C.2 Communities and ecosystems

Question 1

What is a biome?

Answer 1

A biome is a community of plants and animals that occupy a major habitat or region eg. tropical rainforest.

Question 2

What is a trophic level?

Answer 2

The position of an organism in a food chain.

Question 3

What are food webs?

Answer 3

They show possible combination of food chains within a community. A food web is made out of multiple food chains.

Question 4

What is biomass?

Answer 4

The total of dry mass in organisms or ecosystem.

Question 5

Explain feed conversion ratio and its implication.

Answer 5

FCR refers to the rate which animals assimilate the food that they consume in order to build biomass and grow. It is important as it affects farmers in economic terms. They determine the food mass required to feed an animal and compare it with the biomass they produce.

Feed ratio: Mass of food consumed (kg) / Body mass gain (kg)

Question 6

Define Poikilotherm

Answer 6

Is an animal that has variable body temperature according to its surroundings (Atlantic salmon has lower FCR because of this.)

Question 7

Define Homeotherm.

Answer 7

Is an animal that maintain regulated body temperature through physiological mechanism

Question 8

What is the difference between climate and weather?

Answer 8

It is a matter of time. Climate refers to temperature and precipitation patterns during a longer period of time. While weather refers to the temperature and precipitation during a shorter time period.

Question 9

What can climate be affected by?

Answer 9

Altitude, longitude, nearby bodies of water such as lakes or rivers. An example is the Caucasus mountains where temperature at sea level is 15C while at higher altitude decreases to 6C. (lower temperature leads to higher rainfall)

Question 10

What is the difference between a biome and an ecosystem?

Answer 10

A biome refers to a community that is shaped by common environmental conditions while an ecosystem refers to interaction between biotic and abiotic factors. There can exists multiple ecosystems in a biome.

Question 11

Describe Robert Whitakers system of biomes.

Answer 11

He classified 9 biomes based on precipitation and temperature. Tropical rainforests, tropical seasonal forest, temperate rainforest, temperate deciduous, Woodland, Taiga, Savanna, desert, tundra,

Question 12

Explain how precipitation and temperature affects biomes

Answer 12

Temperature can affect cellular respiration, photosynthesis, decomposition of organic matter. Precipitation provides water to plants and animals increasing biomass and it connects to temperature to ensure that communities adapt and thrive.

Question 13

How much energy is lost between each trophic level and why?

Answer 13

Typically 90% of energy is lost between each trophic level. This is due to multiple reasons:

• Energy is lost as heat from cellular respiration
• Not all biomass of organisms are consumed, and is broken down by decomposers and lost as heat
• Energy is lost through faeces and urine which is broken down by decomposers and lost as heat
• Some of the biomass is indigestible and excreted, and broken down by decomposers and lost as heat

Question 14

Define excretion

Answer 14

Is the removal of waster products from metabolic reactions.

Question 15

Define egestion

Answer 15

Removal of undigested materials from the body.

Question 16

How is energy represented and what unit is used?

Answer 16

Energy at each trophic level is represented by the pyramid of energy which uses a unit of Kj m-2 yr-1.

Question 17

What is the Gersmehl nutrient cycle?

Answer 17

It brings together abiotic and biotic factors. It is a graphical representation of how Biomass, Litter and Soil is interconnected to recycle nutrients for plants and animals living within an ecosystem.

Question 18

How does a tropical rainforest look like according to Gersmehl nutrient cycle?

Answer 18

The majority of the nutrients are in the biomass and not in litter and soil. There is a fast rate of nutrient transfer between stores. This is due to high temperatures and precipitation causing high productivity and many layers of vegetation. There is also high rate of decomposition by decomposers.

Question 19

How does a desert look like according to Gersmehl nutrient cycle?

Answer 19

Biomass and litter have few nutrients while the soil has the most nutrients. This is due to the low rainfall resulting in low biomass and therefore low litter in form of dead leaves and other vegetation.

Question 20

How does a taiga look like according to Gersmehl nutrient cycle?

Answer 20

In taiga Litter contains the most nutrients. Soil contains low nutrients due to low temperatures restricting weathering. Low temperature also reduces the rate of breakdown due to low saprotroph activity.

Question 21

Why are topical rainforests important ecosystems?

Answer 21

They account for a large uptake of the carbon dioxide in the atmosphere and release of oxygen. They also contain great biodiversity.

Question 22

How does human interference affect rainforest and in turn the environment?

Answer 22

Humans cut down rainforests for farming of wood or for land to farm cattle, agriculture, road networks and so on. This increases amount of carbon dioxide in the atmosphere, reduces protection of moist soil from the heat.

Question 23

What is ecological succession?

Answer 23

It is when there are continual changes in a community until a climax community is reached. Where an ecosystem develops from a simpler colonised community to a climax community.

Question 24

What is primary succession?

Answer 24

It begins with lifeless land.

• Then there are pioneer species that refers to lichens or moss.
• After many years the lichens will breakdown barren land into soil
• Now simple grass can grow
• Grass modify the soil in which other vegetation can grow.
• this continues until a stable climax community is reached.

Question 25

Give examples of primary succession.

Answer 25

Examples are glacier bay; as glacier melts primary succession occurs gradually. The longer ago the melting of the ice the more complex the community.

Krakatau islands; a series of volcanic eruptions led to the lifeless land at the krakatau island. Many years later there were pioneer species seen across the land

Question 26

What is net productivity?

Answer 26

Is the amount of energy available to primary consumers after plants have performed cell respiration. Formula: Gross production - cell respiration (Kj m-2 yr-1)

Question 27

What is gross production?

Answer 27

Total amount of organic matter produced by plants in an ecosystem

Question 28

Distinguish between primary and secondary succession-

Answer 28

In primary succession soil is lifeless, there is no soil, occurs after an environmental upheaval, reproductive remnants are not present, pioneer species arrive from nearby ecosystems, it takes up to 1000 years to reach climax community.

In secondary succession there is soil, it occurs in an area that was recently inhabited, occurs following an environmental upheaval, reproductive remnants are present, pioneer species develop from previous occupants, it takes up to 200 years to reach climax community.

Question 29

Explain different stages of secondary succession.

Answer 29

1. Initial decline in biomass following upheaval
2. There is increase productivity and respiration in the system (aggradation) as biomass increases
3. During transition period there is increased diversity as organisms compete decreasing biomass
4. Climax community is then established in steady phase state

Question 30

Define closed ecosystem

Answer 30

a system where energy enter and leaves however matter stays and cycles around.

Question 31

Define open ecosystem

Answer 31

a system where energy and mass enter and exit