Reproductive Strategies How do different organisms reproduce?

Organisms we have studied:

Wisconsin Fast Plants, Blackworms, Paramecia, Zebrafish, Ladybugs, Coleus
Overview - "The birds & the bees"

There are a wide variety of reproductive strategies being used by organisms of all shapes and sizes. Despite such variety, reproductive strategies are categorized as sexual or asexual. Throughout this unit we have studied a variety of organisms demonstrating both methods of reproduction. Some organisms are capable of only one method, while others are capable of both. Which of the organisms we have studied use asexual reproduction? Which use sexual? Which can do both?

Wisconsin Fast Plants & the Coleus

All life on Earth depends on plants for food, shelter, oxygen, and more. Consequently, all life on earth depends on the ability of plants to reproduce.

Reproductive Strategies - Sexual

Approximately 90% of flowering plants depend on animals (such as birds & bees) to act as pollinators! When a pollinator visits a plant for food (nectar) it will pick up pollen on its feet, back, hairs, feathers, etc.. Then, when it flies to another flower, it transfers pollen grains from its body onto the new plant's stigma. Once in the stigma the pollen will fertilize the eggs, which will eventually turn into seeds. In this scenario the pollen are the male sex cells and the eggs are the female sex cells.

Reproductive Strategies - Asexual

Plants are also capable of asexual reproduction. This can happen in a few different ways:

1. Budding - When parent plants "sprout" a new copy of themselves. Take potatoes for example. Have you ever seen a potato with a bunch of small growths called 'eyes'? Each of these sprouts can produce a clone of the parent potato.

2. Vegetative Propagation - This is often the reproductive strategy used when a small row of plants spreads quickly in a giant mass of plants. Strawberries, for example, will send out "runners" (horizontal stems) that work their way into the ground and form roots, from which a new plant will grow.

3. Fragmentation - Nurseries frequently take advantage of this reproductive strategy to create clones of plants. They do this by breaking off a portion of the stem and planting it in soil or water. Which plant did you and your group do this to?


Reproductive Strategy - ASexual

Though they can produce sexually, hydra mainly reproduce through a process called budding. This allows a hydra to grow a small copy of itself on the side of its body, which falls off when it has matured. It is through this process that a hydra doesn't really age. Scientists are fascinated by hydra because they can basically live forever.

Normal hydra
Budding hydra with attached copy of itself
Would you like to be able to make a copy of yourself and continue to live forever?


Casper Fish
Long-fin Zebrafish
Reproductive strategies - Sexual

Like the Wisconsin Fast Plants, Zebrafish reproduce sexually. Females lay several hundred eggs in a bed of pebbles and vegetation (i.e., plants). At the same time, males release sperm into the water which will fertilize the eggs. Once the eggs are fertilized, they only take a few months to develop into adults. Within only three days of being laid the larvae will hatch; their yolk sacs will remain attached to their bellies serving as a food source, but rendering the fish immobile. After five days the fish begin swimming around and finding food. By four months old, they are adults, and are capable of reproducing.


Paramecia are unicellular (single-celled) organisms that live in freshwater environments. They are part of a group known as the ciliates because they are covered in cilia (small hair-like structures). These cilia help the paramecium to move quickly through the water and escape predators. Do you remember which organs in the digestive system have cilia?

Reproductive Strategies - Asexual
Binary Fission

Binary fission is the division of a single cell into two distinct cells. A number of steps have to happen before division occurs: (1) the paramecia grow in size a little bit, (2) the organelles and DNA are duplicated, and then separated into different areas within the paramecia, and finally (3) the paramecia begins pinching in on itself until it splits into two "daughter" cells.

Reproductive Strategies - Sexual

Conjugation occurs when two cells connect with one another and exchange genetic material. Conjugation doesn't result in any offspring, but it does make cells that are genetically distinct, or "reborn."


Lumbriculus variegatus (a.k.a. blackworms)

Blackworms are found throughout North America and Europe, usually in shallow water such as ponds, lakes, or marshes. They eat decaying plant matter and microorganisms. Sometimes they live in the sediment of deeper water. Whether they are in deep or shallow water, the blackwork will bury its head in the sediment and plant debris to search for food, while its tail stands strait up!

Reproductive Strategies - Asexual
Blackworm regeneration

Like other animals such as starfish and some lizards, blackworms can regenerate themselves. This means that if they become fragmented (or split up into pieces), the various fragments can develop into whole blackworms!

We have learned a lot about the various sexual and asexual reproductive strategies. How are these processes similar? How are they different? What do you think is happening at the cellular level during each type of reproduction?

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