Vascular Plants
Typically all vascular plants have the same structure (even though they vary in sizes). The y have a root system situated underground, and a shoot system situated above ground. All Plants contain cell walls made up of cellulose. Vascular plants are primarily composed of three types of tissues: the dermal tissue, the vascular tissue and the ground tissue.
Vascular Plants
Typically all vascular plants have the same structure (even though they vary in sizes). The y have a root system situated underground, and a shoot system situated above ground. All Plants contain cell walls made up of cellulose. Vascular plants are primarily composed of three types of tissues: the dermal tissue, the vascular tissue and the ground tissue.
Dermal TissuesAre located on the outermost layer of the plant, they often have thicker call walls and are covered with a waxy cuticle to ensure that the plant is protected and that the plant does not lose any water. There are two kinds of dermal tissues epidermal and peridermal.
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Vascular TissuesVascular tissues transport water, nutrients and support the plant body. There are two types of vascular tissues: the xylem which have thick cell walls and they are dead at maturity, and there’s the phylum which are thin walled cells that are living at maturity.
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Ground TissuesThere are three types of ground tissues: Parenchyma which are thin walled cells that are living at maturity, they store carbohydrates and along with collenchyma they perform cellular process to support growth and development. Collenchyma have thick walled cells and are alive at maturity, they support and protect the body along with sclerenchyma. Sclerenchyma cells contain lignin in their cell walls and are dead at maturity.
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Phylogeny of Vascular Plants
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There are three major groups of vascular plants: the lycophytes and pteridophytes (mosses and ferns), the gymnosperms (conifers) and the angiosperms (flowering plants).
Angiosperm seeds contain colydon (stores nutrients) angiosperms divide into five groups, monocots consisting of one cotyledon and four dicots containing two cotyledons, they are: Amborellales, Nymphaeles, other early angiosperms and eudicots. Monocots and Eudicots are the most common angiosperms, monocots take up about 1/4 of all angiosperms and eudicots take up about 2/3. Monocots and Eudicots are what sustain humans, without them we might die. |
Leaves
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Leaves in plants have many roles, they not only act as a protection against herbivores and storage units, but they also create energy for the plant using gas exchange and photosynthesis. During photosynthesis leaves absorb sunlight with the help of chloroplasts, which contain photopigments. Photopigments absorb specific wavelengths of light and undergo both chemical and physical change, the most common photopigments are chlorophylls. Chlorophylls absorb red and blue wavelengths and reflect green, thus giving the leaves a green hue. The wavelengths that are not absorbed by chlorophyll are absorbed by accessory pigments found in chloroplasts. Other than photosynthesis leaves are capable of gas exchange, the epidermis (surface) of many plants contains pores which allow gases to filter in and out of the plant. There are two parts in gas exchange: photosynthesis and cellular respiration. Leaves also are a protection against herbivores, leaves can be unpleasantly textured so that animals would not seek them out, and some even produce specific chemicals that ward off animals.
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Leaves
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Leaves in plants have many roles, they not only act as a protection against herbivores and storage units, but they also create energy for the plant using gas exchange and photosynthesis. During photosynthesis leaves absorb sunlight with the help of chloroplasts, which contain photopigments. Photopigments absorb specific wavelengths of light and undergo both chemical and physical change, the most common photopigments are chlorophylls. Chlorophylls absorb red and blue wavelengths and reflect green, thus giving the leaves a green hue. The wavelengths that are not absorbed by chlorophyll are absorbed by accessory pigments found in chloroplasts. Other than photosynthesis leaves are capable of gas exchange, the epidermis (surface) of many plants contains pores which allow gases to filter in and out of the plant. There are two parts in gas exchange: photosynthesis and cellular respiration. Leaves also are a protection against herbivores, leaves can be unpleasantly textured so that animals would not seek them out, and some even produce specific chemicals that ward off animals.
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In order to carry out photosynthesis efficiently, leaves must have a large surface area to absorb as much sunlight as they possibly can. Most leaves have a flattened area called a blade, which is attached to a petiole (stalk that attaches leaf to a stem). Leaves can have one blade or a series of leaflets attached to to a petiole. The vein running through the leaves form an arrangement called venation, these veins contain vascular tissue. This venation helps distinguish monocots from eudicots, where eudicot venation forms a branch like maze of veins monocot veins are parallel to each other.
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Many different plants have special leaves, that are responsible for more than simply storing water and carbohydrates, many leaves contain special substances/structures that ward off predators. Cacti hide behind a thick outer layer that protects them from losing water, and spikes that are painful for the herbivores to eat/touch, plants like the tobacco plant produce a toxin in their leaf that repels herbivores. Leaves store water, if anything were to happen to leaves the plant would suffer severe damage. In cold areas to avoid suffering severe damage during winter, plants rid themselves of leaves. Then there are gymnosperms that produce specific chemicals that prevent their leaves from being damaged/frozen during cold weather and thus do not need to rid themselves of their leaves during the winter season. |
Stems
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Stems have many uses, typically humans use stems (of trees) to build things, such as: houses, furniture, accessories, and many more... Humans even use stems in food! They are also a valuable asset to our economy. Stems connect the roots to the leaves, they also provide support for the leaves and for the reproductive organs, they try to raise plants as high as possible to maximize their exposure to sunlight and tighten the chances of reproduction plants. In some cases, when the leaves of plants are incapable of storing water and photosynthesizing, stems take on that role. Stems are typically hard in order to provide support for the plant and also to provide protection from the environment and pests.
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Stems
Stems have many uses, typically humans use stems (of trees) to build things, such as: houses, furniture, accessories, and many more... Humans even use stems in food! They are also a valuable asset to our economy. Stems connect the roots to the leaves, they also provide support for the leaves and for the reproductive organs, they try to raise plants as high as possible to maximize their exposure to sunlight and tighten the chances of reproduction plants. In some cases, when the leaves of plants are incapable of storing water and photosynthesizing, stems take on that role. Stems are typically hard in order to provide support for the plant and also to provide protection from the environment and pests.
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There are two types of stems: herbaceous (stems without wood), and woody (stems containing wood). Herbaceous plant stems go through photosynthesis and their stem is easily bendable. Woody plant stems are made out of wood, they are protected by a hard bark and to hot go through photosynthesis. Monocots do not contain woody stems, while most woody eudicots are angiosperms. Herbaceous stems have a distinct vascular tissue arrangement, and consists of ground tissue and vascular bundles (arrangement of vascular tissue, in which the xylem is in the centre while the phloem is on the outside of the bundle). In monocots the vascular bundles are mixed with the ground tissue (a), while in edicts the vascular bungles form a ring around the ground tissue (b). In temperate regions the growth of woody plants occurs only during the spring and the summer, this is why when you cut open a tree it has rings.
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Roots
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Roots are typically located underground, though there are roots that can be seen above ground. The main function of roots it to keep the plant upright, and to absorb nutrients and water. Sometimes roots can act as a storage for water and carbohydrates. There are two basic root systems: the taproot system, which consists of a large ant thick root going downwards called a taproot, the taproot typically has small lateral roots branching off of it. Gymnosperms and angiosperms have taproot systems. Angiosperm monocots have a fibrous root system which are really shallow and consist of many small, branching roots.
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Roots
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Roots are typically located underground, though there are roots that can be seen above ground. The main function of roots it to keep the plant upright, and to absorb nutrients and water. Sometimes roots can act as a storage for water and carbohydrates. There are two basic root systems: the taproot system, which consists of a large ant thick root going downwards called a taproot, the taproot typically has small lateral roots branching off of it. Gymnosperms and angiosperms have taproot systems. Angiosperm monocots have a fibrous root system which are really shallow and consist of many small, branching roots.
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Roots have evolved special traits in order to ensure that they receive the maximum amount of nutrients and water that they possibly can. Many roots develop symbiotic relationships with other organisms, such as fungi, bacteria and even other trees (these roots act as parasites). The roots that humans consume are roots that are rich with carbohydrates (carrots) there are also tuberous roots, roots that specialize in storing carbohydrates (sweet potatoes). Roots rich in carbohydrates are often consumed by other organisms, therefore they must create ways to protect themselves, some roots produce certain toxins that repel predators, sometimes roots even produce toxins that kill off other roots.
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Transport
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The transport of water and nutrients through a plant is a complicated process, unlike many living organisms plants do not have a pump, so how do the water and nutrients get transported through plants? Well first the the water must travel through the roots, then through the stem, and finally it will reach the leaves where it will be stored or used in gas exchange. Water enters the root system by osmosis and nutrients enter with the help of active transport. Once the water molecules and dissolved nutrients have gone through the root system they must enter the stem in a form called xylem sap, which is pushed upwards towards the leaves with the help of root pressure and capillary action. Then finally it reaches the leaves with the help of transpiration.
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Transport
The transport of water and nutrients through a plant is a complicated process, unlike many living organisms plants do not have a pump, so how do the water and nutrients get transported through plants? Well first the the water must travel through the roots, then through the stem, and finally it will reach the leaves where it will be stored or used in gas exchange. Water enters the root system by osmosis and nutrients enter with the help of active transport. Once the water molecules and dissolved nutrients have gone through the root system they must enter the stem in a form called xylem sap, which is pushed upwards towards the leaves with the help of root pressure and capillary action. Then finally it reaches the leaves with the help of transpiration.
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The first thing that happens is nutrients and water get absorbed into the root system. The water enters the system through the cells (root hairs included)Nutrients on the other hand, enter the root system with the help of active transport and end up moving from cell to cell. Once all the required substances are in the cytoplasm of the outer root cells they are moved through the cortex to the endodermis. When the water/nutrients pass through the endodermis, the waxy casparian strip prevents them from re-entering the cortex. Finally the substances enter the vascular cylinder and are pumped into the xylem.
Once the nutrients/water pass through the endodermis they turn into a liquid substance called xylem sap. The xylem sap concentration in the xylem increases as the roots keep filtering more and more water/nutrients, they start creating root pressure which then proceeds to push the xylem sap towards the stem. Capillary action also helps the xylem sap rise up the stem. |
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Unfortunately root pressure and capillary action do not push the xylem sap into the leaves, so the leaves end up finishing this tough process themselves. Gas exchange occurs in leaves and for that the leaves have tiny holes(stomata) in the epidermis that regulate the gases that enter and exit the plant. The leaves release water vapour through the stomata, this process is called transpiration. As the water molecules move out of the leaf they pull other water molecules with them due to the attractive force between molecules. The molecules continue pulling each other along, and thus water reaches the plant everywhere. If the plant suddenly stopped transpiring then the water molecules would not be able to rise to every part of the plant.
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Plants like many other organisms need glucose in order to have energy. Cells that contain high concentrations of glucose are called sources while the cells with a low concentration are called sinks. One way to tell which part of the plant contains sinks is to establish where the plant is growing. Where growth occurs cells are using up lots of energy and thus have low concentrations of sugar (they use it up really quickly to provide energy to create new cells).
Sugars are capable of moving in any direction whether it is up or down the plant. If the source is at the top of the plant then the sink is on the bottom, the sugars will move down, if the sink is on the top and the sugars are on the bottom then the sugars will move up. The direction the sugar moves depends on whether it is spring or summer. In the spring all the starch and carbs that have been stored in the roots rush to the top creating new leaves/seeds. In the summer when the roots have given all their sugars they produce through photosynthesis down into the roots where they will be stored. Seeds/fruit are also sink cells as they require energy to develop. |