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If you were put into a garden full of various plants and then given the job to classify each one, how would you be able to do it? Where would you start? Most people already know that organisms are classified into groups. Animals and plants are not the same. Dogs and bees are different. A person and a tomato cannot be brothers. Living beings have different characteristics that set them apart from one another. This is the same within any group of organisms. They can be further split into smaller groups based on physical, behavioral, or a number of different types of characteristics. Plants are no different. Plants are as diverse as animals, and we use the differences to classify them into groups and subgroups. A plant is any organism that can be classified into the Plant Kingdom. And each member of this kingdom is grouped further based on features such as root depth, stem thickness, and fruit production. To find where a plant belongs, observations and simple questions lead the way. This article is going to focus on four questions that can allow you to figure out where to classify many plants. How does the plant absorb and circulate food? A basic grouping of plants is based on how food is absorbed and circulated. A plant will either be classified as being vascular or nonvascular. Vascular plants have a well-developed system for transporting water and food; therefore, they have true roots, stems, and leaves. Nonvascular plants do not have a well-developed system for transporting water and food; therefore, do not have true roots, stems, or leaves. Vascular plants are the largest group in the Plant Kingdom. These plants have tube-like structures that provide support and help circulate water and food throughout the plant. Xylem transport water and minerals from the roots to the rest of the plant. Phloem transport food from the leaves to the rest of the plant. Examples include trees and many shrubs with woody stems that grow very tall and grasses, dandelions, and tomato plants with soft herbaceous stems. Dandelions are an example of a vascular plant. Nonvascular plants are much different and there are far less plants that fit into this group. Because they do not have root systems, nonvascular plants have other ways of transporting water and food. They must obtain nutrients directly from the environment and distribute it from cell to cell throughout the plant. This usually results in these plants being very small in size. Examples include mosses, liverworts, and hornworts. Mosses (hanging from the trees) are an example of a nonvascular plant. How does the plant reproduce and make new plants? There are two classifications of plants based on how they reproduce: seed-producing plants and spore-producing plants. Seed-producing plants are what we call plants that reproduce through seeds. Seed plants make their own seeds. Seeds contain the plant embryo (the beginnings of roots, stems, and leaves) and stored food (cotyledons) and are surrounded by a seed coat. From those seeds, new plants grow. Flowers and pine trees are both seedproducing plants. Spore-producing plants are plants that produce spores for reproduction instead of seeds. Spores are much smaller than seeds. Almost all flowerless plants produce spores. Examples include mosses and ferns. How does the plant produce seeds? Seed-producing plants are further split into two groups based upon how seeds are produced: flowering plants and cone-bearing plants. Flowering plants differ from cone-bearing plants because they grow their seeds inside an ovary, which is embedded in a flower. The flower then becomes a fruit containing the seeds. Flowering plants are also known as angiosperms. Examples include most trees, shrubs, vines, flowers, fruits, vegetables, and legumes. Cone-bearing plants are different because they never have flowers but produce seeds in cones. These plants are also called conifers or gymnosperms. Most conifers are evergreen with needle-like leaves. Examples include pine, spruce, juniper, redwood, and cedar trees. Gymnosperms like pine trees produce seeds without flowers, but angiosperms produce seeds from flowers. And the final question, what kind of leaves does the plant have? Leaves of a plant give us a lot of clues about the plant’s seeds. The more storage a seed has for food, the more leaves it will have. A seed with one food storage area is called a monocotyledon, or monocot. Flowers of monocots have either three petals or multiples of three. The leaves of monocots are long and slender with veins that are parallel to each other. The vascular tube structures are usually scattered randomly throughout the stem. Examples include grass, corn, rice, lilies, and tulips. A seed with two food storage areas is called a dicotyledon, or dicot. Flowers of dicots have either four or five petals or multiples of these numbers. The leaves are usually wide with branching veins. The vascular tube structures are arranged in circular bundles. Examples include roses, dandelions, maple, and oak trees. The oak tree is an example of a dicot, and the grass surrounding it is an example of a monocot. I’m a Survivor/Not Gonna Give Up… What a Plant Needs Plants are organisms that perform certain processes necessary for survival. A process is something inside of the plant that, usually, happens on a cellular level (in the cells of a plant). Plants cannot live without these three things happening inside of them. The vital/necessary processes are photosynthesis, respiration, and transpiration. Plants are autotrophs. This means that they are organisms that make their own food. Their food is a simple sugar and the process by which they make this sugar is called photosynthesis. Chloroplasts, found in the cells of the leaf, contain chlorophyll, a green pigment that absorbs light energy. During this process, plants use carbon dioxide gas from the air (taken in through openings, or pores, in the leaf called stomata) and water (taken in through the roots) to make sugar (food) in the leaves. During the process of photosynthesis, oxygen is also produced. The oxygen is released into the air through the stomata. Photosynthesis is the process that provides the oxygen in the atmosphere that most living organisms need. The food (sugar) created through the process of photosynthesis is used to provide energy needed by the plants to perform life functions. Sun Light Water Oxygen Chlorophyll traps light energy to make food. Carbon Dioxide Sugar To obtain the energy from the food it produces, plants must break down the sugar in the cells throughout the plant in a process called respiration. In this process, oxygen from the air (taken in through the stomata) combines with the sugar, which is then broken down into carbon dioxide and water. During this process, energy is released. This energy can now be used by the plant to perform life functions. The carbon dioxide and water that are formed are then given off through the stomata in the leaves. Some of the water taken in through the roots of plants is used in the process of photosynthesis. However, plants lose most of the water through the leaves. This process is called transpiration. Without a way to control transpiration, plants would wither up and die. Fortunately, plants are able to slow down transpiration. Guard cells, mostly on the underside of the leaf, open and close the stomata. When the stomata are closed, water cannot escape from the leaf. Just like every other organism on Planet Earth, plants must have food. Photosynthesis is the process by which the food is made from sunlight and water. The food is then broken down by the process of respiration. As a part of these processes, water is lost because of transpiration, but the plant can regulate this water loss by slowing down transpiration. All organisms need food to live, but they also need to respond to changes in the environment. Habitats for plants, animals, and insects are always changing. They change because of weather, season progression, introduction of new species, human intervention, or any number of reasons. When this happens, organisms must respond in order to survive and be able to reproduce. Plants are no different. They need to respond to environmental stimuli (changes or interactions from other organisms). The response depends upon the stimulus. Sometimes seeds do not have the right conditions to grow. Sunlight can be blocked from a growing plant. The direction a plant grows can change because of movement of soil. A water source can change or move. Animals may invade a plant’s habitat and interact directly with a plant. All of these stimuli trigger a behavioral reaction in most plants. Under certain conditions, when a mature plant or seed becomes or remains inactive because of growing conditions, it is said to be dormant. Dormancy is a period of time when the growth or activity of a plant or seed stops due to changes in temperature or amount of water. Dormancy allows various species to survive in particular environments. It helps to ensure that seeds will germinate when conditions are favorable for survival of the small seedlings. For example, leaves fall from trees prior to the conditions of winter and the leaf buds do not open again until conditions are favorable in the spring. This is a bag of corn. Corn is a plant seed. Corn seed bought in a store is an example of a seed in dormancy. Plants also have behavioral response mechanisms once the seed does start growing, During the other types of environmental stimuli, plants can respond by moving (during growth) their stems, roots, or leaves toward or away from the stimulus. This response, or behavior, is called a tropism. There are several types of plant tropisms. Phototropism is the way a plant grows or moves in response to light. A plant will grow in the direction of a light source. Often a plant will grow diagonally or sideways to follow the direction of sunlight. The satellite dish is casting a shadow and blocking the sun from this plant. The plant responds by growing in the direction of the sunlight. Gravitropism is how a plant grows or moves in response to gravity. This can also be called geotropism. Roots will always grow in the direction of gravity (down), and stems will always grow in the opposite direction. If a plant or tree is growing on a hill, it will grow in a slanted direction to the ground around it because it will always grow in a directional relationship to gravity and not the ground. Another example is that if you turn a plant upside down, the stem and leaves will start to grow upwards around the pot. (continued on next page) This tree is on a hill. Because of gravitropism, it grows in a direction diagonal to the ground. This is a very popular as-seen-onTV product that uses gravitropism to allow people to grow strawberries without a yard. Hydrotropism is what happens when a plant grows or moves in response to water sources. Roots will follow water. The roots go where the water is with hydrotropism, as the leaves and stem follow sunlight with phototropism. If a water source dries up or moves, the roots grow out in search of water. When a water source is found, the roots will grow in that direction. Thigmotropism is plant’s response to touch. Some plants have a reaction when touched or touching an object. A rare example being flowers that closed when touched. A very common thigmotropism, one so common it could be in your front yard, is something called morning glories. Morning glories grow a lot like a vine, and the stem has structures called tentacles. When these tentacles are not touching anything, they grow in a spiral shape. As soon as the tentacles touch something, they began to wrap themselves around the object as they grow. This response is a thigmotropism. To the left you see morning glories. Below you can see how the tentacles of the morning glories have wrapped themselves around the stems of other plants. This is a thigmotropism. Roots are another vital structure in plants that allow them to live and reproduce. They help anchor the plant in the ground. They also absorb water and nutrients from the soil and store extra food for the plants. The more surface area on the root that is available, the more water and nutrients it can absorb, and root hairs help to increase this surface area. There are two types of roots: fibrous roots and taproots. Fibrous roots consist of several main roots that branch off to form a mass of roots. Examples are grass, corn, and some trees. Taproots consist of one large, main root with smaller roots branching off. Examples are carrots, dandelions, or cacti. Seeds can also be a survival structure that has developed in plants. Seeds, in of themselves, are a way for plants to reproduce, but there other specific characteristics that some seeds have that help plants to live and thrive. Some seeds have special structures that allow them to be dispersed by wind, water, or animals. The seeds coat helps protect the embryo from injury and also from drying out. Dormancy and tropisms allow plants to adapt to changes in their environment. When they adapt, they have a much better chance of surviving and reproducing. Structured to Live Many flowering plants also have unique structures that aid in their defense and survival. Plants have structures for defense that protect them from threats and without these defenses the plant might die. One example of natural defense that plants have developed is the presence of thorns that can defend the plant from being eaten by some animals. Other examples can be fruits and leaves with poisons so that they are not eaten by animals or the ability to close its leaves when touched (thigmotropism). Holly tree leaves have small thorns on them, and this is a defense mechanism for this type of plant. Plants also have structures that allow them to survive in their habitats when the conditions are not suitable. An example that you probably did not realize was a survival structure is leaves. Leaves function as the site of photosynthesis, respiration, and transpiration in plants. Another well-known part of a plant that serves to aid in survival is the stem. Stems support the plant and hold the leaves up to the light. They also function as food storage sites. The xylem in the stems transports water from the roots to the leaves and other plant parts. The phloem in the stems transport food made in the leaves to growing parts of the plant. Stems are easier to see on flowers and small plants, but not everyone knows that the stem of a tree is the trunk. Without the structures mentioned, plants would have trouble continuing to live in certain areas. These structures developed to help allow plants to live in their environments and adapt will to changes in weather, soil nutrients, and water/sunlight sources. The Cycle of Life All flowering plants have similar life cycles, and each stage of the life cycle is distinct from the others and vital to survival of the plants. When seeds are dispersed from the parent plant, they can either lay dormant or they can begin to grow immediately given the right conditions. This early stage of seed growth is called germination. The roots begin to grow down, while the stem and leaves grow up. Over time the seed grows into a mature plant with the structures necessary to produce more plants. The growth and maturity of a plant is called plant development. It is only when the plant reaches full maturity that it can reproduce. The Life Cycle of Flowering Plants: 1. Germination 2. Plant Development 3. Pollination 4. Fertilization 5. Seed Production When pollen, which is produced in the stamen of a flower, transfers from stamen to pistil (pollination) and then enters the ovule, which is located in the ovary of a flower, fertilization occurs. The next step is seed production. Once the ovule is fertilized it develops into a seed. A fruit (fleshy, pod, or shell) then develops to protect the seed. Seeds are structures that contain the young plant surrounded by a protective covering. The life cycle then begins again once that seed germinates and begins to grow.