Cellular Responses, Movement, and Reproduction Mechanisms

Cellular Interaction and Responses

Cellular interaction is the capacity of cells to detect changes in their environment and respond to them correctly.

Types of Cellular Responses

Static Response

In a static response, there is no movement produced. Rather, the cell responds in a different way, for example, by secreting a substance.

Dynamic Response (Taxis)

In a dynamic response, the cell responds by moving. These movements are collectively called taxis (plural: taxa). They are considered:

• Positive: If the cell moves towards the stimulus.
• Negative: If the cell moves away from the stimulus.

Mechanisms of Cellular Movement

Flagellar and Ciliary Movement

This type of movement is produced in cells that have cilia (many tiny structures) or flagella (longer than cilia and fewer in number). The internal structure of cilia and flagella is very similar and consists of ordered cytoskeleton filaments.

Contractile Movement

This type of movement is characteristic of muscle cells, which are able to contract and relax.

Amoeboid Movement

This type of movement is characteristic of amoebas, although white blood cells also move in this way. In order to move, amoebas send out protrusions of cytoplasm (called pseudopods) from anywhere on their surface.

Cellular Reproduction and Division

Cellular reproduction is the process through which a parent cell divides into two or more identical cells, called daughter cells. This process is known as cell division.

Purpose of Cell Division

• In unicellular organisms (such as protozoa and bacteria), the primary objective of cell division is reproduction.
• In multicellular organisms, cell division enables the organism to increase its size (by increasing the number of cells) and to replace cells in the body that die off.

Essential Steps in Cell Division

DNA Replication (Duplication of Hereditary Information)

DNA replication, or the duplication of hereditary information, is crucial. The DNA must also be equally distributed in order to guarantee both cells receive the same hereditary information.

Cytoplasm Division (Cytokinesis)

Cytoplasm division, or the distribution of the contents of the parent cell among the daughter cells, is the final step. This distribution does not have to be equal; even if a cell only receives a small amount of cytoplasm, it can increase its size until it becomes an adult cell.

Methods of Asexual Reproduction

Unicellular organisms reproduce asexually through various methods:

1. Through Fission: The parent cell divides into two daughter cells of the same size.
2. Through Budding: The parent cell divides into two daughter cells, one of which develops like a small bud on the other.
3. Through Spores (Sporulation): The parent cell forms numerous daughter cells called spores, which are kept inside it until the membrane bursts.