MODULE #1: Biology: The Study of Life
All Life Forms Reproduce
Our final criterion for life says that all living organisms reproduce. Although the necessity of reproduction for the perpetuation of life is rather obvious, it is truly amazing how many different ways God has designed the organisms on earth to accomplish this feat. Some organisms, for example, can split themselves apart under the right circumstances. The two parts can then grow into wholly separate organisms. This is an example of asexual reproduction.
Asexual reproduction – Reproduction accomplished by a single organism
Other organisms, however, require a male and female in order to reproduce. This method of reproduction (which occurs in most of the life forms with which you are familiar) is called sexual reproduction.
Sexual reproduction – Reproduction that requires two organisms
As we go along in this course, we will be studying both of these methods a bit more closely, because there is a great deal of variety among the different means of sexual and asexual reproduction.
Reproduction always involves the concept of inheritance. Although this word has several different meanings, in biology the definition is quite specific.
Inheritance – The process by which physical and biological characteristics are transmitted from the parent (or parents) to the offspring
In asexual reproduction, the characteristics and traits inherited by the offspring are, under normal circumstances, identical to the parent. Thus, the offspring is essentially a “copy” of the parent. In sexual reproduction, under normal circumstances, the offspring's traits and characteristics are, in fact, some mixture of each parent's traits and characteristics. Of course, the parents' traits and characteristics are a mixture of each of their parents' traits and characteristics, and their parents' traits and characteristics are a mixture of each of their parents' traits and characteristics, and so on. In the end, then, the inheritance process in sexual reproduction is quite complicated, and leads to offspring that often can be noticeably different from both parents.
Notice that in describing inheritance for both modes of reproduction, we used the phrase “under normal circumstances.” This is because every now and again, offspring can possess traits that are incredibly different from their parents. These incredibly different traits are the result of mutations.
Mutation – An abrupt and marked change in the DNA of an organism compared to that of its parents
The study of mutations is quite interesting, and we will focus on it later on in the course.
Before we leave this discussion of reproduction, it is important to note that some living organisms cannot actually produce viable offspring. When a horse and a donkey mate, for example, they can produce an offspring called a mule. Adult mules, however, cannot produce offspring of their own. Nevertheless, mules do not fail to meet the reproduction criterion for life. Even though they cannot produce offspring, their cells (we will discuss cells more thoroughly in a while) reproduce quite frequently so that the mules can grow, repair wounds, etc. Thus, they satisfy the reproduction criterion on the cellular level.