State Hesss law. How is it used?
Margaret S Biology 1060 (General Biology II) Week 10 Lecture Notes Unit 3: Plants 3-14-16 Tissue Review Dermal Tissue: mostly parenchyma cells (some specialized cells as well, ex. trichomes) Vascular Tissue: mostly parenchyma and sclerenchyma Ground Tissue: parenchyma, sclerenchyma, and collenchyma Today’s Topic: Plant Organs Leaves: undergo photosynthesis Stems: support plant and transport nutrients/water Roots: anchor plant in place and are responsible for nutrient uptake Plants are Different from Animals: Plants cannot walk or move away/towards danger/more favorable conditions Plants can change their development (they exhibit plastic development): meristems are hugely important to this development as they give rise to totipotent cells throughout the plant’s life SIMILARLY to animals, plant organization is cellstissuesorgans Vascular Plants Have Shoots and Roots Shoots are the above ground portion of the plant o Include stems, leaves, and flowers (flowers are plant reproductive organs) Roots are the below ground portion of the plant Both shoots and roots have apices (sing. Apex), that are located at the tips of each and contain meristems Both shoots and roots have all 3 types of tissue Shoots are Organized into Nodes and Internodes Nodes are the portion of the stem that gives rise to leaves and axillary buds (axillary buds are backup meristems located just above each leaf branch along the stem; they allow for branching in seed plants) Internodes are the portion of the stem that separates the nodes (no leaves come off of the internode regions) All plants have specialized leaf organization; some have alternating leaves along the stem and some only grow pairs of leaves on either side of the stem Shoots are Divided into Zones of Cell Division, Elongation, and Maturation Zone of division=meristem Zone of elongation: just below the meristem; in the meristem cells are circular, while just under the meristem they are more rectangular (they have elongated) Zone of maturation: the lowest part of the plant; contains fully grown and differentiated cells Leaves Evolved to Achieve Maximum Photosynthetic Capacity Early vascular plants had no leaves, but had photosynthetic stems In some early plants, some side branches of the stem lost their apical meristems and developed flat sides that were more efficient at capturing light The development of new meristems allowed tissues to form between side branches of the stem, which lead to the leaves we see today Leaves: Are photosynthetic machines Flattened leaf blades (the “stems” of the leaf) called petioles Contain veins in the form of vascular tissue: they are abundant in leaves in order to allow water to leave via transpiration and for carbohydrates from photosynthesis to be transported to the rest of the plant Eudicots have net-like veins Monocots have parallel veins Leaf Cross Section: The anatomy of leaves is meant to balance water loss, gas exchange, and transport of photosynthetic products (carbohydrates) Simple Leaves vs. Compound Leaves Simple Leaves: a blade and petiole Compound Leaves: a petiole and blade divided into leaflets Needle Leaves: don’t fit into either category, ex. Pine leaves Modified Leaves Have Other Important Functions: Bud scales: cover apical meristems to protect apical meristems from winter Tendrils: curl around support structures to help the plant grow upward (ex. Venus Fly Trap, Pea plants) Colored leaves: help attract pollinators to flowers (ex. Poinsettas) Onion leaves (onion layers) store food Aloe vera leaves store water Pitcher plant leaves trap insects (as do the Venus Fly Trap and sundew leaves) Cacti have protective leaves (spines) Some plants produce tiny plantlets for reproduction; these leaves fall off the plant and grow roots to become a new plant Stems: Primary functions are support of plant and conduction o Conduction is of: water and minerals, which move from roots to leaves o Conduction is also of food, which move from the production site (the source, usually the leaves) to the usage site (the sink, which is normally the roots or the still-developing parts of the plant) Vascular tissues make conduction possible Stems have vascular tissue in bundles o Monocot stems have scattered vascular bundles, with the xylem in each bundle mostly falling closer to the center of the stem and phloem in each bundle mostly falling closer to the outer ring of the stem o Eudicot stems have vascular bundles arranged in a ring around an internal ring of ground tissue called pith; in eudicots, the xylem and phloem are oriented within each bundle the same way as in monocots o Eudicots have a small layer between the xylem and phloem called the vascular cambium, which makes more xylem and phloem when the stem is growing wider Apical meristems just make the plant taller Lateral meristems contribute to secondary growth, and there are 2 types: o The vascular cambium makes more vascular tissue o The cork cambium makes bark around outside Wood is excess secondary xylem (which is dead) produced by the vascular cambium, which also produces secondary phloem (which is alive) Woody eudicot system: The rings within tree trunks are dependent on the availability of water: when there is more rain, wider xylem vessels develop which push the old xylem in, but in winter the xylem are narrow and darker o Narrow ring = slow growth, usually narrow rings are in the center of the tree trunk, these are called the heartwood o Wide ring = increased growth rates, which means favorable conditions; usually wide rings are towards the outer tree trunk, these are called the supwood Tree trunks have vascular cambium itself on the outermost layer under the wood The cork cambium produces the outer protective layer of bark Modified Stems: Examples include: bulbs, rhizomes, stolon/runners, tubers (potatoes, look like roots but are modified stems), tendrils, cladophyll (cactus stems) Roots Grow Similarly To Shoots Root meristems (located towards the bottom tip of the root) have special protective layers called root caps Root meristems are the zone of cell division, and there are subsequent zones of cell elongation and maturation (ex. Root hairs) in roots as well Review Question: Technically speaking, what is wood A. Primary xylem B. Secondary xylem C. Primary phloem D. Secondary phloem E. Bark Answer: B. Secondary xylem 3-16-16 General Roots: Roots need root cap to grow 2 types of roots: o Tap roots: 1 clear main root o Fibrous roots: no clear main root Roots have an endodermis that surrounds dermal tissues o Suberin makes up the watertight coating around the endodermis called the Casparian strip o Xylem and phloem within roots are not organized into bundles, but are surrounded by endodermis The vascular system is enclosed in the stele of the roots, which is surrounded by cortex Monocots have an extra layer of ground tissue in the middle of the root called pith There is no true vascular cambium in any roots New root apical meristems form from the pericycle (a region just within the vascular tissue) in order to create lateral roots, which branch from the main roots Roots do not undergo secondary growth (they don’t get wider) Modified Roots Aerial roots adapted to obtain water from the air (they only grow in humid areas) Pneumatophores (roots that stick up out of the ground) facilitate oxygen uptake above the water line in plants that grow in swampy or marshy areas Storage roots store the products of photosynthesis Potatoes are stems, sweet potatoes are roots Roots vs. Shoots Size o Roots: relatively large o Shoots: relatively large Protection to meristem o Roots: root cap o Shoots: none Lateral organs o Roots: lateral roots o Shoots: leaves and branches Primary growth o Roots: yes: apical meristem o Shoots: yes: apical meristem Secondary growth o Roots: none o Shoots: yes in eudicots Branching o Roots: present o Shoots: present Seeds The endosperm supplies nutrients to the developing embryo as the seed germinates In monocots, the majority of the seed is endosperm Monocots have 1 cotyledon (miniature leaflet inside embryo) while eudicots have 2 cotyledon Root-shoot axes and all 3 tissue layers are determined during embryogenesis Seeds Are Important Land Adaptations They can maintain dormancy in unfavorable conditions They protect young plants when they are the most vulnerable They provide food via the endosperm They facilitate the dispersal of the embryo Seed Germination There are many environmental cues that can stimulate seed germination: o Light o Temperature o Moisture Review Questions 1. The advantage of roots originating at the pericycle, not the epidermis, is that A. Being outside the Casparian strip helps them to absorb more B. They only form at the tips of pre-existing roots C. New roots are directly connected to the xylem and phloem of preexisting plants 2. In roots, vascular tissue is A. Organized in bundles B. Surrounded by endodermis C. Found outside the cortex D. A and B E. All of the above 1. C. New roots are directly connected to the xylem and phloem of preexisting plants 2. B. Surrounded by endodermis 3-18-16 Will be uploaded separately on 3-29-16