A slow reproduction process is a disadvantage of which form of reproduction?

A) Sexual reproduction.

B) Asexual reproduction.

C) Binary fission.

D) Mitosis.

Diagram showing types of cell division that can occur in eukaryotic cells for reproduction
Diagram showing types of cell division that can occur in eukaryotic cells for reproduction

The correct answer is A. Sexual reproduction.

There are different types of reproduction that occur in nature. Some types of cell reproduction are simply for the growth, repair, and replacement of tissues. This is the main function of mitosis in most organisms. However, there are instances where mitosis can be used for actual asexual reproduction of an organism. For instance, binary fission can occur in some organisms.

This is a form of asexual reproduction which occurs in single-celled forms of life. This occurs in both prokaryotes such as bacteria, and eukaryotes such as protists, and is a quick way for the cells and organisms to reproduce.

Sexual reproduction occurs in many eukaryotic organisms but has the disadvantage of being a slower form of reproduction. The advantage of this form of reproduction is that genetic variation is introduced, which has a selective advantage in environments that may change. Variation is introduced into the genome during meiosis which is the cell division that occurs in the sex cells.

Asexual reproduction occurs quickly, but the disadvantage is the lack of genetic variation. However, the population can grow very rapidly which is beneficial. Some organisms have the advantage of being able to undergo either sexual or asexual reproduction depending on the environmental conditions that they are exposed to.

Asexual reproduction

This form of reproduction occurs without sex, meaning that cells from parents do not fuse. Instead, one parent is able to produce offspring through cell division. There are advantages to reproducing in an asexual way. For one thing, a mate does not have to be found and sex cells or gametes do not have to be made.

This saves both time and energy. The type of cell division involved in asexual reproduction is mitosis, which is also much simpler and has only half the number of stages of meiosis which is the cell division that occurs in sexual reproduction. This means that the process is much quicker which is advantageous.

In fact, the rapid pace of asexual reproduction means that large numbers of cells can be produced very quickly. This leads to rapid population growth and in fact, can be exponential in the case of bacterial cells.

A further benefit is that not only does another mate not need to be found but dispersal of gametes is not needed.  Fertilization does not occur so there is no waste of time and energy trying to achieve this.

A major disadvantage is the lack of genetic variation with this type of reproduction. Fortunately, some genetic variation is introduced by random mutations. However, limited genetic variation means that the population is more susceptible to adverse conditions such as disease.

If all individuals are genetically the same then they will respond the same to an adverse event such as a disease or change in environment. The chances of extinction then increase because every individual in the population is similarly vulnerable.

Binary fission

This is a form of asexual reproduction that is most often associated with prokaryotes such as bacteria but can occur in eukaryotic protists.

The process of binary fission in bacteria is different from in protists since bacteria have no membrane-bound organelles, so no true nucleus is present. This means that there are differences in exactly how fission occurs depending on the organisms involved.

The protists are single-celled organisms which can also, in some cases, undergo sexual reproduction depending on environmental conditions. In fact, some species of protists are able to undergo both fission and sexual reproduction, which is an advantage for an organism living in rapidly changing conditions.

Sexual reproduction

Sexual reproduction occurs when two sex cells (gametes) from two parents fuse to form a zygote. The process has advantages and disadvantages.

The greatest advantage is the fact that genetic variation is introduced during the formation of the gametes. This guarantees that all offspring are genetically unique and different from their parents and siblings.

Since such variation is important for natural selection, this is a big advantage. It increases the likelihood that individuals of the population will survive when environmental conditions change.

This is because some individuals will be less susceptible to a change than others. For example, a disease may eliminate some individuals, but chances are that others will survive because they are genetically different.

Over time then the population is unlikely to go extinct. Lack of genetic variation is the main reason that populations of animals become extinct.

Genetic variety also helps if individuals spread to new environments since some will be likely to survive to reproduce. This means that sexually reproducing species may be expected to be better colonists of new environments than asexually reproducing species.

Disadvantages

A big disadvantage of sexual reproduction is that the process is much slower than asexual reproduction. For starters, the cell division, which is meiosis, is more complex and has more stages than mitosis.

After gametes are formed it takes time to find a mate, since this type of reproduction relies on gametes (sperm and egg) from two different individuals.

The process also depends on fertilization and formation of a zygote, which takes time. The result of the time that is needed for the process of sexual reproduction to occur is that a population may grow very slowly.

In some species, only one baby is produced a year. This can become a problem if something happens and no offspring are produced over a number of years. Eventually, it can lead to an organism becoming extinct.

Fertilization

The gametes have to come together, either through external fertilization or internal fertilization. External fertilization can be costly if eggs and sperm are deposited in an environment that suddenly becomes unfavorable; for example, a pond that dries up.

Internal fertilization can be difficult as well because mating depends on individuals being receptive. For example, a male bird may have to spend a lot of time and energy attracting a female bird as a mate.

Singing and courtship behavior takes up time and uses valuable energy. There is also intense competition for mates which can reduce the health of individuals.

Fertilization can also be difficult for plants. For example, a plant with sexual reproduction relies on pollination. In cases where a plant relies on a specific species as a pollinator, the plant becomes vulnerable to extinction if their pollinator species become rare.

References

  1. Editors of Encyclopedia Britannica (2018). Binary fission. Retrieved from Encyclopedia Britannica.
  2. Editors of Encyclopedia Britannica (2018). Protozoan. Retrieved from Encyclopedia Britannica.
  3. NG Smith (2018). Reproductive behaviour. Retrieved from Encyclopedia Britannica.
  4. RL Dorit, WF Walker, RD Barnes (1991).  Philadelphia: USA, Saunders College Publishing.
  5. OFG Kilgour (1982). Mastering Biology.London: UK, MacMillan Press.

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