Bellwork: What makes an animal an animal?

What is an animal? Section 25.1

What characteristics do all animals share? All are heterotrophic All are multicellular All are Eukaryotes No cells have cell walls

How can the animal kingdom be divided? Invertebrates: all animals that lack a backbone 95% of all animals Do not form a clade, as the common feature is lacking a characteristic Highly diverse (33 Phyla) Range in size from dustmite to giant squid

Classifying animals continued… Chordates (less than 5% of animals) Essentially those with a backbone, but it’s a bit more complicated All chordates need to exhibit 4 characteristics during at least one stage of life Dorsal hollow nerve cord Notochord: long supporting rod running through body (common in embryos) A tail extending beyond anus Pharyngeal pouches: paired structure in throat region (pharynx) Most chordates have a backbone, (aside from some odd aquatic mammals) and are called vertebrates Vertebrates include Fish, amphibians, reptiles, birds and mammals.

What essential functions must animals perform to survive? Animals maintain homeostasis by: Gathering and responding to information Obtaining and distributing oxygen and nutrients Collecting and eliminating carbon dioxide and other wastes They also have to reproduce Over time members of different animal phyla have evolved very different animal structures to perform these essential functions

How do animals maintain homeostasis? Often through feedback inhibition, or negative feedback The product or result of a process limits the process itself Example – thermostat Animals have developed a number of different body systems to maintain homeostasis

How do animals gather and respond to information? Animals use several body systems to respond to events in their environments Cells called receptors pass on information, so the body can work out it’s response Can respond to sound, light, chemicals or other stimuli Some invertebrates only have a loose network of nerve cells Most chordates have a large number of nerve cells concentrated into a brain Responses can vary – stimuli can trigger movement through muscle contraction - often works with skeleton But, not all do this. Earthworms have a flexible skeleton that functions using fluid pressure Insects have external skeletons

Do all animals breathe? Yes! Small animals living in water can breathe by allowing oxygen to diffuse across their skin Larger animals use a respiratory system using either gills, lungs or air passages All animals eat and have a digestive system – allows acquisition and breakdown of food into a form that can be easily used Nutrients and oxygen must be transported around the body – how?

How are wastes from vertebrate eliminated? Many gases are simply excreted using the respiratory system Other wastes such as ammonia must be excreted using a specialized system – the excretory system Wastes are concentrated and expelled from the body Wastes must be collected from where they are produced – again, circulatory system required

Why do most animals reproduce sexually? Helps create and maintain genetic diversity Leads to increased rates of evolution Allows organisms to adapt to changing environment A small number can also reproduce asexually – why can this be advantageous?

Key points summary Animals share a number of characteristics – what are they? What is the difference between an invertebrate and a chordate – what 4 characteristics do chordates require What is the difference between a vertebrate and a chordate? What all essential functions do mammals perform? What specialized systems do mammals have to allow them to perform these functions?

Animal body plans and evolution Section 25.2

What is a body plan? Each animal phylum has a unique organization of particular body structures that is often referred to as a body plan Features include: Levels of organization Body symmetry Differentiation of germ layers Formation of body cavities Patterns of embryological development Segmentation Cephalization Limb formation

What is meant by levels of organization? As first cells develop they differentiate into specialized cells that are organized into tissues A tissue is a group of cells that perform a similar function Animals have several types of tissues Epithelial (covers body surfaces), muscle, connective and nervous Tissues combine to form organs Organs work together to make up organ systems

Are humans symmetrical? To some extent – yes Humans (like most animals) display bilateral symmetry A single plane divided animal into left and right side Can be divided into Anterior and Posterior sides And Dorsal and Ventral sides Some animals exhibit radial symmetry – any number of lines through the center could divide the animal into equal halves Other creatures display no symmetry – asymmetrical

What is a germ layer? A germ layer is a group of cells in an embryo that interact with each other as the embryo develops and contribute to the formation of all organs and tissues Most animal embryos have three germ layers Endoderm – innermost Develops into linings of digestive tract and much of the respiratory system Mesoderm – middle layer Muscles, and circulatory, reproductive and excretory organ systems Ectoderm – outer layer Sense organs, nerves and outer layers of skin

What is a body cavity? A fluid filled space between digestive tract and body wall Allows space for organs to both be suspended and grow Most animals have some form of body cavity

Are there patterns in embryo development? Every animal that undergoes sexual reproduction begins life as a zygote As zygote develops it will form a blastula Blastula – hollow ball of cells like an inflated balloon As blastula develops it will fold in on itself Creates an elongated structure with a tube – becomes digestive tract Blastospore – opening to the oustide In protosomes – blastospore becomes mouth, and anus develops Most invertebrates In Deuterostomes, blastospore becomes anus Chordates and echinoderms (closely related??)

Why is segmentation important to certain animals? As many bilaterally symmetrical animals develop, their bodies become divided into numerous repeated parts or segments Examples – worms, animals, vertebrates All have some kind of internal and external body parts that repeat on each side of the body Segmentation is seen as important in animal evolution because of the way genes control the production and growth of body segments A simple mutation can cause changes to number of segments Different segments can also become specialized

What does cephalization mean? The getting of a head! Common in bilaterally symmetrical animals Concentration of sense organs and nerve cells at their anterior end Most successful animal groups have a head Heads are formed from the fusion of many body segments Internal and external body parts combine to to concentrate sense organs Nerve cells that decide what the animal should do also become concentrated in the head Most animals with a head move head first – why?

How do limbs form? Segmented, bilateral animals typically have external apendages on both sides of their bodies Can vary from bristles to jointed legs to wings Different appendages have evolved and been lost several times in various animal groups over the course of history

The cladogram of animals Animal phyla can be defined according to adult body plans and patterns of embryological development

What does the cladogram show us? Cladogram indicates the sequence in which important body plan features developed Remember, being on the right of the cladogram does not mean an organism is better Complex does not mean better! Any system found in a living animals functions well enough for that organism to survive and reproduce

What about variation within phyla? Within each phylum, variations on the basic body plan theme have evolved For example – land vertebrates typically have four legs Frogs – hop on their legs Birds use their front ‘legs’ to fly In primates, front ‘legs’ are arms Essentially each phylum’s body plan can be viewed as an evolutionary experiment

Writing exercise Explain the description of a body plan as an evolutionary experiment. Include in your answer the difference between successful and unsuccessful body plans in terms of the different outcomes

Key points summary What are the eight features of animal body plans? Describe each in one or two sentences How are animal phyla defined?