Transcript Slide 1
Essential idea: Cell respiration supplies energy for the functions of life.
Topic 2: Molecular Biology
2.8 Respiration
Nature of Science
Assessing the ethics of scientific research—the use of invertebrates in respirometer experiments has ethical implications. (4.5)
Understandings
2..8.U1 Cell respiration is the controlled release of energy from organic compounds to produce ATP.
2.8.U2 ATP from cell respiration is immediately available as a source of energy in the cell. 2.8.U3 Anaerobic cell respiration gives a small yield of ATP from glucose.
2.8.U4Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.
Applications and Skills
2.8.A1 Application: Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.
2.8.A2 Application: Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions.
2.8.S1 Skill: Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
Key Terms
Summary of Energy Reactions:
Energy Reactions Photosynthesis
Light Energy --> Chemical energy
Respiration
Chemical Energy --> Chemical energy 6CO 2
sunlight
+ 6H 2 O ----> C 6 H 12 O 6
chlorophyll
+ 6O 2
Occurs in green plant cells
C 6 H 12 O 6 + 6O 2 ----> 6CO 2
ADP + P ATP
+ 6H 2 O + Heat
Occurs in all living cells
Energy for life
Every living cell in your body needs energy. The average adult has about 50 million million cells – that’s a lot of energy!
energy
Where does all this energy come from?
In body cells, the energy needed for life comes from the chemical energy stored in glucose.
What is needed for releasing energy?
Burning is a chemical reaction in which energy is released in the form of heat. What other substance is needed for energy to be released from this fuel?
fuel
Respiration
In respiration, carbohydrates like glucose (fuel) are broken down to provide energy for the body.
This must occur in a controlled manner in order for the body to capture the energy in a usable form.
What is breathing? DON’T GET THESE MIXED UP
What is aerobic respiration?
Respiration is the process used by the body’s cells to release the chemical energy stored in glucose. When
oxygen
is involved in this energy-releasing process, it is called
aerobic respiration
.
What do you think aerobic means?
aerobic = ‘with oxygen’
Aerobic respiration is an efficient process that generates enough energy to supply the whole body.
Our bodies perform aerobic respiration most of the time, as long as the supply of oxygen remains high enough.
Respiration
is the process by which organisms extract the energy stored in complex molecules and use it to generate
adenosine triphosphate (ATP)
.
What is this ‘Useable Form of Energy?
In this way they obtain energy to fuel their metabolic pathways. ATP provides the immediate source of energy for biological processes such as active transport, movement and metabolism.
ATP
Adenosine triphosphate
ATP contains a sugar (ribose), a base (adenine) and three phosphate groups.
ribose adenine phosphates
When ATP is hydrolysed to form ADP and inorganic phosphate, 30.5 kJ of energy are released.
ATP
+
H 2 O
ADP +
+
inorganic phosphat e 30.5 kJ
Biological systems transfer the energy in glucose to ATP because unlike glucose…
Why ATP?
glucose ATP
ATP releases its energy instantly in a single reaction. The hydrolysis of ATP releases a small amount of energy, ideal for fuelling reactions in the body .
Types of Respiration
During
aerobic respiration
glucose. , a respiratory substrate, e.g. glucose, is split in the presence of oxygen to release carbon dioxide and water. A large number of ATP molecules are produced, releasing the energy from the
C 6 H 12 O 6 + 6 O 2
6 CO 2 + 6 H 2 O + 36 ATP
In
anaerobic respiration
absence of oxygen) to either lactate or ethanol. The ATP yield is low.
, glucose is converted (in the
C 6 H 12 O 6
2 C 2 H 5 OH + 2 CO 2 + 2 ATP ethanol C 6 H 12 O 6
2 C 3 H 6 O 3 lactate + 2 ATP
Where Does Respiration Occur?
Respiration occurs in all living cells. In of respiration occur in the cytoplasm. The later stages of respiration are restricted to the
eukaryotes mitochondria
. the early stages Mitochondria contain highly folded inner membranes that hold key respiratory proteins (including the enzyme that makes ATP) over a large surface area.
Mitochondria provide an isolated environment to maintain optimum conditions for respiration.
Mitochondria have their own DNA and ribosomes, so can manufacture their own respiratory enzymes.
The structure of the mitochondria
An overview of respiration
Respiration in detail…………
Cell respiration occurs in 3 main stages: 1. Glycolysis 2. Krebs Cycle 3. Electron Transport Glycolysis means “splitting of sugar” A six-carbon sugar (glucose) is broken into two three-carbon molecules of pyruvate, which still hold most of the energy of glucose.
This occurs in the cytoplasm and
does not
require oxygen.
There is a net yield of two ATP molecules.
The first stage of respiration: glycolysis
The stages of glycolysis
The fate of pyruvate
Krebs cycle
Counting carbons
For each molecule of glucose,
glycolysis
produces:
Keeping track of the products
2 ×
2 ×
2 ×
For each molecule of glucose, the
link reaction
produces:
2 ×
2 ×
2 ×
For each molecule of glucose,
Krebs cycle
generates:
Keeping track of the products
4 ×
produced by
decarboxylation
6 ×
2 ×
produced by
redox reactions
produced by
redox reactions
2 ×
produced by
substrate-level phosphorylation
The NADH and FADH originally locked in glucose. This energy is now transferred to ATP by 2 contain the potential energy
oxidative phosphorylation
in the
electron
transport chain.
The electron transport chain
Understanding the ETC
How much ATP is produced?
Process ATP in ATP produced
glycolysis link reaction Krebs cycle 2 0 0 4 0 2 (per glucose)
Net ATP out
2 0 2 (per glucose) Via the electron transport chain and chemiosmosis, each NADH can yield 2.5 ATP and each FADH
2
1.5 ATP.
From one molecule of glucose, glycolysis yields 2 NADH, the link reaction yields 2 NADH and the Krebs cycle yields 6 NADH and 2 FADH 2 .
10 × 2.5 = 25 ATP from NADH 2 × 1.5 = 3 ATP from FADH 2 total = 2 + 2 + 25 + 3
= 32 ATP overall
The theoretical yield of 32 ATPs for each glucose molecule is rarely achieved. In fact respiration is only about 32% efficient.
Efficiency of aerobic respiration
Some protons leak across the mitochondrial membrane, so not all are available to generate ATP via chemiosmosis.
Some ATP is used up moving pyruvate into the mitochondria by active transport.
Some ATP is used up moving hydrogen from reduced NAD made during glycolysis into the mitochondria.
Some energy is lost as heat. This heat helps to maintain a suitable body temperature for enzyme-controlled reactions.
Adaptations of mitochondria
Evidence for chemiosmosis
The theory of
chemiosmosis matrix
states that the energy in a chemical gradient established by electron movement is used to generate ATP. Evidence includes: The proton gradient across the inner membrane can be measured as it corresponds to a pH gradient.
Isolated ATP synthase enzymes can produce ATP using a proton gradient even if no electron transport is occurring.
Chemicals that block the ETC inhibit the formation of a proton gradient and prevent ATP synthesis.
Respiratory rate
The
respiratory rate
which an organism converts glucose to CO 2 and water. It can be calculated by measuring an organism’s rate of oxygen consumption.
is the rate at Studies on simple animals often use a
respirometer
.
Respirometers measure the change in gas volume in a closed system. Any change is due to the respiratory activity of the study organisms. Potassium hydroxide or soda lime is used to absorb the carbon dioxide produced, meaning any changes in volume are due to oxygen consumption.
The respirometer
Respirometer experiments
Other substances as well as glucose can be respired. Different
respiratory substrates
release different amounts of energy.
Respiratory substrates
Respiratory substrate
carbohydrate lipid protein
Mean energy value (kJ g -1 )
15.8
39.4
17.0
The difference in the relative energy values of these respiratory substrates is due to the amount of hydrogen atoms present in each one. If more hydrogen atoms are available to reduce coenzymes, more energy can subsequently be generated in the electron transport chain.
Respiratory quotient
(
RQ
) is the ratio of the volume of carbon dioxide produced to the volume of oxygen used in the same period of time.
Respiratory quotient
RQ = volume of CO 2 given out volume of O 2 taken in
RQ gives an indication of the respiratory substrate being respired and whether respiration is aerobic or anaerobic.
Type of respiration
anaerobic aerobic
Substrate
glucose carbohydrate protein lipid
RQ
> 1 1.0
approx. 0.9
approx. 0.7
Respiration calculations
Anaerobic Respiration
Anaerobic respiration:
Without oxygen Partial breakdown of glucose molecule Minimal release of energy: 1 glucose 2ATP Occurs in 2 stages: 1. Glycolysis (occurs in the cytoplasm) 2. Fermentation (occurs in the cytoplasm) Glycolysis: Glucose Pyruvate + 2ATP During fermentation: 1. In animals: Pyruvate Lactic acid 2. In plants and yeast: Pyruvate Ethanol + CO2
Anaerobic respiration is useful to the body when energy is needed in a hurry.
The problems with anaerobic respiration
glucose lactic acid energy
There are
two problems
with anaerobic respiration: Anaerobic respiration releases much less energy from glucose compared to aerobic respiration.
Lactic acid is a poisonous waste product. Why is anaerobic respiration not the best way to get energy from glucose?
Lactic acid is the product of anaerobic respiration and is harmful because it can stop muscles from doing their job.
Why is lactic acid so harmful?
If lactic acid builds up in muscle cells, it stops muscles from contracting and relaxing and they become fatigued.
The muscles ache and the body experiences cramp, which forces the body to stop what it is doing and rest.
Why can anaerobic respiration only be carried out for short periods of time?
After anaerobic respiration acid.
,
the body is in recovery and must get rid lactic
Recovery and getting rid of lactic acid
glucose lactic acid energy
The body is now at rest but the breathing rate and heart rate remain high. Why does this happen?
turning it into carbon dioxide and water.
lactic acid oxygen carbon dioxide water
Why do the breathing and heart rates return to normal after a few minutes of recovery?
glucose oxygen carbon dioxide water energy
During anaerobic respiration, muscles get energy from glucose but do not ‘pay’ for it with oxygen.
glucose lactic acid energy
This means that an
oxygen debt
is created.
When and how is this oxygen debt ‘paid off’?
Oxygen debt – pay off
during the recovery period after exercise. It is the oxygen needed to get rid of lactic acid that pays back the oxygen debt.
lactic acid oxygen carbon dioxide water oxygen to pay back ‘oxygen debt’
When is the oxygen debt completely paid off?
Anaerobic respiration: word equation activity
Revision Questions:
1. Write a chemical equation for the process of aerobic respiration.
2. Draw a diagram of the mitochondria and label the parts.
3. Explain why it is possible that the products of anaerobic respiration in animal and plant cells results in different products even though they both start with Pyruvate.
4. Define cell respiration.
5. List the differences between aerobic and anaerobic respiration.
6. Define autotroph and heterotroph in terms of energy and respiration (will need to look this up).