Biological Science Chapter 31: Green Algae and Plants

Green plants

Consist of green algae and land plants.

Green algae

Important photosynthetic organisms in freshwater habitats.
Are unicellular, colonial, or multicellular and live in marine, freshwater, or moist terrestrial habitats.
Traditionally considered protists, but we study them with land plants because:
1. They ar

Land Plants

Key photosynthesizers in terrestrial environments. The first organisms that could thrive with their tissues completely exposed to the air. Before they evolved, terrestrial life was limited to bacteria, archaea, and single-celled protists.
The key to the c

Ecosystem

Consists of all the organisms in a particular area and nonliving physical components of the environment, i.e. the atmosphere, precipitation, surface water, sunlight, soil, and nutrients.

Ecosystem Services

The enhancement of life-supporting attributes of the physical, nonliving components of an ecosystem. Green plants alter the environment in ways that benefit many other organisms.
Ecosystem services provided by green algae and land plants include:
1. Produ

Primary Producers

Land plants are these in terrestrial ecosystems. They convert solar energy (sunlight) into chemical energy (sugars). The sugars produced by land plants support virtually all other organisms in terrestrial habitats.

Herbivores

Plant eaters

Carnivores

Meat eaters

Omnivores

Eat both plants and animals

Artificial Selection

Led to dramatic changes in plant characteristics. We choose the way we want to domesticate the plants/crops we grow.

Fossil Fuels

i.e. coal, petroleum, natural gas; derived from plants (living or long deceased).

Bryophytes

Nonvascular Plants: lack vascular tissue, or specialized groups of cells that conduct water or dissolved nutrients throughout the plant body, i.e. mosses

Vascular Tissue

Specialized groups of cells that conduct water or dissolve nutrients throughout the plant body.

Seedless Vascular Plants

Have well-developed vascular tissue, do not make seeds, make microscopic spores for reproduction, i.e. ferns.

Seed Plants

Have vascular tissue and make seeds, i.e. angiosperms.

Seeds

Consist of an embryo and a store of nutritive tissue, surrounded by a tough protective layer.

Angiosperms

Flowering plants

Using the Fossil Record

The fossil record for green algae begins 700-725 MYA while the fossil record for land plants begins about 475 MYA. This supports the hypothesis that land plants are derived from green algae. The fossil record for plants is massive and there have been 5 ma

Origin of Land Plants

Most of the earliest plant fossils are microscopic. These early plant fossils have reproductive cells (spores) and sheets of waxy coating (cuticles).

Spores

Reproductive cells

Characteristics of Early Land Plants

Support the hypothesis that they grew on land:
1. The cuticle is a watertight barrier that prevents desiccation.
2. The spores are surrounded by a sheetlike coating (almost identical to the protective sporopollenin that encases spores and pollen in modern

Sporangia

Spore-producing structures.

Sporopollenin

Encases spores and pollen in modern land plants.

Silurian-Devonian Explosion

In rocks dated 416-359 MYA, biologists find fossils from most of the major plant lineages. Virtually all of the adaptations that allow plants to occupy dry, terrestrial habitats are present, including: water-conducting vascular tissue, roots, stomata, and

Carboniferous Period

Extensive deposits of coal were found in sediments dated from about 355-299 mya. Coal is a carbon-rich rock packed with fossil spores, branches, leaves, and tree trunks. Most of the fossils are derived from seedless vascular plants.
Coal formation is thou

Gymnosperms

Prominent in the fossil record from 299 mya to 145 mya.
5 major gymnosperms are living today:
1. Ginkgoes
2. Cycads
3. Redwoods, junipers, and yews
4. Pines, spruces, and firs
5. Gnetophytes
Grow readily in dry habitats. Both wet and dry environments prob

Diversification of Angiosperms

The first flowering plants in the fossil record appear about 150 mya and continue to diversify today. These plants that produced the first flowers.

Molecular Phylogenies

Green plants are monophyletic: a single common ancestor gave rise to all the green algae and plants.
Green algae are paraphyletic: the green algae include some but not all of the descendants of a single common ancestor.
Charophyceae are the closest living

Cuticle

A watertight sealant that covers the aboveground parts of the plant and gives them the ability to survive in dry environments.
However, it is a physical barrier, so it also keeps necessary CO2 out of the plant.

Stoma

Consists of an opening called a pore surrounded by specialized guard cells. The pore opens and closes are the guard cells change shape. Gas exchange is accomplished through the pore.
They are present in all land plants except liverworts, which have pores

Tracheids

Long, thin, tapering, water-conducting cells.
Have a thickened, lignin-containing secondary cell wall in addition to a cellulose-based primary cell wall.
Have pits in the sides and ends of the cell, which allow water to flow efficiently between tracheids.

Vessel Elements

The most specialized type of water-conducting cell, appeared about 250-270 mya.
1. Are shorter and wider than tracheids.
2. Have gaps on both ends where cell walls are missing.
These characteristics reduce resistance and make water movement extremely effi

Gemetangia

Specialized reproductive organs that protected gametes from drying and damage. All living land plant groups except angiosperms still have these.
They are distinctive: male and female.

Antheridium

Like animal testes; specialized male reproductive structure.

Archegonia

Like animal ovaries; specialized female reproductive structure. Eggs form here.

Zygotes of Land Plants

Begin development on the parent plant. Form multicellular embryos that remain attached to and can be nourished by the parental plant.

Embryophyta

Embryo-plants." Plants that retain embryos.

Gametophyte

A multicellular haploid phase.

Sporophyte

A multicellular diploid phase.

Alternation of Generations

Always the same sequence of events:
1. The sporophyte produces haploid spores by meiosis.
2. Spores germinate and divide by mitosis and develop into multicellular, haploid gametophytes.
3. Gametophytes produce unicellular haploid gametes by mitosis.
4. Tw

Zygotes versus Spores

1. Both are single cells
2. Both divide by mitosis to form multicellular individuals (zygotes develop into sporophytes/spores develop into gametophytes).
3. Zygotes are diploid; spores are haploid.
4. Only zygotes are formed by the fusion of gametes.
5. S

Heterospory

The production of two distinct types of spores by different structures.

Homosporous

Produce a single type of spore. All spores develop into a bisexual gametophyte that produces both eggs and sperm. These can self-fertilize and produce offspring.
All of the nonvascular plants and most of the seedless vascular plants.
Sporangium -> Spores

Microsporangia

Produce microspores the develop into male gametophytes which produce sperm.
Microsporangia -> microspores -> male gametophyte -> sperm.

Macrosporangia

Produce megaspores that develop into female gametophytes, which produce eggs.
Megasporangia -> megaspores -> female gametophyte -> eggs.

Pollen Grain

Tiny male gametophytes that are surrounded by a tough coat of sporopollenin. Allowed land plants living in dry habitats to reproduce efficiently.
Can be exposed to the air for long periods of time without drying out. Can be carried to the female gametophy

Seed

A structure that includes an embryo and a store of nutrients provided by the mother and surrounded by a tough, protective coat. They allow embryos to be dispersed (often by wind, water, or animals) to a new habitat, away from the parent plant.
The evoluti

Flowers

Or angiosperms, the most diverse land plants living today. About 250,000 species have been described and more are discovered each year.

Stamen

Reproductive structure of flowers. Contains the anther, where microsporangia develop.

Anther

Where microsporangia develop

Carpel

Contains the ovary where the ovules are found.

Ovary

Where ovules are found; protects the female gametophyte.

Ovules

Contain the megasporangia

Angiosperm Fertilization

Unique because it involves two sperm cells:
1. One sperm fuses with the egg to form the diploid (2n) zygotes
2. A second sperm fuses with two nuclei in the female gametophyte to form a triploid (3n) nutritive tissue called endosperm.

Endosperm

A triploid (3n) nutritive tissue

Pollination

The transfer of pollen from one individual's stamen to another individual's carpel.

Directed-Pollination Hypothesis

Natural selection favored structures that reward an animal for carrying pollen directly from one flower to another. Flowers attract pollinators by providing them with food: either protein-rich pollen or sugar-rich nectar.

Pollination Syndroms

When the characteristics of a flower correlate with its pollinator, i.e. scent: the carrion flower produces molecules that smell like rotting flesh, which attracts carrion flies. These flies collect and distribute pollen while looking for a place to lay t

Fruits

A structure that is derived from the ovary and encloses one or more seeds. Tissues derived from the ovary are often nutritious and brightly colored. While the evolution of flowers made efficient pollination possible, the evolution of fruit made efficient

Adaptive Radiation

Occurs when a single lineage produces a large number of descendant species that are adapted to a wide variety of habitats, i.e. angiosperms.

Cotyledons

First leaves; store nutrients and provide them to the embryo.

Monocots

One cotyledon; a monophyletic group.

Dicots

Two cotyledons; a paraphyletic group (eudicots).

Lichens

Stable associations between green algae or cyanobacteria and fungi.
Often found in terrestrial environments that lack soil. Approximately 85% of the 17,000 species of lichens involve green algae.