Science - Combined (0653) | Organisms and their environment

Study Notes: B15 & B16 Organisms and their Environment & Human Influences on Ecosystems (Combined Science 0653)

Welcome to one of the most interesting chapters in Biology! Here, we look at how living things interact with each other and their surroundings, creating complex systems called ecosystems. Understanding this helps us see the huge impact humans have on the planet and what we can do to protect it. Let’s dive into the fascinating world of ecology!

B15.1 Energy Flow in Biological Systems

Every activity in an ecosystem, from a plant growing to a lion hunting, needs energy. The source of almost all this energy is the Sun!

The Principal Energy Source

• The Sun is the principal source of energy input to biological systems.
• Plants (producers) capture this light energy during photosynthesis.

Energy Transfer and Flow

Energy flows through living organisms in a one-way direction:

Light Energy (from Sun)
↓
Chemical Energy (stored in organisms, e.g., glucose)
↓
Transfer to the Environment (eventually lost as heat)

Key Takeaway: Energy is captured by producers and then transferred through feeding, but every time it moves, some is lost as heat. This means ecosystems need a constant energy supply from the Sun.

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B15.2 Food Chains and Food Webs

Feeding relationships show how energy and nutrients move from one organism to another.

Defining Ecosystem Roles

Before we build chains, we need to know the basic roles:

1. Producer

• An organism that makes its own organic nutrients (food).
• They usually use energy from sunlight through photosynthesis (e.g., grass, trees, algae).

2. Consumer

• An organism that gets its energy by feeding on other organisms.
• Consumers are classified by what they eat:
  • Herbivore: An animal that gets its energy by eating only plants (e.g., rabbits, cows).
  • Carnivore: An animal that gets its energy by eating other animals (e.g., lions, eagles).
  • Omnivore: (Not required in the core syllabus but useful context) An animal that eats both plants and animals (e.g., humans).

3. Decomposer

• An organism that gets its energy from dead or waste organic material.
• Decomposers are vital because they break down waste, recycling nutrients back into the soil (e.g., bacteria, fungi).

Food Chains and Trophic Levels

A food chain shows the transfer of energy from one organism to the next, starting with a producer.

Example:
Grass → Rabbit → Fox

Consumers are grouped based on their position in the chain:

• Primary Consumer: Eats the producer (e.g., the Rabbit). They are always herbivores.
• Secondary Consumer: Eats the primary consumer (e.g., the Fox).
• Tertiary Consumer: Eats the secondary consumer (e.g., a larger predator eating the fox).

Memory Aid: Think of Primary as '1st level' consumer.

Food Webs

A food web is a network of interconnected food chains. In real life, most animals eat more than one type of food, so they link together to form a web.

Why are food webs important? A web is much more stable than a chain. If one food source disappears (say, due to disease), the animal can switch to another source.

Supplement: Human Impact on Food Webs

Humans can seriously impact food webs, leading to ecosystem instability:

1. Overharvesting of food species: If humans fish or hunt too much of one species (e.g., tuna), their prey population might explode, and their predator population might crash, destabilising the whole web.
2. Introducing foreign species: Bringing a non-native species (an invasive species) into a habitat can disrupt the web because the new species might have no natural predators or might outcompete native species for food. For example, introducing non-native rats to an island can lead to the extinction of native ground-nesting birds.

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B15.3 The Carbon Cycle

Carbon is an essential element for all life. The carbon cycle describes how carbon moves through the air, water, land, and living organisms. There are six key processes you need to know:

Processes in the Carbon Cycle

1. Photosynthesis: (Takes CO₂ out of the atmosphere.) Plants and algae use carbon dioxide from the air/water to make glucose.
2. Respiration: (Puts CO₂ into the atmosphere.) All living organisms (plants, animals, microbes) break down carbon-containing molecules (like glucose) to release energy, producing CO₂ as a waste product.
3. Feeding: (Moves carbon between organisms.) When a consumer eats a producer, the carbon atoms in the plant become part of the animal's body.
4. Decomposition: (Puts CO₂ into the atmosphere.) Decomposers (like bacteria and fungi) break down dead organisms and waste, releasing carbon back into the atmosphere via their respiration.
5. Formation of fossil fuels: Carbon from dead organisms that did not decompose fully (due to lack of oxygen or pressure) is locked away deep underground over millions of years (forming coal, oil, and natural gas). This is a slow storage process.
6. Combustion: (Puts CO₂ into the atmosphere rapidly.) Burning carbon-containing materials (like wood, fossil fuels, or biomass) releases the stored carbon back into the atmosphere as CO₂.

Did you know? The balance of the carbon cycle is crucial. When humans burn huge amounts of fossil fuels (combustion), we release carbon that was stored millions of years ago, tipping the natural balance and increasing atmospheric CO₂.

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B16.1 Human Influences: Habitat Destruction

Human actions often change or destroy natural environments, which has severe consequences for the organisms that live there.

Defining the Environment

• Ecosystem: A unit containing the community of organisms (all living things) and their environment (non-living things), interacting together.
• Biodiversity: The number of different species that live in an area. High biodiversity means a healthy, stable ecosystem.

Reasons for Habitat Destruction

Humans destroy habitats for several reasons:

1. Increased area for housing, crop plant production, and livestock production: We need land for homes and food, often clearing forests or wetlands to get it.
2. Extraction of natural resources: Mining, quarrying, and drilling require removing large sections of land.
3. Freshwater and marine pollution: Pollutants enter rivers and oceans, killing organisms and destroying aquatic ecosystems (e.g., oil spills, plastic waste).

Case Study: Deforestation (Core and Supplement)

Deforestation is the large-scale cutting down and clearing of forests.

The undesirable effects of deforestation include:

• Reducing biodiversity: Many species that rely on the forest habitat cannot survive elsewhere, leading to the loss of unique plant and animal life.
• Extinction: If a species lives only in that specific forest, losing the habitat leads directly to its extinction.
• Loss of soil (erosion): Tree roots hold the soil together. When trees are removed, heavy rain washes the topsoil away, making the land infertile.
• Flooding: Forests absorb huge amounts of water. Without trees, rainfall runs quickly over the land surface, increasing the risk of river flooding downstream.
• Increase of carbon dioxide in the atmosphere: Trees absorb CO₂ for photosynthesis. Cutting them down (and often burning them) releases CO₂, contributing to global warming.

Key Takeaway: Deforestation is a primary example of habitat destruction that causes cascading negative effects on the soil, water cycles, and climate.

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B16.2 Conservation

Conservation is the protection and wise management of natural resources and species.

Why Species Become Endangered or Extinct (Core)

Organisms become endangered (at high risk of extinction) or extinct (no longer existing) due to:

• Climate change: Changing temperatures and weather patterns destroy habitats or food sources.
• Habitat destruction: Clearing land for human use (as described in B16.1).
• Hunting and Overharvesting: Killing animals or collecting plants faster than they can reproduce.
• Pollution: Toxic substances poisoning organisms or destroying their environment.
• Introduced species: Non-native species competing with or preying on native organisms.

Don't worry if this seems tricky at first! The main idea is that human activity often puts too much pressure on natural systems.

Methods of Conservation (Supplement)

Conservationists use various strategies to protect endangered species:

1. Monitoring and protecting species and habitats: This includes setting up national parks or reserves, using electronic tracking devices, and actively patrolling to prevent illegal hunting (poaching).
2. Education: Teaching people about biodiversity, the importance of conservation, and sustainable practices so that communities are motivated to protect their own local ecosystems.
3. Captive breeding programmes: Breeding animals in protected environments (like zoos or special facilities) to increase their numbers before releasing them back into the wild. This ensures the species doesn't disappear entirely.
4. Seed banks: Storing seeds from a huge variety of plants in special, temperature-controlled vaults. This acts as an "insurance policy" against plant extinction.

Key Takeaway: Conservation requires both protecting the physical environment and actively managing threatened species through various scientific and educational programs.

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You have successfully completed the ecology section! Remember these notes are interconnected: energy flow defines food webs, and human interference (like burning fossil fuels or deforestation) impacts both the carbon cycle and overall biodiversity. Keep reviewing those key terms!