Chapter 5 Ecosystems

Question 1

What is an abiotic factor?

Answer 1

Non-living components of an ecosystem that affect living organisms.

Question 2

What is a biotic factor?

Answer 2

An environmental factor associated with living organisms in an ecosystem that affect each other, e.g. predatation

Question 3

What is an ecosystem?

Answer 3

A community of animals, plants and bacteria interrelated with the physical and chemical environment.

Question 4

What are producers?

Answer 4

Plants (and some other photosynthetic bacteria) which supply chemical energy to all other organisms

Question 5

What are consumers?

Answer 5

Primary consumers are herbivores which feed on plants. Primary consumers are eaten by carnivorous secondary consumers. Secondary consumers are eaten by carnivorous tertiary consumers.

Question 6

What are decomposers?

Answer 6

Decomposers (bacteria, fungi and some animals) feed off waste material or dead organisms.

Question 7

What is a habitat?

Answer 7

The place where an organism lives

Question 8

What is a population?

Answer 8

All of the organisms of one species, who live in the same place at the same time, and who can breed together.

Question 9

What is a community?

Answer 9

All the populations of different species, who live in the same place at the same time, and who can interact with each other.

Question 10

What is a niche?

Answer 10

The role of an organism within its habitat.

Question 11

What are the 3 types of change in ecosystems that affect population size?

Answer 11

• Cyclic changes: changes repeat themselves in a rhythm, e.g. movement of tides, changes in day length and the way in which predator and prey species fluctuate.
• Directional changes: changes in one direction that tend to last longer than the lifetime of organisms in the ecosystem, e.g. erosion of a coastline or deposition of silt in an estuary.
• Unpredictable/ erratic changes: no rhythm and no constant direction, e.g. effect of lightening or a hurricane.

Question 12

What is meant by biomass transfer?

Answer 12

Transfer of biomass from one trophic level to the next.

Question 13

How do you calculate ecological efficiency?

Answer 13

(biomass at higher trophic level / biomass at lower trophic level) x 100

Question 14

How do ecologists measure dry mass of an organism to draw a pyramid of biomass?

Answer 14

Collects the organisms, puts them in an oven at 80°C and periodically checks their mass. Once the mass stops reducing all the water has been evaporated.

Question 15

How is energy lost at each trophic level?

Answer 15

• Energy is used in metabolic reactions, e.g. respiration
• Some parts of animals cannot be digested by consumers, e.g. bones
• Lost in dead organisms, which are then only available to decomposers
• Plants don’t use all available light energy (e.g. sunlight reflected)
• Excretion

Question 16

What happens to light from the sun that is not transferred into plant biomass?

Answer 16

• Reflected off the leaf
• Evaporates water from the leaf
• Energy losses from chemical reactions

Question 17

What is Gross Primary Productivity (GPP)?

Answer 17

The rate at which plants convert light energy into chemical energy through photosynthesis. (Units could be g m^-2 yr^-1 or K calm^-2 yr^-1

Question 18

How do ecologists measure dry mass of an organism to draw a pyramid of biomass?

Answer 18

Collects the organisms, kill organisms, put them in an oven at 80°C and periodically checks their mass. Once the mass stops reducing all the water has been evaporated.

Question 19

How do you calculate Net Primary Productivity?

Answer 19

NPP = GPP- plant respiration

Question 20

How can primary productivity be increased?

Answer 20

• Grown under light banks so light is not a limiting factor
• Drought-resistant crops
• Greenhouses provide warmer temperatures
• Crop rotation (growing a different crop in each field on a rotation cycle) stops reduction in soil level of nutrients such as nitrate
• Spraying with pesticides to kill insects
• Spraying with herbicides to kill weeds
• Spraying with fungicides to prevent fungal infections
• Crops are planted early to provide a longer growing season to harvest more light and avoid impact of temperature
• Irrigation

Question 21

What is Net Primary Productivity (NPP)?

Answer 21

The energy from the sun that enters the food chain.

Question 22

How can secondary productivity be increased?

Answer 22

• Harvest animals just before adulthood as young animals use more energy to grow
• Selective breeding
• Animals treated with antibiotics to prevent loss of energy to parasites
• Zero grazing for pig & cattle farming stops them moving

Question 23

What is the name given to bacteria and fungi involved in decomposition and how do they feed?

Answer 23

Saprotrophs because they feed saprotrophically:
1. Saprotrophs secrete enzymes onto dead and waste material
2. Enzymes digest the material into small molecules which are then absorbed into saprotrophs body
3. The absorbed molecules are stored or respired to release energy.

Question 24

What is nitrogen fixation?

Answer 24

Nitrogen gas in the atmosphere is converted to ammonia by bacteria such as Rhizobium and Azotobacter by anaerobic respiration.

Question 25

Where are Azotobacter found?

Answer 25

Live freely in the soil

Question 26

Where are Rhizobium found?

Answer 26

Inside root nodules of leguminous plants. They form mutualistic relationships with the plants by providing them with nitrogen compounds and receiving carbohydrates.

Question 27

What is ammonification?

Answer 27

Nitrogen compounds in dead organisms and animal waste are converted to ammonia by decomposers which then form ammonium ions.

Question 28

What is the process of nitrification?

Answer 28

1. Nitrifying bacteria ‘nitrosomonas’ change ammonium ions into nitrites
2. Nitrifying bacteria ‘nitrobacter’ change nitrites into nitrates which can be used by plants

Question 29

What is denitrification?

Answer 29

Nitrates in the soil are converted to nitrogen gas by denitrifying bacteria by carrying out anaerobic respiration to produce nitrogen gas (e.g. in waterlogged soils)

Question 30

What is a climax community?

Answer 30

The final stable community that exists after the process of succession has occurred.

Question 31

What is deflected succession?

Answer 31

When succession is stopped or interfered with, e.g. by grazing or when a lawn is mowed.

Question 32

What is a pioneer species?

Answer 32

The species that begin the process of succession, often coloninising an area as the first living things there.

Question 33

What is succession?

Answer 33

Progressive change in a community of organisms over time.

Question 34

What is the process of primary succession?

Answer 34

1. Algae and lichens begin to live on bare rock (pioneer community).
2. Erosion of the rock and build up of dead, rotting organic material produce enough soil for larger plants like mosses and ferns to grow. These replace, or succeed, algae and lichen.
3. In a similar way, larger plants succeed these small plants, until a final, stable community is reached (climax community).

Question 35

What is secondary succession?

Answer 35

Succession from a previously colonised, but disturbed/ damaged area.

Question 36

What is the result of deflected succession?

Answer 36

A plagioclimax

Question 37

What are the stages of succession on sand dunes?

Answer 37

1. Pioneer species like sea rocket colonise the sand just above the high water mark.
2. Wind-blown sand builds up around the base of the plants forming a mini sand dune. As plants die and decay, nutrients accumulate causing the dune to get bigger so plants like sea couch grass colonise it. These have underground stems to stabilise it.
3. With more stability and accumulation of nutrients plants like marram grass start to grow. Marram grass shoot’s trap more sand and as sand accumulates shoots grow taller to stay above the growing dune.
4. As the sand dune and nutrients build up other plants colonise it. Some are leguminous so convert nitrogen to nitrate, causing more species to colonise, stabilising them more.

Question 38

Why does a decline occur when approaching a climax community?

Answer 38

The dominant species out competes the other species, e.g. large plants outcompete those on the woodland floor.

Question 39

Do species in the pioneer community have a high or low biomass?

Answer 39

Low