Module 5
1. Module 5
1.30. Page 5
Module 5—Cell Division: The Processes of Mitosis and Meiosis
Lesson Summary
In this lesson the following focusing questions were examined
- What are the advantages or disadvantages of different reproductive strategies?
- Why do some organisms vary their reproductive strategies?
Organisms can reproduce quickly and effectively by way of mitosis and asexual reproduction. The resulting offspring may take over a habitat and the whole species will benefit by a sheer growth in numbers. However, the entire population will be genetically identical. They may all be susceptible to a virus or disease and experience rapid death.
To balance the need for high numbers of offspring and to reproduce quickly, many organisms include a part of their life cycle that requires meiosis and sexual reproduction. This increases genetic variability and allows for offspring that are different from their parents. Some of these organisms may not be susceptible to a disease or a change in the environment that hurts the general population. These organisms will live to reproduce again.
Some organisms alternate their strategies depending on conditions. This allows for the best of both reproductive worlds. When conditions are good, mitotic or asexual reproduction can quickly help colonize an area. However, when the conditions become unfavourable, meiosis or sexual reproduction will allow for genetic variation that will help the species survive.
Because this is the last lesson in this module, remember to submit the following items:
- Module 5: Lesson 6 Assignment
- Module 5 Assessment
Lesson Glossary
Consult the glossary in the textbook for other definitions that you may need to complete your work.
alternation of generations: a plant life cycle where two distinct multicellular forms of a sporophyte and a gametophyte occur in one generation
A diploid zygote undergoes mitosis to form a diploid sporophyte, which undergoes meiosis to form haploid unicell spores, each of which undergo mitosis to form a multicellular haploid gametophyte, which undergoes mitosis to form unicellular gametes, which fuse with other gametes to produce a diploid zygote. Animals do not display alternation of generations.
binary fission: asexual cell division in prokaryotes; replication of the circular chromosome and division of the DNA and cytoplasm without the use of a spindle; offspring are clones; rate is very rapid
budding: a type of asexual reproduction
In yeast, unequal cytokinesis in mitosis forms a large cell and a tiny cell that buds off; in Hydra, a small multicell mini-polyp breaks off and forms an adult.
conjugation: a type of sexual reproduction that occurs when two cells form a cytoplasm bridge through which they exchange genetic material, producing variation; occurs only in unfavourable environments
fragmentation: an asexual form of reproduction in animals similar to cutting in plants (e.g., a flatworm with tail cut off can regenerate the lost section)
gametophyte: a multicellular stage in alternation of generations that consists of haploid cells that split off to produce haploid gametes
life cycle: the stages an organism goes through to grow, reproduce, and die
parthenogenesis: a rare type of asexual reproduction; an unfertilized haploid egg divides by mitosis, producing a complete multicellular organism in which all cells are haploid; seen in amphibians, reptiles, and birds
prokaryotes: single-celled organisms without a nuclear membrane, such as bacteria; have one circular chromosome; divide asexually by binary fission and “sexually” by conjugation
spore: a haploid cell produced by meiosis in the sporophyte; each is capable of dividing to form a multicellular gametophyte consisting of haploid cells
sporophyte: the diploid multicellular stage in plants that show alternation of generations; produces haploid spores by meiosis