What Characteristics Separates The Plant Kingdom From The Animal Kingdom

Chapter fourteen: Diversity of Plants

The Plant Kingdom

Learning Objectives

By the cease of this section, yous volition be able to:

• Describe the major characteristics of the plant kingdom
• Discuss the challenges to found life on state
• Draw the adaptations that allowed plants to colonize land

Plants are a big and varied grouping of organisms. At that place are shut to 300,000 species of catalogued plants. ¹ Of these, about 260,000 are plants that produce seeds. Mosses, ferns, conifers, and flowering plants are all members of the plant kingdom. The plant kingdom contains generally photosynthetic organisms; a few parasitic forms accept lost the power to photosynthesize. The process of photosynthesis uses chlorophyll, which is located in organelles called chloroplasts. Plants possess cell walls containing cellulose. Near plants reproduce sexually, but they also have diverse methods of asexual reproduction. Plants showroom indeterminate growth, pregnant they do not have a final body grade, merely continue to abound body mass until they die.

Plant Adaptations to Life on Land

Equally organisms suit to life on land, they accept to contend with several challenges in the terrestrial surround. H2o has been described every bit "the stuff of life." The cell's interior—the medium in which most small molecules dissolve and diffuse, and in which the bulk of the chemical reactions of metabolism take place—is a watery soup. Desiccation, or drying out, is a constant danger for an organism exposed to air. Fifty-fifty when parts of a plant are close to a source of water, their aeriform structures are likely to dry out out. Water provides buoyancy to organisms that live in aquatic habitats. On state, plants need to develop structural support in air—a medium that does non give the same lift. Additionally, the male gametes must reach the female gametes using new strategies because swimming is no longer possible. Finally, both gametes and zygotes must be protected from drying out. The successful land plants evolved strategies to deal with all of these challenges, although not all adaptations appeared at once. Some species did non movement far from an aquatic environs, whereas others left the water and went on to conquer the driest environments on Earth.

To balance these survival challenges, life on land offers several advantages. Kickoff, sunlight is abundant. On land, the spectral quality of low-cal absorbed by the photosynthetic pigment, chlorophyll, is non filtered out by h2o or competing photosynthetic species in the h2o column above. Second, carbon dioxide is more than readily available because its concentration is college in air than in h2o. Additionally, land plants evolved before country animals; therefore, until dry land was colonized by animals, no predators threatened the well-being of plants. This situation changed every bit animals emerged from the water and found abundant sources of nutrients in the established flora. In plow, plants evolved strategies to deter predation: from spines and thorns to toxic chemicals.

The early country plants, like the early land animals, did non live far from an abundant source of water and developed survival strategies to combat dryness. One of these strategies is drought tolerance. Mosses, for example, can dry to a brown and breakable mat, just as shortly equally pelting makes water available, mosses will soak it up and regain their healthy, green appearance. Another strategy is to colonize environments with high humidity where droughts are uncommon. Ferns, an early lineage of plants, thrive in damp and absurd places, such as the understory of temperate forests. Later, plants moved away from aquatic environments using resistance to desiccation, rather than tolerance. These plants, similar the cactus, minimize water loss to such an extent they can survive in the driest environments on Earth.

In addition to adaptations specific to life on country, land plants showroom adaptations that were responsible for their multifariousness and predominance in terrestrial ecosystems. Iv major adaptations are establish in many terrestrial plants: the alternation of generations, a sporangium in which spores are formed, a gametangium that produces haploid cells, and in vascular plants, apical meristem tissue in roots and shoots.

Alternation of Generations

Alternation of generations describes a life cycle in which an organism has both haploid and diploid multicellular stages ([Figure 1]).

Figure ane: Alternation of generations betwixt the haploid (1n) gametophyte and diploid (2n) sporophyte is shown. (credit: modification of work past Peter Coxhead)

Haplontic refers to a life cycle in which in that location is a dominant haploid stage. Diplontic refers to a life bike in which the diploid stage is the dominant stage, and the haploid chromosome number is but seen for a brief time in the life bike during sexual reproduction. Humans are diplontic, for case. Most plants exhibit alternation of generations, which is described equally haplodiplontic: the haploid multicellular course known every bit a gametophyte is followed in the development sequence by a multicellular diploid organism, the sporophyte. The gametophyte gives rise to the gametes, or reproductive cells, by mitosis. It can be the most obvious phase of the life cycle of the establish, as in the mosses, or it can occur in a microscopic structure, such as a pollen grain in the higher plants (the commonage term for the vascular plants). The sporophyte stage is barely noticeable in lower plants (the collective term for the institute groups of mosses, liverworts, and hornworts). Towering trees are the diplontic phase in the lifecycles of plants such equally sequoias and pines.

Sporangia in the Seedless Plants

The sporophyte of seedless plants is diploid and results from syngamy or the fusion of 2 gametes ([Figure 1]). The sporophyte bears the sporangia (singular, sporangium), organs that showtime appeared in the land plants. The term "sporangia" literally means "spore in a vessel," every bit information technology is a reproductive sac that contains spores. Within the multicellular sporangia, the diploid sporocytes, or mother cells, produce haploid spores by meiosis, which reduces the iinorthward chromosome number to 1n. The spores are later released by the sporangia and disperse in the environs. Two dissimilar types of spores are produced in land plants, resulting in the separation of sexes at unlike points in the life cycle. Seedless nonvascular plants (more than accordingly referred to as "seedless nonvascular plants with a ascendant gametophyte stage") produce merely one kind of spore, and are called homosporous. After germinating from a spore, the gametophyte produces both male and female gametangia, usually on the same private. In contrast, heterosporous plants produce two morphologically different types of spores. The male person spores are chosen microspores because of their smaller size; the insufficiently larger megaspores will develop into the female gametophyte. Heterospory is observed in a few seedless vascular plants and in all seed plants.

When the haploid spore germinates, it generates a multicellular gametophyte by mitosis. The gametophyte supports the zygote formed from the fusion of gametes and the resulting young sporophyte or vegetative form, and the cycle begins anew ([Effigy 2] and [Figure 3]).

Effigy 2: This life cycle of a fern shows alternation of generations with a dominant sporophyte stage. (credit "fern": modification of work past Cory Zanker; credit "gametophyte": modification of work by "Vlmastra"/Wikimedia Commons)

Figure 3: This life cycle of a moss shows alternation of generations with a dominant gametophyte stage. (credit: modification of piece of work by Mariana Ruiz Villareal)

The spores of seedless plants and the pollen of seed plants are surrounded past thick cell walls containing a tough polymer known as sporopollenin. This substance is characterized past long chains of organic molecules related to fatty acids and carotenoids, and gives near pollen its xanthous colour. Sporopollenin is unusually resistant to chemical and biological deposition. Its toughness explains the existence of well-preserved fossils of pollen. Sporopollenin was in one case thought to be an innovation of land plants; however, the green algae Coleochaetes is now known to form spores that contain sporopollenin.

Protection of the embryo is a major requirement for land plants. The vulnerable embryo must exist sheltered from desiccation and other environmental hazards. In both seedless and seed plants, the female gametophyte provides diet, and in seed plants, the embryo is as well protected as it develops into the new generation of sporophyte.

Gametangia in the Seedless Plants

Gametangia (singular, gametangium) are structures on the gametophytes of seedless plants in which gametes are produced by mitosis. The male gametangium, the antheridium, releases sperm. Many seedless plants produce sperm equipped with flagella that enable them to swim in a moist environment to the archegonia, the female gametangium. The embryo develops inside the archegonium as the sporophyte.

Apical Meristems

The shoots and roots of plants increase in length through rapid jail cell division within a tissue called the apical meristem ([Figure 4]). The apical meristem is a cap of cells at the shoot tip or root tip made of undifferentiated cells that proceed to proliferate throughout the life of the found. Meristematic cells requite rising to all the specialized tissues of the plant. Elongation of the shoots and roots allows a constitute to access additional space and resource: low-cal in the case of the shoot, and h2o and minerals in the case of roots. A separate meristem, chosen the lateral meristem, produces cells that increase the bore of stems and tree trunks. Apical meristems are an adaptation to allow vascular plants to grow in directions essential to their survival: up to greater availability of sunlight, and downward into the soil to obtain water and essential minerals.

Figure 4: This apple seedling is an example of a establish in which the apical meristem gives rise to new shoots and root growth.

Additional Land Plant Adaptations

As plants adapted to dry state and became independent of the constant presence of h2o in damp habitats, new organs and structures fabricated their advent. Early state plants did not abound above a few inches off the ground, and on these depression mats, they competed for light. By evolving a shoot and growing taller, private plants captured more than calorie-free. Considering air offers substantially less back up than water, land plants incorporated more rigid molecules in their stems (and afterward, tree trunks). The evolution of vascular tissue for the distribution of water and solutes was a necessary prerequisite for plants to evolve larger bodies. The vascular system contains xylem and phloem tissues. Xylem conducts water and minerals taken from the soil up to the shoot; phloem transports food derived from photosynthesis throughout the entire plant. The root organization that evolved to take upwards water and minerals likewise anchored the increasingly taller shoot in the soil.

Effigy five: Plants have evolved diverse adaptations to life on land. (a) Early plants grew close to the ground, like this moss, to avoid desiccation. (b) After plants adult a waxy cuticle to prevent desiccation. (c) To grow taller, like these maple copse, plants had to evolve new structural chemicals to strengthen their stems and vascular systems to send water and minerals from the soil and nutrients from the leaves. (d) Plants developed physical and chemic defenses to avoid being eaten by animals. (credit a, b: modification of work past Cory Zanker; credit c: modification of piece of work past Christine Cimala; credit d: modification of work past Jo Naylor)

In country plants, a waxy, waterproof cover called a cuticle coats the aerial parts of the plant: leaves and stems. The cuticle also prevents intake of carbon dioxide needed for the synthesis of carbohydrates through photosynthesis. Stomata, or pores, that open and shut to regulate traffic of gases and water vapor therefore appeared in plants equally they moved into drier habitats.

Plants cannot avoid predatory animals. Instead, they synthesize a large range of poisonous secondary metabolites: circuitous organic molecules such as alkaloids, whose noxious smells and unpleasant taste deter animals. These toxic compounds can cause severe diseases and fifty-fifty death.

Additionally, as plants coevolved with animals, sweet and nutritious metabolites were adult to lure animals into providing valuable assistance in dispersing pollen grains, fruit, or seeds. Plants have been coevolving with brute assembly for hundreds of millions of years ([Effigy five]).

Evolution in Activity

PaleobotanyHow organisms acquired traits that allow them to colonize new environments, and how the contemporary ecosystem is shaped, are fundamental questions of evolution. Paleobotany addresses these questions past specializing in the study of extinct plants. Paleobotanists clarify specimens retrieved from field studies, reconstituting the morphology of organisms that have long disappeared. They trace the evolution of plants by following the modifications in plant morphology, and shed lite on the connection betwixt existing plants by identifying common ancestors that display the same traits. This field seeks to find transitional species that bridge gaps in the path to the development of modern organisms. Fossils are formed when organisms are trapped in sediments or environments where their shapes are preserved ([Figure half dozen]). Paleobotanists decide the geological age of specimens and the nature of their environment using the geological sediments and fossil organisms surrounding them. The activity requires great care to preserve the integrity of the delicate fossils and the layers in which they are plant.

One of the most exciting recent developments in paleobotany is the use of analytical chemistry and molecular biology to study fossils. Preservation of molecular structures requires an surroundings free of oxygen, since oxidation and degradation of material through the activity of microorganisms depend on the presence of oxygen. Ane example of the use of belittling chemistry and molecular biology is in the identification of oleanane, a compound that deters pests and which, upwards to this point, appears to be unique to flowering plants. Oleanane was recovered from sediments dating from the Permian, much earlier than the electric current dates given for the appearance of the first flowering plants. Fossilized nucleic acids—DNA and RNA—yield the most data. Their sequences are analyzed and compared to those of living and related organisms. Through this analysis, evolutionary relationships can exist congenital for establish lineages.

Some paleobotanists are skeptical of the conclusions fatigued from the analysis of molecular fossils. For ane, the chemic materials of involvement degrade quickly during initial isolation when exposed to air, too as in farther manipulations. There is e'er a high take a chance of contaminating the specimens with extraneous material, mostly from microorganisms. Withal, as technology is refined, the analysis of Deoxyribonucleic acid from fossilized plants will provide invaluable information on the evolution of plants and their adaptation to an ever-changing environment.

Figure half-dozen: This fossil of a palm leaf (Palmacites sp.) discovered in Wyoming dates to well-nigh twoscore meg years ago.

The Major Divisions of Land Plants

Land plants are classified into two major groups according to the absence or presence of vascular tissue, as detailed in [Effigy 7]. Plants that lack vascular tissue formed of specialized cells for the transport of water and nutrients are referred to every bit nonvascular plants. The bryophytes, liverworts, mosses, and hornworts are seedless and nonvascular, and probable appeared early in country plant development. Vascular plants adult a network of cells that conduct water and solutes through the plant torso. The start vascular plants appeared in the late Ordovician (461–444 million years ago) and were probably similar to lycophytes, which include gild mosses (non to be dislocated with the mosses) and the pterophytes (ferns, horsetails, and whisk ferns). Lycophytes and pterophytes are referred to as seedless vascular plants. They do not produce seeds, which are embryos with their stored food reserves protected past a hard casing. The seed plants form the largest group of all existing plants and, hence, dominate the landscape. Seed plants include gymnosperms, nearly notably conifers, which produce "naked seeds," and the nearly successful plants, the flowering plants, or angiosperms, which protect their seeds inside chambers at the center of a blossom. The walls of these chambers afterward develop into fruits.

Figure 7: This tabular array shows the major divisions of plants.

Department Summary

Land plants evolved traits that made it possible to colonize land and survive out of water. Adaptations to life on land include vascular tissues, roots, leaves, waxy cuticles, and a tough outer layer that protects the spores. Land plants include nonvascular plants and vascular plants. Vascular plants, which include seedless plants and plants with seeds, have apical meristems, and embryos with nutritional stores. All land plants share the following characteristics: alternation of generations, with the haploid found called a gametophyte and the diploid found called a sporophyte; formation of haploid spores in a sporangium; and formation of gametes in a gametangium.

Multiple Choice

The land plants are probably descendants of which of these groups?

1. greenish algae
2. red algae
3. brown algae
4. angiosperms

[reveal-answer q="675979″]Show Reply[/reveal-answer]
[hidden-answer a="675979″]1[/hidden-answer]

The event that leads from the haploid stage to the diploid stage in alternation of generations is ________.

1. meiosis
2. mitosis
3. fertilization
4. formation

[reveal-answer q="944729″]Show Answer[/reveal-answer]
[hidden-answer a="944729″]3[/hidden-reply]

Moss is an example of which type of plant?

1. haplontic plant
2. vascular plant
3. diplontic institute
4. seed plant

[reveal-answer q="801206″]Show Reply[/reveal-answer]
[hidden-reply a="801206″]1[/hidden-answer]

Free Response

What adaptations do plants have that let them to survive on country?

The sporangium of plants protects the spores from drying out. Apical meristems ensure that a plant is able to grow in the two directions required to larn water and nutrients: up toward sunlight and down into the soil. The multicellular embryo is an important accommodation that improves survival of the developing plant in dry environments. The development of molecules that gave plants structural strength allowed them to grow college on land and obtain more sunlight. A waxy cuticle prevents h2o loss from aerial surfaces.

Footnotes

1. 1 A.D. Chapman (2009) Numbers of Living Species in Australia and the World. 2d edition. A Report for the Australian Biological Resources Written report. Australian Biodiversity Information Services, Toowoomba, Australia. Bachelor online at http://www.environment.gov.au/biodiversity/abrs/publications/other/species-numbers/2009/04-03-groups-plants.html.

Glossary

apical meristem

the growing signal in a vascular establish at the tip of a shoot or root where cell partition occurs

diplontic

describes a life cycle in which the diploid stage is the ascendant stage

gametangium

(plural: gametangia) the structure inside which gametes are produced

gametophyte

the haploid constitute that produces gametes

haplodiplontic

describes a life wheel in which the haploid and diploid stages alternate; likewise known as an alternation of generations life cycle

haplontic

describes a life cycle in which the haploid stage is the dominant stage

heterosporous

having ii kinds of spores that give ascension to male and female gametophytes

homosporous

having one kind of spore that gives rise to gametophytes that give rise to both male person and female gametes

nonvascular plant

a institute that lacks vascular tissue formed of specialized cells for the transport of water and nutrients

sporangium

(plural: sporangia) the organ within which spores are produced

sporophyte

the diploid plant that produces spores

syngamy

the union of ii gametes in fertilization

tracheophyte

a establish in which there is a network of cells that behave water and solutes through the organism

Source: https://opentextbc.ca/conceptsofbiologyopenstax/chapter/the-plant-kingdom/

Posted by: camposbaccomithe.blogspot.com

Share this post