Chapter 27: Introduction to Animals

Chapter 27: Introduction to Animals

Section 2: Animal Body SystemsTissues and OrgansDigestionSingle 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.

Tissues and OrgansSimple animals, such as the hydra and flatworms, have a gastrovascular cavity, a digestive cavity with only one opening.

Tissues and OrgansOther animals have a digestive tract (gut) with two openings, a mouth and an anus.

Tissues and OrgansRespirationIn simple animals, oxygen gas and carbon dioxide gas are exchanged directly with the environment by diffusion.

Tissues and OrgansThe uptake of oxygen and the release of carbon dioxide, called respiration, can take place only across a moist surface.

Tissues and OrgansSome aquatic (and a few terrestrial) animals respire with gills very thin projections of tissue that are rich in blood vessels.

GillsTissues and OrgansIn more advanced animals, lungs are the respiratory organs used to transfer oxygen into the blood and remove carbon dioxide from blood.

Tissues and OrgansCirculationIn complex animals, oxygen and nutrients must be transported to the body cells by a circulatory system.

Tissues and OrgansTwo types of circulatory systems:Open circulatory system: heart pumps fluid containing oxygen and nutrients through a series of vessels out into the body cavity.

Tissues and OrgansClosed circulatory system: a heart pumps blood through a system of blood vessels.

Tissue and OrgansConduction of Nerve ImpulsesNerve cells (neurons) are specialized for carrying messages in form of electrical impulses.Bilaterally symmetric animals have clusters of neurons called ganglia.

Tissue and OrgansMore complex invertbrates, such as the grasshopper, have brains with sensory structures.

Tissue and OrgansSupportMany soft-bodied invertebrates have a hydrostatic skeletal systems.Hydrostatic skeleton - consists of water that is contained under pressure in a closed cavity.

Tissue and OrgansOther invertebrates, such as insects, have an exoskeleton, which is a rigid external skeleton that encases the body of an animal.

Tissue and OrgansAn endoskeleton is composed of a hard material, such as bone, embedded within an animal.

Tissue and OrgansExcretionThe term excretion refers to the removal of wastes produced by cellular metabolism.

Tissue and OrgansSimple aquatic invertebrates and some fishes excrete ammonia into the water through their skin or gills by diffusion.

Tissue and OrgansOther 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.

Reproductive StrategiesAsexual ReproductionReproduction 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.

Reproductive strategiesAnimals that reproduce asexually are usually able to also reproduce sexually.

Reproductive StrategiesSexual ReproductionIn sexual reproduction, a new individual is formed by union of a male and a female gamete.

Reproductive StrategiesGametes are produced in the sex organs.Males have testes that produce sperm.Males produce sperm until death.

Reproductive StrategiesFemales have ovaries that produce eggs.At birth, females have produced all the eggs they will ever have.

Reproductive StrategiesSome species of animals, called hermaphrodites, have both testes and ovaries.

Reproductive StrategiesMost aquatic animals simply release the male and female gametes near one another in the water, where fertilization occurs.This is known as external fertilization.

Reproductive StrategiesMost terrestrial animals sexually reproduce by means of internal fertilization.Internal fertilization occurs when the sperm and egg unite inside of the females body.