Course 2.1Lesson 2 of 3

Simple permanent tissues

Simple permanent tissues are made of one kind of cell. Parenchyma is alive, with thin walls, and stores food. Collenchyma is alive, with walls thick at the corners, and gives flexibility. Sclerenchyma is dead, with walls hardened by lignin, and gives strength. The epidermis covers the plant and has stomata, and cork forms the protective bark.

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

This lesson is free to read. Enroll free to keep your place and take the tests.

Lesson 2 of 3Show all lessons

Try the code and the simulations beside the lesson.

Permanent tissues

Cells that come from a meristem and take a fixed shape and job form permanent tissue. Simple permanent tissues are made of one kind of cell. Complex ones are made of more than one kind; they come in the next lesson.

Parenchyma

Cells: alive, with thin walls, usually round, with small spaces between them.
Job: storing food, filling space and keeping the plant firm.
Where: the soft parts, such as the inside of a stem, a root or a fruit.

Chlorenchyma is parenchyma with chloroplasts, which makes food. Aerenchyma has large air spaces; in water plants such as the water lily, the air helps them float.

Collenchyma

Cells: alive, with walls thick at the corners, from extra cellulose and pectin.
Job: flexibility, so that the plant can bend without breaking.
Where: below the skin of stems, and in leaf stalks.

Sclerenchyma

Cells: dead, long, with very thick walls hardened by lignin. Almost no space is left inside.
Job: strength and hardness.
Where: the husk of a coconut, stems, the veins of leaves, the shell of a nut.

Three drawings of plant cells in cross section. Parenchyma: round cells with thin walls and small spaces between them. Collenchyma: six-sided cells with thick walls at the corners. Sclerenchyma: six-sided cells with very thick walls and a tiny space in the middle.

You should find that a wall 1 µm thick leaves most of the cell as living space. At 9 µm the wall fills almost all of it, as in sclerenchyma, whose cells are dead.

Epidermis

The epidermis is the outer layer of cells, usually one layer thick, joined closely with no gaps. It protects the plant. In the leaf it has tiny pores, stomata. Each stoma has two bean-shaped guard cells that open and close it. Gases pass through the stomata, and water vapour is lost through them.

On leaves and stems, a waxy cuticle on the epidermis cuts water loss. The epidermis of the root has root hairs, which take in water.

Cork

As a tree grows older, its epidermis is replaced by cork. Cork cells are dead, packed with no gaps, and their walls hold a waxy substance, suberin. Water and gases cannot pass. Cork forms the bark, which protects the tree from germs and water loss.

Try it in Python

This program is a small key: it names a plant tissue from three clues.

Practise with new numbers

Common mistakes

Thinking every plant cell is alive. Sclerenchyma and cork are dead.
Mixing up collenchyma and sclerenchyma. Collenchyma bends; sclerenchyma is hard.
Calling the cuticle a layer of cells. It is a layer of wax on the epidermis.
Forgetting the guard cells. They open and close each stoma.

Remember these

Simple permanent tissue has one kind of cell.
Parenchyma: alive, thin walls, stores food. Collenchyma: alive, thick corners, flexible. Sclerenchyma: dead, lignin, hard.
The epidermis protects the plant and has stomata with guard cells. Cork is dead and waterproof, and forms the bark.