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Rhonda Alexander IC Science Robert E. Lee B.10.B describe the interactions that occur among systems that perform the functions of transport, reproduction, and response in plants The tissues of a plant are organized into three tissue systems: the dermal tissue system, the ground tissue system, and the vascular tissue system. The plant body has a hierarchy of organs, tissues, and cells There are three basic plant organs: Roots Stems Leaves Tissue System and Its Functions Component Tissues Dermal Tissue System • protection • prevention of water loss Epidermis Periderm (in older stems and roots) Ground Tissue System • photosynthesis • food storage • regeneration • support • protection Parenchyma tissue Collenchyma tissue Sclerenchyma tissue Vascular Tissue System Xylem tissue • transport of water and minerals Phloem tissue • transport of food Location of Tissue Systems Shoot System: Stems and Leaves • Stems – function primarily to display the leaves. o Terminal Bud – area of growth at the top end of stem o Axillary Buds – area of growth located in the V area between the leaf and the stem (branches) • Leaves – main photosynthetic organ in plants There are three basic groups of plant tissues: Dermal Tissue o Single layer of closely packed cells o Protects plant against water loss and invasion by pathogens and viruses o Cuticle – waxy layer in leaves Vascular Tissue o Xylem and phloem Ground Tissue o Any tissue that’s not Dermal or Vascular tissue o Pith – ground tissue located inside vascular tissue o Cortex – ground tissue located outside the vascular tissue PLANTS VASCULAR SYSTEMS Plants have two different types of 'transport' tissue. Xylem transports water and solutes from the roots to the leaves, phloem transports food from the leaves to the rest of the plant. Transpiration is the process by which water evaporates from the leaves, which results in more water being drawn up from the roots. Plant transport No heart, no blood and no circulation, but plants do need a transport system to move food, water and minerals around. They use two different systems – xylem moves water and solutes from the roots to the leaves – phloem moves food substances from leaves to the rest of the plant. Both of these systems are rows of cells that make continuous tubes running the full length of the plant. Xylem Xylem cells have extra reinforcement in their cell walls, and this helps to support the weight of the plant. For this reason, the transport systems are arranged differently in root and stem – in the root it has to resist forces that could pull the plant out of the ground. In the stem it has to resist compression and bending forces caused by the weight of the plant and the wind. Comparison of xylem and phloem Tissue Process What is moved Structure Xylem Transpiration Moves water and minerals from roots to leaves Columns of hollow, dead reinforced cells Phloem Translocation Moves food substances from leaves to rest of plant Columns of living cells Transpiration Transpiration explains how water moves up the plant against gravity in tubes made of dead xylem cells without the use of a pump. Water on the surface of spongy and palisade cells (inside the leaf) evaporates and then diffuses out of the leaf. This is called transpiration. More water is drawn out of the xylem cells inside the leaf to replace what's lost. As the xylem cells make a continuous tube from the leaf, down the stem to the roots, this acts like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves. Factors that speed up transpiration will also increase the rate of water uptake from the soil. When water is scarce, or the roots are damaged, it increases a plant’s chance of survival if the transpiration rate can be slowed down. Plants can do this themselves by wilting, or it can be done artificially, like removing some of the leaves from cuttings before they have chance to grow new roots. Factors that affect transpiration rate Factor Description Explanation Light In bright light transpiration increases The stomata (openings in the leaf) open wider to allow more carbon dioxide into the leaf for photosynthesis Temperature Transpiration is faster in higher temperatures Evaporation and diffusion are faster at higher temperatures Wind Transpiration is faster in windy conditions Water vapors is removed quickly by air movement, speeding up diffusion of more water vapor out of the leaf Humidity Transpiration is slower in humid conditions Diffusion of water vapor out of the leaf slows down if the leaf is already surrounded by moist air PLANT REPRODUCTION - THEY'LL MAKE MORE . Reproduction is one of two things. (1) One cell can split into two, giving you two identical cells. That type is asexual reproduction. (2) The second type is when two cells, each with half of the DNA needed, combine and create a living cell. That type is sexual reproduction. When plants hit a point in evolution, the second is the one that occurs more often. MAKING MORE MOSSES Sporophytes are the reproductive structures you will find in mosses. They are actually a phase of the moss life cycle that feeds off the green parent plant (the gametophyte). The sporophyte is a stalk that grows after the haploid sperm of one moss plant is able to mix with the haploid egg of a female moss plant. The resulting diploid cell grows into the sporophyte stalk. When ready, spores stored in the sporophyte are released and they grow into new moss plants. CONFIERS AND THEIR CONES While there are male and female mosses, conifers produce two types of cones on the same tree. One of the cone types gives off pollen (the staminate cone). The other type of cone catches the pollen if the wind is moving in the right direction. Better yet, the wind blows the pollen to another conifer of the same species, and a cone (called the ovulate cone) catches the pollen. Again, the pollen and megaspore (receiving haploid cell) are haploid and combine to form a diploid cell. That diploid cell grows into a zygote (baby conifer) that eventually lives in a seed. FLOWERS AND POLLEN The most advanced of the plants have their own way of sexually reproducing. It is a very fancy and very complex process. Plants that rely on flowers for reproduction are also very dependent on outside help such as insects and animals. While conifers have the two structures on one tree, flowering plants went one step further and put the devices that make and receive pollen in the same structure. How does that help? A bee might go to one flower and get a little pollen on its back. If it goes to another flower of the same species, that pollen can land on the stigma. From that point, one haploid male nucleus combines with a female nucleus and the other haploid male nucleus combines with a polar nucleus. If successful, an embryo and seed/fruit develop respectively. Plant Response The interactions of hormones and stimuli in the environment often results in a bending or turning response in the plant called a tropism. When the plant turns toward a stimulus, the tropism is said to be positive. If the plant turns away from a stimulus, the tropism is negative. One of the most familiar plant responses is the bending of the stem toward a light source. Light is the stimulus, and the response of the plant is called a phototropism. A geotropism is a turning of the plant away from or toward the earth. A negative geotropism is a turning away from the earth, such as by a plant stem that grows upward . A positive geotropism is a turning toward the earth, such as in a root that grows downward. What is thigmotropism? It is a plant's response and movement to physical contact. Vascular cylinder Root hair Cortex Epidermis Meristems generate cells for new organs Zone of maturation Zone of elongation Cellulose fibers Zone of cell division Apical meristem region Key Dermal tissue system Ground tissue system Vascular tissue system Root cap Apical meristems o Are located at the tips of roots and in buds of shoots. o Sites of cell division that allow plants to grow in length (primary growth) Lateral meristems o results in growth which thickens the shoots and roots (secondary growth)