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Evolution by Seed Plants

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Presentation on theme: "Evolution by Seed Plants"— Presentation transcript:

1 Evolution by Seed Plants
cyanobacteria on land – 1.2 billion years ago 500 MYA – colonization by plants plant share characteristics with other more primitive organisms 1. multicellular, eukaryotic 2. photosynthetic autotrophs – brown, red, green algae 3. cell walls made of cellulose – green algae, dinoflagellates, brown algae 4. chloroplasts with chlorophyll a and b – green algae, euglenids and a few dinoflagellates

2 Defining the Plant Kingdom
divided into two clades: non-vascular and vascular vascular plants form a single clade – 93% of all plant species categorized into three smaller groups 1. lycophytes – club mosses and relatives 2. pterophytes – ferns and relatives 3. seed vascular plants A. gymnosperms - “naked seed” plants B. angiosperms – flowering plants

3 Seed plants three key reproductive adaptations evolved in seed plants:
1. dominance of the sporophyte generation – reduced gametophyte 2. the seed – ovules and eggs 3. pollen

4 Reduced Gametophytes Sporophyte (2n) Gametophyte (n) Sporophyte dependent on gametophyte (mosses and other bryophytes) Large sporophyte and small, independent game-tophyte (ferns and other seedless vascular plants) Microscopic female gametophytes (n) in ovulate cones (dependent) Microscopic male inside these parts of flowers Sporophyte (2n), the flowering plant (independent) gametophytes (n) in pollen cones Reduced gametophyte dependent on sporophyte (seed plants: gymnosperms and angiosperms) Bryophytes Seedless Vascular Seed Vascular gametophytes of non-vascular mosses are the dominant stage gametophytes of vascular ferns are significantly smaller in size gametophytes of seed plants are microscopic develop within the sporangium of the parental sporophyte protects the gametophyte gives it nourishment

5 Ovaries & Seeds seed plants are unique in the presence of an ovary that will develop an egg most plant ovaries are made up of smaller ovules inside each ovule is the female gametophyte meiosis produces an egg female gametophyte

6 Ovaries & Seeds development of the fertilized egg  Seed
seed = ovule after fertilization – contains the embryo seed = embryo (2n) + food supply (left over female gametophyte) + seed coat (from the parental sporophyte) allows for the developing embryo to resist harsh conditions multicellular structure - in contrast to the spore evolutionary advantage of seeds: seeds carry their own food supply a seed can remain dormant for years following its release Seed coat (derived from integument) Embryo (2n) (new sporophyte) Gymnosperm seed Food supply (female gametophyte tissue) (n)

7 Pollen the male part of the sporophyte produces microspores that develop into pollen grains a pollen grain contains the male gametophyte that will produce sperm via meiosis transfer of pollen to the ovule = pollination pollen grains are carried away from the parent plant by wind, insects or they can travel to the female reproductive structures within the same sporophyte

8 Pollen in order to fertilize - the pollen grain must germinate (grow)
it produces a pollen tube pollen tube allows for the discharge of two sperm (gametes) into the ovule containing the egg Pollen in mosses and ferns – the sperm is flagellated and swims to the female gametophyte in order to fertilize the egg which is also free living in vascular seed plants – the female gametophyte produces an egg which never leaves the sporophyte ovule

9 Gymnosperms “naked seed” – seeds are not enclosed in ovaries
seeds are exposed on modified leaves that form cones in the ferns – development of fronds that bear the sporangium (sori) in gymnosperms – development of modified leaves that cluster together to form cones or strobili

10 Gymnosperms drier environment favored gymnosperms over the bryophytes and ferns gymnosperms with their thick cuticles and reduced leaves as needles – adapted well to the dry climates first seed plant in the fossil record – 360 MYA now extinct earliest fossils of gymnosperms – 305 MYA most common existing gymnosperms are the conifers – spruce, pin, fir and redwood Ponderosa pine

11 Gymnosperms Cycas revoluta Ginko biloba gymnosperms are considered a division with 4 phyla: Cycadophyta, Ginkgophyta, Gnetophyta and Coniferophyta Phylum Cycadophyta – cycads 130 species survive Phylum Ginkgophyta - ginkos only one species left – Ginkgo biloba Phylum Gnetophyta – three genera alive today tropical and desert species Gnetum – 35 species of tropical trees, shrubs and vines (Africa and Asia) Welwitschia – one species, Welswitchia (Africa) Ephedra – 40 species, desert shrubs Phylum Coniferophyta – largest group “cone-bearing” 600 species of conifers many are large trees most are evergreens – retain their leaves throughout the year Welwitschia mirabilis. Ephedra.

12 Phylum Coniferophyta Pine fascicle 575 species largest genus – Pinus
leaves of conifers are always simple needles or scales pine leaves – needles or needle-like arranged in clusters or bundles of two to five leaves each bundle cluster = fascicle needles are covered with a waxy cuticle to minimize water loss Pine fascicle

13 Life Cycle: The Pine pine tree is the sporophyte
sporangia are located on scale-like leaves packed into cones two types of cones produce two types of spores small pollen cones produce microspores  pollen larger ovulate cones produce megaspores  egg Life Cycle: The Pine

14 Life Cycle: The Pine in a conifer - more than a year may pass between pollination & fertilization!!! pollen cones produce pollen which contains the male gametophyte ovulate cones have ovules containing the female gametophytes making eggs pollen lands on ovulate cones and begins to germinate pollen tube delivers sperm to egg = Fertilization fertilized eggs develop into seeds seeds are released from ovulate cones seeds land on new habitat and develop into new sporophyte

15 Pollen grains Male Pine Cone ovule air cells Female Pine Cone

16 Angiosperms commonly known as the flowering plants
angion = “container” angio – refers to seeds contained in fruits and mature ovaries are seed plants that produce reproductive structures called flowers and fruits

17 Angiosperm Diversity only about 1,000 species divided into three groups: 1. magnoliids 2. monocots – embryo with one cotyledon 3. eudicots (dicots) – embryo with two cotyledons

18 Monocots embryo with one cotyledon (embryonic leaf) other traits:
1. veins in leaves are usually parallel 2. vascular bundles scattered in stems 3. root system is usually fibrous 4. most cannot undergo secondary (i.e. woody) growth Monocots

19 Dicots (Eudicots) former classification known as dicots has been abandoned (too polyphyletic) using DNA analysis – clade was created of “true” dicots cotyledons: store food absorbed from the endosperm California poppy zucchini flower

20 Dicots (Eudicots) embryo with two cotyledons other traits: California
1. veins in leaves are usually netlike 2. vascular bundles arranged in a ring in stems 3. root system is usually a taproot 4. many are perennial and undergo secondary (i.e. woody) growth California poppy zucchini flower

21 flower = angiosperm structure that is specialized for sexual reproduction
structure of a flower – 4 rings of modified leaves called flower organs: 1. sepals 2. petals 3. stamens 4. carpels Flowers

22 Flower Anatomy 1. sepals (sterile flower organ)
usually green and enclose the flower before it opens 2. petals (sterile flower organ) interior to the sepals many are brightly colored – to attract pollinators like insects wind pollinated have leaves that are less colorful Flower Anatomy Stamen Filament Anther Stigma Carpel Style Ovary Petal Receptacle Ovule Sepal

23 Flower Anatomy 3. stamens (produce spores)
contain chambers pollen sacs (male sporangia) pollen sacs produce pollen grains containing the male gametophyte consists of a stalk called the filament and a terminal end called the anther (pollen sacs) Flower Anatomy Stamen Filament Anther Stigma Carpel Style Ovary Petal Receptacle Ovule Sepal

24 Flower Anatomy 4. carpels (produce spores)
comprised of the stigma, style and ovary end of the carpel is a sticky stigma that receives pollen the stigma leads to a style which leads to the ovary at the base of the carpel the ovary contains one or more ovules – site of the female gametophyte & the egg these ovules when fertilized develop into seeds within a fruit Flower Anatomy Stamen Filament Anther Stigma Carpel Style Ovary Petal Receptacle Ovule Sepal some flowers have a single carpel – others have multiple (separate or fused together) e.g. fused carpels = strawberry

25 Fruits fruits contain the mature ovary
but can also contain other flower parts the egg is fertilized within the ovule - the embryo begins to develop within the seed as seeds develop – the ovary wall (pericarp) thickens = fruit development fruits protect seeds and aid in their dispersal

26 Fruits fruits can be either fleshy or dry
fleshy = tomatoes, plums, grapes the pericarp becomes soft during ripening dry = beans, nuts and grains some can split open at maturity to release seeds fruits have adapted for seed dispersal in many ways many are eaten – seeds “pooped” out others cling to animals – “burrs” e.g. dandelions and maples – fruits function as parachutes or propellers e.g. coconut – dispersal by water

27 Life Cycle of Angiosperms
parental cells inside pollen sacs inside anther undergo meiosis to make pollen grains (male gametophyte) pollination results in distribution of pollen to the stigma Anther pollen grains

28 Life Cycle of Angiosperms
pollen germinates and develops a pollen tube for delivery of sperm down the style toward the ovary pollen tube stops at the ovule inside the ovary sperm enters into the ovule the sperm fertilizes the egg inside the ovule to produce the zygote the zygote grows into the embryo the surrounding ovule becomes the seed the surrounding ovary becomes the fruit

29 Pollination by numerous methods abiotic: wind
by bees – 65% of all angiosperms by moths & butterflies – detect odors (sweet fragrance) by flies – many are reddish and fleshy with a rotten odor by bats – light colored petals and aromatic by birds – very large and brightly colored (red or yellow) – no scent required but they produce a nectar

30 Seed Development the seed consists of: the endosperm – rich in starch
the embryo the endosperm the seed coat the endosperm – rich in starch usually develops before the embryo initially has a milky consistency thickens as the seed develops stores nutrients that is used by the seedling as it germinates develops leaves for food storage = cotyledons monocot – 1 cotyledon dicot – 2 cotyledons develops an embryonic root = radical

31 Seed coat Radicle Cotyledons Common garden bean, a eudicot with thick cotyledons Maize, a monocot Radicle Endosperm Cotyledon Seed coat

32 And now for some interesting stuff you probably knew but don’t really know

33 The dandelion – Taraxacum (Dandelion - lion’s tooth)
asexually reproduces through apomixis: asexual production of multiple seeds the dandelion produce seeds without pollination and fertilization a diploid cell in the ovule gives rise to the embryo seed development results – dispersed by the wind or you blowing

34 5-7 kg of grain required to produce 1 kg of beef
six crops – maize, rice, wheat, potatoes, cassava and sweet potatoes – yield 80% of all the calories consumed by humans crops domesticated 12,000 years ago seeds of domesticated crops usually much larger than their wilder “cousins” 5-7 kg of grain required to produce 1 kg of beef the outer covering of the grain is called the bran rich source of vitamin B the embryo is located at the upper corner of the grain and is called the germ polishing the grain (e.g. in white rice) removes the bran and germ and leaves the endosperm

35 flowering plants provide many edible products
teas and coffee beans cacao tree – chocolate spices – cloves, saffron fruits and seeds – vanilla, black pepper, mustard many seed plants are sources of wood wood – tough walled xylem cells seed plants also provide numerous medicines belladonna – atropine (dilator) foxglove – digitalis (heart medication) eucalyptus – menthol periwinkle – vinblastin (leukemia)

36 Cloning Happens used to improve crops and ornamental plants
clones from cuttings: plant fragments taken from the stem called a “cutting” at the end of the cutting – development of a callous of undifferentiated cells these cells form new roots can also be done from leaves grafting: a twig or bud from one plant is grafted onto another – to join their genomes the plant that provides the root system = stock the grafted twig = scion test-tube cloning: lab-based methods for cloning cells taken from a plant and cultured on artificial media to form a callous and then a new seedling can also introduce new genes = genetic engineered organism

37 Genetic Engineering in Food
genetically modified cassava: taproot of almost pure carbs transgenic strains with dramatically increased protein levels, iron and vitamin A genetically modified wheat and rice: Norman Borlaug: PhD in plant physiology “father of the green revolution” Nobel prize Laureate work in modifying wheat strains – high yield, but too tall produced a “dwarf” version by selective breeding also developed dwarf rice strains his group was credited with saving millions of people from starvation worked with triticale – wheat and rye given a “shout out” in the Star Trek episode – “The trouble with tribbles” Genetic Engineering in Food


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