Differentiation in multicellular organisms Key Area 4 Differentiation in multicellular organisms

Learning intention What is cellular differentiation and what does differentiation produce in plants?

Success Criteria All pupils will……. Most pupils will…. State the difference between differentiated and undifferentiated cells. Most pupils will…. Identify how old a tree is using annual rings. Some pupils will….. Explain how lateral meristems are formed.

Cellular differentiation Multi-cellular organisms are comprised of a large number of cells. These are specialised to carry out specific roles in the body. Differentiation is the process by which unspecialised cells become altered and adapted to form a special function in the body.

Selective gene expression Every cell in your body has all the genes necessary for constructing the whole organism. Genes can be switched on or switched off when they are required (see Unit 2) otherwise the body would waste energy producing proteins in cells where they are not needed. e.g. insulin produced in pancreas cells only, not in brain or heart cells.

Growth and differentiation in plants In multicellular plants growth is restricted to regions called meristems. These are groups of unspecialised plant cells capable of dividing repeatedly through out the life of the plant (by Mitosis). Some of the cells formed remain merisematic and go on to produce new cells while others become differentiated.

Types of meristem Apical meristem at the tip of the root and the shoot – adding length to the plant. Lateral meristems allow the stems to thicken.

GROWTH IN PLANTS When do plants grow? Where do plants grow? (Hint: What differences can you see in the pictures below)

Apical meristems Apical meristems in the shoot and root allow elongation – or lengthening by production of new cells making a plant grow taller This is called primary growth

The root apical meristem has two roles: 1. Those toward the top differentiate into cells of the dermal (epidermis), ground, and vascular tissue, lengthening the root. 2. Those cells produced toward the bottom of the meristem replenish root cap cells. The root cap protects the apical meristem

The shoot apical meristem : A shoot's apical meristem is a dome-shaped mass of dividing cells at the very tip of the terminal bud UPWARDS GROWTH When these cells elongate they push the apical meristem upwards leaving pockets of meristematic cells behind. These leave lateral buds at bases of new leaves

PLANT TRANSPORT TISSUES Two types of vessels are responsible for transport in plants. Phloem Transport sugar through the plant Xylem Transport water from roots

GROWTH OF TREES Get bigger year after year Needs more xylem for transport of water and for support Extra xylem produced by lateral meristems Causes stem to increase in thickness

Lateral meristems Lateral meristems are secondary growth tissues in woody plants These increase the diameter of roots and stems

Cambium is found in between phloem and xylem in stems. Epidermis Phloem Xylem Cambium The cambium cells divide to form new xylem to the inside and some phloem to the outside. It is the xylem tissue that forms annual rings in stems.

By looking at a tree trunk scientists can: Tell how old the tree is Comment on the environmental conditions during each growing season  Each tree ring (annual ring) represents a year's growth.  It consists of a cylinder of spring wood surrounded by a cylinder of denser summer wood. 

How old is this tree? Answer = 3 years

How old are these trees? A B Answer = 3 years Answer = 2 years

Spring/Summer wood summerwood springwood

 In spring the vessels are wide in diameter with thin walls, whilst in the summer/autumn they are more compact and have thicker walls.

Annual rings Each annual ring represents a years growth. Xylem cells, produced by cambium form the rings. An annual ring is a cylinder of spring wood (light) surrounded by a cylinder of summer wood (dark). Differences in ring width show variation in weather patterns from year to year, such as a particularly wet or dry spring.   Thick ring = Good growth, wet spring Thin ring = poor growth, dry spring or environmental factor

Learning intention What is cellular differentiation and what does differentiation produce in animals?

Success Criteria All pupils will……. Most pupils will….. State what the basic role of a stem cell is. Most pupils will….. Describe how even though all cells share the same genetic code they can perform different functions. Some pupils will…… Explain the difference between a multipotent and pluripotent cell.

Differentiation in animals Each human life begins life as a fertilised egg (zygote) and divides to become approximately 37.2 trillion (37 200 000 000 000) With almost 200 different cell types.

Recap - Mitosis Cell division is the process in living organisms that produces new cells. When organisms grow and repair (e.g cuts or broken bones) they produce new cells by the process of cell division.

HOW DOES A CELL BECOME SPECIALISED? The sequence of DNA = the sequence of amino acids. Amino acids join to form proteins. What roles can proteins play?

CELL SPECIALISATION The cells of our body are controlled by their genetic information. All cells in multicellular organisms contain the same genetic information. So… how does our body create so many different types of cell?

Stem cells Before a cell has differentiated, or specialised, it is called a stem cell. Stem cells are cells that can make more of themselves and can become almost any specialised cell. STEM cells are involved in growth and repair.

GENETIC CONTROL AND SPECIALISATION Cells differ because genes can be switched on and off When a new cell is produced by mitosis it is non-specialised or undifferentiated. Specialisation depends on which genes are switched on and off

GENETIC CONTROL AND SPECIALISATION Not all of the proteins encoded by a cell’s DNA are needed for its specific function To perform their specific function certain genes need to be switched on and certain genes need to be switched off. This means different types of cells make different proteins

Why differentiate and specialise? Differentiated cells have a limit to the number of times they can divide The only 2 cells which can replicate indefinitely are STEM cells and CANCER cells This is what eventually causes old age

VIDEO – STEM CELLS

Types of Stem cells EMBRYONIC STEM CELLS Embryonic STEM Cells are obtained from in-vitro fertilisation embryos that were not used and are cultured in the lab in order to grow more cells. Embryonic STEM cells become differentiated to all possible types of specialised cells. This is known as PLURIPOTENT

Types of stem cells ADULT/TISSUE STEM CELLS Few in the body. Can only form a limited range of cell types. Main function is to maintain growth and repair of the body. They can only specialise if they are taken out of the body and are started by chemicals which switch certain genes on or off. Are more limited than embryonic stem cells and so are known as MULTIPOTENT.

Where can Stem Cells be found? surface of the eye brain skin breast intestines (gut) testes bone marrow muscles

Animation http://www.educationscotland.gov.uk/highersciences/biology/animations/stemcell.asp https://www.youtube.com/watch?v=jF2iXpoG5j8

To finish In your own words write in your jotter your understanding of a what a stem cell is to summarise the lesson. You should be including the words Unspecialised, develop, specialised, genes, tissue, embryonic, multipotent and pluripotent.

Success Criteria All pupils will……. Most pupils will….. State what the basic role of a stem cell is. Most pupils will….. Describe how even though all cells share the same genetic code they can perform different functions. Some pupils will…… Explain the difference between a multipotent and pluripotent cell.