Chapter 23 Ecosystems

Question 1

Give the definition for a population.

Answer 1

Group of organisms of the same species living in the same habitat.

Question 2

Define habitat.

Answer 2

Part of an ecosystem in which particular organisms live.

Question 3

Define community.

Answer 3

All the populations of different species in the same area at the same time.

Question 4

Define ecosystem.

Answer 4

A community and non-living components of an environment (biotic and abiotic factors). Ecosystems can vary in size.

Question 5

Define niche.

Answer 5

An organism’s role in the ecosystem, like position in the food web and habitat. Each species’ niche is determined by their adaption to biotic and abiotic factors.

Question 6

What is carrying capacity?

Answer 6

The maximum population size an ecosystem can support.

Question 7

What are biotic factors? Give examples of biotic factors.

Answer 7

Biotic factors are the impact of interactions between organisms. These interactions include competition for food, space and breeding partners. This can occur within species or between different species.

Question 8

What are abiotic factors? Give examples of abiotic factors.

Answer 8

Abiotic factors are the non living conditions of an ecosystem. This includes light availability, temperature, oxygen availability, water availability and soil factors.

Question 9

How may light affect the conditions of an ecosystem?

Answer 9

Plants require light to undergo photosynthesis- generally, the greater the light, the more successful the plant is. In ecosystems where there is little light availability, plants need to adapt to take in enough light for photosynthesis. Theses adaptions may include having bigger leaves, or photosynthesis pigments that require less light, and more. In ecosystems where there is a lot of light, the stomata is more likely to open, allowing a lot of water vapour to escape. Hence, with greater light availability, lights need to adapt to absorb and retain as much water as possible. Plants are essential in an ecosystem as they act as producers in food webs.

Question 10

How does temperature affect an ecosystem?

Answer 10

Temperature affects enzyme controlling metabolic reactions. So changes in temperature will greatly affect plants and ectothermic animals (animals that rely on environment for a stable temperature. Endothermic animals control their own internal temperature). Hence, ectothermic animals and plants greatly thrive in warmer temperatures. Changes in temperature (due to changing seasons), an cause animals to migrate, or animals to hibernate. In plants, changing temperatures may initiate leaf-fall, dormancy and flowering.

Question 11

How does water availability affect an ecosystem?

Answer 11

Lack of water leads to water stress, or even death. Lack of water can cause plants to wilt, as water causes plants to be turgid which helps the plant to be kept upright. Water is also required for photosynthesis to occur. Xerophytes are plants that are adapted to absorb and retain water due to the surrounding environment (for example, cacti are xerophytes as they need to adapt to retain water in a desert.

Question 12

How does oxygen availability affect an ecosystem?

Answer 12

In aquatic ecosystems, fast flowing cold water means there are high concentrations of oxygen. Hence, when the flow rate of the water is slow or the water is warm, there is a lower concentration of oxygen which can lead to suffocation of aquatic organisms.
In waterlogged soil, there is water in the air spaces between the soil particles. This results in there being less oxygen available for the plant, which leads to a lack of growth, as oxygen is required for respiration.

Question 13

There are 3 main soil types. What are they?

Answer 13

Clay - Fine particles which is easily water logged, and forms clumps when wet.
Loam - Different sized particles that retains but does not become water logged.
Sandy - Course, well separated particles which allows free draining. Sandy soil does not retain water and is easily eroded.

Question 14

Define biomass.

Answer 14

The mass of living material present in a particular place or in particular organisms.

Question 15

Ecosystems are constantly changing and varying in size. Why is this?

Answer 15

Ecosystems are dependent on biotic and abiotic factors. If these factors change, it also causes the ecosystem to change.

Question 16

In food webs and chains, each stage is known as a trophic level. What is in the first trophic level?

Answer 16

The first trophic level contains the produces- this refers to the plants. Producers absorbs light energy from the sun and converts into chemical energy, to be used in processes for the plant to survive. Any remaining energy is transferred to subsequent consumers as biomass.

Question 17

Food chains rarely has more trophic levels that the quaternary consumer (or around this level) as there is insufficient biomass. Why is this?

Answer 17

Between each trophic level in the food web, majority of the energy is used for processes like respiration and excretion. Only the remaining energy, which is a little bit, is converted into new tissue- this is the biomass.

Question 18

How to calculate biomass at a trophic level?

Answer 18

Multiply the biomass present in the organism by the total number of organisms in that trophic level. This biomass calculated is the biomass present at a particular moment in time (so this doesn’t take into consideration any seasonal changes).

Question 19

Why is it a problem to measure the biomass of living organisms?

Answer 19

Measuring the biomass of fresh material in living organisms means that the water content is also taken into account. However, the water content cannot just be discounted because the amount of water content varies in different organisms. Therefore, this technique of calculating biomass is unreliable, unless large samples are used.

Question 20

What does it mean to calculate the ‘dry mass’ of an organism? Why is this method used?

Answer 20

To calculate the ‘dry mass’, the organism must be killed in order for it to be dried. This requires the organism to be place in an oven at 80 degrees Celsius, until all the water has evaporated. ?????????????????

Question 21

What is biomass measured in?

Answer 21

Grams per square metre (for areas of land).
Grams per cubic metre (for areas of water).

Question 22

How are decomposers an essential part to ecosystems?

Answer 22

Decomposers break down dead organisms releasing nutrients back into the ecosystem.

Question 23

Describe the pattern of biomass, when moving along trophic levels.

Answer 23

When moving along trophic levels, the biomass is nearly always less than the trophic level below. This is because not all the biomass is transferred.

Question 24

What is the energy at each trophic level measured in?

Answer 24

It is measured in kilojoules per metre squared per year. This allows there to be changes in photosynthetic production and consumer feeding patterns throughout the year.

Question 25

What is ecological efficiency?

Answer 25

Ecological efficiency id the efficiency in which biomass or energy is transferred from one trophic level to another.

Question 26

Producers only convert 1-3 % of the sunlight they receive into chemical energy, and hence biomass. Why is this?

Answer 26

Not all energy available is used for photosynthesis; around 90% of energy is reflected, or some is reflected through the leaf. Other factors may limit photosynthesis, like water availability, which means light that was meant to be used for photosynthesis may not be used (as photosynthesis cannot proceed due to other factors). Additionally, a proportion of energy may be ‘lost’ as it is used in photosynthetic reactions. Hence, only a little energy is available to be converted into chemical energy.

Question 27

What is gross production?

Answer 27

This is the total light energy in which plants convert into organic matter. However, 20-50 % of this energy is used in respiration, while the remaining energy is converted into biomass.

Question 28

What is net production? How can this be calculated?

Answer 28

Net production is energy available to be transferred to the next trophic level. This can be calculated by doing:
Gross production - Respiratory Losses

This calculation also gives the biomass within an organism.

Question 29

What does primary production refer to? (And secondary production, and so on)

Answer 29

Primary production is the generation of biomass in a producer. Secondary production is the generation of biomass in a primary consumer. Then tertiary production is the generation of biomass in a secondary consumer.

Question 30

Consumers at each trophic level convert at most 10% of the biomass in their food into their own organic tissue. Why can they not convert more biomass into organic material?

Answer 30

> Not all the biomass of the organism is eaten, such as, animal bones.

> Some energy is transferred to the environment in the form of metabolic heat, due to movement and respiration.

> Parts of the organism that is eaten may be indigestible; these parts is excreted as faeces.

> Also, some energy is lost from the animal in excretory materials, like urine.

Question 31

How to calculate efficiency of energy transfer (biomass transfer)?

Answer 31

(Energy or biomass available after the transfer) /
(Energy or biomass available before the transfer) x 100

Question 32

How can humans manipulate the transfer or biomass through an ecosystem?

Answer 32

Human manipulate the transfer of biomass by reducing the amount of energy lost at each trophic level. This can be done by:

Restricting movement means that respiration will also be limited. This is because not as much energy is required for reduced movement.

Providing animals with higher energy food increases the energy input, and therefore increases the energy transfer to the next trophic level.

Removing competition and predators, reduces movement that would be needed in hunting, defending and survival. This reduced movement also means less energy is needed, so less respiration takes place.

For plants, they are provided with abiotic factors that allows them to thrive- this may be warmth and adequate watering. This can be done by cultivating the plants in a greenhouse.

In agriculture, very simple food chains are used. For example, the producer (animal feed), primary consumer (livestock) and then secondary consumer (humans). When cultivating plants for human consumption, there are two trophic levels; the producer (crops) and primary consumer (humans). The very few trophic levels ensures fewer energy is lost when energy is transferred between trophic levels.

Question 33

How is the biomass of kelp in naturally affected in a marine ecosystem?

Answer 33

Sea urchins are marine invertebrates that feed on kelp, a type of seaweed. When sea urchins are abundant in a certain area, the ecosystem of kelp is disrupted. This is because when the sea urchins feed on kelp, they eat the kelps’ holdfasts- this is a strong structure that help keep the kelps anchored to the seabed. Without this anchor, the kelps floats away. As a result, the remaining area is highly lacking biomass of seaweed- this area is called the ‘urchin barren’. The reduced biomass of seaweed means that less species are able to live in this area. Hence, the absence of kelps has a huge influence on the marine community.

Question 34

Describe decomposition.
Why is decomposition useful?

Answer 34

Decomposition is the process in which a compound is broken down into smaller molecules, or its constituent elements. This is needed because useful elements, like carbon and nitrogen, cannot be used in the organic form- dead or waste matter. Hence, decomposition processes organic material into inorganic elements, in which they are able to be used, and returned to the environment.

Question 35

Define decomposer.
Give some examples of decomposers.

Answer 35

A decomposer is an organism which breaks down a dead plant or animal, in which the organic material is processed into inorganic molecules and elements (nutrients) available to photosynthetic producers in the ecosystem. Examples of decomposers includes microscopic fungi and bacteria.

Question 36

Why are decomposers known as saprophytes?

Answer 36

Decomposers are known as saprophytes as they digest dead matter and material (dead plants and animals) externally by releasing digestive enzymes. Once the material has been broken down, the decomposer absorbs the broken material. During this process, decomposers releases stored inorganic compounds and elements into the environment.

Question 37

What are detritivores?
Give examples of detritivores.

Answer 37

This is another organism that helps with decomposition. They break down detritus (dead and decaying matter) into smaller organic material. This increases the surface area of the organic material, so it increases the rate of decomposition when decomposers breaks them down completely.
Examples of detritivores includes woodlice (breaks down wood) and earthworms (breaks down dead leaves).
Detritivores digests internally.

Question 38

How is nitrogen an essential part to life and ecosystem?

Answer 38

We need nitrogen to make many molecules in our body to allow it to function. It is needed to make amino acids, and hence, proteins. It is also needed to make nucleic acids. Animals take in nitrogen through digesting their food. Plants have to take in nitrogen from the environment (like the soil).

Question 39

What percentage of air in the atmosphere is nitrogen?
Why is nitrogen not useful in its natural form?

Answer 39

The air in the atmosphere is made of 78% nitrogen.
Nitrogen is not useful in its natural form, because this way it is unable to be taken up by plants. In order to be used by living organisms, nitrogen needs to be combined with other elements like oxygen and hydrogen. Bacteria helps with converting natural nitrogen into a useable form by plants.

Question 40

How is ammonia or ammonium ions produced naturally in the environment?

Answer 40

They are produced by nitrogen- fixing bacteria and by decomposers. It is done by combining atmospheric nitrogen and hydrogen.
Ammonia is a form of nitrogen that can be absorbed by plants.

Question 41

How are nitrites formed naturally in the environment?

Answer 41

Nitrites are formed with nitrifying bacteria. They cannot be absorbed by plants.

Question 42

How are nitrates formed naturally in the environment?

Answer 42

Nitrates are formed by other nitrifying bacteria, by using nitrites. Plants are able to absorb these nitrates.

Question 43

Give examples of nitrogen fixing bacteria, and explain how nitrogen fixation works.

Answer 43

Examples of nitrogen fixing bacteria includes Azotobacter and Rhizobium. These bacteria contains an enzyme nitrogenase, which combines atmospheric nitrogen and hydrogen.

Question 44

Define nitrification.

Answer 44

Nitrification is the process in which ammonium compounds are converted into nitrogen containing compounds (via nitrifying bacteria) that can be used by plants.
This process occurs in 2 oxidation reactions, only in well-aerated soil.
1. Nitrifying bacteria oxidises ammonium compounds into nitrites.
2. Nitrites are further oxidised by other denitrifying bacteria to form nitrates.

Question 45

What is denitrification?

Answer 45

Denitrification occurs only in anaerobic conditions, like water-logged soil. Denitrifying bacteria converts nitrates in the soil back into nitrogen to be released in the atmosphere. The bacteria does this as a source of energy for respiration (takes the oxygen needed for respiration).

Question 46

What is ammonification?

Answer 46

When decomposers processes nitrogen containing molecules from dead organisms, faeces and urine into ammonium compounds.

Question 47

Why is carbon essential to living organisms?

Answer 47

Carbon is an element that partially makes up major molecules in our body that allows us to function. These molecules includes proteins, fats and carbohydrates.

Question 48

How can levels of atmospheric carbon vary from day to night, and between seasons?

Answer 48

Carbon dioxide levels can vary from day to night. It is during the day that photosynthesis occurs as plants keeps their stomata open for gas exchange and receive sunlight. Hence, plants take in carbon dioxide (from the atmosphere) needed for photosynthesis during the day. As photosynthesis only occurs during the day, there are higher carbon dioxide levels at night that in the day. In terms of seasons, carbon dioxide levels would be lower on a summer’s day than a winter’s day. This is because on a summer’s day, more sunlight is available, so photosynthesis rates would be higher and more carbon dioxide would be absorbed for this photosynthesis.

Question 49

Over the past 200 years, global atmospheric carbon dioxide levels have raised significantly. Why may this be?

Answer 49

Combustion of fossil fuels in order to gain energy has released carbon dioxide into the atmosphere.
Deforestation has removed a large number of plants. Less plants means less photosynthesis occurs, so less carbon dioxide is taken in for these photosynthesis reactions.

Question 50

How is the amount of carbon dioxide in seas and oceans affected by the temperature of the water?

Answer 50

The higher the temperature of water, the less gas is dissolved.
Due to human activity, more greenhouse gases are released into the atmosphere, which traps thermal energy and heats the Earth- this includes seas and oceans.
With the increasing temperature of seas and oceans, less carbon dioxide is dissolved into the water, and so is released into the atmosphere. This further contributes to the process.

Question 51

How are we able to study how atmospheric carbon dioxide levels varied significantly over million-year timescale?

Answer 51

Samples are taken from deep within a glacier. If the sample of ice is taken from a deeper depth, it had formed at an earlier time in the Earth’s history. When the ice had formed when it did, air bubbles were trapped within the ice. The gases present in these bubbles, reflects the gases present in the atmosphere at that point in history. Hence, through the analysis of the ice, we can deduce what the atmosphere was like back then.

Question 52

Define succession.

Answer 52

The change in an ecological community overtime.

Question 53

What are the two types of succession?

Answer 53

Primary succession- Occurs or newly formed or exposed land, like bare rock. here is no soil or organic material present to begin with.

Secondary succession- Occurs on land where soil is present, but no plant or human species. An example of this could be the bare earth after a forest fire.

Question 54

Give some examples of primary succession.

Answer 54

When volcanoes erupt, they deposit lava. This lava then cools and solidifies to form igneous rock; here succession can start to happen.

Sand may be blown by the wind, or deposited by the sea, to create new sand dunes.

Silt and mud is deposited by river estuaries.

When glaciers retreat, they deposit rubble and exposing rock.

Question 55

In primary succession, the first seral stage is a pioneer community. What is this?

Answer 55

In primary succession, the environment is initially inhabitable to species due to the harsh conditions (abiotic factors not in favour)- this is known as inhospitable environment. However, pioneer species (or pioneer colonisers) are adapted to survive these harsh conditions, so they colonise the environment. Examples of these species include algae and lichen. The species arrive as spores or seeds carried by the wind, or via droppings of birds and animals passing through.

Question 56

How are pioneer species adapted to the inhospitable environment in the first seral stage of primary succession?

Answer 56

Pioneer species has the ability to produce large quantities of seeds and spores, which are blown by the wind to be deposited in new land.

Pioneer species has seeds that germinate very quickly.

Pioneer species can photosynthesise to produce their own energy.

They are adapted to these extreme environments.

Have the ability to fix nitrogen from the atmosphere, so adding mineral content of the soil.

Question 57

The second part of succession is an immediate community. What happens during this period?

Answer 57

Weathering of bare rock forms the basis of soil. Eventually, on its own it is unable to support the pioneer species. The pioneer species starts to die and decompose, which releases small organic products in the soil; this organic part of the soil is called humus. Now that there is organic products in the soil (nutrients, like nitrates and ability to retain water), secondary colonisers are able to grow in this area. Like primary colonisers, the secondary colonisers arrive as seeds and spores, via wind and animal faeces. As pioneer species also acts as a food source for consumers, animals are attracted to the area and starts to colonise as well. Environmental conditions starts to improve and new species starts to arrive to the area- this is tertiary colonisers. At each stage, rock continues to erode and organisms decompose, contributing to organic mass (nutrients) in the soil. Overtime, the soil becomes more nutrient rich and is able to retain more water- this makes the abiotic factors more favourable to small flowering plants. This continues happening until climax conditions are reached.

Question 58

Give examples of secondary colonisers and tertiary colonisers.

Answer 58

An example of secondary coloniser are mosses. An example of tertiary colonisers are ferns. They are highly adapted to survive in conditions without an abundance of water (waxy cuticles).

Question 59

The final seral stage of succession is a climax community. What happens during this period?

Answer 59

This is when the community is in a stable state and changes very little overtime. The species that makes up the climax community (dominant species) depends on the climate. For example, a climate with a mild temperature and plenty of water will be filled with large trees. In general, biodiversity increases as succession takes place, but the climax community is not the most biodiverse. It tends to be most biodiverse in mid succession. After mid-succession, biodiversity decreases as dominant species are out competing pioneer and other species, resulting in their elimination. The more successful the dominant species, the less biodiversity in a given ecosystem.

Question 60

Describe animal progression in succession.

Answer 60

Animals normally undergo a slower progression than plants. Primary consumers, like insects and worms, only approach the area of succession when they find there is enough mosses and lichen (primary and secondary colonisers) to consume and shelter within. They must move into the area succession from neighbouring areas, which is why animal progression is slower, especially if the ‘new land’ is geographically isolated (like a new volcanic island). Then secondary consumers arrive when there is a sufficient food source and a good habitat to live in. Like primary consumers, secondary consumers must move in from neighbouring areas. Eventually, larger organisms like mammals and reptiles will colonise the ‘new land’.

Question 61

What is deflected succession? How many deflected succession occur? What is the result of deflected succession?

Answer 61

Deflected succession is when human activity can halt the natural flow of succession. Human activities that may cause deflected succession includes grazing and trampling of vegetation by domesticated animals; and removing existing vegetation to plant crops (the crops are the final community); and burning as a means of forest clearance (provides space and nutrient rich ash for other species to grow). In deflected succession, the final seral stage is not a climax community, but a plagioclimax.

Question 62

How is deflected succession used to ensure the survival of certain species?

Answer 62

Deflected succession is used to preserve the habitat in its current form. It may require ecological land management to prevent further succession from occurring. Further succession may lead to a dominating species, that could lead to the elimination of prior colonisers that may be endangered.