Ecosystems

Question 1

What is an ecosystem?

Answer 1

• All the living organisms that interact with each other in a defined area

Question 2

What are biotic factors?

Answer 2

Factors associated with living organisms in an ecosystem

Question 3

Name examples of biotic factors

Answer 3

• prey numbers
• predator numbers
• disease
• competition
• presence of producers and decomposers

Question 4

What are abiotic factors

Answer 4

Non living components

Question 5

Name examples of abiotic factors

Answer 5

• oxygen avaliability
• light intensity
• conc of pollutants
• soil type
• humidity
• storms
• temp
• water availibility

Question 6

Why are ecosystems described as being dynamic?

Answer 6

They are constantly changing as a result of changing biotic and abiotic factors

Question 7

Give an example of changing biotic elements

Answer 7

• organisms grow and die so pop sizes increase and decrease
• increase in pred causes decrease in prey

Question 8

Give an example of changing abiotic elements

Answer 8

• changes in light intensity and day length result in migration , hibernation and leaf fall
• loss of mineral ions from soil reduce plant growth

Question 9

What are cyclic changes?

Answer 9

• repeat themselves in a rhythm
• tides and seasons

Question 10

What are directional changes?

Answer 10

• changes which go in one direction only
• silting of an estuary, coastal erosion

Question 11

What is biomass?

Answer 11

• the dry mass of all the living material of an organism
• Proteins, carbs, nucleic acids, fats

Question 12

What are the units we use to scale biomass for land and water?

Answer 12

Land= gm-^2
Water= gm-^3

Question 13

How is biomass lost in a food chain?

Answer 13

• in dead organisms and waste materials
• becomes available to decomposers
• includes indigestible parts

Question 14

What are pyramids of biomass used to represent?

Answer 14

The idea that the higher the food chain level, the less biomass

Question 15

How do you calculate the dry mass of an ogranism?

Answer 15

1. collect organisms and cook then at 80c
2. until water has evaporated
3. check mass regularly, done when mass stops reducing

Question 16

Why is it better to calculate wet mass?

Answer 16

• Dry mass is destructive to ecosystems

Question 17

How can we calculate ecological efficiency?

Answer 17

Biomass at higher level / biomass at lower level

X100

Question 18

What is meant by productivity?

Answer 18

The rate at which energy passes through each trophic level in a food chain

Question 19

What is meant by gross primary productivity? GPP

Answer 19

The rate at which plants convert light energy into chemical energy through photosynthesis

Question 20

How much light energy is used in photosynthesis?

Answer 20

Around 40% and then 2/3 of glucose is used for production of starch, cellulose and lipids while the rest is respired.

Small proportion of energy from the sun enters the food chain

Question 21

What is the net primary productivity of the energy of the sun?

Answer 21

8%

Question 22

How is biomass manipulated?

Answer 22

• Light levels (crops planted early)
• Drought resistant strains and irrigating
• using greenhouses to manipulate temperature
• crop rotation to stop the reduction of inorganic materials in soil
• pesticides as pests remove some biomass
• removing competition
• fungicides

Question 23

How can humans manipulate energy transfer?

Answer 23

1. harvesting animals just before adulthood minimises loss of energy from food chain
2. selective breeding
3. animals treated with antibiotics
4. zero grazing and cattle farming maximises energy allocated to muscle by stopping animals from moving around

Question 24

What are the steps in saprotrophic decomposition?

Answer 24

1. Saprotrophs secrete enzymes onto dead and waste materials
2. enzymes digest material into small molecules which are absorbed into the saprotroph’s body
3. molecules are stored or respired to release energy

Question 25

Why can't plants use nitrogen directly?

Answer 25

It is impossible for plants to use it directly because it is very unreactive. They need a supply of fixed nitrogen

Question 26

How might nitrogen fixation occur?

Answer 26

- lightning strikes - haber process - accounts for only 10% of the world's nitrogen

Question 27

What are Azotobacter?

Answer 27

Bacteria that freely live in the soil and fix nitrogen gas using it to manufacture amino acids

Question 28

What are Rhizobium?

Answer 28

Live inside root nodules that provide fixed nitrogen and receive carbon compounds such as glucose in return

Question 29

What does leghaemoglobin do?

Answer 29

- Found in nodules - absorb oxygen and keep conditions anaerobic

Question 30

How are ammonium ions released?

Answer 30

Through ammonification by bacteria involved in putrefaction of proteins in dead or waste organic matter

Question 31

What type of bacteria are nitrosomonas and how do they gain energy?

Answer 31

Chemoautorophs They obtain energy by oxidising ammonium ions to nitrites