Question:
The "All or Nothing Principle" states ________.
Group of answer choices
A.some muscle can contract and some cannot.
B. a muscle cell is either turned on (contracting) or off (relaxing), without any intermediate states.
C. only one neuron stimulates one muscle fiber.
D. that muscles can only go through one contraction-relaxation phase.
E. that once a muscle cell is stimulated it cannot dO anything.
Answer
B. a muscle cell is either turned on (contracting) or off (relaxing), without any intermediate states.
Explanation
The all or nothing principle applies to cardiac muscle whereby the strength by which a nerve responds to a stimulus is independent of the strength of the stimulus itself. This implies that if the stimulus is greater than the threshold potential, there will be a complete response from the nerve, and if the stimulus is less than the threshold potential, there will be no response.
Question:
Which of the following is false with respect to thymine?
It is found in DNA, not RNA
It bonds with Adenine with two hydrogen bonds
It is a purine
It's nitrogenous base contains one ring
Answer
It's nitrogenous base contains one ring
Explanation
DNA nucleotides are divided into either purines or pyrimidines. The purines are adenine and guanine, while pyrimidines are cytosine and thymine in DNA, and cytosine and uracil in RNA. Purines have two rings in the structures while the pyrimidines have a single ring. Adenine pairs with Thymine in DNA with two hydrogen bonds, while Guanine pairs with Cytosine with three hydrogen bonds.
Question:
What is a selectively permeable membrane?
Answer
A selectively permeable membrane is a membrane that allows only specific type of substances to pass through by sorting either by size or the charge of the substance. An example of selectively permeable membrane is the cell's plasma membrane which allows substances that are small-sized to pass through simple diffusion e.g water.
Explanation
Selectively permeable membranes are commonly found separating organs and tissues whose internal environment depends on the extracellular environment. The cell membrane for instance, is selectively permeable to water molecules that can easily diffuse through, but the membrane cannot allow entry of large-sized molecules like glucose
