TRANSPORT IN THE XYLEM OF PLANTS Basic Leaf Structure: Plant Structure and Function Study Guide Period 6

Transcription

1 TRANSPORT IN THE XYLEM OF PLANTS Basic Leaf Structure: o Water lost in the form of gas from the leave through openings called stomata o Transportation is the loss of water vapour from leaves and other aerial parts of the plant o Water absorption replaces the water that is lost from the plant s upper structures o Leaves consist of a flat part called the blade and a stalk that is called the petiole. o Leaves have a layer of wax as their outermost layer that protects against water loss and insects. o Just like stems and roots the leaves have vascular tissue that includes a xylem and phloem o The xylem brings water to the leaves. The phloem carries the products of photosynthesis to the rest of the plant o A densely packed region of cylindrical cells are in the upper portion of the leaf called the palisade mesophyll. These cells contain a large amount of chloroplasts to carry out photosynthesis. o Bottom of leaf is composed of spongy mesophyll (loosely packed with less chloroplasts) o Stomata occur on the bottom surface of leaves and they allow oxygen and carbon dioxide exchange between the leaf and surrounding areas o As oxygen and CO2 are exchanged, water is lost from the plant. o Specialized guard cells control the openings and closing of the stomata Plant Water and Mineral Movement Xylem is actually a complex tissue composed of many cell types It is involved in supporting the plant as well as being the specialized water-conducting tissue of terrestrial plants The two cells types largely involved in water transport are tracheids and vessel elements Tracheids are dead cells that taper at the ends and connect to one another to form a continuous column. Vessel elements are the most important xylem cells involved in water transport They are attached end to end to form continuous columns, like the tracheids The end of the vessels have perforations in them, allowing water to move freely up the plant. Water passes from one tracheid to another through thin regions called pits In vessel elements, water passes through the pits in the primary wall areas and through the end walls. Stomata and Guard Cells Stomata open and close because of changes in the turgor pressure of the guard cells that surround them. Stomata can only be closed on a short term basis because CO2 must enter for photosynthesis Guard cells are bulge when they re are full of water and swell causing the stoma to open Vice versa guard cells sag towards each other when when they lose water causing the stoma to close.

2 Gain and loss of water in guard cells is due to the transport of potassium ions. K+ are pumped into the cells when blue light triggers ATP - powered protein pumps. When Potassium ions passively leave cells water also leaves. Hormone Abscisic acid causes potassium ions to diffuse rapidly causing stomatal closure. Ths hormone is produced in roots during times of water deficiency. Other factors, (CO2 circadian rhythms) affect stomatal opening and closing The cohesion-tension theory of plant fluid movement Process Water moves down concentration gradients Water lost by transportation is replaced by water from the vessels The vessel water column is maintained by cohesion and adhesion Tension occurs in the columns of water in the xylem Water is pulled from the root cortex into xylem cells Water is pulled from the soil into the roots Explanation The spaces within a leaf have a high concentration of water vapour. Water moves from this location to the atmosphere, which has a lower water concentration Replacing water from the vessels maintains a high water vapour concentration in the air spaces of the leaf Cohesion involves the hydrogen bonds that form between water molecules Adhesion involves the hydrogen bonds that form between water molecules and the sides of the vessel; adhesion counteracts gravity This is because of the loss of water in leaves and the replacement of that lost water by xylem water. The water columns remain continuous because of cohesion and adhesion Cohesion and adhesion maintain the columns under the tension created by transpiration This happens because of the tension created by transpiration and the maintenance of a continuous column of water Roots and Fluid movement in plants: Main function of roots is to provide mineral ion and water uptake for the plant Roots are very efficient because of an extensive branching pattern Specialized epidermal structures called root hairs help with water absorption Root hairs increase the surface area which the water and mineral ions are absorbed by a factor of nearly 3 The three root zones indicate regions of cell development o Zone of cell division: where new undifferentiated cells are forming corresponding with the M phase of the cell cycle o Zone of elongation: where cells are enlarging in size, corresponding with the G1 phase of the cell cycle. o Zone of maturation: where cells become a functional part of the plant

3 Water abosorbs from the soil to the root hairs because the hairs have a higher solute concentration and a lower water concentration than the soil around it. Water moves through the plasma membranes into the root hair cells Most of the water entering a plant comes through by osmosis. Once inside the root, water moves to the vascular cylinder which is where the xylem and phloem is. Mineral Ions It s essential that mineral ions move into the root as well as water. 3 major processes allow mineral ions to pass from the soil to the root: 1. Diffusion of mineral ions and mass flow of water in the soil that carries these ions 2. The action of fungal hyphae 3. Active transport Passive flow of water and minerals dissolved in it occurs when a higher concentration of mineral is dissolved outside the root than inside this is referred to as bulk flow or mass flow. Active transport is required when there is a higher concentration of minerals outside a plant than inside. Plants also use energy to bring in ions that can only pass through certain proteins and not the lipid bilayer. Potassium ions move through specialized proteins called potassium channels. The result of active uptake of mineral ions is a high solute (hypertonic) concentration within the root. Because of this, the amount of water absorbed from the soil by the root through the process of osmosis is increased. Plant adaptations for water conservation Environmental effects on transpiration in most plants Environmental factor Light Humidity Wind Temperature Effect Speeds up transpiration by warming the leaf and opening stomata Decreasing humidity increases transpiration because humid air near the stomata is carried away Increases the rate of transpiration because humid air near the stomata is carried away Increasing temperature causes greater transpiration because more water evaporates

4 Soil Water Carbon Dioxide If the intake of water at the roots does not keep up with transpiration, turgot loss occurs and the stomata close, and the transpiration rate decreases High carbon dioxide levels in the air around the plant usually cause the guard cells to lose turgor and the stomata to close Xerophytes are plants adapted to arid climates with adaptations to reduce transpirational water loss. Some of those adaptations are: Small thick leaves reduce surface area Reduced number of stomata decreases the number of openings for water to escape Stomata are located in pits causing higher humidity near the stomata Waxy cuticle reduces water loss by acting as a barrier Hair-like cells on the leaf surface trap water vapor maintaining higher humidity near the stomata. Shed leaves or become dormant in dry months Succulent plants such as cacti store water in fleshy, watery stems Xerophytes can use alternative photosynthesis processes CAM and C4. o CAM plants close stamota close stomata during the day and incorporate CO2 during the night. o C4 plants have a stomata that open during the day but take in carbon dioxide more rapidly than non-specialized plants. Halophytes are plants adapted to grow in water with high levels of salinity. They are a promising source of biofuel because they don t compete with food crops for resources. They have more adaptations Many store water becoming succulent diluting the salt concentration Several species secrete salt Some species can compartmentalize Na+ and Cl- in their vacuoles Halophytes and Xerophytes share some adaptations to conserve water. One final adaptation they share is to simply close stomata using the action of guard cells.

5 Phloem Overview: Phloem transports everything that xylem cannot (like larger macromolecules). Phloem can transport in various direction, unlike the xylem/(it occurs in all parts of the plant). Phloem transports these materials from a source to a sink using a process called translocation. Translocation depends on the hydrostatic pressure of the xylem. Process of Translocation Translocation is how plants transport organic molecules from a source to a sink Source: organ in the plant that produces sugar Sink: organ in the plant that uses sugar Water dissolves the organic molecules and turns them into phloem sap- This sap includes sugar, amino acids, plant hormones, and small RNA Pressure-flow Hypothesis (The movement of sap during translocation) 1. The xylem vessel inputs water to the sieve tube to help create hydrostatic pressure 2. The source cell inputs sugar to the phloem sieve tube, and the phloem begins to flow from the source to the sink 3. The hydrostatic pressure is diminished at the end when the sugar reaches the sink 4. The xylem carries the almost-pure water back to the source This process requires energy!

6 Two Different Types of Angiosperms: Monocotyledonous Plants & Dicotyledonous Plants Monocot Dicot Leaf venation Flowers Veins usually parallel Floral organs usually open in multiples of three Veins usually netlike Floral organs usually open in multiples of four or five Embryos One cotyledon Two cotyledons Stems Vascular tissue scattered Vascular tissue arranged in a ring Roots Root system fibrous, which means that there is no main root Taproot Pollen One opening in pollen grain Three openings in pollen grain

7 Angiosperm - a plant that has flowers and produces seeds within its carpel. Carpel: consists of stigma, style, and ovary Gymnosperm - a plant that has seeds unprotected by an ovary or fruit. Reproduce by cone and pollen. The pollen is the male reproductive part and the cone is female.

8 Structure Tissue types o o o PLANT GROWTH Dermal tissues- outer covering that protects against physical agents and pathogenic organisms, prevents water loss, and may have specialized structures for various purposes Ground tissues- thin-walled cells that function in storage, photosynthesis, support, and secretion Vascular tissues- consist of xylem and phloem that carry out log-distance conduction of water, minerals, and nutrients within the pant, and provide support Whats up bro? - Mr. Madden Meristems o Meristematic tissue is groups of cells that have the same function as stem cells o They are able to divide and differentiate into different parts of the plant o There are two different categories of meristematic tissue groups, which depends upon their location in the plant Apical meristems (primary meristem) develop at the tips of roots and stems, and they allow for further growth in length of the roots and stems. This growth results in herbaceous, non-woody stems and roots Lateral meristems allow for growth in thickness (secondary growth). They are often times seen in woody plants like trees and shrubs. There are two types of lateral meristems Vascular cambium produces secondary vascular tissue. These include secondary xylem a major component in wood on the inside and secondary phloem on the outside Cork cambium produces cork cells in the outer bark of a plant Chemical Activity and Phototropism Plant Tropism (growth or movement influenced by external stimuli) Stimuli include gravity, touch, light, and chemicals Phototropism - Plant growth in response to light Positive phototropism (towards light source) - Plant Stem

9 Negative phototropism (away from light source) - Plant Roots Purpose of phototropism is to cultivate more productive photosynthesis through exposure to sunlight Essential for growth Plant Hormones - facilitate coordination between plant cells, instrumental to growth, allow for interaction with external stimuli Auxin - Plant hormone that facilitates phototropism Increases flexibility of plant cells, allowing for elongation by buildup between cells that are distanced from light source As cells are exposed to sunlight, Auxin Pumps remove Auxin and transport it to a higher concentration in cells with less sunlight and inactive pumps Plant Hormones Animal Hormones Coordinate and regulate activity Influences reproduction Channeled through interaction between hormone and receptor Balances of several simultaneously present hormones influence function Coordinate and regulate activity Influences reproduction Channeled through specialized gland secretion Single present hormone influences function Growth Indeterminate Growth - Continual pattern of growth (MAIN TYPE) Determinate Growth - Growth ceases after a certain size has been reached (only happens within some plant organs such as leaves) Three Types of Life Cycles o Annual life cycle Plant completes life cycle in one year and then dies Ex. Corn, Rice, etc. o Biennial life cycle Plant completes life cycle in two years before dying Ex. Onions, Parsley, etc. o Perennial life cycle Plant lives for many years and death is usually caused by infection or other environmental factors Ex. Deciduous, Evergreen, etc. Factors that affect plant development and growth: o Environmental factors, such as day length and water availability

10 o o o Receptors, which allow the plant to detect certain environmental factors The genetic makeup of the plant Hormones, which are chemical messengers Study Guide: Flower Reproduction Angiosperms/Flower Structure Reproduction creates variety Angiosperm- any plant that has a flower Monocotyledonous (Monocots) Plants versus Dicotyledonous (Dicots) Plants Monocots Dicots Parallel venation (the system of veins) in leaves Three flower parts, or multiples of three Seeds contain only one cotyledon (seed leaf) Vascular bundles arranged throughout the stem Root system mainly fibrous Pollen grain with one opening Netlike venation pattern in leaves Four or five flowers parts, or multiples of four or five Seeds contain two cotyledons Vascular bundles arranged as a ring in the stem Root system involves a taproot (main root) Pollen grain with three openings Division between the angiosperms is based on morphological characteristics.

11 Flower structure and function: Flower Part Sepals Petals Anther Filament Stigma Style Ovary Function Protect the developing flower while it is in the bud Often colorful to attract pollinators Part of the stamen that produces the male sex cells (pollen) Stalk of the stamen that holds up the anther Sticky top of the carpel, on which pollen lands Structure of the carpel that supports the stigma Base of the carpel, in which the female sex cells develop Fertilization Two Generations Gametophyte Generation: Haploid Sporophyte Generation: Diploid Gametophyte Generation Produces the plant gametes by mitosis o Sperm form in male gametophytes o Eggs form in female gametophytes Sporophyte Generation Produces spores by Meiosis

12 Two Forms: 1. Pollination 2. Fertilization Pollination Pollination is the process by which pollen is placed on the female stigma o It is the first step in the progression towards fertilization and the production of seeds Pollination vectors include: o Insects o Wind o Birds o Water o Other animals Vector attractions in flowers: o Red Flowers - Birds o Yellow/Orange Flowers - bees o Odourless flowers - Wind Two types of Pollination: Self Pollination Cross Pollination Artificial Pollination

13 Self Pollination Pollen from the anther of the same plant falls upon its own stigma Results in less genetic variation Cross Pollination Pollen is carried from the anther of one plant to the stigma of a different plant of the same species Increases genetic variation and results in better fitness The only problem with cross pollination is the female stigma may not receive the male pollen due to long travel distances Artificial Pollination Botanists can select plant genetic characteristics by controlling the process of pollination Fertilization Fertilization happens when the male and female sex cells unite to form a diploid zygote o The female sex cells that are fertilized by the pollen are present within the ovules of the flower o The ovules are present within the ovary of the carpel o Once the pollen grain adheres to the stigma, a pollen tube begins to grow Pollen tube growth and fertilization occur in the following sequence: 1. Pollen germinates to produce a pollen tube 2. The pollen tube grows down the style of the carpel

14 3. Within the growing pollen tube is the nucleus that will produce the sperm 4. The pollen tube completes its growth by entering an opening at the bottom of the ovary 5. The sperm moves from the tube to combine with the egg of the ovule to form a zygote Once the zygote is formed, it develops with the surrounding tissue into the seed As the seed develops, the ovary around the ovule matures into a fruit to protect the seed Seeds Seeds are the means by which an embryo can be dispensed to different locations It s the protective structure for the embryo Parts of the seed Testa: The tough, protective outer coat Cotyledons: seed leaves that function as the nutrient storage structure Micropyle: a scar at the seed opening where the pollen tube entered the ovule Embryo Root and Embryo Shoot: becomes the new plant during germination Germination: the development of the seed into a functional plant Once the seed is formed, it matures o Seed dehydrates until water is 10%-15% the weight o Goes into its dormancy period Dormancy period: where the seed has a low metabolism and no growth or development. Variable for different seed types. General Conditions for Germination Water: rehydrates dried seed tissues Oxygen: allows aerobic respiration to produce ATP Appropriate Temperature: important for enzyme action

15 Many plants have other, specific conditions that must be met before germination to start. Some need the testa to be broken before water can be taken in Some have to be exposed to fire or smoke Light isn t usually mentioned in seed germination because it has variable effects Initial Process of Germination Absorption of water Release of growth hormone Gibberellin or Gibberellic Acid o Causes the production of amylase, which hydrolyses starch into maltose o Maltose is hydrolysed into glucose, which can be used in cellular respiration Glucose can be converted into cellulose so new cells can produce cell walls Germination is uncertain- the seedling is fragile and will be exposed to harsh weather, parasites, predators, etc. o Plants produce many seeds because many of them won t produce a functional plant due to these dangers