Basic leaf structure. Leaf plays essential role. Leaf structures in depth Waxy, outer layer is known as cuticle

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1 Basic leaf structure Leaf plays essential role o Water is lost in form of gas through leaf openings called Stomata o Transpiration is loss of water vapour from leaves and other aerial parts of the plant o Water lost from plant s upper structures must be replaced by water absorption Leaf structures in depth Waxy, outer layer is known as cuticle o Protection from insects and also insulates water If no cuticle, the epidermis protects Within leaves there are vascular tissues o Xylem and phloem

2 Carry products of photosynthesis to rest of plant Connected together in veins or vascular bundles Xylem structure Xylem carries water and minerals from roots to leaves o Two conducting cells- Tracheids and Vessel elements Tracheids o Tapered cells with sloping end walls Xylem Vessels o Shorter and thicker than Tracheids Both perforated by pits to allow sideways movement of water and minerals These walls are formed from recycled, non-living cells Water absorption by osmosis Osmosis is the molecules of a solvent tend to pass through a semipermeable membrane. So The Xylem cells take up water but are supplied by the root structure. Most of the water comes through the root hairs by osmosis. Once in the root, water moves to the vascular cylinder, which contains the xylem and phloem.

3 Soil water enters the root through its epidermis. It appears that water then travels in both the cytoplasm of root cells called the symplast that is, it crosses the plasma membrane and then passes from cell to cell through plasmodesmata. in the nonliving parts of the root called the apoplast that is, in the spaces between the cells and in the cells walls themselves. This water has not crossed a plasma membrane. Once in the xylem, water with the minerals that have been deposited in it (as well as occasional organic molecules supplied by the root tissue) move up in the vessels and tracheids. At the leaves, the xylem passes into the petiole and then into the veins of the leaf. Water leaves the finest veins and enters the cells of the spongy and palisade layers. Here some of the water may be used in metabolism, but most is lost in transpiration.(2014) Cohesion-tension theory of plant fluid movemetheory oant fluid movement 1. Water moves down concentration gradients. a. 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 Water lost by transpiration is replaced by water from the vesicles Replacing water from the vessels maintains a high water vapour concentration in the air spaces of the leaf. 1. The vessel water column is maintained by cohesion and adhesion i) Cohesion involves hydrogen bonds that form between water molecules

4 ii) Adhesion involves the hydrogen bonds that form between water molecules and the sides of the vessels; adhesion counteracts gravity. b) 2) Water is pulled from the soil into the roots. i) This happens because of the tension created by transpiration and the maintenance of a continuous column of water. 3) Tensions occurs in the columns of water in the xylem i) This is because of the loss of water in the leaves and the replacement of that lost water by xylem water. The water columns remain continuous because of cohesion and adhesion. 4) Water is pulled from the root cortex into xylem cells i) Cohesion and adhesion maintain the column under the tension created by transpiration 5) Tensions occurs in the columns of water in the xylem i) This is because of the loss of water in the leaves and the replacement of that lost water by xylem water. The water columns remain continuous because of cohesion and adhesion. 6) Water is pulled from the root cortex into xylem cells i) Cohesion and adhesion maintain the column under the tension created by transpiration

5 What is Phloem? Phloem and Monocots/Dicots A type of conducting tissue, made up of living cells, in plants Consists of sieve tube members and their companion cells o Sieve tubes are narrow, elongated cells joined from end to end. The pores in the sieve plates, within the sieve tubes, allow for the movement of water and other dissolved organic molecules throughout the plant o Companion cells connect to the sieve tubes by plasmodesmata o The sieve tube members lack both a nucleus and cytoplasm, but the companion cell has a nucleus and a dense cytoplasm o The sieve tube members receive instructions from the nucleus of the companion cells The Function of Phloem Transports organic molecules/carbohydrated produced through photosynthesis Transports molecules in various directions Movement of organic compounds takes place in phloem sieve tubes Sugars and amino acids are loaded into phloem sieve tubes by active transport in parts of the pant called sources. Examples of sources: parts of the plant where photosynthesis is occurring (stems and leaves) and storage organs where the stores are being mobilized Sugars and other organic compounds are unloaded from phloem sieve tubes in parts of the plant called sinks. Examples of sinks: roots, storage organs (such as potato tubers and growing fruits including the seeds developing inside them). These are all parts of the plant where organic compounds cannot be produced but they are needed for immediate use or for storage The incompressibility of water allows transport along hydrostatic pressure gradients. Hydrostatic pressure is pressure in a liquid The high concentrations of solutes such as sugars in the phloem sieve tubes at the source lead to water uptake by osmosis and high hydrostatic pressure The low solute concentrations of phloem sieve tubes at the sink lead to exit of water by osmosis and low hydrostatic pressure There is therefore a pressure gradient that makes sap inside phloem sieve tubes flow from sources to sinks The Function of Phloem in active translocation Translocation is the movement of organic molecules in plants Sugars are being transported from where they were made to where they are needed Phloem tissue transports sugars and amino acids from sources including photosynthetic tissue and storage organs, to sinks which includes fruits, seeds and roots of the plant. This is done through dissolving the organic molecules in water (new solution is referred to as phloem sap) Form of transport which requires energy

6 9.2 Transport in Angiospermophytes. IB Biology HL. Tangient LLC Web. 12 January Loading Phloem Sieve Tubes The main sugar carried by phloem sieve tubes is sucrose Active transport is used to load it into the phloem but not by pumping sucrose molecules directly. Instead protons are pumped out of phloem cells by active transport to create a proton gradient Co-transporter proteins in the membrane of phloem cells then use this gradient to move a sucrose molecule into the cell by simultaneously allowing protons out down the concentration gradient Some sucrose is loaded directly into phloem sieve tubes by this process To speed up process: adjacent phloem cells also absorb sucrose by co-transport and then pass it to sieve tubes via narrow cytoplasmic connections (plasmodesmata) The Structure of Phloem Sieve Tubes Phloem sieve tubes develop from columns of cells that break down their nuclei and almost all of their cytoplasmic organelles, but remain alive. Large pores develop in the cross walls between the cells, creating the sieve plates that allow sap to flow.

7 Measuring Phloem Transport Rates Method uses aphids of of obtaining samples of phloem sap from single sieve tubes Aphids have long piercing mouthparts called stylets. Stylets are inserted into stems or leaves and push inwards through the plant tissues until the stylet pierces a sieve tube. The high pressure inside the sieve tube pushes phloem sap out through the stylet into the gut of the aphid To sample phloem sap, the aphid is cut off from its stylet when it has started to feed. The stylet is left as a very narrow tube, through which sap continues to emerge To determine rate of movement, experimenters measure the distance between aphid colonies (mm) and divide the distance by the time taken for radioactive sucrose to emerge from severed aphid stylets (hours)

8 Gymnosperms vs. Angiosperms Angiosperms Identified by their flowers and fruit Any plant with fruit that contains seeds is an angiosperm or that has flowers Not pollinated by the wind- mainly pollinated by birds and insects Sexually reproductive part is the flower. Seeds are enclosed in fruit (mature ovaries) Can be divided into monocots and dicots Generally seasonal plants green, large leaves Grouped into two classes: monocot and dicots Gymnosperms Seeds for reproduction are found in cones and are not generally visible until maturity Survive year-round-evergreen Needle-like leaves Reproduce by wind Ex: coniferous trees Delevoryas, T. Gymnosperm. Encyclopædia Britannica, Encyclopædia Britannica, Inc., 31 Mar. 2016, Monocots vs. Dicots Monocots Dicots Veins are parallel in leaves Netlike veins in leaves Flower in multiples of three Seeds contain one cotyledon* Vascular bundles placed throughout the stem Fibrous root system One opening within the pollen grain Flower in multiples of four or five Seeds contain two cotyledon Vascular bundles arranged as a ring in the stem Root system involves a taproot* Three openings within the pollen grain *Cotyledon-seed leaf *Taproot- one main root Examples: Monocots- Palm trees, orchids Dicot- Geraniums

9 Plant Growth Definitions and key terms- Shoot- Stem with leaves Shoot Apical Meristem- Tip of the shoot that controls mitosis and cell division takes place. Causes leaf and flower formation. Root Apical Meristem- Protected by root cap. Comprised of three zones: zone of cell division, elongation, and maturation Leaf Primordia- Small cellular outgrowths that develop into leaves Auxin- A chemical plant hormone that controls growth. Found in roots and apical meristem Tropisms- response to external stimuli that aid in plant growth. Main use is response to sunlight intensity Phototropins- Photoreceptor proteins that cause chemical responses in the plant to signal auxin displacement based on light intensity Efflux Pump- Found in plasma membrane. Used in the active transport of auxin throughout the cells of the meristem. Also pumps hydrogen ions into the cell wall Turgidity- Caused by osmotic flow of water from low solute concentrations outside the cell to the cell s central vacuole Shoot apical meristem- -Plants use a chemical hormone in the shoot apical meristem called auxin to control cell growth in the vertical direction. -Plants use the apical meristem as a light receptor using proteins that are sensitive to light. -Light sensitive proteins in the shoot apical meristem sense sunlight intensity causing a tropism to form. -A tropism is a response to light intensity that causes the shoot apical meristem to bend towards the sun for maximum light intake.

10 -The chemical Auxin is produced by all cells in the stem of plants. Auxin is moved towards the side of the cell opposite of the light source by efflux pumps. Phototropins sense blue light as do most pigments in plants. This is what causes the movement of Auxin. -Plants are positively phototropic which means the meristems have a tendency to lean towards higher light intensity. When the phototropins sense higher light intensity, the efflux pumps kick on in the opposite side of the cell. -Once auxin binds to the receptors on the hydrogen pump, hydrogen ions flow into the plant cell wall causing the ph level to drop, weakening the hydrogen bonds between cellulose fibers. This allows for cell growth, expansion, and elongation. -During this time the cell s central vacuole undergoes turgor where it rapidly expands upon intake of water via osmosis. Water from outside the cell passively flows into the vacuole because of a higher solute concentration causing the cell to elongate.

11 -Once the cell is elongated, the spaces will be filled in and reformed to hold the shape of the cell during expansion. Lateral Meristems- Secondary growth Two types: 1. Vascular cambium- produces secondary vascular tissue between xylem and phloem in the vascular bundles. On the inside it produces secondary xylem, a major component of wood, and on the outside it produces secondary phloem 2. Cork cambium- Occurs within the bark to produce the cork cells of the outer bark. Adds to rigidity and protection. (Both types aid in expanding the plant s width and transport system while also increasing its durability against weather)

12 Root Meristems- -Root meristems are different in the way that they process signals for growth. Root meristems are negatively phototropic causing them to grow in the direction opposite of the light source. -The apical meristem of the root is covered in a root cap, whereas the shoot meristem is exposed to the elements. This is to prevent damaging during growth. -The root has 3 separate zones during growth. The zone directly behind the meristem is the zone of cell division and primary cell production. The second zone is the zone of elongation where cells begin the uptake of water and expand. The third and final zone is called the zone of maturation as the cells have fully elongated and begun to produce root hairs through cell differentiation. -Root hairs are one of the most important parts of the root s nutrient uptake system as they increase the surface area. A higher surface area allows a greater intake of minerals and nutrients. Water and nutrient absorption is increased by a factor of nearly 3 with the addition of root hairs. Flowers are the plant's reproductive structures. Angiosperms are types of plants that bear fruits and flowers. Flower Structure Sepals: protect the flower while it is still inside the bud Petals: often colorful to attract pollinators Anther: the part of the stamen that produces the male sex cells (pollen) Filament: stalk of the stamen that holds up the anther Stigma: the sticky top of the carpel, on which pollen lands Style: the structure of the carpel that supports the stigma Ovary: the base of the carpel, in which the female sex cells develop Carpel: the entire female part of the flower (pistil: a single carpel or a group of fused carpals) Stamen: the entire male part of the flower

13 Image 1 There are different types of flowers based on the structure o Complete flowers: contains all four basic parts [sepals, petals, stamen, and carpel] o Incomplete flowers: lack at least one of the four basic parts o Staminate flowers: only have stamens (no carpels) o Carpellate flowers: only have carpels (no stamens) **Meiosis occurs in the stamen and carpel to produce sex cells Based on the structure, one can tell what kind of pollination that the flower is adapted for (whether by insect or animal) Fertilization and Pollination Alternation of Generations - the gametophyte generation (haploid) and sporophyte generation (diploid) alternate in the plant Pollination: process where pollen (containing male sex cells) is placed on the female stigma o Methods of Pollination Wind, insects, birds, water, and animals o Self Pollination vs Cross Pollination

14 Self - pollen from the plant's own anther falls on its stigma. Results in less genetic variation Cross - pollen is carried from the anther of one plant to the stigma of another. Increases variation. Fertilization: when the male and female sex cells unite to form a diploid zygote o Steps in Fertilization Pollen germinates to produce a pollen tube The pollen tube grows down the style of the carpel Within the growing pollen tube is the nucleus that will produce sperm The pollen tube completes its growth by entering an opening at the bottom of the ovary The sperm moves from the tube to combine with the egg of the ovule to form a zygote Image 2 Adaptations A. Seed maturation o After the seed is formed, the seed begins to grow in the process of maturation. The process of maturation involves the dehydration of the seed until water levels inside the seed make up 10-15% of the seeds weight. o The seed then goes into a period of dormancy, where the seed s metabolism is low and the seed does not go through any growth or development. o This period of dormancy varies for different types of seeds, an adaptative feature implicated to combat unfavorable environmental conditions. Seed Germination:

15 o o o Many of the seeds will not produce a functional plant because of dangers [such as the fragility of the seed, harsh weather conditions, parasites, predators, and many other hazards]. If the seed germinates, (in favorable conditions) the seed will develop into a functional plant. The favorable conditions which must be present for germination generally include water (for the rehydration of the seed), oxygen (for the allowance of aerobic respiration to produce ATP), and appropriate temperatures (for enzymatic action) Many plants have specific conditions that must be met in order to germinate 1. The testa of some seeds must be disrupted or broken before water uptake can occur 2. Other seeds must be exposed to fire or smoke before they are able to germinate B. Reproductive systems and evolution in vascular plants The eggs and sperm which germinate the plant are produced by various gametophytes in flowering plants; however, anthers and stigmas often come from a single flower. o o o Even with obvious modes of self-fertilization, zygotes most frequently germinate through the eggs and sperm of different plants. Genetically determined self-incompatibility mechanisms have evolved numerous times in flowering plants; however, variances in the time of pollen release and stigma reception in a flower ( & the space between anthers and stigmas) encourage outcrossing even in flowering plants with self-compatibility (CITE). Even with the long term impacts of self-fertilization on the survival of flowering plant population over a long period of time, self-fertilization evolves solely because of selective advantage before fertilization. Self-fertilization presents only two plant advantages self-fertilization aids in increasing the successfulness of reproduction during periods of inefficient pollen exchange and a decline of pollinators, or it can increase the reproductive success of a pollen plant when pollen committed to selfing has a higher chance of fertilization than pollen committed to outcrossing. Works Cited Image 1: Josephine, Nirmala. Reproduction in Flowering Plant. Digital image. SlideShare. SlideShare, 24 Aug Web. 12 Jan Image 2: "Sexual Reproduction in Plants." MV STUDY GUIDE BIOLOGY. N.p., 01 Feb Web. 12 Jan Holsinger, K. E. (2000). Reproductive systems and evolution in vascular plants. Proceedings of the National Academy of Sciences, 97(13), doi: /pnas