Translation guide
The female reproductive cell; an egg cell. In everyday English, 'egg' is more common, but 'ovum' is used in scientific or medical contexts.
The female gamete in animals and humans, used in biology, medicine, or formal contexts.
The ovum and sperm fertilize.
General term for egg, including ovum. In biological contexts, it can mean ovum, but is broader (also bird eggs, etc.).
Mammalian ova are small.
Literally 'egg cell', used in biology to emphasize the cellular nature. More technical.
The egg cell is formed through meiosis.
Referring to a woman's egg in discussions about pregnancy, fertility treatments, or ovulation.
The female reproductive cell in plants or non-mammalian animals.
卵子 (らんし) specifically means ovum, especially in human/animal reproduction. 卵 (らん) is the general word for egg (including chicken eggs, fish eggs, etc.) and can be used for ovum in context. 卵細胞 (らんさいぼう) emphasizes the cellular aspect and is more technical.
卵子 is never used for eggs you eat. Use 卵 (たまご) for culinary eggs. 卵子 is strictly biological.
Egg quality declines with age.
Fish ova are fertilized in water.