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Growth

10 min read

What is growth?

Growth is a permanent increase in size and dry mass of an organism, made by cell division (mitosis), cell enlargement and cell differentiation. It is different from just swelling with water, which is not permanent.

A sigmoid growth curveA graph of size against time. Growth starts slowly in the lag phase, speeds up in the exponential or log phase when resources are plentiful, slows as resources run out, and levels off in the stationary phase. The whole curve is S-shaped. Populations of bacteria and many organisms follow the same pattern.timesize or numberlag phaselog (exponential)stationary phasecarrying capacity
The S-shaped growth curve.

Most organisms follow an S-shaped (sigmoid) curve. Growth is slow at first, then rapid, then slows down and stops when the adult size or the limit of resources is reached.

Slow start, rapid growth in the middle, then a plateau.

Growth in plants

Plants grow at the tips of the shoots and roots, where cells divide at regions called meristems. The germinating seed uses its stored food. Growth is measured by length, fresh mass or dry mass; dry mass is the most reliable.

A seed and germinationA bean seed has a seed coat, two seed leaves called cotyledons that store food, a radicle that becomes the root and a plumule that becomes the shoot. With water, oxygen and warmth the seed germinates: the radicle grows down first, then the plumule grows up and the first leaves open.bean seedseed coatcotyledon (food store)radicle (root)plumule (shoot)germinating seedlingneeds water, oxygen and warmth

Growth in animals

Some animals grow in a smooth way, as humans do. Insects grow by moulting their rigid skin. Many go through metamorphosis: an egg hatches into a larva that is quite different from the adult.

Complete metamorphosisA butterfly or mosquito goes through four stages. The egg hatches into a larva that feeds and grows, such as a caterpillar or a wriggler. The larva becomes a pupa in which its body is rebuilt. An adult comes out of the pupa and can fly and reproduce. In incomplete metamorphosis, as in a grasshopper, a nymph that looks like a small adult grows by moulting.Egglaid on leaves or waterLarvafeeds and growsPupabody is rebuiltAdultflies, reproduces
Try itLogistic growth

Choose how fast the organism grows and the largest size it can reach. See the size after some time.

Check yourself Which measurement of growth is most reliable?
Check yourself Where do plants grow in length?
Check yourself What is metamorphosis?

Key terms

Growth
Permanent increase in size and dry mass.
Meristem
A region of dividing cells in a plant.
Metamorphosis
A change in form between larva and adult.
Sigmoid curve
An S-shaped curve of growth.

Summary

  • Growth is a permanent increase in size and dry mass by division, enlargement and differentiation.
  • Growth follows an S-shaped curve.
  • Plants grow at meristems; insects grow by moulting.
  • Metamorphosis can be complete (egg, larva, pupa, adult) or incomplete.
Genetics