Interactions Between Organisms
Hunt, compete, share, help, or harm: how living things affect each other.
Topic 5 of 5Grade 6 · Life Science
- Teacher:
- Mr. Mohamed Fawzy
- School:
- Oceans Academy
- Unit:
- From Cells to Ecosystems
How this topic is built
- Covers workbook pages 99 to 101 (Week 10: How Do Organisms Interact With Each Other, and the "Which is Which?" pictures) and all eight workbook questions.
- "Survival of the fittest" is kept at the workbook's level, with the common misconception ("fittest = strongest") corrected.
Five ways organisms interact
In an ecosystem, organisms affect each other all the time. There are five main kinds of interactions: competition, predation, commensalism, mutualism, and parasitism.
Three of them are types of symbiosis. In symbiosis, two different species (kinds of living things) live closely together for a long time. Those three are commensalism, mutualism, and parasitism.
Correction from the workbook (page 99)
The workbook says all five interactions "are types of symbiosis." Symbiosis means a close, long-lasting relationship between two different species, which fits commensalism, mutualism and parasitism. Competition (which can even be within one species) and predation are not symbiosis.
Teaching tip
Have students show the + / − / 0 signs with thumbs up, thumbs down, and flat hand for each example.
Quick Check 1
From the workbook, page 99, question 1 (written as multiple choice).
Workbook question
The workbook expects "symbiosis" as a written answer. Because competition and predation are not symbiosis, the best answer is "interactions," with symbiosis naming the three close ones. Choice A covers both.
Competition and predation
Competition: there isn't enough food, space, water, or mates for everyone, so organisms compete for them. It can happen between different species or within the same species.
The organisms best suited to their environment are the most likely to survive and pass their genes on to the next generation. This is called "survival of the fittest." Here, fittest means best suited, not strongest.
Predation: one animal, the predator, hunts and eats another animal, its prey.
Corrections from the workbook (page 99)
- "Only the strongest will live to pass their genes onto the next generation; this is survival of the fittest." In science, "fittest" means best suited to the environment, not strongest; a fast, small or well-hidden animal can be the fittest. Kept at the workbook's level, with this one correction.
- "Predation... one animal hunting and eating another animal or plant." Eating plants is usually called herbivory. To keep the vocabulary light, the slide simply describes predation as an animal eating an animal and leaves the new word out.
Home experiment 1: crowded seeds
What happens when plants have to compete for the same space, water, and light?
Expected result
After 10 to 14 days, the 3 plants in cup A are taller or sturdier, with bigger leaves. The 30 plants in cup B are thin, pale, and weak.
Link
Gardeners "thin" seedlings for this reason. It is competition within one species.
Quick Check 2
Name the interaction.
What this checks
That competition can happen within one species. This is picture 4 from the workbook's "Which is Which?" page.
Commensalism, mutualism, and parasitism
Commensalism
One organism benefits; the other is neither helped nor harmed. A cobia fish swims under a great white shark. It eats scraps the shark leaves behind and gets protection from such a big bodyguard. The shark isn't affected.
Mutualism
Both organisms benefit. Bees visit flowers for nectar and pollen, which they take home to feed the hive and their young. As they fly from flower to flower, they carry pollen, which lets the flowers make seeds (pollination).
Parasitism
One organism, the parasite, benefits, and the other, the host, is harmed. A mosquito bites your skin to drink blood. It gets a meal; you get an itchy bite.
From the workbook (page 99)
All three examples are kept. The cobia–shark example is real: cobia are known to follow sharks, rays, and turtles. A closely related fish, the remora, is the classic textbook example.
Accuracy note
Scientists often call mosquitoes "micropredators" because they visit many hosts briefly; they are commonly taught as a parasite example, as the workbook does. Ticks are a clearer parasite example (used on the sorting slide).
Quick Check 3
From the workbook, page 99, question 2.
Workbook question, unchanged
Answer D, commensalism.
Which is which?
These are the workbook's five pictures. Decide on your answer first, then tap the picture to check.
Corrections to the workbook's pictures (pages 100–101)
- Picture 3 is labeled "A bison and an oxpecker," but the drawing shows an African buffalo with an egret-like bird, and oxpeckers don't live with American bison. It is relabeled as a cattle egret and African buffalo, which is commensalism. With this change the five pictures show all five interactions once.
- Picture 5, "Ant and Fungus," shows mushrooms growing out of an ant: the zombie-ant fungus, which is parasitism. Leafcutter ants, which farm fungus, are a mutualism, so the label is made specific.
Answer key
1 Predation · 2 Mutualism · 3 Commensalism · 4 Competition · 5 Parasitism
Quick Check 4
From the workbook, page 99, question 3.
Workbook question, unchanged
Answer A, mutualism.
Sort it: name the interaction
New examples, many from Virginia. Choose the interaction for each pair.
The planted mix-ups
- Barnacles on a whale: looks like a parasite, but barnacles don't feed on the whale.
- Leafcutter ants and fungus: easily confused with the zombie-ant fungus (parasitism).
- Two cardinals at a feeder: fighting looks like predation, but no one is being eaten.
Predator and prey simulator
Simplified model
How to use it
- Press Play and trace the pattern: rabbits rise, then foxes rise, then rabbits fall, then foxes fall.
- Set foxes to 0: rabbits grow until they run out of food and space (competition).
- "Remove the foxes halfway" shows what happens when a predator disappears (links to Topic 4).
Accuracy note
This is a classic predator–prey model. Real populations also depend on weather, disease, and food plants.
Quick Check 5
Use the simulator's pattern.
What this checks
That predator numbers follow prey numbers, with a delay.
Home experiment 2: the ant picnic
Which food do ants compete for most?
Expected result
Most ants gather at the sugar card within 10 to 20 minutes, crowding and pushing for space. Some ants may visit the salty card, since ants need some salt. Few visit plain water.
Timing
Works best on a warm, dry afternoon from spring to early fall.
One oyster, many interactions
The eastern oyster of the Chesapeake Bay shows almost every kind of interaction.
Predation: blue crabs and rays eat oysters. Commensalism: small fish, crabs, and worms hide in the small spaces of oyster reefs, getting shelter without affecting the oysters. Parasitism: a tiny parasite causes a disease that has killed many Bay oysters. Competition: oysters compete with mussels and barnacles for space on hard surfaces.
Sources
Chesapeake Bay Program and the Virginia Institute of Marine Science: oyster predators (blue crabs, cownose rays, oyster drills), oyster reefs as habitat, and Dermo disease caused by the parasite Perkinsus marinus.
Why this slide
Shows students that one organism can be in several interactions at once, using a Virginia animal.
Interactions in everyday life
Ticks on hiking trails
Ticks in Northern Virginia parks are parasites of deer, mice, and people. After a hike, check yourself for ticks.
Apple orchards
Around Winchester, Virginia's apple region, bees pollinate apple blossoms each spring. The trees get pollinated; the bees get nectar. That's mutualism.
Cobia in the Chesapeake Bay
Every summer, cobia swim into the lower Chesapeake Bay. Anglers know they often follow rays and other large animals, just like the workbook's cobia and shark.
Mistletoe in oak trees
In winter, look up at bare oak trees: the green clumps are mistletoe. It takes water and food materials from the tree, so it is a parasite.
Sources for the local examples
- Ticks and tick checks: Virginia Department of Health.
- Winchester and the Shenandoah Valley are Virginia's main apple-growing region.
- Cobia arrive in the lower Bay in late spring and summer: Virginia Marine Resources Commission, VIMS.
- Oak mistletoe grows in Virginia and is a hemiparasite (it makes some of its own food but takes water and minerals from the tree).
Vocabulary flip cards
Say the meaning out loud, then tap the card to check.
Game idea
Students act out an interaction in pairs; the class guesses which flip card it matches.
Final quiz: Interactions Between Organisms
Answer all 8, then check your answers. Every answer comes with an explanation.
Answer key
1 A · 2 B · 3 C · 4 D · 5 A · 6 C · 7 B · 8 D
Workbook questions: page 99 Q1 to Q3 are Quick Checks 1, 3 and 4; the five pictures are on slide 8, with gazelles also in Quick Check 2 and the egret in quiz question 8.