<u>Answer</u>: Large collection of stars, gas, and dust held together by gravity.
<u>Explanation:</u>
- The name <em>galaxy</em> has been derived from the word <em>galaxies</em> which is a Greek word meaning milky.
- In simple words a galaxy is a collection of a large number of stars, however, to be more precise <em>a galaxy is a gravity-bound collection of stars, dust, gas, dark matter and stellar remnants. </em>
- There are different types of galaxies found in various shapes and size, some of the most common shapes being elliptical, irregular and spiral.
- An example is the milky way galaxy that contains our solar system.
This is False
Natural selection is the mechanism in which organisms inherit the traits that are necessary for survival and thus change. Those who do not have these traits die.
Answer:
The answer is 'D'- Their arm bones have the same structure, but not function. These are homologous structures.
Explanation:
Homologous structures are those which share a basic common structure but perform different function. The hand of a human performs functions like <em>writing, cutting, washing, chopping</em> etc. The wings of a bat are used for the purpose of <em>flying</em>.
Also, <em>a dolphin's flippers, a bird's wing, a cat's leg</em> are all <u>homologous structures</u>. The structures which are homologous have the following features:
- They share a <em>common origin</em>
- Their <em>anatomy</em> is similar
- They have a <em>similar pattern of development</em>.
Answer:
Ozone
Explanation:
In the stratosphere, ozone is created primarily by ultraviolet radiation. When high-energy ultraviolet rays strike ordinary oxygen molecules (O2), they split the molecule into two single oxygen atoms, known as atomic oxygen.
