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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