Symbiotic Relationships

Term 1, Week 2, Lesson 4

Do Now

Read the scenario below and answer the questions.

A small bird called an oxpecker sits on the back of a large buffalo. The oxpecker eats ticks and parasites from the buffalo’s skin. The buffalo has fewer parasites as a result.

1. Which organism benefits from this relationship?
2. Is either organism harmed? Explain.
3. What would you call this type of relationship? Make your best prediction.

Daily Review

1. An interaction where one organism hunts and consumes another is called:
   • 1. Competition
   • 2. Symbiosis
   • 3. Predation
   • 4. Decomposition
2. Which of the following is a prey adaptation?
   • 1. Sharp claws for catching food
   • 2. Venom to immobilise prey
   • 3. Warning colouration to deter predators
   • 4. Speed for chasing down prey
3. In a predator-prey graph, when the prey population increases, what typically happens to the predator population shortly after?
   • 1. It decreases immediately
   • 2. It increases after a time lag
   • 3. It stays the same
   • 4. It drops to zero
4. Competition between members of different species is called:
   • 1. Intraspecific competition
   • 2. Predation
   • 3. Interspecific competition
   • 4. Mutualism
5. Which of the following best describes the competitive exclusion principle?
   • 1. All species in an ecosystem must compete
   • 2. Predators always exclude prey from an area
   • 3. Two species competing for the same niche cannot coexist indefinitely
   • 4. Competition always leads to extinction

Learning Intentions

Today we are learning about the three types of symbiotic relationships and evaluating their effects on the organisms involved.

Success Criteria

• Define symbiosis and distinguish between mutualism, commensalism, and parasitism
• Describe real-world examples of each type of symbiotic relationship
• Evaluate how symbiotic relationships contribute to the stability and biodiversity of ecosystems

Keywords

symbiosis

A close, long-term interaction between two different species living in close association.

mutualism

A symbiotic relationship where both organisms benefit.

commensalism

A symbiotic relationship where one organism benefits and the other is unaffected.

parasitism

A symbiotic relationship where one organism benefits at the expense of the other (the host).

host

The organism that a parasite lives on or in.

parasite

An organism that lives on or in a host and benefits at the host’s expense.

Learning Activities

Activity 1 — I DO: The Three Types of Symbiosis

Teacher introduces mutualism, commensalism, and parasitism with definitions and Australian examples.

Symbiosis means “living together” — it describes any close, long-term relationship between two different species. There are three main types:

1. Mutualism (+/+) — Both organisms benefit

• Clownfish and sea anemone: The clownfish is protected by the anemone’s stinging tentacles; the clownfish drives away butterfly fish that would eat the anemone.
• Bees and flowering plants: Bees get nectar for food; plants get pollinated.
• Mycorrhizal fungi and eucalyptus roots: The fungus helps the tree absorb water and nutrients; the tree provides sugars to the fungus.

2. Commensalism (+/0) — One benefits, the other is unaffected

• Remora fish and sharks: The remora attaches to the shark and feeds on scraps; the shark is unaffected.
• Epiphytic orchids on rainforest trees: The orchid gets a position high in the canopy for better light; the tree is unaffected.
• Cattle egrets and livestock: The egret eats insects disturbed by grazing cattle; the cattle are unaffected.

3. Parasitism (+/−) — One benefits, the other is harmed

• Ticks on kangaroos: The tick feeds on the kangaroo’s blood; the kangaroo may lose condition or contract disease.
• Mistletoe on eucalyptus: The mistletoe takes water and nutrients from the tree; the tree is weakened.
• Tapeworms in mammals: The tapeworm absorbs nutrients from the host’s digestive system; the host may become malnourished.

Benefit/Harm Summary Table:

Type	Organism A	Organism B
Mutualism	Benefits (+)	Benefits (+)
Commensalism	Benefits (+)	Unaffected (0)
Parasitism	Benefits (+)	Harmed (−)

Check for Understanding: Students hold up cards labelled M, C, or P for quick-fire scenarios read aloud by the teacher.

Diagram showing the three types of symbiotic relationships with examples.

Activity 2 — WE DO: Symbiosis Sorting Activity

In small groups, students sort symbiosis scenario cards and complete a summary table.

Instructions:

1. Each group receives a set of 9 scenario cards describing symbiotic relationships.
2. Read each card carefully and sort it into one of three categories: Mutualism, Commensalism, or Parasitism.
3. For each card, complete the summary table below.

Scenario	Type of Symbiosis	Organism A Benefit/Harm	Organism B Benefit/Harm
Clownfish living among sea anemone tentacles
Fleas feeding on a dog’s blood
Barnacles growing on a whale’s skin
Bees collecting nectar from flowers
Leeches attached to a freshwater turtle
Small birds nesting in the branches of a large tree
Mycorrhizal fungi on plant roots
Mistletoe growing on a eucalyptus tree
Cattle egrets following grazing cattle

4. As a group, discuss: Which relationships were the hardest to classify? Why?
5. Choose one relationship to present to the class — explain your reasoning for the classification.

Activity 3 — YOU DO: Australian Symbiosis Research

Students independently research one Australian symbiotic relationship and write a short explanation.

Choose one of the following Australian symbiotic relationships to research (or choose your own with teacher approval):

• Cleaner wrasse and reef fish on the Great Barrier Reef
• Mistletoe and eucalyptus trees
• Wombats and their gut microbes
• Ticks and kangaroos
• Fig wasps and fig trees
• Remora fish and manta rays

Write a response (8–10 sentences) that includes:

1. The names of the two organisms involved.
2. A description of the relationship — what does each organism do?
3. Classification: Is this mutualism, commensalism, or parasitism? Justify your choice.
4. How does each organism benefit or suffer? Use (+), (0), or (−) notation.
5. Explain why this relationship is important for the broader ecosystem.

Reflection

1. Define symbiosis in one sentence.
2. What is the key difference between mutualism and commensalism?
3. A tick feeds on the blood of a kangaroo. Classify this relationship and explain your reasoning.
4. Give one example of mutualism found in Australian ecosystems.
5. Explain how symbiotic relationships can contribute to the stability of an ecosystem. Use an example in your answer.
6. Extended response: Compare mutualism and parasitism. In your answer, define each type, provide one example of each, and explain how the organisms are affected differently.