The document discusses key concepts about biotic environments and ecosystems. It covers the relationships between organisms like predator-prey and parasitism. An ecosystem consists of communities of interacting living and non-living elements. Energy transfers through ecosystems from producers to various consumer trophic levels and decomposers. Nutrient cycles like carbon and nitrogen are essential to replenish nutrients in an ecosystem. Human activities like pollution, deforestation and overuse can upset the balance of ecosystems, so conservation efforts aim to protect biodiversity and natural resources.

1. Biotic Environment
- Living organism never exist alone.
- Biotic environment – refers to all living organisms in a habitat
- Relationships between organisms in a habitat :
1. Predator-prey
 an animal live by killing & eating other animal – predator
Eg. Lion
 an animal killed &eaten by another animal – prey
Eg. Zebra
2. Parasitism
 one (the parasite) benefits at the expense of the other (the host )
 A parasite normally does some harm to its host.
3. Mutualism
 two organisms both benefit
Eg. Ant protect aphid from their predator, aphid secrete honeydew for food.
Ecosystems
- In any habitat, more than one kind of organism.
- A group of organism of the same kind – population
- Different population live together in same habitat – form a community
- Ecosystem consists of communities of living organisms interacting with one another and
with their physical environment.
- Types :
There are many ecosystems in the world.
Eg. Tropical rainforest, grassland, tundra, mountains, deserts, oceans, sea shores,
mangroves, ponds
Earth itself is a big ecosystem – called biosphere
Transfer of energy in an ecosystem
- Living organisms 3 types : producer , consumer, decomposer
- Ultimate source of energy in any ecosystem is sun.
- Producers
 Green plants that manufacture food substance from simple nutrients (Eg. Carbon
Dioxide, water).
 Convert energy from sunlight to chemical energy and store as complex nutrients like
carbohydrates.
- Consumer
 Animals obtain energy and nutrients from organisms they feed on.
 Animals that directly feed on plants – primary consumer
 Animals that feed on primary consumer – secondary consumer
 Animals that feed on secondary consumer – tertiary consumer
- Decomposers
 (Eg. Fungi & bacteria) break down complex nutrients in excreta & dead bodies of
organisms to free

2. 1. Carbon dioxide escape into atmosphere
2. Soluble mineral salts dissolve in the soil water
- Consumers get rid of undigested food matter from their body as faeces, containing complex
nutrients they cannot digest.
- When producer & consumer die, body also contains complex nutrients that green plants
cannot use unless broken down to simple nutrients.
Food chain & Food webs
- Food chain &food webs -> a series of organisms thru energy and food are transferred from
one organism to another
- Each stage in a food chain is called trophic level.
- In a community, food chains are inter-linked to form food web.
- Food web – complex food relationships that exist in communities in natural ecosystems.
- Energy loss / total energy level decrease along food chain , up to 90% from one trophic level
to the next -> because a lot energy lost to environment as food transferred
lost as heat during respiration’
energy pass out of body of consumer as faeces / excretory products
physical activities
- The most amount of energy lost from producer to primary consumer.
- The energy present in each level of food chain called – pyramid of energy
Nutrients cycle
- Nutrients & energy continuously used and transferred.
- In stable & balanced ecosystem, no nutrients lost because nutrients taken up by physical
environment and used by living organisms, released into physical environment and reused
by living organism again.
- Use & reuse of nutrients is recycling.
- Recycling of nutrients allow ecosystem to be self-sustaining.
- Carbon cycle (pg. 237)
Removal of CO2 from atmosphere Inclusion of CO2 into the atmosphere
During photosynthesis, green plants take in CO2 During respiration, food like glucose broken
to make glucose. down and CO2 released.
Preserved in fossil fuel. (Eg. Coal, oil) When decomposers break down dead organism,
CO2 released.
Burning of fossil fuel release CO2.
 process by which carbon dioxide removed, returned to atmosphere
 helps to keep concentration of carbon dioxide in air relative constant – 0.03%
- Nitrogen cycle (pg. 238)
Nitrogen returned to the soil Nitrogen lost from the soil
Nitrogen in plants converted to proteins and Nitrates in soil absorbed by roots of a plant.
protoplasm in body of animal after feeding. After
both plant & animal die, their remains

3. decompose and the process of decay produce
ammonium compounds which form nitrates in
soil.
Atmospheric nitrogen thru lightning becomes Atmospheric nitrogen thru nitrogen-fixation to
nitrates in soil. the roots of the plant ……
Atmospheric nitrogen thru nitrogen-fixation at
roots of plants.
 process by which nitrogen removed from soil, returned to its form of nitrates
- Importance of carbon cycle
enable carbon compounds rich in energy to be supplied to other organisms in food
chains
ensure carbon dioxide not lost but continuously recycled in ecosystem
- Importance of nitrogen cycle
ensure continuous supply of nitrates for green plants to make proteins and protoplasm
enable proteins to be supplied to other organisms in food chain
ensure nitrogen not lost but continuously recycled within ecosystem
Keep nature’s balance
- In balance & stable ecosystem, population size of producer and consumer remain relatively
constant so that there are enough producers to provide food for consumer and consumer
have enough food to eat.
- Populations are – in balance.
- Ecosystem upset by :
introduction of new animals and plants into habitat
disease outbreak that kill one kind or animal or plant
human activity (Eg. deforestation and over-fishing)
Conservation
- Physical environment important to living organisms for air, water, food.
Good Bad
Clean fresh air for healthy life Unhealthy , polluted air (exhaust from motor
vehicles)
Clean river teeming with life Lifeless, polluted river (discharge of chemical
waste into river by factories)
Fertile, properly managed agricultural land Desert formation of land (overuse and poor
management)
- Environment constantly destroyed by human activities
deforestation
pollution (land/air/water)
over-fishing / over-farming (excessive use of pesticide)
- Such activity provides food, home, make our life comfortable but destroy environment.

4. - If we continue to destroy our environment , effects :
Rich biodiversity on earth threatened
*Biodiversity – range of species present in ecosystem
Large area of land becomes unproductive desert.
Lake, river, sea become polluted and devoid of life.
Clean air, fresh water, and fertile land very scarce.
- Protecting, preserving natural environment – conservation (not limited to preventing
pollution)
- Reasons :
1. Protect plants and animal species from extinction
2. Prevent global warming & disruption of natural cycles (Eg. Carbon dioxide & nitrogen
cycles)
3. Ensure the conservation of tropical rainforest. Many tropical plants are source of food
and raw materials for medicinal drugs and industries.
4. Protect marine life, esp. fish that make up important part of human food supply.