Is The Animal Kingdom Prokaryotic Or Eukaryotic

Introduction to Animal Diversity

137 Features of the Animal Kingdom

Learning Objectives

By the finish of this department, you volition be able to exercise the following:

• List the features that distinguish the kingdom Animalia from other kingdoms
• Explain the processes of animal reproduction and embryonic development
• Draw the roles that Hox genes play in development

2 different groups inside the Domain Eukaryota have produced circuitous multicellular organisms: The plants arose inside the Archaeplastida, whereas the animals (and their close relatives, the fungi) arose within the Opisthokonta. However, plants and animals not only have different life styles, they also have unlike cellular histories equally eukaryotes. The opisthokonts share the possession of a single posterior flagellum in flagellated cells, e.g., sperm cells.

Nearly animals likewise share other features that distinguish them from organisms in other kingdoms. All animals require a source of nutrient and are therefore heterotrophic, ingesting other living or dead organisms. This feature distinguishes them from autotrophic organisms, such every bit nearly plants, which synthesize their own nutrients through photosynthesis. Equally heterotrophs, animals may be carnivores, herbivores, omnivores, or parasites ((Figure)a,b). Every bit with plants, almost all animals have a complex tissue structure with differentiated and specialized tissues. The necessity to collect food has made most animals motile, at least during sure life stages. The typical life cycle in animals is diplontic (like you, the diploid state is multicellular, whereas the haploid state is gametic, such every bit sperm or egg). We should note that the alternation of generations characteristic of the state plants is typically not found in animals. In animals whose life histories include several to multiple trunk forms (e.g., insect larvae or the medusae of some Cnidarians), all trunk forms are diploid. Animal embryos laissez passer through a series of developmental stages that establish a determined and fixed body plan. The body plan refers to the morphology of an fauna, determined by developmental cues.

Heterotrophy. All animals are heterotrophs and thus derive free energy from a variety of food sources. The (a) black bear is an omnivore, eating both plants and animals. The (b) heartworm Dirofilaria immitis is a parasite that derives energy from its hosts. Information technology spends its larval stage in mosquitoes and its developed phase infesting the centre of dogs and other mammals, as shown hither. (credit a: modification of piece of work by USDA Forest Service; credit b: modification of work past Clyde Robinson)

Complex Tissue Structure

Many of the specialized tissues of animals are associated with the requirements and hazards of seeking and processing food. This explains why animals typically take evolved special structures associated with specific methods of food capture and complex digestive systems supported by accompaniment organs. Sensory structures help animals navigate their surroundings, notice nutrient sources (and avert becoming a food source for other animals!). Motility is driven by muscle tissue fastened to supportive structures similar bone or chitin, and is coordinated by neural communication. Brute cells may besides have unique structures for intercellular communication (such as gap junctions). The development of nerve tissues and muscle tissues has resulted in animals' unique power to quickly sense and respond to changes in their environs. This allows animals to survive in environments where they must compete with other species to encounter their nutritional demands.

The tissues of animals differ from those of the other major multicellular eukaryotes, plants and fungi, considering their cells don't take prison cell walls. However, cells of animal tissues may be embedded in an extracellular matrix (e.one thousand., mature os cells reside within a mineralized organic matrix secreted by the cells). In vertebrates, bone tissue is a blazon of connective tissue that supports the entire torso structure. The complex bodies and activities of vertebrates demand such supportive tissues. Epithelial tissues cover and protect both external and internal body surfaces, and may also have secretory functions. Epithelial tissues include the epidermis of the integument, the lining of the digestive tract and trachea, as well every bit the layers of cells that brand up the ducts of the liver and glands of avant-garde animals, for example. The unlike types of tissues in true animals are responsible for carrying out specific functions for the organism. This differentiation and specialization of tissues is part of what allows for such incredible animal diversity.

But as there are multiple ways to be a eukaryote, there are multiple means to be a multicellular brute. The fauna kingdom is currently divided into v monophyletic clades: Parazoa or Porifera (sponges), Placozoa (tiny parasitic creatures that resemble multicellular amoebae), Cnidaria (jellyfish and their relatives), Ctenophora (the comb jellies), and Bilateria (all other animals). The Placozoa ("flat animate being") and Parazoa ("beside animal") practise not have specialized tissues derived from germ layers of the embryo; although they do possess specialized cells that human activity functionally like tissues. The Placozoa accept but four cell types, while the sponges have nearly two dozen. The three other clades do include animals with specialized tissues derived from the germ layers of the embryo. In spite of their superficial similarity to Cnidarian medusae, recent molecular studies indicate that the Ctenophores are only distantly related to the Cnidarians, which together with the Bilateria establish the Eumetazoa ("true animals"). When we think of animals, we unremarkably think of Eumetazoa, since most animals fall into this category.

Link to Learning

Watch a presentation past biologist E.O. Wilson on the importance of multifariousness.

Animal Reproduction and Development

Most animals are diploid organisms, meaning that their body (somatic) cells are diploid and haploid reproductive (gamete) cells are produced through meiosis. Some exceptions exist: for example, in bees, wasps, and ants, the male is haploid because it develops from unfertilized eggs. Virtually animals undergo sexual reproduction. Yet, a few groups, such every bit cnidarians, flatworms, and roundworms, may also undergo asexual reproduction, in which offspring originate from part of the parental torso.

Processes of Beast Reproduction and Embryonic Evolution

During sexual reproduction, the haploid gametes of the male person and female individuals of a species combine in a process called fertilization. Typically, both male and female gametes are required: the small, motile male person sperm fertilizes the typically much larger, sessile female egg. This process produces a diploid fertilized egg chosen a zygote.

Some brute species—including sea stars and sea anemones—are capable of asexual reproduction. The most common forms of asexual reproduction for stationary aquatic animals include budding and fragmentation, where office of a parent individual can separate and grow into a new private. This blazon of asexual reproduction produces genetically identical offspring, which would appear to be disadvantageous from the perspective of evolutionary adaptability, only because of the potential buildup of deleterious mutations.

In dissimilarity, a class of uniparental reproduction found in some insects and a few vertebrates is called parthenogenesis (or "virgin outset"). In this case, progeny develop from a gamete, just without fertilization. Because of the nutrients stored in eggs, only females produce parthenogenetic offspring. In some insects, unfertilized eggs develop into new male offspring. This type of sex decision is called haplodiploidy, since females are diploid (with both maternal and paternal chromosomes) and males are haploid (with only maternal chromosomes). A few vertebrates, eastward.g., some fish, turkeys, rattlesnakes, and whiptail lizards, are also capable of parthenogenesis. In the case of turkeys and rattlesnakes, parthenogenetically reproducing females also produce only male offspring, but non because the males are haploid. In birds and rattlesnakes, the female is the heterogametic (ZW) sex, and so the only surviving progeny of mail-meiotic parthenogenesis would exist ZZ males. In the whiptail lizards, on the other hand, only female progeny are produced past parthenogenesis. These animals may not be identical to their parent, although they have just maternal chromosomes. However, for animals that are limited in their access to mates, uniparental reproduction can ensure genetic propagation.

In animals, the zygote progresses through a series of developmental stages, during which primary germ layers (ectoderm, endoderm, and mesoderm) are established and reorganize to course an embryo. During this procedure, fauna tissues brainstorm to specialize and organize into organs and organ systems, determining their future morphology and physiology.

Animal evolution begins with cleavage, a serial of mitotic cell divisions, of the zygote ((Figure)). Cleavage differs from somatic cell sectionalization in that the egg is subdivided by successive cleavages into smaller and smaller cells, with no actual cell growth. The cells resulting from subdivision of the textile of the egg in this mode are called blastomeres. Iii cell divisions transform the unmarried-celled zygote into an eight-celled structure. After further prison cell segmentation and rearrangement of existing cells, a solid morula is formed, followed by a hollow structure called a blastula. The blastula is hollow only in invertebrates whose eggs have relatively small amounts of yolk. In very yolky eggs of vertebrates, the yolk remains undivided, with virtually cells forming an embryonic layer on the surface of the yolk (imagine a craven embryo growing over the egg'southward yolk), which serve as nutrient for the developing embryo.

Further jail cell sectionalization and cellular rearrangement leads to a procedure called gastrulation. Gastrulation results in 2 of import events: the formation of the archaic gut (archenteron) or digestive cavity, and the formation of the embryonic germ layers, every bit we have discussed above. These germ layers are programmed to develop into certain tissue types, organs, and organ systems during a process called organogenesis. Diploblastic organisms accept two germ layers, endoderm and ectoderm. Endoderm forms the wall of the digestive tract, and ectoderm covers the surface of the animal. In triploblastic animals, a tertiary layer forms: mesoderm, which differentiates into various structures between the ectoderm and endoderm, including the lining of the body cavity.

Development of a simple embryo. During embryonic development, the zygote undergoes a series of mitotic cell divisions, or cleavages, that subdivide the egg into smaller and smaller blastomeres. Note that the 8-prison cell phase and the blastula are about the same size equally the original zygote. In many invertebrates, the blastula consists of a single layer of cells effectually a hollow space. During a process chosen gastrulation, the cells from the blastula move inward on 1 side to form an inner cavity. This inner cavity becomes the primitive gut (archenteron) of the gastrula ("petty gut") stage. The opening into this cavity is called the blastopore, and in some invertebrates it is destined to form the mouth.

Some animals produce larval forms that are different from the adult. In insects with incomplete metamorphosis, such as grasshoppers, the young resemble wingless adults, merely gradually produce larger and larger wing buds during successive molts, until finally producing functional wings and sex organs during the last molt. Other animals, such every bit some insects and echinoderms, undergo complete metamorphosis in which the embryo develops into ane or more feeding larval stages that may differ profoundly in construction and function from the adult ((Figure)). The developed trunk then develops from one or more regions of larval tissue. For animals with complete metamorphosis, the larva and the developed may have different diets, limiting competition for nutrient between them. Regardless of whether a species undergoes complete or incomplete metamorphosis, the series of developmental stages of the embryo remains largely the same for well-nigh members of the fauna kingdom.

Insect metamorphosis. (a) The grasshopper undergoes incomplete metamorphosis. (b) The butterfly undergoes complete metamorphosis. (credit: South.E. Snodgrass, USDA)

Link to Learning

Watch the following video to see how human embryonic development (after the blastula and gastrula stages of development) reflects evolution.

The Role of Homeobox (Hox) Genes in Animal Development

Since the early nineteenth century, scientists have observed that many animals, from the very elementary to the complex, shared similar embryonic morphology and evolution. Surprisingly, a human embryo and a frog embryo, at a sure stage of embryonic development, look remarkably akin! For a long time, scientists did non sympathize why so many animate being species looked similar during embryonic development but were very different every bit adults. They wondered what dictated the developmental management that a fly, mouse, frog, or human embryo would take. Near the terminate of the twentieth century, a particular class of genes was discovered that had this very job. These genes that determine animal construction are called "homeotic genes," and they contain DNA sequences called homeoboxes. Genes with homeoboxes encode protein transcription factors. One grouping of brute genes containing homeobox sequences is specifically referred to as Hox genes. This cluster of genes is responsible for determining the full general body programme, such as the number of body segments of an beast, the number and placement of appendages, and animal head-tail directionality. The first Hox genes to be sequenced were those from the fruit fly (Drosophila melanogaster). A unmarried Hox mutation in the fruit fly tin effect in an extra pair of wings or even legs growing from the caput in place of antennae (this is because antennae and legs are embryologic homologous structures and their advent as antennae or legs is dictated past their origination within specific trunk segments of the head and thorax during development). Now, Hox genes are known from almost all other animals likewise.

While there are a peachy many genes that play roles in the morphological development of an animate being, including other homeobox-containing genes, what makes Hox genes so powerful is that they serve as "master control genes" that tin turn on or off big numbers of other genes. Hox genes practice this past encoding transcription factors that command the expression of numerous other genes. Hox genes are homologous across the animal kingdom, that is, the genetic sequences of Hox genes and their positions on chromosomes are remarkably similar beyond most animals because of their presence in a common ancestor, from worms to flies, mice, and humans ((Effigy)). In addition, the society of the genes reflects the inductive-posterior axis of the beast's body. 1 of the contributions to increased animal body complexity is that Hox genes have undergone at least 2 and peradventure as many as 4 duplication events during brute evolution, with the additional genes assuasive for more complex body types to evolve. All vertebrates have 4 (or more) sets of Hox genes, while invertebrates take only ane set.

Visual Connection

Hox genes. Hox genes are highly conserved genes encoding transcription factors that determine the course of embryonic development in animals. In vertebrates, the genes have been duplicated into four clusters on different chromosomes: Hox-A, Hox-B, Hox-C, and Hox-D. Genes within these clusters are expressed in certain body segments at sure stages of development. Shown hither is the homology between Hox genes in mice and humans. Notation how Hox gene expression, as indicated with orange, pink, blue, and green shading, occurs in the aforementioned body segments in both the mouse and the human being. While at least one copy of each Hox gene is present in humans and other vertebrates, some Hox genes are missing in some chromosomal sets.

If a Hox xiii gene in a mouse was replaced with a Hox 1 gene, how might this alter animal development?

Two of the five clades inside the fauna kingdom do not have Hox genes: the Ctenophora and the Porifera. In spite of the superficial similarities between the Cnidaria and the Ctenophora, the Cnidaria have a number of Hox genes, but the Ctenophora have none. The absence of Hox genes from the ctenophores has led to the proffer that they might be "basal" animals, in spite of their tissue differentiation. Ironically, the Placozoa, which have only a few jail cell types, exercise have at least one Hox gene. The presence of a Hox cistron in the Placozoa, in addition to similarities in the genomic organization of the Placozoa, Cnidaria and Bilateria, has led to the inclusion of the three groups in a "Parahoxozoa" clade. However, nosotros should note that at this time the reclassification of the Animate being Kingdom is still tentative and requires much more study.

<!–<para>The brute might develop 2 heads and no tail.–>

Department Summary

Animals institute an incredibly diverse kingdom of organisms. Although animals range in complexity from simple bounding main sponges to human beings, most members of the creature kingdom share sure features. Animals are eukaryotic, multicellular, heterotrophic organisms that ingest their food and usually develop into motile creatures with a fixed torso plan. A major characteristic unique to the brute kingdom is the presence of differentiated tissues, such as nerve, musculus, and connective tissues, which are specialized to perform specific functions. Most animals undergo sexual reproduction, leading to a serial of developmental embryonic stages that are relatively similar across the animal kingdom. A form of transcriptional command genes called Hox genes directs the organization of the major animal body plans, and these genes are strongly homologous across the animal kingdom.

Visual Connection Questions

(Figure) If a Hox xiii factor in a mouse was replaced with a Hox ane cistron, how might this change animal development?

(Figure) The animal might develop two heads and no tail.

Review Questions

Which of the following is not a feature common to most animals?

1. development into a fixed body program
2. asexual reproduction
3. specialized tissues
4. heterotrophic nutrient sourcing

B

During embryonic evolution, unique cell layers develop into specific groups of tissues or organs during a stage chosen ________.

1. the blastula stage
2. the germ layer stage
3. the gastrula phase
4. the organogenesis phase

C

Which of the following phenotypes would well-nigh likely be the result of a Hox gene mutation?

1. abnormal torso length or elevation
2. two different center colors
3. the contraction of a genetic illness
4. two fewer appendages than normal

D

Critical Thinking Questions

Why might the development of specialized tissues be important for beast function and complication?

The evolution of specialized tissues affords more circuitous animal anatomy and physiology because differentiated tissue types can perform unique functions and work together in tandem to allow the animate being to perform more functions. For case, specialized musculus tissue allows directed and efficient movement, and specialized nervous tissue allows for multiple sensory modalities too as the ability to answer to various sensory data; these functions are not necessarily available to other nonanimal organisms.

Describe and give examples of how humans brandish all of the features common to the fauna kingdom.

Humans are multicellular organisms. They too contain differentiated tissues, such equally epithelial, musculus, and nervous tissue, as well as specialized organs and organ systems. As heterotrophs, humans cannot produce their ain nutrients and must obtain them by ingesting other organisms, such as plants, fungi, and animals. Humans undergo sexual reproduction, as well as the same embryonic developmental stages as other animals, which eventually lead to a fixed and motile trunk programme controlled in large role by Hox genes.

How accept Hox genes contributed to the diversity of beast body plans?

Contradistinct expression of homeotic genes can atomic number 82 to major changes in the morphology of the individual. Hox genes tin can touch the spatial arrangements of organs and body parts. If a Hox gene was mutated or duplicated, information technology could bear upon where a leg might be on a fruit fly or how far apart a person's fingers are.

Glossary

blastula

16–32 cell stage of development of an animal embryo

torso program

morphology or defining shape of an organism

cleavage

cell divisions subdividing a fertilized egg (zygote) to form a multicellular embryo

gastrula

stage of fauna development characterized by the formation of the digestive cavity

germ layer

drove of cells formed during embryogenesis that will requite ascent to future body tissues, more pronounced in vertebrate embryogenesis

Hox gene

(also, homeobox gene) primary control gene that tin can plow on or off large numbers of other genes during embryogenesis

organogenesis

formation of organs in animal embryogenesis

Source: https://opentextbc.ca/biology2eopenstax/chapter/features-of-the-animal-kingdom/

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