Ecosystems

Question 1

Components of an ecosystem

Answer 1

-Habitat, where organisms live.
-Population, organisms of one species in an area.
-Community, populations of different species.

Question 2

Biotic factors

Answer 2

-Living organisms within an ecosystem.
-Producers generate energy from autotrophic reactions (eg photosynthesis).
-Consumers feed on other organisms.
-Decomposers feed on waste material or dead organisms.

Question 3

Abiotic factors

Answer 3

-Non-living components of an ecosystem.
-pH, humidity, temperature, pollutants.
-Storms and natural hazards.
-Physical features, rocks, rivers.
-Extreme intensity leads first to lack of reproduction, then growth, and finally survival.

Question 4

Cyclic changes

Answer 4

-Repeat in a rhythm.
-Eg movement of tides, seasons.

Question 5

Directional changes

Answer 5

-Occur in one direction.
-Last longer than the lifetime of organisms.
-Eg deposition, erosion.

Question 6

Trophic level

Answer 6

-A level of the food chain.
-Biomass conserved decreases in higher trophic levels.
-This is because biomass is lost in respiration, metabolism, waste, and organisms dying to factors other than consumers.
-Expressed in a pyramid.

Question 7

Preparation of dry mass

Answer 7

-Organisms put into oven at 80C until water is evaporated.
-Shows biomass of an organism.
-However, is destructive, so wet mass is measure and calculated using old dry mass data.

Question 8

Ecological efficiency

Answer 8

-Biomass transfer between trophic levels.
-Biomass at higher level/Biomass at lower level x 100.

Question 9

Gross primary productivity

Answer 9

-Rate at which plants convert light energy into chemical energy through photosynthesis.
-Optimum 40% of sunlight enters light reaction of photosynthesis.
-Two-thirds of glucose used in production of starch, lipids, cellulose and proteins. Rest respired.

Question 10

Net primary productivity

Answer 10

-Energy from the sun that remains to enter the food chain from photosynthesis.
-8% in natural optimal.

Question 11

Secondary productivity

Answer 11

-Conversion of biomass of lower trophic levels by consumers into their own biomass.
-Small amount due to excretion of waste products, and respiration.

Question 12

Improving primary productivity

Answer 12

-Light banks to increase light harvesting.
-Irrigation and drought-resistance.
-Crop rotation increases available nutrients, stops reduction in inorganic minerals.
-Rotation coupled with nitrogen fixing plants such as peas.
-Pesticides or fungicides, or resistant strains.

Question 13

Improving secondary productivity

Answer 13

-Harvesting animals just before adulthood, as young animals invest more energy into growth.
-Selective breeding for faster growth rates and yields.
-Constant environmental temperature, and availability of food.

Question 14

Saprotrophs

Answer 14

-Decomposers.
-Secrete enzymes onto dead material, digesting it into small molecules.
-Absorbed into saprotroph’s body.
-Molecules are stored or respired to release energy.

Question 15

Nitrogen-fixing

Answer 15

-Nitrogen taken from air to be used by organisms.
-Occurs in Azotobacter bacteria free living in the soil.
-Occurs in Rhizobium in root nodules of leguminous plants.
-N2 becomes NH4+.

Question 16

Nitrification

Answer 16

-Ammonium (NH4) oxidised using Nitrosomonas bacteria into nitrite (NO2).
-Nitrite oxidised using Nitrobacter into nitrate (NO3).
-This can be absorbed by plants.

Question 17

Use of nitrate in plants

Answer 17

-DNA production.
-Protein synthesis.
-Growth.

Question 18

Ammonification

Answer 18

-Waste products (using a urease enzyme), dead plants, and dead animals that have eaten them are decomposed by saprotrophs.
-These release ammonium into the soil, which is then used again in nitrification.

Question 19

Denitrification

Answer 19

-In anaerobic conditions such as waterlogged soil.
-Denitrifying bacteria convert nitrate (NO3) into nitrogen (N2) and released it into the air, where it remains inert.

Question 20

Haber process

Answer 20

-Ammonia (NH2) converted to nitrate in factories and used to make fertilisers.
-Man-made process.

Question 21

Lightning in nitrogen cycle

Answer 21

-Lightning hits soil.
-N2 + O2 becomes either NO2 or NO3.
-If NO2 is produced then it is converted into NO3 by Nitrobacter.
-Eventually nitrate is produced.

Question 22

Carbon cycle

Answer 22

-CO2 in air and water enters plants through photosynthesis, with its products used in growth.
-Respiration from animals and plants releases this back into the air.
-Waste products and dead animals and plants are decomposed by saprotrophs, releasing stored carbon.
-Fossilised plants become fossil fuels, which release carbon dioxide upon combustion.

Question 23

Similarities between carbon cycle and nitrogen cycle

Answer 23

-Gases stored in organic matter, and in atmosphere.
-Influenced by human activity.
-Transfer through death and decomposition by saprotrophs.
-Absorbed from air by processes in plants.

Question 24

Differences between carbon cycle and nitrogen cycle

Answer 24

-No nitrifying bacteria needed in carbon cycle.
-Nitrogen gas is inert and must be converted through nitrification.
-Longer term storage in carbon (fossil fuels).
-Fewer transfers in carbon cycle.
-Different uses in plants.

Question 25

Succession

Answer 25

-The gradual, directional change in the species present in a community over time. -Leads to an increase in biomass.

Question 26

Primary succession

Answer 26

-Colonisation begins on bare rock, sand or water.

Question 27

Secondary succession

Answer 27

-Colonisation begins on pre existing soil, such as a ploughed field or a cleared forest.

Question 28

Climax community

Answer 28

-The final, stable, self-perpetuating community that exists after succession has finished.

Question 29

Deflected succession

Answer 29

-Where an area is kept in one stage of succession by humans. Final stage known as a plagioclimax. -For example, sheep grazing moorland, or burning, to prevent succession into woodland.

Question 30

Pioneer species

Answer 30

-First colonisers during succession. -Withstand extreme environments. -Photosynthesise and aid nitrogen fixation. -Germinate quickly. -Stabilise environment, aiding soil development and aiding water retention.

Question 31

Sere 1

Answer 31

-Pioneer species die. -Organic material enters soil.

Question 32

Sere 2

Answer 32

-New species arrive by vectors such as wind or animals. -Can survive due to increased organic material from dead pioneer species. -Likely outcompete existing species. -These die, and organic material in the soil further increases.

Question 32

Change in biomass in succession

Answer 32

-Increases as plants grow bigger due to increased habitat, and organic material in the soil. -Seres continue until climax community is reached.