After subjecting his PCR reaction to gel electrophoresis, the student sees no PCR product on the gel. What error(s) might he have made

The given question is incomplete, the complete question is:

A student carries out PCR using the following steps: Step 1: 94°C for 1 minute Step 2: 60°C for 30 seconds Step 3: 72°C for 30 seconds After subjecting his PCR reaction to gel electrophoresis, the student sees no PCR product on the gel. What error(s) might he have made? (Select all that apply.) a. He carried out step 1 at too low a temperature. b. He carried out step 1 at too high a temperature. c. He carried out step 2 at too low a temperature. d. He carried out step 2 at too high a temperature. e. He carried out step 3 for too short a time.

The correct answers are options d and e, that is, the student might have carried the step 2 at too high temperature, and he would have carried the step 3 for a brief duration.

Explanation:

In the PCR, step 1 is termed as the denaturation step and it generally takes place at 94 or 95 degrees Celsius. Thus, option a and b are incorrect. In step 2 of the PCR reaction, the combination of primers takes place with the template, this step is known as the annealing step. The temperatures in the annealing step are important for PCR, if the temperature of annealing is too much, it can lead to no product formation, and if it is too less than the formation of products would be non-specific.

In step 3 of the PCR reaction, the temperature is extended and the Taq polymerase enzyme is used to perform the reaction, which supplements nucleotides to the newly developed stand, at the frequency of 1 kilobase pair per minute. If the product of PCR is one kilobase or more, then a 30 seconds extension time would be not enough and the product would fail to appear. Hence, the correct options would be d and e.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.