ICSE 8 Biology Ecosystems Short

⚡ Quick Revision: Ecosystems

Definition & Structure

• ✔ An Ecosystem is a self-sustaining unit where biotic (living) and abiotic (non-living) components interact.
• ✔ Biotic components: Producers (Plants), Consumers (Animals), and Decomposers (Bacteria/Fungi).
• ✔ Abiotic components: Physical factors like Sunlight, Temperature, Soil, Water, and Air.

Term Card

Biosphere: The global sum of all ecosystems; the zone of life on Earth including land, water, and air.

❌ Don't Confuse:

Habitat with Ecosystem. A habitat is just the "address" or place where an organism lives, while an ecosystem includes the community and its interactions.

⚡ Quick Revision: Biotic Components & Roles

Category	Role in Ecosystem	Example
Producers	Autotrophs; convert solar energy into chemical energy (food).	Green Plants, Phytoplankton
Consumers	Heterotrophs; depend on producers directly or indirectly for food.	Herbivores, Carnivores, Omnivores
Decomposers	Saprotrophs; break down dead matter and return nutrients to soil.	Bacteria, Fungi

Consumer Hierarchy

• ✔ Primary Consumers: Herbivores that eat plants (e.g., Rabbit, Deer).
• ✔ Secondary Consumers: Carnivores that eat herbivores (e.g., Frog, Snake).
• ✔ Tertiary Consumers: Top carnivores that eat secondary consumers (e.g., Lion, Eagle).

❌ Don't Confuse:

Scavengers with Decomposers. Scavengers (like Vultures) eat dead animals, whereas Decomposers (Bacteria) break down organic matter at a molecular level.

⚡ Quick Revision: Food Chains & Food Webs

Term Card

Trophic Level: Each step or level in a food chain representing a specific position in the flow of energy.

Energy Flow Dynamics

• ✔ Unidirectional Flow: Energy moves in one direction from producers to consumers (cannot flow back).
• ✔ 10% Rule: Only about 10% of the energy is transferred to the next trophic level; 90% is lost as heat/metabolism.
• ✔ Food Web: A complex network of interconnected food chains showing all possible feeding relationships.

[Grass → Grasshopper → Frog → Snake → Eagle]

Typical Terrestrial Food Chain

❌ Don't Confuse:

A Food Chain with a Food Web. A chain is a linear path; a web is a realistic, complex interlinking of many chains.

⚡ Quick Revision: Ecological Pyramids

Types of Pyramids

• ✔ Pyramid of Numbers: Shows the total number of individual organisms at each trophic level.
• ✔ Pyramid of Biomass: Represents the total living organic matter (weight) at each level.
• ✔ Pyramid of Energy: Shows the amount of energy available at each level; always upright.

Upright Ecological Pyramid

❌ Don't Confuse:

Upright with Inverted pyramids. While energy pyramids are always upright, pyramids of numbers can be inverted (e.g., many insects feeding on a single large tree).

Term Card

Biomass: The total mass of living organisms in a given area or volume at a specific time.

⚡ Quick Revision: Interactions & Interdependence

Biotic Interactions

• ✔ Symbioses: Mutualism (+/+) where both benefit (e.g., Lichens - Algae & Fungi).
• ✔ Parasitism: (+/-) one benefits at the expense of the host (e.g., Cuscuta on plants).
• ✔ Predation: (+/-) one organism (predator) kills and eats another (prey).

Interaction	Species A	Species B
Mutualism	Benefited (+)	Benefited (+)
Commensalism	Benefited (+)	Unaffected (0)

Term Card

Flora and Fauna: Collective terms for the plants (flora) and animals (fauna) of a particular region or ecosystem.

❌ Don't Confuse:

Intraspecific with Interspecific competition. Intra is within the same species; Inter is between different species.

⚡ Quick Revision: Summary & Ecosystem Balance

Chapter Master-List

• ✔ Interdependence: Plants provide O2 and food; animals provide CO2 and aid in pollination/dispersal.
• ✔ Human Impact: Deforestation and pollution disrupt the delicate balance of food webs.
• ✔ Conservation: Protecting "keystone species" is vital to maintaining the entire ecosystem structure.

Exam Strategy

Critical Logic: Always remember that energy is lost at each level. This is why top predators are fewer in number than producers.