Variety of Life


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The Variety of Life
10.1 Haemoglobin
Haemoglobin Molecules
The haemoglobin are a group of chemically similar molecules found in a wide variety of organisms.
Structure as follows:
-primary structure: consisting of 4 polypeptide chains
-secondary structure: in which each of these polypeptide chains is coiled into a helix
-tertiary structure: in which each polypeptide chain is folded into a precise shape- an
important factor in its ability to carry oxygen
-quaternary structure: in which all four polypeptides are linked together to form an almost
spherical molecule. Each polypeptide is associated with a haem group- which contains a
Fe2+ ion. Each Fe29 ion can combine with a single oxygen molecule making a total of four o2
molecules that can be carried by a single haemoglobin molecule in humans.
Role of Haemoglobin
Role of haemoglobin is to transport oxygen. To be efficient at transporting oxygen, haemoglobin
Readily associate with oxygen at the surface where gas exchange takes place
Readily dissociate from oxygen at those tissues requiring it
These two requirements may appear to contradict themselves each other but they are achieved by a
remarkable property of haemoglobin.
It changes its affinity of oxygen under different conditions.
It achieves this because its shape changes in the presence of certain substances, such as carbon
In the presence of carbon dioxide, the new shape of the haemoglobin molecule binds more loosely
to oxygen.
As a result haemoglobin releases oxygen.
Region of body Oxygen Carbon dioxide Affinity of Result
Concentration Concentration haemoglobin for
Gas Exchange High Low High Oxygen is
Surface attached
Respiring Tissues Low High Low Oxygen is
Why have different haemoglobins?
Carried oxygen from the gas exchange surface to the tissues that needed it for respiration
Haemoglobin with a high affinity for oxygen: These take up oxygen more easily but release it
less readily
Haemoglobin with a low affinity for oxygen: These take up oxygen les easily but release it more
Correlation between the type of haemoglobin in an organism and factors such as the environment in
which it lived or its metabolic rate.
Explanations for some of these correlations are as follows:

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An organism living in an environment with little oxygen requires haemoglobin to readily combine
with oxygen, if it to absorb enough of it. Provided that the organisms metabolic rate is not very
high, the fact that this form of haemoglobin does not release its oxygen as readily into the
tissues will not be a problem.
An organism with a high metabolic rate needs to release oxygen readily into its tissues.…read more

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Effects of carbon dioxide concentration
Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide.
The greater the concentration of carbon dioxide, the more readily the haemoglobin releases its
oxygen (the Bohr Effect).
Explains why the behaviour of haemoglobin changes in different regions of the body.
At the gas exchange (e.g. lungs), the level of carbon dioxide is low because it diffuses across
the exchange surface and is expelled from the organism.…read more

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Unbranched chains are wound into a tight coil that makes the molecule compact.
Structure of a starch molecule
Main role of starch is energy storage, something that it is
suited for because
Insoluble and therefore does not tend to draw water into
the cells by osmosis.
Being insoluble, it does not easily diffuse out of cells
Compact, stored into small spaces
When hydrolysed it forms alpha glucose, which is both
easily transported and readily used in respiration
Never found in animal cells.…read more

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Plant cell are also eukaryotic cells. Therefore have a distinct nucleus and membrane-bound
organelles, such as mitochondria and chloroplasts. An example of a plant cell is the leaf palisade cell.
Leaf Palisade cell
Leaf palisade cell is a typical plant cell.
Function to carry out photosynthesis
Main features suit it to its function of photosynthesis.…read more

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Differences between plant and animal cells
Plant Cells Animal Cells
Cellulose cell wall surrounds the cell as well as a Only a cell-surface membrane surrounds the cell
cell-surface membrane
Chloroplasts are present in large numbers in Chloroplast are never present
most cells
Normally have a large, single, central vacuole If vacuoles are present they are small and
filled with cell sap scattered throughout the cell
Starch grains are used for storage Glycogen granules are used for storage.…read more


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