Take- Take-Home Message 12.1 The inability of plants to Plants are multicellular move shapes the way theyorganisms that spend most obtain food, reproduce, of their lives anchored to and protect themselves one place by their roots. from predation. Characteristics evolved that made it possible for plants to succeed on land despite their inability to move. 8
12.2–12.4 The firstplants had neither roots nor seeds.
12.2 Colonizing land brings new opportunities and challenges for plants. 10
The First Land Plants Appeared About 475 Million Years Ago 12
Take-Take-Home Message 12.2 The first land plants were small and had no leaves, roots or flowers and could grow only at the water’s edge. These inconspicuous little plants set the stage for the enormous diversity of terrestrial plants and animals on earth today. 13
12.3 Mosses and other non- non-vascular plants lack vessels for transporting nutrients and water. 14
Take- Take-Home Message 12.3Non-vascular plants—mosses, liverworts, and hornworts— They lack roots and vessels tohave scarcely evolved beyond move water and nutrientsthe stage of the earliest land from the soil into the plant. plants. They reproduce with spores that form when a sperm from a male reproductive structure “swims” through a drop of rainwater to the egg in a female reproductive structure. 20
12.4 The evolution of vascular tissue made large plants possible. 21
Take-Take-Home Message 12.4 Vessels are an effective “circulatory system” to carry water and nutrients up from the soil to a plant’s leaves. The first vascular plants— including the earliest ferns and horsetails—were able to grow much taller than their non-vascular predecessors. 24
12.5–12.7The advent of theseed opened newworlds to plants.
Seeds Are Goodbye Gifts• DNA, RNA, a few proteins• A multicellular embryo and a store of nutrients• Endosperm• Gymnosperms and angiosperms
How are seeds formed? The gametophyte • a life stage that produces haploid gametes Pollen grains and ovules • Pollen produces a pollen tube that grows into the ovule. The external layer of the ovule forms the seed coat. 28
Seed Dispersal Only opportunity most plants have to send their offspring away from home Seeds and seed pods have many ways to do this: • forceful send-off of exploding seed pods • seeds that hitch rides on passing animals • seeds that float in water or almost fly 29
Take- Take-Home Message 12.5 Seeds are the way A seed contains a plants give their multicellular embryo ofoffspring a good start in the plant, plus a store life and get them to of carbohydrate and leave home. nutrients. Seeds are distributed by wind, animals, or water. 30
12.6 With the evolution of theseed, gymnosperms became the dominant plants on Earth. 31
Take- Take-Home Message 12.6 This mode of reproduction offered advantages over the Gymnosperms (pine trees and spores of earlier plants and gavetheir relatives) were the earliest gymnosperms the boost they plants to produce seeds. needed to become the dominant plants of the early and middle Mesozoic era.Gymnosperms depend on wind Conifers protect the developing to carry their pollen—not an seeds in the female cone. efficient method of dispersal. 36
12.7 Conifers include thetallest and longest-living longest- trees. 37
How can trees grow large and live to great ages? Woody plants can be exceptionally strong and resistant to attack by herbivores Heartwood Bark Exuding a sticky pine pitch 39
Take-Take-Home Message 12.7 Conifers are the success stories among gymnosperms, with more species and a larger geographic range than all of their relatives combined. Rigidity, an exterior layer of bark, and the ability to exude sticky pitch protects conifers, helping make it possible for conifers to grow taller and reach older ages than any other plants. 40
12.8–12.10 Flowering plants are the mostdiverse andsuccessful plants.
12.8 Angiosperms are the dominant plants today. 42
Take-Take-Home Message 12.8 Flowering plants appeared in the Cretaceous period, about 100 million years ago, and diversified rapidly to become the dominant plants in the modern world. A flower houses a plant’s reproductive structures, and most flowers have both male and female structures, although some flowers have only male or only female reproductive structures. 44
12.9 A flower is nothing without a pollinator.
Why are flowers so flashy? Trickery and Bribery
Take- Take-Home Message 12.9Angiosperms have found a Flowers are conspicuous way to transfer pollen structures that advertiseefficiently from the anthers their presence with colors,of one flower to the stigma patterns, movements, and of another—let an animal odors. carry it. Using these devices, plants are able to trick or bribe animals into transporting male gametes to female gametes, where fertilization can occur. 49
12.10 Angiosperms improveseeds with double fertilization. An embryo + a substantial, ready- made food source
What advantage does doublefertilization give to angiosperms? Two Important Advantages
Two Advantages of Double Fertilization Initiatesformation of endosperm only when an egg is fertilized Smaller gametes can be produced. • Ensures that seeds are produced quickly
Take-Take-Home Message 12.10 Angiosperms undergo a process called double fertilization. Double fertilization ensures that a plant does not invest energy in forming endosperm for an ovule that has not been fertilized. 55
12.11–12.12 Plants andanimals have a love-hate relationship.
12.11 Fleshy fruits are bribes that flowering plants pay animals to disperse seeds.
How does this system work? Fruits are colorful. Fruits taste good. Fruit is good for animals.
Can seeds still sprout after being eaten by an animal? Test it yourself!
Take-Take-Home Message 12.11 Plants often use the assistance of animals to disperse their fruits (containing seeds), depositing them at a new location where they can grow. Fruits are made up from the ovary and, occasionally some surrounding tissue. 60
12.12 Unable to escape, plants must resist predation in other ways.
Chemical Defenses as Medicines? Medicinal plants Salicin, opium, digitalin, ipecac Bioprospecting
Insect Attack! Volatile chemicals Plants can also warn nearby plants! • Methyl jasmonate (MeJa)
Take- Take-Home Message 12.12 Plants have a wide range ofdefenses against herbivorous Plants respond to insect attack animals: physical defenses by synthesizing chemicals thatsuch as thorns and chemicals, make the plant that is beingwhich have complex effects on eaten less palatable. the physiology of animals. Some plants living in soil that is deficient in nitrogen have switched roles, preying on insects. 66