Biology 2; Exam 3; Plants

How much land do Bryophyta cover?

Mosses cover about 3% of the land surface

Are plants sexual or asexual?

Most plants reproduce sexually, and most are also capable of asexual propagation.

What does Chemical adaptations include?

Secretion of a waxy cuticle, a coating on the surface of plants that helps prevent desiccation.

Megaspores

Develop into female gametophytes possessing archegonia (female).

Bryophytes

(Non-Vascular Plants) A. The embryophyte = (Land plants) adaptation evolved in bryophytes B. The gametophyte is the dominant generation in the life cycles of bryophytes C. The three groups of bryophytes are mosses, liverworts, and hornworts

Embryophytes

(embryo/plant) Emphasizing this terrestrial adaptation, plants.

Alternation of Generation

All plants have life cycles Also occurs in some groups of algae.

Microspores

Develop into male gametophytes possessing antheridia (male).

Vascular plants display two distinct reproductive strategies:

Homosporous and heterosporous

Gametophyte

Is a generation of plant. It is haploid and vascular. Produces Sporophytes and alternates with the other generation.

How is gas exchanged in most plants?

Occurs via stomata, special pores on the surfaces of leaves.

The sporophyte of a homosporous plant

Produces a single type of spore (e.g., ferns); each spore develops into a bisexual gametophyte with both male (antheridia) and female (archegonia) sex organs.

Bryophytes display a pivotal adaptation that made the move onto land possible:

The embryophyte condition.

Anthocerophyta (Hornworts)

They resemble liverworts, but sporophytes are horn-shaped, elongated capsules that grow from the matlike gametophyte. Their photosynthetic cells have only one large chloroplast, unlike the many smaller ones of other plants.

What do secondary products include?

Waxy cuticle; Lignin cell wall component of "woody" plants); Sporopollenin (a resilient polymer in the walls of spores and pollen grains)

Land plants share the following characteristics with their green algal ancestors:

• Chloroplasts with photosynthetic pigments: chlorophyll a, chlorophyll b, and carotenoids • Cell walls containing cellulose • Food reserve that is starch stored in plastids

What are the two groups of seedless vascular plants?

1. Lycophytes (Lycophyta) 2. Pteridophytes (Pteridophyta)

There are four major periods of plant evolution that opened new adaptive zones on land:

1. Origin of plants from aquatic ancestors (probably green algae) in the Ordovician about 475 million years ago (mya). 2. Diversification of seedless vascular plants, such as ferns, during the early Devonian about 400 mya. 3. Origin of the seed near the end of the Devonian about 360 mya. 4. Emergence of flowering plants during the early Cretaceous, about 130 mya. NOTE: Don't need to know Ordovician, Devonian, Cretaceous. Just know that it was many years ago.

Structural, chemical, and reproductive adaptations enabled plants to colonize land

1. Some characteristics of plants. 2. Land Plats as embryophytes (embryo / plant) 3. Alternation of generations 4. Some highlights of plant phylogeny (plant evolution)

Bryophytes are not totally free from their ancestral aquatic habitat:

1. They need water to reproduce. 2. Their flagellated sperm cells must swim from the antheridium to the archegonium to fertilize the egg. 3. • Most have no vascular tissue to carry water from the soil to aerial (above the level of the soil) plant parts; they imbibe water and distribute it throughout the plant by the relatively slow processes of diffusion (low concentration to high concentration), capillary action (allows water to travel up the stem like structures), and cytoplasmic streaming.

Bryophyta (Mosses)

A tight pact of many moss plants forms a spongy mat that can absorb and retain water. Each plant grips the substratum with rhizoids, elongate cells or cellular filaments. Photosynthesis occurs mostly in the small stemlike and leaflike structures found in upper parts of the plant; these structures are not homologous with stems and leaves in vascular plants.

Seedless Vascular Plants

A. A sporophyte-dominant life cycle evolved in seedless vascular plants B. The two groups of seedless vascular plants are lycophytes and pteridophytes

The Origin of Land Plants

A. Land Plants probably evolved from a common ancestor shared with the green algae called Charophytes (Charophyta) (charales). B. Adaptations to shallow water preadapted plants for living on land

Characteristics of land plants

Land plants are multicellular eukaryotes that are photosynthetic autotrophs.

What is an example of a Hepatophyta?

Marchantia The leaves are Thalloid and Leafy. Palm tree = archegoniophore; The flat ones = antheridiophore

Life Cycle of Polytrichum

Operculum; Protonemato; Peristome teeth

Gametangia

Organs with protective jackets of sterile (nonreproductive) cells that prevent gametes from drying out. The egg is fertilized within the female organ. 1) Archegonia - Eggs 2) Anthendia - Sperm Great evolutionary advanced.

Plant Evolution

Plants appeared on land about 475 million years ago, and the evolutionary history of the plant kingdom reflects increasing adaptation to the terrestrial environment. The colonization of land by plants transformed the biosphere. This transformation created new adaptive zones and paved the way for other organisms.

What distinguishes land plants from algae?

The set of structural, chemical, and reproductive adaptations associated with terrestrial life

What is the dominant stage in the life cycle in all extant vascular plants.

The sporophyte (diploid generation emerged as the larger and more complex plant from the time of early vascular plants.

Hepatophyta (Liverworts)

They are less conspicuous than mosses. They sometimes have bodies divided into lobes. They have a life cycle similar to mosses. Their sporangia have elaters, coil-shaped cells, that spring out of the capsule and disperse spores. They can also reproduce asexually from gemmae (small bundles of cells that can bounce out of cups on the surface of the gametophyte when hit by rainwater). They display their greatest diversity in tropical forests.

What does Bryophyta contain?

They contain vast amounts of organic carbon.

Cuticle waxes

secondary products, so named because they arise through metabolic pathways not common to all plants. (Cellulose is an example of a primary product).

The bryophytes include plants found in three groups:

• Bryophyta (mosses) (Polytrichum) • Hepatophyta (liverworts) (Marchantia) • Anthocerophyta (hornworts)

The green algae are likely the photosynthetic organisms most closely related to land plants. This conclusion is based on homologies in:

• Cell wall composition • Structure and pigmentation of chloroplasts (When you look at algae vs. Land Plants there is almost no difference on the cellular level.)

Origin of plants from aquatic ancestors (probably green algae) many years ago.

• Cuticle and jacketed gametangia evolved which protected gametes and embryos. • Vascular tissue evolved with conducting cells that transport water and nutrients throughout the plant. (Bryophytes (nonvascular plants) diffusion and osmosis)

A comparison of life cycles among plant divisions instructive because:

• It points to an important trend in plant evolution: reduction of the haploid gametophyte generation and dominance of the diploid sporophyte. • Certain life cycle features are adaptations to a terrestrial environment; for example the replacement of flagellated sperm by pollen.

Adaptations to shallow water preadapted plants for living on land

• Many modern charophytes live in shallow water, and some ancient charophytes may have also lived in shallow-water habitats subject to occasional drying. • About 440 million year ago, during the transition from Ordivician to Silurian, repeated glaciations and climatic changes caused fluctuations in the water levels of lakes and ponds. • Natural selection may have favored shallow-water plants tolerant to periodic drying. Adaptations to shallow water may also have been preadaptive for terrestrial life. • Eventually, accumulated adaptations made it possible for ancestral plants to live permanently above the water line, opening a new adaptive zone with

Origin of the seed:

• Seed = Plant embryo packaged with a store of food within a resistant coat. Food (endosperm --> Starch) • Early seed plans bore seeds as naked structures and evolved into gymnosperms including conifers. (Gymnosperms are naked seeds) • Conifers (cone bearing) and ferns coexisted in the landscape for more than 200 million years.

Eventually, accumulated adaptations made it possible for ancestral plants to live permanently above the water line, opening a new adaptive zone with:

• Sunlight unfiltered by water and algae • Soil rich in minerals • Absence of terrestrial herbivores (an important one)

The sporophyte-dominant life cycle is exemplified by ferns, one group of the seedless vascular plants.

• The familiar leafy plant is the sporophyte. • Gametophytes are quite small and grow on or below the surface of the soil.

The life cycle of a bryophyte alternates between haploid and diploid generations.

• The sporophyte (2n) produces haploid spores by meiosis in a sporanigium; the spores divide by mitosis to form new gametophytes. • Contrary to the life cycles of vascular plants, the haploid gametophyte is the dominant generation in mosses and other bryophytes. Sporophytes are generally smaller and depend on the gametophyte for water and nutrients.

Emergence of flowering plants during the early Cretaceous

• Unlike gymnosperms, flowering plants bear seeds within the flower's protective ovaries. • Most contemporary plants are flowering plants or angiosperms.

Natural selection may have favored shallow-water plants tolerant to periodic drying. Adaptations to shallow water may also have been preadaptive for terrestrial life. Examples:

• Waxy cuticles • Protection of gametes • Protection of developing embryos

The life cycle of plants

Heteromorphic; that is, sporophytes and gametophytes differ in morphology.

With the move from an aquatic to terrestrial environment, a new mode of reproduction was necessary to solve two problems:

1. Gametes must be dispersed in a nonaquatic environment. Plants produce gamete within gametangia, organs with protective jackets of sterile (nonreproductive) cells that prevent gametes from drying out. The egg is fertilized within the female organ. 2. Embryos must be protected against desiccation. The zygote develops into an embryo that is retained for awhile within the female gametangia's jacket of protective cells. Emphasizing this terrestrial adaptation, plants are often referred to as embryophytes.

Available evidence supports the hypothesis that land plants and green algae called charophytes both evolved from a common ancestor. Researchers have found the following homologies between charophytes and land plants:

1. Homologous chloroplasts 2. Biochemical similarity 3. Similarity in sperm ultrastructure. Charophyte sperm ultrastructure (as seen under the electron microscope) is more similar to certain plants than to other green algae. 4. Genetic relationship. DNA and rRNA similarities in charophytes and land plants provides additional evidence for the hypothesis that charophytes are the closest relatives of land plants.

What is the dominant generation of Bryophytes?

Gametophyte

What are the generations of plants?

Gametophyte & Sporophyte

Sporophyte

Is a generation of plant. It is diploid and non-vascular. Produces Gametophytes and alternates with the other generation.

What have land plants evolved complex bodies with cell specialization for different functions.

Land Plants have developed structural specializations in order to extract the resources needed for photosynthesis (water, minerals, carbon dioxide, light) from the terrestrial environment (above and below ground). (Have stems, leaves, roots)

Phylogeny

Plant evolution

What is an examples of Bryophyta?

Polytrichum

The sporophyte of a heterosporous plant

Produces two kinds of spores: Megaspores Microspores

Which generation is larger and more noticeable?

Sporophyte is larger and more noticeable than the gametophyte in all plants but mosses and their relatives.

Lycophytes (Lycophyta)

The Lycophyta includes the club mosses and ground pines. Lycophytes survived through the Devonian period and dominated land during the Carboniferous Period (340-280 million years ago).

Land Plants probably evolved from a common ancestor shared with the green algae called Charophytes (Charophyta) (charales).

The green algae are likely the photosynthetic organisms most closely related to land plants. This conclusion is based on homologies in

True or False All plants have ATP (adenosine triphosphate)?

True, it is the primary product.

True or False The earliest vascular plants were seedless?

True, they dominated the Carboniferous forests. Modern flora includes two divisions of seedless vascular plants.

What do Bryophytes lack that won't allow them to support tall plants?

Woody tissue (xylem) and cannot support tall plants on land; they may sprawl horizontally as mats, but always have a low profile.

Gametangia protect developing gametes.

a. Antheridium, or male gametangium, produces flagellated sperm cells. b. Archegonium, or female gametangium, produces a single egg; fertilization occurs within the archegonium, and the zygote develops into an embryo within the protective jacket of the female organ (embryophyte condition).