SEXUAL REPRODUCTION: it's

natural!!

In this wiki, I will cover sexual reproduction in animals and flowers, though there are more methods of sexual reproduction.

Sexual Reproduction is the main form of reproduction among almost all animals and plants! Yes, amazing, but what is it?

What is sexual reproduction?

Sexual reproduction: A type of reproduction in which male and female reproductive cells (gametes) and their nuclei combine to form offspring with genetic material from both cells.

Yeah, this probably doesn't make much sense yet, but, it will, don't worry, after you read this page!

Ok, so, there's some vocab that you need to know for any of this to make sense...

Gametes: cells that contain half the usual number of chromosomes-one chromosome from each pair. They are n cells, AKA haploid cells. They are found in the reproductive organs of plants and animals.

Egg: a gamete that forms in the female reproductive organs, or a female gamete. Depending on which organism, there may be multiple eggs, such as in most animals and plants, or only one, which is the case for most humans.

Sperm: a gamete that forms in the male reproductive organs, or a male gamete.

Fertilization: the process that takes place when sperm and an egg combine to form one new cell that develops into an offspring.

MEIOSIS (this is important. you can tell by the caps!): a special type of cell division that produces haploid cells (gametes). There are 2 phases: meiosis I and meiosis II. It only takes place in reproductive organs.

Chromosomes: the physical structure in a cell that contains the cell's genetic material.

Chromotids: one-half of a replicated chromosome.

Well, that's enough... FOR NOW...

Meiosis!!! (See this IS important!)

This is very similar to mitosis, which you can learn about in Mitosis by Christina. Anyway, in this part, gametes form so that they can combine and everything. Meiosis is broken is broken up into 2 different parts, which is then broken up into 4 different parts, 8 in total.

Meiosis I:

Prophase I: Chromosomes condense. The nuclear membrane breaks down.

Metaphase I: Chromosomes arrange as pairs in the middle of the cell.

Anaphase I: The chromosomes of each pair separate and are pulled to opposite ends of the cell.

Telophase I/Cytokinesis: The cell divides into two daughter cells. Each cell has half the usual number of chromosome.

Meiosis II:

Prophase II: Each chromosome is made up of two chromotids.

Metaphase II: Chromosomes line up in the middle of the cell.

Anaphase II: The chromatids separate and are pulled to opposite ends of the cell.

Telophase II/Cytokinesis: Both cells divide, producing four gamete cells.

These gametes become sperm and eggs. Isn't that awesome?

For those of you who like visuals:

Once meiosis is over, the egg has to get fertilized. It gets fertilized when a sperm cell combines with an egg cell. Once an egg is fertilized, it is called a zygote, which contains a combination of the DNA from the parents. There are many different ways to fertilize the egg.

SEXUAL REPRODUCTION in: Animals!

Animals fertilize eggs 2 different ways: external and internal fertilization.

External Fertilization

Most animals that live or reproduce in water (fish and amphibians) fertilize eggs using external fertilization, meaning the eggs are fertilized outside of the female's body. First, the female lays her eggs in the water. The male then releases his sperm nearby. The sperm swim to the eggs and fertilize. Almost no parental care is involved among animals that use external fertilization. This means parents can produce large numbers of offspring because they don't have to care for each one. Once the offspring hatch, they can swim and find food on their own right away. 

Internal Fertilization

Mammals, birds, and reptiles fertilize eggs in the mother's body which is called internal fertilization. In some animals, like birds and reptiles, the fertilized eggs are placed in a nest. Some species, like the emperer penguin, care for the eggs very well by having the fathers sit on the eggs to keep them warm, yet the green sea turtle lay their eggs in sand pits and return to the sea, leaving the offspring to return to the sea by themselves.

The offspring of all mammals, with the exception of the echidna and the platypus, develop inside the mother's body after fertilization. The body of the female holds and protects the developing young until birth. Even after birth, the parents feed, protect, and teach the offspring how to survive until the offspring can survive on it's own.

^^WOW!  A  PREGNANT  ELEPHANT!^^

SEXUAL REPRODUCTION in: Flowers!

I'm only going to cover sexual reproduction in flowers, but know that sexual reproduction in most other plants are very similar, if not the same!

Okay, so here's some more vocab that you need to know!

Stamen: the male reproductive structure of the flower that includes the anther and the filament.

Anther: part of the male reproductive structure that is on a stalk called the filament that produces sperm cells, which are enclosed in pollen grains and transported to egg cells by wind, water, or animals.

Sepal: in some flowers, the sepal look like the petals, but in many other flowers, they are green and look like leaves.

Petal: part of a flower that help attract animal pollinators.

Pistil: the female reproductive structure of the flower that includes the stigma and the ovary.

Ovule: a structure that holds an immature egg cell that is at the base if the ovary.

Fruit: a ripened plant ovary that may contain one or more than one seed.

Pollen grain: a dry structure that holds a sperm cell and a tube cell.

Seed: a structure that encloses a plant embryo and stored food in a protective coat.

Embryo: the immature form of an organism that has the potential to grow and develop.

This video is for those of you who like visuals and listening. If you want a written explanation, scroll down a little.

So basically, there are 4 steps in sexual reproduction in flowers:

1. Meiosis: God, I hope you know what this is. ANYWAY, meiosis in the anther produces sperm cells, which are enclosed in pollen grains, and meiosis in the ovary produces egg cells, which are enclosed in the ovules.

2. Pollination: Pollen grains are released. When a pollen grain is caught on the pistil of a flower, the pollen grain produces a tube that grows into the pistil. At that time, an egg cell in the ovary begins to mature.

3. Fertilization: When the pollen tube reaches the ovary and penetrates an ovule, the sperm move through the pollen tube to fertilize the egg.

4. Seeds and Fruit: The fertilized egg becomes an embryo within a seed. The ovary wall thickens and forms a fruit around the seed. If the fruit lands in a place where it can develop, it will grow to be another flower.

Some types of seeds include:

             Apples!!!                   Sunflower Seeds!!!                  Cherries!!!

Advantages and Disadvantages of Sexual Reproduction

Sexual reproduction is much more complex than asexual reproduction. First of all, individuals must find partners. This takes time and energy. Because of this, fewer offspring are produced over a given period of time.

Yet sexual reproduction provides a very important benefit - it increases genetic variation. Offspring produced asexually receive their genes from only one parent. But offspring produced sexually receive a combination of genes from two parents. This means that sexually reproducing populations are more genetically diverse than asexually populations. This is important because genetic diversity helps a species survive changes in an environment.

Conclusion

In conclusion, sexual reproduction is a very complex process. First, cells and DNA divide in meiosis to produce gametes. Then, the gametes combine to make a fertilized egg, a zygote. The zygote develops into an organism that is the parents' offspring.

Practice Questions!

You can use these questions to quiz yourself and make sure you got the major points of sexual reproduction. Try not to look at the above info, but if all else fails, you can. You'll find the answers by scrolling down.

1. Where do the eggs of mammals develop?

2. What is the main advantage of sexual reproduction?

3. True or false? Amphibians use internal fertilization to fertilize their eggs.

4. List the 4 steps of sexual reproduction in flowers.

5. What happens to the plant ovary after fertilization?

6. True or false? The stamen includes the anther and the stigma.

7. How do pollen grains get to the pistil?

8. What is a pollen grain?

9. Where are the sperm and egg located on a flower?

10. At what point in sexual reproduction in flowers does the embryo begin to grow?

1. Inside of the female.

2. It provides genetic variation that is essential to survival.

3. False, external fertilization

4. Meiosis, Pollination, Fertilization, and Seeds and Fruit.

5. It develops into fruit.

6. False, anther and the filament.

7. Through wind, water, or animals.

8. A dry structure that holds a sperm cell and a tube cell.

9. The sperm cell is located on the anther, and the egg cell is in the ovary.

10. During pollination.

Sources

McDougal Littel Science: Focus on Life Science © 2007 pages 317-320, 325-329, February 10-19, 2009

Wikipedia.com, January 28, 2009 

For links to the pictures, just click them.

Related Information

For more information on mitosis, you can go to Mitosis by ChristinaT. 

For more information on flowers, you can go to Flowers by GiavonnaC.

For more information on asexual reproduction, you can go to Asexual Reproduction by RobertoZ.

For more information on how individual species reproduce, you can click on any page of any organism.

Thanks for reading my wiki page! :D Hope it was interesting!