Chapter 28: Seed Plants (Part 3 & 4)

Conifers

a tree that bears cones and needle-like or scale-like leaves that are typically evergreen. Conifers are of major importance as the source of softwood, and also supply resins and turpentine.

Ovule

what seeds develop from.

Cones

where microsporangia and megasporangium develop in gymnosperm species.

Pollen

• Pollen grains are male gametophytes surrounded by protective coat •Pollenation -Transfer of pollen to megaspore (ovule) •Pollen is resistant to drying -Eliminates dependence of water for fertilization

Cotyledon

("seed-leaf") stores nutrients and supplies them to the developing embryonic plant. Monocot & Dicots: The names of the two groups were inspired by differences in the embryonic leaf that develops in seeds, a structure called the cotyledon.

Five lineages of Gymnosperms:

-Ginkgoes -Cycads -Redwood groups -Pine group -Gnetophytes

Gnetophytes are an odd group.

. There are only three genera and they share some characteristics with angiosperms. For the sake of time I'm only going to mention one genus - Ephedra. This is a desert plant that produces flower-like sporangia (but they aren't technically flowers since this is a gymnosperm). We mentioned the many drugs we get from plants and Ephedra produces the drug known as ephedrine (and the related pseudoephedrine), which has been used as a weight loss supplement as well as for controlling allergies and congestion, and it can also be used to make meth.

Ginkgoes (Ginkgophyta)

1 known species Also called maidenhair tree -Loses leaves in winter (is deciduous). Leaves are virtually identical to 150-million-year-old fossils, so Ginkgo is considered a "living fossil." -Separate male and female plants. Pollen carried by wind; motile sperm released into female gametophyte swim to egg. -Widely planted as ornamentals; resistant to air pollution. Leaf extracts used as dietary supplement thought to improve memory, vision, and help maintain overall health.

Cycads (Cycadophyta)

140 known species Also called sago palms -Have been around for approximately 300 million years. Resemble palms. Unique among gymnosperms in having compound leaves. -Separate male and female plants. Pollen carried by wind; motile sperm released into female gametophyte swim to egg. -Roots contain symbiotic cyanobacteria that fix nitrogen. Popular landscaping plants.

Gnetophytes (Gnetophyta)

70 known species -Grow as vines, trees, or shrubs. Closely related to angiosperms. Display several angiosperm features, including wood that contains vessel elements. -Pollen is transferred by wind or insects. Double fertilization occurs, but results in the formation of two embryos (endosperm is not formed). -The drug ephedrine was originally isolated from Ephedra (also called Mormon's tea). Welwitschia lives only in the Namib desert and may live up to 1500 years.

Seeds

An encapsulated plant embryo; a fertilized ovule of a plant. A seed is a fertilized ovule containing the plant embryo.

In most cases, the animals are attracted to flowers for food.

Animal pollinated flowers often contain NECTAR, a sugary solution that animals like this hummingbird and butterfly are feeding on. Some insects also collect some of the pollen for food.

Angiosperm pollination typically occurs via wind or animal pollinators.

Animal pollinators are hugely beneficial to their plants and have often co-evolved with them in mutualistic relationships.

The most common pollinators are insects such as bees and butterflies (although there are many, many more types on insects that act as pollinators).

Birds and some mammals can also act as pollinators.

Angiosperms have one other additional feature that gymnosperms don't have. They undergo double fertilization using two sperm.

Both sperm are released from the pollen grain and travel down the carpel to the egg via a pollen tube. One sperm fuses with the egg to form the 2n zygote.

Fruits

Develop from ovary (usually); surrounds seed(s)

Dicots include all other flowering plants - the list is too long but here are some examples.

Dicots have two cotyledons, branching veins in their leaves and petals in multiples of 4 or 5.

Two lineages of seed plants evolved.

First came the gymnosperms, following later by the angiosperms.

Angiosperms do have ovaries, which surround and give another layer of protection to the ovules.

Following fertilization in angiosperms, the ovules become the seeds and the ovary becomes a fruit. This is the only group of plants that produces seeds enclosed within fruits. Angiosperms also produce flowers, which are reproductive structures where the ovules and pollen develop. So flowers and fruits are unique to the angiosperm group.

The middle line of the diagram shows what happens on the female cones. Those cones contain the ovules. Within each ovule, a megasporangium produces a megaspore via meiosis.

Following pollination, the megaspore develops into the female gametophyte, which then produces an egg. The pollen produces and release sperm which will then fertilize the egg and create a new zygote. Following fertilization, each fertilized ovule develops into a seed. The zygote comes the embryo, the female gametophyte tissue becomes the food source, and the integument becomes the seed coat. The mature seeds are then released to disperse to new environments. If they land in suitable habitat, they will germinate to grow into a new plant - a new sp

We'll discuss gymnosperms first. The gymnosperm group (those that produce naked seeds - no fruits, no flowers) are classified into five separate lineages: ginkgoes, cycads, the redwood groups, the pine group and the gnetophytes.

Gymnosperms began to diversify after the Carboniferous when the climate became warmer and drier. They had an advantage over seedless plants due to their decreased dependence on water for reproduction.

Monocots includes the grasses, palm trees, irises and others.

In addition to having a single cotyledon, they have parallel veins (vascular tissue) within their leaves and their flower petals are in multiples of three. (3, 6, 9, etc). We'll learn more about the stem vascular tissue arrangement in next chapter

Pollen grain

In heterosporous seed plants, the microspore germinates to form a tiny male gametophyte that is surrounded by a tough coat of sporopollenin, resulting in a pollen grain. each of the microscopic particles, typically single cells, of which pollen is composed. Pollen grains have a tough coat that has a form characteristic of the pollen-producing plant and which can still be recognized in some archaeological deposits.

The female portion of the flower is the carpel.

It contains the ovary and enclosed ovules. At the tip of the carpel is a stigma. This is where pollen must land during pollination.

In seed plants, the spores remain on the sporophyte (they aren't dispersed).

It's the embryo stage (the seed) that is dispersed.

Following pollination, the pollen grains (which are the male gametophytes) produce sperm which fertilize the eggs within the ovules.

LOOK AT DIAGRAM FROM LECTURE PP TO UNDERSTAND PROCESS OF POLLINATION DESCRIBED As mentioned previously, the ovule is the female structure containing the megasporangium, which produces a haploid megaspore via meiosis. This entire structure is protected by an integument. So this first picture is the unfertilized ovule.

The sporophyte is the dominant generation - that's the tree, the mature plant. Once mature, that sporophyte produces male and female cones (female cones are also called ovulate cones).

Let's follow the top line to see what happens within the male cones...male cones contain the microsporangia. This is where meiosis occurs to produce haploid microspores. Those microspores develop into the male gametophytes - the pollen grains. So pollen forms o the male cones. In conifers, pollination typically occurs via the wind. Pollen grains are released from the male cones, where they are carried by wind currents to the female cones. There's a massive amount of pollen that gets released - think about the yellow pine pollen that fills the air and blankets your cars in the spring.

Angiosperms are the only plants that produce flowers. Flowers are reproductive organs.

Like the cones of the conifers, this is where the ovule and pollen develop.

The reproductive structures of conifers are called cones. These are the structures where the pollen and ovules are produced.

Male cones produce microsporangia and pollen, while female cones produce megasporangia and ovules. The male and female cones typically look different. These images show male and female pine cones. The typical pine cone that comes to mind is actually the female version. Male cones are the smaller structures that litter the ground around here in the spring. You'll get a chance to view both types in lab.

While getting nectar, the animals pick up pollen on their bodies and carry it around to other flowers. It's a DIRECTED type of pollination.

Many species of pollinators only visit certain types of flowers, so they can pick up and deliver pollen between flowers of the same species on different plants. This is different from wind pollination, which is indirect and based on chance. Wind blown pollen may fall in the right place on the carpels of flowers, but much of it does not and is wasted. Animal pollination eliminates the "chance" part - they specifically carry the pollen where it needs to go. Petal color and shape, and the scents of flower are all adaptations to particular pollinators.

Most flowers also have petals, which are often brightly colored to attract animal pollinators.

Not all flowers look like this; some only contain male or female parts, some lack petals and there are a great variety of shapes and colors if petals are present.

LOOK AT LECTURE PP FOR DIAGRAM ON ANGIOSPERM LIFE CYCLE

Now that we've covered reproductive structures of angiosperms, let's look at their life cycle - this is the last alternation of generation cycle we'll cover this semester!

Two new structures evolved in the seed plant group that provided additional advantages for reproduction on land - ovules and pollen.

Ovules are female structures; this is where the female gametophytes develop. Pollen represents the male gametophyte generation of the seed plants. Let's take a closer look at each of these structures.

The evolution of pollen and the process of pollination eliminated plants dependence on water for fertilization.

Recall that in seedless plants, the flagellated sperm must swim from the antheridia to the archegonia in order to fertilize the eggs. With seed plants, these gametangia are replaced by pollen and ovules, pollen is transferred to the ovules via wind or animals, not water (usually). The protective coat on pollen prevents it from drying out until it reaches the ovule. With these structures in place, plants were no longer dependent on rainfall or other moisture to get the sperm to the eggs.

Seeds are structures that contain the diploid plant embryo, stored food and a tough protective seed coat.

Seeds allow the diploid embryo to serve as the dispersal phase of the life cycle. In seedless plants, the zygote/embryo doesn't disperse, it remains attached to gametophyte. Spores are the only dispersal stage.

For flowering plants, pollination is the process of transferring pollen from the stamen to the carpel.

Some plants are capable of self-fertilization, and with sperm and eggs from the same plant able to form zygotes. Other plants need cross pollination, where the pollen must be transferred from the flowers of one plant to the carpels of another.

Let's take a look at flower structure. The male portion of the flower is called the stamen.

Stamens produce pollen grains in a structure called the anther.

Make sure you review the life cycle information carefully, and let me know what questions you have.

Studying these phylogenetic trees from the textbook is also very helpful in remembering the classifications and which groups have which traits.

After pollen arrives, the megaspore undergoes mitosis to produce the multicellular female gametophyte (in the transition from the first to second image, the megaspore has become the female gametophyte).

That female gametophyte then produces an egg. Once the egg is produced, the pollen (male gametophyte) produces sperm to fertilize the egg.

Which of the following is a fruit? a. Peach b. Acorn c. Lima beans d. Pecan e. All of the above

The answer is E - all of the above. In biology, the term fruit applies to any structure surrounding the seeds of a flowering plant. That includes the fruits we typically think of - like peaches or apples or grapes, but also applies to nuts and many vegetables.

. The seeds have a greater chance of survival than spores because they come packaged with their own food source, and the seed coat is more protective than sporopollenin.

The embryo can remain dormant within the seed for several month to several years, depending on the species. When conditions are good, it will germinate and grow into a new sporophyte, with the pre-packaged food source giving it a head start until it can photosynthesize on its own.

All of the seed plants are heterosporous, producing both micro and megaspores.

The male and female gametophytes that develop from these spores are microscopic and dependent on the sporophyte. (it's the reverse of the nonvascular life cycle, in which in the sporophyte is dependent on the gametophyte).

The last bit of information to cover are the two major groups of angiosperms: the monocots and the dicots (or eudicots).

The monocots are a monophyletic branch (you can see them in black on this tree). The dicots are not monophyletic, but a group called the eudicots ("true" dicots) are.

LOOK AT LECTURE PP FOR CONIFER LIFE CYCLE

The typical conifer life cycle is show here. Because we now have heterospory, the gymnosperm and angiosperm life cycles are more complex, but it is still an alternation of generations life cycle.

These groups have several differences.

Their names are based on how many cotyledons they contain. Cotyledons are seed leaves (or embryonic leaves). They absorb nutrients from the endosperm and are the first leaves that are present when the seed germinates

Gymnosperms have exposed, or "naked" seeds.

Their ovules are not enclosed within an organ called an ovary.

Some of the common species the belong to this group are pines, spruces, firs (think Christmas trees), redwoods, cedars and cypresses.

These are all large, woody plants with needle-like or scale-like leaves. Most of them are evergreen, keeping their green leaves year-round.

Ovules are composed of the megasporangium (the multicellular tissue where megaspores develop) and a protective coat called the integument.

These structures develop on the mature sporophyte plant. The integument protects the megasporangium tissue, and within that tissue, the megaspore(s) are produced via meiosis.

Angiosperm ovules are completely enclosed within organs called ovaries. These ovaries offer more protection for the ovules (against dry weather, insect pests, etc).

They also lead to the development of fruit. Following fertilization, when the ovules become seeds, the surrounding ovarian tissue becomes the fruit. Fruits protect the seeds and help in seed dispersal.

The last group of plants to discuss are the angiosperms, the flowering plants. Angiosperms make up a single phylum - Phylum Anthophyta.

They are the largest group of living plants, with over 250,000 recognized species. They occupy a diverse variety of habitats and come in a wide range of sizes and structures - from small grasses to huge oak trees.

Other animal dispersed seeds may be sticky.

They have Velcro-like fibers that allow them to stick to passing animals and be carried to other places. (Velcro was actually invented by a guy who was inspired by the seeds sticking to his dog).

Cycads are another group that don't occur naturally in our area but we can find them here as ornamental plants.

They look a bit like palm trees (and they're sometimes called sago palms) but they aren't true palms (palms are angiosperms).

Unlike the nonvasculars and seedless vascular plants, the spores produced by seed plants do not disperse.

They remain on the parent sporophyte and develop into gametophytes on that parent plant. (This whole transition from sporangia to spores to gametophytes occurs on the sporophyte plant).

Angiosperms are the the most common and recognizable plants and are the source of all of our major foods (corn, rice, wheat, nuts, all of the possible fruits and vegetables you can think of, etc).

They're also the group that gives us most of the medicines, clothing fibers and other economic benefits.

The second sperm fuses with two haploid nuclei in female gametophyte to form a 3n tissue called endosperm.

This endosperm serves as the food source within the seed.

We only have one surviving species with the Ginkgo group today - Ginkgo biloba.

This is an Asian species but it's used a lot as an ornamental tree in landscaping; we have ginkgoes on campus. You might also recognize that name as an herbal supplement - it's supposed to be good for brain function and memory.

The male portion - the stamen - produces microspores via meiosis.

This specifically occurs within the anthers at the tips of the stamen. Those microspores then develop into pollen grains (the male gametophytes) and are carried via wind or animal pollinators to the female portion of flowers - the carpel.

Pollen grains are mature male gametophytes surrounded by a protective coating of sporopollenin.

This structure will eventually produce sperm following a process called pollination. Pollination is the transfer of pollen to the ovule (which contains the megaspore). We'll talk more about this process later, but it is typically accomplished by wind or animal pollinators.

After fertilization, the ovule becomes a seed and the ovary develops into a fruit.

Those fruits protect the seeds and aid in their dispersal to new environments. When the seeds land in a suitable habitat, they can germinate into a new sporophyte plant.

Angiosperms

Two Major Groups -Monocots -Dicots

Like the ferns we discussed in the previous lecture, seed plants have vascular tissue and can thus grow larger and survive in drier habitats.

Unlike the ferns they produce both seeds and pollen, two structures that further decrease their dependence on water. All of the seed plants have several structures and characteristics in common: reduced gametophytes, heterospory, seeds, ovules and pollen.

Maypops are a type of passionflower native to our area. Bees are typical pollinators. On the maypop flower, the nectar is found in the center of the flower, where this bee is feeding. The stamen (which produce the pollen) are positioned so that the bee walks under them as it feeds, picking up pollen on it's back.

When the bee flies off to go visit another flower, it carries the pollen with it. As it lands on the new flower, some of the pollen is transferred to the stigma of the carpels.

Wind pollinated angiosperms are also common, but these plants typically have less conspicuous flowers. These are oak flowers, and corn is another good example. Since they don't need to attract animal pollinators, these flowers are less "showy".

Wind pollinated species produce a lot more pollen than those of animal pollinators, because they're relying on volume. Massive amounts of pollen must be produced to ensure that some of it lands where it's supposed to.

Like pollen, fruits can disperse via either wind or animals. Wind dispersed fruits often contain wing-like structures that make them light and helps facilitate their movement in air currents. Dandelions are a great example.

With animal dispersal, the fruits are often tasty/nutritious. That's why they are such a big part of our diet. They have adapted to being consumed by the animal. The seeds are either spit out during consumption, or they may travel through the digestive tract of the animal and be excreted as waste. Many seeds actually require a trip through an animal's gut in order to germinate!

At the base of the carpel is the ovary, which contains one or more ovules.

Within each ovule, meiosis occurs to produce a megaspore, which develops into the female gametophyte. Following pollination, the female gametophyte produces an egg.

There are many types of fruits. Simple fruits develop from single ovary. Aggregate fruits develop from single flower with many ovaries. Multiple fruits develop from ovaries of multiple flowers.

You don't need to remember these terms, I just wanted to give you an idea of their variation. All of them surround and protect seeds as well as aid in seed dispersal.

Eudicot

a clade of flowering plants mainly characterized by having two seed leaves upon germination.

Pollination

act of transferring pollen grains from the male anther of a flower to the female stigma.

Gymnosperms differ from angiosperms in that a. Do not produce pollen b. Do not produce fruits c. Do not produce spores d. Do not produce seeds

b. Do not produce fruits

Which of the following process does not take place on the female cone? a. Seed development b. Fertilization c. Microspore formation d. Egg development

c. Microspore formation

Carpel

contains a protective structure called an ovary, where the ovules are found. Meiosis occurs inside ovules, forming megaspores within megasporangia. Megaspores then divide by mitosis, forming female gametophytes.

The ovules of seed plants a. Contain the female gametophyte b. Contain the megaspores c. Contain the eggs d. All of the above

d. All of the above

Seed (Ovulate) cone

female cone contains ovules which, when fertilized by pollen, become seeds.

Gymnosperm

first seed plant to appear. "naked-seeds"

After fertilization, the ovule becomes a seed. Recall that seeds are composed of the diploid embryo, a food source and a protective coating.

g. Following fertilization of the egg within the ovule, the zygote develops into an embryo, the female gametophyte tissue become food supply, and the integument becomes seed coat (so the entire ovule structure develops into seed).

Monocot

have one cotyledon (vein).

Stamen

includes a structure called an anther, where micro-sporangia develop. Meiosis occurs inside the microsporangia, forming microspores. Microspores then divide by mitosis to form pollen grains (male gametophytes).

Double fertilization

involves two sperm cells; one fertilizes the egg cell to form the zygote, while the other fuses with the two polar nuclei that form the endosperm. After fertilization, the fertilized ovule forms the seed while the tissues of the ovary become the fruit.

Pollen cone

produces pollen, where the male sex cells are contained.

Flower

reproductive organ that the success of the plant in terms of geographical distribution, number of individuals, and number of species revolves around.

Seed Plants

•All heterosporous Microsporangia→Microspores→Male gametophyte→Sperm Macrosporangia→Megaspores→Female gametophyte→Eggs •Microscopic gametophytes dependent on sporophytes •Female gametophytes develop within ovule •Male gametophytes develops in pollen grain

Seed Plants

•Following pollination... -Pollen produces sperm which fertilize eggs w/n ovule •Following fertilization, ovule becomes a seed

Monocots

•Grasses, palms, irises, etc.

Seed Plants

•Gymnosperm -Ovules not enclosed within ovaries -Exposed, "naked" seeds •Angiosperms -Ovules enclosed within ovaries -Seeds enclosed within fruits -Flowering plants

Angiosperms

•Known as flowering plants -Flowers are reproductive organs •Ovules completed enclosed in ovary •Seeds enclosed within fruits

Angiosperms (Phylum Anthophyta)

•Largest modern plant group (>250,000 sp) •Diverse habitats, sizes, structures •All major food crops •Other products: medicines, clothing, aromatics, etc.

Ovules

•Megasporangium (and megaspore) surrounded by integument

Eudicots

•Oaks, roses, cacti, sunflowers, etc.

Conifers

•Pinophyta (pines, spruces, firs, etc) •Redwood group (redwoods, junipers, yews) •Woody plants with needle-like or scale-like leaves (usually evergreen)

Conifers

•Produce cones -Male cones produce microsporangia -Female cones produce megasporangia

Seed Plants

•Reduced gametophytes •Heterospory •Seeds •Ovules •Pollen

Seed Plants

•Seeds -2n embryo -Stored food -Seed coat •Seeds protect embryo

Flower Parts

•Stamen (male structure) -Pollen grains produced in anther •Carpel (female structure) -Contains ovary with one or more ovules

Pollination

•Transfer of pollen from stamen to carpel •Facilitated by wind, animals •Flower color, shape, scent adapted to type of pollinator

Fruit/Seed Dispersal

•Wind, animals

Fruit

a structure that is derived from the ovary and encloses one or more seeds.

Angiosperms were the last major group of plants to evolve but quickly came to dominate the landscape.

The evolution of flowers and fruits gave these plants an advantage that led to the adaptive radiation of this group.

Angiosperms produce seeds enclosed in fruits. The seeds develop from ovules and the fruits usually develop from a. ovaries b. female cones c. stamen d. stigma

a. ovaries

Ovary

protective structure a carpel contains.

Angiosperm

flowering plantfollowed with flowers and seeds contained in fruits which can aid in seed dispersal. "encased-seeds"

Endosperm

the part of a seed which acts as a food store for the developing plant embryo, usually containing starch with protein and other nutrients.