Parade through the Plants

Chapter 29 and 30

What is a plant?

• Multicelled• Eukaryotic• Autotrophic• Cell wall made of cellulose• Additional Characteristics– Cuticle– Stomata– Secondary products (poisons, lignin, sporopollenin)– Starch storage

The Four Phyla• Bryophyta – mosses

– nonvascular• Pterophyta – ferns

– Vascular– Seedless

• Gymnosperm – conifers– Vascular– “Naked” seeds – not

enclosed in an ovary• Angiosperm – flowering

plants– Vascular– Seeds contained in fruits –

a mature ovaryPlant kingdom in monophyletic (derived from a common ancestor)

Gametophyte generation becomes reduced

Sperm goes from flagellated to pollen

Vascular plants

Origin of the seed

Emergence of flowering plants

Why are Charophyceans thought to be ancestors of land plants?

1. Homologous Chloroplasts

2. Biochemical similarity

3. Similarity in the mechanisms of mitosis and meiosis

4. Similarity in sperm structure

5. Genetic relationship (rRNA)

*** Modern Charophytes are not the ancestors of plants. Evidence shows that the modern Charophytes and plants both evolved from a common ancestor that would be classified as a Charophyte.

Adaptations of land plants (aka “embryophytes)

• Deal with drying out, UV light and reproduction without water– Lignin– Sporopollenin– Reduced gametophyte– Gametangia– Apical meristem– Seeds– Pollen grain– Vascular tissue (xylem/phloem)

One generation is a Gametophyte (n) – multicelled individual made of haploid cells

-- produces gametangia by mitosis…gametes within the gametangia are protected by a jacket of “sterile” cells (protects gametes and embryos).

Antheridia – male gametangia…produces spermArchegonia – female gametangia…produces egg

One generation is a Sporophyte (2n) – multicelled individual made of diploid cells

-- produce haploid “spores” via meiosis

-- spores divide via mitosis to produce gametophyte

Antheridia

Sterile cells

Sperm

Archegonia

Sterile cells

Egg

Bryophytes

• Nonvascular• Gametophyte is the dominant stage of life cycle• Need water to reproduce• Lack lignin-fortified tissue

Gametophyte generation is dominant generation

sporophyte is smaller and short lived. Depends on the gametophyte for water and nutrients

Diploid sporophyte produces haploid spores via meiosis in a structure called a sporangium

Adaptations of Pteridophytes (ferns) not seen in Bryophytes

1. Subterranean root system (Bryophytes had rhizoids)

2. Stems

3. Leaves

4. Vascular Tissue

a. Xylem – water, minerals up (dead cells)

b. Phloem – sugars, amino acids throughout (living cells)

5. Lignin

a. function in mechanical support

b. Xylem also has lignified cells

Dominant phase of the fern life cycle is the sporophyte phase.

How is the reduced gametophyte an adaptation for seed plants? Spores are retained within the sporangia (not released) Gameotphyte develops within the wall of the spore Exposed to sun’s UV rays (mutations) – diploid can handle mutations more easily than haploids. Sporophyte embryo is dependent on tissues of the maternal gametophyte

Why not completely eliminate the gametophyte generation?

Cooksonia – oldest fossilized vascular plant preserved down to the tissue – sporophyte was dominant stage and it was branched.

What is the significance of the seed? The seed replaced the spore as the main means of dispersing offspring

• Multicelled

• Sporophyte embryo packaged with food and protective coat (can withstand more harsh environments)

• Can disperse offspring more widely

• All seed plants are heterosporous

• Megasporangium is a solid fleshy structure called the nucellus

• Integuments envelop megasporangium

• Megaspores

• Female gametophyte develops within the wall of the megaspore nourished by nucellus. This contains the egg.

Ovule

What is the advantage of pollen?

Pollen grain = Male gametophyte (became vehicles for sperm cells in seed plants)

• Microspores develop into pollen grains which mature to be male gametophytes (protected by sporopollenin

• If it lands close to the ovule, it elongates a tube that discharges one or more sperm into the female gametophyte within the ovule.

• Mode of travel different than water

Four Phyla of Gymnosperms

1. Phylum Cycadophyta (thrived with the dinosaurs)

2. Phylum Ginkgophyta (Ginko biloba is the only surviving species)

3. Phylum Gnetophyta

4. Phylum Coniferophyta – most common

Adaptive value of the flower to plants:

Pollination more specific (rely more on insects and other animals to transfer pollen, not just wind)

Fruits (mature ovaries) protect dormant seeds and aid in their dispersal.

Role of Ovaries and Ovules – the wall of the ovary thickens when an egg (ovule) is fertilized. This is the “fruit.” The seeds are fertilized ovules.

Examples: pea pods, apples, oranges

Features that aid in seed dispersalparachutes or propellers (wind)hollow inside (coconut) so it floatsBurrs to cling to fur (animal dispersal)Edible (animal disperal)

Moss

A Fern

Gymnosperm

Angiosperm