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14.1 Adapting to Terrestrial Living
~ 288,700 species of plants are now in existence These are terrestrial However, green algae, the likely ancestors of plants, are aquatic and not well adapted to living on land Three challenges had to be overcome 1. Mineral absorption 2. Water conservation 3. Reproduction on land
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Mineral Absorption Plants require relatively large amounts of six inorganic minerals Nitrogen, potassium, calcium, phosphorus, magnesium, sulfur Plants absorb these materials through their roots The first plants developed symbiotic associations with fungi These mycorrhizae enabled plants to extract minerals from rocky soil
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Regulate opening and closing of the stoma
Water Conservation To avoid drying out, plants have a watertight outer covering, termed the cuticle Fig. 14.2 Stomata (singular, stoma) are pores in the cuticle that allow gas and vapor exchange Regulate opening and closing of the stoma
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Reproduction on Land Spores developed as a means to protect gametes from drying out on land In a plant life cycle, there is alternation of generations Diploid with haploid Fig Generalized plant life cycle
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Gametophyte barely visible
The diploid generation is called the sporophyte The haploid generation is called the gametophyte As plants evolved, the sporophyte tissue dominated Fig Two types of gametophytes Moss Pine Primitive plant Vascular plant Mostly gametophyte Gametophyte barely visible
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14.2 Plant Evolution Four key evolutionary innovations serve to trace the evolution of the plant kingdom 1. Alternation of generations Plants developed a more dominant diploid phase of the life cycle 2. Vascular tissue Transports water and nutrients throughout the plant body Thus plants were able to grow larger and in drier conditions
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14.2 Plant Evolution Four key evolutionary innovations serve to trace the evolution of the plant kingdom 3. Seeds Protected the embryo, thus allowing plants to dominate their terrestrial environments 4. Flowers and fruits Flowers protected the egg and improved the odds of its fertilization Fruits surrounded the seeds and aided in their dispersal
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Fig. 14.5 The evolution of plants
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The simplest of all living plants
14.3 Nonvascular Plants Only two phyla of living plants lack a vascular system The simplest of all living plants Liverworts (Phylum Hepaticophyta) Hornworts (Phylum Anthocerophyta) Mosses (Phylum Bryophyta) were the first plants to evolve strands of specialized conduction cells The conducting cells do not have specialized wall thickenings Thus, a primitive vascular system, at the most
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Fig. 14.6 The life cycle of a moss
Hair-cup moss, Polytrichum
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14.4 The Evolution of Vascular Tissue
The first vascular plant appeared approximately 430 million years ago (mya) Fig The vascular system of a leaf Early plants became successful colonizers of land through the development of vascular tissue Efficient water- and food-conducting systems
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Early vascular plants exhibited primary growth
Growth by cell division at the tips of the stem and roots About 380 mya, vascular plants developed a new pattern of growth, secondary growth New cells are produced in regions around the plant’s periphery Thus, plants could become thick-trunked and taller Note The product of plant secondary growth is wood
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14.5 Seedless Vascular Plants
Two phyla of modern-day vascular plants lack seeds Ferns (Phylum Pterophyta) Club mosses (Phylum Lycophyta) Both have free-swimming sperm that require free water for fertilization By far, the largest group are ferns ~ 12,000 living species
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The Life of a Fern Ferns have both gametophyte and sporophyte individuals, each independent and self-sufficient Gametophyte Produces eggs and sperm These unite to form the zygote, which develops into the sporophyte Sporophyte Bears and releases haploid spores These germinate to form gametophytes
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Fig. 14.10 Fern life cycle Frond = Vertical leaves
Rhizome = Horizontal stem
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14.6 Evolution of Seed Plants
Seeds are embryo covers that protect the embryonic plant at its most vulnerable stage Seed plants produce two kinds of gametophytes Male gametophytes Called pollen grains Arise from microspores Female gametophytes Contains the egg Develops from a megaspore produced within an ovule Pollination is the transfer of pollen by insects, winds Thus, there is no need for free water for fertilization
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All seed plants are derived from a single common ancestor
There are five living phyla Fig Cycad Four are gymnosperms Ovules not completely enclosed by sporophyte at time of pollination Fifth is angiosperms Ovules completely enclosed by a vessel of sporophyte tissue, the carpel, at time of pollination
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A seed has three parts 1. A sporophyte plant embryo
2. A source of food for the embryo called endosperm 3. A drought-resistant protective cover Fig Used for food storage
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Seeds have greatly improved the adaptations of plants to living on land
1. Dispersal Facilitate migration dispersal 2. Dormancy Postpone development until conditions are favorable 3. Germination Permit embryonic development to be synchronized with habitat 4. Nourishment Offer an energy source of young plants
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14.7 Gymnosperms Gymnosperms are nonflowering seed plants
They include four phyla Conifers (Coniferophyta) Cycads (Cycadophyta) Gnetophytes (Gnetophyta) Ginkgo (Ginkgophyta)
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The most common (and familiar) of the gymnosperms
Conifers The most common (and familiar) of the gymnosperms Fig Include Pine, spruce, cedar, redwood and fir trees Conifers are trees that produce their seeds in cones Seeds (ovules) develop on scales within cones and are exposed at the time of pollination
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Cycads Gnetophytes Have short stems and palmlike leaves
Fig a The predominant land plant in the Jurassic Period Acts like a plant standing on its head! Gnetophytes The most closely related to angiosperms Only three types of plants; all unusual Fig b Welwitschia mirabilis Have flagellated sperm
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Only one living species exists The maidenhair tree, Ginkgo biloba
Fig c Resistant to air pollution Reproductive structures found on different trees Have flagellated sperm
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The Life of a Gymnosperm
Conifer trees form two kinds of cones Large seed cones: contain the female gametophyte Small pollen cones: contain pollen grains Pollen grains are carried by wind to the seed cones Fertilization yields a zygote The zygote matures into a seed Seeds are dispersed into new habitats
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Dominant form of the life cycle
Fig Life cycle of a conifer Dominant form of the life cycle
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14.8 Rise of the Angiosperms
Angiosperms comprise 90% of all living plants > 300,000 species Virtually all our food is derived, directly or indirectly from them In gymnosperm reproduction, pollen grains are carried passively by the wind Angiosperms have evolved a more direct way of transferring pollen Induce animals to carry it for them How? Flowers!
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14.8 Rise of the Angiosperms
Flowers are the reproductive organs of angiosperms A flower employs bright colors to attract insects and nectar, to induce the insects to enter the flower There they are coated with pollen grains, which they carry with them to other flowers
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Outermost whorl (Sepals) Second whorl (Petals) Third whorl (Stamens)
A flower consists of four concentric circles, or whorls, connected to a base called the recepatcle Outermost whorl (Sepals) Protects flower from physical damage Second whorl (Petals) Attracts pollinators Third whorl (Stamens) Produces pollen grains in the anther Innermost whorl (Carpel) Produces eggs in the ovary Rising from the ovary, is a slender stalk, the style, with a sticky tip, the stigma
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Fig. 14.17 An angiosperm flower
Geranium Petals Fused carpel Stamens
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14.9 Why Are There Different Kinds of Flowers?
Different insect pollinators are attracted to specific types of flowers The most numerous insect pollinators are bees Bees are first attracted by the odor of nectar They then focus on the flower’s color and shape Bee-pollinated flowers are usually yellow or blue
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Fig. 14.18 How a bee sees a flower
Ludwigia peruviana Normal light Light emphasizing UV reflection Bee covered in pollen
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Other pollinators include Moths
Attracted to scented, white or pale-colored flowers Flies Attracted to foul-smelling brown flowers Pollen on beak Fig Hummingbirds Attracted to red flowers These are not typically visited by insect pollinators
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14.10 Improving Seeds: Double Fertilization
Within their seeds, angiosperms produce a special, highly nutritious tissue called the endosperm The male gametophyte contains two sperm One fertilizes the egg to form the diploid (2n) zygote The other fuses with two polar nuclei to form the triploid (3n) endosperm This process is called double fertilization It is only found in angiosperms and gnetophytes
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Fig. 14.20 Life cycle of an angiosperm
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Angiosperms are divided into two groups
Fig a Dicotyledons or dicots Embryos have two cotyledons Evolved earlier Monocotyledons or monocots Embryos have a single cotyledon Evolved later
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Angiosperms are divided into two groups
Dicotyledons or dicots Have leaves with netlike veins Have flower parts in fours and fives Monocotyledons or monocots Fig b & c Have leaves with parallel veins Have flower parts in threes
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14.11 Improving Seed Dispersal: Fruits
A fruit is a mature ripened ovary containing fertilized seeds Fruits aid in the dispersal of seeds to new habitats By animals By water By wind
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Fig. 14.22 Different ways of dispersing fruit
Berries Coconuts Maples By animals By water By wind
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