The Importance of Plants
  1. plants produce an array of materials that are important to humans
    1. they are the basis of the food chain
    2. they supply the materials for building structures
    3. they produce the materials for most of our clothing
    4. they produce extracts that are important to specific products
    5. they produced the fossil fuels that we use today
    6. they produce numerous medicines that we use today
The General Structure of Plants
  1. root system functions: anchors a plant in soil; absorbs water and minerals; transports water and minerals to shoot system; store food fibrous root systems are common in grasses and seedless vascular plants
  2. shoot system - consists of stems and leaves
  3. stems: support structures of the shoot system; cells of parenchyma have turgor and rigidity for support; transport substances between the roots and
  4. leaves; produce food; store substances, such as food or water
  5. buds are often located at nodes for the production of new shoot parts
Plants as Producers
  1. leaves obtain their water from the xylem system of the shoot
  2. leaves obtain carbon dioxide from the air
  3. the sun provides the energy for photosynthesis
  4. the oxygen produced by the leaf is either used by its mitochondria or it diffuses out into the air
  5. the sugar produced by the leaf is either burned by its mitochondria (as pyruvate) or transported to the phloem system of the shoot
  6. photosynthesis equation: 6H2O + 6CO2 ----> C6H12O6 + 6O2
Plant Nutritional Requirements
  1. plants require three soil nutrients in large amounts, N, P, K
  2. these macronutrients are in every fertilizer bag
  3. nitrogen is used to build proteins which serve as enzymes or building components
  4. phosphorus is used in the energy economy of the plant cells and in its DNA
  5. potassium is used as a cofactor for many enzymes, and as an aid to control turgor in cells
  6. magnesium is part of the structure of chlorophyll
  7. sulfur is used in protein construction
  8. calcium is used as a component of cell walls
Plant Productivity
  1. GPP = total amount of energy fixed by a plant
  2. NPP = GPP minus the respiration rate, equals the rate of biomass production
  3. rainforests have the highest NPP, with deserts at the lowest
  4. to find the relative growth rate of a plant, divide the increase in dry mass per unit time by the original dry mass of the plant
  5. the neat assimilation rate divides the increase in dry mass per unit time by the leaf area of the plant
  6. the standing crop, mass of plant material present at any one time, is used to calculate NPP
Support in Plants
  1. plants support themselves in two ways: turgor and lignified cell walls
  2. turgor is the internal hydrostatic pressure created by water inside a plant cell
  3. turgor is important in thin-walled parenchyma cells to support the stems and leaves of herbaceous plants
  4. large plants use protein called lignin that reinforces the cell wall and makes it rigid enough to support huge masses above ground
  5. lignin is important to the xylem of woody plants to hold their large masses upright
Leaf Structure
  1. epidermis - covers outside of leaf, often producing hairs or sticky/toxic juices to repel herbivores
  2. cuticle - wax surface produced by epidermis
  3. stomata - holes in the leaf surface surrounded by guard cells that regulate the passage of water from leaf, and allow carbon dioxide and oxygen exchange with atmosphere
  4. stomata are found in stems, flower parts, and leaves
  5. mesophyll - layers of leaf between epidermal layers, photosynthesize
  6. vascular tissue - xylem and phloem cells that form a framework for transport of water and food
  7. vein - a strand of vascular tissue in a leaf
  8. venation - the vein pattern in blade
  9. monocot leaves lack palisade mesophyll and often have stoma on both the upper and lower epidermis; monocots have parallel-vein leaves while dicots have branch-veined leaves
Adaptations for Photosynthesis
  1. sun plants have increasing rates of psyn as light intensity increases whereas shade plants do not; they also have
  2. shade plants have lower compensation points than sun plants (where respiration and photosynthesis balance out); shade plants also have
Stem Structure
  1. internodes = spaces between nodes, mark the growth pattern of the plant
  2. stems have sequences of nodes where leaves/flowers attach
  3. buds are often located at nodes for the production of new shoot parts
  4. axillary buds produce lateral structures
  5. terminal buds are located at the tips of shoots
  6. primary growth is growth in length, or the production of new stems
  7. secondary growth is growth in girth or the thickening of an existing stem
  8. dicot stem structure
  9. monocot stem structure differs from dicot in that the vascular bundles are scattered in the monocot, rather than in a ring
Xylem
  1. xylem cells form the water conducting tubes within a plant
  2. xylem cells have secondary wall thickening which makes them a sclerenchyma cell type
  3. sclerenchyma includes tracheids (long thin water conducting cells); vessel elements (shorter and wider water conducting cells); fibers (long thin nonconducting cells); sclerids (cube shaped nonconducting cells)
  4. tracheids are the oldest water conducting cells present in ferns and gymnosperms; they are long and thin with slanted end walls; perforations in the end walls allow water to flow from cell to cell through a fern or conifer
  5. vessels are more advanced for water flow, and make pipes; the end walls of vessels are enzymatically removed to make a pipe which has the least resistance to water flow; vessels supply the leaves of angiosperms with water
  6. sclerids are very thick-walled cells to reinforce specific areas of a plant, such as seed coatings
  7. fibers are long and thin tapered cells that are heavily thickened with lignified cell walls to provide extra support to stems
Phloem
  1. phloem cells are the food conducting cells of a plant
  2. the specialized food conducting cells of phloem called sieve tube members that have perforated sieve plates for passage of food
  3. the end walls are called sieve plates which have pores to allow fluids to pass
  4. companion cells adjacent to sieve tube members aid in sap transport; they have nuclei and control the sieve tube members which lose their nucleus
  5. fibers are also present in the phloem system of a plant to provide support
Root Structure
  1. epidermis - outermost layer, one cell thick, including root hairs
  2. cortex - several cells thick, inside epidermis, are a type of parenchyma, contain amyloplasts that store starch
  3. endodermis - inside cortex, one cell thick, plays a role in controlling water and solute movement between root cortex and root interior
  4. pericycle - just inside the endodermis, undifferentiated meristematic cells
  5. vascular tissues - inside pericycle, for transport of substances, come in two types - xylem and phloem
  6. the endodermis and all cells within are referred to as the central cylinder or stele
  7. monocots have their root vascular tissue in a ring configuration whereas dicots have their xylem in the shape of a cross with their phloem in the arms of the cross
Uptake in the Root
  1. the soil solution moves freely into the cell wall spaces between the cellulose fibers of the cell walls and on into the spaces between the cells of the root cortex
  2. Alden Crafts and Theodor Broyer proposed the symplast theory of mineral uptake in the roots of plants; all the cells in the epidermis and cortex absorb minerals (sodium and potassium) from the soil solution in the apoplast, minerals are transported through the symplast which continues right through the endodermal layer and into the living cells around the xylem
  3. the apoplast provides for rapid substance movement while the symplast allows for selectivity
  4. most soil nutrients are taken in by active transport and once having passed through the endodermis they leave the symplast and move into the dead xylem to go up to the shoot system
  5. the movement of solutes into root cells decreases their water potential and water essentially moves into the roots following the gradient
  6. a plant can take up water and minerals through the entire surface area of the plasma membranes of the epidermis and cortex
  7. the root's cell wall spaces and intercellular spaces form a functional unit filled with nonliving material called the apoplast - which is virtually continuous with the external soil solution
  8. about 90% of the water moving into the root is apoplastic; the remaining 10% is symplastic
  9. the endodermis acts as a barrier dividing the apoplast into outer and inner areas
Gas Exchange in Plants
  1. leaf cells undergo photosynthesis and during the day give off oxygen gas while taking in carbon dioxide from the air
  2. roots are nonphotosynthetic and constantly respire, using the energy sent to them via the phloem from the leaves and oxygen from the soil spaces; they give off carbon dioxide to the soil spaces
  3. lenticels in the root and stem surface allow gases to enter and exit
  4. some plants like baldcypress trees and mangroves have aerial roots to facilitate root gas exchange with the air in submerged environments
  5. aquatic plants exchange gases directly with the water, except for lily pads which have stomata on their surface to obtain gases from the air
Gas Exchange and Stomata
  1. leaf transpiration has the added effect of regulating leaf temperature and preventing denaturation of enzymes
  2. each stoma is surrounded by two guard cells
  3. guard cell structure is peculiar - the side to the stomata has the thickest cell wall
  4. guard cells open the stoma by accumulating solutes to lower their osmotic potential and absorb water, become turgid, and expand to a curved shape (because of their unevenly formed wall
  5. the opening of stomata is correlated with the active transport of protons out of guard cells, which drives potassium into the cell through membrane channels
  6. stomata are opened when the CO2 concentration in the guard cells is low, normally in the daytime; also in response to blue-light receptors in the guard cells stimulating the activity of the protons pumps
  7. if water is lost too quickly, abscissic acid release from nearby cells triggers potassium release from guard cells and they collapse, closing the stoma
Transpiration
  1. transpiration pulls water up a stem
  2. Cohesive Strength of Water
  3. Rate of Transpiration
Translocation
  1. in a living plant, some areas are sucrose sources (in making sugar through photosynthesis or hydrolyzing it from starch) and other areas are sucrose sinks (polymerizing it or respiring it)
  2. sources include leaves (photosynthesis) but can be roots (hydrolyis from starch)
  3. sinks include fruits, tubers, bulbs, etc...
  4. sugar enters phloem conducting cells in the smallest leaf veins, which are surrounded by companion cells or transfer cells that actively transport the sugar up to concentrations of 10 to 25% (the source); transfer cells remove the sugar in roots, fruits, or flowers (the sink)
  5. sucrose is actually cotransported through the leaf mesophyll membranes and into the phloem cells using the proton pump at the source
  6. at the sink, a variety of methods are used to lower the sucrose concentration
  7. due to pressure differences between source and sink, sap moves through the phloem
Modifications in Plants
  1. plants produce a variety of structures to adapt to their environments
  2. bulbs are underground shoots that are compressed and contain leaves surrounding a central shoot
  3. tubers are swollen underground stems or roots that store food
  4. rhizomes are underground stems, as in ferns
  5. corms are underground stems that lack the leaves that bulbs have
  6. prop roots are used to support mangroves in oxygen-poor soils
  7. pneumatophores are roots that grow upward out of the soil in mangroves to facilitate gas exchange
  8. aerial roots are sent down by some epiphytic (plants that grow on other plants) plants to help anchor them to the soil
  9. venus fly traps have specialized leaves for catching and digesting insects
  10. pitcher plants and sundew plants also have specialized leaves for catching and digesting insects
  11. succulent leaves on some desert plants store water
  12. tendrils allow vines to grasp other plants
  13. cacti have needles to protect them from herbivores
Adaptations of Xerophytes
  1. in the desert, plants have many adaptations for survival
  2. spines thwart herbivores
  3. deep roots find water sources deep down in the bedrock
  4. hairy leaves help reflect excess sun
  5. excess wax on plant parts helps to retain water
  6. CAM metabolism allows for carbon fixation only at night
  7. sunken stomata prevents excess water evaporation
Adaptations of Hydrophytes
  1. hydrophytes are plants that grow in the water
  2. hydrophytes often lack a thick cuticle
  3. leaves often have air spaces to allow them to float which maximizes photosynthesis and gas exchange
  4. little or no xylem or lignin in the stem system