B4 - ecosystems (from PMT)

Question 1

give 3 molecules which are cycled through ecosystems

Answer 1

oxygen, carbon dioxide and water

Question 2

briefly describe how water is cycled through an ecosystem

Answer 2

-water evaporates from rivers and lakes and from transpiration
-water condenses as clouds
-water is returned through precipitation

Question 3

describe how carbon dioxide is cycled through an ecosystem

Answer 3

-carbon dioxide is fixed through photosynthesis
-respiration releases carbon dioxide
-decomposition releases carbon dioxide
-combustion releases carbon dioxide

Question 4

briefly describe how nitrogen is cycled through an ecosystem

Answer 4

-nitrogen is fixed by lightning, the Haber process and bacteria
-denitrifying bacteria release nitrogen back to the atmosphere

Question 5

why is recycling in ecosystems necessary?

Answer 5

-to create a continuous flow of nutrients
-to provide fresh water

Question 6

how would a decrease in oxygen availability affect the rate of decomposition?

Answer 6

-lack of oxygen causes microorganisms to respire anaerobically
-anaerobic decay is slower than aerobic decay

Question 7

how would a decrease in water availability affect the rate of decomposition?

Answer 7

-decomposing microorganisms need water for chemical processes
-the less water available, the slower the rate of these processes

Question 8

how would a change in temperature affect the rate of decomposition?

Answer 8

-a decrease in temperature slows the rate of the decomposition reactions
-a large increase in temperature will denature enzymes, slowing or even stopping decomposition

Question 9

give 4 abiotic factors that affect communities

Answer 9

-light intensity
-temperature
-soil pH
-moisture levels

Question 10

give 4 biotic factors that affect communities

Answer 10

-number of predators
-food availability
-disease
-human activity

Question 11

what are the 3 types of interdependence?

Answer 11

mutualism, parasitism and predation

Question 12

give 4 things that animals compete for

Answer 12

-mates
-space
-food
-water

Question 13

give 4 things that plants compete for

Answer 13

-light
-water
-minerals
-space

Question 14

what is a producer?

Answer 14

an organism that makes its own food

Question 15

what is biomass

Answer 15

the dry mass of all of the living organisms in an area

Question 16

why is dry mass used for biomass?

Answer 16

because the wet mass varies as the amount of water in the organism varies

Question 17

why are biomass transfers not 100% efficient?

Answer 17

energy is lost through:
-egestion
-excretion
-respiration
-the production of inedible bones and shells