National 5 Biology Course Notes

Unit 2 : Multicellular Organisms

Part 1 : Cells, tissues and organs

Tissues

Tissues are groups of cells that have the same structure and function.

Each tissue consists of similar specialised cells.

e.g. ciliated epithelium in the windpipe – specialised to sweep dust out of the windpipeOrgans

An organ is made up of different types of tissue

e.g. the heart

The heart is an organ that pumps blood around the body

It is composed of several tissues, e.g.

MuscleNervous tissueBlood

A plant organ – the leaf

A leaf is an organ whose function is photosynthesis.The diagram shows the layers of cells found inside the leaf

Upper epidermis

Palisade mesophyll

Leaf tissues

Spongy mesophyll

Lower epidermis

The leaf also contains two transport tissues xylem(transports water) and phloem (transports sugar) in the leaf veins

Summary of organisation of cells in multicellular organisms

CELLSAre grouped together in

TISSUESGroups of similar cells

with the same function

Several different tissues are found in an ORGAN

Organs with similar functions are grouped into

ORGAN SYSTEMS

For example, the digestive system, the nervous system