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Complex Plants: Chapters 22, 23 and 25 22-1 Seed Plants Benefits to plants of living on land are: 1. Abundant Sunlight for Photosynthesis 2. Free movement of carbon dioxide and oxygen Problems encountered by life on land are: 1.Water and nutrients available only from the soil. 2.Evaporation 3.Tissues must be held upright 4.Reproduction must occur without water. Seed plants – designed for life on land Seed plants exhibit numerous adaptations that allow them to survive the difficulties of life on land. They evolved a variety of new adaptations that enabled them to live where ferns and mosses could not. II. Roots, Stems, Leaves A. The three main organs in a plant are roots, stems and leaves. Roots perform three jobs: 1. The absorb water and nutrients. 2. They anchor plants 3. They hold plants upright B. Stems hold a plants leaves up to the sun. C. Leaves are vital to the process of photosynthesis. III. Vascular Tissue Tall plants face a challenge, water must be lifted from roots to leaves and compounds produced in leaves must be sent to the roots. A. Xylem is responsible for carrying water and nutrients up. They have thick cell walls so also provide strength to the woody parts. B. Phloem carries the products of photosynthesis from one part of the plant to another. IV. Reproduction Free From Water The seed plants you see around you are members of the sporophyte generation. Flowers and cones are the reproductive structures where the gametophyte generation of the seed plant develops. Male gametophytes are called pollen grains. Pollen grains are carried to the female gametophyte so no water is required. Seeds protect the zygotes of seed plants. They are surrounded by a seed coat so can wait until conditions are right 23-5 Leaves The leaves of green plants are the world’s oldest solar energy collectors. Leaves are also the world’s most important manufacturers of food. I. Leaf Structure A. Leaves consist of two parts: the blade and the petiole. B. Blades are adapted to the specific environments in which the live. Adaptations range from simple to compound. Leaves contain specialized tissues such as: 1. Epidermal Cells 2. Inner layers of parenchyma cells 3. Vascular tissues II. Epidermis: Controlling Water Loss A. Epidermal cells are tough and do not contain chloroplasts. Together with the Cuticle, this layer protects delicate leaf tissues by slowing down the loss of water through evaporation. B. BUT, plants still need to “breathe” just as we do. They need to: 1. Exchange CO2 for O2 during photosynthesis. 2. Exchange O2 for CO2 in order to function (like us). C. Leaves must stay moist to carry out these gas exchanges. Seed plants solve this problem by balancing their need for gas exchange with water conservation. They use small openings called stomata. Stomata are generally located on the undersides of leaves. D. The specialized cells on either side of a stoma are called guard cells. When water pressure is high, the cells are forced into a curved shape, opening the stoma. When water pressure is low, the cells spring together and close the stoma. E. Each type of plant has guard cells that balance water loss against the need for CO2. III. Vascular tissues: The Veins of a leaf A. Vascular tissue in leaves is directly connected to the vascular tissues of stems. In monocot leaves, veins run parallel. In dicot leaves, they have different patterns. IV. Mesophyll Tissue: The food factory of the leaf A. Most leaf tissue is called mesophyll. This is separated into two layers: 1. Palisade layer 2. spongy mesophyll B. The surfaces of the mesophyll layer are kept moist so that gases can enter and leave the cells easily. A substantial amount of water is still lost to the outside through evaporation. 25-1 Cones & Flowers as Reproductive Organs I. Introduction A. Sexual Reproductive Organs 1. Gymnosperms have cones 2. Angiosperms have flowers B. Review: Plant Life Cycles 1. Two generations a) diploid (2n) sporophyte b) haploid (1n) gametophyte which produces male and female gametes 2. Fusion of gametes forms a zygote that grows into the next generation, the sporophyte C. Sizes in Seed Plants 1. Dominant generation (the one that is large & obvious) = sporophyte 2. Gametophyte is hidden in the cones/flowers D. Advantages of Cones/Flowers 1. Enable seed plants to reproduce without standing water 2. An adaptation that helps them survive: the dry conditions of life on land 22-2 Evolution of Seed Plants I. Gymnosperms Gymno means naked, sperm means seed. There are three classes of gymnosperms: 1.Cycads 2.Ginkgoes 3.Conifers Reproductive structures are called cones. Male cones produce male gametophytes called pollen. Female cones produce female gametophytes called eggs Cycads are palm like plants. They only grow in tropical and subtropical places. Ginkgoes are represented by one species, Ginkgo biloba. It is a living fossil. II. Conifers Are the most abundant gymnosperms today. A.The leaves are called needles. Conifers appear to be “evergreen” because older needles drop off but are gradually replaced. B. Male cones, or pollen cones, and female cones, or seed cones, contain the very small gametophytes. In the Spring, pollen cones release millions of dustlike pollen grains to be carried by the wind. These land on seed cones and fertilize them. The zygotes grow into seeds on the scales of the seed cones. from ….. 25-1 Cones & Flowers as Reproductive Organs II. Life Cycle of Gymnosperms A. Pine Tree Example 1. Tree grew from a zygote contained in a seed 2. It is the diploid (2n) sporophyte generation 3. Seedling matures, makes two types of cones: a) Male: contain microsporangia that produce pollen (male gametophyte) b) Female: contain megasporangia that produce ovules (female gametophyte) B. Process 1. Pollen grains (from male cones) carried by wind 2. Female cones make a sticky secretion that traps pollen 3. Grain splits open, grows a pollen tube, which contains sperm 4. Pollen tube grows into the ovule, located in female cone 5. Sperm break out of the tube and fertilize egg in the ovule 6. Zygote grows into an embryo 7. Embryo is encased in a package; now called a seed a) seed = embryo plant + food supply for growth from….. 22-2 Evolution of Seed Plants III.Angiosperms A. These are flowering plants. They reproduce sexually through their flowers in a process called pollination. Angiosperm seeds are contained within a protective wall that develops into a fruit. B. Angiosperms are the most widespread of all land plants. They range from frigid mountains to blazing deserts. Some even live under water. C.There are two main subclasses: Subclass Number of cotyledons (seed leaves) Leaves Monocots One. Dicots Two. Veins are parallel. Flower Parts in threes or multiples. Scattered throughout. Stems do not thicken from year to year. Corn, wheat, palms, orchids, lilies. Veins are branching. Parts in fours or fives or multiples. Arranged in a ring. Xylem/Phloem Stems Examples Stems grow thicker every year. Roses, tomatoes, oaks, daisies, sunflowers. C.There are two main subclasses: from ….. 25-1 Cones & Flowers as Reproductive Organs III. Structure of a Flower A. Typical Flower 1. produces both male and female gametes B. Other ‘strategies’: 1. specialized male and female flowers on same plant (e.g. corn) 2. male and female flowers on separate plants (e.g. willow) C. Flower Parts 1. Are specialized leaves 2. Arranged in circles 3. Four kinds NAME LOCATION DESCRIPTION FUNCTION GROUP NAME Sepals Outermost Green Leaflike Protect flower while developing Calyx Petals Just inside the sepals Often brightly coloured Attract pollinators Corolla Stamens Just inside the petals Long thin filament supporting the anther on the top Makes, releases male gametophyte (pollen) Carpels Center Ovary, the base Style: Stalk Stigma: where the pollen lands; often sticky and rough surfaced Makes, Pistil houses, female gametophyte (ovules) IV. Pollination A. Definition: the transfer of pollen from anther to stigma B. Two types: 1. Self-pollination: when pollen comes from the same flower 2. Cross pollination: when pollen comes from a different plant C. Most plants cross-pollinate, which increases variation in their offspring Animation VIII. Fertilization A. Process 1. Pollen grain lands on stigma of same species 2. Pollen tube grows down the style, following a chemical trail 3. Tube reaches ovary and enters the ovule 4. Inside pollen tube are two sperm nuclei (Note: no tails needed; don’t need propel themselves!) a) one sperm fuses with egg to form the zygote b) other sperm fuses with spare female nuclei to form endosperm (3N) 5. Endosperm = food source for baby plant Click for animation B. 1. Ecological Importance Endosperm is rich in important nutrients 2. Examples: grass endosperm: corn, wheat, rice C. After fertilization 1. Outer parts of ovule toughen into seed coat 2. Ovary wall thickens, merges with other parts to become fruit 3. Plants may use bright colours and sweet tastes to make fruit attractive to animals Fruit Formation IX. Formation of Seeds A. The evolution of seeds was: a major factor in the success of angiosperms on land B. Seeds assist embryos by providing: 1. nourishment 2. protection C. Structure 1. Cotyledon= seed leaf; they contain stored food that is used when seed germinates a) monocots (e.g. corn) have one b) dicots (e.g. beans) have two 2. Seed coats: Function: to protect seed from a) environment: (e.g. dryness, salt water) b) animal teeth, digestive chemicals D. When animals eat seeds: 1. They germinate after their trip through the digestive tract 2. Animal waste acts as fertilizer 3. Usually deposited some distance away from where fruit was eaten 4. Reduces competition between adult (plant) and offspring (seeds) 25-2 I. Seed Development Germination A. Process: 1. Water absorption causes endosperm & cotyledons to swell 2. seed coat cracks open 3. Radicle emerges; grows into primary root 4. Growing shoot pushes up through soil III. Seed Dormancy A. Definiton: A period during which the embryo is alive but not growing B. Purposes: 1. A long time required for dispersal a) e.g. coconut 2. To wait until environmental conditions will support plant growth a) e.g. plants from temperate regions; dormant in winter, germinate in spring 22-3 Coevolution of Flowering Plants and Animals Coevolution: the process by which two organisms evolve structures and behaviours in response to changes in each other over time. The first flowering plants evolved at about the same time as the earliest mammals, shortly after birds and a while after the earliest insects. Evolution of angiosperms with modern insects, birds and mammals is very important. I. Flower Pollination A. Wind: small, plain simple flowers with little or no fragrance. B. Birds, insects, mammals: carry pollen from one plant to another. 1. Plants provide food in the form of pollen or nectar. 2. Animals provide direct transportation between male and female gametophyte. Attractants for Pollinators Pollinator Flower Bee Special ultraviolet color. Moth Fragrance. Fly Bad odor. Bird Bright red and orange colours. Fly on corpse flower II. Seed Dispersal The process of distributing seeds away from parent plants. There are 2 reasons for dispersal: 1. Prevent competition with parent plans for resources. 2. Colonize new environments Dispers Description al Method Wind Blown to different places. Pressure Fruit ‘explodes’, spreading seeds. Barbed or hooked fruits Attach to animal fur or feathers and are carried to new habitat. Tasty Fruit Digested by animals, carried to new habitat, seeds ‘deposited’ with fertilizer.