Animals without backbones 2 PDF

Preview

Summary

What Is This Module About?This module is about three groups of worms—the flatworms, the roundworms and the segmented worms. This module is the second in a series of modules on animals without backbones. It has three lessons:Lesson 1 – The FlatwormsLesson 2 – The RoundwormsLesson 3 – The Segmented Wo...

Description

What Is This Module About? This module is about three groups of worms—the flatworms, the roundworms and the segmented worms. This module is the second in a series of modules on animals without backbones. It has three lessons: Lesson 1 – The Flatworms Lesson 2 – The Roundworms Lesson 3 – The Segmented Worms

What Will You Learn From This Module? After studying this module, you should be able to: describe what flatworms, roundworms and segmented worms are; and explain how they affect people.

1

Let’s See What You Already Know Before you start studying this module, take this simple test first to find out how much you already know about the topics in this module. Encircle the letter of the correct answer to each of the following. 1.

Which of the following is an example of a flatworm? a. b. c. d.

2.

Which of the following is an example of a non-parasitic worm? a. b. c. d.

3.

trichinosis elephantiasis amoebiasis sarcocystis

Why do earthworms live in wet and moist places? a. b. c. d.

6.

liver fluke liverwort trichina hookworm

Which among the following diseases can most likely occur by eating half-cooked pork? a. b. c. d.

5.

hookworm earthworm liver fluke pinworm

Which of the following is an example of a parasite found in the livers of animals? a. b. c. d.

4.

ascaris pinworm tapeworm hookworm

to keep their bodies cool to lower their body temperatures for better gas exchange for better blood circulation

Which of the following is an example of a non-parasitic flatworm? a. b. c. d.

earthworm sandworm vinegar eel planaria

2

7.

Which of the following is a parasite? a. b. c. d.

8.

What do you call the small roundworms found at the perianal opening in humans? a. b. c. d.

9.

pinworms trichinas vinegar eels flukes

Among the three kinds of worms that will be discussed in this module, which one is composed mostly of non-parasitic forms? a. b. c.

10.

earthworm planaria sandworm trichina

roundworms segmented worms flatworms

What specific part of the body is an ideal place for parasites? a. b. c. d.

brain intestine liver heart

Well, how was it? Do you think you fared well? Compare your answers with those in the Answer Key on page 33 to find out. If all your answers are correct, very good! This shows that you already know much about the topics in this module. You may still study the module to review what you already know. Who knows, you might learn a few more new things as well. If you got a low score, don’t feel bad. This means that this module is for you. It will help you understand some important concepts that you can apply in your daily life. If you study this module carefully, you will learn the answers to all the items in the test and a lot more! Are you ready? You may go now to the next page to begin Lesson 1.

3

LESSON 1

The Flatworms The animal that you most likely think of when you hear the word “worm” is the earthworm — the worm that you see on pavements or in the soil after the rain. Sometimes, they are even used as baits by fishermen. You probably wouldn’t think immediately of tapeworms or any other type of worms. Just what is a worm? Worms are invertebrates with soft bodies and bilateral symmetry. They have tissues, organs and organ systems. Have you ever experienced deworming a puppy? If so, did your veterinarian give your pet some medicine to get rid of the parasitic worms in its intestines? Examples of deworming medicines include Antiox and Combantrin. They are effective if given in the right dosage. Not all worms are parasitic though. Some do not need hosts and are even helpful. However, in this lesson, we will concentrate on the species that affect our health and only talk a little about the non-parasitic forms.

Let’s Think About This Before we start our discussion, try to reflect on the following questions first: 1. How do parasitic flatworms live? 2. How can we avoid infection from these worms? In this lesson, we will try to answer these questions and see how they relate to our daily lives.

Let’s Try This You can visit science laboratories in schools near your place. They usually have bottled specimens of different worms on display. Their collections can help you a lot. You can ask permission from the right authority and as you start studying the specimens, try to note the following: 1.

shapes and sizes of the worms;

2.

sources of the worms;

3.

whether the worms are segmented or not; and

4.

prominent features of the worms.

4

If no school laboratory specimens are available, just study the illustrations provided below. These are examples of flatworms, roundworms and segmented worms that you can see around you. Prostomium

Clitellum

Mouth

Setae

Scolex

Surrounding pharynx

Eyespot

Earthworm Pharynx sheath

Immature proglottio

Gastrovascular Auricle cavity Turbellarian (Planaria) Ventral Sucker

Intestine Oral sucker Mature proglottio

Tape worm

Uterus Testes Excretory Bladder

Gravid proglottio Vitellaria

Genital pore

Ovary Liver fluke

Vateline duct

Answer the following questions briefly. 1. How many types of worms did you see? Are you familiar with all of them? ________________________________________________________________ ________________________________________________________________ 2.

From what animals were they taken? ________________________________________________________________ ________________________________________________________________

3.

Describe the sizes and shapes of the different specimens collected. ________________________________________________________________ ________________________________________________________________

Have your Instructional Manager or Facilitator check your answers.

5

Let’s Learn The first group of worms that we will discuss is the flatworms. All flatworms belong to the phylum Platyhelminthes. This phylum is divided into four classes or groups: the turbellarians (Turbellaria), the monogeneans (Monogenea), the flukes (Trematoda) and the tapeworms (Cestoda). Most turbellarians are free-living, meaning they do not depend on other organisms for food. The other three are exclusively parasitic, meaning they depend on other organisms (hosts) for food and may even cause damage to their hosts. As their common name suggests, flatworms are flat. They are also soft-bodied. Let us first discuss the turbellarians. Look at their parts below. Ganglia Auricle

Auricle

Eyespot Nerve

Gastrovascular cavity Pharynx sheath Surrounding pharynx Mouth

Parts of a turbellarian

There are around 6000 species of flatworms. Their bodies are dorso-ventrally flattened, meaning flattened from back to front. Some flatworms live in freshwater while others live in seawater. Most flatworms such as flukes and tapeworms are parasites. They live in or on other organisms that supply their food. The freshwater planaria is around 3 centimeters (cm) long. This worm is free-living. It uses its digestive system to break down food. Planarians are capable of regeneration, growing lost parts of their bodies again.

6

Let’s Try This Prepare the following materials then do the experiment below. 1 small collecting bottle 4 bottle caps 1 sharp blade 4 planarians 1. 2.

Put the four planarians in separate bottle caps. Cut each planarian in the following manner: a. crosswise in half b. crosswise into three equal parts c. crosswise at the base of the head d. lengthwise half Refer to the illustration below for guidance.

3.

Observe them daily. Find out which piece will be able to regenerate its missing parts.

Now, the illustration on the next page will show you what to expect after a few days.

7

cut # 2 cut # 1

discard

(a) (a)

discard

discard

(b) (b) cuts

cut # 2 discard (c) (c)

Notice how interesting planarians are. From this activity, you can conclude that the more you cut a worm, the more it can increase in number. Imagine if humans are capable of regeneration too. The world would surely be jampacked with people then.

Let’s Try This Answer the following questions briefly. 1.

Why are these animals called free-living forms? ________________________________________________________________ ________________________________________________________________

2.

What are the advantages of being able to regenerate body parts? ________________________________________________________________ ________________________________________________________________

Have your Instructional Manager or Facilitator check your work. 8

Let’s Learn Do you know what liver flukes are? Liver flukes are leaf-shaped worms with weakly developed suckers. Adult liver flukes are usually found attached in the bile ducts of the livers of some reptiles, birds and mammals. Two species are commonly found in human livers, the Chlonorchis sinensis and Heterophyes katsuradai. However, we will focus only on Chlonorchis sinensis, the liver fluke that causes the disease chlonorchiasis in humans. This liver fluke is found in many regions of the Orient especially in China, Southern Asia, Japan and Hong Kong. Adult Chlonorchis sinensis measure 8 to 25 millimeters (mm) long and 1.5 to 5 mm wide. They were first discovered in the bile passages of a Chinese carpenter in Calcutta in 1875. Look at the diagram below to know the different parts of the Chlonorchis sinensis. Mouth Oral sucker Pharynx Brain Gastrovascular cavity Ventral sucker

Uterus Sperm duct Yolk glands Excretory duct Testes

Parts of Clonorchis sinensis

Chlonorchis sinensis require three hosts to complete their life cycles. Humans are their primary hosts, while snails and fish act as intermediate hosts. They spend most of their adult lives in human bodies and their larval stages in the bodies of snails and fish. Study the life cycle of a liver fluke on the next page.

9

Metacercarial cysts in fish muscle

Liver

Adult fluke

Bile duct

Shelled miracidium

Miracidium hatches after being eaten by snail

Cercaria

Redia Life cycle of a liver fluke

1.

Based on the life cycle of the liver fluke, how can you avoid being infected with this worm? ________________________________________________________________ ________________________________________________________________

2.

What measures can you recommend to stop the spread of the liver flukes in humans? Is it always safe to use pesticides in order to exterminate snails? Why or why not? ________________________________________________________________ ________________________________________________________________

Compare your answers with mine below. 1.

Infection with liver flukes can be avoided by not eating raw fish or exterminating snails that serve as intermediate hosts to the parasites.

2.

It’s not always safe to use pesticides to exterminate snails. They may affect other organisms and pollute the soil.

So how does the liver fluke develop? An adult fluke sheds or releases eggs with larvae through the feces of humans. If these are ingested by certain freshwater snails, they develop inside the bodies of the snails, and free-swimming cercariae emerge. They then find suitable bodies of fish to live in and further develop. When these are eaten raw by humans, the flukes migrate to their livers and mature, living there for 15 to 30 years.

10

People infected with Chlonorchis sinensis may suffer from chlonorchiasis. These worms may multiply to as much as 10000 to 20000 in a person’s liver. They depend on the person’s blood and liver cells for food. Because of this, the host may suffer from anemia thereby making him/her appear thin and malnourished. The presence of these worms can also cause inflammation of and edema in the liver. Jaundice has also been diagnosed in some cases. To prevent the spread of this infection it is necessary to have sanitary toilets. This way, the eggs of these worms will not be able to spread. It would also help if ponds, irrigation ditches and other bodies of water will be treated with snail-killing pesticides. People should also avoid eating raw fish to prevent infection from these worms.

Let’s Review Label the steps in the life cycle of a liver fluke below.

Compare your answers with the illustration on page 10. How well did you do?

11

Let’s Learn We will now discuss what tapeworms are. Examine closely the illustration below. It shows the external features of the beef tapeworm, Taeniarhyncus saginatus. By far, this is the most common tapeworm that infects humans.

Double row of hooks Scolex

Suckers (Acetabula) Neck Young proglottids

External parts of a Taeniarhyncus saginatus

The Taeniarhyncus saginatus is the most common parasite found nearly in all beefeating countries. They can grow up to a length of over 75 feet. The most common of these though are only 10 to 15 feet in length. Their smallest specimens may consist of as many as 2000 proglottids or segments. Their heads have four powerful suckers and some species even have hooks on their heads. Study the life cycle of the Taeniarhyncus saginatus on the next page. Just like with the liver flukes, note how infection with these can occur. Can you imagine how these worms can live in our intestines? They must coil back and forth so they can fit in our 24-foot long intestines.

12

Eaten by human in raw beef Evaginated cysticerus in upper intestine

Yolk gland

Invaginated cysticerus

Cysts in muscle (“Measly beef”)

Ovary Vagina Genital pore Sperm Uterus duct Sperm

Excretory canal Testes

Gravid proglottid

Grass, contaminated with eggs, ingested by cow Life cycle of a tapeworm

The embryonated eggs of beef tapeworms are shed from a human host through his/her feces and remain viable for many weeks on the ground. When ingested by cows or cattle nearby, the six-hooked larvae hatch, burrow into their blood or lymph vessels and migrate to their skeletal muscles. They encyst in the cow’s muscles and become bladder worms or cysticerci. The cows or cattle then contract the disease cysticercosis bovis. Each of these cysticerci develops and remains inside the cows or cattle until the beef is eaten raw by humans. In the new host, the worms open up, attach to his/her intestine and mature in two to three weeks. The ripe proglottids then may be expelled daily for many years. Humans may be infected by eating raw or “measly” beef. The adult worm may stay in the intestine for many years folded many times. Do you have any question about the life cycle? Is everything clear? If so, try the following simple activity to see if you understood the cycle.

13

Let’s Review Complete the illustration of a life cycle of a beef tapeworm below by labeling all the steps.

Compare your work with the illustration on page 13. How well did you do?

Let’s Learn Human infection with cysticercosis bovis is highest in areas of the world where beef is a major food and sanitation is of little concern. Diarrhea and intestinal obstruction are common results of this infection. Hunger pains may be experienced too. This also has psychological effects on the infected person observing the continued migration of the proglottids out of his/her anus. Prevention of taeniasis, the disease caused by tapeworms, is easy. Just cook beef until it is no longer pink in the center, since cystecerci are killed at 56°C. Beef can also be rendered safe by freezing it at –5°C for at least one week. Using sanitary toilets can also prevent the spread of the disease. Discouraging the use of human feces as fertilizer will also help.

14

Let’s Try This Go around your neighborhood or barangay and do the following: 1.

Check if all your neighbors’ houses have sanitary toilets.

2.

Check too whether cattle or pigs are roaming around.

3.

Report your findings to your municipal health officer or barangay captain for immediate action.

Let’s See What You Have Learned A.

Match the terms in Column A with their definitions/descriptions in Column B. Write only the letters of the correct answers in the blanks provided. A

____ 1. ____ 2. ____ 3. ____ 4. ____ 5. ____ 6. ____ 7. ____ 8. ____ 9. ____10.

B Worms Flatworms Free-living Parasitic Dorso-ventrically flattened Planaria Regeneration Liver flukes Proglottids Cystecerci

a. Worms with flattened bodies and definite heads but no true cavities b. Obtaining food and protection from a living organism of another species c. An aquatic type of flatworm d. A leaf-like parasitic flatworm that invades the liver of vertebrates and is a serious pest of domesticated animals e. Bladder worms f. Soft-bodied limbless invertebrates that are either cylindrical, segmented or flat g. Non-parasitic h. Flattened both in front and at the back i. The ability to produce again j. Segments

B.

Answer the questions briefly.

1.

In what ways can you help your community stop the spread of tapeworm infection? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________

15

2.

How can you make beef safe for human consumption? ________________________________________________________________ ________________________________________________________________ ________________________________________________________________

Compare your answers with those in the Answer Key on page 33. How well did you do?

Let’s Remember Flatworms are worms that have soft and dorso-ventrally flattened bodies. The planaria is an example of a free-living worm. Tapeworms and flukes are generally parasitic. Adult liver flukes can be found in the livers of humans while adult tapeworms can be found in their intestines. Proper health habits are recommended to avoid the spread of infections from the different kinds of worms.

16

LESSON 2

The Roundworms Members of this phylum can be found almost everywhere. There are more than half a million species of roundworms under the phylum Nematoda. In fact, there may be a million in a kilogram of soil! They can be found in freshwater, seawater and in or on plants, humans and other living organisms. Roundworms are more complex than flatworms. Their digestive systems run along the whole length of their bodies. Their digestive systems have two openings — the mouth and the anus. Many roundworms are parasitic. However, most of them are free-living. Some are even helpful because they act as decomposers. They digest dead and decaying organic matter and return their materials to the soil. Roundworms are commonly found in pigs, humans and dogs. They live in the intestines of these organisms in big numbers.