Vascular Plant Botany
- Roots: Roots anchor the plant, absorb minerals and water,conduct water and nutrients, and store food. These are two types of root systems.
- Taproot System: This system consists of a single main vertical root with many smaller side roots. Examples of this type of system are: carrots, turnips, and dandelions. They serve as excellent reserves for food and anchor the plant well.
- Fibrous System: This system consists of many small lateral roots that spread out just below the soil's surface. The plants containing this type of root system has excellent exposure to water in the soil. It helps anchor the plant and helps prevent soil erosion.
- Adventitious roots are roots that grow from plant structures other than the roots.
- Stems: The stem consists of vegetative shoots which produce leaves and floral shoots that end with the flower.
- Stem Anatomy: Areas where side branches and leaves develop from are called nodes. The area in-between the nodes are the inter nodes. At the node axially buds are found. These buds contain embryonic tissue which will allow the stem to grow. Lenticels are small holes located on the stem. These holes allow air into the stem while they are active. As the stem gets older they disappear. Many stems end with a terminal bud. This bud allows the stem to grow in length.
- Leaves: Leaves carry on photosynthesis. Their position and shape allow them to absorb the maximum amount of sunlight as possible. The leaf consists of the flattened portion called the blade, the edge or the margin, the petiole, and the veins. Leaves can be classified based on the these characteristics.
Leaf Arrangement opposite alternate whorled Blade Complexity simple pinnately compound palmately compound Shape triangular oval lancolate Margin entire serrate lobed Venation parallel palmately netted pinnately netted
- Angiosperms (flowering plants) can be classified into 2 main groups based on the types of roots, stems, leaves, flowers, and seeds they contain.
One seed leaf
Parallel venation Stem vascular bundles scattered Fibrous root system Floral parts in multiples of 3 Dicots
Two seed leaves
Stem vascular bundles arranged in rings Taproot system Floral parts in multiples of 4 or 5
- Types of Plant Cells:
- Parenchyma Cells. These cells are the most general of plant cells. They consist of thin flexible cell walls. They contain a large central vacuole and can carry out most of the metabolic functions of the plant. Mesophyll cells of the leaf are parenchyma cells. The fleshy tissue of most fruits also contain much parenchyma.
- Collenchyma Cells. These cells have a much thicker primary wall than the parenchyma cell. Grouped in strands or cylinders they support young plants.
- Sclerenchyma Cells. Function in support of the plant. They contain a thick secondary wall containing lignin. For all intent and purpose these cells function best when dead.
- Tracheids. These are water conducting elements. These cells are dead and are found along with vessel elements making up the plants xylem.
- Sieve-tubes. These function in carrying food throughout the plant. They are kept alive and nourished by companion cells. These are found in the plants phloem.
- Tissue Types:
- Dermal Tissue. generally a single layer of cells. They are tightly packed and covered with a transparent, waxy, material called the cuticle.
- Vascular Tissue. functions in support and transportation of food and water throughout the plant.
- Ground Tissue. makes up the bulk of a young plant. It fills the space between the dermal and the vascular tissues.
Vascular Plant Anatomy
- Tissues of vascular plant leaves: Leaves are cloaked by a single layer of cells called the epidermis. It protects the leaf from physical damage and pathogens. A transparent, waxy, colorless cuticle coats the epidermis. The stomata ( small holes) are located on the lower epidermis of the leaf. The stomata allow gases and water vapor into and out of the leaf. Each stoma is controlled by two bean shaped guard cells. The palisade mesophyll is a layer of elongated cells containing chloroplasts found just under the upper epidermis. The majority of photosynthesis takes place within this area. Just below the palisade mesophyll is an area of loosely packed parenchyma called the spongy mesophyll. The spongy mesophyll contains air spaces in which gases circulate. The petiole of the leaf connects the blade with the stem. The vascular tissues pass through with the xylem positioned in the top section of the vein while the phloem occupies the lower section.
- Primary Growth: Apical meristem is responsible for primary root and stem growth in vascular plants.
- Primary Root Growth: is concentrated near the tip and results in the root growing in length. The root tip contains 4 zones of development: The root cap, which protects the area behind it and softens the soil ahead of it by producing a polysaccharide. The apical meristem, is an area of rapidly dividing cells. It will replace the cells of the root cap as they wear away and push cells above them that will develop into the main tissues of the plant. The zone of elongation, is an area where the cells elongate 10 times their original length. This elongation helps push the root into the soil. The zone of maturation, is the area farthest from the root tip. Here the new cells will specialize and carry out the functions of the epidermal, ground, and vascular tissue. The primary tissues in a dicot root are arranges in a central x pattern for the xylem with the phloem located in each of the angles of the xylem. In a monocot the vascular tissues are alternated in a circle.
- Primary Stem Growth: begins at the tip of the terminal bud in the area called the apical meristem. The cell divisions are responsible for the stem's growth in length. The primary vascular tissue in monocots takes on a scattered arrangement. In a dicot, it takes a circular pattern.
- Secondary Growth: Increases the girth of a stem it is caused by the vascular and cork cambium.
- Vascular Cambium: meristematic parenchyma produces xylem on the inside and phloem on its outer side. The secondary xylem accumulates and forms the wood. The secondary phloem does not accumulate and is sloughed off with the bark.
- Cork Cambium: forms in the outer cortex. Produces cork and epidermal tissues.
- Wood has 2 zones: Heartwood- the older (inner) layers of xylem blocked with resins. It is non -functional in water transport. Sap wood- outer xylem, vascular cambium, phloem and cork cambium. Conducts water and food.
- Transport in Plants:
- Absorption of water and minerals by roots: Water and mineral enter through root epidermis, cross the cortex, pass into the stele, and are carried upward in the xylem.
- Active accumulation of Mineral Ions. The cells cannot get enough mineral ions from the soil by diffusion alone. The soils solution is too dilute.
- ACTIVE TRANSPORT of these ions must occur. Specific carrier proteins in the plasma membrane attract and carry their specific mineral into the cell. A Proton Pump: H+ is pumped out of the cell causing a change in pH and a voltage across the membrane. This helps drive the anions and cations into the cell. Water and minerals cross the cortex in one of 2 ways: Via SYMPLAST which is the living continuum of cytoplasm connected by PLASMODESMATA. Via APOPLAST which is nonliving matrix of cell walls. At the endodermis the apoplastic route is blocked by the CASPARIAN STRIP. this is a ring of suberin around each endodermal cell. Here water and minerals MUST enter the stele through the cells of the endodermis. Water and minerals enter the stele via symplast, but xylem is part of the apoplast. Transfer cells selectively pump ions out of the symplast into the apoplast so they may enter the xylem. This action requires energy.
- ASCENT of XYLEM SAP:
- Water transported up from the roots must replace water lost by transpiration.
- WATER POTENTIAL: Xylem sap rises against gravity, driven by a gradient of water potential. Water flows from an area of high potential to an area of low potential. Water Potential is expressed in units of pressure: 1 bar is the pressure needed to push up a column of water 10 meters. 1 megapascal = 10 bars. Pure water has a potential of 0. Addition of pressure increases water potential. Addition of solutes decreases it.
- ROOT PRESSURE: When transpiration is low, ions pumped into the stele decrease water potential and cause water uptake by the stele. This uptake force is called root pressure. It Cannot keep pace with transpiration, and can only force water up a few meters.
- TRANSPIRATION-COHESION-ADHESION THEORY:
- a). water exits leaf through stomata.
- b). this water loss is replaced by evaporation from mesophyll cells, lowering their water potential, causing them to take water from neighboring cells.
- c). the process connects back to the tracheids causing water to be taken from the xylem.
- d).Water travels from the tracheids to the air following a water potential gradient.
- e). Waters cohesive and adhesive properties and the small diameter of xylem aid in its movement of up the tube.
- f). This pull decreases water pressure in the xylem causing the roots to take water from the soil.
- How Stomata Operate:
- Turgid guard cells open the stomata, while flaccid ones close them.
- The potassium (K+) ion is responsible for the stomatal action.
- Uptake of K+ causes the cell to become turgid decreasing its water potential.
- The stomata open at dawn caused by the light inducing the cells to take in K+. An internal clock (circadian rhythm) will make them open even if in they are kept in the dark.
- Guard cells will close due to water deficiency and high temperatures.
- Phloem Transport:
- Translocation refers to the transport of produced products to the rest of the plant via the phloem. Phloem carries sucrose, minerals, amino acids, and hormones.
- Source to Sink Transport:
- Source refers to the origin of the sugar produced. Sink refers to the organ that consumes or stores the sugar.
- Flow is always from the source to the sink.
- Phloem is loaded by active transport.
- Click here to develop the concept of Transpiration by completing the AP Lab 9: Transpiration.
The angiosperm life cycle includes alternation of generations. Here a multicellular haploid (N) gametophyte generation alternates with a diploid (2N) sporophyte generation.
- The sporophytes produce the haploid (N) spores by meiosis.
- The sporophytes are the large plants we see dotting our landscape.
- These spores will undergo mitosis and become the male and female gametophytes.
- Gametes are produced by the gametophytes through the process of mitosis.
- The gametes fuse and develop into the multicellular sporophyte.
The flower is the sexual reproductive part of an angiosperm. It consists of four whorls of modified leaves : sepals, petals, stamens and carpals. The stamens are the male reproductive parts which includes the sporangia which produces pollen. The carpals are the female reproductive parts and includes the sporangia that produces the egg.
Flowers are classified according to the number and type of their structures.
- Complete flower. The flower contains all four basic whorls of modified leaves.
- Incomplete flower. A flower missing one or more of its parts.
- Perfect flower. A flower containing both male and female parts. Could be complete or incomplete.
- Imperfect flower. A flower that is either male or female due to its missing of either reproductive organ.
- Monoecious. Plants having both male and female flowers on the same plant.
- Dioecious. Plants having male and female flowers on separate plants.
- A pollen grain is an immature male gametophyte.
- It is produced within the sporangium of the anthers.
- The diploid microspore mother cell will undergo meiosis and form 4 haploid microspores.
- The microspores nuclei will undergo mitosis and produce a tube nucleus and a generative nucleus.
- A thick wall forms around the spore in a specific pattern, producing the pollen grain or immature male gametophyte.
- The ovule is an immature seed. It is formed within the ovary and contains the female gametophyte.
- The female gametophyte is the embryo sac and forms in the following way.
- The megaspore mother cell undergoes meiosis to form 4 haploid (N) megaspores.
- One of the 4 will continue to develop, while the other 3 dissolve.
- The remaining megaspore grows and its nucleus will undergo 3 mitotic divisions, forming 1 large cell with 8 haploid nuclei.
- This will develop into the embryo sac. This sac contains a specific arrangement of these nuclei in the following order: The egg cell is located near the micropyle surrounded by 2 other cells called synergids. At the opposite end 3 antipodal cells are found. In the center of the sac will be found 2 polar nuclei.
Pollination is the placement of the pollen on the stigma of the carpal. This pollen transfer can be accomplished by wind, insects, built in mechanical discharge, and man. Once the pollen lands on the stigma, a series of chemical reactions takes place allowing the pollen grain to begin producing a structure called the pollen tube. As this is happening, the generative nucleus will divide and produce 2 sperm nuclei. This pollen grain with the pollen tube and 3 nuclei is considered the mature gametophyte. The pollen tube will work its way through the style of the carpal and touch the micropyle of the ovule. Here the sperm nuclei will enter the embryo sac and fertilize the egg and the two polar nuclei; hence the term double fertilization. The fertilized egg (2N) will develop into the immature seed plant, while the (3N) central cell will develop into the endosperm or food storage area of the seed.
Structure of the Mature Seed:
- The seed is protected by the seed coat or testa.
- The micropyle is the only opening into the seed. It is through here that the water will enter to start germination.
- The seed contains stored food in the form of seed leaves (cotyledons). Some seeds contain one ( monocots) while other contain 2 ( dicots).
- The embryo plant contains several areas : the area above the attachment of the cotyledons is the epicotyl. This will develop into the shoots and leaves of the developing plant. The area below the attachment is called the hypocotyl. This will develop into the roots of the plant.
Development of Fruit:
The fruit of a flower develops from the ovary. They protect the seeds and allow for their dispersal. Fruits may be classified in many ways. Below find one of such classification schemes.
- Simple Fruits: These fruits develop from a single ovary. Peach, cherry, soybean.
- Aggregate Fruits: These fruits develop from a single flower with many carpals. Strawberry.
- Multiple Fruits: Fruit develops from a group of tightly clustered flowers. Pineapple.