Parasitism Harms the Host
Definition
Parasitism
A relationship in which a parasite gains resources from a host and the host is harmed.
- Parasitism is a relationship in which a parasite gains resources from a host and the host is harmed.
- A parasite lives on or inside another organism and takes nutrients or other resources from it.
- A host is the organism from which the parasite obtains resources.
- The parasite benefits because it gains food, water, shelter or a place to reproduce.
- The host is harmed because resources are removed, tissues may be damaged, or disease may be transmitted.
Example
- Mistletoe is the parasite and the tree is the host.
- Mistletoe takes water and mineral ions from the tree.
- The tree is harmed because fewer resources remain available for its own growth.
Mutualism Benefits Both Species
Definition
Mutualism
A relationship between two species in which both organisms benefit.
- Mutualism is a relationship between two species in which both organisms benefit.
- Each benefit must be specific: one species may gain food, while the other gains pollination, protection, cleaning or seed dispersal.
- Both species may survive or reproduce more successfully because of the resources or services exchanged.
Example
- A pollinating insect gains energy-rich nectar from a flower.
- The plant gains pollen transfer to another flower, which increases the chance of fertilisation.
- Both species benefit, so the relationship is mutualism.
Compare the Two Relationships
- Parasitism has one beneficiary and one harmed organism.
- Mutualism has two beneficiaries.
- The identity of each organism matters: state which species gains, what it gains, and whether the other species gains or is harmed.
Common Mistake
Do not write only that one organism benefits because this does not identify the host, the resource taken or the harm caused.
Exam technique
- A complete parasitism explanation follows the chain: parasite gains a named resource, the host loses that resource, and the loss damages the host.
- If the question already states that an organism is a parasite, repeating the word parasitic does not explain the relationship.
Survival Depends on Other Species
- A parasite depends on a suitable host for the resources and conditions needed to survive or reproduce.
- Mutualists may depend on each other when the exchanged food or service is difficult to obtain from another species.
Self review
- What is parasitism?
- What is a host?
- How does mistletoe benefit and how is its host harmed?
- What is mutualism?
- What two benefits are exchanged between a pollinating insect and a flowering plant?
