Re: Comparing the transport systems of Euglena and Crayfish

Euglena is a unicellular organism while an crayfish is a multicellular 
organism.  A crayfish and many other plants and animals have their cells in 
organized structures.  These form the organs (eg lungs, liver, kidneys) 
that have specialized roles in the uptake and excretion of chemical 
compounds.  

These differences noted, there are strong similarities between the 
transport processes in unicellular and multicellular organisms at the 
cellular level.  The individual cells of an animal transport materials by 
the same processes used by unicellular organisms.  Organs are often 
constructed in such a way that there is close contact between the blood, 
fluid, or air carrying a potential nutrient or carrying away a waste 
product.  This percolation allows materials to be taken up by the cells of 
the organ.  Insects and other arthropods (like crayfish) are particularly 
interesting in this regard in that they have an open circulatory system.  
The blood (hemolymph) is carried in vessels in large parts of the insect.  
But in the gut regions, the blood flows free to percolate through the 
tissues.

Transport processes in cells are a matter of passing through the cell 
membrane and possibly a cell wall.  Some substances can enter the cell by 
simple diffusion.  The uptake of other compounds is either facilitated or 
actively performed by enzymes.  Ion balances across membranes are 
controlled by influx and efflux pumps.  Pores act to move larger molecules.  
Many cells can also phagocytize (eat one bite) or pinocytize (drink in one 
gulp) larger portions and pieces by invagination and membrane vessicle 
formation.

You can learn more about these subjects by looking in any number of general 
biology textbooks.

Hope this helps.

Cheers,

Dr. Mark.