BC Science Connections 9 Unit 1: The continuity of life depends on cells being derived from cells

Topic 1.4: How does reproduction contribute to the variety of life on Earth? Asexual reproduction results in many genetically identical offspring in a short amount of time. Sexual reproduction results in genetically varied offspring.

Algae are plant-like organisms that mainly reproduce asexually Concept 1: Asexual reproduction results in many genetically identical offspring in a short amount of time. Algae are plant-like organisms that mainly reproduce asexually Can multiply very quickly under optimum temperature and nutrient conditions to form an algal bloom Algal blooms pollute shellfish and make them toxic Figure 1.24: Algal blooms are a common sight along the Pacific coast any time of year but especially in the summer. Why would algal blooms be especially common in summer?

Some Advantages of Asexual Reproduction Only one parent is needed (no need to find a mate) Reproduction occurs quickly Offspring mature and start reproduction quickly Offspring are genetically identical to the parent Can live and interact with their environment with the same success as their parent

Some Disadvantages of Asexual Reproduction Lack of genetic diversity All individuals in a population are vulnerable to changes in their environment (example: drought, disease) Since all the individuals are genetically identical, they will all respond in the same way (example: die or become diseased) Figure 1.26: If the conditions change or a disease occurs, it may cause a crop to die or the yield of produce to be severely reduced.

Asexual Reproduction Advantages Disadvantages Only one parent needed • Unfavourable conditions such as extreme temperatures can wipe out entire colonies due to lack of genetic diversity • Large numbers of offspring are reproduced very quickly when conditions are favourable. • Offspring are genetic clones. A negative mutation can make asexually produced organisms susceptible to disease and can destroy large numbers of offspring. • Large colonies can form that can out-compete other organisms for nutrients and water. • Some methods of asexual reproduction produce offspring that are close together and compete with each other for food and space. • Large numbers of organisms mean that species may survive when conditions or the number of predators change.   • Energy is not required to find a mate. Offspring able to grow to reach maturity quicker.

Discussion Questions Describe one advantage and one disadvantage of asexual reproduction.

Concept 2: Sexual reproduction results in genetically varied offspring. Genetic variation: Variation in the DNA sequences of each individual in a species Variation in DNA results from sexual reproduction Figure 1.27: Although members of this family share similar traits, their different genetic material makes them unique individuals. genetic variation: variation in the DNA sequences of each individual in a species

Some Advantages of Sexual Reproduction Genetic variation/diversity Genetic diversity allows some individuals in a population to survive if the environment changes Example: If the environment changes, some individuals will be less successful at living and reproducing Other individuals may have certain features (due to genetic differences) that allow them to live and reproduce in the new conditions more easily

Some Disadvantages of Sexual Reproduction Searching for a mate takes time, and may expose individuals to predators, disease, or harsh environmental conditions Fewer offspring are produced (takes longer for a population to grow) Offspring take longer to reach maturity (and reproduce) Offspring require a lot of time and energy to raise until they are independent from their parents

Sexual Reproduction Advantages Disadvantages Genetic diversity allows a harmful mutation to be less harmful to the entire population More time is required to produce offspring More offspring survive because of increased parental care. Requires more energy to find a mate Genetic variation allows for survivors in the case of disaster Fewer offspring means it takes longer for populations to grow Fewer offspring leaves more food and space for young Takes more time for young to grow (and reach sexual maturity)

Discussion Questions Describe one advantage and one disadvantage of sexual reproduction.

Topic 1.4 Summary: How does reproduction contribute to the variety of life on Earth? Asexual reproduction results in many genetically identical offspring in a short amount of time. Sexual reproduction results in genetically varied offspring.