UPCAT General Science (Extended) — Ecology, Biogeochemical Cycles & Species RelationshipsCheat Sheet
A printable cheat sheet for Ecology, Biogeochemical Cycles & Species Relationships, built for UPCAT reviewers who want one go-to reference in the final stretch. Covers formulas, key definitions, common question types, and the University of the Philippines-specific twists you will see on UPCAT day.
Exam context
On the UPCAT 2026, the General Science (Extended) subtest carries a "Extended coverage for UP Science programs" weight in University of the Philippines's pattern. Ecology, Biogeochemical Cycles & Species Relationships lands at position 6th out of 6 in the standard review order. Target score is UPG ≤ 2.2 typical, and roughly 20 items come from General Science (Extended) on a typical UPCAT paper.
Ecology, Biogeochemical Cycles & Species Relationships - Cheat sheet
Your last-minute revision companion for mastering ecology concepts, biogeochemical cycles, and species interactions for UPCAT and other college entrance exams.
Sections
Section Title
Levels of Ecological Organization
Important Facts
- Organization levels: Organism → Population → Community → Ecosystem → Biosphere
- Each level is more inclusive than the previous one
- Biosphere is the most comprehensive level of organization
Key Definitions
Term
Biosphere
Example
Global zone where all living organisms exist
Definition
Thin layer of Earth and its atmosphere that supports all life
Term
Ecosystem
Example
Forest with trees, animals, soil, water, and climate
Definition
All organisms and non-living environment in a particular area functioning together
Term
Community
Example
All plants, animals, fungi in a forest
Definition
All interacting organisms of different species living in a particular area
Term
Population
Example
All deer in a forest
Definition
Group of individuals of the same species living in a specific area
Term
Organism
Example
Single deer adapted to forest life
Definition
Individual living being with adaptations to overcome environmental challenges
Diagrams To Know
- Hierarchical pyramid showing levels of organization
- Ecosystem diagram showing biotic and abiotic components
Common Values
Value
10%
Symbol
Per trophic level
Quantity
Energy transfer efficiency
Section Title
Feeding Relationships and Energy Flow
Important Facts
- Energy flows one-way through ecosystems, matter cycles
- 10% rule: Only 10% of energy transfers to next trophic level
- Food chains typically have 3-5 trophic levels maximum
- Decomposers are essential for nutrient cycling
Key Definitions
Term
Producers (Autotrophs)
Example
Plants, algae, photosynthetic bacteria
Definition
Organisms that capture energy to make their own food through photosynthesis
Term
Consumers (Heterotrophs)
Example
Animals, fungi, most bacteria
Definition
Organisms that obtain energy by consuming other organisms
Term
Herbivores
Example
Rabbits, deer, caterpillars
Definition
Primary consumers that eat only plants
Term
Carnivores
Example
Lions, eagles, sharks
Definition
Consumers that eat other consumers (meat eaters)
Term
Omnivores
Example
Humans, bears, pigs
Definition
Consumers that eat both producers and consumers
Term
Decomposers (Saprovores)
Example
Bacteria, fungi, earthworms
Definition
Organisms that break down dead organic material
Diagrams To Know
- Food chain diagram with arrows showing energy flow
- Food web showing interconnected feeding relationships
- Energy pyramid showing 10% rule
Section Title
Biogeochemical Cycles
Important Facts
- Water cycle: evaporation → condensation → precipitation → collection
- Carbon cycle involves photosynthesis and cellular respiration
- Nitrogen fixation converts N2 to ammonia (NH3)
- Phosphorus has no gaseous phase in its cycle
- Sulfur cycle includes volcanic activity and acid rain formation
Key Definitions
Term
Water Cycle
Example
Ocean → clouds → rain → rivers → ocean
Definition
Continuous movement of water through evaporation, condensation, precipitation, and collection
Term
Carbon Cycle
Example
CO2 in air → plants → animals → decomposition → CO2
Definition
Movement of carbon through atmosphere, biosphere, hydrosphere, and geosphere
Term
Nitrogen Cycle
Example
N2 → nitrogen fixation → plants → animals → decomposition
Definition
Conversion of nitrogen gas into usable forms for organisms
Term
Phosphorus Cycle
Example
Rock weathering → soil → plants → animals → decomposition
Definition
Movement of phosphorus through rocks, soil, water, and living organisms
Diagrams To Know
- Water cycle with evaporation, condensation, precipitation
- Carbon cycle showing photosynthesis and respiration
- Nitrogen cycle with fixation, nitrification, denitrification
- Phosphorus cycle through rocks, soil, and organisms
Reactions Or Equations
Note
Carbon fixation in carbon cycle
Equation
6CO2 + 6H2O → C6H12O6 + 6O2
Conditions
Photosynthesis (light energy)
Note
Carbon release in carbon cycle
Equation
C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP
Conditions
Cellular respiration
Note
Converting atmospheric nitrogen to usable form
Equation
N2 + 3H2 → 2NH3
Conditions
Nitrogen fixation by bacteria
Section Title
Species Relationships (Symbiosis)
Important Facts
- Intraspecific: within same species; Interspecific: between different species
- Symbiosis involves at least one organism benefiting
- Competition can be for food, space, mates, or other resources
- Neutralism: neither species affects the other
Key Definitions
Term
Mutualism
Example
Bee and flower, nitrogen-fixing bacteria and legumes
Definition
Both species benefit from the relationship (obligatory)
Term
Commensalism
Example
Orchid on tree, remora fish on shark
Definition
One species benefits, the other is unaffected
Term
Parasitism
Example
Lice on human, tapeworm in intestine
Definition
One species benefits at the expense of the other
Term
Predation
Example
Cat eating mouse, hawk catching rabbit
Definition
Predator kills and consumes prey for survival
Term
Competition
Example
Lions and cheetahs competing for prey
Definition
Both species compete for limited resources, both may suffer
Term
Amensalism
Example
Algal bloom killing fish
Definition
One species is harmed, the other is unaffected
Term
Protocooperation
Example
Sea anemone and clownfish
Definition
Both species benefit but relationship is not obligatory
Diagrams To Know
- Symbiosis relationship chart with +, -, 0 symbols
- Examples of each type of species relationship
Section Title
Ecological Principles and Succession
Important Facts
- Primary succession starts from bare substrate (no soil)
- Secondary succession starts from disturbed but soil-rich area
- Pioneer species are first to colonize in succession
- Climax community is the stable final stage
- Succession involves predictable changes in species composition
Key Definitions
Term
Ecological Niche
Example
What an organism does, where it lives, what it eats
Definition
The ecological role of an organism including conditions, resources, and interactions needed
Term
Competitive Exclusion Principle
Example
Gause's law - one species will outcompete the other
Definition
Two species cannot coexist if they occupy identical ecological niches
Term
Resource Partitioning
Example
Birds feeding at different tree heights
Definition
Species with overlapping niches evolve to occupy more distinct niches
Term
Primary Succession
Example
Life developing on volcanic island or bare rock
Definition
Development of new community in previously uncolonized area
Term
Secondary Succession
Example
Forest regrowth after fire or abandoned farmland
Definition
Recovery of community after disturbance in previously colonized area
Diagrams To Know
- Primary succession stages from bare rock to climax forest
- Secondary succession from grassland to forest
- Resource partitioning example with different feeding levels
Must Remember
- Ecological organization: Organism → Population → Community → Ecosystem → Biosphere
- Energy flows one-way, matter cycles in ecosystems
- 10% rule: Only 10% of energy transfers between trophic levels
- Photosynthesis: 6CO2 + 6H2O → C6H12O6 + 6O2
- Mutualism (+,+), Commensalism (+,0), Parasitism (+,-), Competition (-,-)
- Nitrogen fixation converts N2 to NH3 by bacteria
- Competitive Exclusion Principle: identical niches cannot coexist
- Primary succession starts from bare rock, secondary from disturbed soil
- Water cycle: evaporation → condensation → precipitation → collection
- Decomposers are essential for nutrient cycling back to producers
Last Minute Tips
- Remember the '+', '0', '-' symbols for each symbiotic relationship type
- Know that phosphorus cycle has NO gaseous phase (unlike carbon and nitrogen)
- Primary succession takes much longer than secondary succession
- Energy pyramids always get smaller going up due to 10% rule
- Nitrogen fixation is done by bacteria, not plants themselves
Comparison Tables
Rows
Values
- +
- +
- Bee and flower
Property
Mutualism
Values
- +
- 0
- Orchid on tree
Property
Commensalism
Values
- +
- -
- Lice on human
Property
Parasitism
Values
- +
- -
- Cat and mouse
Property
Predation
Values
- -
- -
- Lions and cheetahs
Property
Competition
Values
- 0
- -
- Algal bloom and fish
Property
Amensalism
Columns
- Relationship
- Species A Effect
- Species B Effect
- Example
Table Title
Types of Species Relationships
Rows
Values
- Bare substrate, no soil
- Disturbed area with soil
Property
Starting Point
Values
- Hundreds to thousands of years
- Decades to centuries
Property
Time Required
Values
- Lichens, mosses
- Grasses, weeds
Property
Pioneer Species
Values
- Volcanic island
- Forest after fire
Property
Example
Columns
- Aspect
- Primary Succession
- Secondary Succession
Table Title
Primary vs Secondary Succession
Rows
Values
- Make own food
- Consume other organisms
Property
Energy Source
Values
- Producers
- Consumers
Property
Role in Ecosystem
Values
- Plants, algae
- Animals, fungi
Property
Examples
Values
- First level
- Second level and above
Property
Trophic Level
Columns
- Characteristic
- Autotrophs
- Heterotrophs
Table Title
Autotrophs vs Heterotrophs
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