HOW DO CELLS GROW?
• Asexual reproduction is the when a single organism produces offspring. The offspring gets genes from only that one parent. Fusions of gametes are not needed and chromosomes numbers typically stay the same.
•Asexual reproduction is typically how clones are formed. These clones can be used in agriculture and planting. As well as in research in order to develop injured organisms, tissues and genes if needed.
5 types of Asexual reproduction and examples: In class we discussed five different types of asexual reproduction and different examples of each type.
Binary Fission: Binary fission is when a single celled organism splits into identical copies. Example of this is Bacteria reproducing.
Budding: Budding is repeated mitosis over and over again to form more and more copies. In budding the buds formed can break off to form separate organisms. Example of this would be Yeast.
Fragmentation: Fragmentation is when for example a starfish breaks of an arm and then the arm grows a whole new starfish. Fragmentation is not when a lizard regenerates a tail because in order for it to be considered as fragmentation the lizard tail must grow a whole new lizard. More examples of fragmentation are annelid worms or mitochondrial eukaryotic.
Vegetative Reproduction: Vegetative reproduction happens with cells in plants that are meant to develop into new structures that form identical plants. Examples of Vegetative Reproduction include plants and crops such as corn, apples, mangoes and avocados.
Spore Formation: Spores are single cells that can grow into a whole new organism, for example plants, algae and fungi.
Advantages of Asexual Reproduction:
No energy required to find a mate. Large amount of offsprings reproduced, when conditions are favourable. Large colonies are produced that can out-compete other organisms for nutrients and water. If a species is endanger Asexual Reproduction can help the species to survive.
Disadvantages of Asexual Reproduction:
Since they are all copies if there is a mutation the whole offspring will be susceptible to the same disease. As well as if there are unfavourable conditions, like extreme temperature it can kill the whole offspring. If they are produced to close together they will have to compete with each other for space, nutrients.
•Sexual reproduction is the fusing off reproductive cels (gametes) fusing together. For this too happen it must involve a females ovum (egg) and a males sperm.
•Mating is when the gametes arrive in the same place at the same time.
•Gametes contain 23 chromosomes which is half the amount of chromosomes a regular cell contains.
When a males sperm cell goes into the female body and fertilizes the an egg cell. The sperm penetrates the egg and a fetus begins to develop. After the fertilization the embryo continues to develop and become nourished in the female/mothers body.
Advantages: of Internal fertilization protects the fertilized egg from dehydration once it comes out. Since it is inside the female it protects the embryo from predation. Enhances the fertilization of eggs for the male.
Disadvantages: of Internal Fertilization only produces a limited amount of offspring. Generally 1 fetus or twins rare cases produce up to 8 but that is it. Internal Fertilization risks the chance of Sexually Transmitted Diseases.
•Fetal Development: Internal Fertilization leads to Embryonic Development which leads to Fetal Development. In fetal development there are three different stages (trimesters) Trimester one lasts till eight weeks. The fetus is developing organ systems; brain, spinal, ears, kidneys, livers,muscles and you can almost tell the sex of the baby. In the second trimester which lasts from week 12-16 of the pregnancy; the fetal movement is felt which means that the mom can feel the kicking of the baby, and the eyelids start to open. The baby if needed to be removed at this stage has a chance at survival. At third trimester the baby continues to develop and grow, gaining weight. Until 9 months when it is completely healthy to be removed.
External Fertilization: External Fertilization happens through spawning which is when, for example a male fish releases sperm when a female fish releases an egg, when they meet fertilization begins. This is common underwater and when it happens underwater it protects the eggs from drying out. Broadcast spawning leads to a more mix of genes and a diverse range of species. Which means that some of them will survive higher extreme cases. The Disadvantage is the fact that it is external and the Mother is not protecting the egg in her uterus like in internal fertilization.
Conditions needed for mating: There has to be enough nutrients for the embryo, the temperature must be warm and there must be sufficient moisture so that the embryo does not dry out. The embryo just be safe from predators and from other extreme conditions such as radiation, or extreme temperature.
Pollination: Pollination is the transfer of Pollen (a powdery yellow substance) to a plant for fertilization (fertilizations is the fusion of male and female gametes. The pollen is transferred by Bees, Butterflies, Moths, Flies, Hummingbirds and The wind. It can also be manufactural done by people. The embryo develops in the female part of the plant. Advantages: Pollination maintains race and species, that specific plant won’t need to produce as much pollen grains because there is now a new plant. Pollination eliminates bad recessive characteristics. Disadvantages of Pollination; makes the plan less immune to disease, and makes the health and physical strength decrease and makes the plant less adaptable to its surroundings and conditions.
Mitosis is how the process of cell division. There are 4 “official” stages in Mitosis. I remember them as PMAT. Prophase, Metaphase, Anaphase and Telophase. However in order for the full cell cycle to take place we stat with Interphase.
Interphase: is when there are 46 chromosomes that duplicate to form identical pairs of chromosomes. The copies attach on to each other to form X-shaped chromosomes.
Prophase: Now going into Mitosis Prophase is when the spindle fibres begin to form with centrioles in the cell and the nucleolus disappears. The X-shaped chromosomes stay attached and the centromere forms at the center. However in plant cells there are no centrioles and the spindle fibres form without them.
Metaphase: Metaphase is the phase where all of the X-Chromosones begin to move into a straight sign along the equator of the cell.
Anaphase: Anaphase means “Away phase” Which is what it is. The X chromosomes are split apart pulled away by the spindle fibres. The chromosomes are now single chromosomes and are on opposite sides of the cell.
Telophase: Telophase is when new nucleolus forms around the two separate sides of the cell creating two cells. New nuclei are formed in each cell and the spindle fibres disappear.
Cytokinesis: Isn’t officially part of PMAT but is when cleavage happens and the two cells are split up making them officially two separate cells. (Known as daughter cells) These new cells contain each 46 cells.
Meiosis has double the amount of steps as Mitosis, and the result is twice as many as mitosis each cell however has 23 chromosomes which is half of the parent cell.
Interphase: Meiosis starts off where the DNA is copied which leads to two full identical sets of chromosomes.
Prophase I: The chromosomes become X-shaped chromosomes by bonding together with their copies and pairing up. They share DNA (recombination) Again the Nucleus disappears and the spindle fibres form.
Metaphase I: The chromosomes line up at the equator and the spindle fibres attach to each one of the chromosomes.
Anaphase I: The spindle fibres pull the chromosomes away from each other so now they have a mixture of genes on each side. But the pairs stay together unlike in mitosis.
Telophase I and cytokinesis: When cleavage happens and two daughter cells are formed.
The next steps happen to the two daughter cells.
Prophase II: Each daughter cell has 23 pairs of chromatid, they bond together into visible X-shaped structures. The nucleus membrane disappears. The centrioles duplicate and spindle fibres form again.
Metaphase II: They line up along the equator of both cells. The spindle fibres attach on to them.
Anaphase II: The spindle fibres pull them away to opposite poles of the cell.
Telophase II and cytokinesis: Both cells have two new cells form within. The chromosomes gathering together and a new membrane forming around each set. In Cytokinesis cleavage happens and there are now 4 new cells. In males all four cells are sperm cells. In females one is the egg and the other three are polar bodies. Polar bodies don’t develop into eggs.