5 Energy and Ecosystems

Question 1

ecosystem

Answer 1

includes all the organisms living in a particular area known as the community as well as all the non-living elements of that particular environment.

Question 2

what is the source of all energy in an ecosystem?

Answer 2

the sun

with photosynthetic organisms using this to produce their own food.

Question 3

what 3 groups can organisms be divided into according to how they obtain their energy and nutrients?

Answer 3

producers
consumes
saprobionts

Question 4

producers

Answer 4

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

Question 5

consumers

Answer 5

organisms that obtain their energy by feeding on other organisms

Question 6

primary consumers

Answer 6

those that directly eat producers

Question 7

secondary consumers

Answer 7

those eating primary consumers

usually predators

Question 8

tertiary consumers

Answer 8

those eating secondary consumers

usually predators

Question 9

saprobionts

Answer 9

decomposers
a group of organisms that break down the complex materials in dead organisms into simple ones
in doing so, they release valuable materials 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 10

food chain

Answer 10

describes a feeding relationship in which the producers are eaten by primary consumers
these in turn are eaten by secondary consumers, which are then eaten by tertiary consumers
each stage in this chain is referred to as a trophic level
the arrows on a food chain diagram represents the direction of energy flow

Question 11

food web

Answer 11

within a single habitat many food chains linked together to form a web
most animals don’t rely on a single food source

Question 12

biomass

Answer 12

the total mass of living material in a specific area at a given time
can be measured in terms of mass of carbon or dry mass of tissue per given area per given time.
The dry mass is used as the wet mass can vary too much.
The chemical energy stored in dry biomass can be estimated using calorimetry. This is carried out in a bomb calorimeter in which a sample of known mass is burnt in pure oxygen.
The bomb calorimeter is submerged in water and therefore the change in water temperature can be used to calculate the energy in the sample.

Question 13

what is biomass measured in?

Answer 13

grams per square metre

gm-2

Question 14

gross primary production

Answer 14

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

Question 15

net primary production

Answer 15

the chemical energy store in plant biomass after respiratory losses to the environment have been taken
into account
NPP = GPP – R
The net primary production is available for plant growth and reproduction as well as to other trophic levels in the ecosystem such as decomposers and herbivores.

Question 16

why is a low percentage of energy transferred at each stage?

Answer 16

• some of the organisms is not consumed
• some parts are consumed but cannot be digested and are therefore lost in the 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. these losses are high in mammals and birds because of their high body temp. much energy is needed to maintain their body temp when heat is constantly being lost to the environment.

Question 17

net production of consumers equation

Answer 17

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

Question 18

the inefficiency of energy transfer between trophic levels means…

Answer 18

• most food chains only have 4 or 5 trophic levels because insufficient energy is available to support a large enough breeding population at TLs higher than these
• the total mass of organisms in a particular place (biomass) is less at higher TL
• the total amount of energy available is less at each TL as one moves up a food chain

Question 19

nutrient cycles

Answer 19

Nutrients are recycled within natural ecosystems, exemplified by the nitrogen cycle and the phosphorus cycle.

Question 20

what vital roles in recycling chemical elements such

as phosphorus and nitrogen do Microorganisms play?

Answer 20

• The role of saprobionts in decomposition.
• The role of mycorrhizae in facilitating the uptake of water and inorganic ions by plants.
• The role of bacteria in the nitrogen cycle:
Nitrogen-fixing bacteria in the soil and within the root nodules of some plants convert nitrogen gas in the atmosphere to ammonia. Nitrifying bacteria convert ammonia to nitrites or nitrates. Denitrifying bacteria converts nitrates back to nitrogen gas.

Question 21

what sequence do all nutrient cycles have?

Answer 21

• the nutrient is taken up by producers (plants) as simple, inorganic molecules
• the producer incorporates the nutrient into complex organic molecules
• when the producer is eaten, the nutrient passes into consumers (animals)
• it then passes along the food chain when these animals are eaten by other consumers
• when the producers and consumers die, their complex molecules are broken down by saprobiontic MOs (decomposers) that release the nutrient in its original simple form. the cycle is then complete. the role of these saprobionts in nutrient cycles is important. without them, nutrients would remain locked up as part of complex molecules that cannot be taken up and used again by plants

Question 22

nitrogen cycle

Answer 22

Nitrogen is an element used in many biological molecules of which there is a finite amount on earth. Due to this it must be recycled from dead organisms and waste products. Most of this is carried out by bacteria in the soil.
although 78% of the atmosphere is nitrogen, very few organisms can use nitrogen gas directly. plants take up most of the N they require in the form of nitrate ions (NO3-), from the soil. these ions are absorbed using active transport by the roots.

Question 23

4 stages of nitrogen cycle

Answer 23

ammonification
nitrification
nitrogen fixation
denitrification

Question 24

ammonification

Answer 24

When an organism dies or produces waste (e.g. faeces), it is decomposed by saprobionts.
This releases the nutrients contained inside.
Saprobionts decompose the organisms’ biomass by extracellular digestion and inorganic ammonium ions are released into the soil.
Ammonification is a by-product of saprobiont nutrition.

Question 25

nitrification

Answer 25

Ammonium ions that are released from ammonification are converted into nitrates by bacteria in the soil.
it is carried out by soil MOs called nitrifying bacteria. this conversion occurs in 2 stages:
-oxidation of ammonium ions (NH4+) to nitrite ions (NO2-)
-oxidation of nitrite ions to nitrate ions (NO3-)

nitrifying bacteria require O2 to carry out these conversions and so require a soil that has many air spaces

Question 26

what do farmers do to increase productivity- nitrification

Answer 26

keep soil structure light and well aerated by ploughing

good drainage also prevents air being forced out of the soil

Question 27

nitrogen fixation

Answer 27

Atmospheric nitrogen (N2) is converted to ammonia (NH3) by nitrogen-fixing bacteria in the soil.
Bacteria (e.g. Rhizobia) form a mutualistic (as it is beneficial to both organisms) relationship with leguminous plants by inhabiting their root nodules.
Leguminous plants (e.g. alfalfa, peas, beans) are a family of plants.
The bacteria provide a source of ammonium ions for the plants and the plant provides sugars.

Question 28

denitrification

Answer 28

where nitrate ions, NO3-, are converted to nitrogen gas, N2, by the denitryfing bacteria. This process is wasteful and can be prevented from occurring by soil being well drained and aerated.
when soils are waterlogged and have a low O2 conc, the type of MO present changes. 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. this reduces the availability of nitrogen-containing compounds for plants

Question 29

what do farmers do to increase productivity- denitrification

Answer 29

the soils on which crops grow must therefore be kept well aerated to prevent the build up of denitrifying bacteria

Question 30

phosphorus cycle

Answer 30

Phosphorus is another element found in many biological molecules that needs to be recycled.
the main reservoir is in mineral form rather than in the atmosphere - the PC lacks a gaseous phase
phosphorus exists mostly as phosphate ions PO43- in the form of sedimentary rock deposits.
Phosphate is released from sedimentary rocks as a result of weathering
Plants can take in phosphate ions, PO43-, from soil
The P ions pass into animals which feed on the plants
Excess P ions are excreted by animals and may accumulate in waste material- excreta of some birds
On the death of plants and animals, decomposers such as certain bacteria and fungi break them down releasing P ions into the water or soil.
some P ions remain in parts of animal, such as bones or shell, that are very slow to breakdown.
P ions in excreta, released by decomposition and dissolved out of rocks, are transported by streams and rivers into lakes and oceans where they form sedimentary rocks thus completing the cycle

Question 31

role of mycorrhizae in nutrient cycles

Answer 31

Important in facilitating the uptake of water and inorganic ions by plants.
These are associations between certain types of fungi and the roots of the vast majority of plants. They increase the surface area and act as a sponge holding water and minerals. As a result a plant can better resist drought and take up inorganic ions more easily.

Question 32

mycorrhizae relationship between plants and fungi

Answer 32

mutualistic
plant benefits from improved water and inorganic ion uptake while the fungus receives organic compounds such as sugars and AAs from the plant

Question 33

​Free-Living Nitrogen-Fixing Bacteria

Answer 33

in the soil, they reduce nitrogen gas to ammonia.

Question 34

​Mutualistic Nitrogen-Fixing Bacteria

Answer 34

​Use nitrogen gas to produce amino acids

Question 35

​Nitrifying bacteria

Answer 35

​Free living in soil, oxidise ammonium ions into nitrites and nitrites into nitrates

Question 36

use of fertilisers

Answer 36

Fertilisers can be used to provide plants with minerals, particularly nitrates, to support their growth
In agriculture systems, the harvesting of crops prevents the reintroduction of minerals to the soil

Question 37

natural (organic) fertilisers

Answer 37

ferilisers consist of dead and decaying remains of plants, animals and their waste

Question 38

artificial (inorganic) fertilisers

Answer 38

are mined from rocks before being converted into different forms with their composition tailored for specific crops

Question 39

how do fertilisers increase productivity?

Answer 39

nitrogen is an essential component of amino acids, ATP, and nucleotides in DNA
both are needed for plant growth
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 PS and improves crop productivity
nitrogen-containing fertilisers have been of considerable benefit in providing us with cheaper food

Question 40

Effects of using fertilisers

Answer 40

​Reduced species diversity
​Leaching (pollutes waterways)
​Eutrophication

Question 41

how do nitrogen-containing fertilisers reduce species diversity?

Answer 41

nitrogen-rich soils favour the growth of grasses, nettles and other rapidly growing species.
these out-compete many other species, which die as a result
species-rich hay meadows only survive when soil nitrogen concs are low enough to allow other species to compete with the grasses

Question 42

leaching

Answer 42

Rainwater dissolves soluble nutrients (e.g. nitrates) and carries them deep into the soil and into waterways such as streams, rivers and lakes.
This can have a harmful effect on humans if the river or lake is a source of drinking water
high nitrate ion concs in drinking water can prevent efficient O2 transport in babies and a link to stomach cancer in humans has been suggested

Question 43

eutrophication

Answer 43

Eutrophication is the process by which nutrients build up in bodies of water. It is a natural process that occurs mostly in freshwater lakes.

1. In most lakes and rivers there is naturally little nitrate so nitrate is a limiting factor for plant and algal growth
2. As the nitrate conc increases as a result of leaching, it stops being a limiting factor for the growth of plants and algae and both grow
3. As algae growth occurs mostly at the surface, the upper layers of water become densely populated with algae
4. This dense surface layer of algae absorbs light and prevents it from penetrating to lower depths
5. Light then becomes the LF for the growth of plants and algae at lower depths and so they eventually die
6. The lack of dead plants and algae is no longer a LF for the growth of saprobiotic algae and so these too grow exponentially using the dead organisms as food
7. The saprobiotic bacteria require oxygen for their respiration, creating an increased demand for oxygen
8. The conc of O2 in the water is reduced and nitrates are released from the decaying organisms
9. Oxygen then becomes the LF for the population of aerobic organisms such as fish. These organisms ultimately die as the oxygen is used up altogether
10. Without the aerobic organisms there is less competition for the anaerobic organisms whose populations now rise
11. The anaerobic organisms further decompose dead material, releasing more nitrates and some toxic wastes, such as hydrogen sulphide which makes the water putrid

Question 44

extracellular digestion

Answer 44

The type of digestion where enzymes are secreted onto dead organic matter by saprobionts.