10.1 Nature of Ecosystems

What is an ecosystem? (3)

- An ecosystem is a self-sustaining environment.

- It includes all the living organisms that interact with one another.

- It also consists of the nutrients cycling through the system and the physical and chemical environment.

What is a species? (3)

- A species is a group of organisms that share similar morphological, physiological, biochemical, and behavioural features.

- Organisms of the same species can interbreed with one another to produce fertile offspring.

- They are reproductively isolated from other species.

What are a population and a community? (2)

- A population is a group of individuals belonging to the same species that are found living in the same habitat.

- A community is a group of populations of different organisms living together in a particular habitat.

What is a biotic factor? (2)

- A biotic factor is a living component of an ecosystem.

- Grazing is an interaction where herbivores feed on plants, and the herbivore population is limited by the quality and quantity of the available plants.

What are predation, parasitism, and mutualism? (3)

- Predation is an interaction in which a predator kills and consumes its prey.

- Parasitism is a close association between two organisms of different species, in which the parasite benefits and the host is harmed.

- Mutualism is an interaction between two organisms of different species, in which both species benefit from the relationship.

What is competition in an ecosystem? (3)

- Competition occurs when two or more organisms require a specific resource that is in limited supply.

- This can be between organisms of the same species, known as intraspecific, or between organisms of different species, known as interspecific.

What are abiotic, biotic, and edaphic factors? (3)

- Abiotic factors are a non-living component of an organism's habitat.

- Biotic factors are a living component of an organism's habitat.

- Edaphic factors are those that relate to the structure and composition of the soil, including its pH and mineral ion concentration.

How do temperature and light intensity act as an abiotic factor? (2)

- Temperature affects the rate of metabolic reactions in both endothermic and ectothermic organisms.

- Light affects the rate of photosynthesis by influencing the light-dependent reactions in plants.

What are three key abiotic factors of photosynthesis? (3)

- Water.

- Oxygen and carbon dioxide concentration.

- Water supply and drainage.

How does oxygen concentration affect organisms in an ecosystem? (2)

- Oxygen concentration impacts organisms that respire aerobically.

- Carbon dioxide concentration affects photosynthetic plants and bacteria.

How do the pH of water and soil affect organisms? (2)

- The pH of water or soil directly affects the organisms living in that medium.

- It also influences the activity of enzymes involved in metabolic reactions.

Why are inorganic ions important in an ecosystem? (2)

- The availability and concentration of inorganic ions are needed to produce chlorophyll.

- For example, magnesium is required for the synthesis of chlorophyll.

How do atmospheric humidity and wind speed affect organisms? (3)

- Atmospheric humidity affects the rate of water loss from an organism's body via evaporation and transpiration in plants.

- Wind speed impacts the ventilation across the surfaces of leaves, thereby affecting the rate of transpiration.

- It also serves as a cooling mechanism when the environmental temperature is lower than the organism's body temperature.

What is an ecosystem in terms of its components and energy flow? (2)

- Ecosystems are dynamic systems involving continuous interactions between both biotic and abiotic components.

- Within them, energy and materials are constantly flowing from one organism to another and between the organisms and the abiotic environment.

What is the biosphere? (3)

- The biosphere is the part of the Earth where life exists.

- It extends from the deep oceans to the lower regions of the atmosphere.

- It is a large-scale ecosystem made up of many smaller, interconnected ecosystems.

What are biomes? (2)

- Biomes are the smaller components that make up the biosphere.

- They are large regions distinguished by their similar climates and plant communities.

What are the climate and vegetation of a tropical rainforest biome? (2)

- The climate is tropical, with a constant high temperature and lacks significant temperature seasons.

- The vegetation is an evergreen tropical rainforest.

What are the climate and vegetation of a tropical seasonal forest or savanna biome? (2)

- The climate is tropical, with a summer rainy season followed by a dry winter season.

- The vegetation consists of seasonal forest, scrub, or savanna.

What are the climate and vegetation of a subtropical desert biome? (2)

- The climate is highly seasonal and arid.

- The vegetation is typical of a desert, with a considerable amount of exposed ground.

What are the climate and vegetation of a woodland or shrubland biome? (2)

- The climate is Mediterranean, characterized by a rainy winter and a dry summer with drought conditions.

- The vegetation is drought-adapted and includes frost-sensitive shrublands and woodlands.

What are the climate and vegetation of a temperate seasonal forest biome? (2)

- The climate is a nemoral climate with moderate winters and freezing temperatures.

- The vegetation is a frost-resistant, deciduous, temperate forest.

What are the climate and vegetation of a temperate rainforest biome? (2)

- The climate is a cold temperate featuring cool summers and long winters.

- The vegetation is an evergreen, frost-hardy, needle-leafed forest, also known as taiga.

What are the climate and vegetation of a tundra biome? (3)

- The climate is polar, with very short, cool summers and long, very cold winters.

- The vegetation is low, evergreen, and does not have trees.

- A key characteristic of the tundra is that the soil is permanently frozen.

What is succession and where does it occur? (2)

- Succession is the progressive change in the composition of a community over a period of time.

- Primary succession occurs on a previously uncolonised substrate, such as bare rock or sand dunes.

What is the role of pioneer plants in succession? (3)

- They are the first organisms to colonize a new habitat.

- They are opportunistic and can tolerate harsh conditions, such as desiccation and a lack of soil.

- They initiate the process of soil formation by decomposing rock and trapping organic material.

How is soil initially formed during primary succession? (3)

- Pioneer organisms generate a fine rock surface by breaking it down into smaller grains.

- When they die and decompose, they form a substance called humus.

- The mixture of humus and inorganic rock grains begins the formation of soil, increasing its water retention and fertility.

What is the role of mosses in primary succession? (3)

- Mosses colonize an area once a thin layer of soil has been prepared by pioneer species.

- They have rhizoids that attach to surfaces, so they do not need deep soil to grow.

- Mosses form a dense mat that continues to weather the rock and helps dust particles accumulate.

What is the role of invasive organic debris and grass during succession? (3)

- The accumulation of dual invasive organic debris and grass leads to the formation of shallow soil.

- This allows secondary colonisers, such as ferns and grasses, to establish root systems.

- The binding action of their roots helps to stabilise the soil.

What is a climax community? (2)

- A climax community is the final, stable stage of succession.

- It is a self-perpetuating community with relatively constant biodiversity and species composition.

How do environmental changes occur during succession? (2)

- Each successive group of organisms that a particular environment can support modifies the environment.

- As the environment is modified by the colonisers, plant diversity increases, becoming richer in different plant and tree species.

What is a plagioclimax? (2)

- A plagioclimax is a climax community.

- It is at least partly the result of human intervention.

What is a sere? (2)

- A sere is the entire sequence of communities that develop during succession.

- It starts from the pioneer community and ends with the final climax community.

How do seral stages facilitate succession? (2)

- A seral stage is any distinct community that exists for a time within the sere.

- Each group of plant species alters the habitat in a way that makes it easier for the next group of species to become established.

What is the mutualistic relationship between early colonizing plants and nitrogen-fixing bacteria? (3)

- Early herbaceous plants may have a mutualistic relationship with nitrogen-fixing bacteria.

- These bacteria convert nitrogen gas from the atmosphere into ammonium ions.

- The plants can then use these ammonium ions to synthesize amino acids and proteins.

How does the pH of the soil change during succession? (2)

- Initially, the substrate's pH is alkaline due to the presence of carbonates.

- As humus builds up, it neutralizes the carbonates, and the pH becomes more neutral, favouring the growth of other plant species.

Why are earlier pioneer species unable to be sustained in later stages of succession? (3)

- Earlier pioneer species cannot survive due to changes in abiotic factors, such as light intensity.

- They are also affected by changes in edaphic factors.

- An increase in competition from later-arriving species also contributes to their decline.

What is secondary succession? (3)

- Secondary succession is the development of an ecosystem from existing soil that has already been created.

- It typically occurs after a disturbance such as a fire, flood, or human activity.

- Species colonise and grow significantly faster than in primary succession due to the pre-existing soil system and nutrient-rich soil.

What are three typical stages of a sand dune succession? (3)

- The embryo dune and fore dune.

- The yellow dune and grey dune.

- The dune slack and finally shrubland.

What is zonation? (2)

- Zonation occurs in an area where an environmental gradient affects the distribution of organisms.

- This results in organisms being found in distinct bands or zones along the gradient.

How can succession be studied using a belt transect? (3)

1. Establish a line transect parallel to the area of study to identify the development of zonation or succession.

2. Place quadrats at regular intervals along the line transect.

3. Record the presence and abundance of organisms found within each quadrat to analyse the changes in the community.

What is the difference between a continuous and an interrupted transect? (2)

- In a continuous transect, a record of organisms is made along the entire length of the transect.

- In an interrupted transect, records are taken only at regular, predetermined intervals along the line.

What is a microclimate? (2)

- A microclimate is a small area within a larger habitat where the climate differs from the surrounding area.

- They are created by variations in abiotic factors and provide different niches, which allow different species to exist in the habitat.

How does light availability affect plant populations? (3)

- The amount of light directly influences the density of organisms in a habitat through its role in photosynthesis.

- Plants in low-light conditions may adapt by reproducing early to minimise shading by larger plants.

- Other adaptations include having additional chlorophyll, different photosynthetic pigments, or leaf mosaics to maximise light absorption.

How does light indirectly affect animals? (3)

- Light availability impacts the distribution and availability of food plants that animals feed on.

- Seasonal changes in light can affect the reproductive patterns of many animal species.

- The daily cycle of light and dark regulates circadian rhythms, which control feeding and sleeping patterns.

How does temperature affect organisms? (3)

- Specialist organisms can only grow and reproduce successfully within a particular temperature range.

- The temperature extremes of a habitat determine which organisms can live there.

- A change in temperature also affects the rate of enzyme-controlled reactions in plants and ectothermic animals.

What are two effects of wind on organisms? (2)

- Wind increases water loss from organisms through evaporation from gaseous exchange surfaces, like the stomata of plants.

- Windy conditions also provide a cooling mechanism, which can add environmental stress to an organism.

What are three factors that affect water availability in terrestrial environments? (3)

- Water availability is influenced by edaphic factors, which are related to the soil.

- The rate of evaporation from the surfaces of leaves affects water retention.

- How well water drains through the soil also plays a significant role.

What is the role of water currents in aquatic environments? (2)

- Organisms that live in water with strong currents must be able to flow with the current, be strong swimmers, or attach themselves to a surface to resist the force.

- It is a vital component of aquatic habitats that can affect population size because it is a vital nutrient for growth and reproduction.

What are three factors that affect oxygen concentration in an aquatic environment? (3)

- Cold, fast-flowing water contains a higher concentration of dissolved oxygen.

- Increasing water temperatures or stagnant conditions reduce the oxygen content.

- A waterlogged soil can lead to anaerobic conditions due to a lack of oxygen.

Why is soil aeration important? (2)

- Aeration is important for the respiration of plant roots.

- It is also necessary for the respiration of soil organisms, like nitrogen-fixing bacteria.

How does a classic predator-prey relationship cycle over time? (3)

- An increase in the prey population provides more food for the predator, leading to an increase in the predator population.

- The increased predator population consumes more prey, causing the prey population to decrease.

- This leads to a decrease in the predator population, which allows the prey population to recover and the cycle to repeat.

What are the circumstances under which a classic predator-prey cyclical relationship is most evident? (2)

- The relationship is most clear when the predator specializes in consuming only one source of prey.

- The predator is unable to switch to an alternative food source if its standard prey population decreases.

What are the main limiting factor for a prey population and a predator population in this type of relationship? (2)

- For the prey population, predation is the main limiting factor.

- For the predator population, their food supply is the main limiting factor.

Why is reproduction important for the establishment of a population in a habitat? (3)

- Reproduction is a major factor that contributes to the growth of a population.

- The likelihood of finding a mate or achieving pollination helps determine the types of organisms found in a habitat.

- To become established in a specific niche, a species must have a sustainable population of both males and females to allow for reproduction.

Define territorial behaviour? (3)

- Territorial behaviour is when an animal or a group of animals holds and defends an area against other organisms.

- The defence can be against members of the same species or different species.

- Functionally, territories are important for providing the necessary resources for a breeding pair to raise offspring.

How can diseases affect individual animals and their populations? (4)

- Diseased animals are weakened and may be unsuccessful in reproduction.

- A sick predator will be less effective at hunting prey.

- A sick prey animal would be less able to defend itself from predators.

- The spread of an infectious disease can be devastating for a population, significantly reducing its size.

What is meant by density-dependent factors using parasitism and disease as examples? (2)

- Density-dependent factors are factors whose effects on a population change as the population density changes.

- Parasitism and disease are examples, as their spread increases when the density of the host population increases.

Why is a biodiverse community less likely to be severely affected by disease? (2)

- A biodiverse community has a high variety of species.

- The depletion of one population by disease will have a less significant impact on the community as a whole.

What is meant by competition? (2)

- Competition is an interaction where individuals compete for density-dependent factors.

- It occurs when a shared resource is in limited supply.

What types of abiotic and biotic resources can organisms compete for? (2)

- Abiotic resources include minerals, sunlight, and oxygen.

- Biotic resources include territories, nest sites, and mates.

What is meant by sexual selection and sexual dimorphism? (2)

- Sexual selection is a process that arises from competition for mates.

- Sexual dimorphism refers to the distinct differences in morphology between males and females of a species.

What is meant by intraspecific competition? (2)

- Intraspecific competition is competition that occurs between individuals of the same species.

- They compete for limited resources like food, space, water, and mates.

What is the role of intraspecific competition in natural selection? (3)

- Intraspecific competition is a mechanism involved in natural selection.

- Organisms with advantageous phenotypes are better competitors.

- These individuals are more likely to survive, reproduce, and pass their alleles on to their offspring.

What is meant by interspecific competition? (2)

- Interspecific competition is competition between individuals of different species for the same resources.

- It only occurs when the ecological niches of the two species overlap.

What is the principle of competitive exclusion? (2)

- Competitive exclusion is the prevention of one species from maintaining a viable population due to competition with another.

- It suggests that two species with identical ecological niches cannot coexist in the same habitat.

How would you conduct an investigation to show how the distribution of lichens is affected by an abiotic factor? (6)

1. Light intensity is selected as the abiotic factor to be investigated. Other valid factors include temperature or distance from the sea.

2. An environmental gradient is established by placing a transect line from an area of low light intensity, such as under a tree, to an area of high light intensity, such as an open field.

3. A quadrat is placed at regular intervals along the transect line to select sample sites.

4. Within each quadrat, the percentage cover of the lichens is calculated to measure their presence and distribution.

5. At each sample site, a light meter is used to measure the light intensity, and other abiotic variables like temperature are controlled or measured.

6. A statistical test, such as a correlation test, is then carried out to determine if there is a significant relationship between the chosen abiotic factor and the distribution of the lichens.