Science (Double Award) | Ecology and the environment

Welcome to Ecology: Life and Its Surroundings!

Hey future biologists! This chapter is all about Ecology – studying how living things (like you and me, trees, and bacteria) interact with each other and their surroundings. It’s a crucial topic because it explains how our planet works and how we can protect it.

Don't worry if some terms look long or complicated; we'll break them down step-by-step using simple analogies. By the end, you'll see that everything in nature is connected!

Section 1: The Basics – Levels of Organization and Ecosystems

1. Defining the Terms

To study nature effectively, ecologists classify life into different groups based on complexity. Think of this like zooming out on a map:

• Organism: A single, individual living thing. (Example: One lion, one daisy, one bacterium.)
• Population: All the organisms of one species living in the same place at the same time. (Example: All the lions living in the Serengeti National Park.)
• Community: All the different populations (all the different species) living and interacting in the same area. (Example: Lions, zebras, acacia trees, and grasshoppers all together in the Serengeti.)
• Ecosystem: The Community PLUS the non-living parts of the environment. (Example: The Serengeti, including the animals, plants, temperature, sunlight, water, and soil.)

2. Biotic vs. Abiotic Factors

Factors that influence organisms can be divided into two main categories:

• Biotic Factors: Factors related to living things. (Example: Predators, competition for food, disease, other species.)
• Abiotic Factors: Factors related to the non-living environment. (Example: Temperature, light intensity, pH of the soil/water, water availability, wind.)

Section 2: Energy Flow and Feeding Relationships

The main way organisms interact is by feeding. Energy flows through an ecosystem, but it is not recycled – it is constantly lost as heat.

1. Trophic Levels and Food Chains

A Food Chain shows the transfer of energy from one organism to the next:

• Producers: Organisms that produce their own food, usually using sunlight (photosynthesis). They are always the start of any food chain. (Example: Plants, algae.)
• Consumers: Organisms that obtain energy by feeding on other organisms.
• Primary Consumers: Eat producers (herbivores).
• Secondary Consumers: Eat primary consumers (carnivores/omnivores).
• Tertiary Consumers: Eat secondary consumers.
• Decomposers: Bacteria and fungi that break down dead material (waste and dead organisms), returning nutrients to the soil.

Example Chain:
Grass (Producer) → Rabbit (Primary Consumer) → Fox (Secondary Consumer)

2. Food Webs

In reality, ecosystems are complex. An organism rarely eats only one type of food. A Food Web is a network of interconnected food chains, showing the true, complex feeding relationships in a community.

Tip: If an arrow points from A to B, it means "A is eaten by B," showing the direction of energy flow.

3. Energy Transfer and Pyramids of Biomass

When an organism is eaten, most of the energy it consumed is lost to the environment before it is passed on. Only about 10% of the energy (or biomass) is transferred from one trophic level to the next.

Where does the other 90% go?

• It is lost as heat during respiration.
• It is used for movement or life processes.
• It is lost as undigested material (faeces).

The massive loss of energy explains why we usually draw Pyramids of Biomass. These pyramids represent the total dry mass of living material at each trophic level. Because 90% is lost at each step, the pyramid shape is almost always upright (wide base, narrow top).

Analogy: To feed a small number of top predators, you need a massive amount of plant life at the base!

Section 3: Nutrient Cycling

Unlike energy, essential materials (like carbon, water, and nitrogen) are finite. They must be continuously reused or cycled through the ecosystem to support life.

1. The Carbon Cycle

Carbon is the backbone of all organic molecules (sugars, proteins, fats).

The four key processes in the Carbon Cycle are:

1. Photosynthesis: Producers (plants) remove carbon dioxide (CO₂) from the atmosphere to make glucose. This locks carbon into living things.
2. Feeding: Carbon is passed from plants to animals (consumers).
3. Respiration: All living organisms (plants, animals, decomposers) break down food for energy and release CO₂ back into the atmosphere.
4. Decomposition and Combustion: Decomposers release CO₂ when they break down dead organisms. Also, burning wood or fossil fuels (combustion) releases stored carbon back into the atmosphere very quickly.

Memory Aid: P. F. R. D. C. (Photosynthesis, Feeding, Respiration, Decomposition, Combustion)

2. The Water Cycle (Hydrological Cycle)

The water cycle continuously moves water between land, air, and living organisms.

1. Evaporation: Heat from the sun turns liquid water into water vapour (gas).
2. Transpiration: Plants release water vapour from their leaves into the atmosphere.
3. Condensation: Water vapour rises, cools, and turns back into liquid droplets, forming clouds.
4. Precipitation: Water falls back to Earth (rain, snow, hail).

Takeaway: Cycles are vital – if decomposers stopped working, nutrients would be permanently locked up in dead matter, and life would halt!

Section 4: Humans and the Environment – Impact and Management

Human population growth and industrialisation have drastically affected global ecosystems. We must understand these impacts to manage them sustainably.

1. Pollution of Water and Air

a) Acid Rain:

Burning fossil fuels (especially coal and oil) releases sulfur dioxide and nitrogen oxides. These gases dissolve in atmospheric water vapour and return to Earth as weak sulfuric and nitric acids (acid rain).

• Harm: Lowers the pH of lakes, killing fish and aquatic life; damages forests; erodes buildings.

b) Eutrophication (Water Pollution):

This common problem occurs when excess nitrates and phosphates from farm fertilisers or sewage drain into rivers and lakes.

1. The high nutrient level causes Algal Blooms (rapid growth of surface algae).
2. The algal layer blocks sunlight, killing plants below.
3. When the plants and algae die, decomposers (bacteria) multiply rapidly.
4. These decomposers use up all the dissolved oxygen in the water through respiration, causing fish and other organisms to suffocate and die.

2. Greenhouse Effect and Climate Change

The Earth’s atmosphere naturally traps some of the sun’s heat using gases like carbon dioxide and methane (the Greenhouse Effect). This keeps the Earth habitable.

However, human activity (burning fossil fuels, deforestation) increases the concentration of these gases, leading to the Enhanced Greenhouse Effect, which causes Global Warming (the overall increase in the Earth's average temperature).

• Key Consequence: Melting ice caps, rising sea levels, more extreme weather patterns, and habitat destruction.

3. Deforestation and Soil Erosion

Deforestation (clearing forests) mainly happens to create space for farming or to harvest timber.

• It reduces the amount of photosynthesis taking place, meaning less CO₂ is removed from the atmosphere.
• It destroys habitat, leading to a massive loss of biodiversity.
• Tree roots hold soil together. Without trees, the soil is easily washed away by rain (soil erosion), leading to nutrient loss and desertification.

4. Ozone Depletion

The ozone layer is a protective layer in the atmosphere that blocks harmful UV radiation from the sun.

Chemicals called CFCs (Chlorofluorocarbons – once used in aerosols and refrigeration) reacted with and destroyed ozone molecules. Although CFC use is now largely banned worldwide, the slow recovery of the ozone layer is a major environmental concern.

Section 5: Conservation and Sustainability

Conservation involves the wise management and protection of ecosystems and species.

1. What is Biodiversity and Why Conserve It?

Biodiversity is the variety of life (genes, species, and ecosystems) on Earth.

It is important to conserve biodiversity because:

1. Ethical Reasons: We have a moral obligation to protect other species.
2. Resource/Economic Reasons: Many plants and animals are sources of food, medicines, and raw materials. If we lose them, we lose potential resources.
3. Ecological Stability: Ecosystems with high biodiversity are more stable and can recover better from disasters.

2. Sustainable Use

Sustainability means using resources at a rate that allows them to replenish themselves, ensuring they are available for future generations.

Examples of sustainable practices:

• Renewable Energy: Using solar, wind, or wave power instead of fossil fuels.
• Sustainable Forestry: Cutting down trees at a rate that allows new trees to grow back.
• Recycling and Reusing: Reducing the demand for new raw materials.
• Fishing Quotas: Limiting the amount of fish caught to allow fish stocks to recover.