Energy Transfers in and between Organisms

Question 1

what is an ecosystem?

Answer 1

an ecosystem includes all the organisms living in a particular area and all the non-living conditions.

Question 2

what is biomass?

Answer 2

biological molecules from glucose, as the product of photosynthesis, make up the plants biomass which is the mass of the living material

Question 3

how can biomass be measured?

Answer 3

biomass can be measured in terms of the mass of carbon that an organism contains or the dry mass of its tissue per unit area.

Question 4

what is dry mass?

Answer 4

dry mass is the mass of the organism with the water removed.

Question 5

how is dry mass measured?

Answer 5

a sample of the organism is dried, often in an oven set to a low temperature.
the sample is then weighed at regular time intervals. once the mass becomes constant you know that all the water has been removed.
the mass of carbon present is generally taken to be 50% of the dry mass.

Question 6

how can we calculate the amount of chemical energy stored in biomass?

Answer 6

using a calorimeter.
a sample of dry biomass is burnt and the energy released is used to heat a known volume of water.
the change in temperature of the water is used to calculate the chemical energy of the dry biomass.

Question 7

what is gross primary production (GPP)?

Answer 7

the total amount of chemical energy converted from light energy by plants, in a given area.

Question 8

what is respiratory loss (R)?

Answer 8

where approximately 50% of the gross primary production is lost to the environment as heat when the plants respire.

Question 9

what is net primary production (NPP)?

Answer 9

the remaining chemical energy once respiratory loss has taken place.
this is the energy available to the plant for growth and reproduction, stored in the plant’s biomass, as well as the energy available to organisms at the next stage in the food chain.

Question 10

what is the formula for NPP?

Answer 10

NPP = GPP - R

Question 11

what specific properties does ATP have that makes it a good energy source?

Answer 11

-ATP stores or releases only a small, manageable amount of energy at a time, so no energy is wasted as heat.
-it’s a small, soluble molecule so it can be easily transported around the cell.
-it’s easily broken down, so energy can be easily released instantaneously.
-it can be quickly remade.
-it can make other molecules more reactive by transferring one of its phosphate groups to them.
-ATP can’t pass out of the cell, so the cell always has an immediate supply of energy.

Question 12

define metabolic pathways

Answer 12

a series of small reactions controlled by enzymes

Question 13

define phosphorylation

Answer 13

adding phosphate to a molecule

Question 14

define photophosphorylation

Answer 14

adding phosphate to a molecule using light

Question 15

define photolysis

Answer 15

the splitting of a molecule using light (photo) energy

Question 16

define photoionisation

Answer 16

when light energy ‘excites’ electrons in an atom or molecule, giving them more energy and causing them to be released. the release of electrons causes the atom or molecule to become a positively charged ion

Question 17

define hydrolysis

Answer 17

the splitting of a molecule using water

Question 18

define decarboxylation

Answer 18

the removal of carbon dioxide from a molecule

Question 19

define dehydrogenation

Answer 19

the removal of hydrogen from a moleculedef

Question 20

define redox reactions

Answer 20

reactions that involve oxidation and reduction

Question 21

what is a coenzyme?

Answer 21

a molecule that aids the function of an enzyme.
they work by transferring a chemical group from one molecule to another

Question 22

what coenzyme is used photosynthesis?

Answer 22

NADP. this transfers hydrogen from one molecule to another; this means it can reduce (give hydrogen to) or oxidise (take hydrogen from) a molecule

Question 23

what are chloroplasts?

Answer 23

they are flattened organelles surrounded by a double membrane. they are found in plant cells.

Question 24

what features are in chloroplasts?

Answer 24

-double membrane
-thylakoids
-grana
-stroma
-starch grains
-photosynthetic pigments

Question 25

what are thylakoids?

Answer 25

they are fluid-filled sacs which are stacked up in the chloroplast into structures called grana. the grana are linked together by the thylakoid membrane called lamellae.

Question 26

what is the stroma?

Answer 26

a gel-like substance contained within the inner membrane of the chloroplast, that surrounds the thylakoids.
the stroma contains enzymes, sugars and organic acids

Question 27

what are starch grains?

Answer 27

carbohydrates produced by photosynthesis but are not used straight away are stored as starch grains in the stroma.

Question 28

what are photosynthetic pigments? and list 3 examples

Answer 28

these are coloured substances that absorb light energy needed for photosynthesis. the pigments are found in the thylakoid membranes; attached to the proteins.
e.g chlorophyll a, chlorophyll b and carotene

Question 29

what is a photosystem?

Answer 29

the attachment of a protein and pigment. they are used by plants to capture light energy.

Question 30

what are the two photosystems?

Answer 30

photosystem I
photosystem II

Question 31

at what wavelengths do the photosystems absorb light best?

Answer 31

photosystem I - 700nm
photosystem II - 680nm

Question 32

what two stages make up photosynthesis?

Answer 32

the light-dependent reaction and the light-independent reaction

Question 33

where does the light-dependent reaction take place?

Answer 33

it takes place in the thylakoid membranes of the chloroplasts

Question 34

what occurs in the light-dependent reaction?

Answer 34

light energy is absorbed by chlorophyll and other photosynthetic pigments in the photosystems.
the light energy excites the electrons in the chlorophyll, leading to their eventual release from the molecule. the chlorophyll has been photoionised.
some of the energy from the released electrons is used to add a phosphate group to ADP to form ATP, and some is used to reduce NADP to form reduced NADP.
ATP transfers energy and reduced NADP transfers hydrogen to the light-independent reaction
during the process H2O is oxidised to O2.

Question 35

what is the light-independent reaction also known as?

Answer 35

the Calvin cycle.

Question 36

where does the light-independent reaction take place?

Answer 36

it takes place in the stroma of the cholorplast.

Question 37

what occurs in the light-independent reaction?

Answer 37

the ATP and reduced NADP from the light-dependent reaction supply the energy and hydrogen to make simple sugars from CO2.

Question 38

what is the energy, resulted from the photoionisation of cholorphyll in the light-dependent reaction, used for?

Answer 38

making ATP from ADP and inorganic phosphate. this reaction called photophosphorylation.
making reduced NADP from NADP.
splitting water into protons (H+ ions), electrons and oxygen. this is called photolysis.

Question 39

what are the two types of photophosphorylation?

Answer 39

non-cyclic and cyclic

Question 40

what is involved in non-cyclic photophosphorylation? and what 3 substances does it produce?

Answer 40

it involves photosystem I (PSI) and photosystem II (PSII).
and it produces ATP and reduced NADP and oxygen

Question 41

explain stage 1 in the process of non-cyclic photophosphorylation

Answer 41

stage 1 is the photoionisation of chlorophyll in PSII.
chlorophyll in photosystem II absorbs light energy. this energy causes an electron in the chlorophylll to be excited. the electron is emitted/lost from the chlorophyll molecule. the excited electron is captured by an electron acceptor and it moves along the electron transport chain to PSI.
the cholorphyll molecule is oxidised and becomes positively charged.

Question 42

explain stage 2 in the process of non-cyclic photophosphorylation

Answer 42

stage 2 is the photolysis of water
photoionisation of chlorophyll results in the photolysis of water into oxygen, hydrogen ions and electrons.
the electron lost form the chlorophyll molecule can now be replaced by a reduced chlorophyll molecule.

Question 43

explain stage 3 in the process of non-cyclic photophosphorylation

Answer 43

stage 3 is the electron transport chain and photophosphorylation (chemiosmosis)
as the electron is passed from carrier to carrier along the electron transport chain in a series of redox reactions, energy is released at each stage.
the energy is used to move hydrogen ions from the stroma into the thylakoid space against their concentration gradient creating an electrochemical gradient.
the hydrogen ions pumped into the thylakoid space move down their concentration gradient through the enzyme ATP synthase which is embedded in the thylakoid membrane. the energy from this movement combines ADP + inorganic phosphate to form ATP.

Question 44

explain stage 4 in the process of non-cyclic photophosphorylation

Answer 44

stage 4 is the photoionisation of chlorophyll in PSI
at the exact same time as photoionisation of chlorophyll in PSII: chlorophyll in PSI also absorbs light energy.
an electron gets excited and is emitted/lost from the chlorophyll molecule.
the excited electron is captured by an electron acceptor. the electron lost from the molecule in PSI is replaced by electron that passed down the electron transport chain lost from the chlorophyll in PSII.

Question 45

explain stage 5 in the process of non-cyclic photophosphorylation

Answer 45

stage 5 is the reduction of NADP to reduced NADP
the excited electron from the chlorophyll molecules in photosystem I is passed along a series of electron carriers across another electron transport chain to the final acceptor molecule NADP.
the hydrogen ions from the photolysis of water also combine with NADP to form reduced NADP (NADPH).

Question 46

what is involved in cyclic photophosphorylation? and what substance does it produce?

Answer 46

it involves only PSI.
it only produces ATP.

Question 47

why is cyclic photophosphorylation called ‘cyclic’?

Answer 47

it is called ‘cyclic’ because the electrons from the chlorophyll molecule aren’t passed onto NADP, but are passed back to PSI via electron carriers.

Question 48

what are the three stages of the calvin cycle?

Answer 48

stage 1: fixation of carbon dioxide from an inorganic molecule into an organic molecule
stage 2: reduction of GP using reduced NADP and ATP
stage 3: regeneration of RuBP using ATP so the cycle can continue

Question 49

explain stage 1 of the calvin cycle

Answer 49

carbon dioxide reacts with ribulose bisphosphate (RuBP), a 5C compound, in a reaction catalysed by the enzyme Rubisco.
the resulting 6C compound is unstable and immediately breaks down into two molecules of a 3C compound called glycerate-3-phosphate (GP).

Question 50

explain stage 2 of the calvin cycle

Answer 50

the GP is reduced to two molecules of triose phosphate (TP), a 3C compound, using hydrogen (H+)/electrons from reduced NADP and energy from ATP.
TP is then converted to complex organic molecules e.g glucose, sucrose, starch, cellulose, amino acids etc.

Question 51

explain stage 3 of the calvin cycle

Answer 51

five out of every six molecules of TP produced in the cycle are used to regenerate RuBP in a series of enzyme catalysed reactions. this uses energy from ATP.

Question 52

why does the calvin cycle need to turn six times to make one hexose sugar?

Answer 52

-three turns of the calvin cycle produces six molecules of TP because two molecules of TP are made for every one carbon dioxide molecule used.
-five out of six of these TP molecules are used to regenerate RuBP.
-this means that for three turns of the cycle only one TP is produced that’s used to make a hexose sugar.
-a hexose sugar has six carbons though, so only two TP molecules are needed to form one hexose sugar.
-this means the cycle must turn six times to produce two molecules of TP that can be used to make one hexose sugar.
-six turns of the cycle need 18 ATP and 12 reduced NADP.

Question 53

what are the three factors that limit the rate of photosynthesis?

Answer 53

light intensity
temperature
carbon dioxide concentration

Question 54

what are the ideal conditions for light intensity in photosynthesis?

Answer 54

-high light intensity of a certain wavelength.
the higher the intensity of the light, the more energy it provides.
only certain wavelengths of light are used for photosynthesis.
the photosynthetic pigments only absorb red and blue in sunlight.

Question 55

what are the ideal conditions for temperature- in photosynthesis?

Answer 55

-temperature around 25 degree celsius.
photosynthesis involves enzymes (e.g ATP synthase, rubisco).
if the temperature falls below 10 degrees the enzymes become inactive, but if the temperature is more than 45 degrees they may start to denature.
also at high temperatures stomata close to avoid losing too much water. this causes photosynthesis to slow down because less CO2 enters the leaf when the stomata are closed.

Question 56

what are the ideal conditions for carbon dioxide concentration in photosynthesis?

Answer 56

-carbon dioxide at 0.4%.
carbon dioxide makes up 0.04% of the gases in the atmosphere.
increasing this to 0.4% gives a higher rate of photosynthesis, but any higher and the stomata start to close.

Question 57

explain the light intensity graph on its approach on limiting the rate of photosynthesis

Answer 57

the graph increases at first and then levels off.
when the graph increases