Unit 3 Life on Earth

Unit Introduction

In this final unit of the course we step back and consider the question 'how do we fit in?' We'll start off by learning about species and ecosystems, how these can be studied, and how they have come about. We'll then conclude by considering ways in which we as a species have impacted upon our environment.

As you're hopefully aware, the impact of humans on the planet's ecosystems couldn't be more relevant or pressing. It is crucial that we therefore learn about these issues, but we also need do something about them too.

Learning Outcomes

    • Biotic, abiotic and human influences are all factors that affect biodiversity in an ecosystem.

    • Grazing and predation are biotic factors; pH and temperature are abiotic factors.

    • Biomes are the various regions of our planet as distinguished by their similar climate, fauna and flora.

      • Global distribution of biomes can be influenced by temperature and rainfall.

    • An ecosystem consists of all the organisms living in a particular area and the non-living components with which the organisms interact.

    • A niche is the role that an organism plays within a community.

      • It includes the use it makes of the resources in its ecosystem and its interactions with other organisms in the community including competition, parasitism, predation, light, temperature and nutrient availability.

    • Definitions of the terms species, population, producer, consumer, herbivore, carnivore and omnivore.

    • At each level in a food chain 90% of energy is lost as heat, movement or undigested materials.

    • Definitions and comparison of pyramids of biomass, energy and numbers.

    • Nitrogen in ecosystems

      • Animal and plant proteins are produced from nitrates.

      • The roles of nitrifying, denitrifying, root nodule and free-fixing soil bacteria.

      • Decomposers convert proteins and nitrogenous wastes to ammonium and nitrate.

    • Competition in ecosystems

      • Interspecific competition is when individuals of different species compete for the same resource in an ecosystem.

      • Intraspecific competition is when individuals of the same species compete for exactly the same resources.

    • Sampling plants and animals using quantitative techniques including quadrats and pitfall traps.

    • Evaluation of limitations and sources of error in pitfall traps and quadrats.

    • Measuring abiotic factors including light intensity, temperature, pH and soil moisture.

    • A mutation is a random change to genetic material.

      • Mutations may be neutral, confer an advantage or a disadvantage.

      • Mutations are spontaneous and are the only source of new alleles.

      • Environmental factors, such as radiation and chemicals, can increase rate of mutation.

    • Variation within a population makes it possible for a population to evolve over time in response to changing environmental conditions.

    • Natural selection/survival of the fittest occurs when more offspring are produced than the environment can sustain.

      • Only the best adapted individuals survive to reproduce, passing on the genes that confer the selective advantage.

    • Speciation occurs after a population becomes isolated and natural selection follows a different path due to different conditions/selection pressures.

    • Increasing human population requires an increased food yield.

    • Fertilisers can leach into fresh water, causing algal blooms.

      • This leads to a reduction in oxygen levels.

    • Pesticides sprayed onto crops can accumulate in the bodies of organisms over time.

      • As they are passed along food chains, toxicity increases and can reach fatal levels.

    • Indicator species are species that by their presence or absence indicate environmental quality/levels of pollution.

    • Biological control and GM crops may be alternatives to mitigate the effects of intensive farming on the environment.

Source: SQA