Chapter 32 Plants I 25.ppt PDF

Chapter 32 The Evolution of Plants 1  Adapting to Terrestrial Living Plants are complex multicellular organisms that are autotrophs – they feed themselves by photosynthesis – they occur almost exclusively on land – they are the dominant organisms on the...

Chapter 32 The Evolution of Plants 1  Adapting to Terrestrial Living Plants are complex multicellular organisms that are autotrophs – they feed themselves by photosynthesis – they occur almost exclusively on land – they are the dominant organisms on the surface of the earth – there are nearly 300,000 species of plants today 2  Adapting to Terrestrial Living The green algae that were probably the ancestors of today’s plants are aquatic organisms that are not well adapted to living on land Before their descendants could live on land, they had to overcome many environmental challenges – how to absorb minerals? – how to conserve water? – how to reproduce on land? 3  Adapting to Terrestrial Living One of the key challenges of living on land is to avoid drying out – plants have a watertight outer covering called a cuticle, which has a waxy consistency – water enters plants only through the roots while the cuticle prevents water loss to the air – specialized pores called stomata (singular, stoma) allow passage for oxygen, carbon dioxide andwater through the cuticle. 4  Figure 32.2 A stoma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Leaf Cross- interior section of leaf Epidermis Cuticle Stoma Guard cells 5 (bottom): © Terry Ashley/Tom Stack & Associates  Adapting to Terrestrial Living Reproducing sexually on land presented unique challenges The first plants needed a film of water for a sperm to swim to an egg and fertilize it Later, pollen evolved, providing a means of transferring gametes without drying out 6  Adapting to Terrestrial Living Alternation of generations, in which a diploid generation alternates with a haploid one – the diploid generation is called the sporophyte – the haploid generation is called the gametophyte 7 Figure 32.3 Generalized plant life cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Haploid Gametophyte (n) 1 5 Mitosis Spore Sperm n n Egg n n Spores 2 Meiosis Gamete fusion Spore mother 2n Zygote 4 2n cell 2n Embryo Sporangia Sporophyte 3 (2n) Diploid 8  Plant Evolution Four key evolutionary advances occurred in the evolution of the plant kingdom – Alternation of generations the sporophyte became the dominant generation in all but the earliest plants – Vascular tissue transports water and nutrients through the plant body and provides structural support – Seeds seeds provide nutrients and protection for the plant embryo until it encounters favorable growing conditions – Flowers and fruits improved the chances of successful mating in sedentary organisms and facilitated dispersal of their seeds 9 Figure 32.4 The evolution of plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Angiosperms Gymnosperms Nonvascular plants Seedless vascular plants 10  Nonvascular Plants Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The first successful land plants had no vascular system – limited size – only two phyla of living plants completely lack a vascular system liverworts (phylum Hepaticophyta) hornworts (phylum Anthocerophyta) – a third phylum of plants has a simple conducting tissue system of soft strands mosses (phylum Bryophyta) 11  Moss Life Cycle Development of mature sporophyte (still attached to Zygote gametophyte) Diploid Stage Fertilization Meiosis Haploid Stage Spores released male gametophyte tip Sperm Male gametophyte female gametophyte Female gametophyte Egg tip  The Evolution of Vascular Tissue Seven phyla of plants have vascular systems and are called vascular plants Vascular tissues are specialized cylindrical or elongated cells that form a network throughout a plant There are two types of vascular tissue – xylem conducts water and minerals from the roots upward to the rest of the plant – Phloem conducts carbohydrates throughout the plant 13  The Evolution of Vascular Tissue The earliest vascular plants grew by cell division at the tips of the stem and roots – this primary growth made plants longer or taller Later vascular plants developed a new pattern of growth in which a ring of cells could divide around the periphery of the plant – this secondary growth made it possible for a plant stem to increase in diameter – the product of secondary growth is wood 14  Seedless Vascular Plants There are two phyla of living seedless vascular plants – ferns (phylum Pterophyta) in ferns, the sporophyte generation is much larger and more complex than the gametophyte the leaves on the sporophyte are called fronds this phylum also includes the whisk ferns and horsetails – club mosses (phylum Lycophyta) 15 Seedless vascular plants 16  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Archegonium Mitosis Antheridium Egg Rhizoids Gametophyte Spore Sperm n MEIOSIS FERTILIZATION Figure 32.9 Mature 2n sporangium Mature Fern life cycle frond Embryo Sorus (cluster Leaf of young of sporangia) sporophyte Gametophyte Adult Rhizome sporophyte 17  Evolution of Seed Plants The seed is a crucial adaptation to life on land because it protects the embryonic plant when it is at its most vulnerable stage Seed plants produce two kinds of gametophytes, male and female, which develop completely within the sporophyte – male gametophytes are called pollen grains they arise from microspores – a female gametophyte contains the egg within an ovule it develops from a megaspore 18  Evolution of Seed Plants In seed plants, free water is not required in the fertilization process – pollination by insects, wind, or other agents transfers pollen to an ovule – the pollen grain then cracks open and sprouts as a pollen tube, bringing sperm cells directly to the egg 19  Evolution of Seed Plants All seed plants are derived from a single common ancestor – gymnosperms in these seed plants, the ovules are not completely enclosed by sporophyte tissue at the time of pollination – angiosperms in these seed plants, the most recently evolved of all plant phyla, the ovules are completely enclosed in sporophyte tissue called the carpel at the time of pollination 20  Evolution of Seed Plants A seed has three visible parts: 1. a sporophyte embryo 2. endosperm, a source of food for the developing embryo in some seeds, the endosperm is used up by the embryo and stored as food in structures called cotyledons 3. a drought-resistant protective cover 21 Figure 32.11 Basic structure of seeds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endosperm Embryo Cotyledon (a) Corn Embryo Cotyledon (b) Bean 22  Evolution of Seed Plants Seeds improved plants’ ability to adapt to living on land in the following respects: – dispersal facilitates the migration and dispersal into new habitats – dormancy permits plants to postpone development until conditions are favorable – germination controls when the plant develops so that it can be synchronized with critical aspects of the plant’s habitat – nourishment provisions the young plant during the critical period just after germination 23  Gymnosperms Four phyla constitute the Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nonvascular plants Seedless vascular Gymnosperms gymnosperms Angiosperms plants – conifers (phylum Coniferophyta) trees that produce their seeds in cones and most have needlelike leaves – cycads (phylum Cycadophyta) have short stems and palmlike leaves – gnetophytes (phylum Gnetophyta) contains only three kinds of very unusual plants – ginkgo (Ginkgophyta) only one living species, the maidenhair tree, which has fan-shaped leaves 24 Figure 32.13 Gymnosperms 25  Gymnosperms The life cycle of conifers is typical of gymnosperms – conifers form two types of cones seed cones contain the female gametophytes pollen cones contain the pollen grains (male gametophytes) – pollen grains are dispersed by wind to the seed cones – the fertilized seed cones produce seeds, which are also wind-dispersed – the germinated seed will grow into a new sporophyte plant 26  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mature seed 5 cone (2nd year) Egg cell Megaspore 4 Pollen Mitosis Pollination tube 2 FERTILIZATION Pollen (15 months after Nutritive pollination) tissue Mitosis n Microspores Embryo Figure 32.14 EIOS IS 2n Seed, showing embryo M Life cycle of a Pine conifer 1 Pollen-bearing cone seed 6 Scale Seedling 3 7 Ovulate (seed-bearing) 27 Sporophyte cone  Rise of the Angiosperms Ninety percent of all living plant species are angiosperms (phylum Anthophyta) – angiosperms use flowers to induce insects and other animals to carry pollen for them 28  The basic structure of a flower consists of four concentric circles, or whorls, connected to a base called a receptacle Stamen Stigma Anther Style Carpel Petal Ovary Sepal Receptacle (right). 674: © Ed Pembleton 29 Figure 32.16 Red flowers are pollinated by hummingbirds 30  Double Fertilization Angiosperms produce a special, highly nutritious tissue called endosperm within their seeds When a flower is pollinated, – a pollen tube grows down from the pollen grain on the stigma – the pollen grain contains two haploid sperm the first sperm fuses with the egg at the base of the ovary the second sperm fuses with polar nuclei to form a triploid endosperm cell, which divides faster than the zygote and gives rise to the endosperm tissue – the process of fertilization to produce both a zygote and endosperm is called double fertilization 31  Figure 32.17 Life cycle of an angiosperm Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2 Pollen sac MEIOSIS Pollen grains (n) Microspore mother cell (2n) Pollen grain Microspores (n) Anther Stigma Megaspore mother cell (2n) Pollen Sperm Ovary Eight-nucleate embryo sac (n) tube cell cells 1 Ovule Tube cell MEIOSIS nucleus Style Carpel 4 3 Adult sporophyte (2n) Pollen with flowers Formation of tube pollen tube (n) Embryo Seed coat Polar nuclei Endosperm (3n) Egg 6 Seed (2n) Young DOUBLE 5 32 embryo (2n) FERTILIZATION  Double Fertilization In some angiosperms, the endosperm is fully used up by the time the seed is mature – food reserves are stored by the embryo in swollen, fleshly leaves called cotyledons, or seed leaves dicots have two cotyledons monocots have one cotyledon 33  Figure 32.18 Dicots and monocots Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DICOTS Flower parts Two cotyledons Netlike (reticulate) veins in fours and fives MONOCOTS Flower parts in threes Endosperm Parallel One veins cotyledon 34  Fruits A mature ovary that surrounds the ovule becomes all or part of the fruit – angiosperms use fruits to induce animals to disperse the seeds although eaten by animals, the seeds within the fruit are resistant to chewing and digestion they pass out of the animal with the feces, ready to germinate at a new location far from the plant – some fruits are dispersed by water or wind 35