Characteristics of Living Things: Living things

Full text

(1)1 BIOLOGY - 2201 . Unit 2 : BIODIVERSITY. Characteristics of Living Things: Living things. — — — — — —. are organized systems made up of one or more cells. metabolize matter and energy. interact with their environment and are homeostatic. grow and develop. reproduce themselves (biogenesis). are adapted to their surroundings.. If something does not have these characteristics (cells, biogenesis growth and development, metabolism, water requirements, organic compound production, reproduction with inheritance and adaptations), then it is not considered a living thing. A fox would be a living thing whereas a rock would not (ie.) nonliving. Classification: How to classify living organisms on the earth? Classification refers to organization (ie.) to place ideas or groups together on the basis of similarity. Taxonomy is the branch of biology that deals the classification of living things. A person who works in this field is a taxonomist. A classification system is a way to identify an organism and place it into the correct group with related organisms. It is also a way of referring to an organism by name so that scientists in each part of the world can understand each other regardless of language (ie.) a universal system. The first attempt at classification was made by the Greek philosopher, Aristotle, over two thousand years ago. There were about 1000 different organisms identified at this time. Aristotle used a twokingdom system for classifying organisms — Kingdom Animalia and Kingdom Plantae. In his classification scheme, animals were classified by where they lived (land, water, air) and plants according to structure (herbs, shrubs, trees). Why was this not a good system ? (eg.) Bats and mosquitoes are air dwellers. Ants and mice are land dwellers. Which organisms are more closely related ? A student of Aristotle , Theophrastus , grouped plants according to reproductive structures and types of external tissues. Invention of the microscope and the discovery of microorganisms forced scientists to rethink the criteria for classification. The microscope was instrumental in the discovery of microorganisms. For example: Euglena — Is it an animal or plant? It is a photosynthetic plant that moves like an animal. This set the stage to have a third kingdom. I n 1866, Ernst Haeckel, a German biologist, proposed a third kingdom called Protista to classify micro-organisms (which were neither plants nor animals). As biologists learned more about structure and the way of life of different organisms , they added more kingdoms to the classification system. Fungi were once included in the plant kingdom. Fungi are not photosynthetic and are heterotrophic (obtain food from other sources). They become a separate kingdom called Fungi..

(2) 2 In1969, Robert Whittaker, a biologist at Cornell University, proposed a 5 Kingdom classification system based on: a) number of cells; b) presence or absence of a nucleus; c) mode of nutrition. This system gained wide acceptance, but it has been replaced by a six-kingdom system currently used by many biologists. Our text uses a 6 - kingdom classification system. Kingdoms : 1. Animalia 2. Plantae 3. Fungi 4. Protista 5. Bacteria 6. Archaea The three domains of life : 1) Domain Bacteria – Kingdom Bacteria 2) Domain Archaea – Kingdom Archaea 3) Domain Eukarya –Kingdoms Protista , Fungi, Plantae, Animalia Although bacteria and Archaea are prokaryotic , RNA evidence shows that they are as different from each other as either is from eukaryotes. That is why biologists have created a new level of classification above kingdoms, the domain. Six Kingdom System : Plantae :. multicellular ; specialized tissues and organs ; photosynthetic autotrophs ; most are non - motile.. Animalia :. multicellular ; specialized tissues and organs ; heterotrophs ; most are motile at some point in life cycle. Fungi :. unicellular or multicellular ; heterotrophs ; absorb nutrients ; nonmotile. Protista :. unicellular , colonial , or multicellular ; autotrophs or heterotrophs ; some are motile. Bacteria :. majority are unicellular; some are colonial or link up in chains to form filaments ; autotrophs or heterotrophs ; microscopic ; no membrane - bound organelles (ie.) prokaryotic; movement by flagella or no movement at all; 3 main shapes — cocci (round), bacilli (rod-shaped), and spirilli (spiral-shaped). Archaea :. survive in extreme environmental conditions such a hot springs, volcanoes, etc. ; biochemically and genetically different from bacteria; 3 main shapes — cocci (round), bacilli (rod-shaped), and spirilli (spiral-shaped);. Note : Eukaryote has a membrane bound nucleus while a prokaryote has a cell with no membrane bound nucleus..

(3) 3. Modern taxonomy : Modern taxonomy is based on the work of Carolus Linnaeus, a Swedish botanist (1707 - 1778). He is said to be the founder of modern taxonomy. He based his system on the structural similarities in organisms. Each group in this system is referred to as a taxon (pl., taxa). The taxa are arranged from the largest and broadest division, a Kingdom, to the smallest and most specific, a species. People could accurately identify an organism by comparing its characteristics against a checklist. Hierarchical classification of a Human: 1) Kingdom 2) Phylum 3) Class 4) Order 5) Family 6) Genus 7) Species. Animalia Chordata Mammalia Primates Hominidae Homo sapiens. Linnaeus used a two word naming system. It was based on Latin or Greek. New species are given Latin names. They are usually descriptive or may honour a scientist or historical figure.To distinguish between degrees of similarity each Kingdom is divided into progressively smaller groups. Each group is called a taxon — (Kingdom , Phylum , Class , Order , Family , Genus , Species). These range from general to specific. The species taxon includes members that resemble each other so closely that they can interbreed and produce fertile offspring. Nomenclature refers to a system for naming living things. The two-word naming system for each species is called binomial nomenclature. The name of the genus is the first word and is capitalized. The species is the second word. The entire system is based on starting with the general and moving to the specific. Each kind of organism has a two-word Latin name called its scientific name. (eg.) Felis domesticus / Felis leo / Felis tigris Sometimes the genus can be abbreviated. For example, the fruit fly is Drosophila melanogaster and can be abbreviated to D. melanogaster. Many new organisms and some sub - groups have been added. Most large plants and animals have common names, which can lead to confusion. Modern techniques consider the evolutionary history of a species (called phylogeny). A phylogenetic tree is used to show the relationships among various organisms. (See Figure 4-14, p. 116) The phylogenetic tree represents a hypothesis about the evolutionary relationships among a group of phylogeny). A phylogenetic tree is used to show the relationships among various organisms. Cladistics: Cladistics refers to a classification scheme that is based on phylogeny. It is based on the idea that each group of related species had one common ancestor, and organisms retain some ancestral characteristics and gain some unique derived characteristics as they evolve and diverge from the common ancestor. ( p.117).

(4) 4 Why not use common names to identify different species? - Many different common names for same animals. - Many different tree species called mahogany. - Common names can give misleading information. Modern techniques used to help classify organisms — How organisms are classified: 1.. Evidence from fossil records : Radioactive dating is the use the decay of carbon-14 to find the ages of some organisms. They can then tell if they were ancestors of some species. Protein comparisons of amino acid sequences are checked for similarities and differences. The blood proteins in horseshoe crab reveal that it is more closely related to spiders than crabs.. 2.. Evidence from anatomy : Structural information is the comparison of bones found in certain animals. For example, the human arm , horse’s leg , bat’s wing , whale flipper are all quite similar. They have similar arrangement and the similarities of bone structure indicate the same evolutionary origin.. 3.. Evidence from embryonic development : Comparative embryology is the comparisons of early embryonic development. For example, tunicates, in their larval stage, have structures that are similar to tadpoles such as long dorsal nerve cords and a flexible notocord. They are therefore classified with other vertebrates.. 4.. Evidence from biochemistry — (DNA): Biochemical techniques can look at the arrangement of amino acids. For example, human blood and baboon blood are very close therefore humans are more closely related to baboons than horses. Similar DNA patterns would suggest that the relationship between organisms is closer.. 5.. Evidence from DNA : DNA analysis is a good way measuring the closeness of relationships among organisms.. 6.. Metabolic Behaviour such as the ability to digest certain substances or if an organism is a producer, a consumer, or a decomposer can also be used in classifying organisms.. In Summary : Area of Science anatomy biochemistry DNA phylogeny. Type of Evidence homologous structures similar appearance similarity in amino acid sequence of important proteins similarity in DNA nucleotide sequence classification based on common ancestry.

(5) 5 Dichotomous keys : A dichotomous key is an identification key that uses a series of paired comparisons to sort organisms into smaller and smaller groups. - used as a way to classify organisms -available for almost all living things -used by all types of scientists - consists of many numbered steps - first few steps key on gross external features - moves from general to specific - each step contains two or more statements of which only one is true about a single organism - the true step directs the user to the next step or to the organism A key is a listing of specific characteristics, divided into two equal parts. A dichotomous key is a series of two choices or opposing statements, known as a couplet. Some specific characteristics for identification of organisms could be structure and function. A Point to Consider : No classification system is etched in stone. The advantage of the Linnaeus system is its adaptability. This is evident in the fact that today biologists use a six-kingdom classification system as compared to a five-kingdom classification system. General Characteristics of the Six-Kingdoms : Kingdom Characteristic. Archaea. Bacteria. Protista. Fungi. Plantae. Animalia. cell type. prokaryotic. prokaryotic. eukaryotic. eukaryotic. eukaryotic. eukaryotic. nutrition. heterotrophs (absorption). photosynthesis; chemosynthesis; absorption. photosynthesis; ingestion or absorption. absorption. photosynthesis. ingestion. body form. mostly unicellular; some colonial. mostly unicellular; some colonial. most unicellular; some simple multicellular. most multicellular. multicellular. multicellular; organs and organ systems. reproduction. asexual. asexual. asexual and sexual. asexual and sexual. sexual. sexual. locomotion. present in some. present in some. present in some. absent. absent. present. NOTE :. A More- Detailed Reference : See Table 1 : Kingdom Worksheet (a handout). Core STSE #1 : “Modern Classification Techniques”.

(6) 6 A VIRUS : Viruses are not organisms. They do not have any cellular structure and are not classified into any of the six kingdoms of classification. Viruses are very successful at invading the cells of organisms because they can only reproduce using the metabolism of a host cell. Viruses consist of strands of DNA or RNA surrounded by a protective protein coat called a capsid. Virus particles have a variety of shapes; (determined by the type and arrangement of proteins in the capsid). A virus cannot replicate (reproduce) without a host. It is believed that viruses probably originated as fragments of nucleic acid that escaped from their original cell. They survived becoming parasitic on specific hosts. This would suggest that viruses and their hosts probably evolved together. This would make a virus and a host more closely related than a particular virus with other viruses. Example of Viral Reproduction : T4 virus — Lytic Cycle (steps in viral replication): (See Figure 4.21, p. 123). 1). Attachment: The T4 phage is a complex virus that attaches to a specific receptor site on a host’s (such as E. coli) cell wall. Weak chemical bonds form between the attachment and receptor sites, adhering the virus to the host.. 2). Entry (Penetration): T4 injects its nucleic acid (DNA) into the host (E. coli). The viral DNA passes through the core and into the cell. The capsid remains outside.. 3). Replication: Host protein synthesis is stopped by viral degradation of host DNA. The host’s metabolism will replicate the viral DNA (or RNA).. 4). Assembly: Spontaneous assembly of new virus particles occurs.. 5). Lysis and Release: The host cell, (ie.) E. coli’s plasma membrane and cell wall, lyses (or breaks open), releasing the new virus particles. The host (E. coli) cell dies.. Kingdom Bacteria : Bacteria are simple, prokaryotic organisms. They can be classified according to shape : cocci (roundshaped); bacilli (rod-shaped) and spirilli (spiral-shaped). Bacterial cells reproduce by means of asexual reproduction (one parental cell gives rise to 2 or more identical offspring). It is the process of binary fission in bacterial cells.(p. 134 - 135) Example of Life Cycle of Eubacteria and Archaebacteria : The bacterial cell, (E. coli), reproduces by binary fission. (See Figure 5.4, p. 134). 1. 2. 3. 4. 5.. As the bacterial cell grows, it makes a copy of its original, single chromosome. The cell elongates and separates into the two chromosomes. Cell partition or septum forms between the two chromosomes. The septum completes itself and distinct walls form. The cells separate and two new cells are produced..

(7) 7 Kingdom Protista : Protists are microscopic, eukaryotic organisms. They are classified into three major groups according to their type of nutrition. The groups are: 1) Protozoa (animal-like protists) : heterotrophs that ingest or absorb food. 2) Algae (plant-like protists) : autotrophs that carry out photosynthesis. 3) Slime moulds and Water moulds (fungus-like) : heterotrophic.. Example of a Protist Life Cycle: (See Figure 5.15, p. 146). Plasmodium vivax (a human parasite), a Sporozoan (Phylum Sporozoa), is responsible for one type of malaria in humans. 1. 2.. 3. 4.. 5.. A mosquito bites an infected person and ingests the reproductive cells of the Plasmodium present in red blood cells. The gametes (reproductive cells) fuse to form a (diploid) zygote inside the gut wall of the mosquito and divide many times to form numerous spore-like fragments or sporozoites. The zygote breaks open releasing the sporozoites (spore cells). The sporozoites migrate and invade the salivary glands of the mosquito. From here, they will be injected into a new human host when bitten by the mosquito. Once inside the new human host, sporozoites will reproduce asexually in the liver to form a second type of sporelike cell. The cells leave the liver and enter the bloodstream where they invade red blood cells. Once inside the red blood cells, they multiply at a very rapid rate. Red blood cells rupture releasing toxic substances and spores. These spores infect other red blood cells. The cycle repeats itself when a mosquito bites the infected person..

(8) 8 Kingdom Fungi : Fungi are non-photosynthetic heterotrophs that grow in the ground and possess cell walls. They have some plant-like qualities. The bodies of fungi are made up of a network of fine filaments called hyphae (singular hypha). A loose, branching network of hyphae that makes up the bulk of a fungus is called a mycelium. Fungi are classified according to their reproductive characteristics. They are : 1) Zygomycotes — zygospores — sexual reproduction. 2) Basidiomycotes — basidiospores — sexual reproduction. 3) Ascomycotes — asci (spores spread by wind) — sexual reproduction. 4) Deuteromycotes — conida — asexual reproduction. Example of a Fungus Life Cycle : (See Figure5.28, p. 154). Rhizopus stolonifera is the common black bread mould. The small black dots or fuzz on bread are the reproductive structures of the bread mould. The bread mould reproduces by asexual reproduction, but can also reproduce by sexual reproduction when times are unfavourable (producing zygospores). These are diploid cells that contain two copies of every chromosome. Rhizopus belongs to the Phylum Zygomycota or the zygospore fungi. Sexual Reproduction Phase: The zygospores develop after two haploid (monoploid) hyphae of opposite types (+ and - mating strains) combine and fuse together to form the zygospores. The bread mould is made up of two forms of hyphae. The horizontal hyphae are the stolons and the downward growing hyphae are the rhizoids. The stolons spread out over the surface of the bread while the rhizoids anchor the mycelium to the bread surface. The rhizoids secrete enzymes that digest the food (the bread) and then absorb the digested nutrients. A thick wall develops around the zygospore for protection. The zygospore will remain dormant until conditions are favourable for growth. Once this happens, the zygospore will absorb water and the nuclei will undergo meiosis. Asexual Reproduction Phase: The bread mould will develop sporangiophores, a third form of hyphae. The sporangia or spore-bearing capsules are located at the ends of the sporangiophores. The asexual sores develop inside the sporangia and are released when the capsules split open. Kingdom Plantae (Plants) : Botany is the study of plants. All plants are said to have a common ancestor; (ie.) it is thought that plants have evolved from an ancient group of green algae. Plants and green algae share a common evolutionary ancestry. The general characteristics of plants are the following : I) photosynthesis II) ability to absorb water and nutrients III) ability to conserve water and reduce the drying effect of air IV) process of gas exchange V) presence of supporting tissues VI) ability to reproduce.

(9) 9 Plants can be classified according to the presence or absence of vascular tissue. Vascular tissue is the tissue that supports water and the products of photosynthesis throughout a plant. Plants lacking vascular tissue are called bryophytes. Plants which have vascular tissue are called tracheophytes. Vascular tissue is made up of xylem and phloem cells. Xylem carries water and minerals to the leaves of plants. Phloem transports food synthesized in leaves throughout the plant. Land plants have a cuticle and stomata (sing. stoma) present. A cuticle is a noncellular layer secreted by epidermal cells which helps to protect cells from drying out. Stomata are pores in the epidermis of a plant, particularly the leaves, which permit the exchange of gases between the plant and the air around it. Classification system (land plants) : Nonvascular (Bryophytes) (eg.) mosses, liverworts, hornworts Vascular (Tracheophytes) º Seedless (Spores) (Spore-bearing plants) (eg.) whiskferns, club mosses, horesetails, ferns º Seed (embryo + stored food + tough water proof coat or seed coat) Gymnosperms (cone-bearing plants) : conifers. Angiosperms (flowering plants) : classified into two groups according to number of seed leaves or cotyledons on the embryo within the seed — monocots (one seed leaf) and dicots (two seed leaves). BRYOPHYTES (Phylum Bryophyta): Bryophytes are nonvascular land plants that are small in size and grow close to the ground. Examples would be mosses, liverworts and hornworts. They reproduce by alternation of generations; a two part life cycle with alternating monoploid (n) and diploid (2n) phases. For bryophytes, the dominant part of the life cycle is the gametophyte generation (what is actually seen). (See Figure 6.3, p. 166). Characteristics : 1. They lack specialized tissue that transports water as in vascular plants. There is a problem of dessication or drying out in these plants. 2. They lack true roots, stems and leaves and are anchored to the ground by structures called rhizoids. A rhizoid is a simple structure (other than a true root) which doesn’t channel water to other parts of the plant. 3. They require water for sexual reproduction. Water is needed for fertilization to occur. Sperm must swim through water in order to reach the egg. TRACHEOPHYTES (Phylum Tracheophyta): Tracheophytes are “true” terrestrial plants. Examples would be ferns, herbs, shrubs, trees and flowering plants. They are vascular plants and have vascular tissue. These are modern-day plants and the.

(10) 10 sporophyte generation is predominant. Some tracheophytes are spore-producing vascular plants; such as whiskferns, club mosses, horesetails and ferns. Characteristics : 1. They are vascular plants having specialized conducting tissue; xylem(water) and phloem (food). 2. Means of reproduction: spores - club mosses, horsetails , ferns seeds - flowering plants, conifers (Note: All spore bearing vascular plants require water, which reflects their aquatic ancestry.) 3. Dominant phase in the life cycle is the sporophyte generation (larger than gametophyte) ; gametophyte generation is very small, only mm in length. (Note : This is an evolutionary trend.) 4. Evolution of the reproductive cycle is such that water is not an essential requirement for reproduction. It enables plants to survive in a terrestrial environment. This allows for greater adaptability and less dependence on a wet environment (like the bryophytes). Diversity and success of the Angiosperms : The angiosperms are the flowering plants and are the most diverse plant group. This diversity is due to a variety of factors, such as: 1) the assistance of animals and wind in pollination; 2) the presence of structures in plants specific to attracting certain animal pollinators whom the plants supply with food; 3) the way seeds are protected; 4) the function of fruits in seed dispersal, and 5) the presence of specialized tissues in plants to help them survive heat, cold, and droughts. Explanation of the key factors: 1. Assistance of animals and wind in pollination. Pollination is the process by which pollen reaches the stigma or the transfer of pollen to female reproductive structures of a plant. The agents of pollination would be animals, wind and flower structure. Animals such as bees, bats, birds, butterflies, etc. are able to move from one flower to another and are known as pollinators. Animals move from plant to plant in search of a sugary food called nectar. The animals will usually use a specific flower. Flower colour, odour, size and shape are related to the specific pollinators of the plant. For example, butterflies and moths have long sucking mouth parts. Therefore, certain plants evolved structures that have petals which form a long tube with the nectar at the base. In this way, only certain insects can pollinate the plant. This parallel evolution of plants and pollinators was a major factor in the domination of flowering plants on the earth; (ie). pollinators are specific. Pollination by wind is very inefficient and therefore plants produce large amounts of pollen. Almost all of the pollen falls within 100 m of the parent plant. This means that this is only good within a large population which grows close together. The characteristics of plants pollinated by wind would be: - flowers are small and grow in clusters - drab colour , odourless , no nectar - petals absent or small - stamen is exposed , pollen easily catches wind - feathery stigmas also increase the amount of pollen which is caught by the wind (eg.) grasses , trees such as oak , maple and birch.

(11) 11 Some plants don’t need a pollinator. Pollen from the anther fertilizes egg in the same flower. This is called self - fertilization. It is very uncommon. In some plants, the pollen grains and the ovules mature at different times making self - fertilization impossible. 2. Structures present specific to attract pollinators. Flowering plants attract pollinators by supplying them with food. How a pollinator distinguishes a plant? This can be done by sighting the plant or by detecting an odour. Bees cannot distinguish the colour red and therefore are not usually found around red flowers but those with blue and yellow flowers. Some plants also have patterns or stripes which lead bees to nectar. Some flowers can produce sweet smelling scents. For example, there are some flowers that smell like decaying meat; (eg). skunk cabbage attracts flies. Hummingbirds have a poor sense of smell and therefore pollinate flowers which have little smell. Beetles usually pollinate white or dull coloured flowers with have strong odours. 3. Seed protection. Flowers are diploid sporophytes and do not produce spores. Fertilization will produce a diploid sporophyte embryo. The embryo is enclosed in hard tissue to form a seed. The seed case or hard tissue enables the embryonic plant to survive adverse weather conditions such as drought, hot or arid periods and cold. 4. Fruits have a function in seed dispersal. The fruit or fleshy walls of the ovary is another means of seed protection. Some seeds in fruits are easily dispersed by wind and by water. Some fruits are eaten and dispersed by animals. The seed resist digestion and will pass intact in an animal’s feces to germinate in a new spot. 5. Specialized tissues for survival. Angiosperms have a specialized leaf structure; such as sunken stomata which helps reduce water loss. Some angiosperms have small leaf hairs which also help to reduce water loss. The most important structure for survival is the reproductive organ, the flower; the female reproductive organ is the pistil (or carpel) and the male reproductive organ is the stamen. Example of the Fern Life Cycle as a representative (seedless) plant: (See Figure 6.9, p. 173). 1. 2. 3. 4. 5. 6.. A sporangium produces haploid (monoploid) spores that germinate to form a gametophyte called a prothallus. The prothallus produces antheridia (male organs) and archegonia (female organs). Sperm swim through a droplet of water to an egg produced by the archegonium. The fertilized egg begins to grow into a sporophyte. The sporophyte matures and roots and fronds develop out of the growing rhizome. Sori develop on the pinnae. Spores are formed in the sori by meiosis.. r See the completed table below for a summary of plant characteristics:.

(12) 12 Table # 2 : Plants. Kingdom Animalia (Animals) : Zoology is the study of animals. Animals are multicellular and eukaryotic. Animals consume organic materials and digest it and are termed heterotrophs. Most animals are motile at some time in their lives through some simple forms are attached to a substrate (sessile). Many animals have tissues specialized for specific functions (nerve tissue, muscle). Many lower forms have simple asexual and sexual reproduction while higher forms reproduce sexually exclusively. There are two main types of animals, vertebrates and invertebrates. A vertebrate has a backbone while an invertebrate has no backbone (no bones at all usually!!!) Chracteristics of Various Animal Phyla : - body organization (cells organized into tissues, organs and organ systems) - number of germ layers (tissues from which more specialized tissues develop) - body symmetry - a complete or incomplete digestive tract - development (or not) of an internal cavity called a coelom Symmetry in Animals : Body symmetry refers to the body being cut in two halves having matching shapes. Animals with no symmetry are asymmetrical (sponges). Radial symmetry is based around the point in the central axis of a tube (anemone). Animals like humans have two equal halves, bilateral symmetry. The sides of the body have special names: dorsal, ventral, anterior, posterior, medial, lateral, proximal, distal. Kinds of symmetry : 1. Asymmetrical : lack symmetry, cannot be cut into two matching halves (eg.) most sponges 2. Radial symmetry : division into equal halves by passing a plane through the central axis of the animal in any direction (eg.) starfish, jellyfish 3. Bilateral symmetry : division into equal halves only along a single plane. Each half is a mirror image of the other (eg.) most animals, humans ( not perfect ) Spatial relationships (bilateral symmetry) : Dorsal - upper side or back Ventral - lower side or belly Anterior - front region or head Posterior - hind , rear , or tail end Lateral - side Note : Animals with bilateral symmetry have a true head. It shows cephalization which refers to a concentration of nerve tissue and receptors at the anterior end of the animal’s body. Body cavity : A coelom is afluid filled cavity surrounded by the mesoderm — a layer of epithelial cells that line the body cavity and gut ; (found in all vertebrates and many invertebrates)..

(13) 13 Importance of a body cavity : 1. Provides space where internal organs can be suspended without being affected by muscle pressure and body movement 2. Provide space for internal organs to develop and expand 3. Contain fluids which may assist in internal transport of nutrients , and gas exchange ; contains a peritoneum which is a covering membrane that lines the body cavity and covers the internal organs. Less complex vertebrates have a pseudocoelom, a fluid filled cavity of variable shape which has no peritoneum. Animals with a fluid-filled body cavity or coelom are called coelomates. Animals with a fluid-filled cavity and no peritoneum are pseudocoelomates. Animals without a coelom are called acoelomates. The development of a body cavity demonstrates complexity and evolutionary development in animals. The simplest animals have a single opening that acts as a mouth and anus. Complex animals have a gut with two openings, a mouth and anus. Number of Germ Layers: Animal development depends on cell layers or germ layers. Layers : 1. 2. 3.. Endoderm is inner layer of cells. It gives rise to digestive tract Ectoderm is the outer layer of cells. It gives rise to the skin and to the nervous system. Mesoderm is the middle layer of cells. It gives rise to the circulatory, skeletal and reproductive systems.. r See the completed table below for a summary of invertebrate characteristics: Table # 3 : Invertebrates. Developmental trends — Invertebrates: 1. We go from simple to complex as organisms evolve. 2. Simplest organisms have asymmetry. As complexity increases, we go to radial and finally bilateral symmetry. 3. Organisms go from having no cavity to a false cavity to a true body cavity. 4. Simpler organisms may reproduce sexually and asexually. As complexity increases, organisms reproduce only sexually. 5. Simpler ones have two tissue layers, more complex have three tissue layers. 6. Sessile to motile. 7. Simpler ones have no tissue, no systems. As complexity increases, the more systems an organism has (both in # and complexity). Note : Many invertebrates are hermaphrodites (contain male and female parts) , but rarely can they self-fertilize..

(14) 14 r See the completed table below for a summary of vertebrate characteristics: Table # 4 : Vertebrates. Common characteristics for all vertebrates would be: i) presence of a notochord (backbone) ii) a dorsal nerve cord iii) gill slits General Characteristics : 1. endoskeleton , appendages ,and skin 2. closed circulatory system with an increasingly complex heart structure 3. increased cephalization and increased size and complexity of the cerebrum 4. presence of a coelom to hold increasingly complex systems for digestion, excretion, reproduction, circulation and respiration Evolutionary developmental Trends - Vertebrates : 1. Adaptations leading from total dependence on water to survival on land (evolutionary trend from external fertilization towards internal fertilization). 2. Development of a more complex heart structure (from a two chambered to three chambered to four chambered heart). 3. Increase in cephalization (concentration of nerve tissue in anterior region). 4. Increase in size and complexity of the cerebrum (anterior part of brain). 5. Body system functions increase in complexity with evolution.. Why arthropods are the most successful class of animals? The main characteristics of an arthropod are: exoskeleton, jointed appendages, segmented bodies, and an open circulatory system. They are found in a wide range of habitats. It seems that they have evolved from a segmented ancestor. They undergo sexual reproduction with internal fertilization and separate sexes: (although some may be hermaphroditic). Diversity (Phylum Arthropoda) is due to their: 1. rigid, jointed external skeleton or exoskeleton (for protection). 2. well-defined head with jointed appendages 3. specialized body segments fused into distinct regions such as head, thorax and abdomen. 4. well-developed nervous system. 5. different structures and functions for obtaining nourishment.

(15) 15. Example of the Frog Life Cycle (as an example of an animal): (See Figure 6.26, p. 193). A frog is an example of an amphibian. A frog will undergo external fertilization; (the sperm and egg meet outside the bodies of both parents).The male frog produces the sperm and the female frog produces the eggs. Fertilization of frog eggs is external. During mating, the male frog mounts a female frog and helps to squeeze the eggs from the female’s body. The male will then release sperm on top of the eggs. Once an egg has been fertilized, development begins immediately. The larva of the frog or tadpole will emerge from the egg in a few days. The young tadpole has a tail for swimming and gills for respiration. This tadpole stage of a frog may last a few months up to two years, depending on the frog species. Tadpoles eat plants and algae. The tadpole will undergo a complete change in form or metamorphosis; (older tadpoles start to develop legs). This metamorphosis usually takes one or two months and the young frog will have well-developed legs, but no tail. It eventually becomes an adult frog fully adapted for life on the land..

(16)

No results found