Distinguish between i) Egg and Embryo ii) Foetus and Embryo
Hint: Fertilisation, also known as generative fertilisation, syngamy, and impregnation, is the fusion of gametes that results in the birth of a new individual organism or offspring and the beginning of its growth.
Complete answer: Process of fertilization The first two weeks of pregnancy are regarded as the period preceding ovulation, during which the body prepares to release an egg. Week 3 starts with the release of an egg, also known as ovulation. A zygote is a fertilised egg that has been fertilised by a sperm cell. The zygote divides and develops into a blastocyst, which is a group of cells. The blastocyst implants in the uterine wall and grows into the placenta and embryo in week 4 of pregnancy. When the amniotic sac forms (around day 10 to 12 after fertilisation, or at the start of week 5 of pregnancy), the blastocyst is called an embryo. An embryo is the early stage of human development, approximately equivalent to the fifth to tenth weeks of pregnancy. Egg or zygote: Fertilization occurs when a sperm cell enters an egg cell in the fallopian tube. When fertilisation occurs, the newly fertilised cell is referred to as a zygote. Embryo: An embryo is a multicellular organism in its early stages of development. In general, embryonic development is the stage of life in sexually reproducing species that begins shortly after fertilisation and continues through the creation of body structures such as tissues and organs. Fetus: embryo is now considered a foetus after the embryonic cycle has ended at the end of the 10th week of pregnancy. Beginning in the 11th week of pregnancy, a foetus is a growing infant.
Note: The foetal stage lasts from the beginning of the ninth week after fertilisation until the average time of birth, which is about 38 weeks after fertilisation The foetal stage is a period of development for the developing baby. Organs and structures developed during the embryonic phase continue to evolve and expand.