Physiology study of the adaptations by which organisms function in their environ. 1.) Plants, Tissues and Function Plant types and their evolution Terrestrial plants evolved from aquatic green algae There are three main types: Bryophytes- mosses and hornwarts Leaves have a cuticle to conserve water A rudimentary root system anchors them to substratum and allows for absorption Need to live in moist environment Have no vascular system Produce spores and free swimming sperm need water Most can survive drying out by going dormant Ferns, Lycophytes and horsetails Share features with Bryophytes Have rudimentary root and vascular system Seed producing plants (Gymnosperms and angiosperms) Gymnosperms (naked seed) includes conifers Produce cone-like structure Wind pollinated- pollen reach exposed reproductive structure Have true leaves, roots, vascular tissues, etc Do not need water to reproduce Angiosperms (vessel seed) Flowering Plants Include all adaptations for living on land found in gymnosperms plus flowers, with some adaptations to extreme environments ( e.g. cacti) Three types: Monocots (one cotyledon)- grasses, bamboo, etc Emerging shoots open into blade-like leaves Three floral parts (or multiple of three) Veins run parallel to each other Vascular bundles distributed throughout shoot Magnoliids- effectively ancestral dicots Eudicots (two cotyledons)- dominate plant kingdom Emerging shoots and leateral buds open into two leaves Four of five floral parts (or multiple of four or five) Veins are net-like Vascular bundles organized into ring (in shoots) Plant body is divided into shoots and roots Plant organ and tissue systems Shoots Produce food by photosynthesis Carry out reproductive functions Roots SRJCA. Carranza Page 1 7/25/2015
Anchor the plant Penetrate the soil and absorb water and dissolved minerals Store food Plant Body Plan Meristems Regions where cell divisions produce plant growth Apical meristems Lengthen stems and roots Responsible for primary growth Lateral meristems Increase width of stems Responsible for secondary growth Simple Tissues Made up of one type of cell Parenchyma alive Found in soft photosynthetic tissues Collenchyma alive Provides support Sclerenchyma dead at maturity Provides even more support Complex Tissues Composed of mixed cell types Vascular Tissues Xylem Conducts water and dissolved minerals Conducting cells are dead and hollow at maturity Phloem Transports sugars Main conducting cells are sieve-tube members Companion cells assist in the loading of sugars Epidermis Covers and protects plant surfaces Secretes a waxy, waterproof cuticle Contains stomata In woody plants, periderm replaces epidermis Stem Growth and Development Cells at tip of apical meristem divide Their descendents divide and differentiate, giving rise to specialized tissues Lateral buds are undeveloped meristematic tissue that gives rise to stems, leaves, and flowers Root Systems, Growth and Development Root Structure Fibrous root system- typical of monocots, just a mass of small roots Tap root- typical of dicots, a single main root that reaches deep into soil Root cap covers tip, protects against abrasion Apical meristem produces the cap SRJCA. Carranza Page 2 7/25/2015
Cell divisions at the apical meristem cause the root to lengthen Farther up, cells differentiate and mature Root hairs Provide large surface area for water and mineral absorption Internal Structure of a Root Outermost layer is epidermis Root cortex is beneath the epidermis Vascular cylinder contains vascular tissues, surrounded by endodermis Xylem conducts water, forms an X in some plant roots Phloem conducts nutrients and sugars, forms P s around xylem in some plants Endodermis Endodermis, then pericycle surround the vascular cylinder In some plants, there is a central pith Secondary Growth- increases girth Occurs in woody plants A ring of vascular cambium produces secondary xylem and phloem Xylem grows in phloem grows out Wood is the accumulation of these secondary tissues, especially xylem Tree Rings Form as a result of xylem tubes with different diameters Wide tubes develop during wet season (winter or spring) Narrow tubes develop during dry months Different diameters create discernable pattern of year s growth 2.) Plant Nutrition, Transport and Gas Exchange Soil Minerals mixed with humus Minerals come from weathering of rock Humus is decomposing organic material Composition of soil varies Suitability for plant growth depends largely on proportions of soil particles Macronutrients Mineral elements that are required in amounts above 0.5% of the plant s dry weight Carbon Nitrogen Magnesium Hydrogen Potassium Phosphorus Oxygen Calcium Sulfur Micronutrients Elements that are required in trace amounts for normal plant growth Chlorine Iron Copper Boron Manganese Zinc Molybdenum SRJCA. Carranza Page 3 7/25/2015
Leaching Removal of nutrients from soil by water that percolates through it Most pronounced in sandy soils Clays are best at holding onto nutrients Soil Erosion Loss of soil to wind and water Often the result of deforestation Nutrient loss affects entire food chain Root Hairs Extensions from the root epidermis Greatly increase the surface area available for absorption Root Nodules Swelling on roots of some plants Contain nitrogen-fixing bacteria Bacteria convert nitrogen gas to forms plants can use Mycorrhizae Symbiosis between young plant root and fungus Fungal filaments may cover or penetrate root Fungus absorbs sugars and nitrogen from plant Roots obtain minerals absorbed from soil by fungus Root Structure and Absorption Roots of most flowering plants have: Endodermis (innermost skin): surrounds vascular cylinder Exodermis (outer skin): just below surface Both layers contain a Casparian strip Controls the flow of water and nutrients Plant Gas Exchange Simple Diffusion- passive transport or movement of substances along concentration gradients Osmosis- movement of water across a semi-permeable membrane, along a concentration gradient Active Transport- uses ATP to move substances across a membrane ATP - high energy molecule Small Cells Simple diffusion is adequate Larger Cells Cytoplasmic Streaming Transpiration-water is transpired from leaves creates transport through plant Water moves through xylem Xylem cells are tracheids or vessel members Both are dead at maturity Cohesion-Tension- Theory of Water Transport Transpiration creates negative tension in xylem Tension extends downward from leaves to roots SRJCA. Carranza Page 4 7/25/2015
Hydrogen-bonded water molecules are pulled upward through xylem as continuous columns Replacement water is drawn in through roots Hydrogen bonds hold water molecules together in conducting tubes of xylem Weak bonds still allow water to evaporate through stomata during transpiration Wilting Water regulation maintains turgor Cuticle Translucent coating secreted by epidermal cells Consists of waxes in cutin Allows light to pass through but restricts water loss Stomata Openings across the cuticle and epidermis; allow gases in and out Guard cells on either side of a stoma Turgor pressure in guard cells affects opening and closing of stomata CAM Plants Most plants stomata open during day and photosynthesis proceeds CAM plants are better at water conservation Stomata open at night and carbon dioxide is fixed Next day, stomata remain closed while carbon dioxide is used Nutrient Transport Pressure Flow Theory Transport through phloem driven by pressure (concentration) gradients Phloem Carry transportable organic compounds Conducting tubes are sieve tubes Consist of living sieve-tube members Companion cells lie next to sieve tubes A type of parenchyma Help load organic compounds into sieve tubes Transportable organic compounds Carbohydrates are stored as starches Starches, proteins, and fats are too large or insoluble for transport Cells break them down to smaller molecules for transport Sucrose is main carbohydrate transported SRJCA. Carranza Page 5 7/25/2015