Course 2.1Lesson 1 of 3

Tissues and growth: meristematic tissue

A tissue is a group of similar cells that do one job together. Plants grow where their cells divide, in regions of meristematic tissue. The apical meristem makes the plant longer, the lateral meristem makes it thicker, and the intercalary meristem adds length at the base of leaves. New cells then differentiate into permanent tissue.

about 25 min1 simulation2 practice questions1 Python program5 questions to check yourself

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Many cells, shared work

An amoeba is one cell. It eats, breathes and moves, all in that one cell. A tree or a human being has many cells, and they do not all do the same job. Some cells carry messages, and some store food. This sharing of work is called division of labour.

A group of cells that are alike in structure and work together to do a particular job is a tissue. Tissues join to make organs, such as a leaf or a heart, and organs work together as an organ system.

Plants grow in some places only

A root grows longer, and a shoot grows taller. A tree trunk grows thicker year by year. But the middle of a leaf does not grow in length. Growth happens only in some regions, where the cells keep dividing. The tissue there is the meristematic tissue, or meristem.

Meristem cells are small and round, with thin walls and a large nucleus. They are packed closely with no gaps and very little vacuole. They are alive, and they divide again and again.

Three kinds of meristem

Apical meristem is at the tips of the root and the shoot. It makes them longer.
Lateral meristem, the cambium, lies in a ring along the sides of the stem and root. It makes them thicker.
Intercalary meristem is at the base of a leaf or at a node. It adds length there, which is why grass grows back after it is cut.

Two drawings. On the left, a young plant with a red dot at the tip of the shoot, at the tip of the root and at a node. These are the apical meristems and the intercalary meristem, where the plant grows in length. On the right, a cross section of a stem with a red ring between the wood and the bark. This is the lateral meristem, the cambium, where the stem grows thicker.

How fast does a meristem make cells?

Each division turns one cell into two, so the number doubles every time: 1, 2, 4, 8, 16. After $n$ divisions there are $2^n$ cells.

You should find that halving the time for one division does far more than double the cells. In two days, divisions every 12 hours give 16 cells, but divisions every 6 hours give 256.

From meristem to permanent tissue

The new cells made by a meristem do not stay the same. They take up a shape and a job, and they lose the power to divide. This is differentiation. They become permanent tissue, the subject of the next lessons.

Try it in Python

Practise with new numbers

Common mistakes

Thinking a plant grows everywhere. It grows only where meristems are.
Mixing up the meristems. Apical: tips, length. Lateral: sides, thickness. Intercalary: base of leaves.
Adding 2 cells each division. The cells double: $2^n$ .
Thinking permanent tissue keeps dividing. Differentiated cells have lost that power.

Remember these

A tissue is a group of similar cells that do one job together.
Meristematic tissue is where cells divide and the plant grows.
Apical meristem: tips, length. Lateral meristem (cambium): sides, thickness. Intercalary meristem: base of leaves.
Differentiation: cells from a meristem become permanent tissue with a shape and a job.