Natural sciences Year 5: Sex cells and mating rituals
Natural sciences, Year 5 (Portugal): Two sex cells join to make a new living thing that inherits from both parents; mating rituals help the right partners meet, so that features pass on and species continue.
Two sex cells make a new individual
In sexual reproduction the key is the sex cells (gametes). The male gamete (sperm, in animals) and the female gamete (egg cell) join in fertilisation and form a fertilised egg (zygote), which grows into a new living thing. It receives features from both parents, so it resembles them without being identical. This variety is the raw material of the evolution of species.
Why animals court
Before mating, many animals perform rituals: the male peacock opens his tail, many birds sing and dance, red deer roar and fight in autumn, and white storks clatter their bills. They let animals recognise their own species, show that they are healthy and time the mating. So mating happens with a suitable partner, features pass to the offspring and the species continues.
Following a red deer's autumn
Step 1: in autumn the male red deer roars and, if another male challenges him, they fight with their antlers. Step 2: the strongest and healthiest males tend to win and to mate with more females. Step 3: in mating, the sex cells join inside the female (fertilisation). Step 4: she gives birth to a calf with features of both parents. Step 5: if the fittest males mate, useful features can pass to the calves and help the species continue.
A child is not a copy of one parent
A common idea is «the puppy is just like its mother» or «like its father». In sexual reproduction each parent gives one sex cell, so the offspring receive information from both. They may look more like one parent, like the other or like neither, but they are not a copy of anyone. And not all living things need two parents: a bacterium divides in two, and its daughter cells are almost copies of it (asexual reproduction).
Litters and pollen
The puppies in a litter are not identical to each other or to their parents: each comes from different sex cells. In flowers, bees carry pollen, which holds the male gamete, from flower to flower, and this lets seeds and fruit form: many fruit trees depend on it. People who breed animals or grow plants choose which parents to use, to get the features they want.
Test what you learned
What happens in fertilisation?
- a) One parent divides in two
- b) A male sex cell and a female sex cell join and form a fertilised egg (zygote)
- c) Two fertilised eggs merge into one adult
Correct answer: b) A male sex cell and a female sex cell join and form a fertilised egg (zygote) — Right: the zygote grows into a new living thing with features from both parents.
Why are the puppies of one litter not identical to each other?
- a) Because they eat different food
- b) Because they all copy their mother
- c) Because each puppy comes from different sex cells that combine features of both parents
Correct answer: c) Because each puppy comes from different sex cells that combine features of both parents — Right: different sex cells give different combinations, so siblings are similar but not identical.
A calf is born to a red deer stag and a hind. From whom does it inherit features?
- a) From both parents, so it can resemble one, the other or neither more closely
- b) Only from its mother
- c) Only from the stronger parent
Correct answer: a) From both parents, so it can resemble one, the other or neither more closely — Right: it gets information from both, and is not a copy of either.
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