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

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

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

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. 14.3 Generalized plant life cycle

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. 14.4 Two types of gametophytes Moss Pine Primitive plant Vascular plant Mostly gametophyte Gametophyte barely visible

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

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

Fig. 14.5 The evolution of plants

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

Fig. 14.6 The life cycle of a moss Hair-cup moss, Polytrichum

14.4 The Evolution of Vascular Tissue The first vascular plant appeared approximately 430 million years ago (mya) Fig. 14.8 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

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

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

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

Fig. 14.10 Fern life cycle Frond = Vertical leaves Rhizome = Horizontal stem

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

All seed plants are derived from a single common ancestor There are five living phyla Fig. 14.11 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

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. 14.12 Used for food storage

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

14.7 Gymnosperms Gymnosperms are nonflowering seed plants They include four phyla Conifers (Coniferophyta) Cycads (Cycadophyta) Gnetophytes (Gnetophyta) Ginkgo (Ginkgophyta)

The most common (and familiar) of the gymnosperms Conifers The most common (and familiar) of the gymnosperms Fig. 14.14 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

Cycads Gnetophytes Have short stems and palmlike leaves Fig. 14.15a 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. 14.15b Welwitschia mirabilis Have flagellated sperm

Only one living species exists The maidenhair tree, Ginkgo biloba Fig. 14.15c Resistant to air pollution Reproductive structures found on different trees Have flagellated sperm

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

Dominant form of the life cycle Fig. 14.16 Life cycle of a conifer Dominant form of the life cycle

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!

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

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

Fig. 14.17 An angiosperm flower Geranium Petals Fused carpel Stamens

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

Fig. 14.18 How a bee sees a flower Ludwigia peruviana Normal light Light emphasizing UV reflection Bee covered in pollen

Other pollinators include Moths Attracted to scented, white or pale-colored flowers Flies Attracted to foul-smelling brown flowers Pollen on beak Fig. 14.19 Hummingbirds Attracted to red flowers These are not typically visited by insect pollinators

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

Fig. 14.20 Life cycle of an angiosperm

Angiosperms are divided into two groups Fig. 14.21a Dicotyledons or dicots Embryos have two cotyledons Evolved earlier Monocotyledons or monocots Embryos have a single cotyledon Evolved later

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. 14.21b & c Have leaves with parallel veins Have flower parts in threes

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

Fig. 14.22 Different ways of dispersing fruit Berries Coconuts Maples By animals By water By wind