Unit 5: Energy Transfers In & Between Organisms

Question 1

what is the site of the light dependent stage of photosynthesis

Answer 1

the grana

Question 2

describe the stroma

Answer 2

a fluid-filled matrix where the light independent stage of photosynthesis takes place. it contains a number of other structures like starch grains.

Question 3

what does the chloroplast genome code for

Answer 3

ribosomal RNA

Question 4

define community

Answer 4

all the living organisms that live in a habitat at the same time

Question 5

define population

Answer 5

the number of the same species that live in a habitat at the same time

Question 6

define ecosystem

Answer 6

a community in conjunction with the non living components of the environment

Question 7

define abiotic

Answer 7

the non living, chemical and physical components of the ecosystem

Question 8

define biomass

Answer 8

the total mass of living matter within an organism

Question 9

define respiratory substrate

Answer 9

the organic molecules that can be oxidised by respiration, releasing energy to make molecules of ATP

Question 10

define calorimetry

Answer 10

a technique used to measure the quantity of heat gained/lost by a system

Question 11

the measure of biomass

Answer 11

dry mass of tissue per given area

Question 12

use of calorimetry

Answer 12

to estimate the chemical energy store in dry biomass

Question 13

what do the sugars synthesised by plants form

Answer 13

most are used as respiratory substrates and the rest make other groups of biological molecules which form the biomass

Question 14

define gross primary production

Answer 14

the total quantity of the chemical energy store in plant biomass, in a given area or volume, in a given time

Question 15

define net primary production

Answer 15

the chemical energy store which is left in plant biomass after respiratory losses to the environment have been taken into the account

Question 16

what is NPP available for

Answer 16

plant growth, reproduction, to other trophic levels in the ecosystem such as herbivores/consumers and decomposers

Question 17

the equation for net production of consumers

Answer 17

net = I - (F+R)
I = chemical energy store in ingested food
F = chemical energy store lost to the environment in faeces and urine
R = respiratory losses to the environment

Question 18

explain the reasons why a low percentage of energy is transferred between trophic levels

Answer 18

some of the organism is not consumed
some parts cannot be digested
some energy lost in excretory materials
some energy lost as heat from respiration, lost to the environment

Question 19

equation for percentage efficiency

Answer 19

energy available after transfer divided by energy available before transfer x 100

Question 20

one aim of a farming practice and an example

Answer 20

to reduce respiratory losses in a human food chain in order to reduce energy loss and increase yield.
e.g keeping animals in confined spaces to reduce muscle movement and can keep them warm to reduce heat loss (ethical concerns)

Question 21

second aim for farming practice and an example

Answer 21

to simplify food webs in order to reduce energy losses to non-human food chains.
e.g reduce/eliminate organisms that compete with the organism being farmed (crops compete with plants for water, space and light etc)

Question 22

benefit of natural predators introduced into the ecosystem

Answer 22

crops lose less biomass and increase productivities

Question 24

explain ammonification

Answer 24

• saprobiontic microorganisms feed off faeces, urine, and dead organisms
• this releases ammonia which forms ammonium ions in the soil
• the nitrogen returns to the non living component of the ecosystem

Question 25

explain nitrification

Answer 25

oxidation reactions occurs which releases energy
oxidation occurs by free-living soil microorganisms known as nitrifying bacteria
first the oxidation of ammonium ions to nitrite ions
then the oxidation of nitrite ions to nitrate ions
the nitrifying bacteria need oxygen for these conversions

Question 26

explain the farming practice of ploughing

Answer 26

nitrifying bacteria need oxygen for conversions of nitrate ions so lots of air spaces are preferable in the soil

Question 27

explain nitrogen fixation

Answer 27

free-living nitrogen fixing bacteria reduce gaseous nitrogen to ammonia which they then manufacture into amino acids
when the bacteria decay/die, nitrogen rich compounds are released
mutualistic nitrogen fixing bacteria live on nodules on the roots of plants and obtain carbs from the plants
in exchange the plant gets amino acids from them.

Question 28

explain denitrification

Answer 28

waterlogged soils means a decrease in oxygen concentration so there is a drop in aerobic nitrifying bacteria
therefore there is an increase anaerobic denitrifying bacteria which convert soil nitrates

Question 29

how do farmers prevent build up of denitrifying bacteria

Answer 29

ensure well aerated land

Question 30

define ammonification

Answer 30

the production of ammonia from organic nitrogen-containing compounds

Question 31

define nitrification

Answer 31

the conversion of ammonium ions to nitrate ions

Question 32

define nitrogen fixation

Answer 32

nitrogen gas is converted to nitrogen containing compounds

Question 33

outline the phosphorous cycle

Answer 33

phosphorous exists mostly as phosphate ions in sedimentary rock but weathering/erosion dissolves the ions
the ions are then absorbed by plants and are incorporated into their biomass
animals obtain the ions when they feed on these plants
excess ions are excreted and may accumulated in waste material
decomposers break down these dead plants and animals which releases phosphate ions into the water and soil
some of the ions are left in remains such as bone or shell because it is slower to decompose
the phosphate ions are then released by decomposition or dissolve out of rocks and are transported by rivers/streams into lakes/oceans where they form sedimentary rock and complete the cycle

Question 34

explain the role of mycorrhizae in nutrient cycles

Answer 34

fungi increase surface area for absorption of water/minerals
also acts as a sponge in the soil so holds water/minerals in the neighbourhood of the roots
this increases drought resistance and takes up inorganic ions more readily, improving the uptake of scarce phosphate ions

Question 35

describe the relationship between mycorrhizae and plants

Answer 35

a mutualistic/symbiotic relationship
the fungi gets sugars and amino acids from the plant
the plant benefits from increased water/ion uptake

Question 36

why does agriculture cause a loss in nutrients

Answer 36

when crops are harvested, minerals are removed and are not returned upon decomposition because the crops are taken away for consumption so minerals are not replaced by their remains/waste products

Question 37

define fertilisers

Answer 37

they replace the lost materials so increase energy efficiency of the food chain

Question 38

define natural fertilisers

Answer 38

organic matter such as manure, compost, sewage sludge, seaweed etc

Question 39

define artificial fertilisers

Answer 39

inorganic matter such as pure chemicals (ammonium nitrate as powder/pellets)

Question 40

describe the environmental issues with fertilisers

Answer 40

if more is added than can be used, the fertilisers are susceptible to leaching into waterways by rain or irrigation which can lead to eutrophication

Question 41

when is leaching more likely and with which fertiliser

Answer 41

if the fertiliser is applied just before rainfall.
artificial fertiliser is more soluble so more likely to leach

Question 42

benefit of natural fertiliser being less soluble

Answer 42

the fertiliser is released slower and with more control so it is harder to add in excess, less leaching

Question 43

relevance of phosphate-nitrate solubility

Answer 43

phosphates less likely to leach than nitrates as they are less soluble in water

Question 44

explain eutrophication

Answer 44

Caused by excess nutrients leaching into waterways/oceans etc)
The leached excess minerals stimulate rapid growth of algae, naturally nitrate ions are a limiting factor for plant and algal growth as in low concentrations
The new large amount of algae block light reaching plants beneath them, light becomes the limiting factor for growth at lower depths
These plants cannot photosynthesise enough so die
Saprobiontic bacteria then feed on the dead plants, as lack of dead organisms is no longer a limiting factor, they use up all remaining oxygen through aerobic respiration
Fish and other organisms in the water die because there is not enough dissolved oxygen to survive, oxygen becomes the limiting factor for the aerobic organisms
Less competition for the anaerobic organisms now so their populations rise
They further decompose dead material releasing more nitrates and making the water putrid.

Question 45

photolysis

Answer 45

a chlorophyll molecule absorbs a photon of light, splitting water into protons, electrons and oxygen
the electrons replace those lost due to photoionization
they provide energy for the proton pump and lead to chemiosmosis

Question 46

photoionization of chlorophyll

Answer 46

When a photon of light is absorbed, a pair of electrons gain energy and are excited
They become unstable and are transferred to an electron chain acceptor
Results in production of atp and reduced nadp

Question 47

chemiosmosis

Answer 47

Each electron carrier is at a lower energy level so electrons lose energy through the chain
This energy is used to transport protons from the stroma across into the thylakoid
Makes a concentration gradient of protons so they diffuse down the gradient through ATP synthase
This causes a change to the structure of ATP synthase and causes it to rotate, converts ADP and a Pi into ATP

Question 48

production of ATP and reduced NADP

Answer 48

ATP and NADPH are results of photolysis producing electrons and photoionisation moving those electrons outside the chlorophyll, through the electron transfer chain
Then chemiosmosis occurs to get the protons on the stroma side, producing ATP and NADP

Question 49

adaptations of the chloroplasts

Answer 49

Thylakoid membranes give a large surface area for the attachment of chlorophyll, electron carriers and enzymes for the LDR
Protein network in grana holds chlorophyll precisely to allow maximum light absorption
Granal membranes have ATP synthase to catalyze the production of ATP, selectively permeable to ensure a proton gradient
Contain dna and ribosomes to manufacturer some of the proteins involved in the LDR

Question 50

cyclic electron pathway

Answer 50

A photon is absorbed by chlorophyll a in PSI
Two electrons in this molecule is excited and attains a higher energy level and becomes unstable so is transferred to an electron acceptor
Acceptor is reduced, molecule is oxidized (photoionisation)
These redox reactions occur along the electron transport chain until the electron is accepted by ferredoxin
Each new carrier is at a lower energy level so electrons lose energy at each stage
Ferredoxin transfers the electron to the cytochrome proton pump which transfers it back to PSI
Protons are pumped across the thylakoid membrane from the chloroplast stroma to the thylakoid lumen which creates a proton gradient
The protons flow through ATP synthase channel protein which changes the structure of the enzyme and causes it to rotate
This catalyses the addition of a phosphate and a proton to form ATP
Known as photo phosphorylation

Question 51

non cyclic photophosphorylation pathway

Answer 51

A photon is absorbed by a molecule of water which breaks down into electrons, protons and oxygen
The electrons move into the reaction centre of PS2
The chlorophyll a molecule in PS2 absorbs a photon and an electron in this molecule is excited
The electron is donated between the electron acceptors, creating a series of redox known as the electron transfer chain
A section of the chain involves the transfer of the electrons between PS2 and PS1 which is performed by cytochrome proton pump
Protons are pumped across the thylakoid membrane from stroma to lumen, creating a gradient
High concentration inside the thylakoid space and low in the stroma
Protons flow through the channel protein associated with ATP synthase, causing the enzyme to rotate
Atp synthase catalyses the addition of ADP and a phosphate, forming ATP
Electron moves into reaction centre in PS1
The electron is excited again when P700 absorbs a photon and it is transferred between electron acceptors to ferredoxin
Electron transferred from ferredoxin to NADP, this cofactor also joins with a hydrogen ion to form reduced NADP
The electron in PS2 is replenished when another molecule of water is photolysed