University:
Bradley University
Course:
BIO 250 | Organismal Biology
Academic year:

2023
Views:

463

Pages:

31
Author:

Angelica Rose

27–2 Roundworms 27–2 Roundworms What Is a Roundworm? What Is a Roundworm? Most species of roundworms are free-living, inhabiting soil, salt flats, aquatic sediments, and water, from polar regions to the tropics. Others are parasitic and live in hosts. 27–2 Roundworms What Is a Roundworm? What are the defining features of roundworms? 27–2 Roundworms What Is a Roundworm? Roundworms are unsegmented worms that have pseudocoeloms and digestive systems with two openings—a mouth and an anus. 27–2 Roundworms What Is a Roundworm? Roundworms have a body cavity between the endoderm and mesoderm tissues. 27–2 Roundworms What Is a Roundworm? This cavity is partially lined with tissue derived from the mesoderm and is called a pseudocoelom, meaning, “false coelom.” 27–2 Roundworms What Is a Roundworm? Roundworms have a digestive tract with two openings. Food moves in one direction through the digestive tract of roundworms. Any food that is not digested leaves the body through the anus. 27–2 Roundworms Form and Function in Roundworms Form and Function in Roundworms Roundworms have specialized tissues and organ systems that carry out essential physiological functions. 27–2 Roundworms Form and Function in Roundworms Feeding Many free-living roundworms use grasping mouthparts and spines to catch and eat other small animals. 27–2 Roundworms Form and Function in Roundworms Respiration, Circulation, and Excretion Roundworms exchange gases and excrete metabolic waste through their body walls. They depend on diffusion to carry nutrients and waste through their bodies. 27–2 Roundworms Form and Function in Roundworms Response Roundworms have simple nervous systems, consisting of several ganglia. Several nerves extend from ganglia in the head and run the length of the body. These nerves transmit sensory information and control movement. 27–2 Roundworms Form and Function in Roundworms Movement Fluid in the pseudocoelom and muscles extending the length of their bodies function as a hydrostatic skeleton. Aquatic roundworms contract muscles to move like snakes through the water. Soil-dwelling roundworms push their way through the soil by thrashing around. 27–2 Roundworms Form and Function in Roundworms Reproduction Roundworms reproduce sexually. Most species have separate sexes. Roundworms reproduce using internal fertilization. Parasitic roundworms often have life cycles that involve two or three different hosts or several organs within a single host. 27–2 Roundworms Roundworms and Human Disease What roundworms cause human disease? 27–2 Roundworms Roundworms and Human Disease Roundworms and Human Disease Parasitic roundworms include trichinosis-causing worms, filarial worms, ascarid worms, and hookworms. 27–2 Roundworms Roundworms and Human Disease Trichinosis-Causing Worms Adult Trichinella worms live and mate in the intestines of their hosts. Female worms carrying fertilized eggs burrow into the intestinal wall and release larvae. Larvae travel through the bloodstream and burrow into organs and tissues. 27–2 Roundworms Roundworms and Human Disease The larvae form cysts and become inactive in the host’s muscle tissue. Trichinella completes its life cycle only when another animal eats muscle tissue containing these cysts. Humans can get trichinosis by eating raw or incompletely cooked pork. 27–2 Roundworms Roundworms and Human Disease Filarial Worms Filarial worms are threadlike worms that live in the blood and lymph vessels of birds and mammals. They are transmitted by biting insects. Large numbers of filarial worms may block the passage of fluids within lymph vessels and cause swelling. 27–2 Roundworms Roundworms and Human Disease Ascarid Worms Ascaris lumbricoides is a serious parasite of humans and many other vertebrate animals. It absorbs digested food from the host’s small intestine. Ascaris lumbricoides is commonly spread by eating foods that are not washed properly. 27–2 Roundworms Roundworms and Human Disease Ascaris Life Cycle 1 Human ingests food or water containing Ascaris eggs. 27–2 Roundworms Roundworms and Human Disease Ascaris Life Cycle 2 The eggs travel to the small intestine and develop into larvae. 27–2 Roundworms Roundworms and Human Disease Ascaris Life Cycle 3 Larvae enter blood vessels and are carried to the lungs 27–2 Roundworms Roundworms and Human Disease Ascaris Life Cycle 4 Larvae are coughed up and swallowed. They then travel to the small intestine where they develop to maturity 27–2 Roundworms Roundworms and Human Disease Ascaris Life Cycle 5 Eggs are released and leave the host in faces. of 33 27–2 Roundworms Roundworms and Human Disease Hookworms Hookworm eggs hatch and develop in the soil. They use sharp toothlike plates and hooks to burrow into the skin and enter the bloodstream. 27–2 Roundworms Roundworms and Human Disease Hookworms travel through the blood of their host to the lungs and down to the intestines. There, they suck the host’s blood, causing weakness and poor growth. 27–2 In roundworms, the body cavity that forms between the endoderm and mesoderm is the a. ganglion. b. hydrostatic skeleton. c. pseudocoelom. d. coelom. 27–2 All of the following are parasitic roundworms EXCEPT a. tapeworms b. filarial worms c. hookworms d. ascarid worms 27–2 Characteristics of roundworms include a digestive system with a. one opening and a pseudocoelom. b. one opening but no pseudocoelom. c. two openings and a pseudocoelom. d. two openings but no pseudocoelom. 27–2 Gas exchange and excretion of metabolic wastes in roundworms occurs a. via a complex system of alveoli. b. through their body walls. c. through excretory tubules. d. by flame cells. 27–2 The roundworms called ascarids cause harm by a. causing serious body swelling. b. burrowing into body tissues and causing pain. c. causing malnutrition. d. causing weakness and poor growth.

What Is a Roundworm

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