13 Energy And Ecosystems

Question 1

Three groups of organisms according to how they obtain their energy and nutrients

Answer 1

Producers, photosynthetic organisms, manufacture organic substances using light H2O CO2 and mineral ions Consumers, feed on other organisms, 2ndary and tertiary consumers are usually predators but can be scavengers or parasites Saprobionts (decomposers ), break down complex materials in dead organisms into simple ones, so release valuable minerals, contribute to recycling, majority of work carried out by fungi and bacteria

Question 2

Food chains and food webs

Answer 2

Food chain: feeding relationship, each stage in chain is referred to as trophic level, arrows represent direction of energy flow Food webs: most animals do not rely on a single food source, many food chains will be linked together to form a food web

Question 3

Biomass

Answer 3

Total mass of living material in a specific area at a given time

Question 4

How to measure biomass

Answer 4

Measure dry mass but organism must be killed Units are gm^-2 dry mass per given area in a given time Where volume is being sampled gm^-3 (grams per cubic metre) Chemical energy store can be estimated using calorimetry

Question 5

What is bomb calorimetry

Answer 5

Sample of dry material weighed, then burnt and pure oxygen within sealed chamber called a bomb Bum is surrounded by water bath and heat of combustion causes small temperature rise in water Can calculate the energy released from mass of burnt biomass

Question 6

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

Answer 6

Over 90% of suns energy reflected back into space by clouds dust or absorbed by atmosphere Not all wavelengths of light can be absorbed Light may not fall on chlorophyll Factor may limit rate of photosynthesis

Question 7

What is the Grove primary production

Answer 7

Total quantity of chemical energy store in plant biomass in a given area of volume in a given time Plants use 20 to 50% of this energy in respiration

Question 8

Net primary productivity

Answer 8

Chemical energy store left after respiration Net primary production = gross primary production - respiratory losses NPP = GPP - R

Question 9

Which consumer is more efficient

Answer 9

Less Then 10% of net primary production implants is used by primary consumers for growth Secondary and tertiary consumers more efficient transferring up to about 20% of energy available from prey into their own bodies

Question 10

Why is there a low percentage of energy transferred at each stage

Answer 10

Some of organism not consumed Some parts consumed but cannot be digested so lost in faeces Some of energy lost in excretory material such as urine Some energy losses occur as heats from respiration and loss to environment high and mammals because must maintain high body temperature

Question 11

Net production of consumers equation

Answer 11

See card 1

Question 12

Relative inefficiency of energy transfer between trophic levels explains why….

Answer 12

Most food chains have only four or five trophic levels, insufficient energy to support trophic levels higher than these Total mass of organism in a place is less at higher trophic levels Total amount of energy available less at each level

Question 13

Efficiency of energy transfer equation

Answer 13

Percentage efficiency = (energy available after the transfer/ energy available before the transfer) x 100

Question 14

How does intensive rearing/ factory farming increase energy conversion rate

Answer 14

Animals are kept in confined spaces This means movement is restricted as energy used in muscle contraction environment can be kept warm to reduce heat loss from body feeding is controlled optimum amount and type of food for maximum growth, no wastage predators are excluded

Question 15

How can pest control increase productivity

Answer 15

Pests of domesticated animals may cause disease animals may not grow as rapidly, be unfit for human consumption or die all of which lead to reduced productivity Aim of pest control is to simplify the food web so limit the effects of pests on productivity

Question 16

The flow of energy through an ecosystem is

Answer 16

In One Direction, linear

Question 17

The flow of nutrients within an ecosystem is

Answer 17

Not linear but mostly cyclic there is limited availability of nutrient ions in usable form it is important that elements e.g. carbon and nitrogen are recycled

Question 18

Sequence of all nutrient cycles

Answer 18

Nutrients taken up by produces as simple inorganic molecules Producer incorporates nutrients into complex organic molecules when producing eaten, nutrient passes into consumer Then passes along the food chain When producers and consumers die complex molecules are broken down by saprobiontic micro organisms that release nutrients in original simple form cycle is complete nutrients are released for reuse

Question 19

Basic sequence of all nutrient cycles

Answer 19

See card 2

Question 20

Why do living organisms require a source of nitrogen

Answer 20

To manufacture proteins, nucleic acids, ATP, nucleotides in DNA Components needed for plant growth plants are likely to develop earlier grow taller and have greater leaf area which increases rate of photosynthesis and improves crop productivity

Question 21

How do organisms take up nitrogen

Answer 21

Very few organisms can use nitrogen gas directly plants take up most nitrogen in form of nitrate irons NO3- from soil ions are absorbed using active transport by roots Animals obtain nitrogen-containing compounds by eating and digesting plants

Question 22

Difference between natural and agricultural ecosystems

Answer 22

Nitrate irons very soluble and easily leach (wash) through the soil beyond reach of plant roots In natural ecosystems nitrate concentration is restored largely by recycling of nitrogen-containing compounds. Release of nitrate ions by decomposition most important because very few nitrate irons available from other sources In agricultural ecosystems crop is harvested and transported away, concentration of mineral irons will fall ‏and must be replenished otherwise will be limiting factor and productivity is reduced Conc of soil nitrate can be further increased by addition of fertilisers

Question 23

Four main stages of nitrogen

Answer 23

Ammonification, nitrification, nitrogen fixation, and denitrification SEE TXTBOOK PG 307 for summary

Question 24

Ammonification

Answer 24

Production of ammonia from organic nitrogen-containing compounds Example includes urea proteins and nucleic acid’s and vitamins Saprobiontic Micro organisms mainly fungi and bacteria feed on faeces and dead organisms releasing ammonia Which forms ammonium ions in soil

Question 25

Nitrification

Answer 25

Plants use light energy to produce organic compounds some bacteria obtain energy from chemical reactions e.g. conversion of ammonium ions to nitrate ions This is an oxidation reaction so releases energy Carried out by soil microorganisms called nitrifying bacteria Conversion occurs in two stages: 1. Oxidation of ammonium ions to nitrite ions (NO2-) 2. Oxidation of nitrite ions to nitrate ions (NO3-)

Question 26

Why is aerated soil important

Answer 26

Nitrifying bacteria require oxygen to carry out conversions Soil has to have many air spaces Soil structure must be kept light and well aerated by ploughing Good drainage prevents airspaces being filled with water, so prevents air being forced out of soil This raises productivity

Question 27

Nitrogen fixation

Answer 27

Process by which nitrogen gas converted into nitrogen-containing compounds occurs naturally when lightning passes thru atmosphere Two microorganisms carry out nitrogen fixation: Free-living nitrogen fixing bacteria, Bacteria reduce gaseous nitrogen to ammonia which they use to manufacture amino acids, nitrogen rich compounds released from them when they die and decay Mutualistic nitrogen fixing bacteria, bacteria live in nodules on roots of plants, obtain carbs from plants and plant requires amino acids from bacteria

Question 28

Denitrification

Answer 28

When soil becomes waterlogged and low oxygen concentration fewer aerobic nitrifying and nitrogen fixing bacteria are found, increase in anaerobic denitrifying bacteria, Please convert soil nitrates into gaseous nitrogen, reduces availability of nitrogen containing compounds for plants For productive land soil must be kept well aerated to prevent buildup of denitrifying bacteria

Question 29

Importance of phosphorus

Answer 29

Component of ATP phospholipids and nucleic acids Main form is in mineral form, lacks gaseous phase

Question 30

Where does phosphorus come from

Answer 30

Exists mostly as phosphate ions (PO4 ^3-) in form of sedimentary rock deposits Weathering and erosion of rocks helps phosphate ions become dissolved XS phosphate ions excreted by animals and can accumulate in waste material On death of plants and animals decomposes break them down releasing phosphate ions into soil or water where they form sedimentary rocks again

Question 31

Role of Mycorrhizae in nutrient cycles

Answer 31

Associations between certain types of fungi and the roots of the vast majority of plants The fungi acts like extensions of the plant root system and increase total SA for absorption of water and minerals Acts like A sponge and holds water and minerals near roots Enables plant to better resist drought and take up scarce inorganic ions eg phosphate ions more readily

Question 32

Mycorrhizal relationship is

Answer 32

Mutualistic one Plants benefits from improved water and inorganic ion uptake While fungus receives organic compounds e.g. sugars and amino acids from plants

Question 33

Two types of fertilisers

Answer 33

Natural organic fertilisers: dead and decaying remains of plants and animal waste Artificial inorganic fertilisers: Mined from rocks and deposits then converted into different forms and blended, N, P, K present Combo of natural and artificial gives greatest increase in productivity, there is pt where further increases in quantity of fertiliser no longer results in increased productivity

Question 34

Detrimental effects of nitrogen-containing fertilisers

Answer 34

Reduced species diversity, nitrogen rich soil favours growth of rapidly growing species, please outcompete many other species which die Leaching which may lead to pollution of water course Eutrophication caused by leaching of fertiliser into watercourse

Question 35

Leaching

Answer 35

Process where nutrients removed from soil Rainwater dissolves any soluble nutrients such as nitrate ions, carries them deep into soil, beyond reach of roots, leaches nitrate ions fins way into watercourse Harmful effects on humans if water is source of drinking water High nitrate ion concentrations in water can prevent efficient oxygen transport in babies and link to stomach cancer

Question 36

Eutrophication

Answer 36

Process where nutrient concentrations increase in bodies of water In Most lakes very low concentration of nitrate, nitrate ions limiting factor for plants and algae growth As nitrate ion conc increases as result of leaching, no longer limiting factor, plants grow, algal grows at surface and densely populates upper layers of water, called algal bloom Dense layer of algae absorbs light preventing it penetrating to lower depths Light becomes limiting factor for growth of plants and algae at lower depths, they die Lack of dead plants and algae no longer limiting factor for growth of saprobiontic bacteria, so these grow Saprobiontic Bacteria need O for respiration, demand for oxygen Conc of O in H20 reduced, nitrates are released from decaying organisms O Becomes a limiting factor for population of aerobic organisms, fish die Without aerobic organisms less competition for anaerobic organisms, which increase Anaerobic organisms further decompose dead material releasing nitrate and toxic waste e.g. hydrogen sulphide which makes water putrid