1. Bellwork: What makes an animal an animal?

2. What is an animal?
Section 25.1

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

4. 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

5. 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.

6. 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

7. 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

8. 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

9. 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?

10. 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

11. 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?

12. 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?

13. Animal body plans and evolution
Section 25.2

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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??)

20. 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

21. 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?

22. 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

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

24. 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

25. 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

26. 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

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