Summarize the experimental evidence in sponges showing that animal cells adhere to each other selectively. Explain the molecular basis of selective adhesion.

Verified step by step guidance

1. Step 1: Start by understanding the concept of cell adhesion. Cell adhesion is the process by which cells interact and attach to neighbouring cells through specialized molecules of the cell surface. This process is vital in the formation and maintenance of tissue structures.
2. Step 2: Discuss the experimental evidence in sponges. In the 19th century, biologist H.V. Wilson conducted experiments on marine sponges. He dissociated sponge cells by passing them through a fine mesh. The cells separated but later reaggregated to form a sponge again. This experiment showed that cells of a particular species of sponge would only reaggregate with cells of their own kind, demonstrating selective adhesion.
3. Step 3: Explain the molecular basis of selective adhesion. Selective adhesion is primarily due to cell adhesion molecules (CAMs) on the cell surface. These molecules allow cells to identify each other and adhere accordingly. Different types of cells have different CAMs, which is why cells of the same type stick together.
4. Step 4: Discuss the role of calcium ions in cell adhesion. Calcium ions are necessary for many types of cell adhesion. In the case of sponges, if calcium ions are removed from the environment, the cells will not adhere. When calcium ions are reintroduced, adhesion resumes.
5. Step 5: Conclude by summarizing the importance of selective adhesion. Selective adhesion is crucial for the formation of tissues and organs in animals. It allows cells of the same type to stick together, forming a specific structure. The understanding of this process has significant implications in the fields of developmental biology and regenerative medicine.

Key Concepts

Cell Adhesion Molecules (CAMs)

Cell adhesion molecules (CAMs) are proteins located on the cell surface that facilitate cell-cell adhesion. They play a crucial role in the selective adhesion of animal cells by recognizing and binding to specific receptors on adjacent cells. This selective binding is essential for the formation of tissues and organs, as it helps maintain the structural integrity and function of multicellular organisms.

Extracellular Matrix (ECM)

The extracellular matrix (ECM) is a complex network of proteins and carbohydrates that provides structural and biochemical support to surrounding cells. In sponges, the ECM plays a vital role in cell adhesion by providing a scaffold for cells to attach to and interact with one another. The composition of the ECM can influence the types of cells that adhere, contributing to the selective nature of cell adhesion.

Experimental Evidence in Sponges

Experimental evidence in sponges, such as the use of cell aggregation assays, demonstrates that sponge cells can selectively adhere to cells of the same species while rejecting those from different species. This selective adhesion is often tested by mixing cells from different sponges and observing their behavior. The results highlight the importance of specific molecular interactions, such as the recognition of unique surface markers, in determining cell adhesion patterns.