3.5.3 Energy and Ecosystems

Question 1

Define producer

Answer 1

photosynthetic organisms that make organic substances using light energy, water, carbon dioxide and mineral ions

Question 2

Define Consumer

Answer 2

organisms that obtain energy by feeding on other organisms (primary, secondary and tertiary

Question 3

Define Saprobionts

Answer 3

organisms which break down complex materials in dead organisms into simple ones - allows recycling of minerals
- mostly carried out by fungi and bacteria

Question 4

Define Biomass

Answer 4

the total mass of living material in a specific area at a given time

Question 5

How can biomass be measured - why is fresh mass not used?

Answer 5

1. Dry mass (per given area in a given time - grams per square metre)
2. Mass of carbon

• Fresh mass is not used as varying amounts of water makes it unreliable

Question 6

How can the chemical energy store in dry biomass be estimated?

Answer 6

calorimetry
1. dry sample by heating in an oven at 50 - 80 degrees
2. regularly weigh until there is no mass change (in three consecutive weighings)
3. place in cup and ignite in a sealed oxygen rich atmosphere (complete combustion - all chemical energy released)
4. heat from combustion is transferred to the water - thermostat measures final and initial temp

Question 7

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

Answer 7

1. 90% is reflected or absorbed by the atmosphere
2. not all wavelengths of light can be absorbed by the chlorophyll in the leaf
3. other factors such as low carbon dioxide levele could limit the rate of photosynthesis

Question 8

Define gross primary production (GPP)

Answer 8

chemical energy store in plant biomass in a given area or volume, in a given time

Question 9

Define net primary production/productivity (NPP)

Answer 9

chemical energy store in plant biomass once respiratory losses have been taken into account
- this is available for plant growth and reproduction, as well as other trophic levels

Question 10

What is the equation for net primary production?

Answer 10

net primary production = gross primary production - respiratory losses

Question 11

What percentage of NPP is used by primary and secondary/tertiary consumers for growth?

Answer 11

primary = 10%
secondary/tertiary = 20%

Question 12

Why is the percentage of energy transferred between trophic levels low?

Answer 12

1. some of the food is not consumed
2. some parts can’t be digested so are lost in faeces
3. some are lost as excretory materials - urine
4. energy loss as heat from respiration - so efficiency is lower in primary consumers, warm blooded or older animals

Question 13

Why are there only 4 to 5 trophic levels in a food chain?

Answer 13

1. total biomass of organisms is less at higher trophic levels
2. total amount of energy stored is less as you move up the food chain -** insufficient energy is available to support a large breeding population** above trophic levels four and five

Question 14

What is the equation for NET PRODUCTION (N) of CONSUMERS?

Answer 14

N = I - (F+R)
N = net production
I = chemical energy store of ingested food
F = energy lost in faeces and urine
R = energy lost in respiration

Question 15

What is the equation for percentage efficiency of energy transfer?

Answer 15

( energy available after transfer / energy available **before transfer **) x 100

Question 16

How can farmers increase efficiency?

Answer 16

1. reduce energy lost by livestock in respiration - limit movement and maintain a warm temp - ensures more energy is stored in biomass which increased the net primary production
2. reduce energy lost by crops to other organisms (pests) - remove pests with insecticides, herbicides - so net primary production will increase

Question 17

What are the common features of a standard nutrient cycle?

Answer 17

1. producers take up nutrients
2. complex organic molecules are made
3. producer is eaten by consumer and nutrients are passed on
4. producers and consumers die and are broken down by saprobiotic organisms - nutrients released and can be recycled

Question 18

Role of nitrogen

Answer 18

proteins, nucleic acids and other nitrogen containing compounds

Question 19

Where is most nitrogen found?

Answer 19

the atmosphere
- plants take up most of the nitrogen in the form of nitrate ions in the soil

Question 20

Nitrogen cycle - what happens during nitrogen fixation (3 types) and what microogansisms are involved?

Answer 20

• nitrogen molecule breaks apart so nitrogen can combine with other atoms to form nitrogen containing compounds
• atmospheric fixation - lightning
• industrial fixation
• biological fixation - NITROGEN FIXING BACTERIA combine atmospheric nitrogen with hydrogen to form ammonia

Question 21

What are the two types of nitrogen fixing bacteria?

Answer 21

1. free living - reduce gaseous nitrogen to ammonia which is used to manufacture amino acids
2. mutualistic - live in root nodules of legume plants - provide plants with amino acids (uptake requires active transport) in exchange for carbohydrates

Question 22

What enzyme is involved in nitrogen fixation - what conditions are required?

Answer 22

nitrogenase - needs anaerobic conditions

Question 23

Nitrogen cycle - what happens during ammonification and what microorganisms are involved?

Answer 23

• Aerobic Saprobiotic organisms break down dead organisms
• **nitrogen containing compounds **(urea and proteins) are converted into ammonia which then forms ammonium ions in the soil - nitrogen enters the ecosystem

Question 24

Nitrogen cycle - what happens during nitrification and what *microorganisms *are involved?

Answer 24

• *Aerobic nitrifying bacteria *
• OXIDIDE ammonium ions to for NITRITE ions
• NITRITE ions are oxidised to form NITRATE ions
• which can enters the roots of plants via active transport

Question 25

Nitrogen cycle - what happens during denitrification and what* microorganisms* are involved?

Answer 25

• Anaerobic denitrifying bacteria *
• convert nitrates in the soil into gaseous nitrogen

Question 26

Role of phosphorous

Answer 26

ATP, phospholipids and nucleic acids

Question 27

Where is most phosphorous found?

Answer 27

phosphate ions in sedimentary rock deposits - weathering and erosion allows the ions to be dissolved and absorbed by plants
- no gas phase

Question 28

What are the main stages of the phosphorous cycle?

Answer 28

1. most phosphorous is stored in sedimentary rock
2. phosphorous is released into soil and water via phosphate ions
3. uptake of phosphate ions by plants and algae
4. uptake of phosphate by consumers who have eaten plants/algae
5. phosphates return to the environment after death and excretion - waste is decomposed by saprobionts

Question 29

How do Mycorrhizae aid the uptake of water and inorganic ions by plants?
What type of relationship ?

Answer 29

Mycorrhizae - a type of fungi which grows around the roots of some plants
- They extend the plants root system and increase total surface area for absorption of water and minerals - allows plant to take up scarce inorganic ions (phosphates) more easily
- hyphae secrete enzymes that hydrolyse bio molecules - can be absorbed and transported to plant roots
- MUTUALISTIC relationship - fungus gains organic compounds (sugars and amino acids) from the plant

Question 30

What two properties should soil have for maximum productivity?

Answer 30

1. aerobic conditions (well aerated) - for aerobic nitrifying bacteria, saprobionts and nitrogen fixing bacteria - prevents build up of denitrifying bacteria
2. well drained - prevents air spaces being filled with water and forcing air out

Question 31

Define artificial fertiliser - give the advantages

Answer 31

mined from rocks and deposits - usually have nitrogen, phosphorous and potassium
- guaranteed composition - easier to know how much to apply
- can be applied in smaller amounts - saves on transport
- clean and apply evenly

Question 32

Define natural fertiliser

Answer 32

decaying remains of plants and animals, and their waste (manure)
- add organic matter to the crop - improves soil structure, reduces erosion and improves water holding properties
- release nutrients over a longer period - less chance of leaching

Question 33

Why are fertilisers needed?

Answer 33

most farming is intensive so a lot of the biomass is harvested and removed
- mineral ions in the soil need to be replaced or concentrations will decrease and crop yield falls - reduced productivity

Question 34

What are the three main environmental issues with nitrogen containing fertilisers?

Answer 34

• reduced species diversity - nitrogen rich soil favours fast growing species like grass and nettles - outcompete other species
• leaching - pollutes water
• eutrophication - caused by leaching

Question 35

Define leaching

Answer 35

process by which nutrients are removed from the soil

Question 36

How does leaching affect the environment?

Answer 36

• nutrients are dissolved and carried deep into the soil - beyond the reach of plant roots
• nitrate ions enter streams, rivers and lakes
• can be harmfull if the lake is a source of drinking water, and can also cause eutrophication

Question 37

Define eutrophication

Answer 37

process by which nutrient concentrations increase in a body of water

Question 38

What are the main stages of eutrophication?

Answer 38

1. leaching causes nitrate ion conc to increase -** growth of plants and algae** as nitrates are no longer a limiting factor
   2.upper layer of water becomes densely populated by algae - algal bloom **
   3.algae absorbs light and prevents it reaching the lower depths
   4.light becomes a limiting factor in plant growth so they die** - less oxygen produced
   5.Saprobiontic bacteria grow - using dead organisms as food (more decomposition)
   6.increased oxygen demand- sapriobionts need it for respiration
   7.concentration of oxygen is reduced and further nitrates are released from decaying organisms
   8.oxygen becomes a limiting factor for aerobic organisms who die
   9.less competition for anaerobic organisms, whose populations rise - these further decompose dead material - releasing more nitrates and toxic waste - water turns putrid