Kingdom Plantae,

Continued

Sexualsperm + egg zygote

Asexualspores and runners

(man can use grafts and cuttings)

Alternation Of Generations

All plants have a life cycle thatinvolves two alternating stages- a

diploid,(2n), sporophyte stage and a

haploid, (1n), gametophyte__ stage.

1n = means it has half the usual chromosome number2n = means it has the full chromosome number

Moss and Ferns have similar life cycles, yet there are a few

differences.

 *are small, low-lying, (generally) moisture-loving plants*have no roots, only filamentous rhizoids (so, they are a good example of a NONVASCULAR plant.).  The dominant generation is the 1n gametophyte. The 2n sporophyte is actually parasitic on the gametophyte.

* Needs water for sexual reproduction; sperm must swim to egg

MOSS MOVIE

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

sporophyte (2n)       

gametophyte (n)

Pterophyta (Ferns)

About 97% of living seedless, vascular plants are ferns. In fact, there are probably about 12,000 species of ferns in the world, most of these are found in the tropics. The ferns are highly successful and are virtually found in any habitat flowering plants are found. 

Ferns   In ferns, as in other seedless, vascular plants, the sporophyte is the dominant generation. The gametophyte is short-lived, a few mm in size, and virtually hidden from view. 

Two features of ferns especially stand out:   

Large, typically pinnate, leaves - often termed fronds.     

The protective coiling of young fern leaves into a spiral like ashepherd's crook or a

fiddle head.  

  Ferns typically have a horizontal

(often underground) stem or rhizome, swollen with food reserves, from which the leavesand roots arise.

Some ferns, rather than having spores on the underside of all of their leaflets, have separate specialized spore-bearing (fertile) leaflets and separate photosynthetic, sterile leaflets. A Caribbean example of this is the "flowering fern", Anemia adiantifolia, shown at right.

FERN MOVIE

QuickTime™ and aSorenson Video decompressorare needed to see this picture.

Similarities =

1. The gametophyte stage produces an egg and sperm through a type of cell division called mitosis.

2. An egg and sperm unite to form a zygote which develops into a sporophyte.

3. Moisture is needed in order for the sperm to swim to the egg to fertilize it.

4. The sporophyte stage produces spores through a type of cell division called meiosis.

Main difference = The gametophyte stage in

the moss is much larger than its sporophyte stage. While in the fern, the

sporophyte stage is so large that

it crushes the gametophyte (which is only10 mm, one-

half of an inch) as it grows.

Seed Plants

Gymnosperms - cone producers

Angiosperms - flower and fruit producers

The Gymnosperms include the oldest and largest trees known.

The Bristle Cone Pines, some over 4000 years old are the oldest living plants. The Giant Redwoods are over 100 m tall - the tallest plants known. Both are native to California. 

Cycads (A type of gymnosperm)Gymnosperms are Cone producers.   Their seeds are considered to be “naked” or not protected by a fruit.

The cycads are ancient gymnosperms which were at their peak in the Jurassic Period, the "Age of the Dinosaurs", about 150 million years ago.

Phylum Coniferophyta(The Conifers)  The conifers form the dominant climax vegetation in cold regions. They have a world wide economic importance as a source of timber and pulp for paper. 

Conifer features  Their leaves are simple (not-pinnate), highly-reduced, and generally evergreen = needles. 

Male & female reproductive organs borne in cones (conifer means bearing cones) 

Male reproductive organs    

The male cone or microstrobilus contains the pollen. The pollen contains the microgametophytes (the “sperm). 

  Male cones are short-lived, shedding their pollen in the spring, then withering and dying. Female cones are long-lived. 

Female reproductive organs  

The female cone (megastrobilus) is a spiral cluster of scales each bearing 2 ovules (megagametophytes). The ovules are exposed to the air.

1st year female pine cones 2nd year immature female pine cones 2nd year mature female pine cones

There is a period of 1 year between pollination and fertilization and up to a further year before maturation and release of the seed.

Flowering PlantsThe flowering plants or Angiosperms emerged in the Cretaceous period, some 130 million years ago. Angiosperm means "contained seeds”The ovules, which after fertilization mature into seeds, are found and protected within structures called carpelswithin the ovary of the flower. So, unlike the previous seed plants examined, the ovules are protected withinthese carpels and the seeds later sealed within a fruit. 

 So, a fruit is the ripened ovary of a flower!!!!!!

(see handout on “Life Cycle of an Angiosperm”)

And, a flower is nothing more than a cluster ofgamete-bearing leaves surrounded by whorls of  protective and often very beautiful leaves. 

Fruit -   Remember, a fruit is the ripened ovary of a flowerwhich contains the developing seeds (fertilized ovules). The botanist's definition of a fruit often differs from the lay person's. Fruit are not necessarily sweet and juicy. They can be dry and woody. Tomatoes and cucumbers are fruits even if to the average person they are vegetables.

Incompatibility mechanisms -  A pollen tube must grow through the carpel to get to the ovule (unfertilized egg). As a result, a range of incompatibility mechanisms have evolved to control what pollen grain is allowed to germinate on the stigma, what pollen tubes are permitted to grow through the style, and ultimately what male gamete will fuse with the egg.

Unique double fertilization -  One sperm fuses with the egg to form the zygote which develops into a miniature plant, the embryo. A second sperm (“male” nucleus) fuses with two polar nuclei to form a triploid endosperm (orange at right) which develops simply as a food reserve for the developing embryo (red at right). [Coconut water is actually a liquid endosperm which helps to feed the young embryo in the coconut fruit!]  

In summary, Angiosperms:

Like all seed plants, the sporophyte is the dominant generation.and the gametophyte has been internalized (endospory).

The complete enclosure of the ovules by the carpels has led to the evolution of mechanisms which prevent certain types ofpollen access to the ovules. 

Double fertilization, in which both male gametes in the pollentube are functional, is unique to the Angiosperms.

The further development of the ovary of the flower to produce a structure to aid in the dispersal of the seed(s) - the fruit -is also unique to Angiosperms.

More on those Angiosperms

Phylum - Anthophyta

Class Monocotyledones

Class Dicotyledones

The Monocot-Dicot Divide

All (well, the vast majority of!) flowering plants fall neatly into two categories - the Monocotyledons and the Dicotyledons. These names come from the number of seed leaves or cotyledons (1 or 2) on the embryo in the seed but there are other major differences:   Monocotyledons DicotyledonsFlower parts in 3's or multiples of 3 Flower parts not usually in 3's

or multiples of 3Leaves parallel-veined Leaves net-veinedStem vascular bundles scattered Stem vascular bundles in a ringNo secondary growth - no true trees! Secondary growth - many woody plantsFibrous rooted Tap-rooted

 

Corn Sunflower

Cotyledon - seed leaf in a plant

embryo

Monocots - 1 cotyledon, flower part in 3’s

Dicots - 2 cotyledons, flower parts in 4’s or 5’s