7 2 organisation of an ecosystem

Food chains show feeding relationships within communities, specifically the transfer of energy between trophic levels.

A producer is an organism that can produce its own carbon compounds, e.g. glucose, by chemical processes such as photosynthesis.

The investigation shown will determine the effect of altitude on the distribution of buttercups on a hillside.

A primary consumer is an organism that eats producers. Primary consumers are also known as herbivores.

The primary consumer in this food chain is the mouse, as it is eating grass, which is the producer.

A secondary consumer is an organism that eats primary consumers.

False. Herbivores are primary consumers. Secondary consumers eat primary consumers, making them carnivores.

Tertiary consumers are organisms that feed on secondary consumers. They are carnivores and are present at the fourth trophic level of food chains.

True. In a stable community the numbers of predators will rise when prey numbers are high, then as prey numbers decline the predator numbers will also decline.

A quadrat is a square frame that is placed on the ground to study the organisms within.

The term abundance is how common a species is within a quadrat. Abundance across a series of quadrats can be used to estimate the size of a population.

The abundance of a species can be measured within a quadrat as follows:

Percentage cover is often used to measure the abundance of a species where individual organisms are difficult to tell apart, e.g. grass or barnacles

Placing quadrats randomly avoids bias in an investigation, e.g. a student might choose to place all of their quadrats on bare ground because it would make counting easier, resulting in a biased sample.

Variables that should be kept the same when using quadrats to compare the populations of a species in two areas include:

Challenges of using quadrats to investigate populations include:

True. Carrying out more quadrats will increase the sample size, meaning that the results are more likely to be a good representation of the area sampled.

Distribution refers to where a species occurs within its habitat.

Quadrats can be used to investigate the effects of a factor on the distributions on a species as follows:

Nutrients cycling is important because it allows nutrients to be released from tissues so that they become available again for other organisms to use. Without nutrient cycling ecosystems would run out of essential nutrients.

Carbon is taken out of the atmosphere in the form of carbon dioxide by plants during photosynthesis.

Carbon is returned to the atmosphere when it is released as carbon dioxide by the following processes:

Mass deforestation (cutting down many trees) affects the carbon cycle as follows:

False. While the water cycle does provide fresh water to land plants and animals, this occurs due to continuous evaporation and precipitation, not by passing water between different living organisms.

Water moves from the ocean to the atmosphere by evaporation.

Precipitation occurs when water falls from clouds, e.g. in the form of rain, snow or sleet.

False. Microorganisms do not return carbon to the soil, but instead release it into the atmosphere when they respire. Microorganisms do return mineral ions to the soil during nutrient cycling.

Decomposers are organisms that break down dead and waste material, e.g. bacteria and fungi

True. Decomposers do not fit into any particular trophic level, as they can feed on waste or dead organisms from any part of a food chain.

The rate of decay is influenced by: pH can also affect the activity of decomposers.

True. Higher temperatures increase the rate of decay. This is because the enzyme controlled reactions required for decomposition occur faster at higher temperatures.

Oxygen availability impacts the rate of decay because decomposers require oxygen for respiration. If oxygen levels become depleted decomposers will die and decomposition will slow down or stop.

A gardener can use a compost heap to improve growing conditions in their garden as follows:

Anaerobic decay describes the process of decomposition when it is carried out in the absence of oxygen.

Methane gas is produced during anaerobic decay.

In an investigation into the effect of temperature on the rate of decay of fresh milk the independent variable would be temperature.

The rate of decay of fresh milk is likely to increase as temperature increases from 10°C to 30°C. This is because the enzyme-controlled reactions required for decomposition occur faster at higher temperatures.

In an investigation into the effect of temperature on the rate of decay of fresh milk, a decrease in pH indicates decay because the microorganisms use the sugars in milk to fuel anaerobic respiration, producing lactic acid. In some versions of this practical lipase may be used to speed up the decay process; in this case the pH change occurs due to the breakdown of fats into fatty acids.

In an investigation into the effect of temperature on the rate of decay of fresh milk, increasing the temperature to 90°C would denature any enzymes involved in decay.

Environmental changes that might affect the distribution of organisms in an ecosystem include changes in:

Rising average temperatures can cause the distribution of plant species to: These changes would provide the species with habitats where average temperatures are lower.

True. Changes in the availability of water can affect the distribution of living organisms because water is a fundamental requirement for biological processes.

Oxygen is required for aerobic respiration in aquatic animals, and some species can only survive in water with high oxygen concentrations. If water oxygen levels fall, these aerobic organisms may migrate to other locations or die out.

Environmental change can be caused by: