Energy and Respiration Flashcards
(84 cards)
1
Q
What are living organisms composed of ?
A
Cells and within each cell many activities and process are constanlty being carried out to maintain life
- work in a living organism requires energy and usable carbon compounds
2
Q
Essential work within organisms - type of work
Transporting substances across membranes EG
A
- Active transprot using Na+ K+ pump in cell membranes
- exocytosis of digested bacteria from WBC
3
Q
Essential work within organisms - type of work
Anabolic reactions EG
A
- synthesis of DNA from nucleotides
- Synthesis of protein from amino acids
4
Q
Essential work within organisms - type of work
movement
A
- cellular movement of chromosomes via the spindle
- mechanical contraction of muscles
5
Q
Essential work within organisms - type of work
Maintaining body temp
A
- Only occurs in mammals and birds
6
Q
pneumonic for essential work within organisms
MMAT
A
- Movement
- Maintaining body temp
- Anabolic reactions
- Transporting substances across membranes
7
Q
For nearly all organisms what is the primary source of energy?
A
the sun
8
Q
Glucose equation
A
glucose + oxygen → carbon dioxide + water + energy
C6H12O6 + 6 O2 → **6 CO2 + 6** H20 + 2870kJ
9
Q
the reactions of photosyntheis stores energy in organic molecules
A
-Light energy from the sun is transformed into chemical potential energy in the synthesis of carbohydrates
- The carbohydrates formed used in the synthesis of ATP (from their breakdown) or are combined and modified to form all the usable organic molecules that are** essential for all metabolic processes within the plant**
10
Q
Photosynthesis is carried out by..
A
the first organism in a food chain, such as plants and some other small organisms
11
Q
what does respiration cause all living cells to release?
A
energy from the breakdown of organic molecuels
12
Q
what does respiration involve?
A
The transfer of chemical potential energy from nutrient molecules (such as carbs,fats and proteins) into usable energy form (through synthesis of ATP) that can be used for work within an organism.
13
Q
Energy released during the reactions of respiration is transferred to which molecule?
A
ATP - adenosine triphosphate
14
Q
ATP
A
- small and soluble molecule
- provides short-term store of chemical energy that cells can use to do work
- vital in linking energy-requiring and energy-yielding reactions
15
Q
what is ATP described as?
A
a Universal energy currency
- Universal: **used in all **organisms
- Currency: Like money,used for diff purposes(reactions) and is** reused countless** times
16
Q
The use of ATP as an ‘energy-currency’ is beneficial for many reasons:
A
-The hydrolysis of ATP can be carried out quickly and easily wherever energy is required within the cell by the action of just one enzyme, ATPase
- A useful (not too small, not too large) **quantity of energy is released from the hydrolysis of one ATP **molecule - this is beneficial as it reduces waste but also gives the cell control over what processes occur
- ATP is** relatively stable at cellular pH levels**
17
Q
structure of ATP
A
- is a phosphorylated nucleotide
made up of:
- Ribose sugar
- Adenine base
- 3 phosphate groups
18
Q
hydrolyis of ATP
A
ADP + phosphate produced
- ADP forms -> free energy is released that can be used for process within a cell -> eg DNA synthesis
19
Q
Features of ATP
Releases a small but sufficent amount of energy (75.8KJmol-1 from the complete hydrolyis of ATP) what is the benefit ?
A
this is enough energy to drive important metabolic reactions while keeping energy wastage low
20
Q
Features of ATP
exists as a stable molecule - what is the benefit?
A
It doesn’t break down unless a catalyst (ATPase) is present so energy won’t be wasted
21
Q
Features of ATP
can be recycled - what is the benefit?
A
the breakdown of ATP is a reversible reaction, ATP can be refomed from ADP and Pi. This means the same molecule can be reused elesewhere in cell for different reactions
22
Q
Features of ATP
Hydrolyis is quick and easy
A
allows cells to respond to a sudden increase in energy demand
23
Q
Features of ATP
soluble and moves easily within cells - what is the benefit?
A
can transport energy to different areas of the cell
24
Q
Features of ATP
forms phosphorylated intermediates -what is the benefit?
A
this can make metabolites more reactive and lower the Ea required for a reaction
Ea - activation energy
25
ATP is formed when ADP is combined with an inorganic phosphate (Pi) group. What type of reaction is this and what is the waste product produced?
This is an **energy-requiring reaction**
**Water** is released as a **waste product** (therefore ATP synthesis is a condensation reaction)
26
Organisms cannot build up large stores of ATP and it rarely passes through the cell surface membrane
This means ...
the cells must make ATP as and when they need it
27
when is ATP made?
during reactions of respiration and photosynthesis
- all of animals ATP comes from respiration
28
ATP can be made 2 different ways
-Substrate-linked phosphorylation
-Chemiosmosis
29
Substrate-linked phosphorylation: describe Process, Location and Quantity of ATP produced during respiration
Process: The phosphate of a substrate molecule is direcly transferred to ADP to form ATP
**ADP + Pi —> ATP**
It uses energy directly provided by another chemical reaction
Location: Cytoplasm of cells/Matrix of mitochondira
Quantity produced: Small (4/6 per glucose molecule)
This type of ATP synthesis takes place in glycolysis
30
Chemiosmosis: describe Process, Location and Quantity of ATP produced during respiration
Process: The energy released by the movement of H+ ions down conc grad is used to synthesise ATP via enzyme ATP synthase. Oxygen acts as final e- acceptor.
Location: Inner mitochondrial membraine/Thylakoid membrane of chloroplast
Quantity: Large (32/34 per glucose molecule)
31
What is the main respiratory substrate for aerobic respiration in most cells?
Glucose
32
When the supply of glucose in a cell has been used up a cell may continue respiration using other substrates
These may be:
- Other carbohydrates
- Lipids
- Proteins
33
Amino acids from proteins are only respired aerobically when all other substrates have been used up. Why is this ?
often have **essential functions elsewhere** in the cell.
Amino acids are required to **make proteins** which have **structural** and **functional** roles
| structural role eg in cytoskeleton
functional role eg enzymatic
34
When carbs,lipids and proteins are broken down what are their energy values?
## Footnote
When these different substrates are broken down in respiration, they release different amounts of energy
- Carbohydrates: **15.4** kJg^-1
- Lipid:**39.5** kJg^-1
- Protein:**17.0**kJg^-1
| Lipids highest value, proteins then carbs lowest
## Footnote
**question:Explain why carbohydrates, lipids and proteins have different relative energy values as substrates in respiration in aerobic conditions. (6 marks):
**
The 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
35
During respiration what is the vital role of the Hydrogen atom?
- substrate moleule is broken down -> Hydrogen atom becomes available
- Hydrogen carrier molecules: NAD + FAD pick them up (become reduced) + transfer them to inner mitochondiral membrane
- reduced NAD + FAD release H atoms which split into protons and electrons
- protons pumped across inner mitochondiral membrane into intermembrane space - forming a proton/chemosmotic grad
- proton gradient 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
-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
36
what is the Respiratory Quotient (RQ)
the **ratio of CO2** molecules **produced** to **Oxygen** molecules **taken in** during **respiration**
**RQ= CO2/O2**
37
Carbohydrates, lipids and proteins have different typical RQ values why ?
Because of the numbr of carbon-hydrogen bonds differ in each type of biolgoical molecule
- **More C-H** bonds: More H atoms used to create proton grad
- **More Hydrogen**-> more ATP molecules produced
- **More Oxygen is then required** to breakdown molecule (in last step of oxidative phosphorylation to form water)
38
When glucose is aerobically respired equal amounts of carbon dioxide are produced to oxygen taken in what would the RQ value be?
1
39
The respiratory quotient is calculated from respiration equations
It involves comparing the ratios of carbon dioxide given out to oxygen taken in.
What is the formula?
RQ= moles/molecules of CO2 given out/ moles/molecules of oxygen taken in
## Footnote
step 1: create respiration equation
step 2: balance eq
step 3: create full eq
Step 4: use RQ formula
EG:
C18H32O2 + 25O2 → 18CO2 + 16H2O
CO2 / O2 = RQ
18 / 25 = 0.72
40
Can the RQ value be calculated for anaerobic respiration in muscle cells?
No as oxygen is used and no CO2 is produced during lactate fermentation
41
For yeast cells what does the RQ value tend to be towards?
Infinity as no oxgen is used while CO2 is still being produced.
## Footnote
C6H12O6 → 2C2H5OH + 2CO2 + energy
Step 3: Calculate the RQ value
CO2 / O2 = RQ
2 / 0 = ∞ Infinity
42
Depending on the organism anaerobic respiration in cells can be done via lactate or ethanol fermentation. What is it for mammalian muscle cells and plant tissues cells and yeast?
- Mammalian muscle cells use **lactate fermentation**
- Plant tissue cells and yeast use **ethanol fermentation**
43
what are Respirometers used to measure and investigate ?
- the rate of oxygen consuption during respiration in organisms
- used to calculate respiratory quotients
- The experiments usually involve organisms such as seeds or invertebrates
44
Equation for calculating change in gas volume
in a respiromiter
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:
**πr^2h**
45
Using a respirometer to determine the Respiratory Quotient
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
46
respiromiter 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)
- The two measurements x and y can be used to calculate the RQ
FORMULAS:
**RQ= CO2/O2
RQ= x+y/x**
Worked example: Calculating RQ from a respirometer experiment
x = 2.9 cm3 min-1
y = -0.8 cm3 min-1
(x + y) / x = RQ
(2.9 - 0.8) / 2.9 = 0.724
When equal volumes of oxygen are consumed and carbon dioxide produced (as seen with glucose) the manometer fluid will not move and y will be 0, making the RQ 1.
47
Analysis of respirometer
- used to investigate how diff factors affect RQ of organisms over time.
EG: temp -> using a series of water baths
- RQ value changes it means the substrate being respired has changed
- Some cells may also be using a mixture of substrates in respiration e.g. An RQ value of 0.85 suggests both carbohydrates and lipids are being used
- This is because the RQ of glucose is 1 and the RQ of lipids is 0.7
- Under normal cell conditions the order substrates are used in respiration: carbohydrates, lipids then proteins
- The RQ can also give an indication of under or overfeeding:
An RQ value of more than 1 suggests excessive carbohydrate/calorie intake
An RQ value of less than 0.7 suggests underfeeding
48
What is the diameter of a mitochondria?
0.5-1.0 um - micrometres
49
Mitochondria are the site of ..
aerobic respiration in eukaryotic cells
50
what is the function of a mitochondria?
- synthesizes ATP
- occurs during the last stage of respiration - oxidative phosphorylation
- this relies on membrane proteins that make up the ‘electron transport chain’ and the ATP synthase enzyme
51
Structure of the mitcochondria
**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
52
Relationship between structure + function in mitochondria
- have large SA due to presence of cristae (inner folds) - enables membrane to hold many electron transport chain protiens and ATP synthase enzymes
- more active cell types can have larger mitochondria with longer an dmore tightly packed cristae - enables synthesis of more ATP as have large SA
- number of mitochondria in each cell varies depending on cell activitiy
## Footnote
EG: Muscle cells are more active and have more mitochondria per cell than fat cells
53
What is Aerobic respiration
is the process of breaking down a respiratory substrate in order to produce ATP using oxygen
54
The process of aerobic respiration using glucose can be split into four stages. What are the 4 stages with location and overall description?
| Each stage occurs at a particular location in a eukaryotic cell
1.Glycolysis : Location -takes place in the cell cytoplasm.
Description: Is the Phosphorylation and splitting of glucose
2.The Link reaction: Location - takes place in the matrix of the mitochondria
Description: Decarboxylation and dehydrogenation of pyruvate
3.The Krebs cycle: Location - takes place in the matrix of the mitochondria
Description: Cyclical pathway with enzyme controlled reactions
4.Oxidative phosphorylation: Location- occurs at the inner membrane of the mitochondria
Description:Prodiction of ATP through oxidation of H atoms
55
# 1st stage of respiration
Glycolysis
Phosphorylation: glucose (6C) is phosphorylated by 2 ATP to form fructose bisphosphate (6C)
Glucose + 2ATP → Fructose bisphosphate
Lysis: fructose bisphosphate (6C) splits into two molecules of triose phosphate (3C)
Fructose bisphosphate → 2 Triose phosphate
Oxidation: hydrogen is removed from each molecule of triose phosphate and transferred to coenzyme NAD to form 2 reduced NAD
4H + 2NAD → 2NADH + 2H+
Dephosphorylation: phosphates are transferred from the intermediate substrate molecules to form 4 ATP through substrate-linked phosphorylation
4Pi + 4ADP → 4ATP
Pyruvate is produced: the end product of glycolysis which can be used in the next stage of respiration
2 Triose phosphate → 2 Pyruvate
56
products of glycolysis
2 Pyruvate (3C) molecules
Net gain 2 ATP
2 reduced NAD
57
Link Reaction
1. Decarboxylation and dehydrogenation of pyruvate by enzymes to produce an acetyl group, CH3C(O)-
2. Combination with coenzyme A to form acetyl CoA
pyruvate + NAD + CoA → acetyl CoA + carbon dioxide + reduced NAD
58
what is a coenzyme?
is a molecule that helps an enzyme carry out its function but is not used in the reaction itself
59
role of coenzyme A
Coenzyme A consists of a nucleoside (ribose and adenine) and a vitamin
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
60
Describe how oxidation of electron carriers is used to generate ATP by the electron transport chain.
Electron carriers/NADH and FADH2 oxidised;
Electrons donated to electron transport chain;
Electrons decrease in energy as they move down the chain;
Energy from electrons used to pump H+;
H+ pumped into inter-membrane space (from matrix);
Concentration of H+ generates proton motive force;
Facilitated diffusion of H+ ions back into matrix called chemiosmosis;
Energy used to phosphorylate ADP+Pi;
ATP generated by ATP synthase;
Low energy electrons reduce oxygen;
Oxygen accepts protons;
Water formed.
61
Steps of krebs cycle
Oxaloacetate is regenerated in the Krebs cycle through a series of reactions
Decarboxylation of citrate
Releasing 2 CO2 as waste gas
Dehydrogenation of citrate
Releasing H atoms that reduce coenzymes NAD and FAD
8H + 3NAD + FAD → 3NADH + 3H+ + FADH2
Substrate-level phosphorylation
A phosphate is transferred from one of the intermediates to ADP, forming 1 ATP
## Footnote
The Krebs cycle (sometimes called the citric acid cycle) consists of a series of enzyme-controlled reactions
Acetyl CoA (2C) enters the circular pathway via the link reaction
4 carbon (4C) oxaloacetate accepts the 2C acetyl fragment from acetyl CoA to form citrate (6C)
Citrate is then converted back to oxaloacetate through a series of small reactions
62
what is the role of NAD and FAD in aerobic respiration?
When hydrogen atoms become available at different points during respiration NAD and FAD accept these hydrogen atoms
A hydrogen atom consists of a hydrogen ion and an electron
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’
63
Hydrogen ions and electrons are important in the electron transport chain at the end of respiration as they play a role in the synthesis of ATP
Electrons from reduced NAD (NADH) and reduced FAD (FADH2) are given to the electron transport chain
Hydrogen ions from reduced NAD (NADH) and reduced FAD (FADH2) are released when the electrons are lost
The electron transport chain drives the movement of these hydrogen ions (protons) across the inner mitochondrial membrane into the intermembrane space, creating a proton gradient (more hydrogen ions in the intermembrane space)
Movement of hydrogen ions down the proton gradient, back into the mitochondrial matrix, gives the energy required for ATP synthesis
64
A certain amount of reduced NAD and FAD is produced during the aerobic respiration of a single glucose molecule
Reduced NAD:
2 x 1 = 2 from Glycolysis
2 x 1 = 2 from the Link Reaction
2 x 3 = 6 from the Krebs cycle
Reduced FAD:
2 x 1 = 2 from the Krebs cycle
## Footnote
Note at all stages there is a doubling (2x) of reduced NAD and FAD. This is because one glucose molecule is split in two in glycolysis and so these reactions occur twice per single molecule of glucose.
65
# last step in aerobic respiration.
Oxidative phosphorylation steps
## Footnote
It takes place at the inner membrane of the mitochondria
Hydrogen atoms are donated by reduced NAD and FAD
Hydrogen atoms split into protons and electrons
The high energy electrons release energy as they move through the electron transport chain
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
The protons return to the matrix via facilitated diffusion through the channel protein ATP synthase
The movement of protons down their concentration gradient provides energy for ATP synthesis
Oxygen combines with protons and electrons at the end of the electron transport chain to form water
66
Oxidative phosphorylation - ETC
| ETC - electron transport chain
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
67
Why is oxygen so important for aerobic respiration?
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.
68
Sometimes cells experience conditions with little or no oxygen what are the several consequences when there is not enough oxygen available for respiration?
There is no final acceptor of electrons from the electron transport chain
The electron transport chain stops functioning
No more ATP is produced via oxidative phosphorylation
Reduced NAD and FAD aren’t oxidised by an electron carrier
No oxidised NAD and FAD are available for dehydrogenation in the Krebs cycle
The Krebs cycle stops
However, there is still a way for cells to produce some ATP in low oxygen conditions through anaerobic respiration
69
Some cells are able to oxidise the reduced NAD produced during glycolysis so it can be used for further hydrogen transport. This means that glycolysis can continue and small amounts of ATP are still produced
What are the different pathways to achieve this?
Yeast and microorganisms use ethanol fermentation
Other microorganisms and mammalian muscle cells use lactate fermentation
70
Ethanol fermentation
In this pathway reduced NAD transfers its hydrogens to ethanal to form ethanol
In the first step of the pathway pyruvate is decarboxylated to ethanal
Producing CO2
Then ethanal is reduced to ethanol by the enzyme ethanol dehydrogenase
Ethanal is the hydrogen acceptor
Ethanol cannot be further metabolised; it is a waste product
## Footnote
Note that ethanol fermentation is a two-step process (lactate fermentation is a one-step process).
71
Lactate fermentation
In this pathway reduced NAD transfers its hydrogens to pyruvate to form lactate
Pyruvate is reduced to lactate by enzyme lactate dehydrogenase
Pyruvate is the hydrogen acceptor
The final product lactate can be further metabolised
72
metabolization of lactate. After lactate is produced what are the 2 things that 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
73
why does aerobic respiration produces substantially more ATP than anaerobic respiration ?
In cells there is a much greater energy yield from respiration in aerobic conditions than in anaerobic conditions
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 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)
74
**Anaerobic** respiration - adaptations of rice
When there isn’t enough energy being supplied to the cells by aerobic respiration plants resort to anaerobic respiration as a source of ATP
Plants use ethanol fermentation during anaerobic respiration
Toxic ethanol is produced which can build up in the plant tissue causing damage
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
75
**Aerobic** respiration - adaptations of rice
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
76
Problems - Adaptations of rice
Flooding is a major problem when growing crops
As water rises and it covers the different parts of a plant it can create problems:
Plant roots don’t get the oxygen they need for aerobic respiration
Plant leaves don’t get the carbon dioxide they need for photosynthesis
These gases are less readily available in water as they diffuse more slowly in liquid compared to air
Rice plants possess several adaptations that enable them to survive and grow in waterlogged conditions
77
What is a redox indicator?
is a substance that changes colour when it is reduced or oxidised
DCPIP and methylene blue are redox indicators
They are used to investigate the effects of temperature and substrate concentration on the rate of respiration in yeast
These dyes can be added to a suspension of living yeast cells as they don’t damage cells
Yeast can respire both aerobically and anaerobically, in this experiment it is their rate of anaerobic respiration that is being investigated
78
Aerobic Respiration: Effect of Temperature & Substrate Concentration - Mechanism
Dehydrogenation happens regularly throughout the different stages of aerobic respiration
The hydrogens that are removed from substrate molecules are transferred to the final stage of aerobic respiration, oxidative phosphorylation, via the hydrogen carriers NAD and FAD
When DCPIP and methylene blue are present they can also 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 (s)
79
Investigating the effect of temperature & substrate concentration on the rate of respiration in yeast
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
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
80
Investigating the effect of temperature & substrate concentration on the rate of respiration in yeast
**Controlling other variables
**
It is important when investigating one variable to ensure that the other variables in the experiment are being controlled
**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
Exam
81
Effect of Temperature: Respirometer
why are they used ?
used to measure and investigate the rate of oxygen consumption during aerobic respiration in organisms
By adding the apparatus to a thermostatically controlled water bath the effect of temperature on the rate of respiration can be investigated
The experiments usually involve organisms such as seeds or invertebrates
82
respirometer method
**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 reenter 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
83
respirometer calculation
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
84
Respirometer analysis
The rate of oxygen consumption (cm3 min-1) is often taken as the rate of respiration for organisms
The different volumes of oxygen consumed obtained for the different temperatures can be presented in table or graph form to show the effects of temperature
