F214 OCR A2 Biology Module 2 Excretion

Here is a very detailed document answering every part of the specification. It is like the other F214 and F215 documents I have put on here. 

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  • Created by: Emily
  • Created on: 20-06-11 19:12
Preview of F214 OCR A2 Biology Module 2 Excretion

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F214 Communication, Homeostasis and Energy
Module 2 Excretion
4.2.1 Excretion
a. Define the term excretion
Excretion-The removal of metabolic waste from the body which are by products
or unwanted substances from cell processes.
b. Explain the importance of removing metabolic wastes, including carbon dioxide and
nitrogenous waste from the body
Carbon dioxide
o Excess carbon dioxide is toxic and has three main effects:
The majority of carbon dioxide is carried in the blood as
hydrogencarbonate ions but in the process hydrogen ions are
made inside red blood cells with carbonic anhydrase. These
hydrogen ions compete with oxygen for space on the haemoglobin.
Therefore too much carbon dioxide can cause a reduction in
oxygen transportation.
Carbon dioxide can also combine with haemoglobin to make
carbaminohaemoglobin which has a lower affinity for oxygen.
Excess carbon dioxide can also cause respiratory acidosis by
dissolving in the blood plasma and reacting with water to make
carbonic acid which dissociates and releases hydrogen ions. This
lowers the pH by making the blood more acidic. If the change is
small is leads to an increased breathing rate but if it is larger it
can cause difficult breathing, drowsiness, headaches and
confusion. It could cause a rapid heart rate and changes in blood
Nitrogenous compounds
o The body cannot store proteins or amino acids.
o But because they contain a lot of energy, amino acids are transported to
the liver where they get the toxic amino acid group removed via
o The amino acid then forms the very soluble but highly toxic ammonium
before being converted to urea and is then transported to the liver for
o There is some remaining keto acid which can be respired or converted to
a carbohydrate or fat for storage.
c. Describe the histology and gross structure of the liver
Hepatic artery
o Supplies the liver with oxygenated blood from the heart.
o The oxygen supplied is need for aerobic respiration.

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Hepatic portal vein
o This carries oxygenated blood to the liver.
o The blood is rich in the products of digestion some of which may be toxic
Hepatic vein
o This is where blood leaves the liver which then re-joins the vena cava.
Bile duct
o Bile is secreted from the liver.
o Bile has a digestive and excretory function.…read more

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Describe the formation of urea in the liver including an outline of the ornithine cycle
o Amino acid + O2 Keto acid + ammonia
Ornithine cycle
o 2NH3 + CO2 CO(NH2)2 + H2O
o Ammonia + carbon dioxide Urea + water
e. Describe the roles of the liver in detoxification
Liver cells contain enzymes that make toxic molecules less toxic.…read more

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E.g. Catalase which converts hydrogen peroxide to oxygen and water.
Detoxification of alcohol
o Ethanol contains chemical potential energy that can be used in respiration.
o It is broken down in the hepatocytes using ethanol dehydrogenase.
o This makes ethanal which is dehydrogenated further using ethanal dehydrogenase.
o Then ethanoate is produced with coenzyme A to form acetyl coenzyme A.
o Hydrogen atoms are released which are combined with NAD to produce reduced
f. Describe the histology and gross structure of the kidney
g.…read more

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The blood pressure in the glomerulus is higher than in the Bowman's
4. So fluid from the blood is pushed in the Bowman's capsule.
5. Molecules with a higher molecular mass than 69,000 cannot get through
the basement membrane so are held in the capillaries of the glomerulus.
Molecules with a higher mass include most proteins and all blood cells.
6. The substances which are filtered out of the blood include: water, amino
acids, glucose, urea and inorganic ions including sodium, chloride and
potassium.…read more

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Active transport is used to adjust the concentrations of various
o Collecting duct
Water moves by osmosis from the tubule fluid into the
surrounding tissue. It then enters the blood capillaries.
Antidiuretic hormone (ADH)
o Cells in the wall of the collecting duct have receptors for ADH.
o ADH causes a chain of enzyme controlled reactions inside the cells,
inserting vesicles containing water permeable channels (aquaporins) into
the cell surface membrane.…read more

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Blood from a vein is passed through a machine that has an
artificial membrane.
Heparin is added to avoid clotting.
It is usually performed at a clinic, three times a week for several
o Peritoneal dialysis
The filter is the body's own abdominal membrane (peritoneum).
A permanent tube is implanted into the abdomen.
Dialysis solution is put through the tube which fills the gap
between the abdomen and organs.
After several hours the solution is usually drained.…read more

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This is analysed to create a chromatogram.
Standard examples are then run so that the drugs can be
identified and quantified in the chromatograms.
o Mass spectrometry can also be used to analyse a urine sample.…read more



I've found a few errors in your notes :/ for instance the hepatic portal vein doesn't carry oxygenated blood but deoxy from the digestive system, full of nutrients. I'm not saying your wrong but you may have made some typo's and I would recommend you check it again before publishing it again :S 


but appologise if I'm indeed wrong.

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