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A-level Biology > Unit 3.5 - Energy transfers in and between organisms > Flashcards

Unit 3.5 - Energy transfers in and between organisms Flashcards

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1
Q

what is photosynthesis?

A

its the process where energy from light is used to make glucose from H20 and CO2. the light energy is converted to chemical energy in the form of glucose
6H2O + 6CO2 -> Energy -> C6H12O6 + 6O2

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2
Q

where is energy stored in plants?

A
  • its stored in the glucose until the plants release it by respiration. animals obtain glucose by eating plants or other animals then respire the glucose to release energy
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3
Q

how do plants and animals release energy?

A
  • they release energy from glucose in respiration, which is used in all biological processes.
  • aerobic respiration uses oxygen and anaerobic respiration is without oxygen
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4
Q

what does anaerobic respiration make?

A

in plants and yeast it produces ethanol and carbon dioxide and releases energy. in humans, it produces lactase and releases energy

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5
Q

what happens to the energy in respiration?

A

the energy released from glucose is used to make ATP which carries energy around the cell to where its needed. ATP is synthesised via a condensation reaction between ADP and inorganic phosphate using energy from and energy-releasing reaction.

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6
Q

describe and energy-releasing reaction?

A

eg the breakdown of glucose in respiration. the energy is stored as chemical energy in the phosphate bond. the enzyme ATP synthase catalyses the reaction.

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7
Q

what happens after ATP synthase catalyses the reaction?

A
  • ATP diffuses to the part of the cell that needs energy. here its hydrolysed back into ADP and inorganic phosphate. chemical energy is released from the phosphate bond and used by the cell. ATP hydrolase catalyses this reaction.
  • the ADP and Pi are recycled and it starts again
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8
Q

what are the pros of ATP?

A
  • it releases energy in a small, manageable amounts so none is wasted as heat
  • its soluble so can be transported easily
  • easily broken down so can be released instantaneously
  • make other molecules more reactive by transferring a phosphate to them (phosphorylation)
  • it cant pass out the cell so the cell always has an immediate supply of energy
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9
Q

what is a metabolic pathway?

A

a series of small reactions controlled by enzymes eg photosynthesis

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10
Q

what is phosphorylation?

A

adding phosphate to a molecule

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11
Q

what is photophosphorylation?

A

adding phosphate to a molecule using light

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12
Q

what is photolysis?

A

the splitting (lysis) of a molecule using light (photo) energy

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13
Q

what is photoionisation?

A

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

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14
Q

what is hydrolysis?

A

the splitting (lysis) of a molecule using water (hydro)

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15
Q

what is decarboxylation?

A

the removal of co2 from a molecule

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16
Q

what is dehydrogenation?

A

the removal of hydrogen from a molecule

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17
Q

what are redox reactions?

A

reactions that involve oxidation and reduction

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18
Q

what is a coenzyme?

A

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

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19
Q

what is the coenzyme in photosynthesis?

A

its NADP which transfers hydrogen from one molecule to another which means it can reduce (give hydrogen) or oxidise (take hydrogen from) a molecule

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20
Q

what do chloroplasts contain?

A

they have photosynthetic pigments like chlorophyll a, chlorophyll b and carotene. these are coloured substances that absorb light energy needed for PHS.
- they are found in the thylakoid membranes where they’re attached to proteins.

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21
Q

what is a photosystem?

A

its made up of a protein and pigment together. there are two photosystems used by plants to capture light energy.
- photosystem I (PSI) and photosystem II (PSII)

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22
Q

what is stroma?

A
  • its contained within the inner membrane of the chloroplast and surrounds the thylakoid. its a gel like substance and contains enzymes, sugars and organic acids
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23
Q

what is the energy resulting from the photoionisation of chlorophyll used for?

A

1 - making ATP from ADP and Pi in photophosphorylation
2 - making reduced NADP from NADP
3 - splitting water into protons (H+ ions), electrons and oxygen in photolysis

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24
Q

what are photosystems linked by?

A
  • they are linked by electron carriers, which are proteins that transfer electrons. the photosystems and electron carriers form an electron transport chain- a chain of proteins which excited electrons flow through
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25
Q

what is Step 1 of the LDR?

A

light energy is absorbed by PSII which excites electrons in the chlorophyll. the electrons move to a higher energy level to where they’re released from the chlorophyll and move down the electron transport chain to PSI.
the chlorophyll has been photoionised

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26
Q

what is Step 2 of the LDR?

A

as the excited electrons leave PSII to move down the transport chain, they must be replaced. light energy splits water into protons (H+ ions), electrons and oxygen in photolysis.
(so the O2 in PHS comes from water and is made in the LDR = H20 -> 2H+ + 0.5O2

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27
Q

what is Step 3 of the LDR?

A

the electrons lose energy as they move down the chain. this energy is used to transport protons into the thylakoid, so that it has a higher concentration of protons than the stroma.
- this forms a proton gradient across the membrane, where they move down into the stroma via ATP synthase which is embedded in the thylakoid membrane. the energy from their movement combines ADP and Pi to ATP.

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28
Q

what is Step 4 of the LDR?

A

light energy is absorbed by PSI, which excites the electrons to a higher energy level. the electrons are transferred to NADP, along with a proton (H+ ion) from the stroma to form reduced NADP.

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29
Q

what is chemiosmosis?

A

its the process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis

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30
Q

what is cyclic photophosphorylation?

A

it only uses PSI. it is cyclic as the electrons from the chlorophyll molecule aren’t passed onto NADP, but they’re passed back to PSI via the electron carriers. this means the electrons are recycled and can flow through PSI.
- this process produces small amounts of ATP only

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31
Q

what is the Light independent reaction/calvin cycle?

A

it takes place in the stroma of the chloroplasts. it makes a molecule called triose phosphate from CO2 and ribulose bisphosphate

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32
Q

what is Step 1 of the calvin cycle?

A

CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast. it’s combined with ribulose bisphosphate RuBP, a 5cc. reaction is catalysed by enzyme rubisco.
this makes in unstable 6-carbon compound, which breaks down into 2 molecules of 3-carbon compound called glycerate 3-phosphate, GP

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33
Q

what is Step 2 of the calvin cycle?

A

the hydrolysis of ATP from LDR provides energy to turn the GP into a different 3-carbin compound called triose phosphate TP. this reaction require H+ ions which come from the reduced NADP from the LDR.
some TP is converted into useful organic compounds eg glucose and some continues in the cycle to regenerate RuBP

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34
Q

what is Step 3 of the calvin cycle?

A

five out of every six molecules of TP produced in the cycle aren’t to make hexose sugars, but to regenerate RuBP. regenerating RuBP uses the rest of the ATP produced by the LIR.

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35
Q

how are carbohydrates made?

A

hexose sugars eg glucose are made by joining two triose phosphate molecules together and larger carbohydrates are made by joining hexose sugars together in different ways

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36
Q

how are lipids and amino acids made?

A

lipids - made using glycerol which is synthesised from triose phosphate and fatty acids which are synthesised from glycerate 3-phosphate
amino acids - some are also made from glycerate 3-phosphate

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37
Q

how does light intensity affect PHS?

A

light is needed to provide the energy for the LDR so the higher the intensity of light, the more energy it provides. only certain wavelengths of light are used eg chlorophyll a and b and carotene only absorb red and blue light in sunlight

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38
Q

how does temperature affect PHS?

A

PHS involves enzymes therefore if it falls below optimum enzymes become inactive but if its too high they may start to denature. also at high temps, stomata close to avoid losing too much water which causes PHS to slow down as less CO2 enters

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39
Q

how does CO2 affect PHS?

A

having too high CO2 levels means the stomata start to close
- also plants need a constant supply of water, too little PHS has to stop but too much and the soil becomes waterlogged reducing uptake of minerals

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40
Q

describe glycolysis? A

A

it involves splitting one molecule of glucose (with 6C) into two smaller molecules of pyruvate (3C). the process happens in the cytoplasm of cells outside the mitochondria, its an anaerobic process.

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41
Q

what happens in phosphorylation in glycolysis? A

A

glucose is phosphorylated using a phosphate from a molecule of ATP. this creates 1 molecule of glucose phosphate and 1 molecule of ADP. ATP is then used to add another phosphate, forming hexose bisphosphate, which is then split into 2 molecules of TP

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42
Q

what happens in oxidation in glycolysis? A

A

TP is oxidised forming 2 molecules of pyruvate. NAD collects the hydrogen ions, forming 2-reduced NAD. 4 ATP are produced, but 2 were used up in phosphorylation, so there’s a net gain of 2 ATP

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43
Q

describe the link reaction? B

A

pyruvate is decarboxylated (one carbon atom is removed from pyruvate in the form of CO2). pyruvate is oxidised to form acectate and NAD is reduced to form NAD, the acectate is combined with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA). no ATP is made.

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44
Q

how many pyruvate molecules are made for every glucose?

A

two pyruvate molecules are made for every glucose molecules that enters glycolysis. this means the link reaction and the krebs cycle happen twice for every glucose molecule.

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45
Q

describe the molecules that go into krebs cycle?

A

1- two molecules of acetyl CoA go into the krebs cycle
2- two CO2 molecules are released as a waste product of respiration
3- two molecules of reduced NAD are formed and go into the last stage (oxidative phosphorylation)

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46
Q

describe the krebs cycle?

A

it involves a series of oxidation - reduction reactions, which take place in the matrix of the mitochondria. the cycle happens once for every pyruvate molecule, it goes round twice for every glucose molecule

47
Q

what is part 1 of the krebs cycle?

A

acetyl coA from the link reaction combines with a 4C molecule (oxaloacetate) to form a 6C molecule citrate. coenzyme A goes back to the link reaction to be used again

48
Q

what is part 2 of the krebs cycle?

A

the 6C citrate molecule is converted to a 5C molceule. decarboxylation occurs where CO2 is removed, dehydrogenation also occurs, where hydrogen is removed. the hydrogen is used to produce reduced NAD from NAD.

49
Q

what is part 3 of the krebs cycle?

A

the 5C molecule is converted to a 4C molecule. decarboxylation and dehyrdogenation occur, producing one molecule of reduced FAD and two of reduced NAD, ATP is made by the direct transfer of phosphate group from an intermediate compound to ADP

50
Q

what is part 1 of oxidative phosphorylation?

A

hydrogen atoms are released from reduced NAD and FAD as they’re oxidised to NAD and FAD. the H atoms split into H+ protons and electrons. the electrons move down the electron tranport chain losing energy at each carrier

51
Q

what is part 2 of oxidative phosphorylation?

A

the energy is used up by the electron carriers to pump protons from the mitochondiral matrix into the intermembrance space. the concentration of protons is now higher in the intermembrance space than in the mitochondiral matrix, this forms a electrochemical gradient

52
Q

what is part 3 of oxidative phosphorylation?

A

protons then move down the electrochemical gradient, back across the inner mitochondrial membrane and into the mitochondrial matrix, via ATP synthase protein channel. this movement causes changes to the enzyme which then catalyses the combination of ATP from ADP and Pi.

53
Q

what is oxidative phosphorylation?

A

its the process where the energy carried by the electrons, from reduced coenzymes is used to make ATP

54
Q

how do mitochondrial diseases affect the functioning of mitochondria?

A

they can affect how proteins involved in oxidative phosphorylation or the krebs cycle function, by reducing ATP production. this may cause anaerobic respiration to increase, to try and make up some of the ATP storage

55
Q

what happens due to an increase in the amount of anaerobic respiration occurring?

A

it results in lots of lactate being produced, which can cause muscle fatigue and weakness. some lactate will diffuse into the bloodstream leading to high lactate concentrations in the blood

56
Q

what is the pyruvate converted into in anaerobic respiration?

A

the pyruvate in glycolysis is converted into ethanol or lactate. the production of ethanol or lactate regenerates oxidised NAD. this means glycolysis can continue even when there isn’t much O2 around, so a small amount of ATP can still be produced to keep some processes going.

57
Q

what happens in the mitochondrial matrix at the end of oxidative phosphorylation?

A

In the mitochondrial matrix at the end of the transport chain, the protons, electrons and O2 combine to form water. oxygen is said to be the final electron acceptor.

58
Q

what are producers?

A

they are organisms that make their own food, through photosynthesis. during photosynthesis, plants use energy from the sun and co2 to make glucose

59
Q

what makes up biomass?

A

biological molecules eg cellulose make up the plants biomass, it can be thought of as the chemical energy stored in plants.
- it is measured in the terms of the mass of carbon that an organism contains or the dry mass of its tissue per unit

60
Q

what is GPP?

A

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

61
Q

what is the respiratory loss R?

A

approx 50% of the GPP is lost to the environment as heat when the plants respire. this is respiratory loss

62
Q

what is NPP?

A

the remaining chemical energy is called the net primary productivity, it is the energy available to the plant for growth and reproduction and is the energy available to organisms in the next trophic level.

63
Q

what is primary production expressed as?

A

its expressed as a rate, primary productivity kJ ha-1 year -1

64
Q

how do consumers also store their energy?

A

they also store chemical energy in their biomass. they get their energy by ingesting plant material or animals that have eaten plant material.

65
Q

how is energy lost through trophic levels?

A
  • some parts of the organism is not consumed
  • some parts are consumed but cannot be digested and are therefore lost in faeces
  • some is lost as urine
  • some energy is lost as heat from respiration and lost to the environment
66
Q

what is the equation for net production?

A

N = I - (F+R)

  • net production N
  • chemical energy I
  • chemical energy lost in faeces and urine F
  • energy lost through respiration R
  • the net production of consumers can also be called secondary production
67
Q

what are food chains?

A

they show simple lines of energy transfer, where each stage is a trophic level

68
Q

what are food webs?

A

they show lots of food chains in an ecosystem and how they overlap. decomposers are also apart of food webs, they break down dead or undigested material

69
Q

what are most farming practices’ aim?

A

they aim to increase the amount of energy that’s available for human consumption by reducing the energy they lose to other organisms

70
Q

how do farmers reduce pests?

A

by using pesticides eg insecticides which kill insects meaning less biomass is lost from crops, so they grow to be larger which means NPP is greater. herbicides kill weeds which remove direct competition with the crop for energy from the sun

71
Q

how do biological agents reduce number of pests?

A

they reduce the number of pests so crops lose less energy and biomass increasing efficiency of energy transfer to humans

72
Q

what are integrated systems do?

A

they combine both chemical and physical methods. the combined effect of using both can reduce pest numbers even more than either method alone, meaning NPP is increased even more

73
Q

how do farmers increase the net production of their livestock?

A

by controlling the conditions that they live in so that more of their energy is used for growth and less in lost through respiration

74
Q

how movement in animals reduce NPP?

A

it increases the rate of respiration, so animals may be kept in pens where their movement is restricted. they’re often indoors and kept warm, so less energy is wasted by generating body heat
- this means that more biomass is produced and more chemical energy can be stored, increasing net production

75
Q

what are the benefits of farmers reducing animal movement?

A
  • more food can be produced in a shorter space of time often at a lower cost. however there are ethical issues, people believe these conditions cause pain, distress or restricts their natural behaviour
76
Q

what is a natural ecosystem?

A

its one that hasnt been changed by human activity. in natural ecosystems nutrients are recycled through the food webs, but human activity often disrupts the cycling of nutrients

77
Q

what are saprobionts?

A

they are a group of organisms that break down complex materials in dead organisms into simple ones, where they then release minerals and elements in a form that can be absorbed by plants.

78
Q

what is extracellular digestion?

A

saprobionts excrete enzymes and digest their food externally, then absorb the nutrients they need. this is extracellular digestion. during this process, organic molecules are broken down into inorganic ions.

79
Q

what is saprobiotic nutrition?

A

obtaining nutrients from dead organic matter using extracellular digestion is saprobiotic nutrition

80
Q

describe a fungi’s symbiotic relationship?

A

1- the fungi are made up of long, thin strands called hyphae, which connect to the plant’s roots
2- the hyphae greatly increase the surface area of the plant’s root system, helping the plant to absorb ions from the soil that are usually scarce. hyphae also increase the uptake of water by the plant
3- in turn, the fungi obtain organic compounds such as glucose

81
Q

what is the nitrogen cycle?

A

shows how nitrogen is converted into a unstable form and then passed between different living organsims and the non-living environment

82
Q

describe nitrogen fixation? 1

A

it is when nitrogen gas in the atmosphere is turned into nitrogen-containing compounds, biological nitrogen fixation is carried out by bacteria which turn nitrogen into ammonia, which goes on to form ammonium ions in solution that can be used by plants

83
Q

describe ammonification? 2

A

ammonification is the production of ammonia from organic nitrogen containing compounds. saprobionts feed on faeces and dead materials, releasing ammonia, which then forms ammonium ions in the soil, this is where nitrogen returns to the non-living parts of the ecosystem.

84
Q

describe nitrification? 3

A

it is when ammonium salts in the soil are changed into nitrogen compounds that can be used by plants (nitrates). first nitrifying bacteria oxidise ammonium ions into nitrite ions then other nitrifying bacteria oxidise nitrite ions and nitrate ions

85
Q

describe denitrification? 4

A

when soils become waterlogged, and have low oxygen concentration, there is an increase in anaerobic denitrifying bacteria. these convert soil nitrates into gaseous nitrogen, which reduces the availability of nitrogen’containing compounds of plants.

86
Q

what are the other ways nitrogen enter an ecosystem?

A

by lightening which fixes atmospheric nitrogen or by artificial fertilisers they’re produced from atmospheric nitrogen on an industrial scale

87
Q

what is part 1 of the phosphorus cycle?

A

phosphate ions in rocks are released into the soil by weathering

88
Q

what is part 2 of the phosphorus cycle?

A

phosphate ions are taken into the plants through the rocks. mycorrhizae greatly increase the rate at which phosphorus can be assimilated.

89
Q

what is part 3 of the phosphorus cycle?

A

phosphate ions are transferred through the food chain as animals eat plants and are in turn eaten by other animals. the ions are lost from the animals in waste products

90
Q

what is part 4 of the phosphorus cycle?

A

when plants and animals die, saprobionts are involved in breaking down the organic compounds, releasing phosphate ions into the soil for assimilation by plants. these microorganisms also release the ions from urine and faeces

91
Q

what is part 5 of the phosphorus cycle?

A

weathering of rocks also releases phosphate ions into seas, lakes and rivers. this is taken up by aqautic producers eg algae and passed along the food chain to birds

92
Q

what is part 6 of the phosphorus cycle?

A

the waste produced by sea birds known as guano and contains a high proportion of ions. guano returns a significant amount of phosphate ions to soils, often used as natural fertiliser

93
Q

what happens when crops take in minerals from the soil?

A

as they grow and use them to build their own tissues, when crops are harvested they’re removed from the fields where they’re grown rather than being allowed to die and decompose. this means the mineral ions that they contain aren’t returned to the soil by decomposes in the nitrogen or phosphorus cycles.

94
Q

how are phosphates and nitrates lost from the system?

A

when animals or animal products are removed from the land. animals eat grass and other plants, taking in their nutrients. when they are taken elsewhere for slaughter or transferred to another field, the nutrients aren’t replaced through their remains or waste products

95
Q

who do fertilisers do?

A

ones that include nitrogen increase the rate of photosynthesis and improves crop productivity, as nitrate ions are needed for growth. with them present plants are likely to develop earlier and have a bigger SA.

96
Q

what do artificial and natural fertilisers do?

A
  • artificial are inorganic and are mined from rocks and then converted into different forms and blended together
    natural are organic which consists of the dead and decaying remains of plants and animals as well as animal waste
97
Q

what is leaching?

A

is when water soluble compounds in the soil are washed away by rain into nearby ponds which can lead to eutrophication

98
Q

what are inorganic ions in fertilisers like?

A

they’re relatively soluble. this means that excess minerals that aren’t used immediately are more likely to leach into waterways

99
Q

what are nitrogen and phosphorus in natural fertilisers like?

A

they are still contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed by plants. this means that their release into the soil for the uptake by plants is more controlled and leaching is less likely

100
Q

describe eutrophication? 1

A

1 - in most lakes, there is a very low concentration os nitrate and so nitrate ions are a limiting factor for plant and algal growth
2 - as thr nitrate ion concentration increases as a result of leaching, it stops becoming a limiting factor for plants and animals so they both grow
3 - the upper layer of water become densley populated with algae ‘algal bloom’
4 - the algae absorbs light and prevents it from penetrating to lower depths

101
Q

what are the adaptations of a leaf for photosynthesis?

A

1- a large surface area that absorbs lots of light
2- a transparent cuticle and epidermis that let light through to mesophyll cells
3- stomata that open and close in response to light
4- many air spaces in mesophyll layer to allow rapid diffusion
5- arrangement of leaves on the plant that minimise overlapping and so avoids the shadowing of one leaf by another

102
Q

how is a chloroplast adapted in the LDR?

A

1- the thylakoid membrane has a large SA for the attachment of chlorophyll
2- the granal membranes have ATP synthase channels within them, they are also selectively permeable which allows establishment of a proton gradient
3- chloroplasts contain both DNA and ribosomes so they easily manufacture some of the proteins involved in the LDR

103
Q

what happens when oxygen is in short supply?

A

NAD from glycolysis can accumulate and must be removed. Each pyruvate molecule produced takes up two hydrogen atoms from the reduced NAD produced in glycolysis to form lactate. the lactate produced is oxidised back to pyruvate.

104
Q

what is free-living nitrogen fixing bacteria?

A

these bacteria reduce gaseous nitrogen to ammonia, which they then use to manufacture amino acids. nitrogen-rich compounds are released from them when they die and decay

105
Q

what is mutualistic nitrogen-fixing bacteria?

A

these bacteria live in nodules on the roots of plants. they obtain carbohydrates from the plant and the plant acquires amino acids from the bacteria.

106
Q

what are mycorrhizae?

A

they are associations between certain types of fungi and the roots of plants. the fungi act like extensions of the plant’s root system and increase the SA for the absorption of water and minerals.

107
Q

what do the mycorrihizae act as?

A

they act as a sponge and so holds water and minerals of the roots. this enables the plant to better resist drought and to take up inorganic ions more readily. they improve the uptake of relatively scarce ions eg phosphate.

108
Q

what is the relationship between plants and fungi like?

A

its a mutualistic one. the plant benefits from improved water and inorganic ion uptake while the fungi receives sugars and amino acids from the plant

109
Q

describe eutrophication? 3

A

9 - oxygen becomes the limiting factor for the population of aerobic organisms, which then die.
10 - without aerobic organisms, there is less competition for the anaerobic organisms, whose populations now rise
11 - the anaerobic organisms decompose dead material releasing more nitrates and toxic wastes

110
Q

describe eutrophication? 2

A

5 - light then becomes the limiting factor for growth at lower depths so plants die
6 - the lack of dead plants and algae is no longer a limiting factor for the growth of saprobiontic bacteria and so these populations now grow
7 - the bacteria require oxygen for their respiration, creating in increased amount for O2
8 - the conc of oxygen in the water is reduced and nitrates are released from the decaying organisms

111
Q

what is the overall yield from one glucose molecule undergoing glycolysis?

A
  1. two molecules of ATP (two were used in phosphorylation, net gain of two)
  2. two molecules of reduced NAD
  3. two molecules of pyruvate
112
Q

describe NAD, FAD and NADP?

A

NAD: important throughout respiration
FAD: important in krebs
NADP: important in photosynthesis

113
Q

What is the significance of Krebs?

A
  • breaks down pyruvate into CO2
  • produces hydrogen atoms that are carried by NAD to the electron chain and provide energy for oxidative phosphorylation
  • regenerates 4-carbon molecule with acetylcoenzyme A which would otherwise accumulate
114
Q

what is the equation for formation of ethanol at end of glycolysis?

A

pyruvate + reduced NAD -> ethanol + CO2 + oxidised NAD

A-level Biology (8 decks)

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