chapter 23 - ecosystems

Question 1

What are ecosystems?

Answer 1

• its the distrubution of organisms that are controlled biotic and abiotic factors

Question 2

What is meant by tropic level?

Answer 2

• each stage of the food chain

Question 3

What is gross primary productivity and what is it made up of?

Answer 3

• its the total amount of energy made by producers
• its made up of respiratory loss and net primary production(biomass)

Question 4

What is the difference between respiratory loss and net primary production?

Answer 4

• respiratory loss, the energy used by organisms for respiration (e.g active transport, movement, heat)
• net primary production, is the amount of chemical energy a producer stores as biomass

Question 5

why is the energy tranfer from the sun to the producer very low(roughly 2%)?

Answer 5

• wrong wavelength
• light strikes non photosynthetic region
• light reflected
• lost as heat

Question 6

why is energy tranfer from the producer to the primary consumer low(roughly 10%)?

Answer 6

• there is respiratory loss, plant uses energy for metabolism(e.g active transport)
• lost as heat
• not all the plant is eaten(roots)
• some food is not digested

Question 7

Why is the energy tranfer from the primary consumer to the secondary consumer low(roughly 10-15%)?

Answer 7

• there is respiratory loss, primary consumer uses energy for metabolism (e.g muscle contraction)
• lost as heat
• not all the animal is eaten
• some of the food not digested (e.g faeces)

Question 8

describe and explain the two ways in which we can increase energy tranfer in crop plants?

Answer 8

• shorten the food web, reduce competition so the plant has more energy to create biomass(herbicide to kill weeds, fungicide to reduce infection, insecticide to chemically control pests)
• fertilisers(e.g nitrates), prevent growth being limited by lack of nutrients

Question 9

What four ways can we increase the energy transfer in animals and livestock?

Answer 9

• reduce respiratory loss, restrict movement and so less respiration and more energy is used to make biomass
• slaughter animal while growing
• controlled diet, higher yield of food will be digested
• keep predators away

Question 10

What way can we increase energy transfer in both animals and plants?

Answer 10

• artificially select organisms with a high yield

Question 11

What are the two ways to measure biomass?

Answer 11

• dry biomass
• mass of carbon

Question 12

How is dry biomass used to measure biomass?

Answer 12

• a sample is taken of biomass and is warmed until the mass is constant (all the water has evapourated)
• the temperature must be low to avoid combustion as there would be a loss of biomass/co2

Question 13

Why isnt a wet sample used when using the dry biomass method in measuring biomass?

Answer 13

• the amount of water in biomass samples varies a lot
• and so dry biomass gives a more representative sample

Question 14

How is energy stored in biomass calculated and explain how it works?

Answer 14

• calorimetry
• burn a sample of biomass completely
• heat a known volume of water
• measure the temperature change of water
• calculate energy released

Question 15

how is the mass of carbon used to measure biomass?

Answer 15

• organisms are made from organic compounds
• mass of carbon is a good indicator for biomass
• difficult to measure
• carbon is about 50% of the dry biomass

Question 16

What is succession?

Answer 16

• a series of changes in a species composition in a given place over time

Question 17

explain the process of succession

Answer 17

• an area is colonised by pioneer species, this changes the enviornmental conditions to make it less hostile(increase in nutrients)
• this allows other species to outcompete the preceeding species
• continues until climax community is reached (woodland)

Question 18

What is a climax community?

Answer 18

• final stage of succesion, few species dominate, and stable equilibrium of species

Question 19

As succession takes place what increaeses?

Answer 19

• biodiversity
• niches
• plant height
• soil depth
• h20 + nutrients available

Question 20

As succession takes place what decreases?

Answer 20

• light intensity at ground

Question 21

describe primary succession

Answer 21

• starts from newly formed land (e.g volcanic rock)
• harsh abiotic factors (e.g no soil, little H20/nutrients)

Question 22

describe secondary succession

Answer 22

• starts from land where vegetation has been cleared (e.g human deforestation/forest fire)
• less harsh abiotic factors(soil already exists, more h20/nutrients available)
• much faster
• pioneer species can be larger

Question 23

describe deflected succession

Answer 23

• a community that remains stable because human activity prevents natural succession from taking place (mowing)
• this stops succession and stops tall plants growing and these plants can outcompete low growing grass
• grassland becomes climax community

Question 24

What are the 3 ways in which nitrogen fixation occurs?

Answer 24

• industrially
• with the use of bacteria
• lightning

Question 25

What is the name of the bacteria used to fix nitrogen gas in the atmosphere into ammonium ions?

Answer 25

• aztobacter

Question 26

What is the name of the bacteria used in denitrification?
what type of conditions does this bacteria live in?

Answer 26

• pseudomonas
• aerobic conditions

Question 27

How does the bacteria
Rhizobium convert nitrogen and hydrogen to ammonia

Answer 27

• it contains an enzyme called hydrogenase

Question 28

To convert ammonium ions to nitrate what processes does it undergo?

Answer 28

• undergoes nitrification twice

Question 29

What is saprobioutic nutrition?

Answer 29

• digestion of dead organic matter by extracellular enzymes

Question 30

Where can nitrogen be found in animals and plants?

Answer 30

• protein
• dna

Question 31

What is the only way in which co2 is removed from the atmosphere?

Answer 31

• photosynthesis by plants

Question 32

what are decomposers?

Answer 32

• they are organisms that feed on dead plants or animal matter