C4.2 Transfers of energy and matter (CTs)

Question 1

Define species

Answer 1

A group of organisms that can interbreed and produce fertile (and viable) offspring

Question 2

Define habitat

Answer 2

The environment within which a species normally lives

Question 3

Define population

Answer 3

A group of organisms of the same species who live in the same area at the same time

Question 4

Community

Answer 4

Populations of different species (plants & animals) living and interacting in the same area

Question 5

Ecosystem

Answer 5

A community (all organisms in an area together) and its abiotic (non-living, physical and chemical components) environment

Question 6

Compare open and closed systems

Answer 6

Open systems are where resources can enter or exit, including both chemical substances and energy
Closed systems are where energy can enter or exit, but chemical resources cannot be replaced/ removed

Question 7

Sunlight as the principal energy source for most ecosystems

Answer 7

Initial source of energy for most ecosystems is sunlight
- living organisms harvest this energy by photosynthesis (producers)
- energy fixed by these producers in carbon compounds is available to other organisms

Question 8

Ocean as an exception of sunlight as principal energy source

Answer 8

In marine & freshwater ecosystems, light must pass through water to reach producers but light transmission is not 100%
- photosynthesis uses light with wavelength 400nm (violet) to 700nm (red) –> shorter wavelength penetrate further in pure water –> why sea always appears blue
- living organisms & non-living matter in water further reduces light penetration

In open oceans there is little to no light at depths greater than 200m
- coastal waters are often turbind due to suspended clay/ silt and dense populations of phytoplankton –> little light below 50m
- deeper ecosystems must rely on other sources of energy

Question 9

Caves as an exception of sunlight as principal energy source

Answer 9

Caves are very dark –> streams entering a cave may bring dead organic matter which provides supply of energy (eg dead leaves with energy by photosynthesis in ecosystems outside cave)

BUT some caves very isolated and don’t receive inputs of energy from outside ecosystems
- eg Movile cave near the Black Sea coast in Romania
- the producers in sealed caves are archaebacteria –> they gain energy from chemical reactions that have methane, sulphides, or other inorganic compounds as substrates

• energy from these reactions is used to synthesis carbon compounds in a type of metabolism called chemosynthesis
• microscopic invertebrates feed on biofilms of chemosynthetic archaebacteria, with other invertebrates feeding on them

Question 10

Define food chain

Answer 10

Represents the simple linear flow of chemical energy in an ecosystem from one trophic level to another between the diff populations, as indicated by the direction of arrows

Question 11

What to include in a food chain

Answer 11

• producer and consumer but NOT decomposers
• named organisms at either species or genus level
• arrow indicates direction of energy flow

Question 12

Define food webs

Answer 12

Food webs show how food chains are linked together into more complex feeding relationships in an ecosystem bc it is unusual for an animal to eat only one organism

Question 13

Types of decomposers

Answer 13

Sapotrophs (eg fungi and bacteria)
- an organism that lives on or in dead organic matter, secreting extracellular digestive enzymes into it and absorbing the products of the digestion (external digestion)

Detritivores (eg earthworm)
- ingest dead organic matter which is broken down during digestion within the body into smaller particles and useful materials are absorbed before the rest is passed out of body

Question 14

Outline the role of decomposers in a food web

Answer 14

Decomposers obtain food and nutrients from the breakdown of dead organic matter
They breakdown dead tissues, release nutrients locked in bodies or waste products of organisms into environment to be absorbed by producers
Also build up of humus (nutrient rich topsoil) and improve nutrient retention capacity on soil

Question 15

Supply of energy to decomposers

Answer 15

Carbon compounds in faeces, dead parts of organism and dead whole organisms

Question 16

Define autotrophs

Answer 16

Autotrophs are organisms that use external energy sources to synthesise carbon compounds from simple inorganic substances (self-feeding)

Question 17

Two primary sources of external energy in autotrophs

Answer 17

1. Chemical reactions - carbon dioxide or hydrogen carbonate as carbon source and nitrate, phosphate and other simple inorganic substances as sources of other elements
2. light

These give energy required for carbon fixation and anabolic reactions that build macromolecules

Question 18

Photoautotrophs VS chemoautotrophs

Answer 18

Photoautotrophs (plants, eukaryotic algae, cyanobacteria) use light as the energy source
- fusion reactions in sun generate vast amounts of energy in form of electromagnetic radiation but only a very small proportion reaches earth

Chemoautotrophs (eg prokaryotes, bacteria, archaebacteria) use exothermic inorganic oxidation reactions
- substrate in reduced state (eg sulfur, hydrogen sulphide, iron, hydrogen or ammonia) is oxidised which releases energy used to synthesise carbon compounds

Question 19

Iron-oxidising bacteria as an example of a chemoautotroph

Answer 19

Iron-oxidising bacteria such as Mariprofundus ferrooxydans, a bacterium that thrives near hydrothermal vents like those near Hawaii, hundreds of metres below the ocean surface and far from where sunlight can penetrate are capable of obtaining electrons from iron.
- they take one form of iron: iron (ii) and remove an electron to transform it into iron (iii)
- for every negative electron lost, iron will gain a positive charge
- the lost electron from this oxidation reaction can be used to generate ATP for the cell
- these microbes are producers for food chains near hydrothermal vents where they live

Question 20

Define heterotrophs

Answer 20

Organisms that obtain organic molecules/ carbon compounds from other organisms to synthesise the carbon compounds they need

Question 21

Outline the functions of digestion, assimilation and synthesis of carbon compounds in heterotrophs

Answer 21

They ingest autotrophs or other heterotrophs, digest the macromolecules like protein, lipids, polysaccharides, DNA, RNA into monomers before absorbing them to create new molecules for their own use (assimilation) –> involves the transfer of energy

Question 22

How to autotrophs and heterotrophs release energy

Answer 22

In both, ATP is produced by cell respiration
- carbon compounds like carbohydrates and lipids are oxidised to release energy and this energy is used to phosphorylate ADP, producing ATP

Question 22

Define trophic level

Answer 22

Trophic level refers to the position of an organism in a food web or chain, showing how many organisms the energy in the system has flowed through
- they have varied diets and hence occupy different trophic levels

Question 23

Classification into trophic levels

Answer 23

Producers: first trophic level (aka autotrophs)
Consumers: second, third or higher trophic levels (primary consumer is second trophic level and so on) (aka heterotrophs)

• each consumer depends on the trophic level below it for energy

Question 24

Construction of energy pyramids

Answer 24

1. Drawn in steps than triangle 2. drawn to scale (shd be at least 1/5 of the box below it) and annotated with appropriate numeric values 3. label producer, primary consumer and secondary consumer correctly Units of pyramids of energy is energy per unit area per unit time eg kJ m^-2 yr^-1

Question 25

Define pyramid of energy

Answer 25

They are diagrams that show how much energy flows through each trophic level in a community over a fixed period, usually a year. It shows the decreasing amounts of energy, living tissue, or number of organisms at successive feeding levels

Question 26

Outline three reasons why the amount of energy decreases at higher trophic levels

Answer 26

1. most of the energy in food which is digested and absorbed by organisms in a trophic level is used (chemical respiration is converted to KE) in cellular respiration for the various metabolic activities & much energy is also lost in the form of heat --> less energy is available to the next trophic level in the form in chemical energy in tissues 2. the organisms in a tropic level are not entirely consumed by organisms of the next trophic level (left as bones, hair, leaves) --> energy in these uneaten materials will pass to detritivores and saprophytes 3. not all parts of the food eaten by organisms of the next trophic level are digested and absorbed --> some is indigestible and egested in faeces. Faeces will pass to detritivores and saprophytes 4. only 10% of energy is transferred from one trophic level to the next (trophic efficiency) *decomposers are not considered to be part of food chain *energy is NOT RECYCLED bc the decomposers take energy from the wastes and bodies for their own use *energy is measured in energy per unit area per time

Question 27

Describe the reasons why heat created by living organisms is eventually lost from the ecosystem.

Answer 27

Energy transfers are not 100% efficient so heat is produced both when ATP is produced in cell respiration and when used in cells 1. cellular respiration releases energy as ATP from carbon compounds --> energy is lost as heat during cellular respiration 2. when living organisms perform various energy conversions, heat energy is released *it is assumed all energy released from cell respiration is ultimately lost

Question 28

State that at each successive trophic level there are few organisms and less biomass

Answer 28

At each successive stage in food chains there are fewer organisms or smaller organisms. There is hence less biomass, but the energy content per unit mass is not reduced. 1. only small portion of energy in biomass of organisms in one trophic level will become part of biomass of organisms in next trophic level --> after only a few stages in a food chain, the amt of energy remaining is not enough to support another trophic level 2. energy is released by respiration and lost as heat and also due to uneaten parts and faeces in egestion 3. biomass also diminishes along food chains, due to loss of carbon dioxide and water from respiration and loss from the food chain of uneaten and undigested parts of organisms

Question 29

Define biomass

Answer 29

Biomass is the dry weight of organic matter of a community in a particular habitat/ total mass of individuals in a population Units: mass of carbon per unit area per unit time ( g m-2 yr-1)

Question 30

Outline why different biomes vary in their capacity to accumulate biomass

Answer 30

Production in ecosystems is the accumulation of carbon compounds in biomass. 1. both autotrophs and heterotrophs produce biomass by growth and reproduction

Question 31

Define gross and net primary production

Answer 31

Gross primary production (GPP) is the total biomass of carbon compounds made in plants by photosynthesis Net primary production is GPP minus the biomass lost due to respiration of the plant --> this is the amt of biomass available to consumers

Question 32

Explain why secondary production is lower than primary production in an ecosystem. ​

Answer 32

As with energy, not all biomass will be passed on from producers to environment so secondary production is always lower than primary production - bc carbon compounds are converted to carbon dioxide and water in cell respiration

Question 32

Define secondary production

Answer 32

It is the accumulation of carbon compounds in biomass by animals and other heterotrophs when heterotrophs consume and assimilates the organic molecules.

Question 33

Constructing carbon cycle

Answer 33

1. respiration - carbon compounds like glucose are broken down and carbon dioxide is released to environment 2. photosynthesis - co2 is removed and fixed as organic compounds 3. feeding - in which carbon of organic molecules is moved from one link in the food chain to another 4. combustion - burning of fossil fuels, like coal and natural gas releases carbon dioxide to the environment 5. fossilisation - in which carbon as organic molecules become trapped in sediment as coal, gas, oil 6. decomposition - dead materials are broken down into simplier organic and inorganic substances by decomposers such as bacteria/ fungi * decomposers respire and carbon dioxide is released into environment & carbon dioxide is also released as one of the inorganic end products of decomposition

Question 34

Ecosystems as carbon reservoirs/ sinks

Answer 34

atmospheres, water bodies, plant & animal bodies, soil, sedimentary rocks, fossil fuels

Question 35

Carbon sink

Answer 35

If photosynthesis exceeds respiration, there is net uptake

Question 36

Carbon source

Answer 36

If respiration exceeds photosynthesis, there is net release - saprotrophs digest dead organic matter & release carbon as carbon dioxide due to respiration

Question 37

Define sequestration in relation to carbon sink

Answer 37

Sequestration is the removal of carbon from the cycle - periodic fires occur naturally in some ecosystems --> carbon dioxide is produced from the combustion of carbon compounds in living and dead organic matter --> ecosystem becomes a carbon source

Question 38

Carbon sinks and their dates of formation

Answer 38

1. Natural gas and oil - formed over past 550 million years or more, from Precambrian geological period onwards - deep burial of partially decomposed organic matter under sediments where high temps cause chemical changes and produced oil and natural gas trapped in porous rocks 2. Coal - mostly formed 325-250 million years ago, during Pennsylvanian and Permian geological periods - accumulation of wood and other plant matter in swamps where it was buried under other sediments 3. Peat - formed over past 10000 years in period since the last glaciation of the earth - incomplete decomposition of dead plant matter due to acidic anaerobic conditions in waterlogged bogs and swamps 4. Biomass - wood in trees has accumulated over the past few thousand years and other organic matter is more recent - plant biomass is derived from photosynthesis, with transfer along food chains to animal biomass

Question 39

Combustion

Answer 39

Combustion is burning in air - only begins if a specific ignition temperature is reached --> flash point - volcanic activity and lighting strikes can cause fires --> reach this flash point - humans discovered fire which allowed them to burn carbon sinks to release energy --> combustion of fossil fuels have risen rapidly --> balance of co2 production and uptake is radically shifted

Question 40

Analysis of Keeling Curve (photosynthesis, respiration, combustion)

Answer 40

1. annual fluctuations - every year, conc of co2 increases between October and may then falls from may to October - due to global imbalances in rates of co2 fixation by photosynthesis and release due to respiration - photosynthesis is higher overall during northern hemisphere summer, when plants over most of the earth's land surface are in main growth season 2. long-term trend - graph of co2 conc for one year shows that increase is not completely reversed by the decrease, so the conc at the end of year is higher - also shown by full keeling curve, from 1959 onwards - trend is largely due to burning of fossil fuels by humans, tgt with other anthropogenic factors like deforestation

Question 41

Dependence of aerobic respiration on atmospheric oxygen produced by photosynthesis and of photosynthesis on atmospheric carbon dioxide produced by respiration

Answer 41

the fluxes involved per year are huge, which is a major interaction between autotrophs and heterotrophs - respiring heterotrophs depend on photosynthesising autotrophs for oxygen supply - autotrophs dependent on heterotrophs for continued supply of carbon dioxide global carbon fluxes are extremely large they are estimates in gigatonnes (120 gigatonnes)

Question 42

All elements used by living organisms are recycled and decomposers plat a key role

Answer 42

Autotrophs obtain all of the elements they need as inorganic nutrients from the abiotic environment, incl carbon and nitrogen Heterotrophs obtain these two elements and several others as part of the carbon compounds in their food - they also do obtain other elements as inorganic nutrients from abiotic environment, incl sodium, potassium, calcium Organsisms absorb these elements as inorganic nutrients from abiotic environment, use them, and return them to the environment Decomposers play a key role bc they break down the carbon compounds containing chemical elements and release them