Plant tissues
Types:
vASCULAR
PERMANENT:
XYLEM: water and minerals
PHLOEM: organic/manufactured foods
meristematic:
ground
Epidermis
SCHELERNCHYMA
PARENCHYMA
COLLENCHYMA
CHLORENCHYMA
Tips of roots and stem
THEY CONTINUOUSLY DIVIDE BY MITOSIS AND
PRODUCE
NEW CELLS FOR GROWTH, REPAIR AND
Apical meristem: length
REPLACEMENT OF WORN-OUT / DAMAGED
Lateral meristem: width
TISSUE.
Cork cambium: barky/woody parts from cork cells
vascular cambium: Vascular bundle between phloem and xylem
permanent tissues=> ground -> Epidermis LINES THE SURFACES OF ROOT, STEMS AND LEAVES
IN STEM AND LEAVES, EPIDERMAL CELLS ARE COVERED BY WAXY CUTICLE
PROTECT PLANT ORGANS AND DECREASES WATER LOSS​
NO INTERCELLULAR SPACE IS PRESENT BETWEEN EPIDERMAL CELLS
permanent tissues-> parenchyma
P- packaging tissue
=FILLS UP LARGE SPACES BETWEEN
OTHER TISSUES IN ROOTS AND
STEMS​
SERVES AS PACKAGING TISSUE​
=STORES FOOD IN THE FORM OF
STARCH: large vacuole​
=ALLOWS MOVEMENT OF WATER
AND GASES THROUGH
INTERCELLULAR AIR SPACES
=large intercellular space and
2 types:
thin cell membrane and
palisade: fence-like, tightly packed
irregular
spongy: random circles, fill area
=living
MAY BE MODIFIED TO GUARD CELLS THAT CONTROL STOMATAL OPENING
MAY BE MODIFIED TO ROOT HAIRS THAT ABSORB
WATER AND MINERAL SALTS FROM SOIL
*no chloroplast
Functions:
permanent tissues->
chlorenchyma
FOUND IN LEAVES​
PRODUCES FOOD BY PHOTOSYNTHESIS
permanent tissues-> collenchyma
Collenchyma is a simple, permanent tissue typically found in
the shoots and leaves of plants. Collenchyma cells are thinwalled but the corners of the cell wall are thickened with
cellulose. This tissue gives strength, particularly in growing
shoots and leaves due to the thickened corners. The cells are
tightly packed and have fewer inter-cellular spaces.
permanent tissues-> sclerenchyma
Sclerenchyma is a simple, permanent tissue. It is the supporting tissue in
plants, making the plants hard and stiff. Two types of sclerenchyma
cells exist: fibres and sclereids.
Sclerenchyma fibres are long and narrow and have thick lignified cell
walls. They provide mechanical strength to the plant and allow for the
conduction of water.
Sclereids are specialised sclerenchyma cells with thickened, highly
lignified walls with pits running through the walls. They support the
soft tissues of pears and guavas and are found in the shells of some
nuts.
xylem
Xylem has the dual function of supporting the plant and
transporting water and dissolved mineral salts from the roots
to the stems and leaves. It is made up of vessels, tracheids, fibres
and parenchyma cells. The vessels and tracheids are non-living
at maturity and are hollow to allow the transport of water.
Both vessels and tracheids have lignin in their secondary walls,
which provides additional strength and support.
Xylem vessels are composed of a long chain of straight,
elongated, tough, dead cells known as vessel elements. The vessel
elements are long and hollow (lack protoplasm) and they make
a long tube because the cells are arranged end to end, and the
point of contact between two cells is dissolved away. The role
of xylem vessels is to transport water from roots to leaves.
Xylem vessels often have patterns of thickening in their
secondary walls. Secondary wall thickening can be in the form
of spirals, rings or pits.
Tracheids have thick secondary cell walls and are tapered at the
ends. The thick walls of the tracheids provide support and
tracheids do not have end openings like the vessels. The
tracheids' ends overlap with one another, with pairs of pits
present which allow water to pass through horizontally from
cell to cell.
vascular tissues
phloem
Phloem tissue is the living tissue responsible for transporting
organic nutrients produced during photosynthesis (mainly as
the carbohydrate sucrose) to all parts of the plant where these are
required.
sieve elements: these are conducting cells which transport sucrose.
parenchyma cells: which store food for transport in phloem.
companion cells: are associated with parenchyma cells and control the
activities of sieve tube elements, since the latter have no nuclei. Companion
cells are responsible for providing energy to the sieve elements to allow for
the transport of sucrose. Companion cells play an important role in loading
sieve tubes with sucrose produced during photosynthesis. Companion cells and
sieve tube elements are connected via connecting strands of cytoplasm called
plasmodesmata.
fibres: unspecialised cells and supportive cells
cross section of a plant root
cross section of a plant stem
phloem
xylem
cambium