The cortical reaction of sea urchin eggs functions directly in a. the formation of a fertilization envelope. b. the production of a fast block to polyspermy. c. the generation of an electrical impulse by the egg. d. the fusion of egg and sperm nuclei.

Video transcript

Hi everyone. Now we'll look at the next question. Which one of the following is not true about cortical reactions. So when we talk about cortical reactions, we're talking about um reactions that take place after the fertilization of an egg causing the release of cortical Granules. This is part of a system called the slow block preventing further sperm from coming into an egg after fertilization. So let's look at our choices here, remembering that we are looking for a false answer to our to our problem. So let's look at choice A. They prevent policy for me polly spur me meaning multiple sperm entering an egg. This is true. That is what the purpose of these cortical reactions are. So Choice B. Says they include the formation of a fertilization envelope. Well this is also true. The cortical reactions involve a process where the cortical Granules are released. They merge with the egg membrane, release their contents which meld with the membrane around the egg and that leads to the fertilization envelope. That barrier that will permanently block further sperm from entering the egg. Choice C. Says they are initiated during fertilization. Yes that is true. That is what they're there for. Now let's look at Choice D. It's our only remaining answer. They temporarily block additional sperm from fertilizing the egg. Well they do block sperm from fertilizing the egg but the temporary block is part of what's called the fast block which is immediately after fertilization. The electric potential changes around the egg cell preventing sperm from coming in. That is the temporary step the cortical reactions lead to the permanent formation of the fertilization envelope, so Choice D. Is false. That is not describing cortical reactions, so it is our correct answer. Choice D. Is not true about the cortical reactions. Thanks for watching. See you in the next video.