Ugh. It's too late at night to type out a decent response to this sucker. Just note that complexity is not something that happens overnight. Also keep this in mind - if he makes you explain how everything could evolve, he could win simply by wearing you out. So, if you use these, keep hammering him at the same time.
Getting a heart is relatively easy. In small creatures, you can transfer nutrients and waste easily enough by diffusion. For instance, moss does not have the more complex systems of trees and grasses, and thus does not grow as tall. Having a system of tubes throughout your body can make nutrient transport easier than having to go through millions of cell membranes, and isn't too complex. With a real primitive animal, you can pump the fluid simply by moving. (That's part of the reason why you're instructed to squeeze your fist when you're giving blood.) All a heart is a special piece of muscle that wraps around a piece of vessel and pumps by itself. Not a difficult thing to alcomplish. More complex hearts go from that depending on metabolism requirements. A two chambered heart is as easy as a flap of muscle growing in, it has the advantage of better efficency. You see this in fish. Three-chambered hearts I believe are in some reptiles, like crocodiles. Four-chambered hearts are in mammals, with high (try 9x the metabolism of a similiarly-sized cold-blood creature) metabolisms, and probably birds as well.
Use the below page to show how an eye can evolve. It has nice pictures that are hard for even him to miss. Note that all an eyespot has to be is a patch with photosenstive chemicals, something that might have even come about unintentionally. It could be as simple as the organism knowing that active chemicals in that region == GUD and simply start swimming faster when the chemicals in that region are inactive, thus ensuring it would stay more in sunny regions. This behavior is a simple one that does not even require a sense of direction to pull off. (Sow, Pill Bugs, or Woodlice use a similar mechanism for clumping up - they move like crazy when in hot, dry, or sunny places but slow down in dark, damp places. This ensures they conserve water, and also means they end up clumping together in large groups, further conserving water due to less overall surface area exposed.)
http://www.cs.colorado.edu/~lindsay/cre ... tages.html
Hands are simple. To propell oneself through water, you can use muscles throughout the entire body, like worms. A worm that is slightly flat along one side gets to be a bit paddle-like. Having a flap of muscle that goes out is also a very, very simple thing to do, espically by accident. However, it also moves water quite effectively, and given that embyro formation often makes it that it's symmetric on both sides anyway, you got simple fins - which makes you move even faster. Even with the relative awkwardness that an early fin might present, it is not hard to see how this would be a huge advantage in gaining another unspoiled niche and now you have something like fish. (Mind you, eels and lampreys don't even have flatish-bodies, but oh well.) Now, to get hands first you get legs, which makes me wonder if it would have made more sense to explain this in a backwards chronological order. Too late now, I guess but this should be easy enough to reverse if you understand it. Now, we can note that fins themselves can act in a leg-like fashion - see a modern mudskipper today. But let's stay in the water a bit longer. Now, one way of life is to lurk at the bottom of the water near some rocks. In fast-moving rivers and streams, it could be advantagous to keep a hold of some rocks to anchor your position - it takes much less effort than swimming in place in this case, and you can stay as still as the rock itself. You can grip better with stronger fins and more fleshy fins, so a population of these animals with this type of lifestyle would get something resemlbing stubby hands. Going back to water/land dwellers, we see that fins themselves do not support weight too well on land, since you no longer have the bounancy of water working for you. In order to move around on land more freely, you need stronger limbs. Less bendable cartilige would provide a better anchor for muscles to pull against, and bone itself that far off from cartilige. I suppose you have to trade off some hydrodyamics for this, but this is far outweighed by the fact you can exploit a new niche by yourself. In any case, by simple matter of degree you get legs - vertical, bony, and muscular. Hands are only a short trip away. (One may note that humans are actually more or less still quadrapeds very early in life, although it's obvious the bone and muscle structure does not make this feasible later in life.) With tree-dwelling animals which you can can simply by running up a tree - you grip the tree as much as you run on it. Look at your average squirrel - claws to help grip the tree, feet that can presumably open and close to grip better - hell, you can even see them standing on the hind legs and eating using their forelimbs! I guess I can stop with the explanation of hands here.
