How Is The Animal Kingdom Different From Other Kingdoms

27.1: Features of the Animal Kingdom

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1963

Skills to Develop

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

Even though members of the animal kingdom are incredibly diverse, near animals share certain features that distinguish them from organisms in other kingdoms. All animals are eukaryotic, multicellular organisms, and about all animals take a complex tissue structure with differentiated and specialized tissues. Well-nigh animals are motile, at least during sure life stages. All animals crave a source of food and are therefore heterotrophic, ingesting other living or dead organisms; this feature distinguishes them from autotrophic organisms, such as most plants, which synthesize their own nutrients through photosynthesis. Every bit heterotrophs, animals may be carnivores, herbivores, omnivores, or parasites (Effigy \(\PageIndex{1}\)). Most animals reproduce sexually, and the offspring pass through a series of developmental stages that establish a determined and stock-still body plan. The body plan refers to the morphology of an animate being, determined by developmental cues.

Figure \(\PageIndex{one}\): All animals are heterotrophs that derive energy from food. The (a) blackness bear is an omnivore, eating both plants and animals. The (b) heartworm Dirofilaria immitis is a parasite that derives energy from its hosts. It spends its larval stage in mosquitoes and its adult phase infesting the eye of dogs and other mammals, as shown here. (credit a: modification of work past USDA Forest Service; credit b: modification of piece of work by Clyde Robinson)

Complex Tissue Structure

Every bit multicellular organisms, animals differ from plants and fungi because their cells don't have cell walls, their cells may be embedded in an extracellular matrix (such every bit os, skin, or connective tissue), and their cells have unique structures for intercellular advice (such as gap junctions). In addition, animals possess unique tissues, absent in fungi and plants, which allow coordination (nervus tissue) of motility (muscle tissue). Animals are also characterized by specialized connective tissues that provide structural support for cells and organs. This connective tissue constitutes the extracellular environs of cells and is made up of organic and inorganic materials. In vertebrates, bone tissue is a blazon of connective tissue that supports the unabridged body structure. The complex bodies and activities of vertebrates demand such supportive tissues. Epithelial tissues cover, line, protect, and secrete. Epithelial tissues include the epidermis of the integument, the lining of the digestive tract and trachea, and make up the ducts of the liver and glands of advanced animals.

The brute kingdom is divided into Parazoa (sponges) and Eumetazoa (all other animals). Equally very elementary animals, the organisms in group Parazoa ("beside animal") practise not contain true specialized tissues; although they do possess specialized cells that perform different functions, those cells are not organized into tissues. These organisms are considered animals since they lack the ability to brand their own food. Animals with truthful tissues are in the group Eumetazoa ("truthful animals"). When we think of animals, we commonly remember of Eumetazoans, since most animals fall into this category.

The different types of tissues in true animals are responsible for conveying out specific functions for the organism. This differentiation and specialization of tissues is office of what allows for such incredible animate being diversity. For case, the development of nerve tissues and musculus tissues has resulted in animals' unique ability to rapidly sense and respond to changes in their environment. This allows animals to survive in environments where they must compete with other species to meet their nutritional demands.

Link to Learning

Watch a presentation past biologist Eastward.O. Wilson on the importance of diversity.

Animal Reproduction and Development

Most animals are diploid organisms, significant 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. Most animals undergo sexual reproduction: This fact distinguishes animals from fungi, protists, and leaner, where asexual reproduction is mutual or exclusive. Yet, a few groups, such every bit cnidarians, flatworm, and roundworms, undergo asexual reproduction, although about all of those animals also accept a sexual phase to their life cycle.

Processes of Animal Reproduction and Embryonic Development

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

Some animate being species—including ocean stars and sea anemones, as well equally some insects, reptiles, and fish—are capable of asexual reproduction. The almost mutual forms of asexual reproduction for stationary aquatic animals include budding and fragmentation, where office of a parent private can carve up and grow into a new individual. In contrast, a form of asexual reproduction found in sure insects and vertebrates is chosen parthenogenesis (or "virgin showtime"), where unfertilized eggs can develop into new male offspring. This type of parthenogenesis is called haplodiploidy. These types of asexual reproduction produce genetically identical offspring, which is disadvantageous from the perspective of evolutionary adaptability because of the potential buildup of deleterious mutations. However, for animals that are limited in their capacity to concenter mates, asexual reproduction tin ensure genetic propagation.

Later fertilization, a series of developmental stages occur during which chief germ layers are established and reorganize to course an embryo. During this process, animal tissues brainstorm to specialize and organize into organs and organ systems, determining their future morphology and physiology. Some animals, such equally grasshoppers, undergo incomplete metamorphosis, in which the young resemble the adult. Other animals, such as some insects, undergo complete metamorphosis where individuals enter ane or more larval stages that may in differ in structure and office from the developed (Figure \(\PageIndex{two}\)). For the latter, the young and the adult may have different diets, limiting competition for nutrient between them. Regardless of whether a species undergoes consummate or incomplete metamorphosis, the series of developmental stages of the embryo remains largely the same for most members of the animal kingdom.

Figure \(\PageIndex{2}\): (a) The grasshopper undergoes incomplete metamorphosis. (b) The butterfly undergoes consummate metamorphosis. (credit: S.Due east. Snodgrass, USDA)

The procedure of animal development begins with the cleavage, or series of mitotic cell divisions, of the zygote (Figure \(\PageIndex{three}\)). Three jail cell divisions transform the single-celled zygote into an eight-celled construction. Subsequently further prison cell division and rearrangement of existing cells, a 6–32-celled hollow structure called a blastula is formed. Next, the blastula undergoes further jail cell division and cellular rearrangement during a procedure called gastrulation. This leads to the formation of the next developmental stage, the gastrula, in which the hereafter digestive cavity is formed. Unlike cell layers (called germ layers) are formed during gastrulation. These germ layers are programmed to develop into certain tissue types, organs, and organ systems during a process called organogenesis.

Figure \(\PageIndex{three}\): During embryonic evolution, the zygote undergoes a series of mitotic cell divisions, or cleavages, to course an eight-cell stage, then a hollow blastula. During a process called gastrulation, the blastula folds in to form a cavity in the gastrula.

Link to Learning

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

The Role of Homeobox (Hox) Genes in Animate being Evolution

Since the early 19^thursday century, scientists have observed that many animals, from the very simple to the complex, shared similar embryonic morphology and development. Surprisingly, a human embryo and a frog embryo, at a certain stage of embryonic development, await remarkably alike. For a long time, scientists did not sympathise why so many creature species looked similar during embryonic evolution simply were very different as adults. They wondered what dictated the developmental direction that a fly, mouse, frog, or human being embryo would accept. Most the finish of the 20^th century, a particular class of genes was discovered that had this very job. These genes that determine fauna structure are called "homeotic genes," and they contain Deoxyribonucleic acid sequences chosen homeoboxes. The animal genes containing homeobox sequences are specifically referred to as Hox genes. This family of genes is responsible for determining the general body programme, such as the number of trunk segments of an animal, the number and placement of appendages, and animal head-tail directionality. The first Hox genes to be sequenced were those from the fruit wing (Drosophila melanogaster). A unmarried Hox mutation in the fruit fly tin result in an actress pair of wings or even appendages growing from the "wrong" body part.

While in that location are a great many genes that play roles in the morphological evolution of an animal, what makes Hox genes so powerful is that they serve as master command genes that can turn on or off large numbers of other genes. Hox genes do this by coding transcription factors that control the expression of numerous other genes. Hox genes are homologous in the beast kingdom, that is, the genetic sequences of Hox genes and their positions on chromosomes are remarkably similar across nearly animals because of their presence in a common ancestor, from worms to flies, mice, and humans (Figure \(\PageIndex{4}\)). One of the contributions to increased animal body complexity is that Hox genes have undergone at to the lowest degree two duplication events during beast evolution, with the additional genes allowing for more complex body types to evolve.

Art Connexion

Effigy \(\PageIndex{4}\): Hox genes are highly conserved genes encoding transcription factors that determine the form of embryonic development in animals. In vertebrates, the genes have been duplicated into four clusters: Hox-A, Hox-B, Hox-C, and Hox-D. Genes within these clusters are expressed in sure body segments at certain stages of evolution. Shown here is the homology between Hox genes in mice and humans. Note how Hox cistron expression, as indicated with orange, pink, blueish and dark-green shading, occurs in the aforementioned body segments in both the mouse and the human.

If a Hox 13 gene in a mouse was replaced with a Hox 1 gene, how might this alter animal evolution?

Summary

Animals plant an incredibly diverse kingdom of organisms. Although animals range in complexity from simple bounding main sponges to human being beings, most members of the animal kingdom share sure features. Animals are eukaryotic, multicellular, heterotrophic organisms that ingest their food and usually develop into motile creatures with a fixed body plan. A major feature unique to the animal kingdom is the presence of differentiated tissues, such equally nerve, muscle, and connective tissues, which are specialized to perform specific functions. About animals undergo sexual reproduction, leading to a series of developmental embryonic stages that are relatively similar across the animal kingdom. A class of transcriptional control genes called Hox genes directs the arrangement of the major animal body plans, and these genes are strongly homologous beyond the animal kingdom.

Art Connections

Figure \(\PageIndex{4}\): If a Hox 13 gene in a mouse was replaced with a Hox 1 gene, how might this alter animal evolution?

Answer

The animal might develop two heads and no tail.

Glossary

blastula

xvi–32 jail cell stage of development of an beast embryo

trunk plan

morphology or abiding shape of an organism

cleavage

prison cell division of a fertilized egg (zygote) to form a multicellular embryo

gastrula

stage of brute development characterized past the germination of the digestive cavity

germ layer

collection of cells formed during embryogenesis that will requite ascension to future torso tissues, more pronounced in vertebrate embryogenesis

Hox factor

(also, homeobox gene) master control factor that can turn on or off large numbers of other genes during embryogenesis

organogenesis

formation of organs in animate being embryogenesis

Source: https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book:_General_Biology_%28OpenStax%29/5:_Biological_Diversity/27:_Introduction_to_Animal_Diversity/27.1:_Features_of_the_Animal_Kingdom

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