Chapter 13 - Energy and Ecosystems

Question 1

What is the source of energy for an ecosystem?

Answer 1

Sunlight

Question 2

Define biomass

Answer 2

Total dry mass of living material measured in specific area or over a given time period. Measured in grams per m2 or m3

Question 3

Define producers

Answer 3

Plants that perform photosynthesis and use light to make biological molecules

Question 4

Define consumers

Answer 4

Organisms that obtain their energy by feeding on other organisms as they cannot make biological molecules from sunlight. Two types: primary and secondary

Question 5

Distinguish between primary and secondary consumers

Answer 5

Primary are first consumers in the chain that feed on producers
Secondary consumers feed on primary consumers

Question 6

Define saprobionts

Answer 6

Also known as decomposers/ Organisms that break down complex materials in dead organisms to simples ones. They include bacteria and fungi and perform saprobiotic decomposition

Question 7

What is a food chain?

Answer 7

Chain describing feeding relationship where producers eaten by consumers etc. Each stage is called a trophic level

Question 8

How can the chemical energy in dry biomass be estimated?

Answer 8

• Bomb calorimetry
• Dry material weighed then burnt in oxygen surrounded by water
• Specific heat capacity used

Question 9

Why do producers need biological molecules?

Answer 9

• Glucose for respiration and make starch/glucose
• Amino acids for proteins
• Fatty acid + Glycerol for triglyceride and membranes

Question 10

Why do consumers need biological molecules?

Answer 10

• Glucose for respiration and store glycogen
• Amino acids for proteins
• Fatty acid + Glycerol for triglyceride, insulation and membranes

Question 11

Why do decomposers need biological molecules?

Answer 11

• Glucose for respiration
• Amino acids for proteins
• Fatty acid + Glycerol for membranes

Question 12

How much energy is harnessed from the sun by producers?

Answer 12

1% - 3%

Question 13

Why is most of the suns energy not converted into organic matter by producers?

Answer 13

• 90% reflected back into space
• Not all wavelengths of light absorbed
• Light does not fall on chlorophyll molecule
• Limiting factors such as low CO2

Question 14

What is gross primary production?

Answer 14

Total chemical energy store in plant biomass in a given area or volume

Question 15

Give the equation for net primary production in plants

Answer 15

Gross primary production MINUS respiratory losses

Question 16

What are the reasons for low energy transfer between trophic levels?

Answer 16

• Some of organism not consumed
• Some parts consumed by not digestible so lost if faeces
• Some lost in excretory materials
• Energy lost as heat from respiration

Question 17

What is the equation for the net production of consumers?

Answer 17

N = I - (F+R)
N = net production
I = Chemical energy of ingested food
- F = Energy lost in p=faeces
R = Energy lost in respiration

Question 18

Inefficiency of energy transfer in trophic levels explains what?

Answer 18

• Max four or five trophic levels
• Total biomass less at higher trophic levels
• Total amount of energy available less as trophic levels progress

Question 19

What is the percentage efficiency equation for energy transfer?

Answer 19

Energy available after transfer divided by energy available before transfer multiplied by 100

Question 20

How much energy is transferred from producer to consumer?

Answer 20

10%

Question 21

How much energy is transferred from consumer to consumer?

Answer 21

20%

Question 22

Why is energy transfer high between consumers?

Answer 22

Consumers more edible and digestible whereas producers made up of cellulose

Question 23

Describe the path taken by nutrients

Answer 23

• Nutrient taken up by producers
• Producer incorporates nutrient into complex molecule
• Consumer eats producer and nutrients
• Passes along food chain
• When consumer dies, saprobiotic decomposition occurs releasing nutrients

Question 24

Summarise the WHOLE nitrogen cycle

Answer 24

• Nitrogen in atmosphere as gas N2
• Plants can only absorb NO3-
• N2 converted into ammonium ions NH4+ by nitrogen fixation by nitrogen fixing bacteria (mutualistic in roots of leguminous plants or free living in soil)
• NH4+ converted into NO3- ions by nitrification by nitrifying bacteria
  where NH4+ oxidised into NO2- then oxidised into NO3-
• NO3- absorbed by plants to make AA/proteins
• Consumers eat plant to obtain AA
• Organic material broken down by saprobiotic decomposers releasing NH4+ into soil (ammonification)
• Nitrate ions (NO3-) converted back into N2 gas by denitrification by denitrifying bacteria
• Denitrifying bacteria work in anaerobic conditions e.g waterlogged fields

Question 25

Why do organisms need phosphorus substances?

Answer 25

- Phospholipids - DNA - ATP

Question 26

Summarise the WHOLE phosphorous cycle

Answer 26

- Phosphorous present in sedimentary rock as phosphate ions PO4 3- - Sedimentary rock erodes leaving soil with PO4 3- - Plants absorb PO4 3- to make phospholipid/DNA/ATP - Consumer eats plants - Saprobiotic decomposers releases PO4 3- back into soil - Mycorrhize fungi in roots of plants support uptake of scarce materials such as phosphate ions by increasing SA and acting like a sponge

Question 27

What is an agricultural ecosystem?

Answer 27

- Farming ecosystems | - Grows crops and raise animals

Question 28

How are crops intensively farmed for high yield?

Answer 28

- Suitable location with lots of water, sunlight and minerals - Clear area of plant and animals (deforestation removes competition and pests) - Selectively breed crop - Greenhouse for high levels of light, CO2 and temperature - Water by irrigation - Fertilisers - Control pests - Crop rotation ensure mineral levels do not deplete - Ploughing to add air spaces, bacteria involved in nutrient cycles can aerobically respire

Question 29

Distinguish between natural and artificial fertilisers

Answer 29

``` Natural = Dead/decaying remains Artificial = Mined from rocks and applied in appropriate balance ```

Question 30

What are pests?

Answer 30

Organisms that harm plants/crops as they compete/eat or disease the plant

Question 31

What are the two ways that pests can be controlled?

Answer 31

Pesticides or biological control

Question 32

What are pesticides?

Answer 32

Chemical sprays that kill the pest

Question 33

What are the advantages and disadvantages of pesticides?

Answer 33

Advantages: Fasting acting and can control area covered Disadvantages: Non-specific and nonbiodegradable so bioaccumulation occurs Pests may be resistant Reapplication

Question 34

What is biological control?

Answer 34

Using predators or parasites to control the pest

Question 35

What are the advantages and disadvantages of biological control

Answer 35

``` Advantages: Specific No bioaccumulation No resistance and no reapplication Disadvantages: Slow acting May become pest Cannot control area covered ```

Question 36

What is bioaccumulation?

Answer 36

Pesticides not biodegradable so remain in organisms tissues. Accumulate along food chain up trophic levels and toxic to consumers on high trophic levels

Question 37

What three minerals do fertilisers provide?

Answer 37

Nitrate for AA Phosphate for DNA/ATP and phospholipids Magnesium for chlorphyll

Question 38

Debate natural and artificial fertilisers

Answer 38

Natural has reduced risk of eutrophication but slower release Artificial has faster release but more risk of eutrophication and lowers water potential of soil

Question 39

What is the benefit of ploughing?

Answer 39

Aerates soil increasing air spaces supporting aerobic respiration (more nitrogen fixation and less denitrifying bacteria)

Question 40

Summarise eutrophication

Answer 40

- Large amounts of fertilisers - Leaching into water sources - Builds up in ponds - Increased algae growth (algae bloom) - Prevents light reaching bottom of water - Plants do not photosynthesis so die - Saprobiotic decomposers use oxygen in water from respiration - Fish die

Question 41

How do the four ways of crop farming affect the environment?

Answer 41

Deforestation reduces species/plant diversity and less habitats/food Monoculture depletes nutrients Selective breeding reduces genetic diversity Pollution causes bioaccumulation and eutrophication

Question 42

What five ways can we reduce the impact of crop farming?

Answer 42

Native trees for species diversity Hedgerows for species diversity Polyculture and crop rotation to prevent depletion of nutrients Wild crops maintain genetic diversity Biological control and natural fertiliser

Question 43

How are animals reared in farming?

Answer 43

- Selectively bred - Pre digested food with antibiotics and vaccines - Hormones - Restricted movement and kept warm