Question

A biologist is using a dichotomous key to identify fish.

Answer 1

Answer:

The next step to take to identify the fish is step 7.

Explanation:

A dichotomous key is relatively simple to interpret. All you need to do is to:

• carefully observe your organism,
• know some technical terms or have a biological dictionary, and
• follow the descriptions.

The dichotomous key is going to lead you to the answer. Each step states two descriptions -a and b-, that are the potential answers. You need to observe your specimen and see which of the descriptions matches the organism. Once you choose the correct description, the key leads you to the next step. In the next step, the procedure is the same. You have to repeat it until you reach the name of your organism.

So, in this example, our organism is a fish, and we know that it has a single dorsal fin and no fin on the back near the tail. So,

1. (a) Has a single dorsal fin ---------------- step 5

  (b) Has a double dorsal fin ----------------step 2

We have two options, single dorsal fin or double dorsal fin. Our fish has a single dorsal fin, so the correct option is (a). By choosing (a), the key sends us to step 5. Note: In the hypothetical scenario of having a double dorsal-finned fish, the correct option would be (b), which would lead us to step 2.

5. (a) Has small fin on the back near tail ---------- step 6

    (b) Has no fin on the back near tail -------------- step 7

Again, we have two options, with a back fin near the tail, or without. Our fish does not have any back fin near the tail, so we choose option (b). This option leads us to step number 7. Note: In the hypothetical scenario of having a fin in the back near the tail, we should choose option (a), which leads us to step 6. But this is not the case. So we go to step 7.

7. (a) Tail is asymmetrical --------------- step 8

   (b) Tail is symmetrical ----------------- step 9

Once in 7, we need to see if our specimen has a symmetrical or asymmetrical tail. Depending on the answer, we go to step 8 or 9. And so on until we get to know the name of the fish.