Plant Organ Systems PDF

GENERAL BIOLOGY 2 PLANT ORGAN SYSTEMS system produces food through photosynthesis, In plants, similar to animals, different types of and the root system absorbs water and nutrients tissues work together to perform unique from the soi...

GENERAL BIOLOGY 2 PLANT ORGAN SYSTEMS system produces food through photosynthesis, In plants, similar to animals, different types of and the root system absorbs water and nutrients tissues work together to perform unique from the soil. These two systems are essential for functions, forming organs. These organs then the survival of all vascular plants. work together in groups to form organ systems. Vascular plants have two distinct organ systems: the shoot system and the root system. 1. Shoot System: The shoot system generally grows above the ground, where it absorbs light needed for photosynthesis. It consists of three main parts: stems, leaves, and buds. Stems: provide support and transport water and nutrients throughout the plant. They can be woody or herbaceous and can grow upright, creeping, or climbing. Leaves: are the main site of Here are some additional details about plant organ photosynthesis, where plants convert systems: sunlight, water, and carbon dioxide into Vascular tissue: Plants have a specialized food (sugar). They come in a wide variety transport system called vascular tissue. of shapes and sizes, and their adaptations This tissue consists of two types of cells: vary depending on the plant's xylem and phloem. Xylem transports environment. water and nutrients from the roots to the Buds: are undeveloped shoots that can leaves, while phloem transports food give rise to new stems, leaves, or flowers. produced by the leaves to the rest of the They allow plants to grow and reproduce. plant. The shoot system is consist of two Meristems: Meristems are regions of portions: the vegetative (non- undifferentiated cells that are responsible reproductive) parts such as the leaves and for plant growth. They are located in the the stems, and the reproductive parts tips of roots and shoots, as well as in other which includes flowers and fruits. parts of the plant. Hormones: Plant hormones are chemical 2. Root System: messengers that help to regulate plant The root system is usually underground, where it growth and development. They are anchors the plant and absorbs water and produced in different parts of the plant nutrients from the soil. and travel throughout the plant to reach It consists of three main parts: primary roots, their target tissues. secondary roots, and root hairs. Primary roots: are the first roots to Plant Tissues develop from a seed. They grow Plants are multicellular eukaryotes with downward and give rise to secondary tissue systems made of various cell types that roots. carry out specific functions. Plant tissue systems Secondary roots: branch off fall into one of two general types: meristematic from primary roots and grow tissue, and permanent (or non-meristematic) outward and downward. They increase tissue. the surface area of the root system, Cells of the meristematic tissue are found in allowing the plant to absorb more water meristems, which are plant regions of continuous and nutrients. cell division and growth. In contrast, permanent Root hairs: are tiny projections that tissue consists of plant cells that are no longer increase the surface area of the roots and actively dividing. help them absorb water and nutrients from the soil. Meristematic tissues consist of three types, based The shoot system and root system work together on their location in the plant. to keep the plant alive and healthy. The shoot  GENERAL BIOLOGY 2 Apical meristems contain meristematic tissue located at the tips of stems and roots, which enable a plant to extend in length. Lateral meristems facilitate growth in thickness or girth in a maturing plant. Intercalary meristems occur only in monocots, at the bases of leaf blades and at nodes (the areas where leaves attach to a stem). This tissue enables the monocot leaf blade to increase in length from the leaf base; for example, it allows lawn grass leaves to elongate even after repeated mowing. Secondary tissues are either simple (composed of similar cell types) or complex (composed of different cell types). Dermal tissue, for example, is a simple tissue that covers the outer surface of the plant and controls gas exchange. STEMS Leaves are attached to the plant stem at areas called nodes. An internode is the stem region Stems are a part of the shoot system of a plant. between two nodes. The petiole is the stalk The stem of the plant connects the roots to the connecting the leaf to the stem. The leaves just leaves, helping to transport absorbed water and above the nodes arose from axillary buds. minerals to different parts of the plant. It also helps to transport the products of Stem Anatomy photosynthesis, namely sugars, from the leaves to Like the rest of the plant, the stem has three tissue the rest of the plant. systems: dermal, vascular, and ground tissue. Each is distinguished by characteristic cell types Plant stems, whether above or below ground, are that perform specific tasks necessary for the characterized by the presence of nodes and plant's growth and survival. internodes. Nodes are points of attachment for leaves, Plant tissues aerial roots, and flowers. All plants have tissues, but not all plants possess The stem region between two nodes is all three of the following types of tissues: called an internode. The stalk that extends from the stem to the DERMAL TISSUE base of the leaf is the petiole. Dermal tissue: Consisting primarily of An axillary bud is usually found in the axil epidermal cells, dermal tissue covers the entire the area between the base of a leaf and the surface of a plant. Guard cells in a plant’s stem where it can give rise to a branch or a epidermis control the opening and closing of little flower. holes called stomates that allow the plant to The apex (tip) of the shoot contains the exchange gases with its environment. apical meristem within the apical bud. The dermal tissue of the stem consists Herbaceous versus woody stems primarily of epidermis, a single layer of cells Biologists use the appearance and feel of a plant’s covering and protecting the underlying tissue. stem to place it into one of two categories: Woody plants have a tough, waterproof outer herbaceous (where the stem remains somewhat layer of cork cells commonly known as bark, soft and flexible) and woody (where the stem has which further protects the plant from damage. developed wood). Epidermal cells are the most numerous All plant cells have primary cell walls made of and least differentiated of the cells in the cellulose, but the cells of woody plants have extra epidermis. The epidermis of a leaf also contains reinforcement from a secondary cell wall that openings known as stomata, through which the contains lots of a tough compound called lignin. exchange of gases takes place. Two cells, known Plants that survive just one or two growing as guard cells, surround each leaf stoma, seasons — that is, annuals or biennials — are controlling its opening and closing and thus typically herbaceous plants. Plants that live year regulating the uptake of carbon dioxide and the after year, called perennials, may become woody. release of oxygen and water vapor. Trichomes are  GENERAL BIOLOGY 2 hair-like structures on the epidermal surface. xylem cells with thinner walls; they are shorter They help to reduce transpiration (the loss of than tracheids. Each vessel element is connected water by aboveground plant parts), increase solar to the next by means of a perforation plate at the reflectance, and store compounds that defend the end walls of the element. leaves against predation by herbivores. Water moves through the perforation plates to travel up the plant. Phloem tissue is composed of sieve-tube cells, companion cells, phloem parenchyma, and phloem fibers. A series of sieve-tube cells (also called sieve-tube elements) are arranged end to end to make up a long sieve tube, which transports organic substances such as sugars and amino acids. The sugars flow from one sieve-tube cell to the next through perforated sieve plates, which VASCULAR TISSUE are found at the end junctions between two cells. Vascular tissue: The system of tubules Although still alive at maturity, the nucleus and inside a plant that carries nutrients around is other cell components of the sieve-tube cells have made up of vascular tissue. Vascular tissue disintegrated. consists of a water-transport system called xylem Companion cells are found alongside the and a sugar-transport system called phloem. sieve-tube cells, providing them with metabolic Vascula tissue also contains the vascular support. The companion cells contain more cambium, a tissue of cells that can divide to ribosomes and mitochondria than the sieve-tube produce new cells for the xylem and phloem. cells, which lack some cellular organelles. The xylem and phloem that make up the vascular tissue of the stem are arranged in distinct strands called vascular bundles, which GROUND TISSUE run up and down the length of the stem. The Ground tissue is mostly made up of vascular bundles of dicot stems are arranged in a parenchyma cells, but may also contain ring. In plants with stems that live for more than collenchyma and sclerenchyma cells that help one year, the individual bundles grow together support the stem. The ground tissue towards the and produce the characteristic growth rings. In interior of the vascular tissue in a stem or root is monocot stems, the vascular bundles are known as pith, while the layer of tissue between randomly scattered throughout the ground the vascular tissue and the epidermis is known as tissue the cortex. Ground tissue: This tissue type makes up most of a plant’s body and contains three types of cells: Parenchyma cells are the most common ground tissue cells. They perform many basic plant cell functions, including storage, photosynthesis, and secretion. Parenchyma cells are the most common plant cells. They are found in the stem, the root, the inside of the leaf, and the pulp of the fruit. Parenchyma cells are responsible for metabolic functions, such as Xylem tissue has three types of cells: xylem photosynthesis, and they help repair and parenchyma, tracheids, and vessel heal wounds. Some parenchyma cells also elements. The latter two types conduct water and store starch. are dead at maturity. Tracheids are xylem cells with thick secondary cell walls that are lignified. Water Collenchyma cells have thick cell walls in order to moves from one tracheid to another through help support the plant. regions on the side walls known as pits, where Collenchyma cells are elongated cells with secondary walls are absent. Vessel elements are unevenly thickened walls. They provide  GENERAL BIOLOGY 2 structural support, mainly to the stem and This alternation of early and late wood is leaves. These cells are alive at maturity and due largely to a seasonal decrease in the number are usually found below the epidermis. The of vessel elements and a seasonal increase in the "strings" of a celery stalk are an example of number of tracheids. An examination of the collenchyma cells. number of annual rings and their nature (such as their size and cell wall thickness) can reveal the Sclerenchyma cells are similar to collenchyma age of the tree and the prevailing climatic cells, but their walls are even thicker — so thick, in conditions during each season. fact, that mature schlerenchyma cells die because they can’t get food or water across their walls via osmosis. Sclerenchyma cells also provide support to the plant, but unlike collenchyma cells, many of them are dead at maturity. There are two types of sclerenchyma cells: fibers and sclereids. Both types have secondary cell walls that are thickened with deposits of lignin, an organic compound that is a key component of wood. Fibers are long, slender cells; sclereids are smaller-sized. Sclereids give pears their gritty texture. Humans use sclerenchyma fibers to make The types of plants linen and rope. Based on the types of tissues they have and reproductive structures they make, plants can be organized into four major groups: Bryophytes are plants such as mosses that don’t have a vascular system and don’t produce flowers or seeds. Ferns have vascular tissue, but they don’t produce seeds. Gymnosperms (also known as conifers) have vascular tissue and produce cones and seeds, but they don’t produce flowers. Angiosperms (or flowering plants) have vascular tissue and produce both flowers and seeds. Two distinct groups exist among flowering plants: Some plant parts, such as stems and roots, Monocots, like corn and lilies, have seeds continue to grow throughout a plant's life: a that contain one cotyledon (tissues within the phenomenon called indeterminate growth. Other seed that supply nutrition to the embryo and plant parts, such as leaves and flowers, exhibit then emerge as the first leaves after the seed determinate growth, which ceases when a plant begins to grow; they’re also referred to as seed part reaches a particular size. leaves). Dicots, like beans, oak trees, and daisies, ANNUAL RINGS have seeds that contain two cotyledons. The activity of the vascular cambium gives rise to annual growth rings. The Three Classes of BRYOPHYTES: During the spring growing season, cells of the secondary xylem have a large internal Liverworts (Marchantiophyta): Known for diameter and their primary cell walls are not their flattened, lobe-shaped thalli, extensively thickened. This is known as early characterized by simple internal structure and wood, or spring wood. no true roots, stems, or leaves. Examples During the fall season, the secondary include the leafy Marchantia and thallose xylem develops thickened cell walls, forming late Riccia. wood, or autumn wood, which is denser than early wood.  GENERAL BIOLOGY 2 Mosses (True Bryophyta): The most familiar Gymnosperms: Plants with "naked" seeds, not bryophytes, featuring leafy structures and enclosed in an ovary. Examples include conifers specialized stems and rhizoids for anchorage. (pines, firs), cycads, and Ginkgo biloba. Examples include the common Haircap moss Angiosperms: Flowering plants with seeds and Sphagnum moss, used in peat bogs. enclosed in an ovary. This diverse group Hornworts (Anthocerotophyta): Possess a encompasses most familiar plants like fruits, unique, horn-shaped sporophyte and vegetables, trees, and grasses. flattened, thallus-like gametophyte. Examples include the Anthoceros and Phaeoceros species. DIVERSITY OF GYMNOSPERMS Modern gymnosperms are classified into LYCOPHYTES: Seedless Vascular Plants four major divisions and comprise about 1000 described species. Coniferophyta, Cycadophyta, Club mosses (Lycophyta): These include true and Ginkgophyta are similar in their production club mosses (Lycopodium) with branching of secondary cambium (cells that generate the stems and scale-like leaves, and quillworts vascular system of the trunk or stem) and their (Isoetes) with quill-like leaves and submerged pattern of seed development, but are not closely bodies. Examples are quillworts, club mosses, related phylogenetically to each other. and spike mosses Gnetophyta are considered the closest group to Spike mosses: Characterized by single, angiosperms (flowering seed plants) because slender stems tipped with a spike-like cone they produce true xylem tissue that contains both containing spores. Examples include tracheids and vessel elements. Selaginella and Huperzia. Water ferns: Aquatic relatives of lycophytes CONIFEROPHYTA with delicate, branching stems and submerged Conifers are the dominant phylum of leaves. Examples include Azolla and Marsilea. gymnosperms, with the most variety of species. Most are tall trees that usually bear PTERIDOPHYTES: scalelike or needle-like leaves. The thin shape of the needles and their waxy cuticle limits water Ferns: The most diverse group with true loss through transpiration. Snow slides easily off leaves (fronds) and complex vascular systems. the needle-shaped leaves, keeping the load light It is considered the most advance seedless and decreasing breaking of branches. These vascular plant. Ferns form large leaves and adaptations to cold and dry weather explain the branching roots. Examples include the predominance of conifers at high altitudes and in cold climates. Maidenhair fern, Boston fern, and Tree fern (Dicksonia). Conifers include familiar evergreen trees such as pines, spruces, firs, cedars, sequoias, and Horsetails: Recognized by scale-like leaves yews. and the presence of joints, or nodes: hence the name Arthrophyta, which means “jointed plant”. The only surviving genus is Equisetum, with species like the Common Horsetail. Whisk ferns: Simplest among pteridophytes, with slender, forked stems and minimal leaves. It lacks booth roots and leaves. Photosynthesis takes place in the green stem of a whisk fern. Examples include Psilotum nudum and Psilotum complanatum. SPERMATOPHYTES Spermatophytes, also known as seed plants, are characterized by the presence of seeds, making them distinct from seedless plants. These are broadly categorized as:  GENERAL BIOLOGY 2 A few species are deciduous and lose their leaves all at once during the fall season in some GNETOPHYTES other countries. The European larch and the Gnetophytes are the closest relatives to tamarack are examples of deciduous conifers. modern angiosperms, and include Many coniferous trees are harvested for paper three dissimilar genera of plants. Like pulp and timber. The wood of conifers is more angiosperms, they have broad leaves. primitive than the wood of angiosperms; it Gnetum species are mostly vines in tropical contains tracheid, but no vessel elements, and is and subtropical zones. referred to as "soft wood." The single species of Welwitschia is an unusual, low-growing plant found in the deserts of Namibia and Angola. It may live for up to 2000 CYCADOPHYTES years. Cycads thrive in mild climates and are The genus Ephedra is represented in North often mistaken for palms because of the shape of America in dry areas of the southwestern United their large, compound leaves. States and Mexico (Figure 14.3.6). Ephedra's small, They bear large cones, and unusually for scale-like leaves are the source of the compound gymnosperms, may be pollinated by beetles ephed- rine, which is used in medicine as a potent rather than wind. They dominated the landscape decongestant and a lifesaving vasoconstrictor. during the age of dinosaurs in the Mesozoic era Because ephedrine is similar to amphetamines, (251-65.5 million years ago). both in chemical structure and neurological effects, Only a hundred or so cycad species its use is restricted to pre- scription drugs. persisted to modern times. They face possible All gnetophytes possess vessel elements in extinction, and several species are protected their xylem, setting them apart from other through international conventions. Because of gymnosperms and making them their attractive shape, they are often used as akin to angiosperms. ornamental plants in gardens. GINKGOPHYTES The single surviving species of ginkgophyte is the Ginkgo biloba. Its fan-shaped leaves, unique among seed plants because they feature a dichotomous venation pattern, turn yellow in autumn and fall from the plant. For centuries, Buddhist monks cultivated Ginkgo biloba, ensuring its preservation. It is planted in public spaces because it is unusually resistant to pollution. Male and female organs are found on separate plants. Usually, only male trees are planted by gardeners because the seeds produced by the female plant have an off-putting smell of rancid butter.