<span>In real life, the presence of friction. Choice B</span>
The nitrogen is captured and converted into a form that is usable by plants in a process called
<span>nitrogen fixation</span>
Answer:
D. Molecules called pumps function to control active transport.
Explanation:
Active transport is one of the two types of transport (the other being passive transport). It is the type of transport in which substances move against their concentration gradient i.e. from a lower concentration to a higher concentration. Hence, due to this, energy input in form of ATP is required by the cell.
However, the process of active transport makes use of certain molecules called PUMPS to control it. The pumps moves ions/molecules against their concentration gradient. An example is the sodium-pottasium pump which moves sodium ions from a region of low conc. to a region of high conc.
Answer:
c. ¼ heavy, ¾ light
Explanation:
DNA replication follows semi conservative model which means that both the strands separate during replication and the newly formed DNA molecule has one old and one new strand. If instead of semi conservative, conservative mechanism is used, old strands will not separate from each other and the two newly synthesised DNA strands will come together to form a DNA molecule.
Here the cells were first grown in heavy 15N medium so all the DNA molecules had 15N and thus were heavy. Then the cells were transferred to 14N medium where only lighter 14N were available for replication process.
In first generation, 14N DNA molecules were synthesised from 15N DNA molecules so 1/2 DNA molecules were 15N and other half were 14N. In the second generation, 14N molecules will give rise to new 14N molecules and 15N molecules will also give rise to 14N molecules hence 1/4 molecules will be 15N (heavy) and 3/4 will be 14N (light).
