plant science - aurora high school：植物科学的极光高中

9.1 Plant structure and growth9.2 transport in angiospermophytes9.3 reproduction in angiospermophytes,Plant Science,Remember,Plant cell!,Plant Evolution,Plants originated from green algae that lived in ponds that occasionally dried out.,Angiosperms,Angiosperms have dominated the land for over 100 million years.Known as “flowering plants”There are about 250,000 known species of flowering plants living today.Most of our food comes from flowering plantsRoots, such as beets and carrotsFruits of trees and vines, such as apples, nuts, berries, and squashesFruits and seeds of legumes, such as peas and beans;Grains, such as rice, wheat, and corn,Angiosperms,Divided into two groups: Names refer to the first leaves that appear on the plant embryo.Embryonic leaves are called seed leaves, or cotyledons:Monocots (embryo has one seed leaf)Dicots (embryo has two seed leaves),Angiosperms,Monocots:Orchids, bamboos, palms, and lilies, as well as grains and other grassesLeaves have parallel veins Stems have vascular tissues arranged in a complex array of bundles.Flowers have petals and other parts in multiples of three.Roots form a fibrous system (a mat of threads) that spread out below the soil surface.Make excellent ground cover that reduces erosion.,Angiosperms,Angiosperms,Dicots:True dicots include most shrubs and trees (except for conifers), as well as many food crops.Leaves have a multibranched network of veinsStems have vascular bundles arranged in a ring.Flower usually has petals and other parts in multiples of four or five.Large, vertical root (called a taproot) goes deep into the soilYou can see this if you try to pull up a dandelion,Angiosperms,Plant Body,Composed of organs with various tissues reflective of their evolutionary history as land-dwelling organisms.Must draw resources from two environments:Water and minerals from soilCO2 and light from air,Plant Body,Plant body is divided up to two main parts:Subterranean part rootAerial part shoot,Plant Body,Root system:Anchors in the soil, absorbs and transports minerals and water, and stores food.Monocots Fibrous root system consists of a mat of generally thin roots spread out shallowly in the soilDicots have one main vertical taproot with many small secondary lateral roots growing outward.Both Monocots and Dicots have tiny projectsions called root hairs:Enormously increase the root surface area for absorption of water and minerals.,Plant Body,Shoot system:Made up of stems, leaves, and adaptations for reproduction (flowers)Stems are parts of the plant that are generally above ground and support the leaves and flowers. Composed of:NodesPoints at which leaves are attachedInternodesPortions of the stem between nodesLeaves are the main photosynthetic organs in most plants (green stems also perform photosynthesis)Consist of a flattened blade and a stalk, or petiole, which joins the leaf to a node of the stem.,Plant Body,Shoot system (continued):Two types of buds that are undeveloped shoots:Terminal budFound at the apex (tip) of the stem, has developing leaves and a compact series of nodes and internodesAxillary budone of each of the angles formed by a leaf and the stem, are usually dormant.,Plant Body,Apical dominanceResults from the terminal bud producing hormones that inhibit growth of the axillary buds.By concentrating resources on growing taller, apical dominance is an evolutionary adaptation that increases the plants exposure to lightImportant where vegetation is dense. Removing the terminal buds usually stimulates growth of the axillary buds. Branching is important for increasing exposure the environment,Modified Roots, Stems, and Leaves,Modified roots:Some plants have unusually large taproots that store food in carbohydrates such as startch:Carrots, turnips, sugar beets, and sweet potatoes,Sugar Beet,Modified Roots, Stems, and Leaves,Modified Stems:Stolon“runner”; has a horizontal stem that grows along the ground surfacePlantlets form at nodes along their length, enabling a plant to grow asexuallyExample: strawberryRhizomesLook like large, brownish, rootlike structuresHorizontal stems that grown just below or along the soil surfaceStore food, and having buds, can also spread and form new plantsPotato plant has enlarged structures specialized for storage called tubers (the potatoes we eat),Modified Roots, Stems, and Leaves,Modified stems (continued)BulbsModified stems that are also used for underground food storage (onions),Modified Roots, Stems, and Leaves,Modified Leaves:TendrilsTips coil around a stem, help plants climbExamples: grapevines, peas,Tendril- Pea Plant,Plant Tissues in Stems and Leaves,Each plant organ- root, stem, or leaf- is made up of three tissue systems:DermalVascularGround tissues,Plant Tissues in Stems and Leaves,Dermal TissueForms an outer protective covering.Acts as first line of defense against physical damage and infectious organisms.Consists of a single layer of tightly packed cells called the epidermis:Epidermis of leaves and most stems is covered with a waxy layer called cuticle, which helps prevent water loss.Typical dicot leaf also has pores on its epidermis called stomata which allow CO2 exchange between the surrounding air and the photosynthetic cells inside the leaf. Surrounded by guard cells:Regulate the size of the stoma,Plant Tissues in Stems and Leaves,Plant Leaf,Plant Tissues in Stems and Leaves,Vascular Tissue:Made up of:Xylem type of vascular tissue that is made up of cells that transport water and dissolved ions from the roots to the leavesPhloem type of vascular tissue that is made up of cells that transport sugars from leaves or storage tissues to other parts of the plant,Plant Tissues in Stems and Leaves,Vascular Tissue (continued):In the stem.Vascular tissue forms vascular bundlesDicots arranged in a circle,Plant Tissues in Stems and Leaves,Vascular Tissue (continued):In the leafVascular tissue form network of veinsIn the veins, the xylem and phloem are continuous with the vascular bundles of the stem.Allows them to be in close contact with photosynthetic tissues, ensuring water and mineral nutrients from the soil are supplied, and that sugars made in the leaves are transported throughout the plant,Plant Tissues in Stems and Leaves,Ground Tissue (continued):Accounts for the bulk of a young plant, by filling in spaces between the epidermis and vascular tissue.Functions include photosynthesis, storage, and support.Ground tissue inside vascular tissue is called pithGround tissue external to vascular tissue is called cortex,Dicot Stem,Plant Tissue in Stems and Leaves,Ground Tissue (continued):Ground tissue of dicot stems consists of both a cortex region and pith regionGround tissue of the leafIs called Mesophyll :Sandwiched between the upper and lower epidermisConsists mainly of photosynthesis cellsLoosely arranged to provide air spaces which CO2 and O2 can circulateMain location of photosynthesis,Plant Growth,Growth in plants is made possible by tissues called meristems.A meristem consists of cells that divide frequently, generating additional cells.Some products of this division remain in the meristem and produce still more cells, while others differentiate and are incorporated into tissues and organs of the growing plant.,Plant Growth,Apical MeristemsMeristems at the tips of roots and in the buds of shootsCell division in the apical meristems produces the new cells that enable a plant cell to grow in length primary growthEnables roots to push through the soil and allows shoots to increase exposure to light and CO2. Growth occurs behind the root tip in three zones of primary growth:Zone of cell division, zone of elongation, and zone of maturationZone of maturation brings about the three tissue systems (dermal, ground, and vascular),Plant Growth,Primary Growth of a Root,Plant Growth,Lateral meristemsAssociated with the increase in thickness of stems and roots secondary growthCaused by the activity of two cylinders of dividing cells that extend along the length of roots and stems:Vascular cambiumSecondary growth adds layers of vascular tissue on both sides of the vascular cambium woodCork cambiumOuter cambium that forms the secondary growth of the epidermis cork,Control of Plant Growth,Auxin is a term used for any chemical substance that promotes seedling elongation.Apical meristem at the tip of a shoot is a major site of auxin synthesis.As auxin moves downward, it stimulates growth of the stem by making cells elongate. Concentration of auxin determines its effectToo low to stimulate shoot cells will cause root cells to elongateHigh conc. stimulates shoots cell and inhibits root cell elongation.Stimulates stem elongation and root growth, differentiation, and branching.,Control of Plant Growth,Auxins also play a part in phototropism, an occurrence that involves plants bending or moving away from light. The shoot tip is responsible for directional movement by the plant in response to sunlight, as this is the area where auxins can be found.Sunlight eradicates auxin, meaning that the part of the shoot tip of the plant which is receiving direct sunlight will have the least amount of auxin.The extra auxin present on the shaded side promotes more cell division and elongation, causing the plant to bend towards the sunlight after this lop-sided growth.,Control of Plant Growth,Cells on the darker side are larger and have elongated faster; causes the shoot to bend towards the light.,If a plant receives sunlight uniformly from all sides or is kept in the dark, the cells all elongate at a similar rate.,Effect of Auxin on Phototropism,Transport in Plants,Several factors necessary for plant growth:CO2 from airabsorbed by leavesO2 from air or soilabsorbed by leaves or rootsH2O from soil absorbed by the rootsMinerals from the soild absorbed by the rootsSugars are made in the leaves from the absorbed molecules and ions and used to build the plants body and provide energy,Solute Uptake From The Roots,Mineral ions from the soil can get into the root of plants by three different ways:1. DiffusionIf the concentration of certain ions is lower inside of the root hair cells, they can simply diffuse into the root hair cells from the soil2. Fungal hyphaeSome plants live in a symbiotic relationship with fungi and use fungal hyphae to increase the surface of the root even more. The combination of plant root and fungal fibers are called mycorrhiza. The fungus benefit from a constant supply of sugar while the plant benefit from the increased surface area that the fungal hyphae provide, they also excrete growth factors and antibiotics3. Mass flow of water into the root can also carry ions passively in dissolved form,Solute Uptake From the Roots,Roots hairs are extensions of epidermal cells that cover the root and form a huge surface areaAllows the plant to absorb the water and minerals it needs for growthWatery solution has to be transported from the soil to epidermal cells to cortex of the root to the xylem (water-conducting vascular tissue)Plasma membrane of the xylem cells are selectively permeable, which helps regulate the mineral composition of a plants vascular system.,Solute Uptake From the Roots,Two possible routes to the xylem:Intracellular routeExtracellular route,Solute Uptake From the Roots,Intracellular route:A.k.a. Symplatic routeCells within roots are connected via plasmodesmata (channels through the walls of adjacent cells) which allows for a continuum of living cytoplasm among the root cellsOnce inside epidermal cells, solution can move inward from cell to cell without crossing membranes,Solute Uptake From the Roots,Extracellular route:Solution moves inward within the hydrophillic walls and extracellular spaces of the root cells but does not enter the cytoplasm of the epidermis or cortex cells.Solution passes through no plasma membranes, and there is no selection of solutes until they reach the endodermis.Endodermis has a waxy barrier called the Casparian strip which stops water and solutes from entering the xylem.Water and ions are forced to cross a plasma membrane into an endodermal cells, then are discharged into the xylem.,Solute Uptake in the Roots,In a real plantWater and solutes rarely follow just the two kinds of routesMay take a combination of these routes, and may pass through numerous plasma membranes and cell walls en route to the xylem.All water and solutes must cross a plasma membrane at some point.,Transpiration,Why transpiration?As a plant grows upward toward sunlight, it needs to get water and minerals from the soil. Must be able to transport resources from the roots to thrive.,Transpiration,Xylem tissue is made of two types of conducting cells: tracheids and vessel elements. When mature, but types of cells are dead, consisting only of cell walls, and both are in the form of very thin tubes that are arranged end to end.Because the cells have openings in their ends, a solution of water and inorganic nutrients, called xylem sap, can flow through these tubes.Xylem sap flows all the way up from the plants roots through the shoot system to the tips of the leaves.,Transpiration,Transpiration,Forces that push xylem sap against gravity are:Root pressureRoot cells actively pump inorganic ions into the xylem, and the roots endodermis holds the ions thereAs ions accumulate in the xylem, water tends to enter by osmosis, pushing xylem sap upward ahead of it. Can push sap up a few metersFor the most part, however, xylem sap is not pushed from below by root pressure by pulled upward by the leaves.TranspirationThe pulling force caused by the loss of water from the leaves and other aerial parts of a plant.Water molecules leave the plant through the stoma of the leaf by diffusion.When the stoma is open, water concentration is higher in the plant cells than in the surrounding atmosphere.,Transpiration,Properties of water stimulate transpiration:CohesionSticking together of molecules of the same kind.Because water is polar, they are attracted to each other by hydrogen bonds Water molecules form continuous strings in xylem tubes, extending all the way from the leaves down to the roots.AdhesionSticking together of molecules of a different kind.Water molecules tend to adhere via hydrogen bonds to hydrophillic cellulose molecules in the walls of xylem cells.,Transpiration,Transpiration-Cohesion-Tension Mechanism:Before a water molecule can leave the leaf, it must break off from the end of the stringIt is pulled off a steep diffusion gradient between the moist interior of the