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level: fertilisation of gametes, embryo development and gastrulation

Questions and Answers List

level questions: fertilisation of gametes, embryo development and gastrulation

QuestionAnswer
define fertilisationfertilisation is the fusion of two gametes to form a zygote
where does internal fertilisation take placein the oviduct - Fallopian tubes in humans
what is an oviductit is where unfertilised eggs reside in terrestrial life forms and it is where fertilisation takes place
what are the four main steps of fertilisation in humans→ the sperm dissolves and penetrates any protective layer around egg reaching the cellular membrane → molecules on the sperm surface bind to receptors (specialised proteins) on the eggs plasma membrane to ensure both gametes are from the same species – sperm nucleus enters the egg → the surface of the egg changes so that no other sperm can enter → the eggs and the sperms nuclei’s fuse to form a zygote
what occurs after fertilisationcleavage
what is cleavageit is the stage after fertilisation and it is when the egg proliferates for three days turning in to 8 cells (morula)
what happens after three days of cleavage divisionsthe zygote becomes a morula which contains approximately 8 cells
what is a zygotea fertilised egg
what is a blastocysteit is the stage of fertilisation after morula and occurs 5-7 days after fertilisation
what are the three components of a blastocytetrophoblast, blastocoel and inner cell mass
what is the trophoblasta single layer of cells forms around blastocyte called a trophoblast which allows it to implant into the uterus – trophoblast will later form the placenta
what is a blastocoelthere is also a fluid filled cavity in the blastocyte called a blastocoel which turns in to the yolk (humans have small ones – provides nutrient)
what is the inner cell massthe inner cell mass will turn in to the embryo (inner cell mass cells are pluripotent – embryonic stem cells)
when does the embryo undergo gastrulationafter 12 days of fertilisation the embryo undergoes gastrulations and becomes a gastrula
when does a gastrula become an embryoafter three weeks of fertilisation
when does an embryo become a foetusafter 8 weeks of fertilisation
define gastrulationThe process when a blastocyte becomes a gastrula – occurs over week 2 and 3 of conception
what is the process of gastrulationInvolves the blastocyte folding in on itself to form 2 cell layers - the third is created from one of the other 2 layers – the layers created are called germ layers
what are germ layersthey are the layers created once a blastocyste undergoes gastrulation
what are organisms called if they have only two germ layersdiploblastic – jelly fish
what does it mean if an organism is diploblasticit means it only has two germ layers
what are organisms called if they have three germ layerstriploblastic (most higher animals including humans)
what does it mean if an organism is triploblasticit means it has three germ layers
what are there three germ layers calledthe inner layer is called the endoderm the middle layer is the mesoderm the outer layer in the echoderm
what cells does the endoderm give rise to (innermost layer)the inner most layer (endoderm) gives rise to lung cells, thyroid cells, and pancreatic cells
what cells does the mesoderm give rise to (middle layer)the middle layer (mesoderm) gives rise to cardiac muscles, skeletal muscle cells, tubule cells of the kidney, red blood cells, and smooth muscle cells (found in the gut)
what cells does the ectoderm give rise to (outermost layer)the outer layer (ectoderm) gives rise to epidermal cells, neurons, and pigment cells
what two membranes are the germ layers protected bythe yolk sac and the amnion sac
what is a yolk sacThe yolk sac is a small, membranous structure situated outside of the embryo with a variety of functions during embryonic development - very small in humans and other animals are viviparous) - larger in animals that are oviparous and ovoviparous as the embryo gets its nutrients from the sac
list the yolk sacs main two functions in viviparous organismsprimary purpose is to provide nutrient to the embryo early in development - responsible for blood circulation for the first 12 weeks before the embryo develops its own circulatory system, and delivers nutrients through a primitive aorta
what is the amnion sacit is a sac that surrounds the embryo and it is full of amniotic fluid
what are two functions of the amnion sac- protect the embryo from impacts - allows the embryo to move as it equalises external pressure