Changes in the DNA sequence, or mutations, help drive evolutionary change
The mass number is the sum of the number of protons and number of neutrons the atom has.
So, we can write the equation as:
x + 20 = 40
x = 20 neutrons.
<span>Around 2.4 billion years ago, the first photosynthetic organisms appeared and used inorganic matter like carbon dioxide and water to produce glucose, with oxygen released in the atmosphere. Because of this, oxygen levels rose; this is called the <em>Great Oxygenation Event</em><span><em>.</em> Through time, photosynthetic organisms evolved to live in land (now as plants). As concentrations of oxygen in the atmosphere became higher, marine animals evolved to utilize oxygen readily available from the atmosphere (rather dissolved in water) hence the evolution of marine animals to land animals capable of respiration in land. </span></span>
<span>Commensalism is an interaction in which one of those species would benefit, and the other one would not be affected. Parasitism is an interaction in which one of those species would benefit at the expense of the host organism. Thus, in commensalism we have one positive and one neutral result while in parasitism we have one positive and one negative result.</span>
