energy and ecosystems

Question 1

What’s an ecosystem

Answer 1

Abiotic and biotic factors in a community

Question 2

What’s biomass

Answer 2

mass of living material

Question 3

How can biomass be measured?

Answer 3

*mass of carbon
*dry mass of tissue (mass of organism/tissue after water removed)

Question 4

What’s GPP

Answer 4

*gross primary production
*chemical energy store in plant biomass

Question 5

How is GPP measured

Answer 5

energy per unit area for eg J m-2 (joules per square metre)

Question 6

What’s gross primary productivity

Answer 6

The rate in which plants are able to store chemical energy via photosynthesis

Question 7

How is gross primary productivity measured

Answer 7

Units of energy/mass per unit area per time for example kg or j km-2 yr-1 (kilograms per square kilometre per year)

Question 8

What’s net primary production

Answer 8

Chemical energy store in plant biomass after respiratory loses to environment

Question 9

How is biomass made?

Answer 9

• in photosynthesis, plants make organic (carbon) compounds from atmospheric or aquatic CO2
  ● Most sugars synthesised are used by the plant as respiratory substrates
  ● Rest used to make other groups of biological molecules (eg. carbs, lipids & proteins) → form biomass

Question 10

In aquatic plants how is GPP measured?

Answer 10

Measured units of area per unit volume for eg- kg m-3 (kilograms per cubic metre)

Question 11

What are the biological molecules that are made by left over sugars that weren’t used in respiration? And what are their roles?

Answer 11

Starch- used as a short term energy store
Proteins- plant cells combine sugars with nitrate to form amino acids used to produce proteins
Cellulose- used for structural support in the cell wall
Lipids- plant cells convert sugars to lipids- used as long term energy stores.

Question 12

If dry mass if the grass from 1m2 of a fuel is 0.2kg, grass has dry mass (biomass) of 0.2kg m-2. If grass field is 200m2, what’s the biomass of the whole field?

Answer 12

0.2 x 200= 40kg

Question 13

Does biomass change over time? Can it be given in units of time?

Answer 13

Yes

Question 14

Does biomass change over time? Can it be given in units of time?

Answer 14

Yes

Question 15

if the average biomass of a group of oaks trees over the course of a year is found to be 13,000 kg, what’s the average biomass in a year?

Answer 15

13,000 kg y⁻¹ (this means 13,000 kg per year)

Question 16

What’s a calorimeter and how’s it used?

Answer 16

*equipment used to estimate chemical energy in dry biomass
*sample is burnt in a calorimeter
*sample heats volume of water
*change in temp shows estimate chemical energy in sample

Question 17

The total biomass of the grass that grows in a 200 m2 field is found to be 1,000 kg. Calculate the gross primary production of the grass field. Give appropriate units.

Answer 17

Step 1: Calculate the total yearly biomass of grass in 1 m2 of the field

1,000 ÷ 200 = 5 (kg)

Step 2: Give the appropriate units

5 kg m-2

Question 18

On average, a patch of rainforest covering an area of 1 km2 is estimated to contain 1,500 kg of biomass. Calculate the gross primary production of this rainforest patch. Give your answer in g m-2.

Answer 18

1km2= 1,000,000 m2 (1km = 1,000 metres to get km2 times 1,000 x1,000)

1kg=1,000g
1,500kg= 1500000g (five zeros)
Gross primary production= 1500000g/1,000,000m2
Answer= 1.5 g m-2

Question 19

The biomass of aquatic algae in a tank is estimated to contain a total of 5,440 joules of chemical energy. The tank has a volume of 4 m3. Calculate the gross primary production of this aquatic algae. Give appropriate units.

Answer 19

Step 1: Calculate the chemical energy of the biomass of aquatic algae in 1 m3

5,440 ÷ 4 = 1,360 (J)

Step 2: Give the appropriate units

Answer= 1,360 J m-3

Question 20

What’s net primary production?

Answer 20

amount of energy available to herbivores in the plant’s biomass after plant respiratory losses

Question 21

How is net primary production calculated?

Answer 21

Gross primary production- Respiration= Net primary production (GPP- R= NPP)

Question 22

What are the units of net primary production?

Answer 22

*units of energy per unit area or volume, for example:
Using area: J m–2 (joules per square metre)
Using volume: J m–3 (joules per cubic metre)

Question 23

What are the units of net primary productivity?

Answer 23

*units of energy or mass per unit area per unit time eg
mass= kg km-2 yr-1 (kilograms per square kilometre per year)
energy= mj m–2 y-1 (megajoules per square metre per year)

Question 24

What are the roles of decomposers?

Answer 24

*they breakdown dead plant/animal material by secreting digestive enzymes onto the surface
*breakdown matter into small soluble food molecules that’s then absorbed by decomposers

Question 25

How do decomposers help?

Answer 25

they help release organic nutrients back into environment for growth of plants and other products

Question 26

How is light energy converted to chemical energy?

Answer 26

light energy is absorbed by chlorophyll and other pigments, and converted into chemical energy in the form of ATP and NADPH.

Question 27

What’s primary production?

Answer 27

storing of chemical energy in the biomass of primary producers

Question 28

How’s primary production measured?

Answer 28

mass or energy per unit area
for eg:
mass= kg ha-1 (kilograms per hectare)
energy= kj ha-1 (kilojoules per hectare)

Question 29

How’s primary/secondary productivity measured?

Answer 29

mass or energy per unit area per unit time (years)

Question 30

Why is not all the chemical energy/biomass transferred to the consumer after eating?

Answer 30

*Not all of the biomass of the food is eaten (e.g. the roots and woody parts of plants or the bones of animals), meaning that the chemical energy this biomass contains is lost to the environment

*Consumers are not able to digest 100% of the food they ingest, so some is always egested as faeces.
* chemical energy is lost to the environment when consumers respire (lost as heat) and during the excretion of waste products

Question 31

What is net production of consumers?

Answer 31

energy that is left after losses is stored as new biomass to the consumer

Question 32

How do you calculate net production of consumers

Answer 32

N= I- (F+R)
I= chemical energy in ingested food
F= energy lost to environment thru urine/faeces
R= respiratory losses

Question 33

In a patch of woodland, caterpillars ingest 2,000 kJ m⁻² yr⁻¹ of chemical energy from the biomass of oak leaves. The caterpillars lose 1,200 kJ m⁻² yr⁻¹ of this energy in faeces and urine. They lose a further 600 kJ m⁻² yr⁻¹ of this energy through respiration. Calculate the net production of the caterpillars.

Answer 33

Step 1: Write out the equation and substitute in the known values

N = I - (F + R)

N = 2,000 - (1,200 + 600)

Step 2: Calculate the net production (N) and give appropriate units

N = 2,000 - 1,800

N = 200 kJ m⁻² yr⁻¹

Question 34

Explain why these units for primary or secondary productivity are used

Answer 34

● Per unit area → takes into account that diff environments vary in size
○ Standardising results for comparison between environments
● Per year → takes into account effect of seasonal variation (temperature etc.) on biomass
○ More representative and enables comparison between environments

Question 35

Explain why most light falling on producers is not used in photosynthesis

Answer 35

● Light is reflected or wrong wavelength
● Light misses chlorophyll / chloroplasts / photosynthetic tissue
● CO2 concentration or temperature is a limiting factor

Question 36

Explain why energy transfer between trophic levels is inefficient

Answer 36

● Heat energy is lost via respiration
● Energy lost via parts of organism that aren’t eaten (eg. bones)
● Energy lost via food not digested → lost as faeces
● Energy lost via excretion eg. urea in urine

Question 37

Explain how crop farming practices increase energy transfer efficiency

Answer 37

● Simplifying food webs to reduce energy / biomass losses to non-human food chains eg.
○ Herbicides kill weeds → less competition (eg. for light) so more energy to create biomass
○ Pesticides kill insects (pests) → reduce loss of biomass from crops
○ Fungicides reduce fungal infections → more energy to create biomass
● Fertilisers e.g. nitrates to prevent poor growth due to lack of nutrients

Question 38

Explain how livestock farming practices increase energy transfer efficiency

Answer 38

● Reducing respiratory losses within a human food chain- more energy to create biomass
○ Restrict movement and keep warm → less energy lost as heat from respiration
○ Slaughter animal while still growing / young, when most of their energy is used for growth
○ Treated with antibiotics → prevent loss of energy due to pathogens
○ Selective breeding to produce breeds with higher growth rates

Question 39

How does slaughtering animals when they’re young increase energy transfer efficiency?

Answer 39

young animals require less energy for maintenance compared to older animals (because they are smaller and have less developed systems) As animals grow, their energy requirements for basic metabolic processes increase. By slaughtering them before they reach full maturity, farmers can reduce the energy lost to maintenance.

young animals- higher growth rates and can convert feed into body mass more efficiently. larger proportion of the energy from their feed goes into growth rather than maintenance.

Question 40

A 2 g sample of biomass was fully combusted in a calorimeter.
The volume of water in the calorimeter was 100 cm3
The increase in temperature recorded was 15.7 °C
4.18 J of energy are needed to increase the temperature of 1 cm3 of water by 1 °C
Use this information to calculate the heat energy released in kJ per g of biomass.
Show your working

Answer 40

3.28 / 3.3 (kJ g−1)

Answer 41

f 1.31/1.3 × 108

Question 42

Chlorella cells can divide rapidly. A culture of 2000 chlorella cells was set up in a fermenter. The cells divided every 90 minutes. You can assume there were no limiting factors and that no cells died during the 24 hours. Give your answer in standard form.

Answer 42

1440/90 = Divide 16 times

2000x2^16

Ans = 1.3x10^8