2.1 Secondary Tissues Flashcards
Medullary rays
Groups of parenchyma cells radiating out from the centre of the tree to outside.
Medullary rays transport substances from xylem and phloem to the inner and outer parts of stem.
Secondary xylem
Located inside vascular cambium
Xylem cells become dead cells
Forms annual rings fo trees
Vascular cambium
Lateral meristem
Responsible for production of cells that become secondary phloem and xylem
Secondary phloem
Produced by vascular cambium during secondary growth.
Inner bark
Transports sugar around plant
Living cells
Tissues that collectively make up ‘bark’
Periderm - outer bark
Phellem - just inside the outer bark; known as cork. Produced via phellogen.
Phellogen - cork cambium, produces cells for tissues outside it (phellem & periderm) and phelloderm.
Phelloderm - lies inside the phellogen - known as secondary cortex.
Phellogen or cork cambium and Vascular cambium
Found in all wood plants and some herbaceous plants.
Lateral meristems.
Produces cells which then differentiate.
Cork cambium produces cells which together comprises the bark.
Vascular cambium produces cells which become secondary xylem and phloem
Secondary tissues
Primary growth generally upwards.
Secondary growth > plant grows laterally and grows thicker.
Secondary growth is driven by two types of meristematic tissue - PHELLOGEN or CORK CANPMBIUM and VASCULAR CAMBIUM.
Role of companion cells
Some uncertainty about rôle.
Thought it regulates the activity in sieve cells.
Plays a rôle in phloem loading and unloading.
Sieve plates - description.
Area with many pores through which adjacent cells are connected by a continuous cytoplasm.
Sieve elements
In angiosperms called sieve tubes.
No nucleus
In gymnosperms and fens they are called sieve cells.
Gymnosperms sieve cells have no sieve plate > have sieve pores throughout cell wall > allow flow between adjacent cells.
Brief description of Meristematic tissue
Undifferentiated cells
All meristematic cells can divide to produce identical undifferentiated daughter cells.
Small cells with thin walls.
Large cell nuclei
Small or absent vacuoles
No inter cellular spaces.
Epidermis - brief description
Dermal tissue
Single layer of closely packed living cells.
Epidermis - position in plant
Either side of leaf
Around young stems
Around roots of vascular plants
Epidermis - function
Like human skin.
Protects inner parts of plant from abrasions and damage.
Reduces water loss.
Protects against infection.
Epidermis - special features
Stomata and guard cells embedded within epidermal layer in leaves.
Epidermal cells secrete waxy substance (cutin) this makes up cuticle and is waterproof - limits water loss.
Adapted epidermal cells called trachoms cover some leaves and stems - they have various functions.
