MULTICELLULAR ORGANISMS

MULTICELLULAR ORGANISMS

Section 2b – Plant Meristems

Re-Cap

• Can you name the following cells:

• Can you describe their functions

Learning Outcomes

• Today we will learn:• - the sites of growth in a plant• - the importance of meristems• - the way that cells specialise in plants

How is the growth of plants different to the growth of animals?

Many plants can continue growing throughout their lifetime.

Most plant growth occurs by cell elongation, not cell division.

Many plant cells retain the ability to differentiate into any cell type. This is why cuttings can be used to create new plants.

Plant vs. animal growth

Growth in plants only occurs in certain tissues.

How do plants grow?

zone ofcell division

zone ofcell elongation

zone ofcell differentiation

Cell division only takes place in regions of the plant called meristems. These tissues are found in the tips of the roots and shoots – they are therefore apical meristems.

meristem

After this, cells differentiate into their final form.

Plants only get taller when cells in meristems elongate following cell division.

Plant Cell differentiation• Initially cells will

elongate• Then they will develop a

vacuole• - vacuolation• Then the cells will

specialise• - differentiation• Xylem• - will lose the vacuole,

and become hollow• - will develop lignin

Animals, plants or both?

Lateral Meristems

• Some plants grow every year - perennial

• Their stems need to thicken to support the extra growth

• This thickening is controlled by lateral meristems

• These cause the stem to get wider every year

• This is seen in rings within the stem

Cambium• A young plant will start off with a

single band of xylem and phloem• Each year a new band (or ring) of

xylem will develop• The phloem will also widen• This allows the xylem and phloem

to reach the top of the plant• In between the xylem and

phloem is a region called cambium

• Cambium is a lateral meristem • – it produces the new xylem and

phloem cells

Re-Cap questions

• 1) What is a meristem?• 2) Identify 2 regions of a plant which possess

an apical meristem?• 3) State 2 differences between a xylem vessel

and a meristematic cell• 4) Give ONE way in which growth in an animal

differs from growth in a plant