Unit 2 KA2-KA3 Flashcards
Cellular respiration
Cellular respiration is a series of metabolic pathways present in all cells in all forms of life.
These metabolic pathways result in the release of energy.
Transfer of energy via ATP
ATP (adenosine triphosphate) is composed of 1 molecule of adenosine and 3 inorganic phosphates (Pi).
ATP stores the energy released by respiration and releases it immediately when a cell requires it.
The addition of a phosphate group onto a molecule (e.g. ADP + Pi = ATP) is known as phosphorylation.
ATP transfers chemical energy from a respiratory substrate (e.g. glucose) to synthetic pathways and other processes in cells which require energy (e.g. muscle contraction, active transport, cell division).
Glycolysis
Stage 1: Glycolysis
This is the breakdown of glucose to pyruvate
glycolysis occurs in the cytoplasm of the cell it does not require oxygen
it is a series of enzyme-controlled steps
The first part of glycolysis is an energy investment phase:-
2 molecules of ATP are used to provide the energy to phosphorylate glucose and intermediates.
Glucose
Energy transfer
energy
ATP
Amino acids
Intermediate molecules
This leads to the generation of more ATP during the energy pay-off stage and results in a net gain of ATP
2ATP 2ADP + 2Pi
4ADP + 4Pi 4ATP
2NAD 2NADH
Pyruvate
The second part is an energy pay-off phase:-
the intermediates are converted into pyruvate and as a result 4 molecules of ATP are made - a net gain of 2 ATPs.
During the energy pay-off phase, hydrogen (H) ions and electrons are removed by dehydrogenase enzymes. These H ions and electrons are passed to a coenzyme molecule called NAD (forming NADH) which transfers them to an electron transport chain.
If oxygen is present, aerobic respiration continues as follows:-
Citric acid cycle
Stage 2: Citric acid cycle
occurs in the matrix of the mitochondrion
is aerobic and requires oxygen
Pyruvate is broken down into an acetyl group, which combines with coenzyme A to form acetyl coenzyme A.
During this process, H ions and electrons are
removed by dehydrogenase enzymes and bound onto NAD forming NADH.
Carbon is lost as CO2.
In the citric acid cycle
the acetyl group from
acetyl coenzyme A combines with oxaloacetate to form citrate.
During a series of enzyme-controlled steps, citrate is gradually converted back into oxaloacetate. This results in the generation of ATP and the release of carbon dioxide.
Hydrogen ions and electrons are once again removed by dehydrogenase enzymes. These are bound onto NAD to form NADH. The hydrogen ions and electrons from NADH are passed to the electron transport chain
Electron transport chain
Stage 3: - Electron transport chain
This is a series of carrier proteins attached to the inner mitochondrial
membrane.
It is aerobic and requires oxygen
NADH releases electrons. These electrons are passed along the electron transport chain.
As they flow along the chain they release energy.
This energy is used to pump H ions across the inner mitochondrial membrane. The return flow of these ions causes part of a membrane protein ATP synthase to rotate and synthesise ATP.
Oxygen is the final electron acceptor in the chain – it combines with H ions and electrons to form water. Most ATP is produced at this stage.
What happens after Glycolysis is oxygen is absent?
In the absence of oxygen, fermentation takes place in the cytoplasm.
Pyruvate undergoes fermentation to lactate (in animals). This is a reversible reaction.
In plants and yeast ethanol and carbon dioxide are produced. This is a reversible reaction.
Metabolic rate
The metabolic rate is the quantity of energy used by an organism in a set period of time.
This energy comes from respiration and can be measured by:-
Calculating the oxygen consumed per unit time
Calculating the carbon dioxide produced per unit time
Calculating the heat produced per unit time
Using a Respirometer to Measure Respiration Rates
Respiration rate in germinating seeds or in small organisms (such as woodlice) can be measured using a respirometer.
The organism takes in oxygen and gives out carbon dioxide during respiration.
The carbon dioxide released is absorbed by chemical. The coloured liquid is drawn up the tube to replace the volume of oxygen taken in by the organism.
Respiration rate can be measured by measuring how far the coloured liquid moves up the scale in a set period of time.
Colorimeter
A calorimeter measures heat production as a measure of metabolic rate. Heat from the body is used to heat water in the pipes.
The temperature of the water going in can be compared with the temperature of the water going out.
This can be used to calculate the change in temperature and therefore the heat produced.
The insulation reduces heat loss in the calorimeter, thus allowing as much heat as possible to heat up the water.
Oxygen Delivery
Organisms with high metabolic rates need an efficient transport system to deliver large supplies of oxygen to their respiring cells.
In vertebrates, oxygen is delivered to the cells via blood pumped by the heart.
Birds and mammals have higher metabolic rates than reptiles and amphibians, which in turn have higher metabolic rates than fish.
Single Circulatory System (in fish)
Fish have a heart with only two chambers (one atrium,
one ventricle).
Since blood passes through the heart once for each complete circuit of the body, it is described as a single circulatory system.
Blood arriving at the gills is under high pressure; however, every time blood passes through a capillary bed, there is a drop in pressure, so blood arriving at the rest of the body is under low pressure
Incomplete Double Circulatory System (in amphibians & most reptiles)
Amphibians & most reptiles have a heart with three chambers (a right & left atrium & one ventricle).
Since blood passes through the heart twice for each complete circuit of the body, it is described as a double circulatory system. Blood arriving at both sets of capillaries is under high pressure and so it is more efficient than a single system.
It is incomplete because there is only one ventricle instead of two. This means that there is mixing of the deoxygenated blood from the body & oxygenated blood from the lungs.
Complete Double Circulatory System (in birds & mammals)
Birds & mammals have a heart with four chambers (two atria & two ventricles).
It is also a double circulatory system (blood passing through the heart twice for every complete circuit of the body).
It is complete because there are two ventricles separated by a septum and there is no mixing of oxygenated & deoxygenated blood. This means that the oxygenated blood can be pumped out at higher pressure.
High pressure
Complete double circulatory systems enable higher
metabolic rates to be maintained and more efficient oxygen delivery to cells.
Metabolism in conformers & regulators
The ability of an organism to maintain its metabolic rate is affected by external abiotic factors such as:-
temperature
pH
salinity (salt present in water).
Conformers
The internal body conditions of a conformer are dependent on its external environment e.g. a conformer’s body temperature varies with that of the outside temperature.
Conformers are use behavioural responses to maintain an optimum metabolic rate (e.g. reptiles sit on rocks warmed by the sun to raise their body temperature and so increase their metabolic rate). These behavioural
responses allow conformers to tolerate variation in their external environment to maintain optimum metabolic rate.
Most conformers live in stable environments (e.g. the ocean) where there is little change to the external abiotic factors.
Advantage – since conformers don’t use physiological mechanisms requiring energy to alter their metabolic rate, they have low metabolic energy costs.
Disadvantage – a conformer is restricted to a narrow range of ecological niches, and is less adaptable to environmental change.
