Olivia Hedges, of Ilam Primary School, asks :-

Do all animals grow?

Graham Fenwick, a zoologist with the Department of Management, University of Canterbury, responded.

Yes. Among the best growers are baby Harbour seals who treble their weight in just 5-6 weeks after birth and Blue whale calves which add the weight of a large man each day to total some 20 tonnes when 5 to 6 months old. Compare this with one of the slowest growers, a tiny deep-sea clam, which takes about 100 years to reach 8 mm long.

A chick grows within a bird's egg when a single cell of the fertilised egg divides in two and each smaller cell divides again many, many times. These cells then change into different types of cells to form the chick's organs (e.g. heart, liver, muscles, skin) until the chick is complete. This type of growth occurs in all animals that reproduce sexually.

Another type of growth is an increase in the numbers of animals, especially in colonial animals like corals. Growth involves producing more coral polyps, minute animals, which secrete more of the hard coral as they grow.

Sometimes animals ungrow as a normal part of their lives. For example, male Emperor penguins lose about a third of their body weight while incubating their single eggs on the tops of their feet.

These examples show that growth of animals is complex and involves changes in cell numbers, cell types, animal sizes and animal numbers.