Homeostasis [7]: Foundation questions (A Level Biology)

Uploaded by freeeschool on 01.09.2012

A Level Biology: Homeostasis 7 – Foundation Questions
Hi! Welcome to today’s video. Today, we are going to be looking at some GCSE stock
questions on Osmoregulation.
Here, we got an example of a paper. The question is asking you, first of all to identify Gland
X. So it is looking for which process controls the composition of blood. ADH is produced
by the pituitary gland so Gland X should be the pituitary gland. The stimulus that causes
Gland X to produce ADH is low water content. So you have receptors within the nephrons
of the kidneys which actually detects both composition, so basically how much water is
in the blood.
ADH stands for Antidiuretic Hormone and so it is obviously the hormone; that is the type
of substance ADH is.
b.) Describe the effect of an increase in ADH production on the kidneys and on the composition
of urine is looking for three main things. If there is an increase in ADH production,
there is obviously going to be more water being reabsorbed by the kidneys which is going
to increase the water content of the blood, therefore, your urine is going to be highly
concentrated. That is what is what it is looking for. More water, reabsorption in the kidneys
and highly concentrated urine.
What they might also ask you is questions related to other animals. So here, you got
a question about camels. It tells you that they can safely lose up to 40% of their body
water but they can also drink large amounts of water at one time. That their red blood
cells can swell up to 240 times their normal size without bursting. Also that they can
produce very concentrated urine as well. So the question is asking you to use your knowledge
and understanding of osmosis to explain why the red blood cells of a camel will swell
after drinking large amounts of water. This question is worth three marks, so they are
looking once again for three points.
The first point, I would note, is drinking a large amount of water increases the water
content of the blood. That will actually get you one mark. The other two marks should come
by talking about water moving from an area of high concentration to an area of low concentration,
which would be within the RBC, which is just shorthand for red blood cells. The final mark
comes by stating that red blood swells due to its larger volume, so due to water coming
into the cell so it swells.
Here, you got a diagram to which shows what is happening. Here, you got your red blood
cell and you can see that it has a lot more solids within the cell than outside the cell.
Therefore, it has low water concentration. Here, you got lots of water or high concentration
of water outside of the cell. Therefore, the water moves into the cell and the cell increases
in volume.
The last question is asking you to describe the process by which the camel produces more
concentrated urine. You need to remember that low water content of urine is caused by the
pituitary gland producing more ADH. The ADH makes the kidneys reabsorb more water. Once
the kidney reabsorbed more water, you are going to have less water going into the urine
which is going to make it more concentrated. What they are looking for is for you to state
that the pituitary gland produces ADH and the kidneys absorb more water within the nephrons,
so less water goes into the urine.
That concludes the short presentation. I hoped you enjoyed it. Don’t forget to keep a lookout
for some more videos coming out soon.
[end of audio – 04:25]