Plant Form and Function

Plant Form and Function: How Do Plants Live in the World? What Important Events Define the History of Plant Life ? • Photosynthesis changed the world • Eukaryotic cells and multicellularity enabled plants to diversify • Plants moved from water to land • Vascular plants dominate the terrain Important Events in Plant Evolution Photosynthesis Changed the World • Plants use chlorophyll to capture the energy of sunlight for use in photosynthesis • Oxygen is the byproduct and has accumulated over the past 2.5 billion years. Evolution of Eukaryotic Cells • Occurred before plants became multicellular. • Evolution of eukaryotic cells due to endosymbiosis. – Evidence to support the theory: Mitochondria and chloroplasts. – Many examples of living prokaryotes that share features of mitochondria and chloroplasts found in eukaryotes. Evolution of Multicellular Cells • Advantages of multicellularity – Cellular organisms have opportunity for cellular specialization. – Decreased vulnerability to changes in temperature, humidity, and nutrient availability that comes with increased size Origin of Multicellularity Double-Click on the movie still for the movie to play in full. Plants Moved From Water To Land • Several evolutionary adaptations made this possible: – Multicellularity. – To prevent water loss • A waxy cuticle. • An epidermal layer. • Structures that protect and enclose the delicate gametes and embryo. Plants Moved From Water To Land • Several evolutionary adaptations made this possible: – Alternation of Generations • Their life cycle is divided into two stages Plants Moved From Water To Land • Life cycle of vascular plants: – Have vascular tissues for moving food and water. – Includes evergreens and flowering plants. Plants Moved From Water To Land • Another evolutionary adaptation that occurred in most vascular plants is – Seed formation – Has helped contribute to the success of vascular plants Vascular Plants Dominate the Terrain Vascular Plants Dominate the Terrain • Most successful vascular plant are angiosperms. – Most diverse – Defining characteristic is the flower. What Do Plants Need and How Do They Get It? • Plant form and function is best understood in terms of their needs: – Light – Gases – Water – Nitrogen and other nutrients Plants Need Light • Needed for photosynthesis. – Asymmetric branch pattern allows for greatest exposure to light. – Leaf • Greatest amount of photosynthesis. • Allow for maximum light absorption • Can do solar tracking Plants Need Light • Leaf interior promotes light absorption – Palisade layer – Spongy mesophyll Plants Need Gases • Plants need carbon dioxide (CO2) – Raw material for making sugar. • Stomates allow CO2 to enter cells. – Water can be lost through stomates Stomata Double-Click on the movie still for the movie to play in full. Plants Need Gases • C4 plants – Can trap CO2 on hot, dry days – Trap CO2 in palisade or spongy cells – Only about 3% of plants Plants Need Gases • CAM plants – Desert dwelling plants • Stomates must be closed all day long to prevent water loss. – Stomates only open at night • Carbon dioxide enters and is stored in 4-carbon molecule . – CO2 molecule is released during the day in order for photosynthesis to occur. Plants Need Water • Roots – Anchor plant to ground and absorb moisture and minerals – Root structure specially designed for absorption Plants Need Water – Root hairs maximize absorption. • Found on root surface • Delicate extensions dramatically increase surface area Plants Need Water – Arrangement of cells in the root • Water is absorbed at epidermal layer and moves from cell to cell through the cortex by diffusion Plants Need Nitrogen • Nitrogen-fixation – Process in which certain microbes fix atmospheric nitrogen into organic compounds. – Some plants have a symbiotic relationship with these microbes. Plants Need Other Nutrients • Plants obtain minerals through their roots. • When water enters the plant roots, so do minerals. – Move up the body of the plant to the leaves and stems. Plants Need Nitrogen and Other Nutrients How Do Higher Plants Transport Substances and Support Themselves? • All large multicellular organisms must have some way of transporting substances through their bodies, including plants. • In some plants, the same tissues are responsible for: – Moving water – Providing support Translocation • The movement of fluids within the plant body • Phloem – Living vascular tissue near the periphery of the stem – Made of columns of sieve tubes – Sap (sugar-rich fluids made by photosynthesis) moves through the phloem Transpiration • Evaporation of water through the stomates of plant leaves. – Creates a negative pressure • Allows water to move upward plant from roots • Also prevents plants from overheating. Water and Minerals Move Through the Xylem • Xylem – Vascular tissue usually found nearer the core, or center, of the stem. – Composed primarily of dead cells that form a hollow interconnected network of tubules. Plants Need Mechanical Support • Reaching for the sun means growing upward – Opposing gravity. • In soft-stemmed plants, mechanical support provided by turgor pressure. • In woody plants, mechanical support provide by xylem. – Reinforced with lignin. How Do Plants Grow? • Plant growth is indeterminate. – Occurs at the meristem • Cells divide by mitosis within meristem tissue. • Found at the – tip of shoots and roots – In periphery of the woody trees and shrubs Three Main Tissue Types in Plants How Do Plants Grow? • Apical meristem – Found at tip of shoots and roots. – Responsible for lengthwise growth. • Called primary growth. How Do Plants Grow? • Vascular cambium – Meristematic tissue that produces new bundles of xylem and phloem. – Increases the girth of the stem or roots. • Called secondary growth. How Do Plants Grow? • Cork cambium – Layer of meristem produced from cells of the ground tissues. – Produces a new layer of cells called cork. • Also contributes to secondary growth. Plants Have Hormones • Phototrophism – Growing plant will bend toward the light. – Due to the presence of auxins. • Class of molecules. Plants Have Hormones • Auxins – Stimulate cell elongation. – Play a role in causing the growing plant root to bend down. – Involved in fruit development. Plants Have Hormones • Gibberellins – Class of 100 similar chemical compounds. – Produced at tips of roots and stems. • Stimulates plant growth. – Most concentrated in seeds. • Facilitates growth of embryo and germination. Plants Have Hormones • Abscisic Acid (ABA) – Hormones that slow growth • Needed on cold days or excessively hot days. • Released when water is scarce. • Plant growth is a balance between ABA and gibberellins. Plants Have Hormones • Ethylene – Causes fruit ripening • As fruit ages, it releases more ethylene – Activates enzymes that digest the cell walls of plants. • Enables plant to respond to environment by by aging or planned cell death Plants Reproduce Sexually • Zygotes are formed by the fusion of male and female gametes • In angiosperms, flowers are the sex organs that produce gametes. Sexual Reproduction in Flowering Plants • Male reproductive organs = stamens – Have anthers – Contain cells that give rise to pollen Sexual Reproduction in Flowering Plants • Female sex organ = carpel – First houses the ovule, – Then the female gametophyte – And finally, the embryo Fertilization in Flowering Plants Fertilization in Flowering Plants Pollination • How does pollen get from the male anther to the female ovary? – Wind – Water – Animal pollinators • Flowers attract animal pollinators. Seeds and Fruits • After fertilization, ovule develops into a seed. • Seed remains dormant until conditions for growth are appropriate. • Ovary that surrounds the seed, or some other parental structure, may develop into the fruit.