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BL 1021 – Unit 3.1 Introduction to Animal Life 3.1.1 The Animal Cell • Animals are a eukaryotic life form like plants and fungi. However, unlike those other groups, animal cells lack cell walls. This makes animal cells less rigid and will often retain a spherical shape. • Animals share many of the organelles that plants have. However, animals lack the chloroplasts, and thus cannot perform photosynthesis. • As well, animals lack the large central vacuole. This makes their cells less rigid but makes animals more vulnerable to changes in the surrounding tonicity, unless they have a protective coating. 3.1.1 The Animal Cell 3.1.2 Characteristics of Animals • Animals as multicellular organisms composed of tissues, organs and organ systems. • The following characteristics describe at least most animals: • • 1. All animals are multicellular. • 2. The cells of an animal exhibit a division of labour. In all but the simplest animals, cells are organized to form tissues, and tissues are organized to form organs. 3.1.2 Characteristics of Animals • 3. Animals are exclusively heterotrophic; they ingest their food first and then digest it inside the body, usually within a digestive system • 4. Most animals are capable of locomotion at some time during their life cycle. (However, there are some animals, such as sponges, that are sessile as adults) 3.1.2 Characteristics of Animals • 5. Most animals have well-developed sensory and nervous systems and respond to external stimuli with adaptive behaviour. • • 6. Most animals reproduce sexually, with large, nonmotile eggs and small flagellated sperm. Sperm and egg unite to form a fertilized egg, or zygote, which goes through a series of embryonic stages before developing into a larva or immature form 3.1.3 Body Plans • Complexity: the level that an animal has multiple tissues of different purposes. More complex organisms will have more organs and organs more specialized for specific tasks. • Body Symmetry: If an organism can be split by an imaginary line with an equal amount on each side. • Bilateral symmetry: there is only one line that can divide the organism into equal halves • Radial symmetry: there are many lines that can cut the organism into equal parts, all the lines are about an axis. 3.1.3 Body Plans 3.1.3 Body Plans • All animals begin as a zygote that divides over and over. During the embryonic stage, animals can have up to three major germ layers. These layers specialize into the innermost, middle, and exterior layers of an adult organism. 3.1.3 Body Plans • Body Cavity (coelom): a fluid-filled space between the digestive tract and the outer body wall. • In the simplest of animals, this is not even present. In more developed animals, it partially developed and in the most complex creatures this is a large space for organs to develop and move. • The body cavity is an internal space where organs can grow, develop and move independently of the outer wall. 3.1.3 Animal Phyla • The next level of organization below kingdom is phyla. Each phyla contains a wide variety of creatures grouped by similar complexity and body symmetry. • The nine major phyla of animals are arranged by increasing complexity. As complexity increases, interdependence of cells increases, and organs become more specialized. For example, fragmentation is only possible with the first few phyla. 3.1.3 Animal Phyla • Porifera • Example: Sea sponges • Lack tissues, cells are loosely held together. • Often made of just cell layers and a jelly • No coelom, but water does flow through random openings • Most lack symmetry, but some are radially symmetrical. 3.1.3 Animal Phyla • Poriferans are generally non-moving and depend on currents to move water through them to obtain food and oxygen. • Poriferans represent the most basic animal – a two-layered tube with only one opening. 3.1.3 Animal Phyla • While poriferans are the most basic of animals, they still have some division of labour/cell specialization. • Due to the relative simplicity of the animal, these cells are able to change roles. 3.1.3 Animal Phyla • Cnidaria • Examples: Jellyfish, sea anemones, hydra • Radially symmetrical • Two distinct tissue layers are present – an inner surface (digestive) and outer surface (epidermis). • No coelom. 3.1.3 Animal Phyla • The general form of a cnidarian is of a tube with a single opening. Food both enters and leaves through this one orifice. • Some neural tissues and muscle sets are present – making them significantly more specialized than poriferans. 3.1.3 Animal Phyla • Many cnidarians can reproduce by budding – by growing an entire second clone on the main body and then detaching it. • Cnidarians also reproduce sexually and can have complex life cycles (both a polyp and medusa form, hermaphroditism, etc) 3.1.3 Animal Phyla • Platyhelminthes • Examples: Planarians, flatworms • Bilateral symmetry – have a definite head and tail. • Even though they have an elongated shape, they only have one digestive opening like cnidarians. 3.1.3 Animal Phyla • As these animals lack complex respiratory and circulatory systems, they take on a very flat shape to allow oxygen and nutrients to move by diffusion. • Diffusion is not powerful/fast enough to support thicker forms. 3.1.3 Animal Phyla • Bilateral animals show cephalization – a trend of focusing sensory organs and nervous tissue towards the head. • In simpler creatures like platyhelminthes, there is more nervous tissue at the brain region, but not nearly to the proportion of humans. 3.1.3 Animal Phyla • The platyhelminthes are simple enough to survive fragmentation. Even though they have a head, the body is so generally uniform that the sections could continue on living long enough to regrow the missing tail/head. 3.1.3 Animal Phyla • Nematoda • Example: Roundworms (non-segmented worms) • Bilateral symmetry • This is the first group we have looked at with a linear digestive tract with two openings (separate mouth and anus). Food travels in one direction only. 3.1.3 Animal Phyla • Nematodes have all three full embryonic tissue layers. • A proper coelom is lined with tissue on all sides. Nematodes have a body cavity, but the inner germ layer is “exposed”. It is considered a pseudocoelom. (pseudo = fake) 3.1.3 Animal Phyla • Nematodes are further cephalized and are generally more specialized along the body than platyhelminthes. • Thus, they are much less likely to survive fragmentation. 3.1.3 Animal Phyla • Mollusca • Clams, snails, slugs • Soft body with mineral shell. • Have a true coelom • Have true tissue systems • Bilateral symmetry 3.1.3 Animal Phyla • The standard mollusk is a very soft organism with a hard protective shell. • While mollusks are very cephalized, many have their breathing/waterfiltering structures to their rear rather than at the head region. 3.1.3 Animal Phyla • Many mollusks have a singular foot with various muscles that allow it to move. • Marine mollusks may have this foot adapted into tentacles or a shell opening/closing muscle. 3.1.3 Animal Phyla • Annelida • Segmented worms, leeches • Coelomates. • Bilaterally symmetrical. • Full tissue systems. 3.1.3 Animal Phyla • Arthropoda • Insects, spiders, crustaceans • Bilaterally symmetrical • Coelomates • Full tissue layers. 3.1.3 Animal Phyla • Arthropods are known for their hard exoskeletons. (exo = outside). • These exoskeletons allow for strong and complex body structures – claws, legs, tails, shells, heads, etc. 3.1.3 Animal Phyla • Many arthropods have to periodically shed their exoskeleton to give themselves room to grow. A new, larger exoskeleton will then solidify on the organism later once it has grown. 3.1.3 Animal Phyla • Echinodermata • Are bilaterally symmetrical during embryonic development but often take on radial symmetry in adulthood. • Coelomates. • Three full tissue layers. 3.1.3 Animal Phyla • Echinoderms have a variety of internal calcium-based skeletons. • Some echinoderms use the coelom as a circulatory system, pumping fluids around in this space rather than in dedicated vessels. 3.1.3 Animal Phyla • This water-based vascular system can also be used for movement (using a system similar to hydraulics) as well as gas exchange (respiration). 3.1.3 Animal Phyla • Chordata • Examples: fish, lizards, birds, mammals • Many have a backbone, but not all. • Most diverse phylum. • Bilateral, coelomates, 3 tissue layers. 3.1.3 Animal Phyla • All chordates have the following features: • A hollow nerve cord running along the back. • This transfers information to and from a brain. • A spine of bone or cartilage protects the nerve cord. 3.1.3 Animal Phyla • All chordates have a notochord – a flexible rod between the digestive tract and nerve cord. • This served as the first prototype of the true backbone. • In most modern chordates, the notochord will develop into a part of the spine, although some animals retain a notochord into adulthood. 3.1.3 Animal Phyla • All chordates will also have pharyngeal slits. • While they resemble gills in the embryo, they develop into the ears, jaws and throat (pharynx). • All chordates also have a post-anal tail in embryonic form. This can develop into many forms as an adult, or may be reduced/lost. 3.1.3 Animal Phyla • The field of comparative embryology studies the similarities of all animal embryos. • The fact that there are so many similarities in both form and function is strong evidence for common ancestry. 3.1.4 Vertebrates • Vertebrates are a subphyla of chordates that have a strong bone or cartilage spine protecting their nerve cord. • All other animals are called invertebrates. • The backbone is vital in allowing animals to be stronger, more powerful and quicker. The backbone acts as a base frame for muscles to attach to. 3.1.7 Adaptations of Vertebrates • Fish • Have jaws – a hinged bone structure that allows for high-pressure biting and chewing. • Use 2 pairs of fins to steer and swim • Use gills to absorb oxygen and release carbon dioxide with the water. • Fish come in two types – depending on the materials making up the skeleton. 3.1.7 Adaptations of Vertebrates • Cartilaginous Fish Sharks, rays Cartilage-based skeleton Have a very powerful sense of smell. Use electrosensors in their head to “feel” nearby animals by detecting the small magnetic fields created by muscle contractions of other animals. • A lateral line system of sensors along the sides of the body allow fish to sense vibrations in the water. • • • • 3.1.7 Adaptations of Vertebrates Bony Fish Fish with skeletons Also have excellent sight and sense of smell Have an operculum, a flap that can cover the gills for protection. This flap also can direct water through the gills while the fish is not moving – allowing it to “breathe” without moving, something which other fish cannot do. • Use a swim bladder to store gas to maintain buoyancy. This allows them to float at a certain depth without constantly swimming. • • • • 3.1.7 Adaptations of Vertebrates • Amphibians • Frogs, salamanders, toads • Begin life as fish-like with gills • Undergo metamorphosis into land animals with lungs • Have very thin skin that needs to stay wet and can do some gas exchange • Have eardrums for hearing 3.1.7 Adaptations of Vertebrates • Reptiles • Lizards, snakes • Have scales made of keratin that prevent water loss and protect • Only use lungs to breathe • Use water-filled, hard-shelled eggs that can survive on land. • Are cold-blooded (ectotherms) and absorb body heat from sunlight rather than generating it internally. 3.1.7 Adaptations of Vertebrates • Birds • Also lay hard-shelled eggs • Have scales on feet and legs • Highly specialized for flight: o Bones have a honeycomb structure for strength and low weight o Lack teeth (less weight) o Airfoil-shaped wings to make them aerodynamic o Powerful breast muscles to power the movements of flight. 3.1.8 Mammals • Features common to all mammals: • Land-based, breathe with lungs • Warm-blooded (endotherms), set their own body temperature, create their own heat • Hair – used to insulate the body to maintain a constant temperature. Can also be used to cool the body • Mammary glands – milk-producing glands that are used to nurse offspring 3.1.8 Mammals • There are 3 types of mammals: • • • • Monotremes Example - platypus Egg-laying mammals Will lie on their eggs to provide warmth, then nurse the young with milk secreted from the mother’s fur. 3.1.8 Mammals • Marsupials • Have a short gestation period and then give birth to very small, embryonic offspring. • These attach to the mother’s nipples and develop inside the marsupium – the pouch. • Example - kangaroo 3.1.8 Mammals • Eutherians/Placentals • Offspring develop within the mother for an extended period of time until fully developed. • During this time they feed off the mother using a placenta • Offspring are born more capable of survival than other types of mammals. • Most successful mammals as the offspring are best able to survive once born. • Example - humans