3 12.1.1 Outline the need for excretion in all living organisms. Topic 12.1 ExcretionOutline the need for excretion in all living organisms.Excretion removes metabolic waste from the body. In animals, nitrogenous waste is excreted from a specialized network of organs created to store and excrete wastes. It needs to be excretedbecause it is toxic.MAIN PAGE
4 When wastes accumulate, they tend to damage cells and metabolic processes,largely by changing the pH balance in theirsurrounding environment. Excretion preventsaccumulation of wastes.
5 In plants, oxygen is excreted when released from photosynthesis. The excretion of wastesalso serves to free up space neededfor products used in metabolism.
6 12.1.2 State that excretory products in plants include oxygen, and in animalsthey include carbon dioxide andnitrogenous compounds.The excretory products in plantsinclude oxygen, and in animalsthey include carbon dioxideand nitrogenous compounds.
7 12.1.3 Discuss the relationship between the different nitrogenous wasteproducts and habitat in mammals,birds and freshwater fish.Surplus amino acids must bedegraded to relatively harmlessnitrogen-containing compounds.Freshwater fish can get rid of ammonia,although highly toxic (due to itsbasicity), because it can be diluted bythe readily available water.
8 Birds are unable to carry too much water so they excrete uric acid whichis insoluble and expelled as a paste(most of the water is removedbefore excretion).
9 Mammals excrete urea, which contains some nitrogenous wastes but is largelywater and not very toxic. Somedesert mammals produce veryconcentrated urine (having a long loopof Henle in their kidneys to filter out themajority of water and fluids
10 Topic 12.2 The Human Kidney 12.2.1 Draw the structure of the kidney. Drawing will be inserted at a later date.MAIN PAGE
11 glomerulus and associated nephron. Draw the structure of aglomerulus and associated nephron.Drawing will be inserted at a later date.
12 12.2.3 Explain the process of ultrafiltration including blood pressure, fenestratedblood capillaries and basement membrane.The renal artery branches inside thekidney and a branch enters each Bowman'scapsule. This branch is called the afferentrenal arteriole. The arteriole branches intoa branch of capillaries called glomerulusinside each Bowman's capsule.
13 The capillaries merge again into one blood vessel that leaves the Bowmancapsule called the efferent renal artery.The blood pressure in the gloerulusis very high due to the fact that thesecapillaries are present between twoarteries and not between an arteryand a vein as is the case with otherparts of circulation. Due to this highblood pressure in the capillaries,fluid is squeezed out.
14 However only the substances that have sizes that enable them to pass out ofthe capillary wall are squeezed out.This is called filtration ( or ultrafiltration).
15 12.2.4 Define osmoregulation. Osmoregulation is the control of thewater balance of the blood,tissue or cytoplasmof a living organism.
16 12.2.5 Explain the reabsorption of glucose, water and salts in the proximal convoluted tubule,including the roles of microvilli,osmosis and active transport.Reabsorption in the kidneys is, under mostconditions, very efficient, able to reabsorbthe vast majority of water and salts from thefluid. The inside of the proximal tubule islined with countless microvili, essentially thesame in structure to those found in thesmall intestine but scaled downsignificantly in size.
17 These microvili are the surface through which substances enter and exit the filtrate, or the fluidinside the proximal tubule. Some substances inthe filtrate, such as the buffer molecule HCO3(bicarbonate) and postassium, diffuse out of thefiltrate passively. However, other substances,including amino acids and glucose, must beactively transported into the microvil andeventually back into the blood stream.
18 The proximal tubule also functions in the reabsorption of salt molecules, whichpassively move out of the tubule andinto the surrounding microvili. Due tothe gradient now forms by the diffusionof salt, water follows the salt out of thetubule by osmosis, thus reclaiming themajority of water in the process.
19 The proximal tubule also functions in expelling poisons or wastes collectedfrom the liver by secreting them intothe filtrate, where they will laterbe excreted.
20 12.2.6 Explain the roles of the loop of Henle, medulla, collecting duct andADH in maintaining the waterbalance of the blood.The descending loop of henle reabsorbswater by osmosis. At the bottom ofthe loop of henle, the loopenters the medulla section.
21 When in the medulla, salts begin to diffuse, and continue to diffuse in the ascendingloop of henle, and in the upper sectionof the loop of henle the salts are pushedout by active transport. In the collecting duct,reabsorption of water, glucose and saltsoccurs depending on the hormone ADH.The more there is in the collecting duct,the more permeable the collectingduct is to water.
22 12.2.7 Compare the composition of blood in the renal artery and renal vein, andcompare the composition of glomerularfiltrate and urine.The renal artery enters the kidney withurea and other unwanted materialand carries oxygen to the kidney.
23 The renal vein leaves the kidney with blood that contains correct levels of urea,salt, and water. It is also rich in CO2.The glomeruler filtrate contains salts,glucose, and vitamins, urea, and othersmall molecules. Urine contains ammoniaand carbon dioxide, as well as water
24 12.2.8 Outline the structure and action of kidney dialysis machines.This machine works on the basis of osmosisand diffusion. It is multiple layers of sheetsof a cellophane material that allows smallmolecules to pass through.
25 The blood passes between the sheets of the dialysis machine and as it does that,movement of the ions according toconcentration gradient will start takingplace. A patient with kidney failure mustbe connected to a dialysis machine in ahospital 2 days a week forabout 12 hours each time.MAIN PAGE
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