Root system extracts minerals (nitrates & phosphates) along with water from the soil. The main root has lateral divisions that are either shallow or deep depending on the water availability of water.
Stem structure supports leaf and contains the vascular tissue that transports substances around the plant.
3. Petioles divisions of the stem. They support the leaf and contains branches of the vascular tissues.
4. Leaf large surface area to absorb light energy for photosynthesis. Concentrated within the palisade tissue of the leaf is chlorophyll to absorb the photons of light.
5. Auxiliary bud provide the tissues for the growth of lateral branches in future growing seasons.
6. Terminal bud contains the structures for the growth and elongation of the main stem.
Tissue types of the plant stem :
Epidermis: made of a number of layers often with a waxy cuticle to reduce water loss.
Cortex Tissue : Forming a cylinder of tissue around the outer edge of the stem providing additional support to the plant.
Vascular bundle : contains xylem, phloem and cambium tissue.
Xylem : tubes that conduct water from the roots upward to the leaves.
Phloem transports sap through the plant tissue in a number of possible directions.
Cambium . The cambium produces the secondary xylem and phloem from lateral meristem tissue.
Pith tissue composed of thin walled cells called parenchyma .
Leaf transverse section (TS)
Lower epidermis contains the stomatal pores
Leaf tissue distribution and function
(a ) Cuticle made of wax for the conservation of water within the leaf. The wax also prevents herbivore or frost damage damage
(b) Upper epidermis supportive and protective function
(c) Palisade mesophyll layer is the main photosynthetic region of the leaf
(d) Spongy mesophyll creates the spaces for the movement of gases and water vapor
(e) Lower epidermis provides a supportive function for the leaf
(f) Stomatal pores which allows gas exchange with the atmosphere
9.1.2 Differences between dicotyledonous and monocotyledonous structure
Monocot of dicot?
Monocot of dicot?
a) The fibrous branching roots of the monocotyledon
b) The tap root structure with lateral roots of the dicotyledon .
Dicot & Monocot
9.1.3 Leaf tissue distribution and function
(a) Phloem transports the products of photosynthesis (sugars, amino acids).
(b) Xylem transports water and minerals into the leaf tissue from the stem and roots.
(c) Epidermis produces a waxy cuticle for the conservation of water.
(d) Palisade layer which is the main photosynthetic region.
(e) Spongy layer creates the spaces and surfaces for the movement of water and gases.
(f) Lower epidermis contains the stomatal pores which allow gas exchange with the leaf.
The xylem and phloem tissues combine in the vascular tissue to provide support to the leaf.
Monocot or Dicot? copyright
Which is the Monocot?
9.1.4 Modification of root, stem and leaf
A. Modification of leaf and stem (Bulbs) :
Onions & Lilies are a collection of thick underground leaves used to store food. Bulbs also contain short underground stems.
The horizontal stems called runners spread out from the main body of the plant, it can establish itself independently. (asexual reproduction).
The horizontal stems are often an adaptation to finding water.
Modification of leaf and stem
: e.g. Cacti
Leaves are reduced to spines to prevent water loss in transpiration.
The stem is enlarged for the storage of water .
The stem carries out photosynthesis
Spines are the leaves
Tap Root modification
Example Carrot :
Function: Storage of water.
Carrot plants are often associated with very sandy soils. The enlarged root is familiar to those who have eaten the vegetable.
The root modification allows the storage of water in the cortex and central stele.
The mass of the root stabilizes the plant in the loose sandy soils.
9.1.5 Apical and lateral (or secondary) meristem in dicotyledonous
Plants growth is restricted to
'embryonic' regions called meristems.
Apical meristems found at the tip of the root and the shoot, adding growth to the plant. The apical meristems tends to add length to root and stem.
Root apical meristem:
(a) Root cap.
(b) Root apical meristem.
(c) Ground meristem.
(e) Epidermal tissue of the root.
(f) Vascular tissue (central stele).
At the Terminal Bud (Apical meristem (AB))
Stem differentiation at the apical meristem.
The diagram illustrate that the tissue added at the apical meristem differentiates into the various primary plant body structure (AB)
This tissue diagram is a cross section of the stem of the primary plant body.
This means that there has been no additional secondary thickening of the cell walls, as in the next slide.
Lateral meristem is secondary growth adding thickness usually in the following years in a perennial plant with two types tissue :
1. Cambium that produces secondary xylem and phloem
2. Cork cambium produces some of the bark layer of a stem.
Auxin role in plant growth
Tropism growth movement either toward or away from a directional stimulus.
Phototropism is the bending-growth towards a source of light.
Auxins are a class of plant growth hormones (growth regulating factor)
Coleptile produces Auxins which promote plant growth
Tropism : plants response to a stimulus Here light is the stimulus
Charles Darwin’s Experiment
Darwin’s studied the of effects auxin on movement.
Darwin studied phototropism using the germinating stem of the canary grass.
The cylindrical shoot is enclosed in a sheath of cells called the coleoptile.
Darwin set out to determine which region of the coleoptile is sensitive to light.
(a) When there is a unilateral light shinning on one side of a coleoptile there is a bending growth movement towards the light.
(b) Decapitation of the tip results in no bending growth suggesting that this region is possibly sensitive to the light stimulus.
(c) The opaque cap prevents light from reaching the tip without damaging the tip as in (b). There is no bending-growth response.
(d) The buried coleoptile (except tip) show that it is not the lower stem section that is responding to light but rather the tip.
Darwin's experiments suggest that the tip is the region sensitive to light. Darwin concluded, " when seedlings are freely exposed to a lateral light some influence is transmitted from the upper to the lower part, causing the latter to bend".
Part 2: Transport in Angiospermophytes
Functions of the root include:
Absorption of minerals and water
Anchor the plant.
Contain root hairs that increase surface area for absorption to occur.
The extension of the cell wall increases the surface area for the absorption of water and minerals at the cellular level.
The root hair cell provides both an increase in the cell wall (apoplastic pathway ) and the cytoplasmic route (symplastic pathway ) for the movement of water
9.2.1 Root systems for the uptake of water and minerals .
Monocotyledon root has a fibrous highly branching structure which increases the surface area for the absorption of water.
(b) Dicotyledon root structure has a main tap root and often a surface branching root system for the absorption of surface run off.Deeper in the soil the tap root branches to access deeper water and mineral.
Tap Root & Fibrous Root
9.2.2 Passive Movement of minerals to the root
Minerals move to the root system by the following pathways without active transport :
1. Diffusion which requires a concentration gradient (Note that in general minerals are in very low concentration in soil).
2. Fungal hyphae is a fungal mutualistic relationship with the plant root provides minerals such as nitrates. Fungal hyphae form a network (mycelium) that increases the surface area within the root to concentrate minerals.
3.Mass flow of soil water (minerals solutions).
• Minerals dissolved in water form hydrogen bonds with water such that the movement of water towards the root 'drags' the minerals with the water .
• The mass flow of the solutions of mineral ions towards the root 'concentrates' them for absorption.
9.2.3 Active Transport of minerals to the root
Any fertile soil contains at least some clay particles within its structure.
Clay particles carry a negative electrical charge to which the mineral ions (K + , Na + , Ca 2+ ) attach.
This attachment effectively prevents the leaching of the mineral ions from the soil.
Unlike animal cell there are no potassium-sodium pumps in the cell membranes of plant cells. Rather there are proton pumps which pump protons ( H + ) outside of the cell. This creates an electro-negative charge within the cell.
When the root cells secrete protons into the surrounding soil water the hydrogen ions displace the mineral ions from the clay particle, freeing them into solution.
The mineral ions in the soil water are free to be absorbed by various pathways.
Absorption of mineral ions
The plasma membrane of the plant cell can bring about the absorption of mineral by two different energy demanding processes:
• Indirect method in which proton pumps (hydrogen pumps) establish electrochemical gradients
• Direct method in which membranes actively transport a particular mineral.
Proteins in the membrane pumps hydrogen ions out into the soil water. This creates a membrane potential of -120 mV.
Two things happen as a result
A. Hydrogen ions combine with negative ions like Cl - and are carried across the membrane.
B. The H + displace K + from the clay particles so that they are free to move by facilitated diffusion.
Direct method of active mineral absorption:
The Positive ions such as K + which are free and in solution in the soil water can be taken up by active transport membrane pumps.
Active transport of Cations: Ion Exchange
Active Tranport of Anions : Symport
9.2.4 Plant support
Plants have a 'architectural‘
structure to provide support
Thick cellulose cell wall.
2. Xylem contains rings of cellulose and lignin.
3. Turgor Pressure
Thickening of the cellulose cell wall
1. Thickened cellulose cell walls
• C hollenchyma acts like a cylinder with extra cellulose tissue.
• S clerenchyma as additional thickening in the cell wall.
In the diagram to the above left the xylem shows a cylinder of cellulose cell wall with annular lignification in rings.
2. The use of Lignin to strength xylem tissue
3. Turgor Pressure: Support for plants generated by wall pressures
• a) Water enters the cell by osmosis
• b) Volume of the cell cytoplasm increases forcing the plasma membrane against the cell wall
• c) The outward pressure is matched by an inward pressure equal in magnitude but opposite indirection
Transpiration—the loss of water vapor from the leaves and stems of plants.
9.2.6 Cohesion- Tension theory of Transpiration
Pathways for water movement:
(a) Water enters epidermal cell cytoplasm by osmosis. The solute concentration is lower than that of soil water due to the active transport of minerals from the soil water to the cytoplasm.
Symplastic Pathway (b) to (c): water moves along a solute concentration gradient. There are small cytoplasmic connections between plant cells called plasmodesmata. In effect making one large continuous cytoplasm.
Apoplastic Pathway (d) to (e): water moves by capillarity through the cellulose cell walls. Hydrogen bonding maintains a cohesion between water molecules which also adhere to the cellulose fibers.
1. From the roots : Loading water into the xylem:
• Minerals are actively loaded into the xylem which in turn causes water to enter the xylem vessel.
• Chloride for example is actively pumped from pericycle cells.
• Creating a low concentration gradient that moves water passively into the xylem.
• Xylem vessels form a continuous pipe from the root up through the stem to the leaf.
• The cytoplasm breaks down the cell wall to form the pipeline
• To support the cell wall extra thickening take place. This often has characteristic patterns. Some spiral some annular (as here). This extra thickening resists the 'tension' created by the rate of evaporation
2. From the stem
• Water evaporates into the air
• The water loss from the leaf draws new water vapor from the spongy mesophyll in the air space.
• In turn the water molecules of the mesophyll space draw water molecules from the end of the xylem (a).
• Water molecules are weakly attracted to each other by hydrogen bonds ( Cohesion ). Therefore this action extends down the xylem creating a 'suction' effect.
Stem : Water up the stem
• Some of the light energy absorbed by the leaf is changed to heat.
• This raises the temperature in the spongy mesophyll tissue, changing liquid water into water vapor causing a saturation of the air space (b).
• With the stomata open water leaves the leaf.
3. Water movement through the leaf:
9.2.7 Guard cells and transpiration regulation
Stomata ( singular Stoma ) are pores in the lower epidermis.
Each stomata is formed by two specialized Guard Cells .
The epidermis and its waxy cuticle is impermeable to carbon dioxide and water.
During the day the pore opens to allow carbon dioxide to enter for photosynthesis. However the plant will experience water loss. If the water loss is too severe the stoma will close.
During the night plants cannot photosynthesis and so the plant closes the pores thereby conserving water.
9.2.8 Abscisic hormone and guard cells
Plants have a mechanism which
closes the stoma at night.
However when a plant is
Suffering water stress (lack of
water) there is another
mechanism to close the
(a) dehydrated (low water potential) of the mesophyll cell causes them to release abscisic acid .
(b) Abscisic acid stimulates the stoma to close.
9.2.9 Abiotic factors and the rate of transpiration 1. Humidity (evaporation) 2. Wind : Moving air reduces the external water vapor concentration, still air allows the build up of boundary layers as shown above and so reduces the rate of transpiration. 3. Temperature : The leaf absorbs light and some of the light energy is lost as heat. Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises. 4. Light The rate of plants transpire is faster in the light than in the dark. This is because light stimulates the opening of the stomata and warming of the leaf.
9.2.10 Xerophytic adaptation to reduce transpiration
Plants adapted to dry environments are called
Xerophytes. Xerophytes are adaptations to
reduce water loss or indeed to conserve water.
They occupy habitats in which there is some
kind of water stress.
Adaptations include :
Life Cycle Adaptations
1. Life Cycle Adaptations
Perennial plants bloom in the wet season
Seeds have the ability to stay dormant for many years until conditions are ideal for growth
2. Physical Adaptations
Waxy Leaves : •The leaves of this plant have waxy cuticle on both the upper and lower epidermis
Rolled leaves The leaf rolls up, with the stomata enclosed space not exposed to the wind.
Hairs on the inner surface also allow water vapor to be retained which reduces water loss through the pores.
Spikes Leaves reduced to spikes to reduce water loss
V. Deep roots to reach water
Rolled Leaves / Stomatal Pits / Hairs on epidermis (Grasses)
3. Metabolic Adaptations
CAM: reduces water loss by opening pores at night but closing them during the day.
At night CO 2 is combined with (C3) to form Malic Acid (C4). This stores the CO 2 until required for photosynthesis during the day.
During the day the pore are closed and the Malic Acid degenerates to PEP (C3) and CO 2 . The CO 2 is then used in photosynthesis.
9.2.11 Active Translocation
1. The movement of organic molecules (sucrose & amino acids) from their source (where they are made) using phloem (sieve tubes and companion cells) to the sink (where they are used or stored) using energy.
2. The movement of the sap (organic molecules) requires energy.
3. In addition to the energy used water follows the high solute in the phloem by osmosis. Mass flow pressure develops moving the phloem sap forward.
*Plants will not transport glucose as it is used directly in respiration and is metabolically active. Sucrose is soluble and transportable but not metabolically active in respiration. At the sink it is necessary to have the transported molecule insoluble (no osmotic effect) and inactive ( no respiration effect).
Active translocation occurs in the Phloem (moving food around)
Sources and Sinks:
• Sources for sucrose it could be leaf, stem or a storage region at the beginning of a growing season (Tuber). For amino acids it could be the roots or tubers.
• Sinks for sucrose and amino acids it could be roots, stem, fruit or flower.
Topic 3: Reproduction in Flowering Plants
Sepals cover the flower structure while the flower is developing. In some species these are modified to ' petals'.
b) Petals surround the male and female flower parts. Function is to attract animal pollinators.
c) Stigma is the surface on which pollen lands and the pollen tube grows down to the ovary.
d) Style connects the stigma to the ovary.
e) Ovary contains the ovules (contain single egg nuclei).
f) Filaments support the anthers that contain the pollen. Together they are called the stamen.
Structure of an animal-pollinated dicotyledonous plant
• The process in which pollen is transferred from the anther to the stigma.
• Requires a vector e.g. insects mammals, winds, birds, water.
• Cross fertilization involves pollen from one plant landing on the stigma of a different plant
• Self pollination involves the transfer of the plants own pollen to its own stigma
Pollination, Fertilization and Seed Dispersal
Transfer of pollen grains from the anther to the stigma
Fusion of the gamete nuclei (in the pollen grain) with the female gamete (in the ovule) to form a zygote.
Pollen grains often contain an additional nuclei used in the ‘fertilization’ of the food store cells.
Fertilized ovules form seeds. The seeds are moved away from the parental plant before germination to reduce competition for limited resources with parental plant. There are variety of seed dispersal mechanism including fruits, winds, water and animals
T esta protects the plant embryo
b) C otyledons contain food store for the seed
c) P lumule embryonic stem
d) R adicle embryonic root
e) M icropyle is a hole in the testa (from pollen tube fertilization) through which water can enter the seed prior to germination
f) S car is where the ovule was attached to the carpel wall
T he C hildren P ureed R ed M eat S moothies
Conditions for Germination
Seeds require a combination of
• oxygen for aerobic respiration
• water to metabolically activate the cells
• temperature for optimal function of enzymes
All are need for successful germination. Each seed
has its own particular combination of the above
Conditions for Germination
It maybe that in a particular species may need to have their
seed more processed by other more specialized conditions such
• passing through digestive system of a seed dispersing animal
• washing to remove inhibitors (beans)
• erosion of the seed coat (Poppy)
These particular conditions required by a seed allows it to
match germination to favorable conditions
Germination of starchy seed
The metabolic events of seed germination :
W ater absorbed and the activation of cotyledon cells
b) Synthesis of g ibberellin which is a plant growth substance. (Hormone is no longer a term used to describe such compounds).
c) The gibberellin brings about the synthesis of the enzyme a mylase
d) S tarch is hydrolyzed to m altose before being a bsorbed by the embryonic plant
e) The maltose can be further hydrolyzed to glucose for respiration and used to g rowth.
Weird green aliens smiled making a greeting
Phytochrome and the control of flowering
Flowering Cues :
Plant have to coordinate the production of flowers to coincide with the best reproductive opportunities. There are many environmental cues that affect flowering however the photoperiod is the most reliable indicator of the time of year and therefore one of the most reliable indicators of the seasonal changes.
Short and Long day Plants :
Short day plants (SDP) typically flower in the spring or autumn when the length of day is short.
Long day plants (LDP) typically flower during the summer months of longer photoperiod
Phytochrome System :
Phytochrome is a chemical light receptor (for photoperiod/day length) in the leaf.
Phytochrome in its inactive form (when light is not striking it) exists as phytochrome red or (P r ).
When light strikes P r it is active and converted into phytochrome far red or (P fr ). The longer the day the more P fr is made.
At night the P fr is converted back into the in active phytochrome P r . The long the length of darkness the more P fr is converted back into P r .
Critical Night Length
Experiments have shown that the important factor determining flowering is the length of night rather than the length of day.
Short Day Plants (SDP) have a critical long night. High amount of (P fr ) inhibit flowering, low amounts of (P fr ) trigger flowering.
Long Day Plants (LDP) have a critical short night. High amount (P fr ) promote flowering, low amounts of (P fr ) inhibit flowering.