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Chapter 27: Introduction to Animals. Section 2: Animal Body Systems. Tissues and Organs. Digestion Single celled organisms and sponges digest their food within their body cells.
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Chapter 27: Introduction to Animals Section 2: Animal Body Systems
Tissues and Organs • 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.
Tissues and Organs • Simple animals, such as the hydra and flatworms, have a gastrovascular cavity, a digestive cavity with only one opening.
Tissues and Organs • Other animals have a digestive tract (gut) with two openings, a mouth and an anus.
Tissues and Organs • Respiration • In simple animals, oxygen gas and carbon dioxide gas are exchanged directly with the environment by diffusion.
Tissues and Organs • The uptake of oxygen and the release of carbon dioxide, called respiration, can take place only across a moist surface.
Tissues and Organs • Some aquatic (and a few terrestrial) animals respire with gills – very thin projections of tissue that are rich in blood vessels. Gills
Tissues and Organs • In more advanced animals, lungs are the respiratory organs used to transfer oxygen into the blood and remove carbon dioxide from blood.
Tissues and Organs • Circulation • In complex animals, oxygen and nutrients must be transported to the body cells by a circulatory system.
Tissues and Organs • 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.
Tissues and Organs • Closed circulatory system:a heart pumps blood through a system of blood vessels.
Tissue and Organs • 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.
Tissue and Organs • More complex invertbrates, such as the grasshopper, have brains with sensory structures.
Tissue and Organs • Support • Many soft-bodied invertebrates have a hydrostatic skeletal systems. • Hydrostatic skeleton - consists of water that is contained under pressure in a closed cavity.
Tissue and Organs • Other invertebrates, such as insects, have an exoskeleton, which is a rigid external skeleton that encases the body of an animal.
Tissue and Organs • An endoskeleton is composed of a hard material, such as bone, embedded within an animal.
Tissue and Organs • Excretion • The term excretion refers to the removal of wastes produced by cellular metabolism.
Tissue and Organs • Simple aquatic invertebrates and some fishes excrete ammonia into the water through their skin or gills by diffusion.
Tissue and Organs • 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.
Reproductive Strategies • 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.
Reproductive strategies • Animals that reproduce asexually are usually able to also reproduce sexually.
Reproductive Strategies • Sexual Reproduction • In sexual reproduction, a new individual is formed by union of a male and a female gamete.
Reproductive Strategies • Gametes are produced in the sex organs. • Males have testes that produce sperm. • Males produce sperm until death.
Reproductive Strategies • Females have ovaries that produce eggs. • At birth, females have produced all the eggs they will ever have.
Reproductive Strategies • Some species of animals, called hermaphrodites, have both testes and ovaries.
Reproductive Strategies • 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.
Reproductive Strategies • 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.
