Download Bio Respiration 2009 Yingxin

Respiration
Gaseous exchange
O
O
O
Process by which oxygen is acquired and carbon dioxide is removed
Cellular respiration creates constant demand for oxygen and need to remove carbon dioxide gas
We breathe as a reflex because we need to get rid of carbon dioxide in our body
Gaseous exchange systems in animals
Animal
Gaseous exchange system
Aquatic insects
Some develop tracheal gills to increase surface area across which gases diffuse
Some are dependent on getting oxygen from the surface with a siphon and releasing
carbon dioxide straight into the air (eg mosquito larva – breathing tubes)
Tadpoles
Juvenile amphibians usually have gills, which are lost as adults take on terrestrial
existence
Protists (unicellular, eg
Simple diffusion across cell surface
amoeba)
Air-breathing vertebrate Lungs
Marine mammals come to surface to breathe
Bony fish, sharks, rays
Gills to breathe dissolved oxygen in water
80% extraction rate: Over 3 times the rate of human lungs from air
Gills have high surface area, many stuck together
Insects
System of branching tubes (tracheal tubes)
Gases diffuse across the moist lining to and from tissues
End of each tube contains a small amount of fluid (spiracle) to regulate the movement
of gases by changing surface area of air in contact with cells
Amphibians
Surface gas exchanges
Surface must be kept moist by secretions from mucous glands
Birds
Air sacs in addition to lungs
Air sacs ventilate lungs, where gaseous exchange takes place
Anterior and posterior air sacs serve as bellows that keep air flowing through lungs
continuously in one direction
Common properties of gaseous exchange systems
O Thin membrane: facilitates diffusion
O Large surface area: facilitates efficient diffusion
O Moist: for gas to dissolve in the transport medium (water in the blood)
Surface area X Difference in concentration across membrane = Diffusion rate across gas exchange surfaces
Thickness of membrane
Larger SA + Bigger difference in concentration + Thinner membrane = Faster diffusion rate
Human gaseous exchange system
Trachea
O
C-rings around trachea supports it and
maintains airway open
O
C-shape allows trachea to collapse
slightly when food goes down oesophagus (directly in front of trachea)
O
Cilia (hair) sweep mucus out of trachea
Alevolus
O
O
O
O
O
Gaseous exchange occurs here
Wrapped extensively in capillaries
Big surface area
Moist
Thin permeable surface
Bronchiole and alveolus help increase surface area for efficient diffusion of gases
Alveolus is moist
O
O
O
O
Near blood vessels so gases can diffuse
into blood streams and be carried to the heart and pumped all over the body
Direct contact with blood vessels
Gases dissolve into the bloodstream
Alveolar surface: gas exchange
membranes are only 0.5 nanometers thick, allowing for rapid and efficient diffusion
Alveolus and lung capillary
O
very closely, allowing for rapid and efficient diffusion of gases
O
capillary, carbon dioxide diffuses from the capillary to the alveoli
O
high, haemoglobin binds with a lot of oxygen
Lung capillaries surround the alveoli
Oxygen diffuses from the alveoli to the
When oxygen levels in the capillary are
Body tissue capillary and body cells
O
Capillaries are very close to the body
cells, allowing for rapid diffusion back and forth
O
When carbon dioxide levels of the body
tissues are high, haemoglobin releases oxygen
o
Oxygen will diffuse into the body cells
from the capillaries
O
Carbon dioxide from the body cells
diffuse into the capillary
o
Most of the carbon dioxide in the blood
is carried as bicarbonate (formed in red blood cells and diffuse out into the plasma)
Inhalation
External intercostal muscles contract
Ribcage moves up and out
Lungs expand
Diaphragm contracts and moves down
Thoracic volume (chest cavity) increases,
a partial vacuum is created, decrease in
air pressure
Air flows in, in response to pressure
gradient
Exhalation
External intercostal muscles relax
Forced breathing
Internal intercostal muscles and
abdominal muscles contract to
increase force of expiration
Ribcage moves down and in
Lungs shrink
Diaphragm relaxes, elasticity of diaphragm causes recoil and moves up
Thoracic volume decrease, air pressure increases
Air flows out in response to pressure gradient
Breathing control
1 Chemoreceptors (in aorta and carotid arteries)
O
O
respiratory centre to increase breathing rate and depth
1 Stretch receptors
O
Monitor the blood’s pH
Low pH (high CO2) will stimulate the
Monitor the amount of lung inflation
O
Vagus nerve carries impulses from
stretch receptors to respiratory centre to inhibit inspiration
2 Respiratory centre
O
allowing voluntary control over breathing
3 Intercostal nerves
O
3 Phrenic nerve
O
stimulate contraction
Connects to the cerebral cortex,
Stimulate inspiration
Sends impulses to diaphragm to
Why can’t we hold our breaths for long? Why do we have a reflex to breathe?
O
If we don’t breathe, there will be raised
+
CO2 levels in our blood, increasing carbonic acid levels and H ions, lowering the blood pH. Chemoreceptors
will monitor this decrease in pH, and stimulate respiratory centre to increase breathing rate and depth.
Respiratory Quotient (RQ)
O Ratio of the amount of carbon dioxide produced during cellular respiration to the amount of oxygen
consumed
O CO2 produced
O2 consumed
Respirometer
O Sealed unit where CO2 produced by respiring tissues is absorbed by soda lime and volume of CO2 consumed is
detected by fluid displacement in a manometer
Cellular Respiration
O
O
O
Glucose is broken down/oxidized to give carbon dioxide, water and energy (ATP)
Energy released is used to manufacture ATP from ADP and phosphate
Oxidation of 1 glucose molecule = energy to synthesize 38 ATP molecules
General Formula
C6H12O6 + 6 O2
Uses of Energy
O Muscle contraction
O Protein synthesis
O Cell division
O Active transport
O Building up of protoplasm for growth
O Transmission of nerve impulses
O Maintenance of a constant body temperature
Adenosine Triphosphate (ATP)
6 CO2 + 6 H2O + Energy
O
O
O
O
High energy compound
ADP (low energy compound with no available energy to fuel metabolic activity) +Free phosphate
ATP: 30.7kj of energy
o 10% captured by cell for processes
o 90% lost to heat
Convenient store of energy because
o Stores energy in relatively small amounts
o Quickly hydrolysed in a one-step reaction to release energy
o Easily moved around in cells, but cannot pass through cell membranes
Phosphorylation: addition of phosphate group to a molecule (ATP > ADP)
Hydrolysis: transfer of phosphate group from molecule to ADP (ADP > ATP)
Oxidation: removal of hydrogen from a molecule (NAD* > NADH)
1.
2.
3.
Glycolysis (cytoplasm)
O
Breakdown of glucose into 2 molecules of
pyruvate
O
2 net ATP
Krebs Cycle (mitochondrial matrix)
O Decomposes a derivative of pyruvate to carbon dioxide
O 2 net ATP
Electron Transport & Oxidative Phosphorylation (inner membrane of mitochondrion)
O Generates 90% of ATP
O 34 ATP
Glycolysis
O Occurs in cytoplasm
O Glucose (6C) is broken into 2 molecules of pyruvate (3C)
O 2ATP and 2 NADH + 2H+ are generated
O No oxygen required (aerobic and anaerobic)
O Products:
o 2 ATP
o 2 NADH (oxidative phosphorylation)
o 2 Pyruvate (converted to acetyl CoA)
Transition reaction
O Occurs in mitochondrial matrix
O Conversion of pyruvate to Acetyl Coenzyme A
O Only occurs in aerobic respiration
O Carbon dioxide removed
O Products:
o 2 Acetyl CoA molecules (Krebs Cycle)
o 2 NADH (oxidative phosphorylation)
o 2 CO2 (exhaled from lungs)
Krebs Cycle
O
O
O
O
O
O
O
O
Only aerobic respiration
Occurs in mitochondrial matrix
Oxidize acetyl CoA through decarboxylation and dehydrogenation
Acetyl group passes into cyclic reaction
Combines with 4-carbon molecule to form a 6-carbon molecule
CoA released for reuse
Remove carbon as carbon dioxide
Products:
o 2 oxaloacetate molecules (reused for Krebs Cycle)
o 6 NADH molecules (oxidative phosphorylation)
o 2 FADH2 molecules (oxidative phosphorylation)
o 2 ATP molecules
o 4 CO2 molecules (exhaled from lungs)
Electron Transport Chain (Oxidative Phosphorylation)
O Occurs in inner membrane of mitochondria
O Hydrogen pairs are transferred to the ETC, a series of hydrogen and electron carriers
O ATP is formed as electrons are transferred from NADH or FADH2 to oxygen via electron carriers (NADH > NAD+,
FADH2 > FAD)
O Each NADH generates 3 ATP (10 NADH > 28 ATP. Note: 2 ATP is used up in transporting 2 NADH produced from
glycolysis from the cytoplasm to the mitochondria), each FADH2 generates 2 ATP (2 FADH2 > 4 ATP)
O Final electron acceptor is oxygen, and is reduced to water
O As electron is transported along ETC, energy from electron transfer is used to pump hydrogen ions from
mitochondrial matrix, across inner mitochondrial membrane and into intermembrane space through active
transport
O Creates proton gradient across inner mitochondrial membrane
O Hydrogen ions diffuse from intermembrane space into mitochondrial matrix through F 0 protein
O ATP synthase synthesize ATP from ADP and phosphate
O Proton gradient is source of potential energy from gradient synthesizes ATP
O Products:
o 34 ATP
Stage
No. of NADH
/ FADH2
Glycolysis
Pyruvate to Acetyl CoA
Krebs Cycle
2 NADH
2 NADH
6 NADH
2 FADH2
No. of ATP formed in
oxidative phosphorylation
(from NADH / FADH2)
6
6
18
4
34
No. of ATP formed by
substrate-level
phosphorylation
2
2
Total no. of ATP
formed
4
38
8
6
24
Chemiosmosis
O Process whereby synthesis of ATP is coupled to electron transport and the movement of protons (H + ions)
O Electron transport carriers are arranged over inner membrane of mitochondrion
O Oxidize NADH + H+ and FADH2
O Energy from this process forces protons to move, against conc gradient, from mitochondrial matrix into space
between two membranes
O
O
O
Eventually, protons flow back to matrix via ATP synthetase molecules in the membrane
As the protons flow down conc grad, energy is released and ATP is synthesized
Chemiosmotic theory explains generation of ATP in light-dependent phase of photosynthesis
Anaerobic Respiration
O Absence of oxygen
O All organism can metabolize glucose anaerobically using glycolysis (in cytoplasm)
O Energy yield very low
O Produces much more toxic waste products
O Yeast and plants: alcoholic fermentation
O Animals: production of lactic acid
O Plants & Yeast
C6H12O6
C2H5OH (Ethanol) + CO2 + small amount of energy
O Animals
C6H12O6
C3H6O3 (Lactic acid)
+ small amount of energy
O Muscle cells can respire anaerobically for short periods of time when there is a shortage of oxygen
O Produces lactic acid
O Incurs oxygen debt (amount of O2 required to oxidize lactic acid produced)
O Lactic acid causes fatigue, hardens muscles, is toxic
O When body is no longer short of O2, lactic acid is transported to the liver and converted back to glucose
Oxygen
ATP Produced
By Products
Aerobic
Present
36
CO2 + H2O
Anaerobic
Absent (can only carry out glycolysis)
2
Lactic acid + H2O