Which Of The Following Is True About All Animals?

Characteristics of the Animal Kingdom

The animal kingdom is very various, but animals share many mutual characteristics, such as methods of development and reproduction.

Learning Objectives

Describe the methods used to classify animals

Key Takeaways

Central Points

• Animals vary in complexity and are classified based on anatomy, morphology, genetic makeup, and evolutionary history.
• All animals are eukaryotic, multicellular organisms, and well-nigh animals have complex tissue construction with differentiated and specialized tissue.
• Animals are heterotrophs; they must swallow living or expressionless organisms since they cannot synthesize their own food and tin can be carnivores, herbivores, omnivores, or parasites.
• Most animals are motile for at to the lowest degree some stages of their lives, and well-nigh animals reproduce sexually.

Key Terms

• trunk plan: an aggregation of morphological features shared amongst many members of a phylum-level group
• heterotroph: an organism that requires an external supply of energy in the form of food, equally it cannot synthesize its own
• extant: withal in existence; non extinct

Introduction: Features of the Animal Kingdom

Animal evolution began in the ocean over 600 million years agone with tiny creatures that probably do non resemble whatever living organism today. Since then, animals have evolved into a highly-diverse kingdom. Although over 1 million extant (currently living) species of animals have been identified, scientists are continually discovering more than species as they explore ecosystems around the world. The number of extant species is estimated to be between three and xxx million.

But what is an animal? While we can hands identify dogs, birds, fish, spiders, and worms equally animals, other organisms, such as corals and sponges, are non equally easy to classify. Animals vary in complication, from body of water sponges to crickets to chimpanzees, and scientists are faced with the difficult task of classifying them within a unified organisation. They must identify traits that are common to all animals also as traits that can exist used to distinguish amid related groups of animals. The brute classification arrangement characterizes animals based on their anatomy, morphology, evolutionary history, features of embryological development, and genetic makeup. This classification scheme is constantly developing equally new information about species arises. Understanding and classifying the bully variety of living species aid us improve sympathize how to conserve the multifariousness of life on world.

Even though members of the animal kingdom are incredibly diverse, most animals share certain features that distinguish them from organisms in other kingdoms. All animals are eukaryotic, multicellular organisms, and nearly all animals accept a complex tissue structure with differentiated and specialized tissues. Most animals are motile, at least during sure life stages. 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 as nigh plants, which synthesize their own nutrients through photosynthesis. Equally heterotrophs, animals may exist carnivores, herbivores, omnivores, or parasites. About animals reproduce sexually with the offspring passing through a series of developmental stages that establish a fixed body plan. The body plan refers to the morphology of an animal, determined by developmental cues.

Heterotrophs: All animals are heterotrophs that derive energy from food. The (a) black behave 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 heart of dogs and other mammals.

Complex Tissue Structure

Animals, likewise Parazoa (sponges), are characterized past specialized tissues such equally muscle, nervus, connective, and epithelial tissues.

Learning Objectives

Listing the various specialized tissue types establish in animals and describe their functions

Primal Takeaways

Key Points

• Animal cells don't have jail cell walls; their cells may be embedded in an extracellular matrix and accept unique structures for intercellular advice.
• Animals take nerve and muscle tissues, which provide coordination and move; these are non nowadays in plants and fungi.
• Complex animal bodies demand connective tissues fabricated upwardly of organic and inorganic materials that provide back up and structure.
• Animals are as well characterized by epithelial tissues, like the epidermis, which part in secretion and protection.
• The animal kingdom is divided into Parazoa (sponges), which do not contain true specialized tissues, and Eumetazoa (all other animals), which do contain true specialized tissues.

Fundamental Terms

• Parazoa: a taxonomic subkingdom within the kingdom Animalia; the sponges
• Eumetazoa: a taxonomic subkingdom, within kingdom Animalia; all animals except the sponges
• epithelial tissue: one of the four basic types of animate being tissue, which line the cavities and surfaces of structures throughout the torso, and besides form many glands

Complex Tissue Structure

As multicellular organisms, animals differ from plants and fungi considering their cells don't take cell walls; their cells may be embedded in an extracellular matrix (such as bone, skin, or connective tissue); and their cells accept unique structures for intercellular communication (such every bit gap junctions). In add-on, animals possess unique tissues, absent-minded in fungi and plants, which let coordination (nerve tissue) and move (muscle tissue). Animals are too characterized past specialized connective tissues that provide structural support for cells and organs. This connective tissue constitutes the extracellular environment of cells and is made up of organic and inorganic materials. In vertebrates, bone tissue is a type of connective tissue that supports the entire body construction. The circuitous bodies and activities of vertebrates need such supportive tissues. Epithelial tissues encompass, line, protect, and secrete; these tissues include the epidermis of the integument: the lining of the digestive tract and trachea. They likewise make up the ducts of the liver and glands of avant-garde animals.

The brute kingdom is divided into Parazoa (sponges) and Eumetazoa (all other animals). Equally very simple animals, the organisms in group Parazoa ("beside brute") do non incorporate true specialized tissues. Although they practise 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 call back of animals, we usually recall of Eumetazoans, since about animals autumn into this category.

Sponges: Sponges, such every bit those in the Caribbean Ocean, are classified as Parazoans because they are very simple animals that do not contain true specialized tissues.

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 part of what allows for such incredible animate being diversity. For example, the development of nerve tissues and muscle 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 come across their nutritional demands.

Animal Reproduction and Development

Virtually animals undergo sexual reproduction and have similar forms of development dictated by Hox genes.

Learning Objectives

Explain the processes of beast reproduction and embryonic evolution

Key Takeaways

Cardinal Points

• Near animals reproduce through sexual reproduction, simply some animals are capable of asexual reproduction through parthenogenesis, budding, or fragmentation.
• Post-obit fertilization, an embryo is formed, and animal tissues organize into organ systems; some animals may also undergo incomplete or consummate metamorphosis.
• Cleavage of the zygote leads to the formation of a blastula, which undergoes further cell division and cellular rearrangement during a process called gastrulation, which leads to the formation of the gastrula.
• During gastrulation, the digestive crenel and germ layers are formed; these volition later develop into certain tissue types, organs, and organ systems during a process called organogenesis.
• Hox genes are responsible for determining the general body program, such as the number of torso segments of an beast, the number and placement of appendages, and fauna head-tail directionality.
• Hox genes, like beyond most animals, can turn on or off other genes by coding transcription factors that control the expression of numerous other genes.

Key Terms

• metamorphosis: a change in the grade and often habits of an animal after the embryonic stage during normal development
• Hox gene: genes responsible for determining the general torso plan, such as the number of trunk segments of an animal, the number and placement of appendages, and animate being head-tail directionality
• blastula: a half dozen-32-celled hollow structure that is formed after a zygote undergoes prison cell sectionalization

Animal Reproduction and Development

Most animals are diploid organisms (their body, or somatic, cells are diploid) with haploid reproductive ( gamete ) cells produced through meiosis. The majority of animals undergo sexual reproduction. This fact distinguishes animals from fungi, protists, and bacteria where asexual reproduction is common or exclusive. All the same, a few groups, such equally cnidarians, flatworms, and roundworms, undergo asexual reproduction, although well-nigh all of those animals also have a sexual phase to their life bicycle.

Processes of Animal Reproduction and Embryonic Development

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

Some animal species (including sea stars and bounding main anemones, as well every bit some insects, reptiles, and fish) are capable of asexual reproduction. The nigh mutual forms of asexual reproduction for stationary aquatic animals include budding and fragmentation where function of a parent individual tin separate and grow into a new individual. In dissimilarity, a form of asexual reproduction constitute in certain insects and vertebrates is called parthenogenesis where unfertilized eggs can develop into new offspring. This type of parthenogenesis in insects is called haplodiploidy and results in male offspring. These types of asexual reproduction produce genetically identical offspring, which is disadvantageous from the perspective of evolutionary adaptability considering of the potential buildup of deleterious mutations. However, for animals that are limited in their capacity to attract mates, asexual reproduction can ensure genetic propagation.

After fertilization, a series of developmental stages occur during which primary germ layers are established and reorganize to course an embryo. During this process, brute tissues begin to specialize and organize into organs and organ systems, determining their hereafter morphology and physiology. Some animals, such every bit grasshoppers, undergo incomplete metamorphosis, in which the immature resemble the developed. Other animals, such as some insects, undergo complete metamorphosis where individuals enter one or more larval stages that may differ in structure and function from the developed. In complete metamorphosis, the young and the developed may accept different diets, limiting contest for food between them. Regardless of whether a species undergoes complete or incomplete metamorphosis, the series of developmental stages of the embryo remains largely the aforementioned for most members of the animal kingdom.

Incomplete and complete metamorphosis: (a) The grasshopper undergoes incomplete metamorphosis. (b) The butterfly undergoes complete metamorphosis.

The procedure of brute development begins with the cleavage, or series of mitotic cell divisions, of the zygote. Three cell divisions transform the unmarried-celled zygote into an eight-celled structure. After further cell division and rearrangement of existing cells, a 6–32-celled hollow structure called a blastula is formed. Next, the blastula undergoes further cell partitioning and cellular rearrangement during a process chosen gastrulation. This leads to the germination of the side by side developmental stage, the gastrula, in which the future digestive crenel is formed. Different jail cell layers (called germ layers) are formed during gastrulation. These germ layers are programed to develop into certain tissue types, organs, and organ systems during a procedure chosen organogenesis.

Embryonic development: During embryonic development, the zygote undergoes a series of mitotic prison cell divisions, or cleavages, to form an 8-prison cell stage, then a hollow blastula. During a process chosen gastrulation, the blastula folds inward to grade a cavity in the gastrula.

The Function of Homeobox (Hox) Genes in Animal Evolution

Since the early on 19^th century, scientists have observed that many animals, from the very simple to the circuitous, shared similar embryonic morphology and development. Surprisingly, a homo embryo and a frog embryo, at a certain stage of embryonic development, appear remarkably like. For a long fourth dimension, scientists did not empathize why then many animate being species looked similar during embryonic development, merely were very different equally adults. About the terminate of the 20^th century, a particular form of genes that dictate developmental direction was discovered. These genes that determine animal construction are called "homeotic genes." They comprise DNA sequences called homeoboxes, with specific sequences referred to as Hox genes. This family of genes is responsible for determining the full general body programme: the number of trunk segments of an animate being, 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 single Hox mutation in the fruit fly can result in an extra pair of wings or even appendages growing from the "incorrect" trunk part.

There are many genes that play roles in the morphological development of an creature, simply Hox genes are so powerful because they tin can plow on or off large numbers of other genes. Hox genes do this past coding transcription factors that control the expression of numerous other genes. Hox genes are homologous in the animal kingdom: the genetic sequences and their positions on chromosomes are remarkably similar beyond most animals (e.g., worms, flies, mice, humans) because of their presence in a common ancestor. Hox genes have undergone at least two duplication events during brute evolution: the additional genes allowed more complex torso types to evolve.

Hox genes: Hox genes are highly-conserved genes encoding transcription factors that make up one's mind the class of embryonic development in animals. In vertebrates, the genes have been duplicated into 4 clusters: Hox-A, Hox-B, Hox-C, and Hox-D. Genes inside these clusters are expressed in certain torso segments at certain stages of evolution. Shown hither is the homology between Hox genes in mice and humans. Annotation how Hox gene expression, equally indicated with orange, pink, blue, and green shading, occurs in the aforementioned body segments in both the mouse and the human.

Source: https://courses.lumenlearning.com/boundless-biology/chapter/features-of-the-animal-kingdom/

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