1. 29.2 Form and Function in Invertebrates
Essential Question
How do different invertebrate phyla carry out life functions?

2. Feeding and Digestion
Simplest animals digest food by intracellular digestion
food digested inside cells
Sponges ingest food in archaeocytes which pass into other cells by diffusion
More complex invertebrates use extracellular digestion
food broken down outside cells in a digestive cavity or tract and then absorbed into the body
Mollusks, annelids, arthropods, echinoderms
Flatworms and cnidarians use both processes

3. Patterns of Extracellular Digestion
Simplest animals such as cnidarians and flatworms ingest and expel food through a single opening
Digested food then diffuses to cell throughout body
More complex animals digest food in a tube called a digestive tract
One-way digestive tract is characteristic of roundworms, annelids, mollusks, arthropods, and echinoderms
Food enters through mouth and waste leave through anus
Specialization allows animals to process food more efficiently

4. Respiration
Respiratory organs have large surface area that are in contact with air or water.
Surfaces must be moist so diffusion to occur
More surface exposed to environment = greater amount of gas exchange that can occur
Cnidarians and flatworms use diffusion
Aquatic invertebrates like mollusks use gills that bring blood closer to surface for gas exchange

5. Terrestrial invertebrates
Snails have surfaces covered by mucous membranes which reduces water loss
Spiders have book lungs
Insects have tracheal tubes and air enters through spiracles

6. Circulation Open circulatory system Closed circulatory system
blood is partially contained within a system of blood vessels
Blood comes into direct contact with tissues and is pumped into system of sinuses that makes its way back to the heart
Found in most mollusks (except octopus) and arthropods
Closed circulatory system
Heart or heart-like organ forces blood through blood vessels
Blood stays in vessels and diffuses into tissues
More efficient than open system
Characteristic of larger more active animals
Found in annelids and some mollusks (octopus)

7. Excretion
Animals must get rid of a byproduct of cellular respiration – ammonia
Must also have way to control the amount of water in tissues
Aquatic invertebrates – ammonia diffuses from body tissues into surrounding water
Flatworms use a system of flame cells to eliminate excess water

8. Terrestrial invertebrates must conserve water while removing wastes
Animals convert ammonia into urea and is eliminated as urine
Some insects and arachnids use Malpighian tubules to capture ammonia and excrete it as uric acid

9. Three trends in evolution of nervous system
Centralization – nerve nets consist of nerve cells that form a net-like arrangement throughout the body
Flatworms have ganglia in their head
Cephalopods have ganglia organized into a brain that coordinates the nervous system
Cephalization – concentration of nervous tissue and organs in one end of the body
Specialization – the more complex animals the more developed sense organs
Flatworms have simple eyespots
Insects have compound eyes

10. Movement and Support
Invertebrates have one of three kinds of skeletal systems
hydrostatic skeletons – skeleton based on a fluid-filled body that supports the muscles; worms
Exoskeletons – external skeleton made of chitin which supports muscles; arthropods
Endoskeletons- structural support inside of body made of calcified plates; echinoderms

11. Sexual Reproduction
Most invertebrates reproduce sexually during at least one part of their life cycle.
Sexual reproduction maintains genetic diversity by allowing for new combinations of genes
Meiosis - fusion of haploid gametes during fertilization to form diploid zygote
Zygote undergoes mitosis and develops into animal by differentiation
Most invertebrates have separate sexes.
Some animals like the flatworm are hermaphrodites

12. Asexual Reproduction
Zygote divides by mitosis after fertilization to grow into multicellular individuals.
Offspring are identical to adults
Involves diploid cells
allows animals to increase its numbers rapidly
Exact copy of original cell
Includes budding and mitosis (division in two)

13. Internal and External Fertilization
External – eggs are fertilized outside of females body
Internal – eggs are fertilized inside of females body