From cells to tissues

In grade 10 you were given one sentence about tissues and then moved on. This chapter is that sentence taken apart — thirteen tissues, one at a time.

Tissue

A group of cells with a common origin, shaped to carry out one definite function, held within the body of a living thing, is called a tissue.

Three things the definition asks of a group of cells

Not every collection of cells is a tissue. All three conditions have to hold at once:

They came from the same source — they are the descendants of the same dividing cells, not a crowd that happened to end up together.
They are shaped for one job. That is the idea you met in grade 10 as cells being shaped for the job they do, now applied to a whole group at once.
They sit inside a living body, as one level of its organisation: cell, then tissue, then organ, then system.

Figure to be added

Figure 1.1 — three plant tissues as they appear under a light microscope: a sheet of thin-walled cells with visible nuclei, a field of large rounded cells with thick walls between them, and a stem section showing several tissues arranged in a ring.

The word you already had, and the part that was missing

Grade 10 said a tissue is a group of cells specialised for one definite job, and stopped there. Two things were left out: that the cells share an origin, and that tissues come in kinds that can be named and told apart. This chapter supplies both.

One question, asked thirteen times

Every tissue in this chapter is met the same way: what do its cells look like, where does it sit, and what does it do. Read in that order the chapter is short, because the third answer is always readable off the first.