4.6 Billion Years Ago: the Earth Formed

PLANT KINGDOM

SEEDLESS PLANTS

I. Origin.

Earth Chronology:

4.6 billion years ago: the earth formed.

4-3.8 billion years ago: life originated.

3.8 billion years ago: prokaryote anaerobes, heterotrophs.

3.5 billion years ago: oldest known fossils: microfossils and stromatolites; photosynthesis.

2.5 billion years ago: photosynthesis established, oxygen accumulated.

1.5 billion years ago: first eukaryotes.

700 million years ago soft-bodies multicellular life.

540 million years ago hard-bodied multicellular life.

The colonization of land by plants probably occurred between 415 and 440 million years ago at the end of the Silurian.

In a relatively short time of about 50 million years, plant diversified abundantly and colonized many land areas.

Land plants probably are probably derived from a group of green algae called charophytes.

Land plants share with the green algae the following traits:

1. Chlorophyll a and b, xanthophylls (yellow carotenoids) and carotenes (orange carotenoids).
2. Store carbohydrates in the form of starch.
3. Cell wall made mostly of cellulose.
4. Details of the formation of the cell plate.
5. DNA and RNA sequences support their close relation to the charophytes.

I. CHARACTERISTICS

1. Multicellular eukaryotes that are photosynthetic autotrophs.

• Chloroplasts

• Chlorophyll a and b.
• Accessory pigments: carotenes and xanthophylls

1. Cell wall made of cellulose, a glucose polymer.

1. Store food in plastids in the form of starch.

1. Alternation of generations.

1. Formation of cell plate during cytokinesis.

Evolutionary trend towards a larger sporophyte generation and a reduced gametophyte generation.

Bryophytes, Seedless Vascular Plants, Gymnosperms, Angiosperms.

II. ADAPTATIONS TO A TERRESTRIAL ENVIRONMENT.

1. Waxy cuticle to protect against desiccation.

1. Stomata for gas exchange and control of transpiration.

1. Multicellular gametangia made of a layer of sterile cells to protect gametes:

• Antheridia produce sperms.

• Archegonia produce eggs.

1. After fertilization, the egg develops into a multicellular embryo within the archegonium.

1. Cell wall contains lignin, a polymer, to strengthen and support upright structures.

1. Transport system or vascular tissue:

• Phloem for the transport of dissolved carbohydrates.
• Xylem for water and mineral transport.

Land plants can be grouped into four groups (non-taxonomic): bryophytes, seedless plants, gymnosperms and flowering plants.

III. ALTERNATION OF GENERATIONS.

A life cycle characterized by a multicellular haploid gametophyte stage followed by a multicellular diploid sporophyte stage.

• Gametophyte (n) produces haploid gametes (n).
• Gametes fuse to form a diploid zygote, the new sporophyte (2n).
• Embryo of the sporophyte (2n) develops in the archegonium of the gametophyte (n).
• Sporophyte (2n) produces spores through meiosis.
• Spores (n) are the first stage of the gametophyte generation (n).

BRYOPHYTES

About 15,000 species worldwide divided into three Divisions: mosses, liverworts and hornworts.

Their life cycle is similar but the three groups may not be closely related.

I. CHARACTERISTICS

1. Small plants found in moist environments, lack woody tissue and usually form mats spread over the ground.

1. Gametophyte generation is dominant; sporophyte is parasitic on the gametophyte.

1. Bryophytes have cuticle, stomata and multicellular gametangia that allow them to survive on land.

1. Bryophytes need water to reproduce and most species lack vascular tissue (xylem and phloem).

1. Water transport is mostly through capillary action, diffusion and cytoplasmic streaming.

II. MOSSES

Gametophyte is a "leafy" plant.

Live in dense colonies forming mats on the ground, rocks, walls, tree trunks, etc.

Lack true roots, stems and leaves.

Rhizoids attach the gametophyte to the substrate.

Some species have water and sugar conducting cells but they lack true xylem and phloem.

The sperm must swim from the antheridium to the archegonium.

III. LIVERWORTS AND HORNWORTS

Liverwort gametophyte can be leafy or thalloid.

Liverworts can reproduce asexually by gemmae, small bundles of cells produced in cup-like structure.

Hornwort gametophytes are all thalloid. The sporophyte is horn-shaped and parasitic on the gametophyte.

Hornworts have a single large chloroplast in their cells.

IV. EVOLUTION.

The evolutionary origin of the bryophytes is obscure.

They do not seem to be in direct line with the vascular plants and might have evolved from a group o green algae.

Alternatively, they may have evolved from early vascular plants by becoming simpler in their anatomy by losing their vascular tissue.

FERNS AND FERN ALLIES.

Also known as pteridophytes, they first appeared about 400 million years ago.

I. CHARACTERISTICS

1. Ferns and fern allies have vascular tissue made of xylem and phloem; they posses true roots, stems (rhizomes) and leaves (megaphylls).

1. The sporophyte is the dominant generation.

1. Gametophyte (prothallus) and sporophyte generations are photosynthetic and independent of one another.

1. All species need water for reproduction; the sperm must swim from the antheridium to the archegonium.

1. Branching is dichotomous.

The Telome Theory attempts to explain the production of megaphylls in vascular plants: evolved from a branch system.

In contrast, microphylls are considered to have evolved from small projections of the stem. They are scale-like projection with a single vein.

II. FERNS

About 14,000 extant species. Many species are extinct.

Sporangia are often produced in clusters called sori (sing. sorus).

Ferns are valuable ornamentals. Azolla, an aquatic fern, is an important fertilizer in the cultivation of rice.

• associated to Anabaena, a nitrogen fixing cyanobacteria.

III. FERN ALLIES

Whiskfern sporophytes consist of a rhizome with rhizoids, and upright branches; they lack true leaves and roots.

Horsetails have true roots, stems and leaves. The stems are hollow. Their epidermal cells are impregnated with silica.

Horsetails were the dominant plants about 300 million years. They were among the main contributors to the formation of coal, gas and petroleum (fossil fuels).

The sporophytes of clubmosses consist of true roots, stems and leaves (microphylls).

Some clubmosses (Selaginella) are heterosporous; Lycopodium is homosporous.

• Homospory: production of one kind of spores.

• Heterospory: production of two kinds of spores.

-Haploid megaspores develop into a female gametophyte.

-Haploid microspores develop into a male gametophyte.

The sporangia of horsetails and clubmosses are arranged into an elongated conical structure called strobilus (pl. strobili).

Seedless vascular plants arose about 420 million years ago in the mid-Silurian.

Coal formed from the remains of horsetails, ferns and other seedless plants that lived during the Carboniferous, about 300 million years ago.

The sporangia of horsetails and clubmosses are arranged into an elongated conical structure called strobilus (pl. strobili).

Chapter 27SEED PLANTS

SEED SPORE

1. Multicellular embryoSingle cell

1. Food supplied by tissueFood only in the cell

1. Multicellular seed coatCovering not cellular

1. Diploid sporophyteHaploid cell

1. Product of fertilizationProduct of meiosis

There are two groups of seed producing plants, gymnosperms and angiosperms.

• Produce seeds.

• Vascular tissue: xylem for water and mineral transport and phloem for dissolved sugars.

• Gametophyte is very reduced and totally dependent on the sporophyte.

• Heterosporous: microspores and megaspores.

GYMNOSPERMS

There are about 720 species found in all terrestrial habitats grouped into four divisions (phyla).

They have great economic importance: lumber, paper, chemicals.

I. CHARACTERISTICS OF GYMNOSPERMS

1. Woody trees and shrubs.

1. Xylem made of tracheids.

1. Seeds are borne, exposed, in cones (megastrobilus).

1. Pollinated by wind, seldom by insects.

1. Single fertilization: sperm + egg  embryo.

1. Most are monoecious: male and female organs on the same individual.

II. CONIPHEROPHYTA or conifers

There are about 550 species of conifers.

Many conifers produce resin, a complex mixture of organic compounds that protect the plant from insect and fungal attack.

• Resin is stored in resin ducts in the roots, stem, leaves and cones,

Cone bearing gymnosperms, e. g. pines, firs, cypresses, etc.

Leaves are needles or scale-like, rarely broad; venation is parallel and open.

A male cone is called microstrobilus, and contains the microsporangia that produce microspores through meiosis that will develop into microgametophytes (pollen grains).

The female cone is called the megastrobilus, which produce megasporangia in each of which a megaspore is produced through meiosis and will develop one megagametophyte. An egg will form within the megagametophyte.

Pollination is by wind.

Note:Study the life cycle of pine and learn the terminology. Pages 572 - 574.

III. CYCADOPHYTA or cycads

Important in the Triassic (248-213 m .y. a), which is called sometimes the Age of Cycads .

Most species are extinct. There are about 140 living species in tropical and subtropical parts of the world.

Cycads are palm or fern-like plants with compound leaves and simple seed cones.

The aredioecious: plants are either male or female.

They have a very large motile sperm within the pollen grain but do not need water for pollen transport.

Pollination is by air and in some cases by ants.

IV. GINKGOPHYTA or ginkgoes

There is a single species of ginkgo alive today. It is native to China where it has been under cultivation for centuries. It has been found in the wild in only two locations.

Ginkgoes are dioecious and have flagellated sperms.

Pollination is by air and seeds are borne exposed rather than in cones.

It is commonly planted in American cities because it is very resistant to pollution.

V. GNETOPHYTA

The gnetophytes consists of three genera and about 70 species.

A group of rare plants that share some traits with angiosperms.

• Efficient water conducting cells in the xylem called vessel elements.
• Reproductive structures resemble flowers.

ANGIOSPERMS

There are about 235,000 species of flowering plants.

This is the dominant group in terrestrial habitats. Our survival depends on them.

• food, medicine, lumber, etc.

There are two groups of angiosperms: monocots and dicots.

First appeared in the Cretaceous about 130 million years ago.

I. CHARACTERISTICS

1. Woody or herbaceous.

1. Xylem elements have vessel elements and tracheids.

1. Produce flowers.

1. Pollinated by wind or animals.

1. Double fertilization: egg + sperm  embryo and 2 polar nuclei + sperm  endosperm.

1. Seeds enclosed in a fruit.

MONOCOTS have floral parts in multiples of three and the seed contains one cotyledon. The endosperm provides the food for the embryo. Venation is usually parallel (there are exceptions). Their vascular bundles are scattered throughout the ground tissue. The root system is fibrous.

DICOTS have floral parts in multiples of four or five, and their seeds contain two cotyledons. The cotyledons usually absorb the food from the endosperm first, and then provide the food for the embryo. Venation is netted. The vascular bundles in the stem cross-section are arranged in circles (rings). They usually have a taproot system for at leas part of their life.

II. THE FLOWER

The flower is a reproductive shoot or branch.

It has four parts arranged in whorls or circles on a stalk or peduncle.

The parts of the flower are the sepals (calyx), petals (corolla), stamens and carpels.

• Stamens consist of a filament and an anther.

• Carpels are also referred to as pistils. They consist of an ovary, a style and a stigma.

Flowers may be borne singly or in clusters called inflorescence.

Flower parts are considered modified leaves.

Flowers may be ...

• Complete if has the four parts or incomplete if it lacks one of the parts.
• Perfect if it has both stamens and carpels or imperfect if it lacks one of them.

See figure 27-10, page 579, for additional details of the floral structure.

III. DOUBLE FERTILIZATION.

It is characteristic of flowering plants.

Double fertilization results in the formation of a diploid zygote and a triploid endosperm.

The female gametophyte or embryo sac has an egg nucleus and two polar nuclei.

One sperm fertilizes the egg nucleus and forms the zygote, 2n.

Another sperm joins the two polar nuclei forming the triploid (3n) nutritive tissue called the endosperm.

See figure 27-12, page 581, for details.

Seeds develop from the ovule following fertilization.

The ovary enlarges and forms the fruit.

In some instances other tissues also enlarge and become part of the fruit.

Fruits serve two purposes: protect the seed and aid in dispersal of the seeds.

EVOLUTION OF SEED PLANTS

Progymnosperms appeared about 375 million years ago in the Devonian.

• they reproduced by spores.
• hadmegaphylls.
• woody tissue of secondary xylem similar to modern gymnosperms.

Their reproductive structures appear to be intermediate between those of spore producing plants and seed plants.

conifers

Progymnosperms

seed ferns  cycads and possibly ginkgoes

Seed producing plants appeared in the Devonian, about 360 m. y. a.

By the end of Jurassic, 180 million years ago, several lines of gymnosperms existed with features that resembled those of flowering plants.

Different groups of seed plants apparently appeared independently several times.

Angiosperms probably arose from ancient gymnosperms. They must have been dicots, which then gave rise to monocots.

The oldest fossil record of angiosperms is pollen from the Cretaceous, about 130 m. y. a.

The oldest flower fossil is 120 m.y.a.

By late Cretaceous angiosperms had began to replace gymnosperms as the dominant group of land plants.

Many angiosperm species apparently arose from changes in chromosome number.

COMPARISON OF GYMNOSPERMS AND ANGIOSPERMS.

GYMNOSPERMSANGIOSPERMS

GROWTH HABITwoody trees and shrubswoody or herbaceous

XYLEM CELLStracheidsvessel elements and

tracheids

REPRODUCTIVE

STRUCTURESusually conesflowers

POLLEN TRANSFERwindanimals, wind, water.

FERTILIZATIONegg + sperm = zygotedouble fertilization

SEEDSexposed, borne on scalesenclosed in the ovary (fruit)

Chapter 28KINGDOM ANIMALIA

CHARACTERISTICS

The following characteristics describe most animals:

1. Diploid multicellular eukaryotes.

1. Cells are specialized and organized into tissues, organs, etc.

1. Heterotrophs that inhabit the sea, fresh water and land.

1. Most are capable of locomotion at some stage of their lives.

1. Most can respond adaptively to external stimuli and have well developed sense organs and nervous system.

1. Most reproduce sexually, with large non-motile eggs and small flagellated sperms.

1. The diploid zygote produced by fertilization divides by mitotic divisions, resulting in a ball of cells that usually hollows out to become a blastula. Sponges are an exception.

About 35 phyla the majority of which are invertebrates.

CLASSIFICATION

Based on type of …

1. Body cavity: acoelomate, pseudocoelomates, coelomates.
2. Developmental pattern: protostomes, deuterostomes.
3. Body symmetry: radial, bilateral.

Types of sectioning a specimen:

• Sagittal section divides the body into right and left parts.
• Cross or transverse section divides the body into anterior and posterior parts.
• Frontal section divides the body into dorsal and ventral parts.

Coelom or body cavity is fluid-filled space located between the outer body wall and the digestive tube.

Germ layers:

• Endoderm forms the lining of the digestive tract.
• Mesoderm forms most body structures: muscles, bones, etc.
• Ectoderm gives rise to the outer covering of the body and the nervous system (if present).

Diploblastic animals (cnidarians and ctenophores) have two germ layers.

Triploblastic animals have three germ layers.

Animals may be...

• Acoelomate: lack coelom or body cavity, e.g. cnidarians, ctenophores, flatworms..
• Pseudocoelomate: coelom is partially lined with mesoderm, e.g. roundworms, rotifers..
• Coelomate: coelom is completely lined with mesoderm.

Animals can be classified as protostomes if the blastopore develops into the mouth and deuterostomes if it develops into the anus.

Deuterostomes and protostomes have different pattern of cleavage:

• Radial cleavage is characteristic of deuterostomes;
• Spiral cleavage is followed by protostomes.

Protostomes also have a determinate cleavage in which the fate of the embryonic cells is fixed very early in development.

Deuterostomes have an indeterminate cleavage in which each cell keeps longer the capacity to develop into a full organism.

Schizocoely method of coelom formation is characteristic of protostomes.

Deuterostomes follow the enterocoely pattern of coelom formation.

PHYLUM PORIFERA

1. Multicellular; body a loose aggregation of cells of mesenchymal origin.

2. Body with pores (ostia), canals, and chambers that serve for passage of water to the central cavity (spongocoel), and out of the open end, the osculum.

3. About 9,000 species have been identified; all are aquatic and mostly marine.

4. Symmetry radial or none.

5. Epidermis of flat pinacocytes; most interior surfaces lined with flagellated collar cells (choanocytes) that create water currents; a gelatinous protein matrix called mesohyl, which contains amebocytes, collencytes (secrete collagen), and skeletal elements (spicules).

6. Skeletal structure of calcareous (Class Calcarea) or siliceous crystalline spicules (Class Hexactinellida), or fibrillar collagen, a protein, and often combined with variously modified collagen (spongin) fibrils (Class Demospongiae).

7. No organs or true tissues; cells form a loose association but there is division of labor; digestion intracellular; excretion and respiration by diffusion.

8. Reactions to stimuli apparently local and independent; nervous system probably absent.

9. All adults sessile and attached to substratum.

10. Asexual reproduction by buds or gemmules and sexual reproduction by eggs and sperm; most are hermaphroditic; free-swimming ciliated larvae.

PHYLUM CNIDARIA

1. Entirely aquatic; some in fresh water but mostly marine. About 10,000 species.

2. Radial symmetry or biradial (radial and bilateral) symmetry around a longitudinal axis with oral and aboral ends; no definite head.

3. Two basic body forms: polyp and medusa.

4. Exoskeleton or endoskeleton of chitinous, calcareous, or protein components in some.

5. Body with two layers, epidermis and gastrodermis; with mesoglea (diploblastic); mesoglea with cells and connective tissue in some (triploblastic).

6. Gastrovascular cavity or coelenteron (often branched or divided with septa) with a single opening that serves as both mouth and anus; extensible tentacles usually encircling the mouth or oral region.