6.3.1 Ecosystems

Question 1

What is a producer?

Answer 1

An organism that produces organic molecules using sunlight energy.

Question 2

What is a consumer?

Answer 2

An organism that eats other organisms. e.g animals and birds.

Question 3

What is a decomposer?

Answer 3

An organism that breaks down dead or undigested organic material e.g bacteria and fungi

Question 4

An ecosystem includes both ___ and ____ factors.

Answer 4

biotic
abiotic

Question 5

What is a biotic factor?

Answer 5

A living feature of ecosystem

Question 6

What is an abiotic factor?

Answer 6

A non-living feature of an ecosystem

Question 7

Give examples of biotic factors.

Answer 7

Predation
Competition
Disease
Parasitism

Question 8

Give some examples of abiotic factors.

Answer 8

Availability of water and light, temperature, humidity, ph of water, salinity of water.

Question 9

What is biomass?

Answer 9

The mass of living material of the organism or tissue.

Question 10

How can we measure biomass?

Answer 10

Working out the dry mass of an organism.
The chemical energy content of the organism when burned in pure oxygen.

Question 11

How can we find the dry mass of a plant sample?

Answer 11

• Weigh the crucible without the sample before placing the sample in the crucible.
• Place the crucible in the oven at at a low temperature.
• Remove and weigh the crucible at regular intervals during the drying process.
• Once the mass of the crucible stops decreasing and becomes constant, the sample is fully dehydrated.
• From this final constant mass, subtract the original mass of the crucible to find the dry mass of the sample.

Question 12

How can we find the energy released by a sample of plant biomass.

Answer 12

-To estimate the chemical energy stored in the dried sample use a calorimeter. This burns the dried sample and uses the energy to heat a known volume of water.
-Measure the temp change of the water and this can estimate the chemical energy (in joules or kiljoules) stored within the sample.
-1 Joule is the amount of heat needed to raise the temperature of 24g/0.23cm^3 or 0.24ml of water by 1ºC.

Question 13

What are some biotic factors that may effect a rock pool ecosystem?

Answer 13

Intense competition for food can limit the number of organisms that are present in the rock pool ecosystem.

Question 14

What are some abiotic factors that may effect a rock pool ecosystem?

Answer 14

Rock pools are heavily influenced by tides. A high tide can mean they are completely submerged by the ocean so experience similar abiotic factors (e.g pH, salinity, temperature etc. as the ocean ecosystem. However, at low tides, they experience more extreme abiotic conditions e.g higher temperatures and salinity which only some organisms can tolerate.

Question 15

What are some biotic factors which may effect a playing field ecosystem.

Answer 15

Producers include grass and some other plants such as daisies, clover and dandelions. The large amounts of these plants might attract a large number of organisms which will use them as a food source e.g rabbits, catapilars etc.

Question 16

What are some abiotic factors that may effect a playing field ecosystem?

Answer 16

Rainfall and sunlight affect the growth of the producers in the ecosystem. In a very wet year, the soil/grass may become waterlogged making it hard for plants to grow. Poor plant growth may decrease the number of consumers that the ecosystem can support.

Question 17

What are some biotic factors which may effect a large tree ecosystem?

Answer 17

Insects, such as catapillars can use the leaves of a tree as a source of food. However if they consume all the leaves on a tree then they will slow tree growth or even cause its death.

Question 18

What are some abiotic factors which may effect a large tree ecosystem

Answer 18

Drought conditions can negatively impact the growth of a tree. In severe cases, it can result in the whole tree (or parts of it) dying.

Question 19

List some reasons why not all energy (e.g from sunlight or food) available to the organisms in a trophic level will be transferred to the next trophic level?

Answer 19

• Light passes through leaves or is reflected away
• light hits part of a plant that does not photosynthesise e.g tree bark
• Light is a mixture of wavelengths, only certain wavelengths stimulate photosynthesis.
• Some parts of food are indigestible so pass through organisms and come out as waste.

Question 20

How much of the energy available to organisms is never taken in by the organisms in the first place?

Answer 20

60%

Question 21

What is gross productivity?

Answer 21

The rest of the energy absorbed by the organisms in a trophic level.

Question 22

Why is not all of the gross productivity available to the next trophic level?

Answer 22

-30% of the total energy available (75% of the gross productivity) is lost to the environment via respiration or body heat.
-10% of the total energy available (25% of the gross productivity) becomes biomass.

Question 23

What is respiratory loss?

Answer 23

When energy is lost to the environment via respiration or body heat.

Question 24

What is net productivity?

Answer 24

The amount of energy available at the next trophic level.

Question 25

formula for efficency.

Answer 25

(Biomass transferred/biomass intake) x100

Question 26

How do we work out net productivity?

Answer 26

Gross productivity- respiratory loss.

Question 27

Give some examples of how human activities can increase the transfer of energy.

Answer 27

-Herbicides
-Fungicides
-insecticides
-natural predators
-fertilisers
-livestock rearing

Question 28

How do herbicides increase the transfer of energy?

Answer 28

Herbicides kill weeds that compete with agricultural crops for energy which reduces competition so crops receive more energy so grow faster and larger and productivity increases.

Question 29

How do fungicides increase the transfer of energy?

Answer 29

Fungicides kill fungal infections that damage agricultural crops. The crops can use more energy for growth and less for fighting infection so they grow faster and larger and productivity increases.

Question 30

How do insecticides increase the transfer of energy?

Answer 30

Insecticides kill insect pests that eat and damage agricultural crops. This means less biomass is lost from crops so they grow larger and productivity increases.

Question 31

How do natural predators increase the transfer of energy?

Answer 31

Natural predators introduced to the ecosystem eat the pest species so the crops use less energy and biomass. Productivity increases.

Question 32

How do fertilisers increase the transfer of energy?

Answer 32

Fertilisers provide crops with the minerals needed for growth e.g nitrates. Crops use up minerals as they grow so if there are not enough minerals they will not grow as fast, Adding fertiliser replaces these lost materials so more energy from the ecosystem can be used to grow.

Question 33

How does livestock rearing increase the transfer of energy?

Answer 33

-Animals may be placed in warm, indoor pens where their movement is restricted. Less energy is wasted keeping warm and moving around.
-Animals may be given feed that’s higher in energy than their natural food which increases the energy input so more energy is available for growth.

Question 34

What is sucession?

Answer 34

The process of an ecosystem changing over time.

Question 35

What are the two types of succession?

Answer 35

Primary succession
Secondary succession

Question 36

What is primary succession?

Answer 36

This happens on land that has been newly formed or exposed. E.g a volcano has erupted to form a new rock surface or sea level has dropped exposing a new area of land. Theres no soil or organic material to start with just bare rock.

Question 37

What is secondary succession?

Answer 37

This happens on land that has been cleared of all the plants, but where soil remains e.g after a forest fire or where a forest has been cut down by humans so the pinoeer species are larger plants e.g shrubs.

Question 38

What is a pioneer species?

Answer 38

The first species to colonise an area.

Question 39

Explain the process of succession.

Answer 39

• Seeds and spores are blown in the wind and begin to grow on the new land surface. The first species to colonise the area are pioneer species.
• The abiotic conditions are harsh e.g no soil to retain water. Pioneer species only grow as they are specialised to cope with these conditions
• As pioneer species die and decompose, the dead organic matter forms a basic soil. This makes conditions less hostile as the soil can retain water which means new organisms can move here and grow. These then die and decompose and the new soil becomes deeper and richer in nutrients and minerals. This means larger plants can grow.
• As plants move in, animals move in due to habitats.
• Finally, the soil is sufficiently deep and contains enough nutrients to support the growth of large trees. The final species to colonise the new land becomes the dominant species of the now relatively complex ecosystem.

Question 40

What is the name of the final community formed, containing all the different plant and animal species that have now colonised the new land?

Answer 40

The climax community.

Question 41

What is a climax community?

Answer 41

The final community formed, containing all the different plant and animal species that have now colonised the new land is known as the climax community.

Question 42

What is the climax community called when succession is stopped artificially?

Answer 42

plagioclimax

Question 43

What is deflected succession?

Answer 43

When succession is prevented by human activities but the plagioclimax that develops is different to any of the natural stages of the ecosystem.

Question 44

Explain any example of deflected succession.

Answer 44

A grassy field would eventually develop into an area of shrubs or trees due to succession. However, regular mowing prevents these larger plants from establishing themselves so succession cannot occur.

Question 45

Why can preventing an area from reaching its climax community be beneficial?

Answer 45

The ecosystem at the intermediate stages of succession often hold a distinct diversity of plant species that would no longer exist if the climax community was reached. These diverse plant species also provide food and habitat from a high diversity of animal species some of which may be of conservation importance.

Question 46

How can we prevent an area from reaching its climax community?

Answer 46

E.g grazing animals may be introduced to temporarily eat the shrubs and trees.
Managed burning and controlled fires can burn away shrubs and trees to reset succession.