Energy and Ecosystems / Nutrient Cycles

Question 1

What is the ultimate source of energy? + Why is it needed?

Answer 1

Sunlight, in order to make organic compounds from CO2/Water

Question 2

What are producers?

Answer 2

photosynthetic organisms that manufacture organic substances using light, water, CO2 and mineral ions

Question 3

What are consumers?

Answer 3

organisms that obtain energy by feeding on other organisms. Those that directly eat producers are called primary consumers and those animals eating primary consumers are called secondary consumers etc.

Question 4

What are saprobionts?

Answer 4

(decomposers) break down complex materials in dead organisms to simpler ones, mainly fungi and bacteria.

Question 5

What is a food chain?

Answer 5

Food chain: stages in a food chain are called trophic levels, arrows show direction of energy flow.

Question 6

What is a food web?

Answer 6

many food chains joined together but they are complex

Question 7

What is biomass?

Answer 7

total mass of living material in a specific area at a given time. Unreliable due to the varying amounts of water, dry biomass involves organisms being killed so sample sizes are small thus it is not representative. Measured in grams per square metre (g m-2)

Question 8

How much of the suns energy is converted into organic matter?

Answer 8

1-3%

Question 9

Why is most of the suns energy not converted to organic matter in photosynthesis?

Answer 9

• rate of photosynthesis may be limited
• not all wavelengths of light can be absorbed
• 90% of energy is reflected back to space by clouds.

Question 10

What is gross primary production (GPP)?

Answer 10

is the total quantity of chemical energy in plant biomass in a given area/volume, in a given time. However 20-50% is used in respiration.

Question 11

What is net primary production (NPP)?

Answer 11

chemical energy left when losses from respiration have been taken into account

Question 12

How is net primary production calculated?

Answer 12

Net primary production (NPP)= gross primary production - respiratory losses

Question 13

Why is a low percentage of energy transferred between each trophic level?

Answer 13

• some organism not consumed
• some parts cannot be digested so lost in faeces
• lost in urine (excretory materials)
• lost as heat in respiration, this is high in mammals/birds because of their high body temperatures (lots of energy is required to maintain this)

Question 14

What is the equation for net production of consumer?

Answer 14

chemical energy store in ingested food - (energy lost in faeces/urine + energy lost in respiration)

N= I - (F + R)

Question 15

What does the inefficiency of energy transfer between trophic levels explain?

Answer 15

• most food chains have only 4-5 trophic levels as there is not enough energy to support a bigger population
• biomass is lower in higher trophic levels
• total amount of energy available at each level is less going up the chain

Question 16

What is a flow chart of energy transfer efficiency?

Answer 16

Sun → 1-3% Primary Producers → 5-10% Primary Consumers → 15-20% Secondary Consumers → 15-20% Primary Consumers

Question 17

What is the equation for energy efficiency?

Answer 17

Percentage efficiency = energy available after / energy available before x 100

Question 18

What percentage of the atmosphere is nitrogen?

Answer 18

78%

Question 19

What are the 4 stages of the nitrogen cycle?

Answer 19

Ammonification, Nitrification, Nitrogen Fixation, Denitrification

Question 20

What occurs in Ammonification?

Answer 20

production of ammonia from organic nitrogen-containing compounds e.g urea, proteins, nucleic acids, vitamins. Saprobionts feed on faeces/dead organisms which releases ammonia and forms ammonium ions.

Question 21

What occurs in Nitrification?

Answer 21

Conversion of ammonium ions to nitrate ions which is an oxidation reaction and releases energy. Carried out by nitrifying bacteria, that require oxygen for these conversions air spaces in, in 2 stages:

• oxidation of ammonium ions to nitrite ions (NO2-)
• oxidation of nitrite ions to nitrate ions (NO3-)

Question 22

What occurs in Nitrogen Fixation? (2 types of bacteria)

Answer 22

Nitrogen gas is converted into nitrogen containing compounds by microorganisms:
-free-living nitrogen-fixing bacteria: gaseous nitrogen is reduced to ammonia to produce amino acids

-mutualistic nitrogen-fixing bacteria: live in roots of plants and obtain carbohydrates from them, give amino acids to the plant

Question 23

What occurs in Denitrification?

Answer 23

Soils become waterlogged thus have a low oxygen concentration and therefore there is fewer aerobic nitrifying/nitrogen fixing bacteria found but there is an increase anaerobic denitrifying bacteria, which convert soil nitrates into nitrogen gas. The availability of nitrogen-containing compounds for plants then reduces. For productivity to be high in land, soil needs to be kept aerated in order to prevent the growth of denitrifying bacteria.

Question 24

Why is phosphorus important?

Answer 24

Phosphorus is a key part of ATP, phospholipids and nucleic acids thus phosphorus needs to be constantly recycled

Question 25

What is Mycorrhizae?

Answer 25

Fungi which allow extensions of a plants root system in order to increase surface area for the absorption of water and minerals

Question 26

Why is Mycorrhizae useful?

Answer 26

plants can resist drought and take up inorganic ions more easily (that may be scarce like phosphate ions).

Question 27

What type of relationship does Mycorrhizae have with plants? + WHY

Answer 27

mutualistic relationship with plants as it receives organic compounds like sugars from the plant whilst the plant receives inorganic ions.

Question 28

What is the purpose of fertilisers?

Answer 28

Increase the efficiency of energy transfer and thus improve productivity
Fertilisers are added to the soil in order to prevent the loss of mineral ions

Question 29

What are organic (natural) fertilisers?

Answer 29

made of dead remains of plants, animals and animal wastes such as manure and bone meal

Question 30

What are inorganic (artificial) fertilisers?

Answer 30

mined from rocks and converted into different forms by being blended together with other minerals to create a balance for crops e.g nitrogen, phosphorus and potassium.

Question 31

What is the best fertiliser for farmers to use?

Answer 31

A combination of natural and artificial fertilisers give the greatest long term increase of productivity

Question 32

Why do fertilisers increase productivity?

Answer 32

they allow minerals to be readily available so that plants cam develop earlier, grow taller, have greater area on their leaves thus this increases rate of photosynthesis and hence productivity.

Question 33

What are detrimental effects of using nitrogen-containing fertilisers?

Answer 33

• reduced species diversity: due to competition between grass, nettles etc which out-compete other species and causes them to die
• leaching: leading to pollution of water sources
• eutrophication: as a result of leaching

Question 34

What is leaching?

Answer 34

process of nutrients being removed from the soil, rainwater dissolves soluble nutrients like nitrate ions and these will be transported to water sources like rivers. This can be harmful to humans if a source of drinking water and can lead to eutrophication

Question 35

What is the process of eutrophication?

Answer 35

Eutrophication - nutrient concentrations increase in water

1. Algae blooms block light
2. No photosynthesis so plants die
3. Saprobiotic decomposition occurs
4. Microorganisms respire aerobically and thus use up all oxygen
5. Not enough oxygen for fish for respiration so they die
6. Microorganisms release harmful toxins/hydrogen sulphide etc
7. Water is polluted

Question 36

Refer to flow charts of nitrogen and phosphorus cycles

Answer 36

;)