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Transcript
Lecture # 16 Date _____ • Chapter #35~ Plant Structure and Growth Seed Plants • There are two categories of seed producing plants: ▫ Gymnosperms (conifers) ▫ Angiosperms (flowering plants) Angiosperms • Angiosperms (flowering plants) can also be divided into two groups based on the amount of cotyledons ▫ Monocots (1 cotyledon) ▫ Dicots (2 cotyledons) Monocot vs. Dicot • Cotyledons – storage tissue that provides nutrition to the developing seed Monocot Dicot - one cotyledon - 2 cotyledons Monocot vs. Dicot • Leaf Venation – the pattern of veins on leaves Monocot Dicot - parallel - netted (branching pattern) Monocot vs. Dicot • Flower Parts– number of petals, sepals, stamen, and other flowering parts Monocot Dicot - in multiples of 3s - in multiples of 4s & 5s Monocot vs. Dicot • Vascular Bundles– arrangement of bundles of vascular tissue (xylem & phloem) in stems Monocot Dicot - scattered - organized in a circle Monocot vs. Dicot • Root– form of root Monocot Dicot - fibrous system (a cluster of many fine roots) - taproot (a large single root) Plant Tissues The entire plant (leaf, stem and root) are composed of 3 major types of tissue groups: • 1) Ground Tissues – includes 3 types of cells that differ only by their cell walls ▫ Parenchyma cells are the most common and have thin walls and serve in a variety of roles including storage, photosynthesis, and secretion ▫ Collenchyma cells have thicker walls and provide support for the plant ▫ Sclerenchyma cells have the thickest walls and provide support Plant tissues • 2) Dermal Tissues – consist of epidermis cells that cover the outside of plant parts and protect it from water loss and bacterial invasion. These cells can also secrete waxy protective substance called cuticle Plant Tissues • 3) Vascular Tissues – is a network of cells that run from root to shoot. It consists of two major tissues, xylem and phloem. They usually occur together as a vascular bundle. ▫ Xylem Tubes that draw water UP from roots to the entire plant has two types of cells for conducting water (tracheids & vessels) has 2 cell walls for added support Most xylem are “dead” at maturity, essentially they are just the left over cell walls Plant Tissues • 3) Vascular Tissues – is a network of cells that run from root to shoot. It consists of two major tissues, xylem and phloem. They usually occur together as a vascular bundle. ▫ Phloem Tubes that draw sugar down from leaves to the entire plant has two types of cells for conducting sugar sieve tubes & companion cells) The sieve tubes are chains of cells that allow materials to be transported Companion cells lie parallel to sieve tubes and provide the molecular needs of the sieve tube The seed • A seed consists of an embryo, a seed coat, and some type of storage material (endosperm or cotyledons •The top part of the embryo (epicotyl) becomes shoot tip •Attached to the epicotyl are tiny leaves called plumule •The hypocotyl is the shoot that connects epicotyl to the cotyledons •sometimes a radicle is present, which becomes the roots *in monocots, there is an extra protective layer for epicotyl called the coleoptile Germination • Most seeds reach maturity and remain dormant until cues are encountered • The most common cue is water • Others may be temperature, light, etc. •Germination begins with absorption of water •The water initiates enzymes, which activate cellular respiration •Water also cracks open the seed coat •Hypocotyl and radicle starts to eloongate creating the shoot and roots •This vertical growth is termed primary growth •Plants can also go through secondary growth which is growth horizontally creating layers of cork and bark Roots •Primary growth in roots leads to specialized tissues 1) epidermis lines the outside surface of the roots. this layer has hairs that help absorb water. As it grows, older layer protect the root 2) cortex cells formt eh bulk of the root. It functions to store starch. It also has a spaces between cells to allow for oxygen to reach cells for cellular respiration 3) endodermis is a ring of cells called the Casparian Strip which creates a waterproof layer to control water entering the plant 4) vascular cylinder AKA stele in the endodermis and is made of xylem and phloem. The very center is called the pith Stems •The tissues in the stem are similar to the root, with the Casparian Strip missing (for water absorption) •Epidermis contains cells covered in cuticle (waxy substance) •Cortex contains cells that contain a lot of chloroplasts •Vascular Cylinder contains xylem, phloem and pith (arrangement differs between dicots and monocots). Generally the xylem and phloem come in bundles with the xylem being inner and phloem being outer. A layer of cells separate the xylem and phloem called the cambium Leaves • A typical leaf is made of several layers of cells •Epidermis protects the outside by producing cuticle (waxy). The cuticle may also function to reduce transpiration (loss of water due to evaporation) •Palisade mesophyll is made of parenchyma cells with a ton of chloroplasts. This layer has the most surface area and is where photosynthesis primarily occurs •spongy mesophyll is parenchyma cells with air pockets to provide CO2 to photosynthesizing cells •Guard cells are epidermal cells that control the openign and closing of the stomata •Vascular bundles consist of xylem and phloem. Transport of Water •Water and dissolved minerals enter the root by osmosis •The movement of water to the center of the root follows two pathways •Apoplast is when water moves between cell walls •Symplast is when water moves through cells (when water reaches the endoplast, this is the only way to travel through xylem •In general, there are 3 mechanisms for water to move through plant: •Osmosis is the movement of water through membranes of high concentration to lower concentration. This creates root pressure which forces water up through xylem •Capillary action is caused by adhesion in a tube (forcing water up) •Cohesion-Tension Theory is the idea where water is transpired, which creates a pressure. This pressure is relieved by water being cohesive and pulling up neighboring molecules, creating an entire bulk flow Transport of Sugar •Translocation is the movement of carbohydrates through the phloem from source (leaves) to sink (site of utilization) •Translocation is described by pressure-flow hypothesis •Sugar enters sieve-tube members •Water enters sieve-tube members •Pressure builds from water entering, forcing water and sugar to move in bulk flow •When sink is reached, the sugars are used, relieving pressure and diffusing water out Control of Stomata •The opening an closing of stomata controls gas exchange, sap production, and photosynthesis rate. •Each stomata (hole) is surrounded by guard cells that swell to close the stomata and shrink to open the stomata •OPEN: transpiration, loses water, CO2 can enter photosynthesis occurs •CLOSED: keeps water, no CO2 entering, “technically” no photosynthesis occurs •Some factors control the opening and closing •Closed when temperatures are high •Open when CO2 levels are low •Closed at night •Open in the day Plant Hormones Hormones are substances produced by specialized cells to influence the physiology of target cells •Auxin promotes plant growth by facilitating the elongation of developing cells •Gibberellins promotes plant growth in the roots and shoots •Cytokinins are a group of hormones that stimulate cytokinesis (cell division) •Ethylene is a gas that promotes the ripening of fruit •Abscisic Acid is a growth inhibitor. It delays growth and causes scales in preparation for winter Plant Response to Stimuli •Tropsim is a growht pattern in response to environmental stimuli •There are 3 types of Tropism in plants •Phototropism is a plant’s response to light. It uses the hormone Auxin to grow in the direction of light •Gravitropism is the response to gravity by stems and roots. It uses Auxin and Gibberellins to always grow roots and shoots in a vertical direction •Thigmotropism is response to touch. This stimuli is what allows vines to climb object Photoperiodism •Photoperiodism is th plant’s response to photoperiod (legnth of daylight and night) •Many flowering plants initiate flowering in response to the photoperiod •Long-day plants flower in the spring and early summer (when daylight is incerasing) •Short-day plants flower in the late summer and early fall (when daylight is decreasing) •Day-neutral plants do not flower in response to daylight. They respond to other cues like water and