IN MULTICELLULAR ORGANISMS

Cells are specialised for specific functions

Similar cells are grouped together into tissues

tissues grouped together into organs

organs grouped into systems 

This increases efficiency 

SINGLE CELLED ORGANISMS

Perform all essential life functions inside one cell

can't be totally efficient 

each funtion requires different cellular structure

no one cell can provide the best conditions for every function

MULTICELLULAR ORGANISMS 

CELL DIFFRENTIATION

Cells are each adapted for a specific role

They begin by all being identical

As the cell matures, it takes on individual charactersitics

cell becomes specialised in structure

This is cell diffrentiation

CELL DIFFRENTIATION 

HOW ARE THE CELLS IN A MULTICELLULAR ORGANISM DERIVED? 

Mitotic divisions of the fertilised egg

so they all contain the same genes

HOW DOES A CELL DIFFRENTIATE? 

Every cells has the same genes - they can develop into any of the cells in the organism

However only a few of the genes are switched on (expressed) 

Different genes are switched on in each type of diffrentiated cell. The rest are switched off.

HOW DO THE CELLS VARY?

Shape

numbers of organelles

e.g sperm has lots of mitochondria - bone cells have little

white blood cells have lots of lysosomes - muscle cells have little

HOW HAVE THE CELLS IN A MULTICELLULAR ORGANISM EVOLVED? 

more and more suited to one specialised function 

they have therefore lost the ability to carry out other functions

dependent on other cells to perform other activities

all cells specially adapted 

whole organism functions efficiently

TISSUES

To work efficiently, cells are aggregated together 

group of similar working cells to perfom a specific function = tissues

e.g epithelial tissue

xylem

EPITHELIAL TISSUE

Found in animals 

sheets of cells 

line surface of organs 

protective or secretory function 

many types - some made of flat thin cells - lines organs where diffusion takes place (alveoli of lungs) 

ciliated epithelium - lines a duct such as the trachea

cilia moves mucus over epithelial surface

XYLEM

Occurs in plants 

made up of lots of cell types 

transports water and mineral ions throughout plant 

also gives mechanical support 

ORGANS

Tissues aggregated into tissues 

combination of tissues

coordinated to perform a variety of functions 

one predominant function

eg. stomach 

leaf

STOMACH

Muscle - churn food and stomach contents

epithelium - protect stomach wall and produce secretions 

connective tissue - hold tissues together

LEAF

Palisade mesophyll - made up of leaf palisade cells - carry out photosynthesis

spongy mesophyll - adapted for gaseous diffusion 

epidermis - protects leaf and allows gaseous diffusion

phloem - transports organic material away from leaf

xylem - transports water and ions to leaf

HOW TO DETERMINE AN ORGAN

made up of more than one tissue

e.g veins and arteries are organs - made up of connective, epithelial and muscle tissue

whereas capillaries - just one epithelium tissue

ORGAN SYSTEMS

Organs work together in a single unit 

system grouped together for particular functions 

e.g digestive system

respiratory system

circulatory system

DIGESTIVE SYSTEM

Digests and processes food

organs - salivary glands 

oesophagus 

stomach

duodenum

ileum

pancreas

liver

RESPIRATORY SYSTEM

Used for breathing

gas exchange

organs - lungs

          trachea

         bronchi

CIRCULATORY SYSTEM

Pumps and circulates blood 

organs - heart

              arteries

           veins