The life cycle of plants depends upon the alternation of generations, the fluctuation between the diploid (sporophyte) and haploid (gametophyte) life stages. In bryophytes, the gametophyte stage is dominant and comprises what we think of as the main plant. Conversely, in tracheophytes the sporophyte stage is dominant and the gametophyte is a relatively small extension of the main plant. In the typical plant life cycle, the diploid sporophyte produces (via meiosis) haploid spores, which give rise to gametophytes. These gametophytes generate male and/or female gametes, which join in sexual reproduction (fertilization) to create a zygote. The zygote becomes an embryo (encased in a seed in gymnosperms and angiosperms) that will eventually become a new sporophyte plant.
|PLANT LIFE CYCLE FOR KIDS|
Fertilization occurs when a male gamete (sperm cell) joins with an egg cell to produce a zygote. In gymnosperms and angiosperms (the seed plants), the ovule containing the egg cell becomes a seed after fertilization takes place. This seed, complete with a food source and a hard outer seed coat, protects the embryo from drying out. In angiosperms (flowering plants), the embryo is given added protection by an ovary, which develops into a fruit.
MORPHOLOGY (Morphe = form, logos = study) deals with the study of forms and features of different plant organs like roots, stems, leaves, flowers, seeds, fruits, etc.
The body of typical angiospermic plant is differentiated into an underground root system and an aerial shoot system.
Parasitic plans Depend on other plants for food and water.
They have special roots for absorption of food and water.
These roots are called Sucking roots or Haustoria.
Saprophytic plants Grow on dead organic matter, e.g., fungi.They are also called humus plant.
Symbiotic plants Symbiosis or mutual beneficial partnership of two organisms, e.g., Lichens and Rhizobium (N2 fixing bacteria).
Roots develop from radicle of seed.
Roots are non-green, underground, (+) geotropic, (-) phototropic and hydrotropic.
They do not bear buds, nodes and internodes.
Roots have unicellular root hairs.
Lateral roots arise endogenously from pericycle.
Tap roots develop from radicle. The primary root grows and gives rise to secondary and tertiary roots forming tap root system, e.g., Dicots.
Adventitious roots develop from any part of the plant body other than the radicle.
b.Absorption of water and minerals.
c.Storage of food.
d.Conduction of water.
e.Photosynthesis (Tinospora) and respiration.
Stem is ascending part of plant, formed by the prolongation of the plumule of embryo.
It bears nodes and internodes.
It has buds and may bear multi cellular hair on external surface.
MODIFICATIONS OF STEM
Rhizone It grows parallel of horizontal to soil surface.It bears nodes, Internodes, buds and leaves, e.g., Ginger.
Tuber It is terminal portion of underground stem branch which is swollen of account of accumulation of food, e.g., Potato.
Corn It grows vertically to soil surface and is covered b thin sheathing leaf bases of dead leaves called scales.
e.g., Colocasia, Gladiolus.
Phylloclade It is green flattened or rounded succulent stem with leaves either feebly developed or modified into spines
e.g., Opuntia, Euphorbia.
Cladode Phylloclade with one or two internode is called cladode.
Thorn It is modification of axillary bud. Thorns not only reduce transpiration but also check browsing by animals.
A leaf is a flat, lateral outgrowth of the stem or the branch, arising from a node and usually having a bud in its axil.
The chief functions of the leaf are photosynthesis and transpiration.
Bracts are specialized leaves arises from the axil of leaves.
The arrangement of veins and the veinlets in the lamina of leaf is called venation.
Reticulate venation The branches or veins forming a network.
Parallel venation The veins and veinlets remain parallel to each other.
Phyllotaxy is an arrangement of the leaves on the stem of branch.
Phyllotaxy is adopted so that each leaf is properly exposed to sunlight.
TYPES OF PHYLLOTAXY
Alternate a single leaf arises at each node.
Opposite single leaf arise at each node of occurs opposite to each other.
Whorled If two or more leaves arise at a node and form a whorl.
Heterophylly is occurrence of more than one type of leaves on the same plant.
e.g., Ranunculus sp.
It is the reproductive organ of a plant.
Complete flower When calyx, corolla, androecium and gynoecium are present.
Bisexual flower Both gynoecium and androecium present on the same flower.
Uni-sexual flower Either androecium (Staminate flower) or gynoecium (Pistillate flower) is present in the flower.
Actinomorphic flower When a flower is divided into two equal halves by any vertical section passing through the center.
e.g., cruciferae, Malvaceae.
Zygomorphic flower When a flower is divided into two equal halves by only one vertical section passing through the centre.
Epicalyx It is an extra whorl of sepal-like structures called bracteoles which occurs on the outside of calyx.
e.g., members of Malvaceae.
When there is no distinction of sepals and petals, the non-essential floral organs are collectively called perianth.
Types of flowers on the basis of position of ovary.
Hypogyny Ovary is at the top. Flowers are hypogynous and ovary is superior.
e.g., Malva, Brassica.
Epigyny Calyx and corolla arise from upper side of ovary. It is completely surrounded by thalamus.Ovary is inferior and flower is epigynous.
e.g., Marigold, Cucurbita maxima.
Perigymy Ovary is half superior, half inferior.
e.g., Rose, plum.
Monoecious plant When both male and female flowers are present on the same plant.
e.g., Cocos, Ricinus, Zea, Colocasia Acalypha.
Dioecious plant When male and female flower are present on separate plants.
Polygamous plant When uni-sexual (Male or female ) bisexual flowers are present on the same plant.
The arrangement of flowers and mode of distribution of flowers on the shoot system of a plant is called inflorescence.
It is of following types
a.Racemose (Indefinite) Main axis of inflorescence does not end in a flower but continues to grow.The development of flowers is acropetal. The opening of flowers is centripetal.
b.Cymose (Definite) Main axis ends in a flower. The development of flower is basipetal and opening of flowers is centrifugal.
c.Special type Capitulum is characteristic type of inflorescence in members of Compositae (Asteraceae).
Verticillaster inflorescence is characteristic of Ocimum.
Cyathium inflorescence is characteristic feature of Euphorbia.
Hypanthodium inflorescence is characteristic feature of family- Moraceae (e.g., ficus).
SOME TERMS RELATED TO ANGIOSPERMS PLANT
The study of structure and development of embryo is called Embryology.
The great embryologist of India is P Maheshwari.
Anther consisting of four microsporangia (Tetrasporangiate) is called dithecous. Anthers are reniform or kidney-shaped and consisting of two microsporangia (bisporangiate) is called as monothecous.
In Cruciferae, Stamens are six (2 outer short and 4 inner long), this condition is called tetradynamous.
Axile placentation is found in members of Malvaceae and Liliaceae.
Cereals are rich in carbohydrates and belong to family-Gramineae.
Monodelphous stamens are found in members of Malvaceae.
In members of Labiatae family, stamens are four of which two are short and two are long.Such conditioins called as didynamous.
Ovary is bicarpellary in members of family-Solanaceae.
Placentation is axile in members of Solanaceae and basal in members of Asteraceae.
Flowers are epigynous in members of family-Compositae.
The fertilized ovule forms seed.
The study of seed is called Spermology.
The seeds are of two types.
Non-endospermic or exalbuminous
Endospermic or Albuminous
Parthenocarpy The formation of fruit without fertilization is called parhenocarpy. Such fruits are seedless.
Parthenogenes is When the unfertilized egg develops into embryo, the process is called parthenogenesis.
Parthenogany When the sexual reproduction fails, then gametes directly behave as spores, these are called parthenospores or azygospores. The phenomena is called parhtenogamy.
Polyembryony The occurrence of more than one embryo in the seed is called polyembryony.
Tissue Culture Tissue culture is the technique to exploit the property of totipotency of the plant cells.
The transfer of pollen grains from the anthers of a flower to stigma of the same of different flower of the same species is called pollination.
Rose, Bryophyllum and marigold can be propagated by cutting.
Homogamy Male and female reproductive parts in bisexual flowers, mature at the same time.
Cleistogamy Sometimes bisexual flowers remain closed and never open, such flowers are known as cleistogamous.
Natural rubber is para rubber, obtained from Hevea brasiliensis.
Seeds of groundnut have 23-30% proteins.
Starch is polymer of glucose.
Coir is obtained from fibrous mesocarp of coconut.
Sunflower is cultivated for oil and ornamental flowers.
Red and black seeds of Abrus are used as jeweler’s weight.
Eucalyptus grows very fast and stem be used in paper and pulp industry.
Chief source of sugar in India is shoot of sugarcane (Saccharum officinarum).
Coffe is obtained from seeds of Coffea arabica (family-Rubiaceae).
Sunnhemp is the plant used for green manuring in India.
Botanical name of tea is Thea sinensis (family-Theaceae).
Most important cereals are rice, wheat, maize, etc.
Banana, mango and citrus are indigenous to India.
Pungent smell in garlic is due to allicin compound.
“Black gold of India”is pepper.
Cutting and peeling of onions brings tears to eyes because onion acids combines with sulphur to form amino acid sulphoxides.
The branch of Botany dealing with the internal organization of plants is called Anatomy.
A group of similar or dissimilar cells that perform a common function and have a common origin is called tissue.The tissues have been classified into two groups:
N Grew (1682) “Father of Plant Anatomy” gave the terms tissue and parenchyma.
Nageli (1850) coined the terms meristem, xylem and phloem.
Some organisms are made up of just one (single) cell, such as Amoeba.
Similar cells packed together form a tissue.
Different tissues arranged together form an organ.
Related organs together constitute an organ system.
Permanent tissues include protective tissue (e.g., Epidermis), supporting tissue (e.g., Parenchyma, collenchyma, sclerenchyma) and conducting tissue (e.g., Xylem, Phloem).
In phloem, three types of cells are sieve element, companion cells and phloem parenchyma.
Xylem consists of trachieds, vessels xylem parenchyma and xylem fibres.
Dendrology is the study of trees.
Number of annual rings decrease as well proceed forms promary xylem, phloem and vascular cambium.
In monocot leaf, mesophyll is undifferentiated and made up of only spongy parenchyma. In bicollateral vascular bundles,xylem is sandwiched between external and internal phloem.
The parenchyma cells which have large intercellular spaces are called aerenchyma, e.g., hydrophytes.
Myrmecophily is the symbiotic relationship between ants and some higher plants.The ants obtain food and shelter from the plant and protect the plant from other animals, e.g., Acacia.
Plants need mineral for growth, these are called nutrients.
There are two types of nutrients:
- Macronutrients Minerals needed in large amount.
e.g., C,H,Ca,P,Mg,O2 and S.
- Micronutrients Minerals needed by plants in trees.
e.g., FE,Zn,Cl,Cu,Mo,B and Mn.
It is the phenomenon of absorption of water of liquid by the solid particles of a substance.
The solid particles which absorb water are called Imbibants.
The liquid which is imbibed is called imbibate.
Imbibition Pressure The pressure that an imbibant develops after being imbibed is called imbibition pressure/metric potential.
It is the net movement of particles from a region of its higher concentration to a region of its lower concentration due to their own kinetic energy.
Rate of diffusion 𝝰 temperature 𝝰 1/Size or mass of particle
Diffusion pressure deficits (DPD) the difference between diffusion pressure of the solution and its solvent at a particular temperature and atmospheric conditions is called DPD.
It can be defined as a degree to which a membrane permits the movement of molecules across it.
TYPES OF MEMBRANES ON THE BASIS OF PERMEABILITY
- Permeable Membrane Allows the diffusion of both the solvent and solute molecules across it.
- Impermeable Membrane Neither the solute or solvent molecules can diffuse across membrane.
- Semipermeable Membrane Allows movement of solvent molecules across it molecules but not the solute.
- Differentially Permeable Membrane Membrane allowing diffusion of only selected molecules across it.
It is the movement of solvent molecules from the region of lower concentration to the region of higher concentration across a semipermeable membrane.
Discovered by Nollet in 1748.
TYPES OF OSMOSIS
Endoosmosis the entry of water into the cell when placed in hypotonic ( less concentrated) solution is called endoosmosis.
Exoosmosis Removal of water from a cell when placed in hypertonic (concentrated) solution is called exoosmosis.
Isotonic solutions are the solutions of same concentration no net movement of molecules occur between isotonic solution.
The Osmotic pressure The actual pressure that develops in a solution when it is separated from pure water by means of a semipermeable membrane.
So Osmotic pressure of a plant cell can vary from 4-5 atm.
Osmotic pressure = -osmotic potential.
Due to osmosis water enters into the cell sap and in turn this force the water into the cell sap, the pressure is thus developed,due to the cell wall being pressed by protoplasm and thus cell becomes turgid.This pressure is called trugor pressure/hydrostatic pressure/pressure potential.
The phenomenon of shrinkage of protoplasm from the cell wall under the influence of some hypertonic solution is called plasmolysis.
Water enter into the cell sap, the cell becomes turgid and the protoplasm again assumes its normal shape, this is called deplasmolysis.
The loss of water vapour from the living tissues of aerial part of plant.
TYPES OF TRANSPIRATION
- Stomatal Transpiration Transpiration though stomata. It accounts for 80-90% of total water loss from the plant.
- Cuticular Transpiration Cuticle is the relatively impermeable covering of plant.If it is thin and green up to 20% of transpiration can take place through it.
- Lenticular Transpiration transpiration through lenticels, i,e, an airy aggregation of cells within the structural surfaces of stem, roots other parts of vascular plants.Very little transpiration occurs through lenticels.
Photosynthesis ( Gk Photon = light, synthesis = putting together) is the anabolic process by which green plants synthesize complex carbohydrates from simple substances like carbon dioxide and water with the help of light energy.
SITE OF PHOTOSYNTHESIS
Chloroplasts are the green plastids which occur in green parts of plants are the site of photosynthesis.
Maximum number of chloroplasts are present in leaves.
Chloroplast is a double membranous organelle enclosing a liquid matrix called stroma. The lamellar system within the stroma forms flattened sac-like lamellae called thylakoids. Thylakoids are stacked to form grana. Stroma is the site of dark reaction and thylakoids for light reaction.
Pigments are the organic molecules that absorb the light of specific wavelength in the visible region.
Different types of pigments are:
b.Carotenoids and phycobilins
Chlorophylls (Gk Chlor = green, phyll = leaf ) are the green photosynthetic pigments present in all photosynthetic autotrophic organisms.
There are about ten types of chlorophylls-chl-a,b,c,d and e, bacteria chlorophyll-a,b,c and d and bacteria viridin,
Chl-a is found in all the oxygen evolving organisms.
Chlorophyll is the primary photosynthetic pigment.
STRUCTURE OF CHLOROPHYLL
It consists of porphyrin head and phytol tail.
The porphyrin head is made up of four purolle rings linked together by methane groups, forming a ring system.The centre of tetrapyrolle is occupied by a divalent Mg2+ which is complexed with the nitrogen atoms of four pyrolle rings.
The phytol tail is made up of 20 carbon alcohol and Gound in ester linkage to the 4th pyrolle ring.
MECHANISM OF PHOTOSYNTHESIS
Photosynthesis is two step process.
The first step is dependent of light and responsible for accumulation of assimilatory power.It is called light reaction.
The second step is called dark reaction as light is not required for the purpose.It is responsible for CO2 fixation into carbohydrate.
All living organisms show various changes in their weight,shape,size and volume during their entire life cycle (birth to death).It is collectively known as growth.
The growth of plants are regulated by certain chemical substances which are synthesized by them and these are called growth hormones or growth regulators.
Plant growth regulators are also called phytohomones.
Auxins promote cell elongation IAA is natural while IBA NAA and 2,4-D are synthetic auxins.
Gibberellins cause cell elongation and increase length.
Where Gibberellins are produced in embryos, roots and young leaves near the shoot tip.
It is helpful in flowering, enzyme synthesis and fruit growth.
Cytokinins promote cytokinesiis (cell division).
Kinetin was first isolated from degraded sample of DNA.
Zeatin was isolated from maize endosperm.
It is responsible for cell division, cell enlargement, prevention of senescence and enzyme synthesis.
It is gaseous hormone which is produced from the ripening fruits and mainly acts as growth inhibitor.
Ethylene hastens ripening of fruits and promote ageing of plant organs.
ABSCISSIC ACID (ABA)
It is a growth inhibitor by counteracting other hormones.
It is responsible for dormancy in buds and seeds ageing in leaves inhibits mitosis, abscission of leaves, flowers and fruits.