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 by-product 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.
