The Plant Kingdom
Introduction To Plants
What exactly makes a plant a plant? Why are mushrooms not considered plants? What characteristics and adaptations do plants have which allow them to live on land? What are stomata and why do plants have them? What are the purposes of flowers?
On this page, which is one in a series on biology, we'll be exploring plants.
Characteristics of Plants
Characteristics of Plants - What makes a plant a plant? How are organisms in the plant kingdom different from organisms in other kingdoms?
- Plants are eukaryotic, unlike bacteria in the Eubacteria and Archaebacteria Kingdoms. This means plants have a nucleus and some organelles within their cells.
- Plants use photosynthesis to gain energy, unlike organisms in the fungi and animalia kingdoms. (There are a few parasitic plants that do not use photosynthesis.)
- Plants are multicellular unlike bacteria, some fungi, and some protists.
- Plants reproduce sexually.
- Plants have an alternation of generations life cycle, which means plants that make gametes alternate with plants that make spores.
- The cells of plants have cell walls unlike the cells of animals.
- Plant cell walls contain cellulose unlike the cell walls of organisms in the Fungi and Eubacteria kingdoms.
- Plants have a waxy coating, called the cuticle, on the surface of the stems and leaves. This helps prevent the plant from drying out.
What adapations do plants have which allow them to live on land?
- A waxy coating, called the cuticle, on the leaves and stems to keep the plant from drying out.
- A way to reproduce on land, since the gametes didn't have water to swim in: pollination.
- A way to absorb water and nutrients from the soil: roots.
- A way to move oxygen and carbon dioxide into or out of the plant: stomata (tiny holes in the bottom of the leaves).
- A transportation system for carrying water and carbohydrates throughout the plant: vascular system.
- A support system for the plant: fibrous/woody structures and vascular tissues.
About the youtube below
This youtube on plant adaptations (below) is fairly long. If you are short on time, you may like to stop watching around 10:16.
Introduction to Plant Diversity
Cuticle - The waxy coating on the surface of plant leaves and stems helps prevent the plant from drying out.
Cuticles work two ways!
Yes, the cuticle on plants keeps some water out, but it also keeps a lot of water IN the plant!
Stomata - Stomata are tiny holes in plant leaves
The Function of Stomata
Stomata allow oxygen and carbon dioxide to pass into or out of the plant. Each stomata has a pair of guard cells on each side of it. As the guard cells change shape, the stomata open or close.
Alternation of Generations Life Cycle
Plants Have An Alternation of Generations Life Cycle
An alternation of generations life cycle means that the two types of reproductive means alternate back and forth. Sporophytes that make spores alternate with gametophytes that make gametes.
I'll explain more, but first take a look at this diagram. There is one sporophyte (near the bottom of the diagram) and two gametophytes (near the top, on the right). Notice also that the bottom half of the diagram is a different color than the top half. Everything in the bottom of the diagram is diploid, which means it has two sets of chromosomes. Everything in the top of the diagram is haploid, which means it only has one set of chromosomes.
Diagram of Alternation of Generations Life Cycle
Alternation of Generations Life Cycle
Each type of plant has two adult forms: a diploid sporophyte and a haploid gametophyte. The sporophyte form of the plant (on the bottom of the diagram) create spores by the process of meiosis. Meiosis reduces the number of chromosomes to half of what the sporophyte had, so the spores are haploid. Spores are reproductive cells that can grow into new plants without joining together with other reproductive cells. The new plants that grow from the spores are the gametophyte form of the plant. Because the spores wer haploid, the gametophytes are haploid too. Gametophytes produce male and female gamates (each of which only has one set of chromosomes) which join together and form a new sporophyte through the process of mitosis. Because the sporophyte gets one set of chromosomes from each parent, it now has two sets of chromosomes.
The Dominant Generation
In some types of plants, we see primarily the sporotphyte form of the plant. In other species, we are mostly aware of the gametophyte form of the plant. The form of the plant that is most obvious to us - the one that is larger and lasts longer - is called the dominant generation. In nonvascular plants, such as mosses, liverworts, and hornworts, the dominate generation is the gametophyte. In other words, when we look at moss, what we are usually seeing is the gametophyte form of moss. In vascular plants, the sporophyte form of the plant is the dominant form. In fact, the gametophyte in cone-bearing plants and flowereing plants is microscopic!
Alternation of Generations in Ferns
The diagram below shows you what the alternation of generations looks like in ferns. Notice that in this diagram, the sporophote is on the top of the picture. This is just the way that the author decided to draw it.
2 Types Of Plants
Vascular Plants and Nonvascular Plants
There are two types of plants. Vascular plants, which have a vascular system, and nonvascular plants, which don't. A vascular system serves to transport water, minerals, and nutrients throughout the plant.
Have you ever seen those long strands inside celery? Or maybe you've done the experiment where you let a piece of celery or a flower sit in colored water, and the colored water travels up the inside of the plant to the top? That "veins" that carried the colored water up the stalk are part of the plant's vascular system.
As you can see in the photo below, leaves have vascular tissue in them as well!
The Functions of a Vascular System
A vascular system doesn't just transport water and nutrients up from the roots though. It also carries sugars made during photosynthesis to other locations within the plant. Xylem is the part of the vascular system that carries water and minerals up from the roots. Phloem is the part that carries sugars to other places within the plant.
Nonvascular plants do not have true roots, stems, or leaves. The nonvascular plants, also called Bryophytes, include mosses, liverworts, and hornworts.
- Nonvascular plants do not have a vascular system to transport water and nutrients throughout the plant. Instead, they use osmosis and diffusion to transport water and nutrients within themselves.
- Because they must rely on osmosis and diffusion, nonvascular plants are small.
- Nonvascular plants require water for reproduction. Unlike vascular plants, the sperm must swim to the eggs of another plant of that same species.
- The gametophytes in nonvascular plants are larger than the sporophytes. When you look at moss, what you are mostly seeing is the gametophyte. The gametophytes are the part of the plant in which gametes are formed. Sporophytes are the part of the plant that produces spores. Remember that in an alternation of generations, gametophytes alternate with sporophytes.
- Rhizoids, which are hairlike projections, hold the gametophyte to the rock, base of a tree trunk, or other surface on which it grows.
- The sporophytes grow on the gametophytes.
Nonvascular Plants Include Mosses, Liverworts, and Hornworts - They do not have a vascular system.
Moss (shown above) has a cuticle (waxy coating), stomato (pores which let gases in or out), and water conducting cells.
Liverworts do not have stomata, cuticle, or water conducting cells.
Hornworts (shown above) have cuticules and stomata, but do not have water conducting cells.
Life Cycle of Moss
Not too long ago, my son and I headed down to the creek near our house. We found some moss on the bank, and stopped to take a look. On top of the green moss was a few very tiny stalks. When we very lightly brushed the stalks with our hands, a small wave of "dust" blew through the air.
The green layer of moss on the bank was the gametophyte. The tiny stalks coming up from the moss were the sporophytes. The dusty stuff coming out of the top of the stalks were spores, located in the sporangium (spore capsule.)
Learn More About Mosses and Liverworts
- Mosses and Liverworts
This is a nice site on mosses and liverworts.
Vascular plants have true roots, stems, and leaves.
The vascular system in vascular plants includes the roots, which carry water and nutrients into the plant from the soil, and the stem, which carries water and nutrients on upward. Even leaves have vascular tissue in them, as you saw in a photo on this page. You can find out more about the vascular system by watching the movie below on Xylem and Phloem.
Vascular plants can be divided into two types: vascular plants without seeds, and vascular plants with seeds.
Seedless Vascular Plants
Seedless Vascular Plants have the following characteristics.
- Seedless vascular plants are larger than nonvascular plants.
- They have true roots, stems, and leaves.
- They have xylem and phloem which carry water, nutrients, and sugars around the plant.
- Seedless vascular plants have sporophytes that are larger than their gametophytes. In fact, the gametophytes are usually below the surface of the soil.
- Seedless vascular plants require water during fertilization to enable the sperm gametes to swim to the egg gametes.
- Seedless vascular plants have drought resistant spores.
- Ferns have leaves that are called fronds. Fronds unroll as they grow.
Types of Seedless Vascular Plants - Club Mosses, Horsetails, Ferns, and Whisk Ferns.
Lycopodium (above) is a type of club moss.
Did You Know?
Horsetails can grow up to 20 feet tall!
Horsetails are tough plants! They aren't soft like ferns.
Two Types of Seeded Vascular Plants
Gymnosperms and Angiosperms
Vascular Plants With Seeds
Gymnosperms and Angiosperms
There are two types of vascular plants with seeds: Gymnosperms and Angiosperms.
Gymnosperm means, "naked seed." The seeds of gymnosperms are not found inside fruit.
Angiosperm means, "case seed." The seeds of angiosperms are found within fruit.
Gymnosperms - Conifers, Cycads, Ginkgo, and Gnetophytes
- Gymnosperms do not have flowers.
- Gymnosperms do not have fruit.
- Gymnosperms do have seeds.
- Most gymnosperms are evergreen trees with needles and cones.
- Gymnosperms do not require water for fertilization. (The sperm do not need to swim through water to get to the eggs. Instead they are carried as pollen in the wind.)
- Pollen is made up of male gametophytes. Seeds contain female gametophytes.
Gymnosperms - "naked seeds"
Angiosperms - Flowering Plants
In Angiosperms, the seeds develop within fruits.
- Angiosperms have seeds, flowers and fruit.
- The fruit often helps spread the seeds.
- Seeds are spread when they pass through animals who have eaten the fruit they were in. Seeds can also be spread by the wind or water.
- Water is not required for fertilization. (The sperm don't need to swim to water to reach the eggs.)
- Seeds have stored food within them. This stored food is called endosperm.
- Angiosperms are divided into two groups: monocots and dicots.
Corn and Bean Lab - Corn is a monocot and beans are a dicot
- Green Thumbs: Corn and Beans
This is an excellent lab to do while studying plants. You plant popcorn and beans, then do various experiments with them, and journal their growth, as the plants grow. For grades 4 to 12.
Monocot (left) and Dicot (right) plants
There are several differences between monocot and dicot plants. What's the first one you notice when you look at the plants in this photo?
Monocots - Flowering plants that have seeds with only 1 seed leaf.
Seed Leaves are the first leaves to pop out of the ground. Sometimes they are different than leaves that come after them. Another name for seed leaves is cotyledon.
Monocots have just one cotyledon. Dicots have two cotyledons.
- Monocots usually have flowers that have petals in multiples of 3.
- Monocots often have long, skinny leaves.
- Their veins run parallel to one another.
- Examples include: corn, grass, asparagus, tulips, crocus, and sunflowers.
Dicots - Flowering plants with two seed leaves.
Dicots have two cotyledons.
- Dicots also usually have flowers with petals in multiples of 2, 4, and 5.
- The veins of dicots are branching, rather than parallel.
- Examples include: broccoli, cabbage, peas, peanuts, peaches, apples, roses, beans, and tomatoes.
Young castor bean plant
This is a dicot plant because it has two seed leaves. (It also has two real leaves.) The seed leaves, or cotyledons, are the two smoother leaves with a rounded shape. The first real leaves are the smaller, lighter green leaves that have indentations.
What's the purpose of flowers?
Flowers serve the purpose of producing pollen and seeds. Flowers also attract birds, insects, and bats. Tiny bits of pollen grains stick to the animals and are then carried to another plant, aiding in the process of cross-pollination. Cross pollination simply means the transfer of pollen from one flower's anther to another flower's stigma.
Parts of a Flower
Parts of a Flower
Seeds - A seed contains the embryo (or baby) of a new plant.
Seeds are another adaptation that allows plants to live on land.
- Seeds have a protective seed coat which protects the plant embryo inside it. Without this seed coat, the embryo might dry out.
- Most seeds have a food supply within them to feed the new plant as it starts to grow.
- Many seeds have structures that help them be spread by the wind, water, or animals.
- Most seeds will only sprout when conditions in the environment are favorable for their growth.
Watch These Seeds Germinating (videos)
- Videos of Plants | Biology teaching Resources selected by D G Mackean
Time lapse film of seeds germinating.
Plant Biology Science Projects - Best Science Projects for Young Adults
This book provides the instructions for about two dozen fascinating science projects about seed plants. Included are experiments on the effect of acid rain on plants, the effects of growing plants in hydroponic solutions, how light effects plants, germination, transpiration, stomata, and a lot more . The projects do not require unusual or hard to obtain equipment and are explained step-by-step, even including suggestions for further investigations.
Paul Anderson (Bozemanbiology) discusses plant structure
Lab on the Structure and Function of Seeds
Life Cycle Of Plants
- The Life Cycle Of Plants - Animated Illustrations
To do the seed growth activity, hover over the arrow at the end of the line.
To do the flower parts activity, drag and drop the flower parts into place. This is difficult if you're not already familiar with where they go.
To do the seed dispersal activity, make sure you close each window before opening the next, or the sound from one will merge with the sound of the next!
Reproduction of Seed Plants
Reproduction of Seed Plants
Water is not needed for reproduction in seed plants.
In seed plants, the spores are not released. Instead, the spores grow into either male gametophytes (called pollen grains) or female gametophytes. The female gametophytes develop inside the ovule, which is located inside the sporophyte, down at the base of the flower.
So How Does Reproduction Occur?
Pollen grains (male reproductive structure) are transferred to the stigma (female reproductive structure in the center of the flower) via the wind or animals, during the process of pollination. When the pollen grains reach the stigma, a pollen tube grows down the flower into the ovule. This allows a sperm to reach an egg.
Reproduction of Flowering Plants
Short Movie of a Bee Pollinating a Flower - close up views
Plant Biology - Cliffs Quick Review
Characteristics of Plants - Paul Anderson discusses the characteristics of plants
Eyewitness Plant - A DK Eyewitness Book
You'll find a listing of all the pages in this biology series at: Biology: Information, Videos, and Labs
© 2012 JanieceTobey