27.1 Features of the Animal Kingdom
3 min read•june 14, 2024
Animals are diverse, organisms with unique traits. They're heterotrophs, lack cell walls, and have specialized tissues. Most can move and reproduce sexually, though some use asexual methods. Their body plans often show and are shaped by .
Animal reproduction can be sexual or asexual. Sexual reproduction mixes genes, creating diverse offspring. Asexual reproduction makes clones. Hox genes guide body development along the head-tail axis. These genes are crucial in forming different body parts and are found in many animal groups.
Defining Characteristics and Reproduction in the Animal Kingdom
Defining characteristics of Animalia
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- Multicellular organisms composed of multiple cells with membrane-bound organelles (nucleus, mitochondria)
- nutrition obtains energy by consuming other organisms (plants, animals, fungi)
- Lack cell walls allows for greater flexibility and mobility compared to plants and fungi
- Specialized tissues and organs perform specific functions
- coordinates responses to stimuli and controls body functions
- enables movement and locomotion
- breaks down food and absorbs nutrients
- produces and facilitates reproduction
- Most exhibit at some point in their life cycle enables searching for food (prey), mates, and avoiding predators (escape)
- Reproduce sexually with some exceptions involves fusion of male and female gametes (sperm and egg)
- can be external (aquatic environments) or internal (terrestrial environments)
- Body plan organization often involves symmetry, which can be radial or bilateral
Sexual vs asexual reproduction in animals
- Sexual reproduction involves the fusion of male and female gametes
- Produces genetically diverse offspring through recombination of genetic material
- generates haploid gametes with half the number of chromosomes
- Fertilization restores the diploid number in the
- Asexual reproduction involves a single parent
- Produces genetically identical offspring (clones) without genetic variation
- Examples include:
- in some invertebrates (amoeba, planaria)
- in hydras and some sponges (new individual grows from parent)
- in some sea stars and flatworms (body splits into multiple parts)
- form of asexual reproduction in which an unfertilized egg develops into a new individual
- Occurs in some insects (aphids), crustaceans (water fleas), and reptiles (some lizards and snakes)
Hox Genes and Body Plan Development
Hox genes in animal development
- Hox genes are a group of related genes that control the body plan of an embryo along the anterior-posterior (head-tail) axis
- Hox genes contain the sequence a 180 base pair DNA sequence
- Homeobox encodes a protein domain called the a 60 amino acid DNA-binding motif
- Homeodomain binds to specific DNA sequences regulates the expression of target genes involved in development
- Hox genes are arranged in clusters on the chromosome order of genes in the cluster corresponds to the order of their expression along the ()
- Mutations in Hox genes can cause transformations of one body part into another
- For example, mutations in the gene in fruit flies can cause legs to develop in place of antennae ()
- Conservation of Hox genes across diverse animal phyla (nematodes, insects, vertebrates) suggests a common evolutionary origin of body plan development
- Hox genes play a crucial role in the development of , which give rise to different tissues and organs
Animal Body Organization and Development
Embryonic development and body structure
- Formation of during early embryonic development
- Ectoderm: outer layer, gives rise to skin and nervous system
- Mesoderm: middle layer, develops into muscles, bones, and circulatory system
- Endoderm: inner layer, forms digestive and respiratory systems
- Presence or absence of a (body cavity) influences organ organization and development
- in some animal groups allows for specialized body regions and improved mobility
- in certain species involves dramatic changes in body structure during development
Thermoregulation strategies
- : body temperature regulated by external environment, common in fish, amphibians, and reptiles
- : internal regulation of body temperature, characteristic of birds and mammals
Key Terms to Review (34)
Antennapedia: Antennapedia is a gene that plays a crucial role in the development of body segmentation and appendage formation in arthropods, particularly in the fruit fly Drosophila melanogaster. This gene is part of a larger group of homeotic genes that determine the identity of body segments and the structures that arise from them. Mutations in the Antennapedia gene can lead to dramatic changes in an organism's morphology, illustrating the importance of genetic regulation in developmental biology.
Anterior-posterior axis: The anterior-posterior axis is a key developmental feature in animals that describes the front-to-back orientation of an organism. This axis is crucial for understanding the body plan and organization of many animals, as it helps to establish the spatial arrangement of structures and systems, influencing how organisms develop and function. The anterior end typically corresponds to the head region, while the posterior end aligns with the tail or rear, playing a vital role in evolutionary adaptations and anatomical symmetry.
Binary fission: Binary fission is a form of asexual reproduction in which a single organism divides into two identical daughter cells. This process is primarily observed in prokaryotic cells and is crucial for their growth and reproduction, enabling rapid population increases. It also plays a significant role in the study of cell division, contributing to our understanding of how organisms reproduce and evolve.
Blastomeres: Blastomeres are the smaller cells formed during the early stages of embryonic development through the process of cleavage. These cells are crucial in forming the blastula, an early stage in animal development.
Budding: Budding is a form of asexual reproduction where a new organism develops from an outgrowth or bud due to cell division at one particular site. This process can be seen in various organisms, including viruses and certain animals like hydras.
Budding: Budding is a form of asexual reproduction where a new organism develops from an outgrowth or bud on the parent organism. This process allows for rapid population increase and is a key feature in some animals, particularly in specific phyla, illustrating how organisms can reproduce without the need for gametes.
Coelom: A coelom is a fluid-filled body cavity located within the mesoderm of triploblastic animals, serving as a cushion for internal organs and providing space for their development and movement. It plays a critical role in the overall organization and function of complex organisms, influencing their structure and physiological processes.
Digestive system: The digestive system is a complex network of organs and glands that work together to break down food, absorb nutrients, and eliminate waste. It plays a crucial role in the overall physiology of animals, influencing metabolism, growth, and energy levels. In the animal kingdom, different species exhibit diverse digestive adaptations that reflect their feeding habits and ecological niches.
Ectothermy: Ectothermy refers to the physiological condition where an organism relies on external environmental sources to regulate its body temperature, as opposed to generating heat internally. This adaptation allows ectothermic animals, such as many reptiles and fish, to conserve energy and survive in varied habitats, affecting their behavior, physiology, and ecological interactions.
Endothermy: Endothermy is the physiological ability of an organism to generate and regulate its own body temperature, maintaining it independently of the external environment. This adaptation allows endothermic animals to remain active in a variety of temperatures, enhancing their survival and reproductive success. By using metabolic heat production, these organisms can thrive in cold climates and continue their activities, unlike ectotherms that depend on environmental heat sources.
Eukaryotic: Eukaryotic refers to a type of cell that has a true nucleus enclosed within membranes, along with other membrane-bound organelles. These cells are more complex than prokaryotic cells and can be unicellular or multicellular, forming the basis for various life forms, including plants, animals, fungi, and protists.
Fertilization: Fertilization is the biological process where male and female gametes unite to form a zygote, marking the beginning of a new organism's development. This event is crucial for sexual reproduction, involving the combination of genetic material from two parents, which contributes to genetic diversity and evolutionary processes.
Fragmentation: Fragmentation is a form of asexual reproduction where an organism splits into fragments, each capable of developing into a new individual. This method is common in some invertebrates and involves regeneration of missing parts.
Fragmentation: Fragmentation is a form of asexual reproduction where an organism breaks into distinct pieces, each capable of developing into a new individual. This method allows for rapid population increase and is seen in various species, including certain animals and plants. The ability to regenerate lost parts not only helps in species survival but also has implications for biodiversity and ecosystem stability.
Gametes: Gametes are specialized reproductive cells that combine during fertilization to form a new organism. They are haploid cells, meaning they contain only one set of chromosomes, which is crucial for maintaining the correct chromosome number in offspring when two gametes fuse during sexual reproduction.
Germ layers: Germ layers are the primary layers of cells that form during embryonic development. These layers differentiate into various tissues and organs in animals.
Germ layers: Germ layers are the primary layers of cells that form during embryonic development in animals, specifically the ectoderm, mesoderm, and endoderm. These layers give rise to all the organs and tissues in an animal's body, playing a crucial role in determining the overall structure and function of the organism. The presence and arrangement of germ layers are key features that differentiate various animal groups and reflect their evolutionary relationships.
Heterotrophic: Heterotrophic refers to organisms that cannot produce their own food and instead obtain energy by consuming other organic matter. These organisms play a vital role in ecosystems as they contribute to nutrient cycling and energy transfer through food webs. By relying on other organisms for sustenance, heterotrophs interact with producers and decomposers, forming a complex network of life that maintains ecological balance.
Homeobox: A homeobox is a DNA sequence found within genes that is critical for regulating the development of anatomical structures in various organisms. These sequences encode proteins known as homeodomain proteins, which play a vital role in the transcriptional regulation of genes involved in developmental processes, ensuring that body structures are formed in the correct place and at the right time.
Homeodomain: A homeodomain is a conserved protein structure of about 60 amino acids that is crucial for the regulation of gene expression during the development of multicellular organisms. It allows proteins, known as transcription factors, to bind to specific DNA sequences and control the transcription of target genes, playing a significant role in defining body patterns and structures in animals.
Homeotic transformation: Homeotic transformation refers to a phenomenon where one body part or structure is replaced by another, often as a result of genetic mutations that affect the expression of homeotic genes. These genes play a crucial role in determining the identity and position of body segments during development, influencing the overall body plan of an organism and highlighting the evolutionary relationships within the animal kingdom.
Hox genes: Hox genes are a group of related genes that play a crucial role in the body plan development of animals, determining the identity and arrangement of various body segments during embryonic development. These genes are highly conserved across different species, indicating their fundamental importance in the evolutionary history of the animal kingdom and their role in organogenesis and vertebrate formation.
Meiosis: Meiosis is a specialized form of cell division that reduces the chromosome number by half, resulting in the production of four genetically diverse gametes, or sex cells. This process is crucial for sexual reproduction, as it ensures genetic diversity and maintains the species' chromosome number across generations.
Metamorphosis: Metamorphosis is a biological process through which an organism undergoes a significant change in form and structure during its development, often transitioning from a juvenile form to an adult form. This transformation can involve drastic physical changes, behavioral shifts, and ecological adaptations, and is particularly evident in certain animal groups, highlighting the diverse strategies of development within the animal kingdom.
Motility: Motility refers to the ability of an organism to move independently, using its own energy. This movement is crucial for various biological functions such as finding food, escaping predators, and mating. In the context of the animal kingdom, motility is a defining feature that distinguishes animals from other life forms, influencing their behavior, ecology, and evolutionary adaptations.
Multicellular: Multicellular refers to organisms that consist of more than one cell, allowing for complex structures and functions. This arrangement enables specialization of cells, where different cells perform distinct tasks, contributing to the overall efficiency and adaptability of the organism. Multicellularity is a key feature in various life forms, especially in certain groups of protists and all animals, highlighting the evolutionary advantages it provides.
Muscular system: The muscular system is a complex network of muscles that enables movement in the body, facilitates posture, and produces heat through muscle contractions. This system plays a crucial role in the functioning of organisms within the animal kingdom, as it interacts closely with the skeletal system to allow for locomotion, and it is vital for various physiological functions such as circulation and digestion.
Nervous system: The nervous system is a complex network of cells and tissues responsible for transmitting signals between different parts of the body, coordinating voluntary and involuntary actions. It plays a crucial role in processing sensory information, controlling motor functions, and regulating homeostasis, thus ensuring the organism can respond appropriately to internal and external stimuli.
Parthenogenesis: Parthenogenesis is a form of asexual reproduction where an egg develops into a new individual without fertilization by sperm. This reproductive strategy allows some organisms to reproduce without the need for a mate, which can be advantageous in certain environmental conditions. While it occurs in various species across the animal kingdom, parthenogenesis is particularly notable in some invertebrates and lower vertebrates, highlighting diverse reproductive strategies beyond traditional sexual reproduction.
Reproductive system: The reproductive system is a biological system that enables organisms to produce offspring and ensures the continuation of their species. This system includes specialized organs and structures that facilitate reproduction, such as gamete production, fertilization, and gestation. In the context of the Animal Kingdom, the reproductive system plays a critical role in evolutionary processes, such as natural selection and adaptation.
Segmentation: Segmentation is the division of an organism's body into repetitive sections, or segments, which often play a role in its structure and function. This body plan is significant as it allows for specialization of segments, providing advantages in movement, flexibility, and the organization of body systems.
Spatial collinearity: Spatial collinearity refers to the phenomenon where multiple morphological features or traits are aligned along a spatial axis, often resulting in a correlation between their distribution in an organism's body plan. This alignment can provide insights into evolutionary relationships and functional adaptations among different species within the animal kingdom. Understanding spatial collinearity helps clarify how structural organization in animals is influenced by evolutionary pressures and ecological roles.
Symmetry: Symmetry refers to a balanced arrangement of body structures in organisms, where parts are organized in a harmonious way, reflecting an overall proportionality. In the context of the animal kingdom, symmetry plays a critical role in anatomy, influencing movement, reproduction, and evolutionary adaptations, and can be categorized mainly into bilateral and radial symmetry.
Zygote: A zygote is the initial cell formed when two gametes, typically a sperm and an egg, fuse during fertilization. This single cell undergoes division and development, leading to the formation of a new organism, making it a crucial stage in sexual reproduction across various life forms.