Ecosystems | Year 8 Biology (Cambridge) PDF Download

Bioaccumulation

• Bioaccumulation refers to the process where organisms absorb and store substances, such as toxins or chemicals, at a rate faster than they can eliminate them. 
• This accumulation occurs within individual organisms and can lead to higher concentrations of these substances over time.

Key Points

• Organisms accumulate toxins from their environment through ingestion, absorption, or inhalation.
• Toxins typically include heavy metals like mercury, pesticides, and persistent organic pollutants (POPs).
• Examples include fish accumulating mercury from polluted waters or birds storing pesticides in their bodies.

Examples

• Fish in polluted lakes accumulating mercury from industrial runoff.
• Birds storing DDT pesticides in their tissues from contaminated prey.

Impact on Organisms

• Bioaccumulated toxins can impair immune function, reproductive systems, and overall health.
• They pose risks to predators at higher trophic levels due to increased concentrations.

Biomagnification

• Biomagnification is the process where concentrations of toxins increase progressively up the food chain. 
• Predators at higher trophic levels accumulate higher concentrations of toxins than their prey.

Key Points

• Toxins become more concentrated as they move up the food chain.
• Top predators, like eagles or sharks, often suffer the most from biomagnification.

Examples

• DDT becoming more concentrated in fish-eating birds compared to the fish they consume.
• PCBs (polychlorinated biphenyls) increasing in seals that eat fish containing these pollutants.

Food Chains

• A food chain is a linear sequence showing the transfer of energy and nutrients from one organism to another through consumption.

Key Points

• Starts with producers (plants) that convert sunlight into energy through photosynthesis.
• Followed by primary consumers (herbivores) that eat producers.
• Secondary consumers (carnivores) eat primary consumers, and so on.

Examples

• Grass (producer) → Rabbit (primary consumer) → Fox (secondary consumer).
• Phytoplankton (producer) → Zooplankton (primary consumer) → Small fish (secondary consumer).

Human Impact

• Human activities significantly contribute to the introduction of toxins into ecosystems, leading to bioaccumulation and biomagnification.

Key Points

• Industrial pollutants like heavy metals and pesticides enter water bodies and soil.
• These pollutants are ingested by organisms and accumulate within their tissues.
• Consumption of contaminated organisms can lead to human health issues.

Examples

• Mercury from industrial waste contaminating fish in rivers.
• Pesticides sprayed on crops ending up in birds of prey through contaminated rodents.

Conclusion

Understanding bioaccumulation, biomagnification, and food chains is crucial for comprehending ecological impacts and human health risks associated with environmental pollutants. These processes illustrate how toxins move through ecosystems and concentrate in organisms, affecting entire food webs and human populations.