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PPLLAA��TTSS TTIISSSSUUEESS

Classification of plants according to their complexity of their body:

a) unicellular – their body contains 1 eukaryotic cell that is responsible for all living functions

b) multicellular – their body is composed of groups of cells of the same type associate together

to form tissues, the cells in a tissue act together to perform common function

Histology – is the study of the microscopic structure plant and animal tissue

Classification of plant tissues

According to their function & structure:

1. Ground tissue (is classified according to the thickness of the cell wall)

a. parenchyma - its cells are usually loosely packed, cubed-shaped or

elongated

- cells contain a large central vacuole and have thin,

flexible cell walls

- fills internal parts of the plant’s organs

- may be adapted for storage, support, photosynthesis

- e.g. onion bulb, mesenchyme of leaf

b. collenchyma - their cell walls are irregular in shape and thickened at

the corners to provide strength and flexibility

- support the growing parts of plant

- e.g. stem of the fruits of pumpkin or cucumber, stem of

potato, stem of dead nettle

c. sclerenchyma

- sclerenchyma cells have thick, rigid cell wall

- support the non-growing parts of the plants

- e.g. pit of plum, apricot

- there are two types of cells:

i. fibres = cells up to 50 cm long that occur in

strands, e.g. linen, flax

ii. sclereids = thick wall lignified cells that cause

gritty texture of a pear

2. Vascular tissue

- carries water and nutrients throughout the plant and helps support the plant

- are typical for higher plants in which they form vascular bundles

- there are two kinds of vascular tissue:

a. xylem - moves water and minerals upward from roots to leaves

- is composed of two types of cells:

i. tracheids – are long, thick, narrow sclerenchyma

cells with thin separations between them

ii. vessel elements – are short, wide sclerenchyma

cells with no end walls; are wider than tracheids

and more water move through them

Angiosperms → contain tracheids and vessel elements

Gymnosperms → contain only tracheids

they conduct water when they are dead

and empty

alive, contain

chloroplasts in the

cells

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they are vital cells

b. phloem

- moves sugar or sap in both directions throughout the

plant originating in the leaves

- contains:

i. sieve tubes – are stacked to form long sieve

tubes with perforated end walls called sieve

plates ii. companion cells – are parenchyma cells that

enable sieve tube tubes to function

Types of vascular bundles:

1. concentrical vascular bundle

2. collateral vascular bundle

3. bicollateral vascular bundle

4. radial vascular bundle

3. Protective tissue = Dermal tissue

- forms the outside covering of the roots, stems and leaves

- its cell are arranged closely together , there are no intercellular spaces

- has protective function

• above the ground = epidermis →prevents the plant from drying out by

reducing water loss from evaporation, also secretes waxy layer called

cuticle

• below the ground = rhizodermis → protects the root, forms root hairs

that absorb water and nutrients

- special structures are derived from epidermis for keeping some specific functions

a. cuticle – thin waxy layer over the epidermis which helps

to reduce water loss

b. stoma/ stomata – openings in the epidermis that regulate

the passage of gases and moisture into and out of the

plant, contain chloroplasts

c. hydathodes – water excreting epidermal structures,

thatare formed from the stomata which lost the irability to

open and close

d. trichome = hair - are epidermal outgrowths

i. glandular – pelargonium

ii. stinging – nettle

iii. absorptive – root hair

4. Meristematic tissue

- contains cells continuously divide → are responsible for plant growth

- forms meristems = growing regions of plants

Classification of meristems according to their location:

Classification of meristems according to their ability to divide:

• primary meristems

- derived from apical meristems

- have ability to divide during whole life

a. dermatogen = protoderm - gives rise to epidermis

b. plerom – gives rise to vascular cylinder = stele

c. periblem – gives rise to primary cortex

• secondary meristems

- are derived from differentiated cells of mature tissue

- restore their ability to divide

a. vascular cambium – produces vascular tissue – secondary

xylem and phloem

b. corc canbium – produces cork (bark)

• latent meristem = “resting” meristem - is activated during the special conditions, e.g. pericycle → produces

lateral roots

PPLLAA��TT OORRGGAA��SS

Classification of plant organs according to their function:

1. vegetative – roots, stems and leaves – they provide nutrition and growth

2. generative – flowers, seeds and fruits – they provide the production of gametes

Root

- root = RADIX

- roots are structures that usually grow underground

Functions :

• to anchor the plant in the soil

• to absorb water, minerals and oxygen from the soil

• to transport water and nutrients from the soil to the rest of the plant

• to store energy reserves for the plant

• gas exchange

Root anatomy:

1 = root cap – is a protective covering of the root tip

– produces a slimy substance that functions

like lubricating oil which allows root to move

easily through the soil as it grows

2 = root tip

– contains apical meristem

3 = rhizodermis

– protective tissue of the root

– forms root hairs

4 = cortex

– is composed of parenchyma cells with

numerous air spaces

– storage place for starch or other metabolites

5 = vascular cylinder = stele

– is the core of the root

– contains:

o pericycle = 7

o phloem = 8

o xylem = 9

o pith = 10

6 = root hair

– root hairs are tiny, hairlike structures

– increase the absorpting surface of a root

system

pith rays = vascular rays (stržňové lúče)

radial vascular

bundle

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The growing part of a root is divided into three zones (they are not sharply delimited but intergrade

into each other):

1. Meristematic zone - includes the apical meristem plus nearby portions in which cell division occurs

- between the apical meristem and the root cap is a region of slowly growing cells

known as the quiescent centre

2. Zone of elongation - is immediately behind the meristematic zone

- elongation of cells in this zone causes increasing in root length

3. Zone of differentiation - here develop the differentiated tissues of the root

Secondary growth of the root

• begins when the vascular cambium and cork cambium are formed between

xylem and phloem

• the vascular cambium produces secondary xylem toward the middle part of

the root and secondary phloem outward the root

• cork cambium produces cork

Root systems

1. Taproot system

- contains 1 main root = taproot and numerous lateral roots

- the main root can grow deep, reaching water far below the surface

of the ground, it is often fleshy and adapted to store food

- the lateral roots absorb water and nutrients from a large soil area

- typical for dicots, e.g. beet, carrot, dandelion, oak

2. Fibrous root system - contains numerous extensively branched

roots which are equal in size

- the main root is usually short-lived → it is

hard to distinguish it

- roots grow near the surface and can collect

water in a wide area

- don't grow as deep as taproots, but they

spread laterally and hold the soil together

→ they are good ground covers to prevent

erosion

- typical for monocots, e.g. grasses

3. Adventitious root system - roots that form on a stem or leaf (adventitious = arising from an unusual place)

- e.g. corn, bulb of onion

Task 1

Assign the type of the root system in the following examples.

fibrous

adventitious

taproot

Shapes of roots

Filamentous root – annual herbs

Cylindrical root – horseradish

Conical root – carrot, parsley

Fusiform root – dahlia

Cylindrical-conical root

Beetlike root - beet

Metamorphosis of roots

- typical of plants which live in unusual places because they form highly specialized

roots

• Prop roots – support a plant in the muddy ground, they exist partly in the air and partly in the

waterlogged soil

e.g. corn, mangrove plant

• Air roots - obtain water and mineral nutrients from the air

e.g. typical of epiphytes such as orchids and bromeliads, philodendron

• Storage and tuberous roots - specialized for food storage

e.g., carrot, beet, sweet potato

• Mycorrhizae – is a beneficial association between roots of plants and fungi

• Root �odules - �itrogen-fixing bacteria - is a beneficial association between rhizobium

bacteria and roots of plants of the bean family

• Haustoria - parasitic plant roots that invade the tissues of a host plant and transfer nutrients

from host to parasite

e.g. mistletoe

Stem

Characteristics:

- stem = CAULOM

- aboveground part of higher plants

- produces leaves up to the sunlight

Functions:

- mechanical function → to form main axis of a plant, to increase the plant surface by

forming its lateral branches

- to hold vegetative and generative organs of the plants

- to transport water and mineral substances from the roots and products of

photosynthesis from leaves to other parts

- in some cases it has also storage function: cactus – water, tuber - nutrients

Structure of the stem:

Stem contains:

a) �odes – regions where leaves attach to a stem

b) Internodes – regions = segments between nodes

c) Axillary bud = Lateral bud – is at the point of attachment of each leaf, is

capable of developing into a new shoot

d) Apical bud = Terminal bud – is at the tip of each stem, contains an apical

meristem which is enclosed by specialized leaves called bud scales

Stem anatomy:

1. Epidermis

• protective tissue of the stem

• is composed of tightly packed cells

• can produce cuticle or may be impregnated by silicon dioxide, e.g. horsetail

2. Primary cortex

• is composed of parenchyma cells

• can contain resin, essential oil ducts and laticifers

3. Vascular cylinder

• contains: pericycle, vascular tissue = phloem (tovard the outside) and xylem

(toward the inside), pith, pith rays

Task 1

Compare the arrangement of the vascular bundles in monocots and dicots.

vascular tissue is continuous

between roots and stems, but the

arrangement of it is different in

stems than in roots

Stem branching:

1 = monopodial stem - lateral branches do not grow out the main stem

2 = sympodial stem - lateral branches grow out the main stem

3 = pleiochasial stem – the main stem stops its growth and its apical tip is divided into 2equal tips

Secondary growth in stem (typical for woody stem)

It is done through:

a) vascular cambium

- produces secondary xylem = wood to the inside and secondary phloem to the outside

of the stem

Annual rings = growth rings – are produced as result of changing between small summerwood cells

and the following year's large springwood cells

b) cork cambium

- produces :

a. cork = phellogen – waterproof, insulate and protect

underlying tissue

b. phelloderm (zelená kôra)- carries metabolic functions

Rhytidome – protective layer of mostly dead cells that covers the outside of woody stem, is produced

by the activity of the cork cambium

Lenticels – pores in the stems of woody plants that allow gas exchange

springwood → is produced during spring and

contains cells that are wide and thin walled; is

light =early wood

summerwood → is produced in summer and

contains cells that are smaller with thicker

walls; is dark = later wood

Metamorphosis of the stems

Above ground:

• runner

• stolon

• tendril - long, slender, coiling branch, adapted for climbing, e.g. vines, lianas,

pumpkin

• tiller - a grass shoot produced from the base of the stem, e.g. couch-grass

• cladode – a flattened main stem resembling a leaf, e.g. cacti, asparagus

• thorn - a sharp-pointed branch, e.g. hawthorn, blackthorn

• dwarf shoot – a lateral branch that is much smaller than the main one which

carries leaves, e.g. pine , juniper, apple tree flowers

Below ground:

• rhizome – a horizontal underground stem, e.g. lily of the valley, iris

• tuber – an underground storage organ, e.g. potato, kohlrabi

• bulb – an underground stem surrounded by fleshy leaves, e.g. onion

• corm – a stubby underground stems that store food, e.g. crocus, daffodil, sword lilly

• cormel – a small corm produced at base of parent corm

elongate, above ground growing stem, with long internodes, rooting

at the tip forming new plants; e.g. strawberry, raspberry

Leaf

Characteristics:

- leaf = PHYLOM

- grows from the node of the stem

- leaf + stem = shoot

Functions:

- is the primary site of photosynthesis because it contains chloroplasts

- provides a flat surface for maximum exposure to sunlight

- is place of transpiration - the evaporative loss of water from leaf surface

- gas exchange

- mineral intake in the form water solution

Types of leaves:

Leaf morphology:

Types of leaf venation:

a. parallel venation- with all the main veins parallel, e.g. grasses, plantain

b. pinnate venation - with a main midrib and secondary veins arising from it at intervals, e.g.

cherry tree, apple tree, linden

c. palmate venation - with the main veins all arising from one point at the base of the leaf,

e.g. maple

1 = stipule - flat, often leaf-like flap below a leaf, e.g.

rose. Not all leaves have stipules. Stipules can be highly

modified into tendrils, spines, scales

2 = petiole - the stalk of a leaf

3 = base

4 = midrib = primary vein

5 = secondary vein

6 = blade = lamina - the flat, expanded portion of the leaf

a) monofacial leaf – upper and lower part of the

blade are the same, e.g. lily of the valley, iris,

tulip

b) bifacial leaf - upper and lower part of the blade

are the different, e.g. maple, linden, dandelion

7 = apex

leaf sheathing – is typical for monocot plants

1 = broad – like leaf

2 = scale-like

3 = needle-like

venation

Forms of leaves according to their complexity:

Leaf attachment:

Petiolate - the blade is attached to the stem by a petiole.

Sessile - the blade is attached directly to the stem without a petiole.

Leaf arrangement on the stem:

compound

A = opposite –leaves are arranged

two per node

B = alternate – leaves are

arranged one per node

C = whorled – leaves are

arranged three or more per node

simple palmately pinnately bi-pinnately

LLEEAAFF AA��AATTOOMMYY

Task 1

Read the text.

The leaf is the primary photosynthetic organ of the plant. It consists of a flattened portion, called the

blade that is attached to the plant by a structure called the petiole. Sometimes leaves are divided into

two or more sections called leaflets. Leaves with a single undivided blade are called simple, those with

two or more leaflets are called compound.

The outer surface of the leaf has a thin waxy covering called the cuticle (A), this layer's primary

function is to prevent water loss within the leaf. (Plants that leave entirely within water do not have a

cuticle). Directly underneath the cuticle is a layer of cells called the epidermis (B). The vascular tissue,

xylem and phloem are found within the veins of the leaf. Veins are actually extensions that run from to

tips of the roots all the way up to the edges of the leaves. The outer layer of the vein is made of cells

called bundle sheath cells (C), and they create a circle around the xylem and the phloem. One the

picture, xylem is the upper layer of cells (D) and is shaded a little lighter than the lower layer of cells -

phloem (E). Recall that xylem transports water and phloem transports sugar (food).

Within the leaf, there is a layer of cells called the mesophyll. The word mesophyll is Greek and means

"middle" (meso) "leaf" (phyllon). Mesophyll can then be divided into two layers, the palisade layer (F)

and the spongy layer (G). Palisade cells are more column-like, and lie just under the epidermis, the

spongy cells are more loosely packed and lie between the palisade layer and the lower epidermis. The

air spaces between the spongy cells allow for gas exchange. Mesophyll cells (both palisade and

spongy) are packed with chloroplasts, and this is where photosynthesis actually occurs.

Epidermis also lines the lower area of the leaf (as does the cuticle). The leaf also has tiny holes within

the epidermis called stomata (H). Specialized cells, called guard cells (I) surround the stomata and are

shaped like two cupped hands. Changes within water pressure cause the stoma (singular of stomata) to

open or close. If the guard cells are full of water, they swell up and bend away from each other which

opens the stoma. During dry times, the guard cells close.

Task 2

Colour and name the structures desribed above. Make sure that the entire picture is coloured.

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Task 3

Answer the questions.

Questions:

1. What two tissues are found within a vein?

2. What does the word "mesophyll" mean?

3. What two layers of the plant contain chloroplasts?

4. The outermost layer of cells: _________________________

5. The waxy covering of the leaf.: _______________________

6. These cells function to open and close stomata. _____________________

7. Outer layer of the vein: ________________________

8. Column like cells that lie just under the epidermis. ___________________

9. Openings that allow for gas exchange. _________________________

10. The stalk that connects the leaf to the stem. ______________________

Anatomy of bifacial leaf:

- mesophyll consists of palisade and spongy parenchyma

- lower epidermis contains stomata

- there are collateral vascular bundles

Anatomy of monofacial leaf:

- mezophyll is not differentiated

- stomata are located on the both parts of epidermis

Leaf categories:

a) cotyledon – embryonic leaf in seed-bearing plants, e.g. monocots = 1, dicots = 2, conifers =

more than two

b) assimilatory leaf – photosynthesis, transpiration

c) stipule d) bract - a modified leaf or leaf like part just below and protecting an inflorescence

e) bracteole – a small bract

f) flower – a modified leaf

Leaf shapes:

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Leaf margins:

Metamorphosis of the leaf

• hairy leaf surface – to lessen water loss

• waxy leaf surface – to prevent water loss

• small, shiny leaves – to deflect the sun’s rays

• thicker leaves – to store water, e.g. rhubarb

• spines – e.g. cactus, acacia, barberry

• leaves to trap insect , e.g. carnivorous plant

• bulb – to store food , e.g. onion

• tendril – e.g. bean, pea

• scales – protect leaf bud