They have a double- bonded oxygen in different locations.
Ionic and Covalent bonds
Ionic bonds : Is a chemical bond between a metal and a non-metal and an electron Transfer takes place.
Covalent bonds: A chemical bond between two non-metals and an electron
Sharing takes place.
B. Sweat glands have special channels through skin
Explanation - The upper layer of skin is made up of epidermis and dead cells which is impermeable to water. However, we are able to sweat during hot weather because the sweat glands have specific opening on the surface of the skin called as pores.
The sweat is discharged through these pores. Sweat also has dissolved salts in it but it does not allows it to diffuse through the skin rather it helps in maintaining the osmoregulation of the body.
Cells build carbohydrate polymers<span> by using energy to form glycosidic linkages, the bonds between monosaccharides. A dehydration synthesis reaction forms a bond between carbon atoms in two monosaccharides, sandwiching an oxygen atom between them and releasing a water molecule</span>