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Unit 7: Plants. Mrs. Korsun. Chapter 20: Plant Diversity. 20.1: Origins of Plant Life. Land plants evolved from green algae Plants are multicellular eukaryotes, most of which produce their own food through photosynthesis and have adapted to life on land.
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Unit 7: Plants Mrs. Korsun
20.1: Origins of Plant Life • Land plants evolved from green algae • Plants are multicellular eukaryotes, most of which produce their own food through photosynthesis and have adapted to life on land. • Both green algae and plants have the same chlorophyll, which gives them green coloring • Both use starch as a storage product • Both have cell walls made of cellulose • Algae reproduction involves sperm traveling to fertilize the egg (in water)
Plants have adaptations that allow them to live on land. • Land plants have evolved adaptations that allow them to: • retain moisture • transport water and other resources • grow upright • reproduce without free-standing water
Retaining Moisture • Plants will die if they dry out from exposure to air and sunlight. • The surfaces of plants are covered with cuticles – waxy, waterproof layer that helps hold in moisture. • Tiny holes in the cuticles, called stomata, allow for gas exchange between the plant and the atmosphere.
Transporting Resources • Plants get sunlight and carbon dioxide from the air and water and nutrients from soil. • The structure that moves these nutrients is the plant’s vascular system – a collection of specialized tissues that bring water and mineral nutrients up from the roots and disperse sugars down from the leaves. • Vascular systems allow plant to grow!
Growing Upright • Plants need structure to support their weight and provide space for vascular tissues. • Lignin is a material that hardens the cell walls of vascular tissues, providing support for plants. • Also provides strength for wood and provides stiffness to plant stems
Reproducing on Land • In all plants, eggs are fertilized within the tissue of the parent plant • Pollens and seeds are adaptations that allow seed plants to reproduce completely free of water. • A pollen grain is a two-celled structure that contains a cell that will divide to for sperm. • A seed is a storage device for a plant embryo.
20.2: Classification of Plants • Mosses are seedless nonvascular plants • Mosses attach themselves to soil, rocks, or tree trunks
Seed Plants • Reproduce without free-standing water by using pollen • Pollination occurs when pollen meets female reproductive parts of the same plant species.
Seed Plants • A gymnosperm is a seed plant whose seeds are not enclosed in fruit. • Most are cone-bearing and evergreen, like pine trees. • A woody cone is the reproduction structure of most gymnosperms. • An angiosperm is a seed plant that has seeds enclosed in some type of fruit.
Flowering Plants • Angiosperms are flowering plants • A flower is the reproductive structure or flowering plants. They protect a plant’s gametes and fertilized eggs. • A fruit is the mature ovary of a flower.
Wood or Herbaceous • Some flowering plants develop woody stems • Wood is a fibrous material made up of dead cells that are part of the vascular system of some plants. • Have high concentrations of cellulose and lignin • Herbaceous plants do not produce wood • Cucumbers, cacti, marigolds
Botany and Pharmacology • Plants are used to fill the basic needs of our species: • Food, shelter, clothing, and medicine. • Botany is the study of plants. • The study of drugs and their effects on the body is called pharmacology. • Many of the drugs used today are derived from plants. • i.e. aloe vera gel for sunburn, alkaloids (potent plant chemicals that contain nitrogen) for diseases and cancers
21.1: Plant Cells and Tissues • Plant tissues are made up of three basic cell types. • Parenchyma cell: most common and found throughout the plant • Stores starch, oils, and water for the plant • Collenchyma cell: provides support and allows plant to grow • Scierenchyma cell: strongest cell type and two cell walls made of lignin
Plant organs are made of three tissue systems. • Dermal tissue: covers the outside of a plant and provides protection • Think about the epidermis (skin) on your body! • Ground tissue: makes up the inside of the plant; surrounded by dermal tissue • Provides support and stores materials in roots and stems • Consists of ALL 3 tissue types • Vascular tissue: transports water, minerals nutrients, and organic compounds to all parts of the plant; surrounded by ground tissue
Vascular Tissue System • A plant’s vascular system is make up of two networks of hollow tubes • Similar to our veins and arteries • Xylem is the vascular tissue that carries water and dissolved mineral nutrients up from the roots to the rest of the plant. • Phloem is the vascular tissue that carries the products of photosynthesis through the plant.
21.1 The Vascular System • Water and dissolved minerals move up from the roots to the rest of the plant through xylem. • The cohesion-tension theory proposes that the physical properties of water allow the rise of water through a plant. • Based on strong attraction of water molecules to one another and to other surfaces.
Transpiration • For most plants, capillary action is not enough force to lift water to the top branches. • Upward force is also provided by the evaporation of water from leaves. • The loss of water vapor from plants is transpiration. • As leaves transpire, the outward flow of water lowers the pressure in the leaf xylem, creating a vacuum that pulls water upward.
Phloem and pressure-flow model • Phloem carries plant nutrients, including minerals and sugars, throughout the plant. Phloem moves the products of photosynthesis out of the leaves to stems and roots. • The pressure-flow model is a well-supported theory that explains how food, or sap, moves through a plant.
21.3: Roots and Stems • Roots anchor plants and absorb mineral nutrients from soil. • Stems support plants, transport materials, and provide storage. • Primary growth is growth that increase a plant’s length – makes stems grow taller or roots grow longer • Secondary growth adds to the width in the stems and roots of woody plants.
Tree Rings • Secondary growth is responsible for the formation of tree rings. • During Spring, when water is plentiful, xylem cells cause light thick rings. • During Winter, when water is limited, xylem cells cause thin dark rings. • The age of a tree can be determined by counting the annual rings. • Each ring, dark OR light, represents one year of tree growth.
21.4: Leaves • Most leaves share some similar structures. • The blade is broad and flat, and it collects the sunlight for the plant. • The blade connects to the stem by a think stalk called the petiole. • Between the two dermal layers of a leaf is a tissue called mesophyll – vascular tissues of xylem and phloem make up the veins that run throughout the mesophyll. • Where most of photosynthesis take place.
Stomata and Guard Cells • A pair of guard cells surround each stoma, and can open and close by changing shape. • During the day, the stomata of most plants are open, allowing carbon dioxide in for photosynthesis to enter. • Potassium ions from neighboring cells accumulate in the guard cells – a high concentration of potassium causes water to flow into the guard cells as well. • Stomata open = water evaporates • Stomata closed = guard cells deflate due to transpiration
22.1: Plant Life Cycle • Plant life cycles alternate between producing spores and gametes. • The plant life cycle in which the plant alternates between haploid (1n) and diploid (2n) phases is called alternation of generations. • The diploid phase o f a plant life cycle begins with a fertilized egg, called a zygote. A zygote divides by mitosis and grows into a mature sporophyte, or spore-producing plant. • A spore makes the beginning of the haploid phase of the plant life cycle. A spore divides by mitosis and grows into a mature gametophyte, or gamete-producing plant.
22.2: Reproduction in Flowering Plants • Flowers contain reproductive organs protected by specialized leaves. • The outermost layer of a flower is made up of sepals – modified leaves that protect the developing flower. • The layer inside the sepals is made up of petals, which are modified leaves.
Some species have flowers with only male or only female structures, but the flowers of most species have BOTH. • A stamen is the male structure of a flower. • Each stamen has a stalk called a filament that support an anther, which produces pollen grains (male gametophytes) • The innermost layer of a flower is made up of the female structure, called a carpel. • Most flowers have several carpals fused together, forming a pistil. • Female gametophytes are produced inside the ovary, which is found at the base of the flower.
Flowering plants can be pollinated by wind or animals. • Pollination is a necessary step of sexual reproduction in flowering plants. • Pollination by animals is more reliable than by wind. • Insects, birds, and animals that visit flowers collect pollen as a food source. When the animal searches for food in another flower, pollen from the first flower brushes against the stigma of another flower.
Fertilization takes place within the flower. • Production of male gametophytes – produce pollen grains – produce 4 spores (meiosis) • Production of female gametophytes – form in flower’s ovary – produce 4 spores (meiosis) • Double Fertilization • The sperm cell that does NOT fertilize the egg has a triploid (3n) nucleus and becomes the endosperm, a food supply for the developing plant embryo. • The process in which one sperm fertilizes an egg and the other forms a triploid cell is called double fertilization. • Only happens in flowering plants!
22.3: Seed Dispersal and Germination • Animals, wind, and water can spread seeds. • Recall that when a seed develops, the surrounding ovary grows into a fruit. • Animals eat the fruit, and use their ‘waste’ as fertilizer (with the indigestive seed inside), to make new seed plants.
Seeds begin to grown when environmental conditions are favorable. • When a seed is dormant, or under dormancy, the embryo stops growing. • This happens if the temperature, moisture, oxygen, and/or light levels are not favorable by the seed. • Many types of seeds begin to grow when there are certain changes in temperature, moisture, or light levels. • During germination, the embryo breaks out of the seed coat and begins to grow into a seedling. • Embryo takes up water • Water causes the seed to swell and crack • Embryonic root breaks through the crack as it grows • Young plant is free of seed coats and grows!
22.4: Asexual Reproduction • Humans can produce plants with desirable traits using vegetative structures. • Example: seedless fruit • Plants can that can grow a new individual from a fragment of a stem, leaf, or root are reproducing by regeneration. • Most plants have a way of cloning themselves through asexual reproduction.
22.5: Plant Hormones and Responses • Plant hormones regulate plant functions. • A hormone is a chemical messenger produced in one part of an organism that stimulates or suppresses the activity of cells in another part. • In humans, hormones control functions vital to survival and reproduction. • In plants, when a hormone meets the right receptor, it triggers a response.
Types of plant hormones and their functions: • Gibberellins – produce increase in size in plants • Ethylene – causes ripening in fruits • Cytokinins – stimulate cytokinesis, the final stage of cell division • Auxins – lengthening of plant cells
Plants can respond to light, touch, gravity, and seasonal change. • Phototrophism – tendency of plant to grow towards light (light) • Thigmotrophism – plants response to touch (touch) • Gravitrophism – up-and-down growth of plant due to Earth’s gravitational pull (gravity) • Photoperiodism – plants response to changing of days and night throughout the year (season changes)
