energy and ecosystems- chapter 13

Question 1

what is biomass

Answer 1

• The total mass of living material in a specific area at a given time.
• Fresh mass is quite easy to access, but the presence of varying amounts of water make its unreliable.
• Measuring the mass of carbon or dry mass overcomes this problem but the organisms must be killed.

Question 1

what is a producer

Answer 1

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

Question 2

what is a consumer

Answer 2

are organisms that obtain their energy by feeding on (consuming) other organisms. Animals are consumers

Question 3

what are saprobionts

Answer 3

(decomposers) are a group of organisms that break down the complex materials in dead organisms into simple ones. They release valuable minerals and elements in a form that can be absorbed by plants and so contribute to recycling. The majority of this work is carried out by fungi and bacteria.

Question 4

what is the food chain

Answer 4

describes a feeding relationship, each stage in this chain is referred to as a trophic level. The arrows on a food chain diagrams represent the direction of energy.

Question 5

what is a food web

Answer 5

in reality, most animals do not rely on a single food source and within a single habitat many food chains will be linked together to form a food web

Question 6

why is not all of the suns energy is converted to organic matter by photosynthesis

Answer 6

• Over 90% of the Sun’s energy is reflected back into space by clouds and dust or absorbed by the atmosphere
• Not all wavelengths of light can be absorbed and used for photosynthesis
• Light may not fall on a chlorophyll molecule.
• A factor, such as low carbon dioxide levels, may limit the rate of photosynthesis.

Question 7

what is the gross primary production (GPP)

Answer 7

The total quantity of the chemical energy store in plant biomass, in a given are or volume, in a given time
however plants use 20-50% of the energy in respiration

Question 8

what is the net primary productivity (NPP)

Answer 8

The chemical energy store which is left when these losses to respiration have been taken into account

Question 9

what is the equation for the net primary production

Answer 9

Gross Primary Production – Respiratory Losses

Question 10

what is net primary production available for

Answer 10

• plant growth and reproduction.
• Less than 10% this NPP in plants can be used by primary consumers for growth.
• Secondary and tertiary consumers are able to transfer up to about 20% of the energy available.

Question 11

what is the low percentage of energy transferred at each stage the result of

Answer 11

• Some of the organism is not consumed
• Some parts are consumed but cannot be digested and are therefore lost in faeces.
• Some of the energy is lost in excretory materials such as urine.
• Some energy losses occur as heat from respiration and lost to the environment.

Question 12

how is the net production of consumers calculated as

Answer 12

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 13

what does the relative inefficiency of energy transfer between trophic levels explain

Answer 13

• Most food chains have only four or five trophic levels because insufficient energy is available to support a large enough breeding population.
• The total mass of organisms in a particular place is less at higher trophic levels.
• The total amount of energy available is less at each level as you move up a food chain.

Question 14

what 3 elements are important that they are recycled

Answer 14

carbon, nitrogen and phosphorus

Question 15

what are the 4 main stages of the nitrogen cycle

Answer 15

ammonification, nitrification, nitrogen fixation and denitrification

Question 16

explain the process of ammonification

Answer 16

• Is the production of ammonia from organic nitrogen-containing compounds.
• In nature, these compounds include urea (from the breakdown of excess amino acids) and proteins, nucleic acids and vitamins (found in faeces and dead organisms)
• Saprobiontic microorganisms, mainly fungi and bacteria, feed on faeces and dead organisms materials, releasing ammonia, which then forms ammonium ions in the soil.
• This is where nitrogen returns to the non-living component of the ecosystems.

Question 17

explain the process of nitrification

Answer 17

• Some bacteria obtain their energy from chemical reactions involving inorganic ions.
• One reaction is the oxidation reaction where ammonium ions are converted to nitrate ions. This releases energy.
• It is carried out by free-living soil microorganisms called nitrifying bacteria. This conversion occur in two stages:
  1. Oxidation of ammonium ions to nitrite ions (NO2-)
  2. Oxidation of nitrite ions to nitrate ions (NO3)-
• Nitrifying bacteria requires oxygen to carry out these conversions, so they require soil that has many air spaces.
• Farmers achieve this by ploughing their fields and having good drainage in their soil.

Question 18

explain the processes of nitrogen fixing

Answer 18

• Process by which nitrogen gas is converted into nitrogen- containing compounds.
• Occurs naturally when lightning passes through the atmosphere.
• There are two types of microorganisms that do this:
  1. Free-living nitrogen-fixing bacteria- reduce gaseous nitrogen to ammonia, which they use to manufacture amino acids. Nitrogen-rich compounds are released from them when they die and decay.
  2. Mutualistic nitrogen-fixing bacteria- live in nodules on the roots of plants such as peas and beans. Obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria.

Question 19

explain the process of denitrification

Answer 19

• When soils become waterlogged and have a low oxygen concentration, fewer aerobic nitrifying and nitrogen-fixing bacteria are found and there is an increase in anaerobic denitrifying bacteria.
• These convert soil nitrates into gaseous nitrogen, reducing the availability to plants.

Question 20

what do living organisms require nitrogen for

Answer 20

to manufacture proteins, nucleic acids and other nitrogen- containing compounds

Question 21

how do plants take up nitrogen

Answer 21

• in the form of nitrate ions (NO3-) from the soil.
• These ions are absorbed, using active transport

Question 22

how do animals obtain nitrogen containing compounds

Answer 22

by eating and digesting plants

Question 23

how can nitrogen concentration be increased in agricultural ecosystems

Answer 23

the addition of fertilisers

Question 24

how can nitrogen concentration be increased in natural ecosystems

Answer 24

restored largely by the recycling of nitrogen-compounds

Question 25

what is the phosphorus cycle

Answer 25

- Phosphorus is an important biological element as it’s a component of ATP, phospholipids and nucleic acids. - It exists mostly as phosphate ions (PO43-) in the form of sedimentary rock deposits. - The weathering and erosion of these rocks helps phosphate ions to become dissolved and available for absorption by plants which incorporate them in their biomass. - Phosphate passes to animals when they consume these plants. - Excess phosphate ions are excreted by animals and may accumulate in waste material. - On the death of plants and animals, decomposers such as certain bacteria and fungi break them down releasing phosphate ions into the water or soil. - Some phosphate ions stay in bones and shells so are very slow to break down. - Phosphate ions excreted are transported by streams and rivers into lakes and oceans where they form sedimentary rocks.

Question 26

what is the role of mycorrhizae in nutrient cycles

Answer 26

- Mycorrhizae are associations between certain types of fungo and the roots of the vast majority of plants. - They act like extensions of the plant’s root system and vastly increase the total surface area for the absorption of water and minerals. - The mycorrhiza holds water and minerals, which enables the plant to better resist drought and take up inorganic ions more readily. - The relationship between them and the fungi is a mutualistic one. The plants benefits from improved water and inorganic ion uptake while the fungus receives organic compounds.

Question 27

what are the two types of fertilisers

Answer 27

- Natural (organic) fertilisers- consist of the dead and decaying remains of plants and animals, as well as animal wastes. - Artificial (inorganic) fertilisers- are mined from rocks and deposits and then converted into different forms and blended together to give the appropriate balance for the particular crop. Nitrogen, phosphorus and potassium are almost always present.

Question 28

why are there large demands on the soil

Answer 28

because mineral ions are continually taken up by the crops being grown on it

Question 29

what increases productivity (from research)

Answer 29

- a combination of natural and artificial fertilisers given the greatest long-term increase in productivity. - it needs to be given in appropriate quantities as there is a point where further increases in the quantity of fertiliser no longer results in increased productivity

Question 30

how do fertilisers increase productivity

Answer 30

- Where nitrate ions are readily available, plants are likely to develop earlier, grow taller and have a greater leaf area. - This increases the rate of photosynthesis and improves crop productivity.

Question 31

what are 3 environmental issues concerning the use of nitrogen-containing fertilisers

Answer 31

- Reduced species diversity- nitrogen-rich soils favour the growth of grasses, nettles and other rapidly growing species. These out-compete many other species. - Leaching- which may lead to pollution of watercourses - Eutrophication- caused by leaching of fertiliser into watercourses.

Question 32

explain leaching

Answer 32

- Process by which nutrients are removed from the soil. - Rainwater will dissolve any soluble nutrients and carry them deep into the soil, beyond the reach of plant roots. - The leached nitrate ions find their way into watercourses that in turn may drain into freshwater lakes which may have a harmful effect on humans if it is a source of drinking water. - Very high nitrate ion concentrations can prevent efficient oxygen transport in babies and a link to stomach cancer in humans has been suggested. - It can also cause eutrophication.

Question 33

explain eutrophication

Answer 33

- Process by which nutrient concentrations increase in bodies of water. 1. As nitrate ion concentration increases as a result of leaching, it ceases to be a limiting factor for the growth of plants and algae whose populations both grow. 2. As algae mostly grow at the surface causing algal bloom. 3. The dense surface absorbs light and prevents it penetrating to lower depths. 4. Light becomes a limiting factor for the growth of plants and algae at lower depths and so they eventually die. 5. The lack of dead plants and algae is no longer a limiting factor for the growth of Saprobiontic bacteria so these grow using the dead organisms as food. 6. Saprobiontic bacteria require oxygen so they create an increased demand for oxygen. 7. The concentration of oxygen in the water is reduced and nitrates are released from the decaying organisms. 8. Oxygen then becomes the limiting factor for the aerobic organisms, so they die. 9. Without the aerobic organisms, there is less competition for the anaerobic organisms, whose populations now rise. 10. Anaerobic organisms further decompose dead materials, releasing more nitrate and toxic wastes.