Plant form and function Flashcards
Tissue
A tissue is a group of 1 or more cell types carrying out specialized functions
What are primary meristems
Apical
Intercalary
Axillary bud
Intra fascicular cambium
What are secondary meristems
Inter fascicular cambium
Cork cambium
During differentiation process, they undergo changes in
cytoplasm, organelles and cell wall
Dermal tissue system
Outer covering of the plant e.g; Epidermis
Protective covering in leaves, stems and roots of primary plant body
Tightly packed single cell layer
Usually covered by a cuticle which is a waxy epidermal covering found at aerial parts
Specialized cells such as root hairs,trichomes and guard cells
Functions of ground tissue system
Storage
Photosynthesis
Support
Short distance transport
Parenchyma cells
Living evem at functional maturity
Cells have primary cell walls which are relatively thin and flexible and most of the cells lack secondary cell walls
Central vacuole present
Parenchyma cells functions
Perform most of the metabolic functions of the plant
E.g: photosynthesis fibre
Storage - some cells contains leucoplasts( plastids) in which starch is stored
Most of the parenchyma cells retain the ability to divide and differenciate under suitable conditions. This ability is important in wound repair and tissue culture practises.
Collencyma cells
Generally elongated
They have thicker primary cell walls than parenchyma and cell walls are unevenly thickned with cellulose
Young petioles and stems often have strands of collenchyma just beneath the epidermis
Living even at functional maturity
Collencyma functions
Giving mechanical support to stems and leaves without restraining growth
Sclerenchyama cells
They produce secondary cell walls after cell elongation
Secondary cell walls are thickned by a large amount of lignin
Dead at maturity
2 types of cells known as sclerides and fibers
Sclerenchyma functions
Sclerides and fibers are specialized to provide strength and support
Sclereids
Sclereids are shorter and wider than fibers and irregular in shape. They have very thick lignified secondary cell walls. They are found in places where growth has stopped e.g.nut shells, seed coats and flesh of coarse fruit
Fibers
Fibers are usually grouped in strands. They are long, slender and tapered. Used commercially to obtain fibers. e.g: coconut husk fiber, hemp fibers
Xylem
Consist of vessel elements, tracheids, fibers and parenchyma
Vessel elements and tracheids mainly conduct water
They are dead at functional maturity
Fibers give mechanical strength
Parenchyma involves in storage and in radial transport
Vessel elements
Found in all angiosperms and some gymnosperms only(Gnetum). Cylindrical and long. Shorter and wider than fibers and have thinner walls than tracheids which are thickened by lignin. They provide support to prevent collapse under tension during water transport.
End walls are perforated with perforation plates while other walls are interrupted by pits. Form xylem vessel by aligning end to end through perforation through which water moves freely.
Phloem
Consist of sieve tube elements, parenchyma, companion cells and fibers.
Sieve tube elements are not found in seedless vascular plants and gymnosperms instead long narrow cells called sieve cells are present.
Sieve tube elements
Lacks a nucleus, ribosomes, distinct vacuole and cytoskeletal structures
Cytoplasm is restricted to a thin pheripheral layer
Porus plate known as the sieve plate is found at end walls
Companion cells
Non conducting cells and are found alongside each sieve tube element. Nucleus and ribosomes serves to adjacent sieve tube elements by forming numerous plasmodesmata
Some companion cells involves in phloem loading and phloem unloading.
indeterminate growth
Plants continue growth throughout the life known as indeterminate growth.
Characteristics of meristematic cells
Living
roughly isodiametric
are structurally and functionally undifferentiated
central nucleus
dense cytoplasm
ability to multiply
During secondary growth cells in the pericycle converts to
Cork cambium
Radial and collateral vascular bundles
If xylem and phloem are not found in the same place (not connected) and have different radii it is known as an radial vascular bundle. Dicot and monocot roots contain radial vascular bundles.
If xylem and phloem are connected it is referred as collateral vascular bundles. Monocot and dicot stems contains collateral vascular bundles.
Exarch and endarch xylems
Early devoloped xylem is the protoxylem while the later developed xylem is the metaxylem
If the protoxylem is found outer to the metaxylem that is if inward growth of the xylem is present such a xylem is known as an exarch xylem. Found in monocot and dicot roots
And if the protoxylem is found inner to the metaxylem (outward growth) is is known as endarch xylem. Found in monocot and dicot stems.
Closed and open vascular bundles
If the primary meristem of intra fascicular cambium is present between the xylem and the phloem it is known as an open vascular bundle
Secondary growth
Increase in diameter of of stems and roots due to the new cells produced by lateral meristems
Periderm consist of
Cork cambium and the cork tissue
What acts as stomata during gaseous exchange of secondary stems
Lenticells
Bark consists of
Bark is all tissues out of the vascular cambium which consists of secondary phloem and periderm ( cork cambium and cork tissue)
Heart wood and sap wood
The secondary xylem no longer transporting water or minerals is known as the heart wood
Newest layers of the secondary xylem which still transports xylem sap is known as sapwood
Hard wood and soft wood
Secondary xylem of dicot angiosperms is known as hard wood while wood of gymnosperms is known as the soft wood.
Role of ABA in stomatal closure
ABA is produced in leaves and roots in response to water deficiency and leads to the closure of stomata by removing K ions. This prevents wilting of the plant.
In dicot leaves, stomata are found mainly in the
Lower epidermis
Only epidermal cells containing chloroplasts
Guard cells
Which mesophyll cells contain lower chloroplast
Spongy mesophyll
Differences between monocot leaves and dicot leaves in relation to the gaseous exchange
Monocot leaves contains stomata on both lower and upper epidermis while in dicot leaves stomata are mainly found in the lower epidermis
There is no distinction in the mesophyll layer of monocot leaves
Vascular cylinders (veins) are arranged in net like venation in dicot leaves while parallel venation is seen in monocot leaves
Structure of stomata
Stomata are microscopic pores surrounded by guard cells which are specialized epidermal cells containing chloroplast. They are typically bean shaped in angiosperms and contains walls of uneven thickness. Inner walls are thicker and relatively inelastic. Some of the microfibrils radially arrange to form inelastic hoops around the guard cells.
In plants gaseous exchange is possible via
stomata and lenticels
Gases can be exchanged via the cuticle as well
Role of ABA in stomatal closure in drought
• ABA is produced in roots and leaves in response to water deficiency.
• Production of ABA leads to close the stomata by removal of K+in guard cells.
• This prevents the wilting of the plant.
Factors affecting stomatal action
Light stimulates accumulation of K+ in guard cells
Decrease in CO2 concentration in substomatal cavity lead to open stomata
Internal clock in the guard cells
Environmental stresses
Collenchyma tissues are absent in
Roots
Passive transport methods
Diffusion
Osmosis
Imbibition
Facilitated diffusion
Bulk flow
Diffusion
In the absence of other forces, the movement of molecules of a substance from a place where it is more concentrated to a place where it is less concentrated due to the random motion of molecules.
Osmosis
The diffusion of free water molecules across a selectively permeable membrane
Imbibition
The physical absorption of water molecules from hydrophilic substances
e.g: Absorption of water molecules from cellulose cell walls
Facilitated diffusion
Movement of water and hydrophilic solutes across membranes passively with the help of transport proteins that span the membrane
Bulk flow
Movement of water and materials (entire solute) in response to a pressure gradient which is independent of solute concentration.
Water potential
The physical property that determines the direction in which water will flow governed by solute concentration and applied pressure
Measured in units of megapascals
Pressure potential of xylem vessels and living cells
Ψp of a xylem vessel is usually less than -2 MPa as xylem vessels are under tension (negative pressure)
Ψp of a living cell is a positive value because living cell is usually under positive pressure due to osmotic uptake of water.
Hypotonic solution
When the water potential of the solution is greater than the cell
Hypertonic solution
When the water potential of the solution is less than the cell
Turgid, flaccid and plasmolyse stages of a cell
Turgid - water potential is greater
Flaccid - At equilibrium (isotonic)
Plasmolysed - water potential is lower
Water and solute movements from soil solution into root hairs
Water enters to root hairs along a concentration gradient and hence it is passive
However the solute concentration in root hairs is much more greater than the soil solution hence solute movement occurs against a concentration gradient and hence active
Radial transport
Transport of water and minerals entered from soil to root cortex into the xylem of the root is known as radial transport.
Routes used in radial transport
Apoplast, symplast and trans-membrane
Apoplastic route
The apoplastic route consists of everything external to the plasma membrane of living cells and includes cell walls, extracellular spaces and the interior of dead cells such as vessel elements and tracheids.
Symplastic route
The symplast consists of the entire mass of cytosol of all living cells in a plant, as well as plasmodesmata, the cytoplasmic channels that interconnect them
Transmembrane route
The transmembrane route requires repeated crossing of plasma membranes as water and solutes exit one cell and enter the next.
Cohesion-tension hypothesis
Transpiration provides the pull for ascent of xylem sap and cohesion of water molecules transmits this pull along the entire length of xylem from roots to shoots. Hence xylem sap is normally under tension (negative pressure)
Movement of sugars from mesophyll cells to sieve tube elements occurs via
Occurs via symplast through plasmodesmata
Constituents of phloem sap
sucrose (as 30% by weight) and it may also contain
amino acids, hormones and minerals.
Phloem sap moves from source to sink at a rate about
1m/hr
Pressure flow hypothesis
- Loading of sugar into the sieve tube reduces water potential inside the sieve tube elements at the source
- This causes the sieve tube to take up water from the xylem by osmosis.
- This uptake of water generates a positive pressure that forces the sap to fl ow along the tube
- The pressure is reduced by unloading of sugar and consequent loss of water from phloem to the xylem at the sink
Transpiration
Removal of water from leaves and other aerial parts of the plant body as water vapour by diffusion is known as transpiration.
water loss takes place in plants mainly
Through stomata.-stomatal transpiration
upto some extent through cuticle-cuticular transpiration
and through lenticels- lenticular transpiration.
About 95% of water in plants is lost through stomatal transpiration.
Factors affecting the rate of transpiration
- Light intensity
- Temperature
- Humidity
- Wind speed
- Concentration of CO2
- Available water in soil
Significance of transpiration to plants
- Distribute minerals and water throughout the plant.
- Ascent of water in the xylem.
- Uptake of water and minerals by roots from the soil solution.
Root pressure and guttation
Due to the entering of water into leaves than that lost as transpiration (formation of root pressure) results in the removal of water droplets from leaf tips or leaf margins of some herbaceous plants.
Root pressure is never sufficient to push water up distance over meters
Guttation takes place through
the hydathode which are formed by special groups of cells located near the ends of small veins and does not take place through the stomata. e.g. Alocasia, Colocasia
Nutrition
Is the process of acquiring raw materials and energy from the environment for metabolic activities of organisms
Symbiosis
Is the ecological relationship in which 2 species live in close contact to each other.
E.g : for mutalism
Legume root nodules with nitrogen fixing bacteria (rhizobium)
Mycorrhizae (Association of plants with fungi)
Coralloid roots of Cycas with Anabaena
E.g : for commensalism
Epipytic Orchids
E.g : for parasitism
Semi parasitic Loranthus and Parasitic Cuscuta
E.g : for carnivorous plants
Nepenthes, Drosera, Utricularia
C,H,O deficiency
Poor growth
N
Stunted growth, chlorosis in mature leaves
K
Brown or yellow margins in leaves
Poorly developed roots
Weak stems
Ca
Crinkling of young leaves
Death of terminal buds
Mg
Chlorosis in between veins of mature leaves
P
Healthy appearance but very slow development
Thin stems
Purpling of veins
Poor flowering and fruiting
S
Chlorosis in young leaves
Cl
Wilting
Stubby roots
Leaf mottling
Fe
Cholrosis between veins in young leaves
Zn
Crinkled leaves,
reduced internode length
B
Death of meristems,
thick leathery, and discolored leaves
Cu
Light green color throughout young leaves
drying of leaf tips
roots stunted and excessively branched
Mo
Death of root and shoot
tips, chlorosis in older
leaves
Ni
Death of leaf tips,
chlorosis in older leaves
Mn
chlorosis between veins in young leaves
Major light receptors involved in photomorphogenesis
Blue light receptors
Phytochromes
Blue light receptors are involved in
Light induced stomatal opening
Phototropism
Light induced slowing of hypocotyl elongation
Phytochromes are involved in
Seed germination
Shade avoidance
Photoperiod
Is the interval in 24 hours which a plant is exposed to light
Statoliths
Plastids specialized to store starch granules
Statolith hypothesis
When a root is horizontally placed statoliths are settled at the bottom if the root cap
This sends signals to the root resulting in Ca2+ distribution which finally results in the movement of auxins to the bottom of the root
As auxins inhibits cell elongation the lower side grows slowly resulting in positive gravitropism.
Types of plant movements are
Tropic
Nastic
Tactic
Thigmonastic movements of Mimosa pudica
Touching results in the sudden loss of turgor pressure of cells in a specialized motor organ called pulvini, causing the leaflets to collapse.
Induced structural and chemical defense mechanisms in plants
Morphological changes in the cell wall
Forming cork and abscission layers
Phenolic compounds
Toxic compounds
Enzymes that can degrade fungal cell walls or damage insect organs
Plant growth regulators definition
Natural or synthetic organic compounds which modify or control physiological processes in plants.
Plant Stress
Certain factors in the environment may have potentially adverse effects on plants survival, growth and reproduction.
What are mobile elements in plants
Elements which are transported from older leaves to young leaves in a deficiency.
Which colours of light involve in stimulation and inhibition of seed germination
Stimulation by red light and inhibition by far red light
Thigmomorphogenesis
Changes in the plant form due to mechanical disturbances
