Anatomy and morphology of plants

Typical Plant Cell

Typical Plant Cell
Composition of plant cell

The Plant Cell
The Plant Cell consists of a more or less rigid cell wall and the protoplast - the contents of the cell
The protoplast consists of the cytoplasm and a nucleus
The cytoplasm includes distinct membrane-bound organelles such as plastids and mitochondria; systems of membranes (endoplasmic reticulum and dictyosomes); nonmembranous entities such as ribosomes, actin filaments and microtubules
The rest of the cytoplasm is a liquid matrix in which the nucleus, various entities and membrane systems are suspended - it is typically referred to as the cytosol or ground substance

Plasma Membrane
The plasma membrane has several functions:
1. it mediates the transport of substances into and out of the protoplasm
2. it coordinates the synthesis and assembly of cellulose microfibrils
3. it relays hormonal and environmental signals involved in the control of cell growth and differentiation

Cell Walls
Found in plants (mostly cellulose) and fungi (contain chitin).
Surrounds plasma membrane

Cell Walls
Cellulose cell walls help distinguish plants from other organisms
The main component of a cell wall is cellulose arranged in microfibers
The cellulose framework is interpenetrated by a cross-linked matrix of noncellulose molecules - primarily hemicelluloses and pectins
Cell walls are layered - there is a primary cell wall, a middle lamella between two cells and sometimes a secondary cell wall

Cell Wall Structure

Cell Nucleus
The nucleus is usually the most prominent structure in the protoplast of eukaryote cells
1. it controls the ongoing activities of the cell by determining which protein molecules are produced by the cell and when they are produced
2. it stores genetic information, passing it onto daughter cells during cell division

Plastids
Plastids are a characteristic component of plant cells
Plastids are classified and named based on the kinds of pigments they contain
Each plastid is surrounded by two membranes and internally the plastid has a system of membranes which form flattened sacs called thylakoids and a ground (fluid) substance called stroma

Proplastids
Proplastids are small, colorless or pale green undifferentiated plastids that occur in meristematic cells of roots and shoots - they will eventually develop into other, differentiated plastids such as the chloroplasts, chromoplasts or leucoplasts

Chloroplasts

Plant Cells with Chloroplasts

Chromoplasts
Chromoplasts lack chlorophyll but synthesize and retain carotenoid pigments which are responsible for the yellow, orange or red colors of many flowers, old leaves, some fruits and some roots

Leucoplasts
Leucoplasts are non-pigmented plastids some of which synthesize starch while others produce oils or proteins
Upon exposure to light they may develop into chloroplasts

Vacuoles
Vacuoles are membrane bound organelles filled with cell sap
The membrane is referred to as the tonoplast
Different kinds of vacuoles may have different functions within the same cell
Along with water based cell sap, vacuoles typically contain salts, sugars and some dissolved proteins

Beetroot cell vacuoles

Vacuole and Turgor Pressure

Mitochondria
Mitochondria are another organelle bounded by two membranes
The inner membrane is folded into many pleats called cristae
Mitochondria are the sites of cellular respiration - converting organic molecules to ATP the main immediate energy source for living eukaryote cells - plant cells may have hundreds to thousands of mitochondria

Mitochondria
Break down fuel molecules (cellular respiration)
Glucose
Fatty acids
Release energy
ATP
Have their own DNA
Bound by double membrane

Endoplasmic Reticulum
Helps move substances within cells
Network of interconnected membranes
Two types
Rough endoplasmic reticulum
Smooth endoplasmic reticulum

Rough Endoplasmic Reticulum
Ribosomes attached to surface
Manufacture proteins
Not all ribosomes attached to rough ER
May modify proteins from ribosomes

Smooth Endoplasmic Reticulum
No attached ribosomes
Has enzymes that help build molecules
Carbohydrates
Lipids

Golgi Apparatus
Involved in synthesis of plant cell wall
Packaging & shipping station of cell

Golgi Apparatus Functions
1. Molecules come in vesicles
2. Vesicles fuse with Golgi membrane
3. Molecules may be modified by Golgi
4. Molecules pinched-off in separate vesicle
5. Vesicle leaves Golgi apparatus
6. Vesicles may combine with plasma membrane to secrete contents

Golgi Apparatus Function: Exocytosis

Lysosomes
Contain digestive enzymes
Functions
Aid in cell renewal
Break down old cell parts
Digests invaders

Plant Tissues Types
All plant organs (roots, stems, leaves) are composed of the same tissue types.
There are four types of tissues:
0. Meristems.
1. Dermal – outermost layer. Dermal tissue includes:
Epidermis
2. Vascular – conducting tissue, transport. Vascular tissue includes:
Xylem tissue
Phloem tissue
3. Ground – bulk of inner layers. Ground tissue includes:
Parenchyma tissue
Chlorenchyma
Collenchyma tissue
Sclerenchyma tissue

Meristems generate cells for new organs
Apical meristem
It is located at the apices or growing points of root and shoot and bring about increase in length.
It includes both pro-meristem as well as primary meristem.
Intercalary meristem
It lies between the region of permanent tissues and is considered as a part of primary meristem which has become detached due to formation of intermediate permanent tissues.
It is found either at the base of leaf e.g. Pinus or at the base of internodes e.g. grasses.
Lateral Meristem
It arranged parallel to the sides of origin and normally divide periclinally or radially and give rise to secondary permanent tissues.
It increases the thickness of the plant part.

MERYSTEM
TOPOGRAPHY

Dermal tissue
Epidermis is the outermost layer of cells
Like the “skin” of animals
In stems and leaves,
epidermis has cuticle,
a waxy layer that prevents
water loss.
Some have trichomes, hairs.
Root epidermis has root hairs, for
water and nutrient absorption

Structure of plant epidermis

Ground tissues
Collenchyma tissue:
SIMPLE
Cells are ALIVE at maturity
Contain unevenly thickened walls
Support young growing stems and organs

Ground tissues
Sclerenchyma tissue:
SIMPLE
Cells are dead at maturity
Typically lack protoplasts
Posses secondary walls with lignin
Strong polymer
Support stems and organs that have stopped growing
fibres
sclereid
Economically important tissue.
e.g. Hemp fibres

Ground tissues
Parenchyma tissue:
SIMPLE
Made up of a single cell type
Cells are ALIVE at maturity
Capable of dividing
TOTIPOTENT
Involved in wound regeneration and range of metabolic functions

Leaf Mesophyll
Middle of the leaf (meso-phyll)
Composed of photosynthetic ground cells:
Palisade parenchyma (long columns below epidermis; have lots chloroplasts for photosynthesis)
Spongy parenchyma
(spherical cells)
with air spaces around,
(for gas exchange)

Vascular tissues
Transports water and organic materials (sugars) throughout the plant
Xylem – transports water and
dissolved ions from the root
to the stem and leaves.
Phloem – carries dissolved sugars
from leaves to rest of the plant

Xylem
Transports water and dissolved minerals
Tracheids: long, thin tube like structures without perforations at the ends
Vessel elements: short, wide tubes perforated at the ends (together form a pipe, called vessel).
Both cells have pits (thin sections) on the walls
Tracheids
Vessel elements

Xylem cells
Xylem cells are dead!
They are hollow cells
and consist
only of cell wall

Phloem
Cells that transport organic materials (sugars)
Phloem cells are ALIVE (unlike xylem).
However, they lack
nucleus and
organelles

Phloem: transports sugars
Phloem composed of cells called sieve tube members (STM)
Companion cells join sieve tube members, are related, and help to load materials into STM
End walls of STM have large pores called
sieve plates
Sieve tube member
Companion cells
Sieve plates

Reproductive shoot (flower)
Apical bud
Node
Internode
Apical
bud
Shoot
system
Vegetative
shoot
Leaf
Blade
Petiole
Axillary
bud
Stem
Taproot
Lateral
branch
roots
Root
system
Plant organs and their structure and functions

Root

The primary growth of roots produces the epidermis, ground tissue, and vascular tissue
In angiosperm roots, the stele is a vascular cylinder
In most eudicots, the xylem is starlike in appearance with phloem between the “arms”
In many monocots, a core of parenchyma cells is surrounded by rings of xylem then phloem
Plant Root

Epidermis
Cortex
Endodermis
Vascular
cylinder
Pericycle
Xylem
Phloem
100 μm
Root with xylem and phloem in the center
(typical of eudicots)
Dermal
Ground
Vascular
Key
to labels

Endodermis
Pericycle
Xylem
Phloem
Dermal
Ground
Vascular
Key
to labels
50 μm
Central part of eudicot plant root
with xylem and phloem

Dermal
Ground
Vascular
Key
to labels
Epidermis
Cortex
Endodermis
Vascular
cylinder
Pericycle
Core of
parenchyma
cells
Xylem
Phloem
100 μm
Root with parenchyma in the center
(typical of monocots)

The ground tissue, mostly parenchyma cells, fills the cortex – the area between the vascular cylinder and epidermis
The innermost layer of the cortex is called the endodermis
The endodermis regulates passage of substances from the soil into the vascular cylinder
Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder
Anatomy of a Root

The emergence of a root from the pericycle

Prop roots
“Strangling”
aerial roots
Storage roots
Buttress roots
Pneumatophores
Root modifications

Types of vascular bundles in plants
1. Simple Bundles: Xylem and phloem strands are located on alternate radii in radial vascular bundles. These are mainly found in roots.
2. Conjoint bundles: Xylem and phloem combine together into one bundles, Xylem lies towards the centre and phloem towards the periphery. There are two types of conjoint bundles.
2.1. Collateral: Xylem and phloem lie on the same radius, xylem towards the centre and phloem towards the periphery. When cambium is present in collateral bundles, such bundle is called open, e.g. in dicot stems and collateral bundle without cambium is called closed, e.g. in monocot stems.
2.2. Bicollateral: The phloem strands are present on both outer and inner side of xylem.
3. Concentric Bundles: In this type of vascular bundle, one tissue is completely surrounded by the other. These are of two types Amphivasal and Amphicribral.
3.1. Amphivasal: Xylem surrounds the phloem, e.g. Dracaena.
3.2. Amphicribral: Phloem surrounds the xylem, e.g. in Ferns.

Types of vascular bundles in plants

Sclerenchyma
(fiber cells)
Phloem
Xylem
Ground tissue
connecting
pith to cortex
Pith
Cortex
Vascular
bundle
Epidermis
1 mm
1 mm
Vascular
bundles
Epidermis
Ground
tissue
Dermal
Ground
Vascular
Key
to labels
(a)
(b)
Differences between stem anatomy of monocots and dicots
In gymnosperms and most eudicots (a)
The vascular tissue consists of vascular bundles arranged in a ring
In most monocot stems (b)
The vascular bundles are scattered throughout the ground tissue, rather than forming a ring

Stem
modifications

Leaves – the main photosynthetic organs
Leaves generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem.
Monocots and eudicots differ in the arrangement of veins, the vascular tissue of leaves:
Most monocots have parallel veins.
Most eudicots have branching veins.

Simple
vs.
Compound Leaves
(a) Simple leaf
Compound
leaf
(b)
Doubly
compound
leaf
(c)
Petiole
Axillary bud
Leaflet
Petiole
Axillary bud
Leaflets
Petiole
Axillary bud

Tissue Organization of Leaves
The epidermis in leaves is interrupted by stomata, which allow CO2 exchange between the air and the photosynthetic cells in a leaf.
Each stomatal pore is flanked by two guard cells, which regulate its opening and closing.
The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis.

Below the palisade mesophyll in the upper part of the leaf is loosely arranged spongy mesophyll, where gas exchange occurs.
The vascular tissue of each leaf is continuous with the vascular tissue of the stem.
Veins are the leaf’s vascular bundles and function as the leaf’s skeleton.
Each vein in a leaf is enclosed by a protective bundle sheath.
Tissue Organization of Leaves

Key
to labels
Dermal
Ground
Vascular
Cuticle
Bundle-
sheath
cell
Xylem
Phloem
Sclerenchyma
fibers
Stoma
Upper
epidermis
Palisade
mesophyll
Spongy
mesophyll
Lower
epidermis
Cuticle
Vein
Guard
cells
Leaf Structure

Tendrils
cling
Spines “prickly” Photosynthesis is
carried out mainly by the fleshy stems
Storage Leaves succulent
plant leaves store water
Reproductive leaves
Little plantlets fall off
and take root in the soil
Bracts
Look like petals
Attract pollinators
Leaf
modifications

Flowers
What is a flower?
= Shoot system bearing modified leaves:
Perianth
Calyx (sepals) - green, protective
Corolla (petals) - colored, attractant
Stamens - male
Carpels - female

Flower parts:

Sepals
Sepals
Sepals are leaf-like structures that form an outer ring around the base of a flower.
Sepals enclose and protect a flower bud before it opens.
The complete ring of sepals is called the calyx.

Petals
Petals
Petals are often the bright and colored part of a flower.
Petal colors and scents attract specific pollinators.

Stamens
Anther
The stamen contains both the filament and the anther.
The filament is a stalk-like structure that holds the anther.
Stamens are the male reproductive parts of a flower.
Filament

Pistil
Stigma
Style
Ovary
The pistil includes
three parts:
1. Stigma
2. Style
3. Ovary

Pistil 1. Stigma
Stigma
The stigma is a sticky, flattened surface that projects upwards towards the pollinator.
Birds and insects collect nectar from previously visited plants and brush against the sticky surface of the stigma.

Pistil 2. Style
Style
The style is a supportive structure that holds the stigma in a position to maximize the chances of pollination.

Pistil 3. Ovary
Ovary
Pollen Tube
Ovule
The ovary is an enlarged structure that contains the female sex cells, or ovules.
The pollen tube grows through the ovary and into an ovule.

Receptacle
The enlarged part of the pedicel where it joins the flower is the receptacle.
Receptacle

Pedicel
Pedicel
The pedicel (flower stalk) supports the flower.

Carpels
Carpel = conduplicate megasporophyll
Conduplicate = folded
Megasporophyll = “female leaf, bearing seeds”
Carpel totally encloses ovules/seeds

Carpels can fuse together
Gynoecium = all female parts
Pistil = ovary + style + stigma
Pistil can be one carpel or many
CCC
CCC
Monocarpous
Apocarpous
Syncarpous

Functions of Carpel
Protects young seeds
Site of pollen germination
- Can induce self-incompatibility reactions
Fruits forming

Flowers can be produced singly or in inflorescences

Flower types
unisexual flowers: they have inside either pistil or stamens (a)
bisexual flowers: they have inside both pistil and stamens (b)
monoecious plant: flowers are of both sexes are in all plants (c)
dioecious plant: in one plant there are male flowers and in the other female (d)
(a)
(c)
(b)
(d)

Flower Symmetry
Flower Symmetry is the divisibility of the flower vertically in two halves.
Actinomorphic: If a flower can be divided into two equal longitudinal halves from more than one vertical planes passing through the center then it is known as an actinomorphic flower.
Zygomorphic: If a flower can be divided into two equal longitudinal halves from only one vertical plane passing through the center then it is known as a zygomorphic flower.
Asymmetrical: If a flower cannot be divided into two equal longitudinal halves from any vertical plane then it is known as an asymmetrical flower.

Fruits
Fruit = mature ovary (plus accessory parts)
Function: seed dispersal
composed of seed and pericarp
pericarp arises by the growth of cells of the ovary
kinds of fruits
Fleshy
Dry

Fleshy Fruits
fleshy fruits are dispersed by animals:
soft pericarp
pome (apple)
drupe (plum)
berry (tomato)