vocabulary List for Young Students: basic parts of plants

Flower

Fruit

Leaf

Root

Seed

Stem


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Glossary

Adaptationa special trait or feature that improves an organisms chances for survival andreproduction.

Branch a large stem that grows from the trunk or main limb of a tree.Bud an undeveloped flower, stem, or leaf of a plant.Chlorophyllthe green pigment in a leaf that stores the suns energy to make food for the plant. Flower the reproductive organ of a plant.Fruit the ripened ovary of a plant that forms a container for the seeds.Germination the process of a seeds sprouting and beginning to grow and develop.Leaf the part of the shoot system of a plant that manufactures food.Nectar a sweet liquid which is secreted at the base of some flowers, to attract pollinators.Petal a modified leaf, usually the most colorful part of a flower.Pistil the female part of a flower composed of a stigma, style, and ovary.Plant a living organism capable of producing its own food through photosynthesis.Pollen the male sperm cells produced in the anther of the flower.Root the underground part of a plant that anchors it to the ground and draws in water andminerals.

Seed a tiny plant in a dormant stage; the ripened ovule of a flowerStamen the male, pollen-bearing part of the flower composed of a filament and an anther.Stem the major support system of a plant, serving as a pipeline to transport water, food, andnutrients.

Tree a woody plant composed of a main trunk, branches, and foliage.Twig a small shoot or branch of a woody plant.

First Look; Background Information

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