C HAPTER 27: I NTRODUCTION TO A NIMALS Section 2: Animal Body Systems

T ISSUES AND O RGANS Digestion Single celled organisms and sponges digest their food within their body cells. All other animals digest their food extracellularity (outside of their body cells) within a digestive cavity.

T ISSUES AND O RGANS Simple animals, such as the hydra and flatworms, have a gastrovascular cavity, a digestive cavity with only one opening.

T ISSUES AND O RGANS Other animals have a digestive tract (gut) with two openings, a mouth and an anus.

T ISSUES AND O RGANS Respiration In simple animals, oxygen gas and carbon dioxide gas are exchanged directly with the environment by diffusion.

T ISSUES AND O RGANS The uptake of oxygen and the release of carbon dioxide, called respiration, can take place only across a moist surface.

T ISSUES AND O RGANS Some aquatic (and a few terrestrial) animals respire with gills – very thin projections of tissue that are rich in blood vessels.

T ISSUES AND O RGANS In more advanced animals, lungs are the respiratory organs used to transfer oxygen into the blood and remove carbon dioxide from blood.

T ISSUES AND O RGANS Circulation In complex animals, oxygen and nutrients must be transported to the body cells by a circulatory system.

T ISSUES AND O RGANS Two types of circulatory systems: Open circulatory system: heart pumps fluid containing oxygen and nutrients through a series of vessels out into the body cavity.

T ISSUES AND O RGANS Closed circulatory system: a heart pumps blood through a system of blood vessels.

T ISSUE AND O RGANS Conduction of Nerve Impulses Nerve cells (neurons) are specialized for carrying messages in form of electrical impulses. Bilaterally symmetric animals have clusters of neurons called ganglia.

T ISSUE AND O RGANS More complex invertbrates, such as the grasshopper, have brains with sensory structures.

T ISSUE AND O RGANS Support Many soft-bodied invertebrates have a hydrostatic skeletal systems. Hydrostatic skeleton - consists of water that is contained under pressure in a closed cavity.

T ISSUE AND O RGANS Other invertebrates, such as insects, have an exoskeleton, which is a rigid external skeleton that encases the body of an animal.

TISSUE AND O RGANS An endoskeleton is composed of a hard material, such as bone, embedded within an animal.

T ISSUE AND O RGANS Excretion The term excretion refers to the removal of wastes produced by cellular metabolism.

T ISSUE AND O RGANS Simple aquatic invertebrates and some fishes excrete ammonia into the water through their skin or gills by diffusion.

T ISSUE AND O RGANS Other animals, especially terrestrial animals, convert ammonia to nontoxic chemicals, like urea. As the excretory system eliminates these wastes, water and other useful substances are returned to the body.

R EPRODUCTIVE S TRATEGIES Asexual Reproduction Reproduction that does not involve the fusion of two gametes is called asexual reproduction. An unusual method of asexual reproduction is parthenogenesis, in which a new individual develops from an unfertilized egg.

R EPRODUCTIVE STRATEGIES Animals that reproduce asexually are usually able to also reproduce sexually.

R EPRODUCTIVE S TRATEGIES Sexual Reproduction In sexual reproduction, a new individual is formed by union of a male and a female gamete.

R EPRODUCTIVE S TRATEGIES Gametes are produced in the sex organs. Males have testes that produce sperm. Males produce sperm until death.

R EPRODUCTIVE S TRATEGIES Females have ovaries that produce eggs. At birth, females have produced all the eggs they will ever have.

R EPRODUCTIVE S TRATEGIES Some species of animals, called hermaphrodites, have both testes and ovaries.

R EPRODUCTIVE S TRATEGIES Most aquatic animals simply release the male and female gametes near one another in the water, where fertilization occurs. This is known as external fertilization.

R EPRODUCTIVE S TRATEGIES Most terrestrial animals sexually reproduce by means of internal fertilization. Internal fertilization occurs when the sperm and egg unite inside of the female’s body.