Biology 152 Chapter 10

Hox genes

The animal genes containing homeobox sequences.

Eumetazoa

- "True" animals with true differentiated tissues. - Are subdivided into radially symmetrical animals and bilaterally symmetrical animals, and are thus classified into the clades Bilateria or Radiata. - Cnidarians and ctenophores are animal phyla with true radial symmetry. All other Eumetazoa are members of the Bilateria clade. - The bilaterally symmetrical animals are further divided into deuterostomes (including chordates and echinoderms) and two distinct clades of protostomes (including ecdysozoans and lophotrochozoans).

Pseudocoelomates

- A third group of triploblasts has a slightly different coelom derived partly from mesoderm and partly from endoderm, which is found between the two layers. - Although still functional, these are considered false coeloms, and those animals are called pseudocoelomates. - The phylum Nematoda (roundworms) is an example of a pseudocoelomate.

Axon

- A tube-like structure that propagates the integrated signal to specialized endings called axon terminals. - Neurons usually have 1 or 2 axons, but some can have none. - Some axons are covered with myelin.

The animal classification system characterizes animals based on:

- Anatomy - Morphology - Evolutionary History - Features of embryological development, - Genetic makeup.

Animal Characterization Based on Features of Embryological Development:

- Animals develop either two or three embryonic germs layers (Figure 4). - The animals that display radial symmetry develop two germ layers, an inner layer (endoderm) and an outer layer (ectoderm). These animals are called diploblasts. Diploblasts have a non-living layer between the endoderm and ectoderm. - More complex animals (those with bilateral symmetry) develop three tissue layers: an inner layer (endoderm), an outer layer (ectoderm), and a middle layer (mesoderm). Animals with three tissue layers are called triploblasts.

Invertebrates

- Animals that do not contain bony structures, such as a cranium and vertebrae. - The simplest of all invertebrate animals are the Parazoans, which include only the phylum Porifera: the sponges.

Eucoelomates

- Animals with a true coelom are called eucoelomates (or coelomates). - A true coelom arises entirely within the mesoderm germ layer and is lined by an epithelial membrane. - This membrane also lines the organs within the coelom, connecting and holding them in position while allowing them some free motion. -Annelids, mollusks, arthropods, echinoderms, and chordates are all eucoelomates.

Why are Hox Genes so powerful?

- They serve as master control 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 animal kingdom. - One of the contributions to increased animal body complexity is that Hox genes have undergone at least two duplication events during animal evolution, with the additional genes allowing for more complex body types to evolve.

What features do Cnidarias have that Porifera do not? A. Cnidarians have simple tissues B. Cnidarians have differentiated cells C. Cnidarians have intercellular connections D. Cnidarians utilize diffusion for gas exchange

A. Cnidarians have simple tissues C. Cnidarians have intercellular connections D. Cnidarians utilize diffusion for gas exchange

Which of the following is NOT possible? A. radially symmetrical diploblast B. diploblastic eucoelomate C. protostomic coelomate D. bilaterally symmetrical deuterostome

B. diploblastic eucoelomate

The most common forms of asexual reproduction for stationary aquatic animals include:

Budding and fragmentation, where part of a parent individual can separate and grow into a new individual.

Which of the following organism is most likely to be a diploblast? A. sea star B. shrimp C. jellyfish D. insect

C. Jellyfish

Neurons contain ________________, which can receive signals from other neurons. A. axons B. mitochondria C. dendrites D. Golgi bodies

C. dendrites

What type of glial cell is involved in the immune defense of the CNS? A. Schwann cells B. oligodendrocytes C. microglia D. astrocytes

C. microglia

During embryonic development, unique cell layers develop and distinguish during a stage called ________. A. the blastula stage B. the germ layer stage C. the gastrula stage D. the organogenesis stage

C. the gastrula stage

Indeterminate Cleavage

Deuterostomes undergo indeterminate cleavage, in which cells are not yet pre-determined at this early stage to develop into specific cell types. -These cells are referred to as Undifferentiated Cells. -This characteristic of deuterostomes is reflected in the existence of familiar embryonic stem cells, which have the ability to develop into any cell type until their fate is programmed at a later developmental stage as well as the capability of producing identical twins.

Radial Cleavage

Deuterostomes undergo radial cleavage, where the cleavage axes are either parallel or perpendicular to the polar axis, resulting in the alignment of the cells between the two poles.

Oocyte

Egg cells in sponges

Dendritic Spines

Further increase surface area for possible synaptic connections.

Homeotic genes:

Genes that determine animal structure and they contain DNA sequences called homeoboxes.

Bipolar Neuron

Has one axon and one dendrite extending from the soma.

Ecdysozoa

Includes nematodes and arthropods; they are so named for a commonly found characteristic among the group: exoskeletal molting (termed ecdysis).

Lophotrochozoa

Named for two structural features, each common to certain phyla within the clade. - Some lophotrochozoan phyla are characterized by a larval stage called trochophore larvae, and other phyla are characterized by the presence of a feeding structure called a lophophore.

Unipolar Neuron

Only have one structure that extends away from the soma. These neurons are not found in vertebrates but are found in insects where they stimulate muscles or glands.

Nematocysts

Organelles called nematocysts that contain coiled threads that may bear barb (stingers). These cells are present around the mouth and tentacles. Found in Cnidarians.

Complete metamorphosis:

Other animals, such as some insects, undergo complete metamorphosis where individuals enter one or more larval stages that may in differ in structure and function from the adult

Archenteron

Primitive digestive tube and related to Enterocoely.

Spongocytes

Produce the protein spongin in the majority of sponges. These cells produce collagen to maintain the consistency of the mesohyl.

Determinate Cleavage

Protostomes also undergo determinate cleavage. This means that even at this early stage, the developmental fate of each embryonic cell is already determined. A cell does not have the ability to develop into any cell type.

Spiral Cleavage

Protostomes undergo spiral cleavage, meaning that the cells of one pole of the embryo are rotated, and thus misaligned, with respect to the cells of the opposite pole. This is due to the oblique angle of the cleavage.

Diploblast/Diploblastic

The animals that display radial symmetry develop two germ layers, an inner layer (endoderm) and an outer layer (ectoderm). They have a non-living layer between the endoderm and ectoderm.

Neurogenesis

The birth of new neurons, continues into adulthood.

The Axon Hillock

The cell body contains a specialized structure, the axon hillock that integrates signals from multiple synapses and serves as a junction between the cell body and an axon.

Gastrula

The future digestive cavity is formed.(Blastopore?)

Gastrodermis

The inner layer (from endoderm) and lines the digestive cavity.

Multipolar Neuron

The most common type of neuron. Each multipolar neuron contains one axon and multiple dendrites. Multipolar neurons can be found in the central nervous system (brain and spinal cord).

Epidermis

The outer layer (from ectoderm) and lines the outside of the animal.

Zygote

The small, motile male sperm fertilizes the much larger, sessile female egg. This process produces a diploid fertilized egg called a zygote

Secondary Radial Symmetry

They are believed to have evolved from bilaterally symmetrical animals; thus, they are classified as bilaterally symmetrical. Ex: Animals in the phylum Echinodermata (such as sea stars, sand dollars, and sea urchins) display radial symmetry as adults, but their larval stages exhibit bilateral symmetry.

Morphologically symmetrical:

This means that their distribution of body parts is balanced along an axis.

Eumetazoa Group:

- Animals with true tissues. - When we think of animals, we usually think of Eumetazoans, since most animals fall into this category.

Amoebocytes

- Another crucial cell to sponges and have a variety of functions: delivering nutrients from choanocytes to other cells within the sponge, giving rise to eggs for sexual reproduction (which remain in the mesohyl), delivering phagocytized sperm from choanocytes to eggs, and differentiating into more-specific cell types. - More-specific cell types include: Collencytes, Lophocytes, Sclerocytes, Spongocytes.

Gemmules

- Are environmentally resistant structures produced by adult sponges wherein the typical sponge morphology is inverted. - In gemmules, an inner layer of amoebocytes is surrounded by a layer of collagen (spongin) that may be reinforced by spicules. - The collagen that is normally found in the mesohyl becomes the outer protective layer. - Are resistant to desiccation, and remain dormant for long periods, they are an excellent means of colonization for a sessile organism.

Choanocytes (collar cells)

- Are present at various locations, depending on the type of sponge, but they always line the inner portions of some space through which water flows (the spongocoel in simple sponges, canals within the body wall in more complex sponges, and chambers scattered throughout the body in the most complex sponges). - Tend to line certain inner portions of the sponge body that surround the mesohyl. - The structure of a choanocyte is critical to its function, which is to generate a water current through the sponge and to trap and ingest food particles by phagocytosis.

Types of Glia Cells

- Astrocytes: Provide nutrients and other substances to neurons, blood brain barrier, transmit calcium waves. - Satellite Glia: Provide nutrients and structural support for neurons in peripheral nervous system. - Microglia scavenge and degrade dead cells and protect brain. - Oligodendrocytes: form myelin sheaths around axons in the central nervous system (CNS). - Schwan cells: form myelin sheaths around axons in the PNS where a single Schwann cell provides myelin for only one axon as the entire Schwann cell surrounds the axon. - Radial Glia: an give rise to new neurons (neurogenesis) and serve as scaffolds for developing neurons as they migrate to their end destinations. - Ependymal cells: line fluid-filled ventricles of the brain and the central canal of the spinal cord. They are involved in the production of cerebrospinal fluid, and is a component for the choroid plexus.

The process of animal development:

- Begins with the Cleavage, or series of mitotic cell divisions, of the Zygote (Figure 4). - 3 cell divisions transform the single-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 division and cellular rearrangement during a process called Gastrulation. This leads to the formation of the next developmental stage, the Gastrula, in which the future digestive cavity is formed. Different 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.

Deuterostomes:

- Blastopore forms the anus/cloaca first. - Undergoes Radial Cleavage + Indeterminate Cleavage - Enterocoelic Coelom - Mesodermal Skeleton - Include more complex animals such as chordates but also some simple animals such as echinoderms.

Protostomes:

- Blastopore forms the mouth first. - Undergoes Spiral Cleavage + Determinate Cleavage - Schizocoelic Coelom - Ectodermal Skeleton - Include arthropods, mollusks, and annelids.

Glia Cells

- Cells that provide support functions for the neurons by playing an information processing role that is complementary to neurons. - Produce Myelin. - The number of glial cells in the brain actually outnumbers the number of neurons by a factor of ten. - Neurons would be unable to function without the vital roles that are fulfilled by these glial cells.

All animals are:

- Eukaryotic, multicellular organisms, and almost all animals have a complex tissue structure with differentiated and specialized tissues. - Require 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. - As heterotrophs, animals may be carnivores, herbivores, omnivores, or parasites.

The Phylum Cnidaria: Cnidarians

- Includes animals that show radial or biradial symmetry and are diploblastic, that is, they develop from two embryonic layers. Nearly all (about 99 percent) cnidarians are marine species. - Cnidarians contain specialized cells known as cnidocytes ("stinging cells") with organelles called nematocysts. Cnidarians display two distinct morphological body plans: polyp or "stalk" and medusa or "bell". -All cnidarians show the presence of two membrane layers in the body, the epidermis and the gastrodermis. Between the two layers there is a mesoglea. - Show the presence of differentiated cell types in each tissue layer, such as nerve cells, contractile epithelial cells, enzyme-secreting cells, and nutrient-absorbing cells, as well as the presence of intercellular connections. - Development of organs or organ systems is not advanced. The nervous system is primitive, with nerve cells scattered across the body. - Predominant signaling molecules in these primitive nervous systems are chemical peptides, which perform both excitatory and inhibitory functions. - The gastrovascular cavity has only one opening that serves as both a mouth and an anus, which is termed an incomplete digestive system.

Endoderm

- Inner Germ Layer - In tetrapod vertebrates, the endoderm gives rise to the lining of the digestive tract (including the stomach, intestines, liver, and pancreas), as well as to the lining of the trachea, bronchi, and lungs of the respiratory tract, along with a few other structures.

Bilateral Symmetry:

- Involves the division of the animal through a sagittal plane, resulting in two mirror image, right and left halves, such as those of a butterfly, crab, or human body. - Animals with bilateral symmetry have a "head" and "tail" (cranial vs. caudal), front and back (dorsal vs. ventral), and right and left sides. - All true animals except those with radial symmetry are bilaterally symmetrical. - The evolution of bilateral symmetry that allowed for the formation of cranial and caudal (head and tail) ends promoted a phenomenon called cephalization, which refers to the collection of an organized nervous system at the animal's cranial end. - Bilateral symmetry allows for streamlined and directional motion. - Promoted active mobility and increased sophistication of resource-seeking and predator-prey relationships.

The Nervous System:

- It processes sensory information from outside (and inside) the body and controls all behaviors. - Nervous systems throughout the animal kingdom vary in structure and complexity. - It's made up of neurons and glia.

Sponge Digestion:

- Lack complex digestive, respiratory, circulatory, reproductive, and nervous systems. - Their food is trapped when water passes through the ostia and out through the osculum. - All other major body functions in the sponge (gas exchange, circulation, excretion) are performed by diffusion between the cells that line the openings within the sponge and the water that is passing through those openings. - All cell types within the sponge obtain oxygen from water through diffusion.

Mesoderm

- Middle Germ Layer - Gives rise to all muscle tissues (including the cardiac tissues and muscles of the intestines), connective tissues such as the skeleton and blood cells, and most other visceral organs such as the kidneys and the spleen.

Triploblasts

- More complex animals (those with bilateral symmetry) develop three tissue layers: an inner layer (endoderm), an outer layer (ectoderm), and a middle layer (mesoderm). - Some Triploblasts develop a Coelom. - Triploblasts that do not develop a coelom are called acoelomates, and their mesoderm region is completely filled with tissue, although they do still have a gut cavity.

Most animals are:

- Motile, at least during certain life stages. - Reproduce sexually, and the offspring pass through a series of developmental stages that establish a determined and fixed body plan. - 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. - Undergo sexual reproduction: This fact distinguishes animals from fungi, protists, and bacteria, where asexual reproduction is common or exclusive. However, a few groups, such as cnidarians, flatworm, and roundworms, undergo asexual reproduction, although nearly all of those animals also have a sexual phase to their life cycle.

Myelin Sheath

- Not part of Neuron. - There are periodic gaps in the myelin sheath. These gaps are sites where the signal is "recharged" as it travels along the axon.

Coelom

- Only Triploblasts - An internal body cavity derived from mesoderm. - Represents a space, usually filled with fluid, which lies between the visceral organs and the body wall. - Provides cushioning and shock absorption for the major organ systems. - Provides space for the diffusion of gases and nutrients, as well as body flexibility, promoting improved animal motility.

Ectoderm

- Outer Germ Layer - Develops into the outer epithelial covering of the body surface, the central nervous system, and a few other structures.

The animal kingdom is divided into:

- Parazoa (sponges) - Eumetazoa (all other animals)

After fertilization, a series of developmental stages occur:

- Primary germ layers are established and reorganize to form an embryo. - Animal tissues begin to specialize and organize into organs and organ systems, determining their future morphology and physiology. - Some animals, such as grasshoppers, undergo incomplete metamorphosis, or other animals, such as some insects, undergo complete metamorphosis.

The Body Plan:

- Refers to the morphology of an animal, determined by developmental cues. - One of the most prominent features of the body plan of true animals is that they are morphologically symmetrical.

Sponge Reproduction:

- Reproduce by sexual as well as asexual methods. - The typical means of asexual reproduction is either fragmentation (where a piece of the sponge breaks off, settles on a new substrate, and develops into a new individual) or budding (a genetically identical outgrowth grows from the parent and eventually detaches or remains attached to form a colony). - An atypical type of asexual reproduction is found only in freshwater sponges and occurs through the formation of gemmules. - Sexual reproduction in sponges occurs when gametes are generated. Sponges are monoecious (hermaphroditic), which means that one individual can produce both gametes (eggs and sperm) at the same time. - Sponges may also become sequentially hermaphroditic, producing oocytes first and spermatozoa later.

Pseudounipolar Neuron

- Share characteristics with both unipolar and bipolar cells. - Has a single process that extends from the soma, like a unipolar cell, but this process later branches into two distinct structures, like a bipolar cell. - Most sensory neurons are pseudounipolar and have an axon that branches into two extensions: one connected to dendrites that receive sensory information and another that transmits this information to the spinal cord.

Parazoans (Sponges)

- Simplest Invertebrates - Do not display tissue-level organization, although they do have specialized cells that perform specific functions. - Structures such as canals, chambers, and cavities enable water to move through the sponge to nearly all body cells.

Choanoflagellates

- Single celled: Cell adhesion, external cell communication, some cell differentiation. - Parazoa and Eumetazoa evolved from a common ancestral organism that resembles the modern-day protists called choanoflagellates.

Neurons

- Specialized cells that can receive and transmit chemical or electrical signals. - The ability to communicate with each other as well as with other types of cells underlies all of these behaviors. - Most neurons share the same cellular components. But neurons are also highly specialized—different types of neurons have different sizes and shapes that relate to their functional roles.

Sponge Movement:

- Sponges generally don't/can't move. - Sponge cells are capable of creeping along substrata via organizational plasticity.

Ostia

- Sponges have multiple pores called ostia on their bodies that allow water to enter the sponge. - In some sponges, ostia are formed by porocytes, single tube-shaped cells that act as valves to regulate the flow of water into the spongocoel. In other sponges, ostia are formed by folds in the body wall of the sponge.

Radial Symmetry:

- The arrangement of body parts around a central axis, as is seen in a pie. - It results in animals having top and bottom surfaces but no left and right sides, or front or back. - The two halves of a radially symmetrical animal may be described as the side with a mouth or "oral side," and the side without a mouth (the "aboral side"). - This form of symmetry marks the body plans of animals in the phyla Ctenophora and Cnidaria, including jellyfish and adult sea anemones. - Radial symmetry equips these sea creatures (which may be sedentary or only capable of slow movement or floating) to experience the environment equally from all directions. - Best suited for stationary or limited-motion lifestyles

Blastopore

- The mouth or anus develops from a structure called the blastopore. - The blastopore is the indentation formed during the initial stages of gastrulation. In later stages, a second opening forms, and these two openings will eventually give rise to the mouth and anus.

Morphology of Sponges

- The simplest sponges takes the shape of a cylinder with a large central cavity, the Spongocoel, occupying the inside of the cylinder. - Water entering the spongocoel is expelled through a large common opening called the Osculum. - Sponges exhibit a range of diversity in body forms, including variations in the size of the spongocoel, the number of osculi, and where the cells that filter food from the water are located. - Do not exhibit tissue-layer organization, they do have different cell types that perform distinct functions. - Pinacocytes, Mesohyl, Ostia, Porocytes, Choanocytes

Ways animals differ from plants and fungi:

- Their cells don't have cell walls, their cells may be embedded in an extracellular matrix (such as bone, skin, or connective tissue). - Their cells have unique structures for intercellular communication (such as gap junctions). - Possess unique tissues, absent in fungi and plants, which allow coordination (nerve tissue) of motility (muscle tissue). - Specialized connective tissues that provide structural support for cells and organs. This connective tissue constitutes the extracellular surroundings of cells and is made up of organic and inorganic materials.

Acoelomates

- Triploblasts that do not develop a coelom are called acoelomates, and their mesoderm region is completely filled with tissue, although they do still have a gut cavity. Examples of acoelomates include animals in the phylum Platyhelminthes, also known as flatworms.

Parazoa Group:

- Very simple animals, the organisms do 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 make their own food. - Asymmetry is a unique feature of Parazoa

Haplodiploidy

- Where unfertilized eggs can develop into new male offspring. - 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. - Asexual reproduction can ensure genetic propagation.

Animal Process Development Simplified

1) Cleavage of the Zygote 2) Eight Celled Stage Forms 3) Cleavage of the Eight Celled Structure forms Blastula Cross Section. 4) The Blastula undergoes Gastrulation 5) Formation of the Gastula 6) Different germ layers(cell layers) are formed through gastrulation. 7) Organogenesis takes place, where germ layers are programmed to develop into certain tissue types, organs, and organ systems.

Neuron Process:

1) Dendrites receive signals from neurons at synapses. 2) When signal received dendrites travel passively to cell body (Soma) to deliver the signal. 3) Axon Hillock --> Axons carry signal to target --> Axon Terminals --> Chemicals released at axon terminals.

Bilaterally symmetrical, tribloblastic eucoelomates can be further divided into two groups based on differences in their early embryonic development:

1) Protostomes 2) Deuterostomes Note: - These two groups are separated based on which opening of the digestive cavity develops first: mouth or anus. - Another distinction between protostomes and deuterostomes is the method of coelom formation, beginning from the gastrula stage. - The earliest distinction between protostomes and deuterostomes is the type of cleavage undergone by the zygote.

True animals can be largely divided into three groups based on the type of symmetry of their body plan:

1) Radially Symmetrical 2) Bilaterally Symmetrical 3) Asymmetrical

4 Types of Neurons

1) Unipolar 2) Bipolar 3) Multipolar 4) Pseudounipolar

Blastula

6-32-celled hollow structure

Parthenogenesis (or "virgin beginning")

A form of asexual reproduction found in certain insects and vertebrates where unfertilized eggs can develop into new male offspring. This type of parthenogenesis is called haplodiploidy.

Fertilization

A process during sexual reproduction, the haploid gametes of the male and female individuals of a species combine.

Schizocoely

A process that the coelom of most protostomes is formed through, meaning that during development, a solid mass of the mesoderm splits apart near the blastopore and forms the hollow opening of the coelom.

Organogenesis

A process where germ layers are programmed to develop into certain tissue types, organs, and organ systems.

Gastrulation

A process which the blastula undergoes further cell division and cellular rearrangement.

An animal whose development is marked by radial cleavage and enterocoely is ________. A. a deuterostome B. an annelid or mollusk C. either an acoelomate or eucoelomate D. none of the above

A. a deuterostome

In what ways does asexual reproduction occur in some animals? A. budding B. fragmentation C. parthenogenesis D. binary fission

A. budding B. fragmentation C. parthenogenesis

What are some of the functions of amoebocytes in sponges? A. delivering nutrients from choanocytes to other cells within the sponge B. giving rise to eggs for sexual reproduction C. delivering phagocytized sperm from choanocytes to eggs D. moving water through the mesohyl

A. delivering nutrients from choanocytes to other cells within the sponge B. giving rise to eggs for sexual reproduction C. delivering phagocytized sperm from choanocytes to eggs

Amongst the different species of sponges how do body forms vary? A. differences in the size of the spongocoel B. differences in the types of tissues that are found in mesophyl C. differences in the number of osculi D. alterations in where the cells that filter food from the water are located

A. differences in the size of the spongocoel C. differences in the number of osculi D. alterations in where the cells that filter food from the water are located

How do the Parazoa (sponges) differ from other animals? A. they do not have cells organized into tissues like other animals. B. they are mostly unicellular and other animals are multicellular. C. they do not display any cell differentiation. D. they are autotrophs and all other animals are heterotrophs.

A. they do not have cells organized into tissues like other animals.

Myelin

Acts as an insulator to minimize dissipation of the electrical signal as it travels down the axon, greatly increasing the speed on conduction. Myelin is produced by glial cells.

Ployp forms

An example of the polyp form is Hydra spp.; perhaps the most well-known medusoid animals are the jellies (jellyfish). Polyp forms are sessile as adults, with a single opening to the digestive system (the mouth) facing up with tentacles surrounding it.

Mesohyl

An extracellular matrix consisting of a collagen-like gel with suspended cells that perform various functions. The gel-like consistency of mesohyl acts like an endoskeleton and maintains the tubular morphology of sponges.

Parazoa

Animal phyla that do not have true differentiated tissues (such as the sponges).

Pinacocytes

Are epithelial-like cells, form the outermost layer of sponges and enclose a jelly-like substance called mesohyl.

Medusa forms

Are motile, with the mouth and tentacles hanging down from an umbrella-shaped bell.

Oocytes (Eggs)

Arise by the differentiation of amoebocytes and are retained within the spongocoel.

Which of the following is not an accurate statement about neurons? A. The soma is the cell body of a nerve cell. B. Myelin sheath provides an insulating layer to the dendrites. C. Axons carry the signal from the soma to the target. D. Dendrites carry the signal to the soma.

B. Myelin sheath provides an insulating layer to the dendrites.

What glial cell types are involved in forming the myelin sheathing of neurons? A. Microglia B. Oligodendrocytes C. Radial glia D. Schwan cells

B. Oligodendrocytes D. Schwan cells

Which of the following statements is false? A. Choanocytes have flagella that propel water through the body. B. Pinacocytes can transform into any cell type. C. Lophocytes secrete collagen. D. Porocytes control the flow of water through pores in the sponge body.

B. Pinacocytes can transform into any cell type.

Which of the following is NOT a feature common to most animals? A. development into a fixed body plan B. asexual reproduction C. specialized tissues D. heterotrophic nutrient sourcing

B. asexual reproduction

A(n) ________ neuron has one axon and one dendrite extending directly from the cell body. A. unipolar B. bipolar C. multipolar D. pseudounipolar

B. bipolar

Porocytes

Controls water flow through ostia.

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.

Which of the following statements about diploblasts and triploblasts is false? A. Animals that display radial symmetry are diploblasts. B. Animals that display bilateral symmetry are triploblasts. C. The endoderm gives rise to the lining of the digestive tract and the respiratory tract. D. The mesoderm gives rise to the central nervous system.

D. The mesoderm gives rise to the central nervous system.

Which of the following phenotypes would most likely be the result of a Hox gene mutation? A. abnormal body length or height B. two different eye colors C. the contraction of a genetic illness D. two fewer appendages than normal

D. two fewer appendages than normal

Homeoboxes

DNA sequences that play a role in the development of embryos.

The Hox Genes are responsible for:

Determining the general body plan, such as the number of body segments of an animal, the number and placement of appendages, and animal head-tail directionality.

Enterocoely

Deuterostomes differ in that their coelom forms through a process called enterocoely. Here, the mesoderm develops as pouches that are pinched off from the endoderm tissue lining the archenteron, or primitive digestive tube. These pouches eventually fuse to form the mesoderm, which then gives rise to the coelom.

Cephalization

Refers to the collection of an organized nervous system at the animal's cranial end. (Bilateral Symmetry)

Spermatozoa (Sperm)

Result from the differentiation of choanocytes and are ejected via the osculum.

Sclerocytes

Secrete spongin fibers and spicules which provide additional stiffiness/support to the sponge and can potentially ward off predators.

Collencytes or Lophocytes

Secretes collagen to maintain the mesohyl.

Cleavage

Series of mitotic cell divisions.

Porocytes,

Single tube-shaped cells that act as valves to regulate the flow of water into the spongocoel in Sponges. Ostia is formed by these.

Incomplete metamorphosis:

Some animals, such as grasshoppers, undergo incomplete metamorphosis, in which the young resemble the adult.

Cnidocytes ("stinging cells")

Specialized cells in Cnidarians.

Axon Terminal:

Synapse on other neurons, muscle, or target organs. Chemicals released at axon terminals allow signals to be communicated to these other cells.

Dendrites

Tree-like structures that extend away from the cell body to receive messages from other neurons at specialized junctions called synapses. Although some neurons do not have any dendrites, some types of neurons have multiple dendrites. Dendrites can have small protrusions called dendritic spines.

In vertebrates bone tissue is a type of...

connective tissue that supports the entire body structure.