Symbiosis

Learning goals

 Studens should understand that;

• Symbiosis is the interaction of two species that are in direct contact and typically affect each other.
• Mutualism is a form of symbiosis where two organisms mutually affect each other in beneficial ways.
• Parasitism is a form of symbiosis where one organism lives off another organism, usually to the detriment of the organism being lived off of.
  

Student shoud know some basic vocabulary about ecology.
 

Special note: This book aims to help students understand the relationship between two organisms. This book is created to be used as a part of science class for Thai middle school students. Glossary contains Thai translations and explanations. 

Coaches: Mana will help students guide students through thinking process. Piti will help students link the lesson to prior knowledge or real life. Petch will explain English vocabulary used in this lesson.

Animal-animal relationships

The Egyptian Plover bird and the crocodile. You might think that if a bird
landed in the mouth of a crocodile, the crocodile would eat it. Well, not the Egyptian Plover bird. Egyptian Plovers and crocodiles have a unique
symbiotic relationship. Because crocodiles can’t use dental floss, they get food stuck in their teeth. All that food rots their teeth and probably causes them some pain. When a crocodile feels the need for a good tooth cleaning it will sit with its mouth wide open. The Egyptian Plover bird recognizes this invitation, and if one is nearby it will fly into the mouth of the crocodile, eat the food stuck in its teeth, and fly away. The plover gets a meal and the crocodile gets a valuable tooth cleaning: they both benefit.

Animal-plant relationships
Bees and flowers. You are all probably familiar with the idea that bees and
flowers have some kind of relationship. A bee goes from flower to flower
gathering nectar. While it is doing this, some of the flower’s pollen ends up
sticking to the bee’s hairy body and legs. When it goes to the next flower,
some of that pollen rubs off of the bee and gets into the flower. The flower
needs pollen to reproduce, but since flowers can’t move to get it themselves, the bees get it for them. Without bees, some flowers would have no way of getting the pollen they need to reproduce. Without flowers, bees wouldn’t get the nectar they need to eat. They both benefit.

Plant–plant relationships

Lichen. The first time you see lichen, you may be surprised that it is alive! It can be flat and not very obvious; it almost looks like a discoloration on a rock. Lichen is special because it can live in places where other organisms cannot. Lichen is a partnership or symbiotic relationship between two different species. Fungi and algae combine to create lichen, because together they can live in places where alone, as just algae or fungi, they could not survive. Their relationship is mutually beneficial—both species benefit from their relationship.

Human-bacteria relationships
Your intestine and bacteria. You might wonder how you can have your very own symbiotic relationship going on right now and not know it. It’s because it happens in your intestine where you can’t see it. When you eat food, very little of it gets digested in your stomach. It travels through your intestine where bacteria further digest the partly digested food. The bacteria also produce vitamins. Your food gets digested, you get vitamins, and the bacteria get a meal. Both benefit from each other. You have your very own partnership, without which, your body would not be as healthy!

Parasitism is a form of symbiosis where one organism lives off another organism, usually to the detriment of the organism being lived off of.

Tapeworms

Tapeworms are long, flat parasites that live in the intestines of pigs, cows, and even humans. A tapeworm gets into its host by laying its eggs in the host’s food source. The host eats this food, and the eggs develop and grow into tapeworms, which attach themselves to the intestines of their host. Tapeworm feed off the food that the host eats, and sometimes a tapeworm has been known to live in a human for ten years without being detected! The tapeworm has a safe, warm home and a constant food source, but the host does not benefit from the relationship. In some rare cases, the tapeworm can make the host sick or even cause death.

Ticks

Ticks are pinhead-sized arachnids that form parasitic relationships with birds,reptiles, animals, and sometimes humans. Ticks attach to their host’s skin and feed off its blood. In this way it gets both food and a home. Ticks can consume enough food to grow 200 to 600 times their original body weight. In this relationship, the tick gets the benefits of a warm home and food, while the host gains nothing. The tick may even give the host a disease, which could weaken or kill it.

Mistletoe

Mistletoe is a plant that people hang above doorways at Christmas-time.
Before it gets picked and hung inside it grows by living off of other plants.
Mistletoe grows on woody plants, taking nutrients and moisture from them. It also “strangles” it—reducing the nutrients that the plant can take in. Mistletoe is considered a parasitic plant, because the mistletoe gets all the benefits, while the woody plant or tree has to support itself as well as the mistletoe.

Summary with symbols

Symbiosis:               -->     because two organisms affect each other.

                               <--

Mutual relationship:

+/+ because both organisms benefit from the relationship

Parasitic relationship:

+/- because host lose while parasites gain benefits.

Reference

Teaching materials from Understanding of Consequence, Project Zero.

Special note

This book aims for Thai middle school students; therefore, it contains some meanings and explanations in Thai language.