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