Bio 212 Final Questions With 100% Correct Answers!!

Fertilization - joining of a sperm and an egg to form a diploid zygote Organisms that use external fertilization - most animals who participate in this live in aquatic environments like tadpoles -tend to produce large number of gametes How are gametes released for external fertilization - -gametogenesis occurs in response to environmental cues( lengthening days and warmer water temperatures) that indicate a favorable season for breeding -gametes are released in response to specific cues from individuals of the same species What draws sea urchin sperm to the egg - follow a gradient of a chemical secreted by the egg's jelly layer Describe the process of sea urchin sperm and egg interaction - 1. Sperm is drawn in by the chemical gradient from the egg's jelly layer 2. head of sperm initially binds to the jelly layer that surrounds the egg cell 3. Binding triggers the acrosome reaction or the release of the sperm's acrosome 4. Acrosome digs through the jelly layer and through the vitelline envelope 5. When the sperm makes contact with the egg surface, specific proteins in plasma membanes of egg and sperm induce membrane fusion 6. Sperm nucleus enters the egg 7. Sperm and egg nuclei fuse 8. Fertilization is complete Acrosome - large vesicle containing digestive enzymes that bore a hole through the jelly layer and through another protective coat called the vitelline envelopeWhat prevents cross-species fertilization - bindin receptors on the egg are specific to the bindin on the sperm What prevents polyspermy - a physical barrier is produced which begins when sperm enter and this causes the calcium ions to be released from storage. Calcium signals for the cortical granules to fuse with the plasma membrane and release their contents by exocytosis to the exterior. The granules then release proteases that digest the exterior-facing portion of the receptor for sperm, so that other sperm cannot intrude. in addition, because of the solute being released by the cortical granules, water flows into the sapce between the plasma membrane and the VL which causes the VL to be lifted away. The cortical granules then form the fertilization envelope What occurs in the cleavage stage - Cytoplasm divides but overall growth does not change