Cell division

Reproduction is another characteristic of living things. To achieve this process, the cell can split up according to the instructions given by DNA. The cell division includes two main steps. Nuclear division and cytokinesis. According to the kind of cell, the nucleus will divide into exact copies or will divide into two halves.

Introductory Questions

How do cells reproduce?
What is a gamete?
What is the importance of the number of chromosomes of a cell?
How cancer can be triggered?

Mitosis

The process that produces exact copies of the nucleus is called mitosis. During mitosis, chromosomes will separate into two identical pieces called chromatids that will have the same genetic information, on this way; the new nuclei will have the same number of chromosomes of the parent cell. Organisms that reproduce asexually and somatic cells will use this method to divide in order to produce new identical cells. Chromosomes in eukaryotic organisms occur in pair containing similar genetic information.

Mitosis in animal cells.

Mitosis in plant cells

FACTS ABOUT MITOSIS

1. Mitosis is used by some organisms to reproduce asexually. It's the natural way of making clones.

2. Multicellular organisms use it to grow new tissues.

3. Multicellular organisms use it to heal injuried tissues.

4. Some cells can keep the ability of dividing and producing a wide variety of new cells. These are called Stem Cells.

5. Some cells specialize but still can divide to produce similar cells,

6. Some cells specialize and lose the ability of dividing.

Meiosis

Organisms that reproduce sexually need to produce special cells called gametes. Gametes are produced by female and male organisms as a strategy to exchange genetic information within the same species. Gametes are produced by a process called meiosis in which the number of chromosomes is reduced to the half because, as the organism reproduce, its gametes will fuse with the gametes of another to exchange genetic information and to complete this number again. In this process homologous chromosomes split up after exchanging information between them.

Meiosis in ovary

Meiosis in testicles

FACTS ABOUT MEIOSIS

1. Meiosis is exclusive of sexual cells or gametes.

2. Meiosis include the exchange of genetic information between two cells. Because of that, we are all mutants.

3. A cell that carries out meiosis will divide just once.

4. Daughter cells in meiosis have half the number of chromosomes of the species, so they will complete the set as they fuse with another gamete during fertilization.

5. Meiosis is a key process to adaptation and evolution.

Activity

PROCEDURE.

1. Observe the different micrographs.

2. Classify each as mitosis and meiosis.

3. Make a drawing of each process and try to identify the different phases.

EXTRA ACTIVITY.

Answer the questions about mitosis and meiosis

1. Which kinds of cells undergo mitosis and which undergo meiosis? Why?

2. According to your observations, how can you identify the different phases of mitosis in the cells of an onion root?

3. What does diploid and haploid mean?

4. According to the drawing of a sperm and an egg, which organelles are conserved? Why?