Unit 5- Respiration

Question 1

the 4 stages in aerobic respiration

Answer 1

the stages are: glycolysis, the link reaction, the krebs cycle and oxidative phosphorylation.
first 3 stages are a series of reactions, and products are used in the final stage to produce lots of ATP

Question 2

GLYCOLYSIS

Answer 2

involves splitting a glucose molecule into two smaller molecules of pyruvate.
this process happens in the cytoplasm of the cells. glycolysis is the first stage of both aerobic and anaerobic respiration and doesnt need oxygen to take place- its an anaerobic process

Question 3

Stage 1 of glycolysis:

Answer 3

there are 2 stages in glycolysis: phosphorylation and oxidation
stage 1-phosphorylation: glucose is phosphorylated by adding 2 phosphates from 2 molecules of ATP. this creates 1 molecule of hexose bisphosphate and 2 molecules of ADP. hexose bisphosphate is then split up into 2 molecules of triose phosphate

Question 4

stage 2 of glycolysis:

Answer 4

stage 2- oxidation: triose phosphate 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 stage 1, so theres a net gain of 2 ATP.
(the two molecules of reduced NAD go to the last stage, and the two pyruvate molecules are actively transported into the matrix of the mitchondria for the link reaction).

Question 5

THE LINK REACTION

Answer 5

converts pyruvate to Acetyl Ceonzyme A.
takes place in the mitochondrial matrix. pyruvate is decarboxylated - one carbon atom is removed from pyruvate in the form of carbon dioxide. NAD is reduced to NADH- collects hydrogen from pyruvate into acetate. acetate is combined with coenzyme A to form acetyl coenzyme A. no ATP is produced in this reaction.

Question 6

the link reaction and krebs cycle occurs twice for every glucose molecule

Answer 6

two pyruvate molceules are made for every glucose molcule that enters glycolysis. this means the link reaction and the krebs cycle happens twice for every glucose molecule:
-two molecules of acetyl coenzyme A go into the krebs cycle
- two co2 molecules are released as a waste prduct for respiration
-two molcules of reduced NAD are formed and go to the last stage.

Question 7

THE KREBS CYCLE 1

Answer 7

involves a series of oxidative-reduction reactions, which takes place in the matrix of the mitochondira, cycle happens once for every pyruvate molecule, goes round twice for every glucose molecule.
-the acetyle group from the acetyl CoA combines with oxaloacetate to form citrate. this is catalysed by citrate synthase. Coenzyme A goes back to the link reaction to be used again.

Question 8

THE KREBS CYCLE 2

Answer 8

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

Question 9

THE KREBS CYCLE 3

Answer 9

the 5C molecule is then converted to a 4C molecule. decarboxylation and dehydrogenation occur, producing one molecule of reduced FAD and two reduced NAD. ATP is produced by the direct tranfer of a phosphate group from an intermediate compound to ADP. when a phosphate group is directly transferred from one molecule to another its called substrate-level phosphorylation. citrate has now been converted to oxaloacetate.

Question 10

where do the products from one krebs cycle go?

Answer 10

• 1 Coenzyme A- reused in the next link reaction
• oxaloacetate- regenerated for use in the next krebs cycle
• 2 CO2- released as a waste product
• 1 ATP - used for energy
• 3 reduced NAD- to oxidative phosphorylation
• 1 reduced FAD- to oxidative phosphorylation

Question 11

OXIDATIVE PHOSPHORYLATION

Answer 11

produces lots of ATP. its the process where the energy carried by electrons, from reduced coenzymes is used to make ATP. oxidative phosphorylation takes place in the inner mitochondrial membrane

Question 12

process of oxidative phosphorylation 1

Answer 12

hydrogen atoms are released from reduced NAD and reduced FAD as theyre oxidised to NAD and FAD. the H atoms are split into protons (H+) and electrons. the electrons move along the electron transport chain (made up of three electron carriers), losing energy at each carrier. ( the electron transport chain is located in the in the inner mitochondrial membrane. this membrane is folded into cristae, which increases the membranes surface area to maximise respiration)

Question 13

process of oxidative phosphorylation 2

Answer 13

this energy is used by the electron carriers to pump protons from the mitochondrial matrix into the intermembrane space. the concentration of protons is now higher in the intermembrane space than in the mitochondrial matrix- this forms an electrochemical gradient (a concentration gradient with ions). protons move down the electrochemical gradient, back into the mitochondrial matrix via ATP synthase. this movement drives the synthesis of ATP from ADP and inorganic phosphate.

Question 14

process of oxidative phosphorylation 3

Answer 14

this process of ATP production driven by the movement of the H+ ions across a membrane (due to electrons moving down the electron transport chain) is called chemiosmosis (which is described by the chemiosmosis theory). in the mitochondrial matrix at the end of the transport chain, the protons, electrons and O2 (from the blood) combine to form water. oxygen is said to be the final electron acceptor.

Question 15

how much ATP can be made from one glucose molecule

Answer 15

glycolysis:
- molecules produced - 2 ATP, 2 reduced NAD
- number of ATP molecules: 7
link reaction (x2):
- molecules produced: 2 reduced NAD
- number of ATP molecules: 5
krebs cycle (x6):
- molecules produced: 2 ATP, 6 reduced NAD. 2 reduced FAD
total ATP=32
(2.5 ATP is produced from each reduced NAD and 1.5 ATP is produced from each reduced FAD)

Question 16

anaerobic respiration

Answer 16

doesnt involve the link reaction, the krebs cycle, or oxidative phosphorylation.
there are two types: lactate fermentation and alcoholic fermantation. they both take place in the cytoplasm and they both start with glycolysis. they differ in which organism they occur in and what happens to the pyruvate.

Question 17

lactate fermentation

Answer 17

lactate fermantation occurs in mammals and produces lactate. reduced NAD (from glycolysis) transfers hydrogen to pyruvate to form lactate and NAD, lactate dehydrogenase catalyses this reaction. NAD can then be reused in glycolysis. the production of lactate regenerates NAD. glycolysis needs NAD in order to take place. this means glycolysis can continue even when there isnt much oxygen around, so a small amount of ATP can still be produced to keep some biological processes going.

Question 18

Lactate

Answer 18

too much lactic acid is toxic and is removed form the cells into the bloodstream. the liver takes up lactate from the bloodstream and converts it back into glucose in a process called gluconeogenesis.

Question 19

alcoholic fermantation

Answer 19

occurs in yeast cells and produces ethanol. CO2 is removed to form ethanal (decarboxylation). reduced NAD (from glycolysis) transfers hydrogen to ethanal to form ethanol and NAD. NAD can then be reused in glycolysis.

Question 20

is the ATP yield lower in anaerobic respiration or aerobic respiration?

Answer 20

the ATP yield from anaerobic respiration is always lower than from aerobic respiration. this is because anaerobic respiration only includes one energy- releasing stage (glycolysis), which only produces 2 ATP per glucose molecule. the energy-releasing reactions of the krebs cycle and oxidative phosphorylation need oxygen, so they cant occur during anaerobic respiration.

Question 21

cells can respire different substrates

Answer 21

cells respire glucose, but they also respire other carbohydrates, lipids and proteins. any biological molecule that can be broken down in respiration to release energy is called a respiratory substrate

Question 22

different repiratory substrates have different energy values.

Answer 22

different repiratory substrates release different amounts of energy when theyre respired. lipids have the highest energy value (39.4 ), followed by proteins (17.0), then carbohydrates (15.8). this is because most ATP is made in oxidative phosphorylation which requires hydrogen atoms from reduced NAD and reduced FAD. this means that repiratory substrates that contain more hydrogen atoms per unit of mass cause more ATP to be produced when respired. lipids contain the most hydrogen atoms per unit of mass, followed by proteins and then carbohydrates.

Question 23

the respiratory quotient

Answer 23

when an organism respires a specific respiratory substrate, the RQ can be worked out. the respiratory quotient is the volume of co2 produced when that substrate is respired, divided by the volume of oxygen consume, in a set period of time. respiratory quotients have been worked out for the respiration of other respiratory substrates. lipids and proteins have an RQ value lower than one because more oxygen is needed to oxidise fats and lipids than to oxidise carbohydrates
carbohydrates -1
proteins- 0.9
lipids- 0.7

Question 24

the respiratory quotient tells you what substrate is being respired

Answer 24

RQ tells you what what kind of respiratory substrate an organism is respiring and what type of respiration is using. e.g under normal conditions the usual RQ for humans is between 0.7 and 1.0. an RQ in this range shows that some fats (lipids) are being used for respiration, as well as carbohydrates like glucose. protein isnt normally used by the body for respiration unless theres nothing else. high RQs (greater than 1) mean that an organism is short for oxygen and is having to respire anaeroblically as well as aerobically. plants sometimes have a low RQ. this is because the co2 released in respiration is used for photosynthesis (so its not measured)

Question 25

(PRACTICAL) respiration experiments: aerobic and anaerobic respiration rates in yeast can be investigated- Aerobic respiration

Answer 25

methylene blue is a redox indicator dye that can take the place of electron acceptors in oxidative phosphorylation, causing its colour to change from blue to colourless. the rate at which this colour change happens can give an indication of the rate of respiration in yeast.
1. put a known volume and conc of substrate solution in a test tube (e.g glucose). add a known volume buffer solution to keep the pH constant.
2. place the test tube in a water bath set to 25’C. this ensures that the temperature stays constant throughout the experiment. leave it there for 10 minutes to allow the temperature of the substrate to stabalise.
3. add a known volume of yeast suspension to the test tube and stir for two minutes.
4. add a known volume of methylene blue and seal the tube with a bung. shake the test tube for a set number of seconds and place it back in the water bath. start a stopwatch immediately afterwards.
5. record how long it takes for the solution in the test tube to change from blue to colourless. you can use a control to compare colours.
6. repeat steps 1-5 three times and calculate a mean time for the colour change to occur.
7. calculate the mean rate of respiration of the yeast using the following equation :
mean rate of respiration = 1/mean time for colour change to occur

Question 26

(PRACTICAL) respiration experiments: Anaerobic respiration

Answer 26

yeast produces co2 when it respires anaerobically, so the rate at which co2 is produced gives an indication of the yeasts respiration rate. you can measure co2 production, and therefore respiration rate, using a gas syringe:
1. set up the apparatus using steps 1-3 of the experiment of aerobic respiration.
2. trickle some liquid paraffin down the inside of the test tube so that it settles on and completely covers the surface of the solution. this will stop oxygen getting in, which will force the yeast to respire anaerobically.
3. put a bung, with a test tube attached to a gas syringe, in the top of the test tube and start a stopwatch. the gas syringe should be set at zero.
4. as the yeast respire, the co2 formed will push gas into the syringe, which is used to measure te volume of co2 released.
5. record the volume of gas in the gas syringe at regular time intervals . do this for a set amount of time
6. repeat the experiment 3 times and calculate the mean rate of co2 production.

Question 27

(PRACTICAL) the rate of reaction can be measured using a respirometer

Answer 27

• each tube contains potassium hydroxide solution (or soda lime), which absorbs co2.
• the control tube is set up exactly the same way as the test tube but without the woodlice to make sure that results are only due to the woodlice respiring (e.g beads containing the same mass).
• coloured fluid is added to the manometer by dipping the end of the cappilary tube into a beaker of fluid. cappilary action will make the fluid move into the tube. the syringe is then used to set the fluid to a known level.
• the apparatus is left for a period of time.
• during that time therell be a decrease in the volume of air in the test tube, due to oxygen consumption by the woodlice (all the co2 produced is absorbed by the potassium hydroxide solution)
• the decrease in the volume of the air will reduce the pressure in the tube and cause the coloured liquid in the manometre to move towards the test tube.
• the distance moved by by the liquid in a given time is measured. this value can then be used to calculate the volume of oxygen taken in by the woodlice per minute. (you also need to know the diameter of the capillary tube to do this)
  -any variables that could affect the results are controlled, e.g temperature, volume of pottassium hydroxide solution in each test tube
• to produce more precise results, the experiment is repeated and a mean volume of o2 is calculated