Biology: Ecology: Symbiosis: Mutualism, Commensalism, Parasitism Worksheet

Question 1

Define symbiosis in ecology. Then describe how mutualism, commensalism, and parasitism differ from one another.

Accepted Answer

Symbiosis is a close, long-term interaction between organisms of different species. In mutualism, both species benefit. In commensalism, one species benefits while the other is not clearly helped or harmed. In parasitism, one species benefits while the host is harmed.

Question 2

Clownfish live among sea anemone tentacles. The clownfish gain protection from predators, and the anemone may gain nutrients from clownfish waste and protection from some anemone-eating fish. Classify this relationship and explain your evidence.

Accepted Answer

This relationship is mutualism because both species can benefit. The clownfish gain shelter and predator protection, while the anemone can gain nutrients and some protection.

Question 3

A cattle egret follows grazing cattle and eats insects that are stirred up by the cattle's movement. The egret gets food, and the cattle are not clearly helped or harmed. Classify this relationship and explain your reasoning.

Accepted Answer

This relationship is commensalism because the egret benefits by getting food, while the cattle are not clearly helped or harmed by the egret's presence.

Question 4

A tick attaches to a deer and feeds on the deer's blood. The tick gains nutrients, while the deer loses blood and may be exposed to disease. Classify this relationship and explain your reasoning.

Accepted Answer

This relationship is parasitism because the tick benefits by feeding, while the deer is harmed by blood loss and possible disease transmission.

Question 5

Many flowering plants provide nectar to bees. Bees collect nectar and pollen for food, and pollen is transferred between flowers during the visit. Classify this relationship using effect symbols for each organism.

Accepted Answer

This relationship is mutualism. The bee has a positive effect because it gains food, and the plant has a positive effect because pollination can help it reproduce, so the symbols are +/+.

Question 6

Barnacles attach to the skin of a whale and are carried to areas with more plankton. In many cases, the whale is not noticeably helped or harmed. Classify this relationship, and include a caution about why this classification might change with new evidence.

Accepted Answer

This relationship is usually classified as commensalism because the barnacles benefit from transportation while the whale is not clearly affected. The classification could change if evidence showed that many barnacles increase drag, damage skin, or provide a benefit such as protection.

Question 7

A tapeworm lives in the intestine of a human. It absorbs nutrients from digested food, and the human may suffer malnutrition, pain, or weakness. Classify this relationship and identify the parasite and the host.

Accepted Answer

This relationship is parasitism. The tapeworm is the parasite because it benefits by taking nutrients, and the human is the host because the human is harmed.

Question 8

Complete the effect-symbol table for the three types of symbiosis: mutualism, commensalism, and parasitism. Use + for benefit, 0 for no clear effect, and - for harm.

Accepted Answer

Mutualism is +/+ because both species benefit. Commensalism is +/0 because one species benefits and the other has no clear effect. Parasitism is +/- because one species benefits and the other is harmed.

Question 9

A student says, "Predation is the same as parasitism because one organism benefits and the other is harmed." Explain why this statement is incomplete or inaccurate.

Accepted Answer

The statement is incomplete because predation usually involves one organism killing and consuming another, while parasitism is typically a close, long-term relationship in which the parasite benefits while the host is harmed but often remains alive for some time. Both can have +/- effects, but they are different types of ecological interactions.

Question 10

Acacia trees provide hollow thorns for ants to live in and produce nectar that ants eat. The ants attack insects and animals that try to feed on the tree. Classify this relationship and explain how each species benefits.

Accepted Answer

This relationship is mutualism because both species benefit. The ants receive shelter and food, while the acacia tree receives protection from herbivores.

Question 11

In a forest, an orchid grows attached to a tree branch. The orchid gains better access to sunlight, and the tree is not significantly affected because the orchid does not take nutrients from it. Classify this relationship and explain why it is not parasitism.

Accepted Answer

This relationship is commensalism because the orchid benefits by getting better light, while the tree is not clearly helped or harmed. It is not parasitism because the orchid is not taking nutrients from the tree or causing clear harm.

Question 12

A fungus infects a crop plant and absorbs sugars from the plant's tissues. The fungus grows and reproduces, while the plant has yellow leaves, reduced growth, and lower seed production. Classify this relationship and describe the evidence for harm.

Accepted Answer

This relationship is parasitism because the fungus benefits by taking sugars from the plant, while the plant is harmed. Evidence for harm includes yellow leaves, reduced growth, and lower seed production.

Question 13

Researchers remove cleaner fish from one section of a reef but leave them in another section. Fish in the section without cleaner fish develop more parasites and spend more time scratching against rocks. What type of relationship is suggested between cleaner fish and their client fish? Explain your reasoning.

Accepted Answer

The data suggest mutualism between cleaner fish and client fish. Cleaner fish benefit by eating parasites, and client fish benefit because parasite loads and irritation are reduced when cleaner fish are present.

Question 14

Classify each interaction as mutualism, commensalism, or parasitism: a remora fish rides on a shark and eats scraps without a clear effect on the shark; nitrogen-fixing bacteria live in legume root nodules and provide usable nitrogen while receiving sugars; a flea feeds on a dog and causes itching.

Accepted Answer

The remora and shark interaction is commensalism because the remora benefits and the shark has no clear effect. The bacteria and legume interaction is mutualism because both benefit. The flea and dog interaction is parasitism because the flea benefits while the dog is harmed.

Question 15

Design a short investigation to test whether a suspected symbiotic relationship is mutualistic rather than commensal. Include the independent variable, one dependent variable, and the type of evidence that would support mutualism.

Accepted Answer

One investigation could compare organisms kept together with organisms kept apart. The independent variable is whether the two species are allowed to interact. A dependent variable could be growth rate, survival, reproduction, or parasite load for one species. Evidence for mutualism would show that both species have higher fitness or improved condition when interacting than when separated.

Biology: Ecology: Symbiosis: Mutualism, Commensalism, Parasitism

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