What are the endoskeleton and evoskeleton?

What are the endoskeleton and evoskeleton?

Answers
Do you mean exoskeleton?
hellouk
29 January 2012
Endoskeleton is the internal body support structure such as bones while the exoskeleton is the external structure which supports body that being shells and scales etc. These are in contrast to the endoskeleton.
anila
31 January 2012
endo-skeleton = internal-skeleton (i.e. your bones). exo-skeleton = external-skeleton (i.e. bug shells). The job of the skeleton is to provide shape, structure and protection.
maestro.alim
16 February 2012
Where would you find an endoskeleton and where would you expect to find an exoskeleton (what kind of animals would have an exoskeleton)? What are their respective roles? What is an endoskeleton made of and how does this compare with an endoskeleton?
hellouk
24 February 2012
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How does tissue fluid return back into the circulatory system? ( AQA AS biology)


Q - How does tissue fluid return to the circulatory system?

In my textbook, it says the main reason is that it re-enters the capillaries by the loss of hydrostatic pressure within them, so by the time the blood gets to the venous end of the capillary the hydrostatic pressure is less within the capillary than outside them in the tissue fluid, so the tissue fluid is forced back into the blood in the capillary. However, when I look at mark schemes it says that it mainly re-enters by osmosis? How does it move in by osmosis? (I know that the remaining moves back into the bloodstream via the lymphatic system)

Answer

As the blood moves through the capillary it is getting further from the heart and pressure is being split between branches. This means hydrostatic pressure, and the force that attempts to push the fluid through the walls, decreases, However, osmotic pressure (basically how big the gradient of water potentials is) must get higher than hydrostatic pressure to ‘over power’ it. With nutrients moving out with the water, this means water potential would hardly be affected. However, there are special proteins in the plasma of the blood called plasma proteins. Being soluble (unlike may proteins) they alter water potential and being large (like many proteins) they are unable to cross the semi-permeable cell membranes of the capillary wall. As water moves out, the concentration of these proteins increases, and the water potential in the capillaries decreases. The gradient of water potential from outside to inside gets higher, as does the osmotic pressure. Eventually, osmotic pressure is higher than hydrostatic pressure, and fluid is forced back in! Any excess is returned via the lymphatic system, entering dead-ended lymphatic capillaries. This system of vessels eventually drains the excess fluid back into the circulatory system.