- Most of the minerals present in the soil can enter into plants through roots. More than 60 types of elements are found in different plants. Which elements are found in plants, can be determined by the method called as Analysis.
- It is an important technique by which we can determine that which type of elements and in which ratio are present in plants.
- For this purpose fresh plant or a part of plant is heated at 70° to 80° C temperature for 1 to 2 days, due to the almost all the water of plant become evaporated. Dry weight of plant is measured by weighing remaining pant.
- For determination of inorganic substances in dry part of plant, dry specimen is heated in furnace at 600°C temperature, due to this all the organic material become evaporated in the form of H2O, CO2, SO2, H2, NH3, CH2 etc. Now only inorganic substances are present in remaining ash, it is called plant ash.
- About more than 60 types of elements are present in the plant body but only 17 elements are considered at essential elements.
C, H, O, N, K, S, Ca, Fe, Mg, P, Cu, Mn, B, Cl, Zn, Mo, Ni
- Except these seventeen essential elements there are some beneficial elements such as Na, Si, Se, Co.
- Among 17 essential elements C, H & O are obtained from the air and soil in the form of CO2 & H2O not in the form of ions, so these are called nonmineral nutrients or elements. Others are mineral nutrients.
Criteria for Essentiality -
- According to Arnon-criteria for essentiality of minerals are:
- The element must be necessary for normal growth and reproduction of all plants.
- The requirement of the element must be specific for plant life. That element is indispensable to the plants and is not replaceable
- The elements must be directly involved in the metabolism of the plant.
2. METHODS TO STUDY THE MINERAL REQUIREMENT OF PLANTS
- In 1860 Julius Von Sachs (a prominent german botanist) demonstrated for the first time, that plants could be grown to maturty in a defined nutrient solution in complete absence of soil.
- The technique of growing plants in a nutrient solution without soil is called as hydroponics.
- By this method, essential elements were identified and their functions and deficiency symptoms were discovered.
- The nutrient solutions must be adequately aerated to obtain the optimum growth.
- Hydroponics has been successfully employed as a technique for the commercial production of vegetables like, tomato, seedless cucumber and lettuce.
3. ESSENTIAL MINERAL ELEMENTs CLASSIFICATION OF NUTRIENTS
- On the basis of function-
- Essential elements can also be grouped into board categories on the basis of their diverse functions. These categories are;
- Essential elements as components of biomolecules and hence structural elements of cells (e.g., carbon, hydrogen, oxygen and nitrogen )
- Essential elements that are components of energy – related chemical compounds in plants (e.g., magnesium in chlorophyll and phosphorous in ATP).
- Essential elements that activate or inhibit enzymes.
(e.g., Mg, Zn, Mo etc.)
- Some essential elements can alter the osmotic potential of a cell.
(e. g., K, Cl etc.)
B. On the basis of Quantity or requirement
Arnon divided essential elements into two group on the basis of their requirement of plants-
i. Major element / Macro nutrients:
- Concentration must be excess of 10 m mole kg–1 of dry matter.
- C, H, O, N, P, K, S, Ca, Mg
ii. Minor element/ Micro nutrients:
- Concentration required less than 10 m mole kg–1 of dry matter.
- Fe, Cu, Zn, B, Cl, Mn, Mo, Ni
Mobility of minerals:
- The deficiency symptoms of highly mobile elements in plants like N, P, K, Mg first appear in older plant parts. These minerals are present as structural constituent of biomolecules of mature plant parts and when plant parts become older these biomolecules are broken down making these elements available for young plant parts.
- The deficiency symptoms of immobile elements like Ca first appear in young plant parts, as that are not transported from older plant parts to young parts.
ROLE & DEFICIENCY SYMPTOMS OF NUTRIENTS
- The concentration of the essential element below which plant growth is retarded is termed as critical concentration.
- If any element is present below the critical concentration in plant it is called deficient.
- Due to the dificiency of essential elements plants show certain morphological changes, these are called deficiency symptoms.
- These symptoms vary from element to element and disappear when the deficient element is provided to the plant.
PHOTOSYNTHESIS IN HIGHER PLANTS
1. EARLY EXPERIMENTS
- Aristotle and Theophrastus (320 BC):- State that plants absorb all food matter from soil (Humus theory).
- J. Priestley (1772):- He carried out very interesting experiment on bell jar, Rat, pudina & Candle. He came to conclude that plants purify air (burning of candles) and gaseous exchange occurs during photosynthesis. (Phlogiston ⇒ Bad air from candles)
- Jan Ingenhousz (1779): - He explained the importance of light and green colour and also suggested the O2releases in the presence of light by green parts.
- J. V. Sachs (1862): -Recognised the relation among photosynthesis, chloroplast and starch. First visible product of photosynthesis is starch. Founder of modern concept of photosynthesis. Some people consider Sachs as father of plant physiology. Three cardinal point concept wal also given by him.
- F.F. Blackman (1905): -Dark reaction associated with light reaction in photosynthesis and law of limiting factors.
- Van NIel: - O2 releases from water and O2of glucose comes from co2.
- Robert Hill & Bendal (1937):– Detailed study of light reaction in isolated chloroplast of Stellaria.
- Photolysis of H2O is the chief role of chloroplast and evolution of O2 only in the presence of suitable e– acceptor, from water in photosynthesis. (Hill–reaction)
- Ruben, Hassid & Kamen (1941):– Used O18 to experimentally show that O2 in photosynthesis released from water.
- Arnon: – ATP formation in presence of light (photophosphorylation) and cyclic and non–cyclic electron transport system.
- M. Calvin and Benson (1954):– Biochemical cyclic pathway of dark reaction and recognised PGA is Ist stable product in dark reaction. (It is formed from unstable 6C Keto Acid)
- C3 – cycle or Calvin – Benson – cycle discovered.
- Chromatography and Radioisotopy (C14) techniques used in Chlorella and Scenedesmus algae. (Nobel Prize 1960).
- Arnon, Allen & Whitley (1954):– CO2 fixation demonstrated in isolated chloroplast by C14O2 isotope.
- Hatch & Slack (1967):– C4 pathway dicarboxylic acid cycle (DCA cycle) in sugarcane and maize. IST stable product is oxaloacetic acid (OAA 4C).
- Moll: -CO2 is essential for photosynthesis by half leaf experiment.
- Bussingault:-photosynthetic Quotient (PQ) or
- Assimilatory coefficient
- Park & Biggins: - photosynthetic unit as Quantasome in chloroplast.
"Photosynthesis is a photo–biochemical process (anabolic & endergonic) in which organic compounds (carbohydrates) are synthesised from the inorganic raw material (H2O & CO2) in presence of light & pigments. O2 is evolved as a by product".
- Light energy is conserved into chemical energy by photosynthesis.
- 90% of total photosynthesis is carried out by aquatic plants (85% algae) & 10% by land plants.
- First true & oxygenic photosynthesis started in cyanobacteria. (BGA)
- Roots of Tinospora & Trapa are assimilatory or photosynthetic.
- Absorption spectrum of photosynthesis is blue & red light. (maximum absorbed part of spectrum)
- Action spectrum of photosynthesis is red & blue light. (most effective in reaction)
- Rate of photosynthesis is higher in red wavelength of light, but highest in white light (Full spectrum), than monochromatic light
IMPORTANT SCIENTIFIC CONTRIBUTION:
- According to van Niel, oxygen comes from water in photosynthesis.
6CO2 + 12H2S → C6H12O6 + 12S +6H2 O
- Ruben, Hassid and Kamen (1941):- Used O18 to show experimentally that O2 in photosynthesis comes from water.
Existence of two steps in Photosynthesis –
- Blackman discovered dark reaction (By study of Q10 value or temperature coefficient).
- Calvin and Benson gave cyclic pathway for this, thus dark reaction is called as Calvin cycle OR C3–cycle.
- Q10 (Temperature coefficient) for light reaction is one, while Q10 for dark reaction is between 2-3. (By Vont Hoff).
- Q10 means the doubling of rate of reaction, which involves chemicals, on 10°C rise in temperature in it's optimum range.
- Experimental evidences for Blackman findings were given by Warburg 1920. He carriedut intermittent light experiment on Chlorella. (by using flash light)
- The product of photosynthesis has been found greater in intermittent light (i.e., light given after intervals of dark periods) than in continuous light.
- This is due to the fact that light reactions are faster than the dark reaction. In continuous light product of light reactions (ATP and NADPH2) are not consumed at the same rate as in subsequent dark reaction. Thus dark reaction is rate limiting step of photosynthesis.
- Photosynthesis – (i) Light reactn/Hill reactn
- (ii) Dark reaction/Blackman reactn.
- Hill Reaction – Experiment on isolated chloroplast (Stelaria plant) study of light reaction, which is called as Hill Reaction.
- O2 gas liberated from photolysis of H2O, only in the presence of suitable e– acceptor. (DCPIP (Dichlorophenol Indophenol- a dye), ferricyanide, NADP+ – Hill reagents)
- Emerson & Arnold –worked on Chlorella and gave the concept of two photosystem or two pigment systems.
- When they gave only monochromatic light, longer than 680 nm wavelength, then quantum yield is suddenly dropped down, this event is called as red drop.
- When Emerson gave only monochromatic light, longer than 680 nm wavelength, then quantum yield is suddenly dropped down, this event is called red drop.
- When Emerson gave light, shorter and greater than 680 nm (combined light) then photosynthetic, activity increases, this is called as Emerson effect or enhancement effect.
- 680 nm ↑ ⇒ PS –I (cyclic process) red drop appears.
- 680 nm ↓ + 680↑ nm (Mixed light) ⇒Both cyclic & non cyclic operates. (Emerson effect)
Quantum requirement –
The number of light Quanta or photons required for the evolution of 1 mol. of O2 in photosynthesis = 8
Quantum Yield –
The number of oxygen molecule evolved by one quantum of light in photosynthesis is called as Quantum yield. Emerson calculated that the quantum requirement is 8. Hence the quantum yield is 0.125 or 12.5%)
PLANT GROWTH AND DEVELOPMENT
- Growth is a characteristic feature of all living organisms.
- Growth is an irreversible increase in size of an organ or its part or even of an individual cell.
- Growth is accompanied by metabolic processes that occurs at the expense of energy.
A. Plant Growth Generally is Indeterminate
- In plants growth continues throughout their life, so it is called as indeterminate or unlimited growth.
- Meristem continuously divides and add new cells to the plant body, such activity of meristem is called as open form of growth or indeterminate growth.
- Growth is diffused in animals but growth in plants is localised. (Presence of meristem at certain locations in plant body)
- Seed germination is the first step of plant growth. Almost all the plants face a period of suspended growth.
- If the suspension of growth is due to exogenously controlled factors (environmental factors) then it is called quiescence.
- When the suspension of growth is due to the endogenously controlled factors (hormonal, genetic) then it is termed as dormancy.
B. Growth is Measurable
- At cellular level growth can be measured by measuring the increases in the amount to protoplasm but it is very difficult to measure directly, so grow this measured by a variety of parameters, they are
- Increase in fresh weight
- Increase in dry weight
- Increase in surface area/volume
- Increase in number or size of cells
- Growth is measured by Auxanometer.
C. Phases of Growth
- Cell division or cell formation or meristematic phase: Number of cells is increased by cell divisional this phase. The cells of this region have rich protoplasm and conspicuous nuclei, thin and primary cell wall & abundant plasmodesmatal connections.
- Cell enlargement or cell elongation phase: Size of cells is increased due to vacuolation & TP (Turgor pressure) and new cell wall depositions in this phase.
- Cell maturation or differentiation phase: Cell wall thickening and Protoplasmic modifications. Qualitative changes in cells is important feature of this phase. It leads to formation of mature tissues.
D. Growth Rate
- Increased growth per unit time is termed as growth rate.
- The growth rate shows an increase that may be arithmetic or geometric.
- Arithmatic grourth= In arithmetic growth only one daughter cell among the two further divides while other differentiates and become mature (stop dividing).
- Ex. Root & Shoot elongation at constant Rate.
- It is mathematically expressed as
- Lt= L0 +rt Where Lt :length at time ‘t’
L0 –length at time ‘zero’
r- growth rate/elongation per unit time.
b. Geometric Growth: - Here both the progeny cells following mitotic decisions retain the ability to divide and continue to do so.
Ex. Early embryonic development/division in zygote, division in unicellular organism. It is mathematically represented as
Where W1- final size (Weight, height, number etc.)
W0 – initial size at the begaining of period.
r - Growth rate
e – base of natural logarithms.
Figure Diagrammatic representation of: a. Arithmatic b. Geometric growth and c. Stages during embryo development showing geometric and arithmetic phases.
TRANSPORT IN PLANTS
1. MEANS OF TRANSPORT
- The study of various vital activities and metabolism of plants is known as plant physiology.
- Plants grow in soil and absorb water and minerals, which are available in soil. So that water has great importance for plant. Water forms 80-90% of fresh weight of plant body. The method or technique, plant cells obtain water, comes under the heading of water relations.
- To understand the plant water relations, we should know the following processes :-
i. Short distance transport:
- Over small distances, substances move by diffusion and by cytoplasmic streaming. Cytoplasmic steaming is supported by active transport.
- For short distance transport vascular tissues (xylem and phloem) are not required.
ii. Long distance transport:
- Transport over long distances proceeds through the vascular system (xylem and phloem) and is called translocation.
- Over long distances substances move by bulk flow or mass flow.
“The movement of molecules or atoms or ions of a materials from an area of higher concentration to an area of their lower concentration is called diffusion”.
- The diffusion is continue till the dynamic equilibrium is not established. At this stage the net movement of molecules is equal in both direction.
- It is slow process & independent of living system.
- The kinetic energy, which is present in the molecules of material is distributed equally in their available space by their nature
Diffusion rate → Gas > Liquid > Solid Diffusion Pressure
The diffused molecules or ions exert a pressure on the substance or medium in which diffusion takes place, known as diffusion pressure.
- This is developed due to difference in the concentration of molecules of the material. Diffusion pressure of a pure solvent (1236 atm) is always higher than its solution.
- Water molecules moves from their higher concentration to the their lower concentration in plants (Down hill movement).
- The rate of diffusion decreases with increasing size of molecules.
Significance of diffusion:
- Exchange of gases like CO2, O2take place through the diffusion.
- The process of transpiration is a diffusion process. The evaporation of water from the intercellular spaces is linked with diffusion during the transpiration.
B. Facilitated Diffusion
- The diffusion of any substance across a membrane also depends on its solubility in lipids, the major constituent of the membrane (hence dependent on living system).
- Substances soluble in lipids diffuse through the membrane faster.
- Substances that have a hydrophilic moiety, find it difficult to pass through the membrane; their movement has to be facilitated.
- Membrane proteins (transmembrane proteins) provide sites at which such molecules cross the membrane.
- They do not set up a concentration gradient: a concentration gradient must already be present for molecules to diffuse even if facilitated by the proteins. This process is called facilitated diffusion.
- In facilitated diffusion special proteins help move substances across membranes without expenditure of ATP energy.
- Facilitated diffusion cannot cause net transport of molecules from a low to a high concentration – this would require input of energy.
- Transport rate reaches a maximum when all of the protein transporters are being used (saturation).
- Facilitated diffusion is very specific: it allows cell to select substances for uptake. It is sensitive to inhibitors which react with protein side chains.
- Concentration gradient = Diffusion α conc. Gradient
- Temperature =Diffusion ∝ temperature
- Diffusion pressure (DF) = D ∝ DF
- Membrane permeability = D ∝ MP
Order of rate of diffusion = Gases > Liquid >Solid
- The proteins form channels in the membrane for molecules to pass through.
- Some channels are always open; others can be controlled. Some are large, allowing a variety of molecules to cross.
- The porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria allowing molecules up to the size of small proteins to pass through.
- The transport protein then rotates and releases the molecule inside the cell, e.g., water channels – made up of eight different types of aquaporins.