Science 9: Unit A – Biological Diversity Topic 3: Passing It On

The Function of Reproduction Adaptations are passed on through reproduction. Any trait that is passed on through reproduction (hair color, eye color) is called a heritable trait. Reproduction among different kinds of organisms takes on a variety of forms or REPRODUCTIVE STRATEGIES.

Asexual Reproduction Occurs when only one organism passes on their genetic material. They basically clone themselves. This method of reproduction is common among bacteria and fungi Benefits – You don’t need to spend energy finding and attracting a mate. Another benefit is that you can produce much more rapidly, producing many more offspring. Drawbacks – Since all of your genetic material is identical, there is little or no variability in a population. One disease, or a change in the ecosystem could wipe out the entire population or species.

Binary Fission Binary Fission – Occurs in unicellular organisms and our own cells. The cell itself divides creating two cellular organisms. The cell first duplicates its entire inside structure: the organelles. The nucleus stores the genetic material and it splits off into two clones with the exact same genetic material. Eventually the cell membrane closes off and splits the cell into two identical daughter cells.

Spores Asexual Spores – Occurs in some fungi. Single cells called spores are formed in the fungus. Millions of spores are then released into the environment. The spores are genetically identical to the parent fungus.

Zoospores – Spores with Flagella Zoospores – Are a special type of spore produced by some fungi and algae. They are equipped with a flagellum which allows them to swim in water and therefore spread their genetics over a larger area.

Asexual Reproduction in Plants Vegetative Reproduction – Plants can reproduce through asexual strategies. Special cells called meristem cells act as stem cells: blank cells that can reproduce themselves and specialize into any kind of cell. By taking a cutting of the plant, you can activate the meristem cells and produce a clone of the parent plant.

Budding Budding – Occurs with sea sponges, yeast and hydra. A bud cell, like the spore, is produced and then attaches itself to the outside of the organism. When it is completely developed, it detaches itself and becomes its own organism. Some buds may remain attached to each other and form a superorganism: a collection of organisms which act together as a single organism.

Most asexual reproducers also reproduce sexually. Note that in each of the above kinds of organisms, they will routinely reproduce sexually in addition to asexually. Why would they do this?

Sexual Reproduction Sexual reproduction usually involves two individuals. Most plants and animals reproduce sexually. The offspring of sexual reproduction will have the characteristics of both parents (ie. a lion cub will share 50% of its genes with each parent). The main benefit of sexual reproduction is increased variation.

Gametes are Sex Cells Sexual reproduction happens through the joining of gametes. Gametes are the reproductive cells that join together to form the zygote. For animals the gametes are the sperm cell from the male, and the egg cell from the female.

Sexual Reproduction in Animals Occurs when the sperm cell from the male and the egg cell from the female join together. This process is called fertilization. After fertilization the two gametes are now one cell called a zygote which will divide repeatedly very quickly. Once it starts dividing we call the new organism an embryo. Mammals have the structural adaptation of internal fertilization and gestation (the growth of the embryo). This helps protect the gametes and embryo until it is mature enough to survive in the environment.

Gametes Must Live in Liquid environments Gametes, like all cells, must live in a liquid environment; therefore fertilization must either occur in water (amphibians, and fish) or inside an internal liquid environment (everything else).

Sexual Reproduction in Plants Most plants have both male and female sex organs and produce both kinds of gametes. Plants that flower have their reproductive organs in the flower area. Stigma contains the male gametes, and is produced in the STAMEN, the male reproductive organ of the plant. Ovary contain the female gametes, and they are found in the PISTIL, which is the female sex organ in the plant. Pollination is for plants what fertilization is for animals: the joining of the two gametes.

Sexual Reproduction in Plants Cont’d Self-pollination occurs when the pollen reaches the pistil of the same plant. This allows a plant to reproduce sexually even if there are no other plants of the same species nearby. Cross pollination occurs when the pollen from plant is carried by wind or insect to another plant of the same species. The advantage here is that maximum variation is achieved. The embryo of the plant is produced in a seed and remains in the seed until the conditions are right.

Sexual Reproduction in Bacteria Bacterial conjugation is a primitive form of sexual reproduction between two bacteria cells (unicellular organisms). Two bacteria cells form a connection with each other and transfer genetic material to each producing two new organisms without producing any offspring.