National 5 Biology Unit 3 Study Notes

Ecosystems Fundamentals

Biodiversity refers to the variety of plants and animals living in any given area - think of it as nature's collection of different species. The more diverse an ecosystem, the healthier it tends to be.

Competition happens everywhere in nature, and there are two main types you need to know. Intraspecific competition occurs when animals of the same species fight for resources like food or territory. Interspecific competition happens between different species that need the same things to survive.

Every organism has a specific role in its ecosystem called a niche. Producers like plants make their own food through photosynthesis, whilst consumers get energy by eating other organisms. Consumers can be herbivores (plant-eaters), carnivores (meat-eaters), or omnivores (eating both).

Quick Tip: Remember that a species is a group that can breed together and produce fertile offspring - this is key for understanding evolution later!

Distribution of Organisms

The distribution of organisms depends on biotic factors (living influences) and abiotic factors (non-living environmental conditions). Biotic factors include predation, disease, competition for resources, and food availability.

Abiotic factors are measurable environmental conditions like temperature, light intensity, oxygen concentration, soil moisture, and pH levels. Scientists use specific tools to measure these: thermometers for temperature, light meters for light intensity, and pH meters for soil acidity.

Sampling techniques help scientists study ecosystems systematically. Quadrats are square frames used to estimate plant abundance in fixed areas. Pitfall traps catch invertebrates when cups are placed level with the ground and covered to protect from predators.

Indicator species are particularly useful because their presence or absence tells us about environmental quality and pollution levels. If certain sensitive species disappear, it often signals environmental problems.

Study Hack: When measuring environmental factors, always clean equipment between samples to avoid contamination - examiners love this detail!

Photosynthesis

Photosynthesis converts light energy into chemical energy, allowing plants to make glucose from carbon dioxide and water. The process has two main stages: light reactions and carbon fixation.

During light reactions, chlorophyll absorbs light energy and converts it into ATP (chemical energy). Light energy also splits water molecules into hydrogen and oxygen. The oxygen either diffuses out of the cell or gets used elsewhere.

Carbon fixation involves enzyme-controlled reactions that combine hydrogen, carbon dioxide, and ATP to create glucose. This glucose can be stored as starch, used immediately in respiration, or converted into cellulose for plant structure.

Limiting factors can restrict the rate of photosynthesis when they're in short supply. The three main limiting factors are light intensity, temperature, and carbon dioxide concentration. Understanding these helps explain why plants grow differently in various environments.

Exam Focus: Remember the photosynthesis equation - it's often tested and shows the direct relationship between inputs and outputs.

Energy in Ecosystems

Energy flows through ecosystems in a predictable pattern, with only 10% of energy passing between each level of the food chain. This means 90% of energy gets lost through movement, heat production, and undigested waste at every step.

Pyramids of energy always have the same shape because of this 10% rule - they get smaller as you move up each level. For example, if grass contains 10,000 energy units, grasshoppers only get 1,000, mice get 100, and owls get just 10.

Pyramids of numbers show how population sizes decrease as you move up the food chain. However, these can look different depending on the ecosystem - one large oak tree can support thousands of caterpillars, creating an inverted pyramid shape.

This energy loss explains why food chains rarely have more than four or five levels. There simply isn't enough energy left to support higher levels of consumers.

Real-World Connection: This 10% rule explains why large predators like tigers are so rare compared to their prey - there's just not enough energy to support many of them.

Food Production Challenges

As human populations grow rapidly, we need more food, leading to increased use of fertilisers and pesticides to boost crop yields. However, these solutions create their own environmental problems.

Fertilisers add nitrates to soil, which plants use to make proteins. But when fertilisers leach into freshwater, they cause algal blooms that block sunlight. This kills aquatic plants, and when the algae die, bacteria multiply rapidly, using up oxygen and killing other organisms.

Pesticides kill crop-damaging pests but can be persistent in the environment. Through bioaccumulation, these chemicals build up in organisms' bodies as you move up food chains, potentially reaching toxic levels in top predators.

Alternative solutions include GM crops that are genetically modified to use nutrients more efficiently or produce natural toxins against pests. Biological control introduces natural predators to manage pest populations without chemicals.

Think Critically: Consider the pros and cons of each farming method - there's rarely a perfect solution, just trade-offs to evaluate.

Evolution of Species

Mutations are random changes in DNA that create new alleles - they're the only source of genetic variation. Most mutations are neutral or harmful, but occasionally they provide survival advantages.

Natural selection favours organisms with beneficial traits, increasing their chances of survival and reproduction. "Survival of the fittest" means those best adapted to their environment pass on advantageous alleles to their offspring.

Selection pressures from the environment determine which traits are favourable. Cold temperatures favour thick coats, predators favour good camouflage, and dry conditions favour extensive root systems or protective scales.

Speciation occurs when populations become isolated and experience different selection pressures. Over many generations, accumulated differences mean they can no longer interbreed to produce fertile offspring - they've become separate species.

Key Insight: Evolution isn't about becoming "better" - it's about becoming better suited to your specific environment and circumstances.