AQA Biology GCSE Topic 7: Ecology Notes

Adaptations, Interdependence and Competition (7.1)

Communities (7.1.1)

An individual belongs to a species and resides in a habitat with others, forming a population.
Multiple populations interact within the same habitat to create a community, where populations are frequently dependent on each other.
An ecosystem consists of a community of organisms interacting with abiotic (non-living) components of the environment.
Organisms are well-adapted to their environmental conditions, leading to competition for resources that various organisms require for survival. - Competition can occur within a species or between different species. - Plants compete for light, space, water, and mineral ions. - Animals compete for space, food, water, and mating partners.
Interdependence characterizes how organisms rely on each other for essential services, such as food, shelter, and reproduction. - Examples include birds seeking shelter in trees and pollination facilitated by bees.
Modifications in a community, such as the removal or introduction of a species, can have significant effects, altering predator and prey dynamics.
A stable community maintains balance between biotic (living) and abiotic (non-living) factors, resulting in relatively constant population sizes. Examples include tropical rainforests, oak woodlands, and coral reefs.

Abiotic Factors (7.1.2)

An abiotic factor is a non-living component of the environment. The impact of changes in abiotic factors on communities must be explained.
Key abiotic factors affecting communities:   1. Light Intensity:      - Required for photosynthesis.      - Affects plant growth rates, influencing food and shelter availability for organisms.   2. Temperature:
     - Can influence photosynthesis rate.   3. Moisture Levels:      - Essential for survival of both plants and animals.   4. Soil pH and Mineral Content:
     - Influences decay rates and mineral return to the soil for uptake by plants. Different plant species thrive under varying nutrient concentrations.   5. Wind Intensity and Direction:
     - Affects transpiration rates, impacting plant temperatures and photosynthesis efficiency.   6. Carbon Dioxide Levels:
     - Directly impacts photosynthesis rates, influencing organism distributions in high CO2 environments.   7. Oxygen Levels:
     - Especially vital for aquatic animals; oxygen levels fluctuate more in water than air. Most fish require high oxygen concentrations to survive.

Biotic Factors (7.1.3)

A biotic factor is a living component that can affect a community. Changes in a biotic factor must also be explained.
Important biotic factors: 1. Food Availability: - Abundant food promotes successful breeding and population increases. 2. New Predators: - Introduction of new predators can destabilize existing population dynamics. 3. New Pathogens: - Emergence of pathogens can rapidly devastate populations lacking immunity. 4. Competition: - If one species is better adapted compared to another, it may outcompete leading to the decline of the less adapted species’ population.

Adaptations (7.1.4)

Organisms possess adaptations to survive in their environmental conditions, categorized as follows:   1. Structural Adaptations:
     - Involve physical traits and appearances, e.g., sharp teeth of carnivores for tearing meat, camouflage to avoid detection (e.g., a lioness’s coat color), and insulation adaptations in cold environments (e.g., thick fat layers).   2. Behavioural Adaptations:
     - Relate to actions of organisms, e.g., playing dead to avoid predation, basking for heat absorption, and courting to attract mates.   3. Functional Adaptations:      - Focus on physiological processes, e.g., late embryonic implantation in some species or water conservation through reduced sweating.
Extremophiles thrive in extreme conditions (high temperatures, pressure, or salinity); e.g., bacteria at deep-sea vents.
Examples of adaptations in varying climates:
1. Cold Climates: - Smaller surface area to volume ratio reduces heat loss, with abundant insulation (fur, blubber). 2. Dry Climates: - Specialized kidneys retain water, produce concentrated urine, and adapt activity patterns to cooler parts of the day. 3. Plant Adaptations:
- Curled leaves minimizing water loss, extensive root systems for optimal water uptake, waxy cuticles preventing evaporation, water-retaining tissues in plant stems.

Organisation of an Ecosystem (7.2)

Levels of Organisation (7.2.1)

Feeding relationships can be depicted through food chains: 1. Begin with a producer (photosynthetic organisms like green plants or algae) that produce glucose via photosynthesis, essential for forming biomass. 2. Producers are consumed by primary consumers (herbivores). 3. Primary consumers are preyed upon by secondary consumers (carnivores). 4. Secondary consumers might be eaten by tertiary consumers.
Tools like transects and quadrats help assess species distribution and abundance within ecosystems, facilitating mean, mode, median calculations, and graphing.
In stable communities, predator-prey population cycles exist: - An increase in prey leads to an increase in predator population, which may eventually cause a decline in prey due to overconsumption, allowing prey population resurgence when predator numbers decrease.

How Materials are Cycled (7.2.2)

Various materials, notably carbon and water, circulate through ecosystems in vital cycles.

The Carbon Cycle

CO2 is REMOVED from the atmosphere via photosynthesis by plants and algae, which convert carbon to form biological macromolecules.
CO2 is RETURNED to the atmosphere through respiration by plants, algae, and animals, including decomposers during decay.
Combustion (burning of fossil fuels and wood) also returns CO2 to the atmosphere as they release stored carbon from photosynthesis.

The Water Cycle

Sunlight energy drives water vapor evaporation from oceans and lakes.
Transpiration from plants also contributes to water vapor in the atmosphere.
Water condenses to form clouds, subsequently returning to land via precipitation (rain, snow, hail), which nourishes plants and animals before re-entering water bodies, restarting the cycle.

Decomposition (7.2.3 - Biology Only)

Rate of decomposition is impacted by: 1. Temperature: Higher temperatures generally increase decomposition until enzymes denature at extreme heat. 2. Water Availability: Microorganisms require water for respiration; moisture accelerates decay. 3. Oxygen Availability: Aerobic respiration by decomposers necessitates oxygen.
Decomposition results in compost, a natural fertilizer for plants, which necessitates optimal decay conditions to increase its production speed.
Methane Gas production: Decomposing organic matter anaerobically generates methane, usable as a fuel source.
Biogas Generators are employed to produce methane, operating at constant temperatures (around 30°C) to facilitate microbial respiration, requiring immediate usage due to non-liquid storage forms.

Impact of Environmental Change (7.2.4 - Biology Only)

Environmental changes can affect species distribution: - Temperature: Climate change can induce migrations of insects to warmer regions. - Water Availability: Populations migrating to locate water sources. - Atmospheric Gas Composition: Certain pollutants lead to species declines (e.g., lichens cannot grow in high sulfur dioxide environments).
Such changes may be seasonal, geographic, or induced by human impact.

Biodiversity and the Effect of Human Interaction on Ecosystems

Biodiversity (7.3.1)

Biodiversity: Refers to the variety of species within an ecosystem or the planet. High biodiversity indicates ecological stability, reducing species reliance on one another for resources such as food and shelter.
Detrimental human activities are increasingly impacting biodiversity: - Increased human population activity leads to resource consumption and waste generation growth, ultimately affecting ecological stability. - Habitat destruction for urbanization, agriculture, and industry. - Pollution can damage ecosystems: - Water pollution through sewage, fertilizers, or toxic chemicals. - Air pollution from smoke and sulfur gases. - Land pollution from landfill and chemicals. - Rapid depletion of materials surpassing production rates.

Waste Management (7.3.2)

The future of human existence on Earth hinges on preserving biodiversity for future food resources and possible medical innovations.

Land Use (4.7.3.3)

Human land use diminishes habitats via construction, resource extraction, and waste disposal.
Peat Bogs: - Form from incompletely decomposed plant materials in low-oxygen, acidic conditions, serving diverse species, especially migratory birds. - Peat bogs contribute to climate regulation but are increasingly drained for agriculture and fuel exploitation, outpacing their natural formation rates.
Deforestation (7.3.4): - Deforestation: The extensive removal of trees from an area for alternative land use (commonly for agriculture). - Most prominent in tropical regions, consequences include: 1. Increased CO2 in the atmosphere via burning trees. 2. Reduced removals of CO2 through decreased tree populations. 3. Significant habitat loss leading to biodiversity reduction.

Global Warming (7.3.5)

Global Warming refers to the ongoing increase in Earth's temperatures due to rising greenhouse gas emissions (notably CO2 and methane), resulting in enhanced heat retention.
The repercussions include: - Melting ice caps and reduced habitats. - Rising sea levels flooding low-lying areas. - Altered migration patterns affecting species viability. - Increased extinctions from habitat losses diminishing biodiversity.

Maintaining Biodiversity (7.3.6)

To mitigate adverse impacts on ecosystems, multiple strategies have been employed to ensure biodiversity preservation. 1. Breeding Programs: Support threatened species’ survival. 2. Habitat Protection: Restoration and safeguarding of rare ecological environments. 3. Hedgerows and Margins Restoration: Enhancing habitats for various organisms. 4. Deforestation Reduction: Helps slow global warming, conserving habitats. 5. Recycling Initiatives: Mitigates landfill pressure and conserves natural resources.

Trophic Levels in an Ecosystem (7.4)

Trophic Levels (7.4.1)

Trophic levels: Stages in a food chain represented by numbers. 1. Level 1: Producers (plants and algae) that manufacture own food through photosynthesis. 2. Level 2: Primary consumers (herbivores) feeding on producers. 3. Level 3: Secondary consumers (carnivores) preying on primary consumers. 4. Level 4: Tertiary consumers (top carnivores) that consume secondary consumers.
Decomposers play a crucial role in nutrient cycling by breaking down dead matter. - Enzymes are secreted for decomposition, releasing nutrients back into the ecosystem.

Pyramids of Biomass (7.4.2)

Pyramids of biomass visually represent the total biological material at each trophic level. - Biomass decreases as one ascends the trophic levels.

Transfer of Biomass (7.4.3)

Approximately 1% of incident solar energy is converted into biomass via producers.
Roughly 10% of biomass at each trophic level is transferred to the succeeding level in the food chain. - Not all consumed food is converted into biomass: - Inglear organs: Such as bones and claws are indivisible by predators. - Respiration: Many nutrients (e.g., glucose) are utilized in metabolism to support life functions, excreted as waste products (carbon dioxide and urea).
- Waste: Herbivores often eject undigested material.
Efficiency of biomass transfers is calculated using: $ext{Efficiency} = rac{ ext{Biomass transferred to the next level}}{ ext{Biomass available at the previous level}} imes 100$
Higher trophic levels typically host fewer organisms due to lower biomass transfer efficiency.

Food Production (7.5 - Biology Only)

Factors Affecting Food Security (7.5.1)

Food security indicates sufficient food availability for the population, influenced by: 1. Rising birth rates necessitating more food.
2. Shifts in dietary preferences in developed countries exacerbating scarcity of limited food resources. 3. Emergence of new pests and pathogens that devastate crops. 4. Climate change-related adversities affecting agricultural yield (e.g., droughts). 5. Conflicts impacting water and food supply.

Farming Techniques (7.5.2)

Farmers aim to optimize energy conversion from food to biomass, enhancing livestock efficiency using various methods: - Constraining movement by keeping animals in confined spaces. - Providing high protein diets to ensure rapid growth.
Ethical concerns exist surrounding these practices, given the stress induced by confinement and heightened transmission risks of diseases.

Sustainable Fisheries (7.5.3)

Overfishing threatens fish populations. To preserve species vitality, guidelines have been implemented: - Mesh size regulations safeguard juvenile fish. - Fishing quotas cap the number of specific species captured within defined limits to supplement regeneration.

Role of Biotechnology (7.5.4)

Fusarium fungus produces mycoprotein, a vegetarian protein source, synthesized in aerobic conditions that offers an alternative to animal proteins, lessening ecological impacts.
Genetically modified bacteria yielding insulin are crucial for diabetes management, demonstrating biotechnology’s pivotal role in health and agriculture through more resilient crops, such as ‘Golden rice’ with elevated Vitamin A levels and disease resistance.

AQA Biology GCSE Topic 6: Inheritance, Variation and Evolution Notes

Reproduction (6.1)

Sexual and Asexual Reproduction (6.1.1)

Meiosis generates four genetically distinct cells from a single parent cell, while Mitosis yields two identical cells.
Sexual reproduction involves the fusion of male and female gametes (sperm and egg in animals; pollen and egg in plants). - Each gamete possesses 23 chromosomes, combining during fertilization to form a zygote with the complete 46 (23 pairs) chromosomes: one from each parent.
Asexual reproduction involves a single parent and mitosis, leading to clones—a genetically identical offspring. - Examples include certain plants (strawberries) and organisms (bacteria).

Meiosis (6.1.2)

Meiosis transpires in reproductive organs, resulting in gametes with a singular chromosome copy, entailing: - Chromosome duplication, followed by two rounds of division producing four genetically diverse gametes.
Fertilization restores the 46 chromosomes, generating an embryo that undergoes further mitosis for cellular proliferation.

Advantages and Disadvantages of Sexual and Asexual Reproduction (6.1.3)

Sexual Reproduction Advantages: - Diversity generation improves the species’ survival chances, especially under changing environmental conditions. - Enhances selective breeding potentials.
Asexual Reproduction Advantages: - Energy-efficient (no mate search required); rapid population increases in favorable circumstances.
Examples of dual reproductive methods: 1. Malarial Parasites: sexual reproduction in the mosquito and asexual reproduction in human hosts. 2. Fungi: alternate reproductive methods involving asexual spore production and sexual reproduction under stress.

DNA and the Genome (6.1.4)

Genetic material comprises DNA within the cell nucleus, organized in structures termed chromosomes, with each containing numerous genes.
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