Problem 8 - Biology: The Dynamic Science

Question

In the embryonic development of the eye: a. the optic vesicle cells permanently adhere to each other to prevent movement, whereas the optic cup cells are very motile. b. signals from the optic cup trigger surface receptors on the lens placode. c. gradients determine that the ectoderm overlying the lens vesicle develops into the optic vesicle. d. microtubules powered by myosins and microfilaments powered by dyneins move the eye components around in the head region. e. cadherins function in the presence of calcium to allow the lens placode and optic cup to break apart.

Step-by-Step Solution

Answer

The statements B and D are partially accurate while statements A, C, E are not correct.

Step 1: Evaluate Statement A

Statement A suggests that optic vesicle cells adhere permanently to each other and optic cup cells do not. However, in reality, the optic vesicle, a structure formed from the diencephalon during embryonic development, does not permanently adhere its cells but rather invaginates to form the optic cup.

Step 2: Evaluate Statement B

Statement B suggests that signals from the optic cup stimulate the lens placode. This is a functionally accurate description of embryonic eye development. The optic cup produces signals that instigate the development of the lens placode into the lens vesicle.

Step 3: Evaluate Statement C

Statement C mentions that the ectoderm overlying the lens vesicle develops into the optic vesicle. This, however, is incorrect. The ectoderm overlying the optic vesicle thickens to form the lens placode, which later invaginates to form the lens vesicle.

Step 4: Evaluate Statement D

Statement D is oversimplified and somewhat misleading. While it is true that cellular movements are involved in development, and that these movements are facilitated by components of the cell’s cytoskeleton (microtubules, microfilaments) powered by motor proteins (myosins for microfilaments, dyneins for microtubules), it doesn't directly explain how the eye components move in the head region.

Step 5: Evaluate Statement E

Statement E denotes that cadherins, in the presence of calcium, allow the lens placode and optic cup to break apart. This is not accurate. Cadherins, calcium-dependent cell adhesion proteins, actually facilitate the adhesion between cells, which is crucial for the invagination process of optic vesicle to optic cup and lens placode to lens vesicle.