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A-LEVEL BIOLOGY > Energy and Respiration > Flashcards

Energy and Respiration Flashcards

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1
Q

Why do living organisms need energy

A

The activities and processes being carried out inside cells to sustain life requires energies

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2
Q

Types of work that require energy

A

-Transporting substances across membrane
-Anabolic reactions (synthesis of materials)
-Movement
-Maintaining body temperature

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3
Q

What is ATP

A

adenosine triphosphate (ATP) is small and soluble molecule that provides short-term store of chemical potential energy that cells can use to do work

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4
Q

Hydrolysis of ATP

A

-When ATP is hydrolysed (broken down), ADP and phosphate are produced
-As ADP forms free energy is released that can be used for processes within a cell eg. DNA synthesis
-Removal of one phosphate group from ATP releases approximately 30.5 kJ mol -1 of energy, forming ADP
-Removal of a second phosphate group from ADP also releases approximately 30.5 kJ mol-1 of energy, forming AMP
-Removal of the third and final phosphate group from AMP releases 14.2 kJ mol-1 of energy, forming adenosine

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5
Q

Features that optimise ATP for its function

A

-Releases a small but sufficient amount of energy
-Exists as a stable molecule
-Can be recycled
-Hydrolysis is quick and easy
-Soluble and moves easily within cells
-Forms phosphorylated intermediates

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6
Q

Analyse how the feature optimises an ATP molecule for its function: Releases a small but sufficient amount of energy (75.8 kJ mol-1 from the complete hydrolysis of ATP)

A

This is enough energy to drive important metabolic reactions while keeping energy wastage low

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7
Q

Analyse how the feature optimises an ATP molecule for its function: Exists as a stable molecule

A

It doesn’t break down unless a catalyst (ATPase) is present so energy won’t be wasted

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8
Q

Analyse how the feature optimises an ATP molecule for its function: Can be recycled

A

The breakdown of ATP is a reversible reaction, ATP can be reformed from ADP and Pi. This means that same molecule can be reused elsewhere in the cell for different reactions

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9
Q

Analyse how the feature optimises an ATP molecule for its function: Hydrolysis is quick and easy

A

Allows cells to respond to a sudden increase in energy demand

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10
Q

Analyse how the feature optimises an ATP molecule for its function: Soluble and moves easily within cells

A

Can transport energy to different areas of the cell

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11
Q

Analyse how the feature optimises an ATP molecule for its function: Forms phosphorylated intermediates

A

This can make metabolites more reactive and lower the activated energy required for a reaction

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12
Q

ATP synthesis

A

-ATP is formed when ADP is combined with an inorganic phosphate (Pi) group
-This is an energy-requiring reaction
-Water is released as a waste product (therefore ATP synthesis is a condensation reaction)

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13
Q

Types of ATP synthesis

A

-Substrate-linked phosphorylation
-Chemiosmosis

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14
Q

Substrate-linked phosphorylation

A

-ATP is formed by transferring a phosphate directly from a substrate molecule to ADP
ADP + Pi —> ATP
-The energy required for the reaction is provided directly by another chemical reaction
-It only accounts for a small amount of the ATP synthesised during aerobic respiration
-This type of ATP synthesis takes place in glycolysis

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15
Q

Chemiosmosis

A

-This specific type of ATP synthesis involves a proton (hydrogen ion) gradient across a membrane
-An electron transport chain helps to establish the proton concentration gradient
-High energy electrons move from carrier to carrier releasing energy that is used to pump protons (up a concentration gradient) across the inner membrane into the intermembrane space
-Protons are pumped from a low concentration in the mitochondrial matrix to a high concentration in the intermembrane space
-The protons then move down the concentration gradient into the matrix which releases energy
-The protons move through the ATP synthase complex which uses the released energy to drive the phosphorylation of ATP
-Oxygen acts as the final electron and proton acceptor to form water
-Most of the ATP made during respiration is synthesised via chemiosmosis

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16
Q

Location of Substrate-linked phosphorylation

A

Cytoplasm of cells
Matrix of mitochondria

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17
Q

Location of chemiosmosis

A

Inner mitochondrial membrane
Thylakoid membrane of chloroplasts

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18
Q

Quantity of ATP produced during substrate-linked phosphorylation

A

4 to 6 per glucose molecule

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19
Q

Quantity of ATP produced during chemiosmosis

A

32-34 per glucose molecule

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20
Q

What is the main respiratory substrate for aerobic respiration in most cells

A

Glucose

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21
Q

Why are amino acids only respired aerobically when other substrates have been used

A

they often have essential functions elsewhere in the cell such as to make proteins which have structural (eg. in the cytoskeleton) and functional (eg. enzymatic) roles

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22
Q

Other substrates that can be used for respiration

A

-Other carbohydrates
-Lipids
-Proteins

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23
Q

The energy released by different substrates during respiration

A

-lipids have the highest energy value (39.4 kJ g-1)
- proteins (17.0 kJ g-1)
-carbohydrates (15.8 kJ g-1)

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24
Q

Why do different respiratory substrates have different energy values

A

-Differences in the energy values of substrates can be explained by their molecular composition. Specifically how many hydrogen atoms become available when the substrate molecules are broken down.
-This means that a molecule with a higher hydrogen content will result in a greater proton gradient across the mitochondrial membrane which allows for the formation of more ATP via chemiosmosis
-Fatty acids in lipids are made up of long hydrocarbon chains with lots of hydrogen atoms. These hydrogen atoms are released when the lipid is broken down

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25
Q

Vital role of hydrogen during respiration

A

-The substrate molecules are broken down and the hydrogen atoms become available
-Hydrogen carrier molecules called NAD and FAD pick them up (become reduced) and transfer them to the inner mitochondrial membrane
-Reduced NAD and FAD release the hydrogen atoms which split into protons and electrons
-The protons are pumped across the inner mitochondrial membrane into the intermembrane space - forming a proton / chemiosmotic gradient
-This proton gradient is used in chemiosmosis to produce ATP
-After the protons have flowed back into the matrix of the mitochondria via ATP synthase they are oxidised to form water

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26
Q

Define Respiratory Quotient

A

the ratio of carbon dioxide molecules produced to oxygen molecules taken in during respiration

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27
Q

RQ =

A

CO2 / O2

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28
Q

why different respiratory substrates have RQ values

A

-Carbohydrates, lipids and proteins have different typical RQ values
-This is because of the number of carbon-hydrogen bonds differs in each type of biological molecule
-More carbon-hydrogen bonds means that more hydrogen atoms can be used to create a proton gradient
-More hydrogens means that more ATP molecules can be produced
-More oxygen is therefore required to breakdown the molecule (in the last step of oxidative phosphorylation to form water)

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29
Q

RQ for anaerobic respiration

A

-The RQ cannot be calculated for anaerobic respiration in muscle cells because no oxygen is used and no carbon dioxide is produced during lactate fermentation
-For yeast cells the RQ tends towards infinity as no oxygen is used while carbon dioxide is still being produced

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30
Q

What is the function of a respirometer

A

-Respirometers are used to measure and investigate the rate of oxygen consumption during respiration in organisms
-They can also be used to calculate respiratory quotients

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31
Q

Equation for calculating change in gas volume

A

The volume of oxygen consumed (cm3 min-1) can be worked out using the diameter of the capillary tube r (cm) and the distance moved by the manometer fluid h (cm) in a minute using the formula:
πr2h

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32
Q

Using a respirometer to determine the Respiratory Quotient

A

Method
-Measure oxygen consumption: set up the respirometer and run the experiment with soda-lime present in both tubes. Use the manometer reading to calculate the change in gas volume within a given time, x cm3 min-1
-Reset the apparatus: allow air to re-enter the tubes via the screw cap and reset the manometer fluid using the syringe
-Run the experiment again: remove the soda-lime from both tubes and use the manometer reading to calculate the change in gas volume in a given time, y cm3 min-1

Calculations
-x tells us the volume of oxygen consumed by respiration within a given time
-y tells us the volume of oxygen consumed by respiration within a given time minus the volume of carbon dioxide produced within a given time
-y may be a positive or negative value depending on the direction that the manometer fluid moves (up = positive value, down = negative value)
RQ = (x+y)/x

33
Q

Ways you can manage variables and increase the reliability of results in respirometer experiments

A

-Use a controlled water bath to keep the temperature constant
-Have a control tube with an equal volume of inert material to the volume of the organisms to compensate for changes in atmospheric pressure
-Repeat the experiment multiple times and use an average

34
Q

Where does each of the four stages in aerobic respiration occur in eukaryotic cells

A

-glycolysis in the cytoplasm
-link reaction in the mitochondrial matrix
-Krebs cycle in the mitochondrial matrix
-oxidative phosphorylation on the inner membrane of mitochondria

35
Q

Glycolysis

A

Phosphorylation and splitting of glucose

36
Q

Link Reaction

A

Decarboxylation and dehydrogenation of pyruvates

37
Q

Kerbs Cycle

A

Cyclical pathway with enzyme-controlled reactions

38
Q

Oxidative Phosphorylation

A

Production of ATP through oxidation of hydrogen atoms

39
Q

Define Phosphorylation

A

the addition of a phosphoryl (PO3) group to a molecule

40
Q

Steps of glycolysis

A

1)Phosphorylation: glucose (6C) is phosphorylated by 2 ATP to form fructose bisphosphate (6C)
Glucose + 2ATP → Fructose bisphosphate

2)Lysis: fructose bisphosphate (6C) splits into two molecules of triose phosphate (3C)
Fructose bisphosphate → 2 Triose phosphate

3)Oxidation: hydrogen is removed from each molecule of triose phosphate and transferred to coenzyme NAD to form 2 reduced NAD
4H + 2NAD → 2NADH + 2H+

4)Dephosphorylation: phosphates are transferred from the intermediate substrate molecules to form 4 ATP through substrate-linked phosphorylation
4Pi + 4ADP → 4ATP

5)Pyruvate is produced: the end product of glycolysis which can be used in the next stage of respiration
2 Triose phosphate → 2 Pyruvate

41
Q

Results of glycolysis

A

-2 Pyruvate (3C) molecules
-Net gain 2 ATP
-2 reduced NAD

42
Q

Function of ATP at the beginning of glycolysis

A

ATP is used to make glucose more reactive (it is usually very stable) and to lower the activation energy of the reaction

43
Q

What condition should be met for pyruvate to enter the link reaction

A

When oxygen is available pyruvate will enter the mitochondrial matrix and aerobic respiration will continue

44
Q

How does a molecule of pyruvate enter the mitochondrial matrix

A

-It moves across the double membrane of the mitochondria via active transport
-It requires a transport protein and a small amount of ATP

45
Q

Steps of Link Reaction

A

1)Decarboxylation and dehydrogenation of pyruvate by enzymes to produce an acetyl group, CH3C(O)-

2)Combination with coenzyme A to form acetyl CoA

46
Q

Results of Link Reaction (per pyruvate molecule)

A

-Acetyl CoA
-Carbon dioxide (CO2)
-Reduced NAD (NADH)

47
Q

pyruvate + NAD + CoA →

A

acetyl CoA + carbon dioxide + reduced NAD

48
Q

Define coenzyme

A

a molecule that helps an enzyme carry out its function but is not used in the reaction itself

49
Q

What does coenzyme A consist of

A

a nucleoside (ribose and adenine) and a vitamin

50
Q

Role of coenzyme A

A

-In the link reaction, CoA binds to the remainder of the pyruvate molecule (acetyl group 2C) to form acetyl CoA
-It then supplies the acetyl group to the Krebs cycle where it is used to continue aerobic respiration
-This is the stage that brings part of the carbohydrate (or lipid/amino acid) into the further stages of respiration and links the initial stage of respiration in the cytoplasm to the later stages in the mitochondria

51
Q

Steps in Kerbs Cycle

A

1)Acetyl CoA (2C) enters the circular pathway via the link reaction

2)4 carbon (4C) oxaloacetate accepts the 2C acetyl fragment from acetyl CoA to form citrate (6C)

3)Decarboxylation of citrate
Releasing 2 CO2 as waste gas

4)Dehydrogenation of citrate
Releasing H atoms that reduce coenzymes NAD and FAD
8H + 3NAD + FAD → 3NADH + 3H+ + FADH2

5)Substrate-level phosphorylation
A phosphate is transferred from one of the intermediates to ADP, forming 1 ATP

6)Oxaloacetate is regenerated in the Krebs cycle

52
Q

Results of Kerb Cycle (per pyruvate molecule)

A

-2 carbon dioxide (CO2)
-3 reduced NAD (NADH)
-1 reduced FAD (FADH)
-1 ATP

53
Q

What type molecules are NAD and FAD

A

coenzymes

54
Q

Role of NAD & FAD

A

-When hydrogen atoms become available at different points during respiration NAD and FAD accept these hydrogen atoms
-When the coenzymes gain a hydrogen they are ‘reduced’
-They transfer the hydrogen atoms (hydrogen ions and electrons) from the different stages of respiration to the electron transport chain on the inner mitochondrial membrane, the site where hydrogens are removed from the coenzymes
-When the hydrogen atoms are removed the coenzymes are ‘oxidised’

55
Q

Sources of reduced NAD

A

-2 x 1 = 2 from Glycolysis
-2 x 1 = 2 from the Link Reaction
-2 x 3 = 6 from the Krebs cycle
per glucose molecule

56
Q

Sources of reduced FAD

A

-2 x 1 = 2 from the Krebs cycle
per glucose molecule

57
Q

Steps in Oxidative Phosphorylation

A

1)Hydrogen atoms donated by reduced NAD and FAD split into protons and electrons

2)energetic electrons release energy as they pass through the electron transport chain

3)The released energy is used to transport protons across the inner mitochondrial membrane from the matrix into the intermembrane space. A concentration gradient of protons is established between the intermembrane space and the matrix

4)protons return to the mitochondrial matrix by facilitated diffusion through channel protein ATP synthase, providing energy for ATP synthesis

5)Oxygen combines with protons and electrons at the end of the electron transport chain to form water

58
Q

The Electron Transport Chain

A

-The electron transport chain is made up of a series of membrane proteins/ electron carriers
-They are positioned close together which allows the electrons to pass from carrier to carrier
-The inner membrane of the mitochondria is impermeable to hydrogen ions so these electron carriers are required to pump the protons across the membrane to establish the concentration gradient

59
Q

Why oxygen is so important for aerobic respiration

A

-Oxygen acts as the final electron acceptor.
-Without oxygen the electron transport chain cannot continue as the electrons have nowhere to go.
-Without oxygen accepting the electrons (and hydrogens) the reduced coenzymes NADH and FADH2 cannot be oxidised to regenerate NAD and FAD, so they can’t be used in further hydrogen transport.

60
Q

Structure of mitochondria

A

-Mitochondria have two phospholipid membranes

-The outer membrane is:
Smooth
Permeable to several small molecules

-The inner membrane is:
Folded (cristae)
Less permeable
The site of the electron transport chain (used in oxidative phosphorylation)
Location of ATP synthase (used in oxidative phosphorylation)

-The intermembrane space:
Has a low pH due to the high concentration of protons
The concentration gradient across the inner membrane is formed during oxidative phosphorylation and is essential for ATP synthesis

-The matrix:
Is an aqueous solution within the inner membranes of the mitochondrion
Contains ribosomes, enzymes and circular mitochondrial DNA necessary for mitochondria to function

61
Q

Relationship between structure of mitochondria and it’s function

A

-They have a large surface area due to the presence of cristae (inner folds) which enables the membrane to hold many electron transport chain proteins and ATP synthase enzymes
-More active cell types can have larger mitochondria with longer and more tightly packed cristae to enable the synthesis of more ATP because they have a larger surface area
-The number of mitochondria in each cell can vary depending on cell activity
-Muscle cells are more active and have more mitochondria per cell than fat cells

62
Q

Steps in ethanol fermentation

A

1)pyruvate is decarboxylated to ethanal producing CO2

2)reduced NAD transfers its hydrogens to ethanal to form ethanol. ethanal is reduced to ethanol by the enzyme alcohol dehydrogenase.

3)Ethanal is the hydrogen acceptor. Ethanol cannot be further metabolised; it is a waste product

63
Q

Steps in lactate fermentation

A

1)Pyruvate is reduced to lactate by enzyme lactate dehydrogenase. In this pathway reduced NAD transfers its hydrogens to pyruvate to form lactate

2)Pyruvate is the hydrogen acceptor. The final product lactate can be further metabolised

64
Q

Metabolization of lactate

A

-After lactate is produced two things can happen:
1)It can be oxidised back to pyruvate which is then channelled into the Krebs cycle for ATP production
2)It can be converted into glycogen for storage in the liver

-The oxidation of lactate back to pyruvate needs extra oxygen
-This extra oxygen is referred to as an oxygen debt
-It explains why animals breathe deeper and faster after exercise

65
Q

Which respiration produces a greater energy yield

A

aerobic respiration

66
Q

Why does aerobic respiration have a greater energy yield

A

-In anaerobic respiration glucose is only partially oxidised meaning only some of its chemical potential energy is released and transferred to ATP
-The only ATP producing reaction in anaerobic conditions that continues is glycolysis (~2 ATP)
-As there is no oxygen to act as the final electron acceptor none of the reactions within the mitochondria can take place
-The stages that take place inside the mitochondria produce much more ATP than glycolysis alone (~36 ATP)

67
Q

how rice is adapted for aerobic respiration

A

-Some types of rice show an increased rate of upward growth away from the waterline. The leaves always remain above water so there is access to oxygen and carbon dioxide through the stomata
-Rice plants possess aerenchyma tissue in the stems and roots. This specialised plant tissue contains useful air spaces that allow gases that enter the stomata to diffuse to other parts of the plant that are above and under the water. Oxygen and carbon dioxide can therefore be held in this tissue even when underwater and can be transferred from parts of the plant that has access to air

68
Q

how rice is adapted for anaerobic respiration

A

-Rice plants can tolerate higher levels of toxic ethanol compared to other plants
-They also produce more ethanol dehydrogenase. This is the enzyme that breaks down ethanol
-The resilience that rice plants have towards ethanol allows them to carry out anaerobic respiration for longer so enough ATP is produced for the plant to survive and actively grow

69
Q

Why farmers grow rice in paddies (intentionally flooded fields)

A

Growing rice in these conditions actually increases the yield. The plants or weeds that would usually be competitors for nutrients and light are unable to survive in these conditions and so the rice has more resources for its growth.

70
Q

What is a redox indicator

A

a substance that changes colour when it is reduced or oxidised

71
Q

State the name of two redox indicators

A

DCPIP and methylene blue

72
Q

Mechanism of redox indicators during aerobic respiration

A

-Dehydrogenation a process that happens regularly during aerobic respiration causes a colour change in redox indicators
-The hydrogens that are removed from substrate molecules are transferred to DCPIP and methylene blue when they are present (just like how in aerobic respiration NAD and FAD take up hydrogens and get reduced)
-Both redox indicators undergo the same colour change when they are reduced
Blue → colourless
-The faster the rate of respiration, the faster the rate of hydrogen release and the faster the dyes get reduced and change colour
-This means that the rate of colour change can correspond to the rate of respiration in yeast
-The rate of respiration is inversely proportional to the time taken
RATE OF RESPIRATION (sec-1) = 1/TIME(sec)

73
Q

Investigating the effect of temperature on the rate of respiration in yeast

A

-The effect of temperature can be investigated by adding the test tubes containing the yeast suspension to a temperature-controlled water bath and recording the time taken for a colour change to occur once the dye is added
-Repeat across a range of temperatures. For example, 30oC, 35oC, 40oC, 45oC

74
Q

Investigating the effect of substrate concentration on the rate of respiration in yeast

A

-The effect of substrate concentration can be investigated by adding different concentrations of a substrate to the suspension of yeast cells and recording the time taken for a colour change to occur once the dye is added
-For example, 0.1% glucose, 0.5% glucose, 1.0% glucose

75
Q

Controlling other variables when investigating the effect of temperature & substrate concentration on the rate of respiration in yeast

A

-Volume of dye added: if there is more dye molecules present then the time taken for the colour change to occur will be longer
-Volume of yeast suspension: when more yeast cells are present the rate of respiration will be inflated
-Type of substrate: yeast cells will respire different substrates at different rates
-Concentration of substrate: if there is limited substrate in one tube then the respiration of those yeast cells will be limited
-Temperature: an increase or decrease in temperature can affect the rate of respiration due to energy demands and kinetic energy changes. The temperature of the dye being added also needs to be considered

76
Q

How the colour of yeast suspension might affect the results when investigating rate of respiration

A

-Yeast suspension in the test tube may have a slight colour (usually yellow)
-Although the DCPIP and methylene blue undergo a colour change from blue to colourless, it is important to remember that they will be an overall yellow colour in the test tube in the end
-If this is the case it can be useful to have a control tube containing the same yeast suspension but with no dye added, then you can tell when the dye has completely changed colour.

77
Q

Method of measuring effect of temperature in Respirometers

A

-Measure oxygen consumption: set up the respirometer and run the experiment with both tubes in a controlled temperature water bath.
-Use the manometer reading to calculate the change in gas volume within a given time, x cm3 min-1
-Reset the apparatus: Allow air to renter the tubes via the screw cap and reset the manometer fluid using the syringe.
-Change the temperature of the water bath and allow the tubes to acclimate, then close the screw clip to begin the experiment
-Run the experiment again: use the manometer reading to calculate the change in gas volume in a given time, y cm3 min-1
-Repeat experiment several times at different temperatures

78
Q

Why temperature affects rate of respiration in a respirometer

A

-rate of respiration reactions rely on enzymes
-at low temperatures, molecules and enzymes don’t collide very frequently as they don’t have a lot of energy so rate of respiration is low
- at extreme high temperatures, the enzymes in respiration become denatured and are unable to carry out their function and thus rate of respiration decreases

A-LEVEL BIOLOGY (8 decks)

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