Biology Notes 3Asexual vs Sexual Reproduction

Asexual Reproduction

• Only one parent is required

• Offspring are genetically identical to parent - clone (Mitosis)

• Lacks variation in a species (they all look alike) – Could this be a detriment to the population?

Examples of Asexually Reproducing Organisms

• Bacteria

• Bread mold

• Tree shoots

Types of Asexual Reproduction Page 154-161

• Binary fission

• Budding

• Fragmentation

• Vegetative reproduction

• Spore formation

Binary Fission

• A single parent cell replicates its genetic material and divides into two equal parts.

• Ex: amoeba, bacteria, algae, protozoa

Budding

• When part of the yeast cell pushes outward to form an outgrowth or bud. The bud then pinches off from the parent cell to become a yeast cell identical to the parent.

• In the case of the hydra and sponge the bud may not detach from the parent.

• Ex: yeast, hydra, sponge

Fragmentation

• If an organism breaks apart as a result of injury, each fragment then develops into a clone of its parent

• Ex: Sea Star, Plants “Japanese Knotweed”

Vegetative Reproduction

• Special cells usually in plant stems and plant roots divide repeatedly to form structures that will eventually develop into a plant identical to the parent

• Ex: tulips, strawberry runners, potato sprouts or eyes, plant cutting

Spore Formation

• A spore is a reproductive cell that grows into a new individual by mitosis. Spores are lightweight, and can be carried by wind or water to a new location. If the new location has the right conditions (food, temperature, moisture) for growth, the spore can start growing immediately.

• Ex: molds

Advantages of Asexual Reproduction

• Large numbers of offspring are produced quickly

• Large colonies can form that can outcompete other organisms for nutrients and water

• 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

Disadvantage of Asexual Reproduction

• Offspring are genetic clones. A negative mutation can make asexually produced organisms susceptible to disease and can destroy large numbers of offspring.

• Some methods of asexual reproduction (ex: strawberry plants) produce offspring that are close together and compete for food and space.

• Unfavourable conditions such as extreme temperatures can wipe out entire colonies.

Sexual Reproduction

• Requires two parents

• Produces offspring that are genetically different from their parents.

• Greater variation in a species.

Sexual Reproduction Involves

• The fusion of an egg cell and a sperm cell to produce a zygote

External Fertilization

• most aquatic organisms, mosses (read Pg 184) and ferns

• Sperm cell and egg cells of the same species unite outside the bodies of the parents. Ex: salmon (both the male and female parents die after spawning

• Ex: Moss – water transports their gametes enabling them to meet. The male and female sex organs develop on the end of the branches of the plants. Fertilization happens by the sperm cells being splashed by raindrops into the female part of the plant.

• External fertilization provides an advantage because very little energy is required to find a mate, and large numbers of offspring are produced at one time creating a greater chance of survival during an environmental disaster. A disadvantage is that the eggs are unprotected and often preyed upon. Since parents do not care for their offspring, few survive to adulthood.

Internal Fertilization

• Whales and most land dwelling animals such as moose and humans.

• Sperm cells are deposited inside the females body where they meet an egg cell

• Embryo develops inside the mothers body for a period of time protecting it from predators

Pollination in Flowering Plants

Pollen Transport

• Bees

• Wind

• Water

• Other animals fur or by eating the fruit (seeds have a tough outer coat and often do not get digested by animals)

• Activity page 191

Sexual Reproduction in Insects (Grasshopper & Butterfly)• The male deposits a package of sperm inside the female to fertilize

the eggs. The female then deposits the fertilized eggs in a protected area under a leaf or in a burrow. Eggs develop and eventually hatch on their own, when conditions are right.

• Insects often change form between hatching and adulthood this is called metamorphosis

Grasshopper – Incomplete Metamorphosis

• Involves subtle changes through three life stages – egg, nymph, and adult

Butterfly Complete Metamorphosis

Advantages of Sexual Reproduction

• Very little energy is required to find a mate (external fertilization)

• Greater numbers of offspring can repopulate an area after a disaster

• More protection and parental care is given to young

• Offspring are genetically different from their parents so they may survive new diseases or other threats that appear in a population

Disadvantages of Sexual Reproduction

• More energy is required to find a mate (internal fertilization)

• Fewer offspring are produced, so if the number of predators increases, a population will decline (internal fertilization)

• Gametes, embryo’s, and offspring are unprotected and are often preyed upon (external fertilization)

• Some beneficial traits may not be passed on from parents to offspring

Study Chart: Asexual vs Sexual Reproduction

Asexual Reproduction Sexual Reproduction

Number of Parent Cells

Gametes (eggs or sperm)

Variation in offspring

Amount of energy required

Parental Care

Mitosis or Meiosis?