DP Biology HL C1.2 Cell Respiration

DP Biology HL C1.2 Cell Respiration - Full notes

RevisionPrep

DP Biology HL | C1.2 Cell Respiration

DP BIOLOGY · THEME C: INTERACTION AND INTERDEPENDENCE

C1.2

Cell Respiration

Full notes for HL · IB-style

Contents

1	ATP: the energy currency of the cell
2	What cell respiration is
3	Aerobic respiration
4	Anaerobic respiration in humans and yeast
5	Comparing aerobic and anaerobic respiration
6	Measuring the rate of respiration
7	Glycolysis and the link reaction (HL only)
8	The Krebs cycle (HL only)
9	The electron transport chain and chemiosmosis (HL only)
10	Respiratory substrates (HL only)
11	ATP: the energy currency
12	Respiration versus gas exchange
13	Aerobic respiration overview
14	Anaerobic respiration in humans
15	Anaerobic respiration in yeast
16	Comparing aerobic and anaerobic respiration
17	Respirometers
18	Factors affecting the rate of respiration
19	Respiratory substrates
20	Respiratory quotient (RQ)
21	Glycolysis (overview)
22	The link reaction and Krebs cycle (HL)
23	Oxidative phosphorylation (HL)
24	Mixed review: worked problems
25	Additional exam-style practice
26	Respiration and exercise
27	Metabolic poisons
28	Common misconceptions and links
29	Exam-style question with markscheme
30	Check your understanding
31	Summary and topic map

These are full teaching notes. Read each section in order, try the Think about it question before you read on, and do every Quick check before moving to the next section.

Before you start

Rate yourself on each statement now, and again after you've worked through the notes. Shade R (not yet), A (getting there) or G (confident).

I can…	R	A	G
explain the properties and roles of ATP
define cell respiration and explain why it is needed
write word equations for aerobic and anaerobic respiration
explain anaerobic respiration in humans and yeast and its uses
compare aerobic and anaerobic respiration
explain how a respirometer measures the rate of respiration
describe glycolysis, the link reaction and the Krebs cycle
explain the electron transport chain and chemiosmosis
explain the role of oxygen
compare carbohydrates and lipids as respiratory substrates

Sections marked HL only (Sections 7 to 10) are Additional Higher Level content. Every other section is common to SL and HL.

Guiding questions

How is energy released from food and made available to cells? Why do cells respire anaerobically when oxygen is short?

How this topic is examined

C1.2 is examined through equations, comparisons of aerobic and anaerobic respiration, and respirometer experiments. At HL, detailed questions on the stages of respiration and chemiosmosis are very common, often using diagrams of the mitochondrion.

State clearly where each process happens and what goes in and comes out.

Command term	What the examiner wants
State / Identify	a brief answer with no explanation needed
Outline	a brief account or summary
Describe	a detailed account, including trends or features, without reasons
Explain	a detailed account including causes, reasons or mechanisms
Distinguish / Compare and contrast	give the differences (and similarities), point by point
Calculate	a numerical answer with working and units
Deduce / Suggest	reach a conclusion from data; propose a reasonable explanation
Evaluate / Discuss	weigh strengths and limitations and reach a judgement

How to use these notes

Each section teaches one part of the syllabus in full. You'll see these boxes throughout; each has one job:

Box	What it's for
Think about it	a question to get you thinking before a section; the answer comes in the section
Key point	the one idea you must not forget
Common mistake	an error examiners see every year, and how to avoid it
In the real world	where the biology shows up outside the classroom
Try this	something quick you can do yourself to test the idea
Worked example	full solutions with IB-style marks (M1 method, A1 answer, R1 reasoning)
Quick check	short questions to test yourself at the end of each section

1 ATP: the energy currency of the cell

ATP carries small, usable packets of energy.

Think about it

Glucose stores a lot of energy, so why don't cells use glucose directly to power muscle contraction or active transport?

Adenosine triphosphate (ATP) is a nucleotide made of adenine, ribose and three phosphate groups. It is the immediate source of energy for almost all processes in cells.

When ATP is hydrolysed to ADP (adenosine diphosphate) and an inorganic phosphate (Pi), energy is released, which can be used to do work. The reaction is reversible: ATP is regenerated from ADP and Pi using energy from respiration (or photosynthesis). A typical cell recycles its whole pool of ATP every minute or so.

ATP is suited to its role because: it is soluble and moves easily within the cell; it releases energy in small, manageable amounts; it is stable at the pH of the cell but easily hydrolysed by enzymes; and it cannot pass through membranes, so each cell keeps its own supply.

Uses of ATP include active transport (B2.1), synthesis of macromolecules (anabolism), movement (muscle contraction, cilia, chromosome movement), and cell division.

Figure 1. The ATP-ADP cycle.

Quick check

1. What are the products of ATP hydrolysis?

2. Give three uses of ATP in cells.

3. Why is ATP better than glucose as an immediate energy source?

Answers: 1. ADP and inorganic phosphate 2. active transport, synthesis, movement 3. releases small usable amounts; easily hydrolysed

2 What cell respiration is

The controlled release of energy from organic compounds to make ATP.

Cell respiration is the controlled release of energy from organic compounds, such as glucose, to produce ATP. It happens in every living cell, all the time. It is not the same as breathing (ventilation), which only moves air into and out of the lungs.

Respiration is a series of enzyme-catalysed reactions that oxidize the organic compound in small steps, so that energy can be captured in ATP rather than lost as heat all at once. Glucose is the main respiratory substrate, but lipids and proteins can also be used.

Common mistake

Confusing respiration with breathing. Breathing is ventilation of the lungs; respiration is a biochemical process in every cell.

3 Aerobic respiration

With oxygen, glucose is fully broken down to CO₂ and water.

Aerobic respiration requires oxygen. Glucose is broken down completely to carbon dioxide and water, releasing a large amount of energy, enough to make about 30 to 32 ATP per glucose molecule. In eukaryotes, most of it happens in the mitochondria.

glucose + oxygen → carbon dioxide + water C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Variables affecting the rate of aerobic respiration include temperature (enzyme activity), availability of substrate and oxygen, and the energy demands of the cell (for example, muscle activity).

4 Anaerobic respiration in humans and yeast

Without oxygen, glucose is only partly broken down.

Anaerobic respiration occurs without oxygen. Glucose is only partially broken down in the cytoplasm, and only 2 ATP are produced per glucose molecule.

In humans (and other animals), anaerobic respiration produces lactate. It happens in muscles during intense exercise, when oxygen cannot be supplied fast enough. It allows a short burst of extra ATP. Lactate accumulates, and afterwards extra oxygen is needed to break it down (the oxygen debt, or excess post-exercise oxygen consumption).

In yeast (and plants), anaerobic respiration produces ethanol and carbon dioxide. This is fermentation. It is used in baking (CO₂ makes bread rise; ethanol evaporates during baking) and in brewing (ethanol in beer and wine), and in producing bioethanol as a fuel.

Humans: glucose → lactate Yeast: glucose → ethanol + carbon dioxide

Quick check

1. What is produced by anaerobic respiration in muscles?

2. What are the products of anaerobic respiration in yeast?

3. Why is anaerobic respiration useful in exercise?

Answers: 1. lactate 2. ethanol and carbon dioxide 3. rapid ATP when oxygen supply is insufficient

5 Comparing aerobic and anaerobic respiration

Same start, very different yields.

	Aerobic	Anaerobic (humans)	Anaerobic (yeast)
Oxygen	required	not required	not required
Location	cytoplasm and mitochondria	cytoplasm	cytoplasm
Products	CO₂ and water	lactate	ethanol and CO₂
ATP per glucose	about 30 to 32	2	2
Breakdown of glucose	complete	incomplete	incomplete

Key point

Both types begin with glycolysis in the cytoplasm. Only aerobic respiration uses mitochondria and oxygen, which is why it yields far more ATP.

6 Measuring the rate of respiration

A respirometer measures oxygen uptake.

A respirometer measures the rate of oxygen consumption by small organisms, such as germinating seeds or woodlice. The organisms are placed in a sealed tube with soda lime (or potassium hydroxide), which absorbs the carbon dioxide they produce. As they take in oxygen, the volume of gas decreases, so a coloured liquid in a capillary tube moves towards the organisms. The distance moved per minute gives the rate of oxygen uptake.

A control tube with glass beads (same volume) instead of organisms corrects for changes in temperature and pressure. Temperature must be kept constant, for example in a water bath. The respirometer can be used to investigate the effect of temperature on respiration rate.

WORKED EXAMPLE 1 Respirometer calculation

In a respirometer, the dye moved 24 mm in 10 minutes. The capillary tube has a cross-sectional area of 0.8 mm². The seeds had a mass of 4.0 g. Calculate the rate of oxygen uptake in mm³ g⁻¹ min⁻¹.

Solution

Volume = 24 × 0.8 = 19.2 mm³M1

Rate = 19.2 ÷ 10 ÷ 4.0 = 0.48 mm³ g⁻¹ min⁻¹A1

Figure 2. Effect of temperature on respiration rate of germinating seeds.

Quick check

1. Why is soda lime used in a respirometer?

2. What is the purpose of the control tube?

Answers: 1. absorbs CO₂ so volume change reflects O₂ uptake 2. corrects for temperature and pressure changes

7 Glycolysis and the link reaction (HL only)

Splitting glucose and preparing pyruvate.

HL only

This section is Additional Higher Level content. SL students do not need it.

Glycolysis occurs in the cytoplasm and does not need oxygen. Glucose (6C) is phosphorylated twice, using 2 ATP, forming hexose bisphosphate, which is unstable. It is split (lysis) into two triose phosphates (3C). Each triose phosphate is oxidized by removal of hydrogen, which is accepted by NAD, forming reduced NAD (NADH). Each is converted to pyruvate (3C), producing 2 ATP by substrate-level phosphorylation. Net yield per glucose: 2 ATP, 2 reduced NAD, 2 pyruvate.

In anaerobic conditions, pyruvate is converted to lactate (animals) or ethanol and CO₂ (yeast). This regenerates NAD from reduced NAD, so glycolysis can continue.

In aerobic conditions, pyruvate is actively transported into the mitochondrial matrix. In the link reaction, pyruvate is decarboxylated (CO₂ removed) and oxidized (hydrogen to NAD), and the remaining 2C acetyl group is attached to coenzyme A, forming acetyl CoA.

Figure 3. Glycolysis.

8 The Krebs cycle (HL only)

Acetyl groups are oxidized to CO₂, producing reduced carriers.

HL only

This section is Additional Higher Level content. SL students do not need it.

The Krebs cycle takes place in the mitochondrial matrix. Acetyl CoA (2C) combines with a 4C compound (oxaloacetate) to form a 6C compound (citrate). In a series of reactions, the 6C compound is decarboxylated twice, releasing 2 CO₂, and oxidized several times, regenerating the 4C compound.

Each turn of the cycle produces 3 reduced NAD, 1 reduced FAD, and 1 ATP (by substrate-level phosphorylation). The cycle turns twice per glucose. Most of the energy from glucose is now held in the reduced coenzymes, which carry high-energy electrons to the electron transport chain.

Stage	Location	Per glucose: products
Glycolysis	cytoplasm	2 ATP (net), 2 NADH, 2 pyruvate
Link reaction	matrix	2 CO₂, 2 NADH, 2 acetyl CoA
Krebs cycle (×2)	matrix	4 CO₂, 6 NADH, 2 FADH₂, 2 ATP
Electron transport chain	inner membrane	about 26 to 28 ATP, water

9 The electron transport chain and chemiosmosis (HL only)

Most ATP is made by a proton gradient.

HL only

This section is Additional Higher Level content. SL students do not need it.

Reduced NAD and reduced FAD deliver electrons to the electron transport chain, a series of protein complexes in the inner mitochondrial membrane (cristae). As electrons pass from carrier to carrier, they release energy, which is used to pump protons (H⁺) from the matrix into the intermembrane space. This creates a high concentration of protons in the intermembrane space: a proton gradient.

Protons then flow back into the matrix down their concentration gradient through ATP synthase, a channel enzyme. The flow drives the rotation of part of ATP synthase, which joins ADP and Pi to form ATP. This is chemiosmosis, and the process is called oxidative phosphorylation.

Oxygen is the final electron acceptor. At the end of the chain, oxygen combines with electrons and protons to form water. Without oxygen, electrons cannot leave the chain, so it stops; reduced NAD cannot be reoxidized, and the Krebs cycle and link reaction stop too. This is why aerobic respiration requires oxygen, and why cyanide, which blocks the chain, is lethal.

Figure 4. The electron transport chain and chemiosmosis.

Quick check

1. Where is the electron transport chain?

2. What is chemiosmosis?

3. What is the role of oxygen?

Answers: 1. inner mitochondrial membrane (cristae) 2. ATP synthesis driven by protons flowing through ATP synthase 3. final electron acceptor, forming water

10 Respiratory substrates (HL only)

Lipids yield more energy than carbohydrates.

HL only

This section is Additional Higher Level content. SL students do not need it.

Lipids can be respired: fatty acids are broken into 2C fragments that enter the Krebs cycle as acetyl CoA, and glycerol enters glycolysis. Because fatty acids contain more hydrogen per carbon atom, they produce more reduced NAD and FAD per gram, so more ATP per gram than carbohydrate. But lipids can only be respired aerobically, because their breakdown products enter at the link reaction and Krebs cycle, not glycolysis. Carbohydrates can be respired anaerobically.

11 ATP: the energy currency

Structure and role.

ATP (adenosine triphosphate) consists of adenine, ribose and three phosphate groups. Hydrolysis of the terminal phosphate releases energy (about 30 kJ mol−1) for active transport, muscle contraction, synthesis of macromolecules and movement of chromosomes. ATP is regenerated from ADP + Pi by respiration.

WORKED EXAMPLE 2 Properties (standard)

Explain why ATP is suited to its role as an energy currency.

Solution

Releases a small, manageable amount of energy per moleculeR1

Easily hydrolysed and regenerated; soluble, moves within cellsR1

Quick check

1. List three processes in cells that require ATP.

Answers: 1. active transport; muscle contraction; protein synthesis

12 Respiration versus gas exchange

Avoiding confusion.

Cell respiration is the controlled release of energy from organic compounds to produce ATP, occurring in every living cell. Gas exchange (ventilation) is the exchange of O2 and CO2 with the environment. They are linked: gas exchange supplies O2 for aerobic respiration and removes CO2.

WORKED EXAMPLE 3 Distinguishing (standard)

Distinguish cell respiration from ventilation.

Solution

Respiration: chemical reactions in cells producing ATPR1

Ventilation: movement of air in and out of the lungsR1

Common mistake

Using 'respiration' to mean breathing. In biology, respiration is a chemical process in cells; breathing is ventilation.

13 Aerobic respiration overview

Glucose to carbon dioxide and water.

C6H12O6 + 6O2 → 6CO2 + 6H2O (+ about 30–32 ATP). Glycolysis occurs in the cytoplasm; the link reaction, Krebs cycle and oxidative phosphorylation occur in mitochondria. Oxygen is the final electron acceptor.

WORKED EXAMPLE 4 Equation (basic)

Write the word and balanced equation for aerobic respiration of glucose.

Solution

glucose + oxygen → carbon dioxide + waterA1

C6H12O6 + 6O2 → 6CO2 + 6H2OA1

14 Anaerobic respiration in humans

Lactate fermentation.

Without enough oxygen, muscle cells convert pyruvate to lactate, regenerating NAD so glycolysis can continue, producing only 2 ATP per glucose. Lactate builds up, lowering pH; it is later converted back in the liver, requiring extra oxygen (oxygen debt / EPOC).

WORKED EXAMPLE 5 Sprinting (exam level)

Explain why sprinters continue to breathe heavily after a race.

Solution

Repay oxygen debtR1

Oxygen needed to oxidize lactate and restore ATP and creatine phosphateR1

15 Anaerobic respiration in yeast

Alcoholic fermentation.

Yeast converts pyruvate to ethanol and CO2 under anaerobic conditions. This is used in brewing (ethanol) and baking (CO2 makes dough rise; ethanol evaporates during baking).

WORKED EXAMPLE 6 Baking (standard)

Explain why dough rises.

Solution

Yeast respires anaerobically producing CO2R1

Gas bubbles trapped in the doughR1

In the real world

Bioethanol fuel is produced by yeast fermentation of sugars from crops such as sugar cane and maize.

16 Comparing aerobic and anaerobic respiration

Yield and products.

Feature	Aerobic	Anaerobic (humans)	Anaerobic (yeast)
oxygen	required	not required	not required
products	CO2, H2O	lactate	ethanol, CO2
ATP per glucose	about 30–32	2	2
location	cytoplasm and mitochondria	cytoplasm	cytoplasm

17 Respirometers

Measuring oxygen uptake.

A respirometer measures the rate of respiration by the uptake of O2: soda lime (or KOH) absorbs CO2, so the volume decrease equals O2 consumed, shown by movement of coloured liquid in a capillary tube. A control tube with glass beads accounts for temperature and pressure changes.

WORKED EXAMPLE 7 Calculation (exam level)

Liquid in a capillary of radius 0.5 mm moves 24 mm in 10 minutes for 2.0 g of germinating peas. Calculate the rate of O2 uptake per gram per minute.

Solution

Volume = π(0.5)2 × 24 = 18.8 mm3M1

Rate = 18.8/(10 × 2.0) = 0.94 mm3 g−1 min−1A1

Quick check

1. Why is soda lime included?

2. Why is a control tube used?

Answers: 1. to absorb CO2 so volume change reflects O2 uptake 2. to correct for temperature and pressure changes

18 Factors affecting the rate of respiration

Temperature and substrate.

Rate of respiration increases with temperature up to an optimum (enzymes), with glucose and oxygen availability, and with activity level. Very high temperatures denature enzymes.

Quick check

1. Predict the effect of cooling germinating seeds on the respirometer reading.

Answers: 1. slower movement: lower rate of respiration

19 Respiratory substrates

Carbohydrates, lipids, proteins.

Glucose is the main substrate, but lipids (fatty acids) and proteins (amino acids) can also be respired. Lipids release more energy per gram because they have more C–H bonds; they require more oxygen per gram.

WORKED EXAMPLE 8 Energy yield (standard)

Why do lipids release more energy per gram than carbohydrates?

Solution

More hydrogen atoms (C–H bonds) per gramR1

More electrons available for the electron transport chainR1

20 Respiratory quotient (RQ)

CO2 produced/O2 used.

RQ = volume of CO2 produced/volume of O2 consumed. Carbohydrates give RQ = 1.0; lipids about 0.7; proteins about 0.9. RQ indicates which substrate is being respired.

WORKED EXAMPLE 9 RQ (standard)

Calculate RQ for the respiration of the fat tripalmitin: 2C51H98O6 + 145O2 → 102CO2 + 98H2O.

Solution

102/145M1

= 0.70A1

21 Glycolysis (overview)

Splitting glucose.

Glycolysis occurs in the cytoplasm: glucose is phosphorylated using 2 ATP, split into two triose phosphates, then oxidized to two pyruvate, producing 4 ATP (net 2 ATP) and 2 reduced NAD. It does not require oxygen.

WORKED EXAMPLE 10 Net yield (standard)

State the net yield of glycolysis per glucose.

Solution

2 ATP, 2 NADH, 2 pyruvateA2

22 The link reaction and Krebs cycle (HL)

In the mitochondrial matrix.

Pyruvate enters the matrix, is decarboxylated and oxidized to acetyl CoA (link reaction), producing NADH and CO2. Acetyl CoA combines with oxaloacetate to form citrate; through decarboxylations and oxidations, the Krebs cycle regenerates oxaloacetate, producing per turn 2 CO2, 3 NADH, 1 FADH2 and 1 ATP.

WORKED EXAMPLE 11 Counting (exam level)

How many CO2 are released per glucose in the link reaction and Krebs cycle combined?

Solution

Link: 2; Krebs: 4M1

6A1

23 Oxidative phosphorylation (HL)

Chemiosmosis.

Electrons from NADH and FADH2 pass along the electron transport chain in the inner membrane. Energy released pumps protons into the intermembrane space. Protons flow back through ATP synthase (chemiosmosis), generating ATP. Oxygen accepts electrons and protons to form water.

WORKED EXAMPLE 12 Role of oxygen (exam level)

Explain the role of oxygen.

Solution

Final electron acceptorR1

Allows the chain to continue; forms water with protonsR1

24 Mixed review: worked problems

Bringing the ideas together.

WORKED EXAMPLE 13 Mixed problem (exam level)

Explain why aerobic respiration yields much more ATP than anaerobic respiration.

Solution

Anaerobic: only glycolysis (2 ATP)R1

Aerobic: pyruvate fully oxidized; electron transport chain produces most ATPR1

25 Additional exam-style practice

Paper 1 and Paper 2.

WORKED EXAMPLE 14 Paper 1 question (standard)

Where does glycolysis occur? A. mitochondrial matrix B. cytoplasm C. inner mitochondrial membrane D. nucleus

Solution

BA1

WORKED EXAMPLE 15 Paper 2 question (exam level)

Describe how to use a respirometer to compare respiration rates of germinating and dry seeds.

Solution

Equal masses in separate respirometers with soda lime; same temperatureR1

Record movement of liquid over time; control tubeR1

Calculate volume of O2 per gram per minuteR1

26 Respiration and exercise

Energy systems.

Short bursts of activity use stored ATP and creatine phosphate; longer intense exercise uses anaerobic glycolysis (lactate); endurance exercise relies on aerobic respiration of glucose and fatty acids. Training increases mitochondria and capillaries in muscles.

Quick check

1. Why does endurance training increase the number of mitochondria?

Answers: 1. more aerobic respiration capacity, more ATP without lactate

27 Metabolic poisons

Disrupting respiration.

Cyanide inhibits cytochrome oxidase in the electron transport chain, stopping aerobic respiration. Uncouplers (such as DNP) let protons leak across the membrane, so energy is released as heat instead of ATP.

Quick check

1. Why is cyanide so toxic?

Answers: 1. it stops the electron transport chain, so cells cannot make enough ATP

28 Common misconceptions and links

Students often think…	Actually…
respiration is breathing	respiration is a chemical process in cells
anaerobic respiration produces no ATP	it produces 2 ATP per glucose
muscles produce ethanol	human muscles produce lactate
oxygen is needed in glycolysis	oxygen is the final electron acceptor in the ETC

How C1.2 connects to the rest of the course

Topic	Connection
C1.1 Enzymes	metabolic pathways
B2.2 Organelles	mitochondrion structure
C1.3 Photosynthesis	chemiosmosis and ATP synthase
B3.3 Muscle (HL)	ATP in contraction
B1.1 Lipids	energy storage

29 Exam-style question with markscheme

Try this under exam conditions (about 15 minutes) before reading the markscheme.

Figure 5. Respiration rate of germinating seeds at different temperatures.

(a) State the word equation for aerobic respiration. [1]

(b) Explain the role of soda lime in a respirometer. [2]

(d) Compare anaerobic respiration in humans and yeast. [3]

(e) Explain how ATP is produced by chemiosmosis. [4]

Markscheme

Part	Answer	Marks
(a)	glucose + oxygen → carbon dioxide + water	A1
(b)	absorbs CO₂	R1
	so volume change reflects O₂ uptake only	R1
(c)	30 × 1.0 = 30 mm³ in 5 min	M1
	6 mm³ min⁻¹	A1
(d)	both in cytoplasm, 2 ATP, no oxygen	A1
	humans: lactate	A1
	yeast: ethanol and CO₂	A1
(e)	electrons pass along ETC on inner membrane	R1
	energy pumps protons into intermembrane space	R1
	protons flow through ATP synthase	R1
	ADP + Pi → ATP; oxygen final acceptor	R1

Examiner's comments. In (d), the best answers gave both similarities and differences.

30 Check your understanding

Section A: multiple choice

1. ATP is hydrolysed to

A. ADP and Pi B. AMP and glucose C. ADP and glucose D. adenine and ribose

2. Anaerobic respiration in human muscle produces

A. ethanol B. carbon dioxide C. lactate D. oxygen

3. Per glucose, anaerobic respiration yields

A. 30 ATP B. 2 ATP C. 0 ATP D. 38 ATP

4. In a respirometer, soda lime absorbs

A. oxygen B. water C. nitrogen D. carbon dioxide

5. Yeast fermentation is used in

A. cheese making only B. baking and brewing C. photosynthesis D. insulin production

6. Aerobic respiration mainly takes place in

A. mitochondria B. chloroplasts C. ribosomes D. nucleus

7. The link reaction occurs in

A. the cytoplasm B. the intermembrane space C. the inner membrane D. the mitochondrial matrix

8. The final electron acceptor is

A. NAD B. FAD C. oxygen D. water

Section B: structured

9. Outline the roles of ATP. [3]

10. Compare aerobic and anaerobic respiration. [4]

11. Describe how a respirometer measures respiration rate. [4]

12. Explain the Krebs cycle. [4]

Answers

1. A 2. C 3. B 4. D 5. B 6. A 7. D 8. C

9. Energy for active transport, synthesis, movement; hydrolysed to ADP + Pi; regenerated by respiration.

10. Aerobic: O₂, mitochondria, CO₂ + water, ~30 ATP; anaerobic: no O₂, cytoplasm, lactate or ethanol + CO₂, 2 ATP.

11. Organisms + soda lime; O₂ uptake reduces volume; dye moves; measure distance per time; control.

12. Acetyl CoA + 4C → 6C; decarboxylation (2 CO₂); oxidation (3 NADH, 1 FADH₂); 1 ATP; 4C regenerated; matrix.

31 Summary and topic map

Idea	Remember
ATP	hydrolysed to ADP + Pi; energy for work
Respiration	controlled release of energy to make ATP
Aerobic	O₂; CO₂ + water; ~30 ATP
Anaerobic	lactate (humans), ethanol + CO₂ (yeast); 2 ATP
Respirometer	soda lime; measures O₂ uptake
HL	glycolysis, link reaction, Krebs, ETC, chemiosmosis, lipids

Before the exam, make sure you…

•never confuse respiration with breathing
•state locations of each process
•give products of anaerobic respiration correctly
•calculate respirometer rates with units

Cell Respiration on one page

Cover this page with a sheet of paper and try to rebuild it from memory. Whatever you can't recall is what to revise next.

Figure 6. Topic map for Cell Respiration.

revisionprep.comIB-style notes · question bank · mock papers