Does a transistor have resistance?
It's much better to think of a bipolar junction transistor (BJT) as being current source, rather than having resistance.

Why you may think? Between the collector and emitter, you can have a voltage across them, and a current flowing between them, and V/I = ohms, right?

The difference between describing a transistor as having resistance, and having a current source (we tend not to make a difference between the terms current source and current sink when using these models), is what stays constant when you change other things. In this case, when you change the collector voltage, the collector current stays more or less constant. 

It's not very useful describing the V/I relationship as a resistance, if the resistance varies with the collector voltage. It's always most useful to find something that's constant.

Let's take two good DMMs which, when on the resistance range, one applies 1v to components and the other applies 2v. If we set them to measuring a 1k resistor, they would both read 1k. If we set them to measuring a transistor whose base current was such that the collector current was 10mA, one would read 100 ohms, the other would read 200 ohms.

This is why although a transistor has a defined V and I, and their ratio has units of resistance, we do not say that it has a resistance, because it will be measured differently by different resistance-measuring devices. Two current measuring devices will give substantially the same reading as each other.

However it's just occured to me that DMM tend not to work like that when measuring resistance. They don't apply a voltage and measure the current, they apply a current and measure the voltage. With an excitation current, things get even worse for our putative 'transistor has a resistance' model. Consider two DMMs, one that measures voltage with a 1mA current, and one that uses 2mA. Let's say the transistor IB has been adjusted to pull 1.5mA when the collector has a sufficient bias. The 1mA DMM will be pulled down to VCEsat, somewhere in the 0.1v to 0.3v range depending on the transistor detail, so will show a 'resistance' of perhaps 0.2v/1mA = 200 ohms. The other DMM's 2mA will not be pulled low by the transistor, and most DMMs read OL (overload) when insufficient current is drawn from the test leads to reduce their output voltage.