energy and ecosystems

Question 1

Explain how energy enters an ecosystem

Answer 1

Energy enters an ecosystem in the form of sunlight which is used by plants in photosynthesis to produce organic molecules

Question 2

Explain how energy is transferred between organisms in an ecosystem

Answer 2

Consumers obtain their energy by feeding on other organisms in the food chain. Saprobionts are decomposers that break down the complex materials in dead organisms into simpler ones that can be recycled.

Question 3

Define the term trophic level

Answer 3

a stage in a food chain

Question 4

define food chain

Answer 4

describes the feeding relationships between organisms - the arrows represent the direction of energy flow

Question 5

define food web

Answer 5

all of the food chains within a specific habitat and how they link

Question 6

define producer

Answer 6

photosynthetic organisms that manufacture organic substances

Question 7

define consumer

Answer 7

organisms that obtain their energy by consuming other organisms

Question 8

define decomposer

Answer 8

also known as saprobionts,break down the complex materials in dead organisms into simpler ones that can be recycled

Question 9

Calculate the percentage of energy that is transferred from one trophic level to the next

Answer 9

-Unit: kilojoules per square metre per year
-Percentage efficiency = energy available after transfer/energy available before transfer x 100”

Question 10

Explain how energy is lost along a food chain

Answer 10

-Plants convert approx 1% of the suns light energy into organic molecules because:
- energy is reflected back to space by clouds or absorbed by atmosphere
- not all wavelengths of light are absorbed by leaves
- light may miss the chlorophyll molecule
- other factors may limit rate of photosynthesis
Energy is lost at each stage in a food chain because:
- some parts of organisms may not be consumed
- some parts of organisms cannot be digested (lost in faeces)
- energy lost in excretory materials (urine)
- energy lost as heat to the environment from respiration - highest in mammals and birds due to maintenance of body temperature”

Question 11

Explain what is meant by gross primary productivity and net primary productivity

Answer 11

-GPP: total quantity of chemical energy stored in plant biomass, in a given area/volume in a given time
-NPP: the chemical energy store remaining in plants after losses through respiration (NPP=GPP-R (respiratory losses))”

Question 12

Summarise the common features of all nutrient cycles

Answer 12

• Nutrient taken up by producers as simple inorganic molecules
• Producer incorporates nutrient into complex organic molecules
• Nutrient passed on to consumers when producer is eaten
• Nutrient passed along food chain to other consumers
• When organisms die the complex molecules are broken down by saprobiontic microorganisms (decomposers) and nutrient is released in it’s original simple form to be recycled

Question 13

Describe the features of the nitrogen cycle

Answer 13

-Living organisms required source of nitrogen to manufacture proteins and nucleic acids, most are unable to access the nitrogen from the atmosphere.
-Plants obtain nitrogen by active transport from nitrate ions in the soil
-Animals obtain nitrogen containing compounds by consuming other organisms
-Microbes return nitrate ions to the soil through decomposition

Question 14

Define the term ammonification

Answer 14

production of ammonia from organic nitrogen containing compounds by saprobiotic organisms

Question 15

define nitrification

Answer 15

nitrifying bacteria carry out oxidation reactions to convert ammonium ions into nitrites and then nitrates

Question 16

define nitrogen fixation

Answer 16

nitrogen gas is converted into nitrogen containing compounds in a variety of ways. Haber process, lightening, by nitrogen fixing bacteria. There are two type of nitrogen fixing bacteria: free living bacteria which convert nitrogen gas into ammonia. Mutualistic nitrogen fixing bacteria live in the root nodules of legumes and obtain carbohydrates from the plant whilst providing a supply of amino acids they have fixed from nitrogen gas.

Question 17

define denitrification

Answer 17

anaerobic denitrifying bacteria reside in waterlogged soil and convert nitrates into gaseous nitrogen

Question 18

Describe the features of the phosphorous cycle

Answer 18

-Phosphorus stored in phosphate ions in sedimentary rock
-Weathering and erosion of phosphate in rock, ions dissolved in water
-Phosphate ions taken up by plant roots and incorporated into biological molecules
Feeding and digestion by consumers
-Phosphate ions in animal waste and remains of animals
-Decomposition by saprobionts
Washed back into the sea and incorporated into sedimentary rock”

Question 19

Explain the roles of saprobiontic organisms in nutrient recycling

Answer 19

-Saprobiontic organisms (decomposers) break down complex molecules in consumers and producers when they die and release the nutrient in its original simple to be taken up by producers