Inquiry Question

How does reproduction ensure the continuity of a species?

Key ideas

  • Reproduction refers to how living things give rise to the next generation of individuals, thus ensuring their continuity over time.

  • Genetic information is transmitted during reproduction from the parental generation to the next generation.

  • There are two specific (and sometimes conflicting) roles that reproduction needs to address:

    • Ensure that the individuals of each generation are largely the same from one generation to the next.

    • Ensure that some biological change is introduced in each generation so that offspring can survive in environmental conditions different from those experienced by their parents.

An overview of the roles that reproduction plays in the maintenance of organisms (multicellular) and the continuity of species.

Inquiry question: How does reproduction ensure the continuity of a species?

Students explain the mechanisms of reproduction that ensure the continuity of a species, by analysing sexual and asexual methods of reproduction in a variety of organisms, including but not limited to:

  • animals: advantages of external and internal fertilisation

  • plants: asexual and sexual reproduction

  • fungi: budding, spores

  • bacteria: binary fission (ACSBL075)

  • protists: binary fission, budding

Mechanisms of reproduction

Figure 1: An overview of the main reproductive strategies. In this figure, the various modes of reproduction are classified as asexual or sexual. In unicellular and multicellular organisms, there are different forms of asexual and sexual reproductive strategies. Note that this figure does not include all of the known reproductive strategies known in biology.

What is a species?

In biology, a species is a group of organisms that can reproduce with one another in nature and produce fertile offspring. In natural conditions, individuals from different species do not breed (referred to as inter-specific mating). This is usually because of a phenomenon known as reproductive isolation. Furthermore, individuals of different species are reproductively incompatible. Therefore, gametes from individuals belonging to different species cannot undergo fertilisation.

This means that the concept of biological species defines a gene pool. A gene pool is the set of genes found across all organisms in a population. Since only the members of a species can breed to produce fertile offspring, the size and diversity of a gene pool are directly related to the species it belongs to.

But what about asexually-reproducing organisms? Are they classified into species groups? Yes. Organisms that reproduce asexually show a high degree of genetic similarity. Therefore, such populations also possess a gene pool, and new genetic traits spread quickly within the pool.

For more information about the concept of a species, refer to 'defining a species' and 'other species concept'.

Key message: The continuity of living things on Earth depends on maintaining biological species. Both asexual and sexual reproductive strategies seek to preserve the genetic identities of biological species.

Asexual vs sexual reproduction

Distinguishing between asexual and sexual reproduction

  • Asexual: where the offspring receives their genetic information from one parent

  • Sexual: where the offspring receive their DNA from two parents

Contrasting biological features of asexual and sexual reproduction

  • Rate: asexually-reproducing organisms multiply quicker than sexually reproducing organisms. Even in organisms that alternate between asexual and sexual reproduction, the asexual phase requires a shorter time frame than the sexual phase. Thus, more progeny can be produced through asexual means than through sexual means.

  • Partners: Since asexual methods do not require a genetic partner, reproduction can occur uninterrupted or undelayed by the partner's absence. In sexually reproducing organisms, elaborate methods are required to unite gametes for fertilisation.

  • Genetics: In asexual reproduction, the offspring are genetic clones of their parent. Hence, genes that provide a selective advantage to the parent will be transmitted unchanged (except for mutations) to the offspring. Beneficial genes can spread through an asexually reproducing gene pool rapidly. In sexually reproducing populations, the frequency of advantageous alleles may be reduced or lost if one parent of an offspring does not possess the advantageous gene.