Plant Diversity II The Evolution of Seed Plants

Plant Diversity II The Evolution of Seed Plants

Plant Diversity II The Evolution of Seed Plants Packet #34 Chapter #30 & Chapter #38 Introduction Evolution of Roots Roots anchor plants and enable them to absorb water and nutrients from the soil Roots allow the shoot system to grow taller. Roots also contain lignified vascular tissue. Introduction Evolution of Leaves

Leaves increase the surface area of vascular plants. Leaves can be classified as microphylls or megaphylls Al lycophytes have small, usually spine-shaped leaves with a single vein Microphylls Leaves of other modern vascular plants are known as megaphylls The larger sized leaves are possible due to the

highly branched vascular system which supports greater photosynthetic activity. Introduction The Evolution of Seed The evolution of seed facilitated reproduction on land Gymnosperms Angiosperms A seed consists of a plant embryo packaged with a food supply in a protective coat

The first vascular plant, according to the theory of evolution, originated about 360 MYBP in the Devonian Period. Those seeds were not enclosed in any special chambers. These plants evolved into the gymnosperms The Naked Seeds Introduction The Evolution of Flowers According to the theory of evolution, flowers evolved in the Cretaceous Period about 130 MYBP

Led to further plant diversity A flower is a complex structure that bears seeds within a protective chamber called an ovary. Most modern day flowering plants are known as angiosperms. Introduction Apical Meristems

Recall, plants cannot move. The elongation of their shoots and roots maximizes their exposure to environmental resources. Growth occurs throughout the life of the plant via cell division in the apical meristematic tissue found at the tips of roots and shoots. Cells produced by meristematic tissue can differentiate into various plant tissues. The stem cell in plants? Hypothesis for the Evolution of Leaves Introduction VI Seed plants are vascular plants that produce

seeds. Earliest fossilized seeds are gymnosperms. 360 MYBP Seed plants dominate modern landscapes and are a large component of plant diversity. Important reproductive adaptations in seed plants Continued reproduction of the gametophyte

The advent of the seed The evolution of pollen Introduction VII The gametophytes of seed plants are even smaller than those of the seedless vascular plants The gametophytes are protected in the ovules and pollen grains, Miniature female gametophytes develop from spores that are retained within the parental sporophyte. Introduction VIII Comparison of Seeds vs. Spores

Seeds are the primary means of reproduction and dispersal of flowering plants. Seeds are reproductively superior to spores. Embryonic development is further advanced in seeds Seeds contain an abundant food supply Each seed has a protective coat. Introduction IX Seeds, Dispersal & Adaptation

Seed dispersal becomes important in adaptations Seed is a resistant structure that is multicellular and complex. Seed consists of a sporophyte embryo packaged with food in a protective coat Seeds can be dispersed by wind, water and animals. Introduction X

Seeds Introduction XI Megaspores Develop into female (egg containing) gametophytes. There is the production of one or more egg cells If egg is fertilized by sperm, the zygote develops into a sporophyte embryo The entire ovule develops into a seed. Seed may be viable for days, months or years.

Introduction XII Microspores Microspores develop into pollen grains Pollen grains mature to become the gametophytes of seed plants Pollination The transfer of pollen to ovules Self Pollination

Cross Pollination HW HW The most common gymnosperms, and all angiosperms sperm, lack flagella. Pollen can be transferred by wind and animals. Gymnosperms Introduction Vascular plants with seeds that are totally exposed or borne on the scales of cones.

Ovules and seeds develop on the surface of specialized leaves called sporophytes. Most familiar are the conifers The cone-bearing plants Produce wind-borne pollen grains. Pines

Feature that seedless vascular plants lack. Gymnosperms, according to the theory of evolution, appear earlier in the fossil record than the angiosperm. Phyla of Gymnosperms Ginkgophyta Cycadophyta

Large cones and palmlike leaves 130 extant species Gnetophyta One extant species 3 very different genera Coniferophyta Pines, firs & spruces 600 species identified Phyla of Gymnosperms

Ginkgophyta Cycadophyta Large cones and palmlike leaves 130 extant species Gnetophyta

One extant species 3 very different genera Coniferophyta Pines, firs & spruces 600 species identified Phylum Coniferophyta Largest phylum of the gymnosperms Conifers (refers to cone) are woody plants that bear needles

Produce seeds in cones. Most conifers are monoecious Leaves that are usually evergreen The needles are a result of adaptations to dry conditions. Have male and female reproductive parts in separate cones on the same plant. Most of the wood used today is from conifers Conifers are among the largest and oldest organisms on the earth.

Life Cycle of A Pine Life Cycle of a Pine Introduction Pine tree is a mature sporophyte. Pine gametophytes are extremely small and nutritionally dependent on the sporophyte generation. Pine is hetereosporous and produces microspores and megaspores in separate cones. Life Cycle of a Pine

Male cones produce microspores that develop into pollen grains (immature male gametophytes) that are carried by air currents to female cones. Female cones produce megaspores. One of each four megaspores produced by meiosis develops into a female gametophyte within an ovule (megasporangium). Once the male and female cones appear, female is normally bigger, it takes approximately three years to produce male and female gametophytes, get

pollinated and form mature seeds. Life Cycle of a Pine After pollination, the transfer of pollen to the female cones, a pollen tube grows through the megasporangium to the egg within the archegonium. After fertilization, the zygote develops into an embryo encased inside a seed adapted for wind dispersal.

The scales of the ovulate cone open and the seeds travel by wind. Angiosperms Introduction Angiosperms Angiosperms, or flowering plants, are vascular plants that produce flowers and seeds enclosed within a fruit.

The most diverse, most successful and geographically widespread group of plants. There are approximately 250,000 species. Oldest fossils, according to the theory of evolution, are found in rocks from the early Cretaceous period about 130 MYBP. Introduction II Angiosperm Clades All angiosperms are placed in Division Anthophyta.

Until the late 1990s, most plant taxonomists divided the angiosperms into two main classes. Monocots Dicots Introduction III Monocots vs. Dicots Eudicots DNA evidence has revealed that not all

plants having the dicot anatomy fall into a single group. Eudicots Include the majority of dicots **However, other dicots belong to lineages that diverged earlier than monocots or eudicots. Evolutionary Adaptations of the Angiosperms

Refinements in the vascular tissue provided more efficient transport of water Both angiosperms and gymnosperms have xylem cells called tracheids Function in mechanical support and water transport. Angiosperms also have vessel elements Shorter and wider than tracheids Facilitate water transport more efficiently. Evolutionary Adaptations of the Angiosperms

The Flower Increased opportunities for successful pollination, fertilization and dispersal The Flower Flower I Petals are often brightly colored and of various shapes

Aid in attracting pollinators Also considered sterile floral parts. Within the ring of petals are the fertile sporophytes, stamens and carpels. Flower II Stamens

Male reproductive organs Fertile floral parts Sporophytes that produce the microspores that develop into male gametophytes. Composed of a terminal sac called an anther where pollen is produced. Anther is also supported by a stalk called a filament. Flower III Carpels

Female reproductive organs Fertile floral parts Sporophytes that produce megaspores and develop into female gametophytes. Tip of carpel is a sticky stigma that collects pollen Style leads to the ovary at the base of the carpel Inside the ovary are ovules

Develop into seeds if fertilized Adaptations in Flowers Over the Years In certain flowers, one or more of the four floral whorls have been eliminated. There are also a variety of flower shapes, sizes and colors which represent adaptations to pollinators. Terminology Complete flowers

Incomplete flowers Lacking one or more of the four floral shorls Bisexual flower Four floral whorls Have stamen and carpels Known as perfect flowers but can be complete or incomplete

Unisexual flower Imperfect flowers Staminate flowers if only the male organs are present Carpellate flowers if only the female organs are present Terminology II Monoecious Plants have staminate and carpellate flowers on the same plant

Corn Dioecious Plants have staminate and carpellate flowers on different plants Ginkgos Date palms The Fruit Introduction

A fruit is a mature ovary As the seed develop, the wall of the ovary thickens The thickened wall becomes the pericarp. As the ovary grows, the other flower parts whither away Fruits protect the seeds and aid in dispersal. Adaptations in Fruit

Dandelions & Maple Trees Thistles & Grasses Wind dispersal is observed Fruits are described as kites or propellers. Animal dispersal is observed Fruits are described as

hitchhickers or burrs. Animal dispersal often provide resources such as fecal material that fertilize the young sporophyte plant. Classification of Fruits Simple Fruits Single ovary Can be fleshy or dry

Aggregate Fruits Arise from a single flower with several carpels Cherry Soy bean pod Blackberry Multiple Fruits Arise from an inflorescence

Many flowers As the walls of the many ovaries thicken, they fuse and become one fruit Pineapple Life Cycle of an Angiosperm Life Cycle of Angiosperm Sporophyte generation is dominant

Gametophytes are extremely reduced in size and nutritionally dependent on the sporophyte generation Flowering plants are hetereosporous Figure 38.4 Figure 38.4 Development of Pollen Grains (a) Development of a male gametophyte (pollen grain) Pollen sac (microsporangium)

1 Each one of the microsporangia contains diploid microsporocytes (microspore mother cells). 2 Each microsporocyte divides by meiosis to produce four haploid microspores, each of which develops into a pollen grain. Figure 38.4a A pollen grain becomes a 3 mature male gametophyte

when its generative nucleus divides and forms two sperm. This usually occurs after a pollen grain lands on the stigma of a carpel and the pollen tube begins to grow. (See Figure 38.2b.) Microsporocyte MEIOSIS Microspores (4) Each of 4 microspores Generative cell (will form 2 sperm)

MITOSIS Male Gametophyte (pollen grain) Nucleus of tube cell 20 mm 75 mm Ragweed pollen grain KEY to labels Haploid (2n) Diploid (2n)

Figure 38.4 Development of Embryo Sacs (b) Development of a female gametophyte (embryo sac) Megasporangium Ovule Megasporocyte MEIOSIS Integuments Micropyle 1 Within the ovules megasporangium is a large diploid

cell called the megasporocyte (megaspore mother cell). 2The megasporocyte divides by meiosis and gives rise to four haploid cells, but in most species only one of these Female gametophyte survives as the megaspore. (embryo sac) Surviving megaspore MITOSIS Ovule Antipodel Cells (3) Polar

Nuclei (2) Egg (1) Integuments Haploid (2n) Diploid (2n) 100 mm Key to labels Synergids (2) 3 Three mitotic divisions of the megaspore form the embryo sac, a multicellular female gametophyte. The ovule now consists of

the embryo sac along with the surrounding integuments (protective tissue). Embryo sac Figure 38.4b Life Cycle of Angiosperm Each microspore develop into a pollen grain. Immature male gametophytes are contained within pollen grains.

Each pollen grain has two haploid (n) cells. One of each four megaspores produced during meiosis develops into an embryo sac (female gametophyte). Embryo sac contains seven cells with eight nuclei The egg cell and the central cell with two polar nuclei participate in fertilization. Life Cycle of Angiosperm

Pollen released from the anther Pollen is carried to the sticky stigma Flowers can selfpollinate or crosspollinate. Transfer of pollen from flowers of one plant to flowers of another plant is called cross-pollination Life Cycle of Angiosperm

Pollen grain germinates after it sticks to the stigma. Pollen grain now contains the mature male gametophyte and extends a tube down through the style. After it reaches the ovary, the pollen tube penetrates the microphyle and discharges two sperm cells into the female gametophyte (embryo sac)

Pollen Tube Life Cycle of Angiosperm Double Fertilization Results in the formation of a diploid zygote and triploid endosperm One sperm nucleus fuses with the egg to form a diploid zygote. Other sperm nucleus fuses with the two

nuclei if the female gametophyte Cell is now triploid (3n). Characteristic of flowering plants. Figure 38.6 Double Fertilization Double fertilization ensures the endosperm will develop only in ovules where the egg has been fertilized

Prevents the angiosperms from wasting resources Life Cycle of Angiosperm After double fertilization, the ovule matures into a seed. The zygote develops into the sporophyte embryo with a rudimentary root and either one or two seed leaves

(cotyledons monocots vs. dicots) Life Cycle of Angiosperm Seed consists of the embryo, endosperm, sporangium and a seed coat. An ovary develops into a fruit as its ovules develop into seeds. Dispersal occurs via wind or

animals Seed germinates if the environmental conditions are favorable. Seed coat ruptures, the embryo emerges as a seedling and uses the stored food in the endosperm and cotyledons to begin growth. Mechanisms to Prevent SelfPollination Chapter 38 Introduction I Some flowers selffertilize but most angiosperms have

mechanism that prevent selfing. Dioecious plants Unisexual Ackee {Barbados} Ginnup {Jamacia} Bisexual flowers Stamens and carpels mature at different times Stamens and carpels are arranged in a way that

makes self-pollination unlikely Introduction II Biochemical Blocking AKA Self-incompatibility Most common method that plants use to prevent selfing Some plants recognize their own pollen and that of closely related individuals Hmmm!

Biochemical block prevents pollen from completing its development and fertilizing the egg The Seed Part II Chapter 38 Structure of Mature Seed If a common bean seed, a eudicot, is opened, several structures are observed

Hypocotyl Radicle Epicotyl Plumule Seed coat endosperm Evolutionary Adaptations to Seed Dormancy & Germination Chapter 38 Introduction I As the seed matures, it dehydrates until only about 5 15% of its weight is water Enters dormancy

Species dependent environmental cues break dormancy Period of extremely low metabolic rate and suspended growth and development Increases the chance that germination will occur at a favorable time Fire; light; water; temperature; digestion through animals gut Sexual reproduction produces seeds with dispersal and dormancy abilities.

Seed Germination Germination I Water HAS to be absorbed Radicle (embryonic root) emerges first from the germination seedlings Hypocotyl pushes way up through the soil

Causes the seed to swell and rupture seed coat Triggers metabolic changes in the embryo promoting growth Protecting fragile shoot apex and large cotyledons Epicotyl spreads true leaves and begin photosynthesis Germination II Cotyledons seed leaves whither

away. Seedling is vulnerable to many hazards and only a small number survive. Plant Biotechnology & Human Warfare Biotechnology Plant Biotechnology Innovations in the use of plants to make products for humans Genetically engineered organisms

GMOs Medicine Food Clothing shelter

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