Plant tissues [2015]
Transcript of Plant tissues [2015]
PLANT TISSUES
Overview
A) ORGANISATION OF THE PLANT BODYB) PLANT GROWTHC) GROUND TISSUED) EPIDERMISE) VASCULAR TISSUEF) ROOT STRUCTUREG) MONOCOT AND DICOT STEM AND VASCULAR
BUNDLES
A)ORGANISATION OF THE PLANT BODY
A tissue is an organised group of cells, working together as a functional unit
Four basic tissues
in plants:
1. Meristematic tissue
Meristem: root tip
gives rise to all other cells and tissues in the plant
2. Ground tissue
consists primarily of parenchyma cells that may live for many years
functions:storagephotosynthesis secretion parenchyma
cells
3. Epidermis (dermal tissue) one cell thick in most plants, forms the outer
protective covering
4. Vascular tissue includes the:
xylem phloem
LS stem
Two types of plant tissues
Sclerenchyma
Simple tissue composed of one type of cell :1. Parenchyma2. Collenchyma3. Sclerenchyma
Complex tissue composed of more than one type of cell: 1. Xylem [4 types]2. Phloem [5 types]
XYLEM
B) PLANT GROWTH
Growth in stems and roots is generated from specific regions of:
cell division cell expansion
Meristems:
the localised regions of cell division in plants
Meristematic tissues retain the ability to produce
new cells indefinitely
Two types of Meristemat tips of:
roots stems buds
1. Apical meristems
2. Lateral meristems
TWO types of Lateral Meristems
1. Vascular cambium:forms new xylem & phloem
2. Cork cambium: forms new protective cells in the outward
direction cell walls have suberin = waterproof
cork
TWIG WITH LENTICELS
Lenticel
Meristems may remain active for
years, or centuries.
Oldest known living plant: a bristlecone
pine, about 4,900 years-old.
Primary growth:Plant elongates
Secondary growth:Increase in girth
Lateral Meristems – secondary growth in woody plants
Basswood – root in cross section
Basswood – stem in cross section; 1, 2, 3 year old stems
C) GROUND TISSUE
collenchyma
parenchyma
sclerenchyma
Parenchyma Cells: unspecialised cells
Act as packing tissue between more specialised tissues
Parenchyma Cells
Appearance: of Parenchyma Cells variable shape with either rounded, lobed
or flattened walls
cells are usually elongated: 2-3 times long as they are wide
have:1) thin primary walls 2) large vacuoles
Primary and Secondary Cell walls
Occurrence of Parenchyma Cells1. pith of stems 1. cortex2. form a large part of the bulk of various organs as
stems and roots3. occur among the xylem vessels and phloem cells
Dicot stemMonocot stem
Parenchyma may be modified to:1. carry out
photosynthesis: chlorenchyma
2. store substances starch in potato tubers
3. help in support especially herbaceous
plants
Which of these is herbaceous?
A B
Herbaceous means
A
Non woody
Chlorenchyma in Leaf: MesophyllUPPER
EPIDERMIS
PALISADEMESOPHYLL
SPONGYMESOPHYLL
LOWEREPIDERMIS
one stoma
cuticle
xylem
phloem
O2 CO2
Aerenchyma in Aquatic Plants
Nymphaea alba (water lilly)
Aerenchyma in Aquatic Plants
LS leaf of Nymphaea alba (water lilly)
1. allow O2 to diffuse to the submerged leaves
2. provide buoyancy
Aerenchyma
Large air spaces form throughout the entire
plant and help to:
Hydrophyte leafThin cuticleUpper epidermis
Stoma
Palisade mesophyll
Buoyancy ~ gas
Spongy mesophyll (Aerenchyma)Sclereid
Lower epidermisThin cuticle
Nymphaea
Junior College MAY 2013 Paper 3 [pg. 34]On a separate blank sheet, draw a low power plan of the Nymphaea sp. (Water lily) leaf section shown. Use a X 0.9 scale. No labels or annotations are required.
NEVER draw individual cells in a LP
plan.
Characteristics of a hydrophyte:1. Aerenchyma for support2. Reduced vascular tissue3. Stomata and a cuticle on
upper epidermis only
Mare’s hare (Hippuris) stem showing reduced
vascular tissue. Cuticle is thin and wax is porous.
4. Large sclereids for support
Aqueous parenchyma• stores water in succulent plants
Cells are large Walls are thin Cells store water
in a large vacuole
• when cells use up water, the cells shrink by enfolding the wall
Aqueous parenchyma
Collenchyma: Structure:- shows many of the features of parenchyma
Is characterised by the deposition of extra cellulose
at the corners of the cells.
L.S. of Collenchyma
Function of Collenchyma- gives support and mechanical strength
Collenchyma cells in cross
section.
Note the unevenly
thickened walls.
Function of Collenchyma:- provides support in the
organs in which it occurs- important in young
plants, herbaceous plants and in leaves
Collenchyma can grow and stretch without
imposing limitations on the growth of other
cells around itCollenchyma
Distribution of Collenchyma• below the epidermis in the outer region of
the cortex and gradually merges into parenchyma towards the inside
Collenchyma
Transverse section of stem of parsnip (Pastinaca)
Transverse section of stem of a monocot
TS of part of a stem of Oxford Ragwort
Learn parts of a leaf
Collenchyma sometimes instead of rings, is deposited in bundles to form:
ridges as along the fleshy petioles of celery
Collenchyma in dicot leaves appears as:
solid masses running the length of the midrib, providing support for the vascular bundles
Transverse section of stem of parsnip (Pastinaca)
SclerenchymaFunction: support and mechanical strength
Two types of sclerenchyma cell:sclereids or stone cells
usually roughly sphericalfibres elongated cells
Sclerenchyma Fibres
Mature sclerenchyma cells are: dead incapable of elongation due to lignin
Sclerenchyma Fibers
Red cell walls: LIGNIN is stained by safranin
Distribution of sclereids:
2. in groups anywhere in the plant:
most common in: cortex, pith, phloem,
fruit and seeds
1. scattered singly
Function of sclereids:
- confer firmness or rigidity where they occur in the flesh of pear fruits =
‘grittiness’ when eaten
Sclereid from macerated tissue
Sclerenchyma sclereids
Very thick secondary
walls
The primary wall is heavily thickened with deposits of lignin
Lignin is a hard substance with high:
Tensile strength: it does not break easily on stretching
Compressional strength:it does not buckle easily
Tensile Forces Compressional
Forces
Sclerenchyma Sclereids
Simple pits
Simple pits: appear in the walls as they thicken occur in both fibres and sclereids
Simple pits arise from
plasmodesmata
Simple pits in sclerenchyma
Fibres individual sclerenchyma fibres are strong due to lignified walls
fibres are elongated with pointed ends
their strength is increased:
1. by their arrangement into strands of tissue that extend for considerable distances
2. as their ends interlock, their combined strength is enhanced
Sclerenchyma Parenchyma Collenchyma
Epidermis
Fibres occur in:1. xylem and
phloem 2. cortex below the epidermis of stems and roots
3. as a ‘cap’ in vascular bundles
Phloem
D) EPIDERMIS
Epidermis: One cell thick layer- secretes a waxy
substance called cutin - forms the cuticle
- contains no chloroplasts except for the guard cells
Function of EpidermisTo protect the plant from: desiccation abrasion infection
Epidermal cells may be specialised:
Guard cells
Trichomes
Root hairs
Epidermis
(b) Surface view of monocot leaf epidermis.
(c) Surface view of dicot leaf epidermis.
Trichomes or Hairsare outgrowths from the epidermis -
unicellular or multicellular
Trichomes or HairsFunctions:1) in climbing plants e.g. goosegrass: hooked
hairs prevent stems from slipping from their supports
2) some hairs retain moist air as in xerophytes to reduce water loss
Trichomes (hairs) in Ziziphus nummularia
Trichomes in pit to reduce water loss
LS Oleander leaf
3) they may secrete:- scents as in lavender or - enzymes as in carnivorous plants
4) glandular trichomes can be used to excrete excess salt absorbed from salty soils
Salt glands on (a) upper epidermis and (b) lower epidermis in a salt marsh plant.
Root Hairs- increase the surface area for absorption of:
water mineral salts
Piliferous layer the root hair region
E) VASCULAR TISSUE
Functions of the Vascular Tissue
XYLEMtwo major functions:1. Conduction of
water & salts2. Support
PHLOEMOne function:Translocation[has no mechanical
function]
Cells in Vascular TissueXYLEM
four cell types: 1. Tracheids2. Vessel elements /
members3. Parenchyma 4. Fibres
PHLOEM five cell types: 1. Sieve tube
elements / members2. Companion cells3. Sclereids4. Parenchyma5. Fibres
Components of Xylem
Vessel Elements/Members
Difference between a vessel and a vessel element:
Vessel
Vessel elementONE cell
MANY elements on top of each other
Tracheids: single cells - elongated and
lignified have tapering end walls that
overlap have mechanical strength give support to the plant
Tapering ends of
tracheids
TWO types of pit
Bordered pits in pine tree tracheids
Torus in pine tree
Torus
Angiosperms (flowering plants) have more vessel members than
tracheids. WHY?Vessels are more efficient for transport.
Tracheids & vessel elements compared
Vessel element
Tracheid
Open at both ends
Closed at both ends
Ends are not tapered
Ends are tapered
Short and wide
Long and narrow
No overlap Overlap
Protoxylem - the first formed xylemlocated in the apex just behind the meristem, where
elongation of surrounding cells is still occurringAnnular
thickeningSpiral
thickeningTwo types of Protoxylem
TS vascular bundle
Protoxylem allows stretchingAnnular
thickeningSpiral
thickening
Three types of Metaxylem
Protoxylem and Metaxylem
TS dicot rootLS vascular bundle (dicot)
Protoxylem and
Metaxylem
CAMBIUM
Short Questions:1. The diagrams below show cells
from a tissue of a flowering plant.a) i) Name cells A and B.
A: vessel element/member B: tracheid
ii) State one way in which the structure of cell A differs from cell B.A – wider / shorter / open at both ends / no tapering ends
b) i) In which tissue are these cells found?Xylem
ii) State two functions of this tissue.
Support. Transport of water and mineral ions.
c) Describe briefly three ways in which cell A is adapted for its functions in the plant.
1. Open at both ends – easy flow 2. No cell contents – no interference with flow3. Narrow diameter – allows for capillary action4. Lignified walls – for support / prevent lateral exit of water
3. The diagrams below show two supporting tissues present in flowering plants.
a) Give TWO structural features shown in the diagram which are characteristic of collenchyma.
1. Thickened corners of cell walls2. No intercellular air spaces.
b)i) Give TWO ways in which sclerenchyma differs from collenchyma.
1. Sclerenchyma has evenly thick cell walls but thickening at corners in collenchyma.
2. Empty lumen in sclerenchyma but living cell contents in collenchyma.
ii) Collenchyma is often present in the petiole and midrib of leaves. Suggest TWO reasons why collenchyma is more suitable than sclerenchyma for support in these locations.
1. Allows surrounding tissues to expand / grow.2. Makes leaf flexible so it will not snap.
Five Components of the Phloem1. Sieve tube elements /
members2. Companion cells3. Sclereids4. Parenchyma5. Fibres
Sieve tube elements/members: have cellulose and
pectic substances in their walls
Sieve tube elements/members: lack nuclei and tonoplast
are alive and depend on adjacent companion cells
have a sieve plate (perforations in end walls)
Callose :- is a plant polysaccharide
- is produced in response to: wounding infection by pathogens heavy metal treatment
- seals phloem sieve tube elements that are no longer functional as in winter
Protophloem and Metaphloem
What is the difference between a sieve tube element and a sieve tube?
Sieve tube element – ONE cell
Sieve tube – MANY elements on top of each other
Short Questions:
2. Complete the table by writing the appropriate word or words in the empty boxes.
Cell type One characteristic structural feature
One function
Sieve tube element
Transport of water and mineral ions
Walls thickened in the corners
Support
2. Complete the table by writing the appropriate word or words in the empty boxes.
Cell type One characteristic structural feature
One function
Sieve tube element
Sieve plate Transport of organic materials
Transport of water and mineral ions
Walls thickened in the corners
Support
2. Complete the table by writing the appropriate word or words in the empty boxes.
Cell type One characteristic structural feature
One function
Sieve tube element
Sieve plate Transport of organic materials
Tracheid / vessel element
Tapering ends /
Open at both endsTransport of water and mineral ions
Walls thickened in the corners
Support
2. Complete the table by writing the appropriate word or words in the empty boxes.
Cell type One characteristic structural feature
One function
Sieve tube element
Sieve plate Transport of organic materials
Tracheid / vessel element
Tapering ends /
Open at both endsTransport of water and mineral ions
Collenchyma Walls thickened in the corners
Support
A – epidermisB – vascular bundleC – pithD – cortexE – ground tissueF – xylemG – phloemH – sclerenchyma cap / fibres
F) ROOT STRUCTURE
Why is the vascular tissue at the centre of the root?
To withstand stretching forces.
Root Structure• Root cap covers tip• Apical meristem produces
the cap • Cell divisions at the apical
meristem cause the root to lengthen
• Further up, cells differentiate and mature
root apical meristem
root cap
Four zones/regions in developing roots:
(protects tissues behind it)
(mitosis goes on)
(cells elongate)
(root hairs develop)
pericycle
phloem
xylemroot hair
epidermis
cortexendodermis
Endodermis a single layer of cells whose primary walls
are impregnated with suberin
Suberin: is a fatty substance that is impervious to wateris produced in bands called Casparian strips
TS root
The Casparian strips are fused to the cell membranes of the endodermal cells
Casparian strip STOPS movement of water & ions via the cell wallsWhy is this important?
Function of endodermis:to protect the centre of the root (STELE) from harmful substances
All tissues interior to the endodermis are collectively called the stele
TS Dicot Root
Root Hairs and Lateral Roots• Both increase the surface area
of a root system
• Root hairs are tiny extensions of epidermal cells
• Lateral roots arise from the pericycle
newlateralroot
Lateral roots arise from the pericycle.
1 2
3 4
The magnification of the tracheid shown below is x100. Using the figure below, find the actual length in µm of the cell.
Question:
REMEMBER: 1mm = 1000 µm Magnification = size drawn actual size
Measure length: 53mmConvert to m: 53000m
100 = 53000 actual size
actual size = 53000 100
Ans: 530 m
Dicot Root
Dicot Root
Low power plan of a TS of a dicot root
LP plan of a TS dicot root
Dicot rootEndodermis having casparian strip
PericyclePhloem
Xylem
Vascular cambium
TS of a dicot root
(a) Drawing of a representative portion of the stele. (b) High power detail of the stele of Ranunculus sp. root
Question
Using the scale bar given, find the:a. magnification of the dicot root section below
13000 = 1083 12Ans: x 1083
Magnification = size drawn actual size
Measure scale bar: 13 mmConvert to m: 13000 m
Using the scale bar given, find the:
b. the actual width in m of the cortex shown in the diagram.
1083 = 24000 actual size
Magnification = size drawn actual size Measure black line in cortex:
24 mmConvert to m: 24000 m
actual size = 24000 1083
Ans: 22.16 m
TS Monocot
Root
Part of a mature root of the Iris sp. [monocot]
Parenchyma
Pith (Parenchyma)
Monocot Root Endodermis
LP of a Monocot Root
LP of a Monocot Root
Pith
Phloem
Xylem
Cortex
Exodermis
G) MONOCOT AND DICOT STEM AND VASCULAR BUNDLES
Internal Structure of a Dicot Stem
- Outermost layer is: epidermis- Cortex lies beneath: epidermis- Ring of vascular bundles separates
the cortex from the: pith
- The pith lies in the center of the stem
Why are the vascular bundles arranged in the form of ring rather than located at the
centre?
This arrangement gives flexibility to the stem.Stem can sway in the wind without breaking.The stem can resist compression and bending forces.
Stem resists:
Bending forces
Dicot Stem
TS of part of a stem of Helianthus annus (Sunflower) (x 30).
Where is the vascular
cambium?
LP plan of TS dicot stem
TS of part of a stem of Ranunculus (Buttercup)
Pith is an empty space
TS of part of a stem of Ranunculus (Buttercup)
TS of vascular
bundle of Ranunculus
Buttercup
Dicot Stem (Helianthus annus) SunflowerVascular bundles form a ring. Ground tissue toward the: inside is called pith outside is called cortex.
TS of the cortex of Helianthus annus stem: a vascular bundle in detail.
TS of the cortex of Helianthus annus stem showing a vascular bundle in detail.
Detail of Dicot Vascular Bundle
sclerenchyma
vascular cambium
phloem xylem
collenchyma
TS of the cortex of Cucurbita pepo (Vegetable Marrow) showing bicollateral arrangement
Collateral arrangement: one phloem region
Outer phloemInnerphloem
Internal Structure of a Monocot Stem
• The vascular bundles are distributed throughout the ground tissue
• No division of ground tissue into cortex and pith
TS Monocot Stem (Zea mays): Maize
TS Monocot Stem (Zea mays): Maize
LP plan of a TS monocot stem (Zea mays): Maize
Detail of Monocot Vascular Bundle Sclerenchyma
Phloem:
Sieve tube element
Companion cell
Xylem vessel element
Air space
Inside
Outside
TS of part of a stem of Triticum aestivum
(wheat)
Ammophila arenaria (Marram Grass)
a xerophyte – a plant which inhabits a dry habitat
lives in sand dunes
TS of a rolled leaf of Ammophila
Tissue map of part of the lamina of A. arenaria
Elodea stem
Elodea is a hydrophyte – a plant which lives in an aquatic environment.
Vascular tissue is: reduced located at the centre Large air spaces
Dicot Vascular Bundle
Phloem fibre cap
Guess what each picture shows:
Parenchyma
LS through a root
Which region shows the meristem?
What type of section is shown? TS
From which plant organ was this section taken?STEM
PITHFIBRES
COLLENCHYMA
What type of section is shown?TS
From which plant organ was this section taken?ROOT
TS Castalia leaf: xerophyte or hydrophyte?
Floating water plant Air spaces surrounded by aerenchyma
Compare!!
A – vascular bundleB – ground tissue
Question: [SEP, 2005]
The photomicrograph in Figure 1 shows part of Sunflower (Helianthus annus) in transverse section.
1. Through which part of the plant has this section been taken? (2)
Stem
2. Label the photomicrograph in Figure 1 to indicate the following structures:
•Epidermis•Collenchyma•Xylem•Phloem (4)
3. Is Helianthus annus a dicot plant or a monocot plant? Give a reason for your answer. (2)
Dicot. Vascular bundles at periphery of stem – scattered in a monocot. / distinct cortex and pith in dicot only.
4. Draw a labelled low power map of the section shown in Figure 1. (4)
5.Given that the magnification of the photomicrograph in Figure 1 is x30, calculate the approximate diameter of the original specimen. Show your working. (3)
Magnification = size drawn actual size
Measure vertical radius and multiply by 2
Differences between: Monocotyledons Dicotyledons
1. A large number of vascular bundles in stem.
1. A limited number of vascular bundles in stem.
2. Vascular bundles are scattered in the ground tissue.
2. The vascular bundles are arranged in a ring.
3. No cambium between the xylem and phloem.
3. Cambium between the xylem and phloem.
4. No secondary thickening.
4. Secondary thickening can occur.
Monocotyledons Dicotyledons5. No annual rings. 5. Annual rings due to
secondary thickening.
Annual rings
Monocotyledons Dicotyledons6.No distinction
between cortex and pith.
6. The cortex and pith distinguished.
7. Large metaxylem vessels.
7. Metaxylem vessels are not so large.
8. Sclerenchyma sheath around vascular bundle.
8. Sclerenchyma cap on top of vascular bundle.
Essay Titles1. Write a detailed, well-illustrated account of
the various types of tissue found in a named herbaceous angiosperm. Your account should include details of the function as well as distribution of these tissues within the plant. [MAY, 2008]
2. Write an account on supporting tissue in plants. [MAY, 2014]
THE END