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http://www
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edu
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A
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 B
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, M
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Email:

 

 

 

iakipm2004@gmail
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, Prof M
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COURSE CONTENT: 
The Plant Cell
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Introduction to Plant Classification: General characteristics and morphology of cryptogams, 
pteridophytes, gymnosperms and angiosperms
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 Students are 
expected to participate in all course activities and have a minimum of 75% attendance to be 
able to write the final examination
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 Campbell, N
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 Biology 4th Ed
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1996
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, Storey, R and Moore, R, Principle of Botany McGraw Hill, New York
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, Amusa, N
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, Soladoye, M
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 and Oyesiku, O
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 Introductory Botany
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All living organisms, large and
small, plant and animal, fish and fowl, man and microbe; are made up of cells
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basically similar to each other, having many structural features in common
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With the exception of eggs, which are the largest cells (in volume) known, cells are small and
mostly invisible to the unaided eye
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Englishman Robert Hooke first saw the remains
of dead cells in1665 in a piece of cork as he was using his newly invented microscope and he
coined the work “cell” to describe the tiny structures, thinking that they resembled the unadorned
cells occupied by the monks
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A year later one of his countrymen, Theodor Schwann,
described animal cells as being similar to plant cells
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Some 20 years after the announcement of Schleiden and Schwann,
Rudolf Virchow, a great German physician, made another important generalization; cells come
only from pre-existing cells
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Everything inside the plasma membrane is sometimes referred to as protoplasm, consisting of the
jelly like cytoplasm (cyto-cell, plasma-thing) and various structures collectively known as
organelles, including the membrane, bound nucleus
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STRUCTURE AND FUNCTIONS
The Plasma membrane: Typically the eukaryotic cell is enclosed within a thin, sturdy,
differentially permeable plasma membrane
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In some cells, such as nerve cells, the plasma membrane
also is involved in intercellular communication
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Chemically, the membrane consists of lipid (fatty material)
and protein
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The space is referred to as the Cisternea
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However, sometimes
the outer surface is filled with small particles called ribosomes, and in this case the endoplasmic
reticulum has a coarse appearance and is spoken of as rough
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E
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is found with greater
frequency and abundance in cells which are actively synthesizing protein
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The E
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by virtue of its extensive branching, functions in transport, the cisternea of the E
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apparently function as roots for transport of certain substances within the cell
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The Golgi complexes: is a stack of smooth, membranous cisternae that functions in the storage,
modification and packaging of protein products, especially secretory products
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As its products mature, the ends
of the cisternea pinch off and become membrane-bound vesicles in the cytoplasm
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Others may
contain digestive enzymes that remain in the cell that produce them
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The
enzymes they contain are involved are so powerful that they kill the cell that formed them if the

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In normal cells the enzymes remain safely enclosed within the
protective membrane
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They are diverse in size, number and shape; some are rodlike, and others are more or less
spherical
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The mitochondrion is
composed of a double membrane
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These characteristics features make
mitochondria easy to identify among the organelles
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ATP, THE MOST IMPORTANT ENERGY STORAGE MOLECULE OF THE
CELLS, IS PRODUCED IN THE ORGANELLE
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Chloroplast: the food we eat and the oxygen we breathe are produced by organelles called
chloroplasts
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They are disc-shaped bodies containing a green
pigment called chlorophyll
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Each chloroplast is surrounded by two
membranes that enclosed its contents and separate if from the cytoplasm
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The membrane system generally consists of a series of multilayered fluid-filled discs
(grana) resembling a stack of coins and a system of closed flat sacs (lamellae) extending
throughout the chloroplast and connecting the grana
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Usually there are two types; the chloroplasts (colored bodies)
and leucoplasts (white or colorless bodies)
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Other
kinds of chloroplasts give many flowers and leaves their kinds of chloroplasts give many flowers
and leaves their colors or yellow, orange or red
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Vacuoles: inner space: the cell may contain fluid filled spaces surrounded by a membrane, called
vacuoles
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These vacuoles fuse to form a large,
conspicuous central vacuole
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The vacuole of plant cells contains primarily water and some other substances
together called cell sap; because cell sap has a higher osmotic pressure than the external medium,
water moves into the cell and the cell becomes turgid
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The turgid nature of the plant cell contributes to the strength of certain plant
stems and the crispness of vegetables such as celery and lettuce
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The red color of roses and red onions is
due to the presence of anthocynanins in their vacuolar fluid
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Microtubules and microfilament: cellular movement involves two kinds of rod like structures;
microtubules and microfilaments
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Microtubules are the structural framework of
cilia and flagella; in the mitotic spindle, microtubules act to move the chromosomes during cell
division
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contain tubulin
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The muscle-like contractions of microfilaments are involved in
cell movement and changes of cell shape and in cytoplasm streaming
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This densely stained granule plays an important role in the division of animal cells
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The centrioles under the election
microscope consist of a circlet of nine microtubules, each of which is further subdivided into
three smaller tubules
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The surface of many cells has short hair like or long whiplike appendages that move fluid across
the surface of the cell
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The hair like appendages are called cilia and the whip like appendages are
called flagella
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Spermatozoa produced in the tests of the human male
are motile because of the activity of their lashing tails, which are really flagella
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Every
cilium and every flagellum is covered by the plasma membrane, and internal to this is a ring of
nine pairs of microtubules surrounding two central tubules
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The ability to move rhythmically or to beat is an inherent property of
cilia and flagella, and even when detached from the cell, they can be made to move
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The
nucleus is a relatively large structure, spherical or avoids in shape and separated from the
cytoplasm by a nuclear membrane
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The nucleus contains chromatin and one or
denser, granular structures called nucleoli (nucleolus)
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Nucleoli are
specialized parts of certain chromosomes that carry multiple copies of the DNA information to
synthesize ribosomal RNA
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The nucleolus may be thought of as the cell’s
pacemaker since any change in the activity of the nucleolus will result in a change in the growth
rate of the cell
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The Prokaryotes, meaning literally “before the nucleus” are the simplest cell known
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1 to 0
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The living portion of the cells of
bacteria and blue-greens is limited externally by a plasma membrane, outside of which a more or
less rigid cell wall and a jellylike mucilaginous capsule or sheath are present
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single chromosome comprised of a single large molecule of DNA not located in a
membranebound
nucleus, but found in a nucleus region, or nucleoid
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During cell division, the nucleoid divides without
visible chromosomes, never by true chromosomes (mitotic) division
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An internal division of labour
has taken place, accomplished by the use of membranes
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The hereditary material is enclosed in a membrane bound
nucleus and is segmented into complex nucleoprotein bodies or chromosomes, the number of
which is characteristics for each species
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Units of Classification
Species: group of individuals having very close resemblance with one another, structurally and
functionally
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Genus: collection of species which bear a close resemblance to one another as far as the
morphological characteristics of the flora in reproductive plants are concerned
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The first refers to the genus and the second to the species
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In this system the two names are latinised
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Each is
underlined/italised
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There are so many systems of
classification that have been used in botany today
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(A) Vegetative (B) Asexual (C) Sexual
Vegetative reproduction is by cell division or fragmentation of part of the plant body
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zoospores(motile spores) or ordinary non-motile spores (Gonidia)
Sexual reproduction takes place by fusion of two gametes
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In advanced members gametes become differentiated into male
gametes (antherozoids, spermatozoid or microgametes) and female gametes (mega
gametes, egg cell or oosphere or ovum)
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In
oogamous members, the male reproduction cells are small, motile, ciliated, active and initiative
while the female gametes are large, non-motile, non-ciliate, passive and receptive
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Alternation of generation
The life cycle (life history) of many flowerless plants especially the higher algae, bryophytes and
the pteridophytes is completed in two alternating stages or generation which differ in
morphology (body structure) and mode of reproduction
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One generation gives rise to the other for the life history to be
complete
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Therefore, two generations regularly alternate with each other
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In terms of chromosome number, the gametophyte with nchromosome
fuse to give a zygote with 2n chromosome (Diploid)
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Meiotic division in some cell of the saprophytic takes place to give haploid spores with n
chromosomes
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Bryophytes (Bryophyta)
The Bryophytes comprise land inhabiting autotrophic plants which prefer moist and shady
places
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True roots are absent
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Bryophytes show an advance over most algae by the development of archegonia, multicellular
antheridia and a distinct alternation of generation
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The gametophytic plant body is either thalloid (flattened) as in
the liverwort or a leaf shoot (Axial) as in the mosses
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THE PTERIDOPHYTES
The pteridophytes are seedless vascular plants
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i
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It has true vascular tissues
iii
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Good
examples are the lycopodium, sellaginella, Fern (Dryopteris)
ANGIOSPERM MORPHOLOGY
Angiosperms are flowering and seed-bearing plants
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Angiosperms are the most successful and most abundant group of
plants
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Over 250,000 species have been
reported
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a) Variability in structure
b) Genetic flexibility
c) Efficient pollination and fertilization mechanisms
d) Production of large number of seeds
e) Fast rate of growth
f) Short life cycle
g) Self fertility/bisexuality etc
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There is great variation among plants and they are grouped or classified based on the similarities
and differences that exist among them
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To classify plants, it is essential to have good knowledge of the variation in the
features of the plants hence the need to study plant morphology
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Plant morphology deals with the study of forms and features of different plant organs such as
roots, stems, leaves, flowers, fruits and seeds
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The
first letter of the generic name is written in capital letter, while the specific name is written in
small letter all through
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Plants are also known by their common and vernacular names which may vary in different
localities, cultures and tribes
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Description based on size
Plants can be described as tree, shrub or herb based on their size
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E
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Mangifera indica, Khaya senegalensis, Delonix regia, Terminalia catapa etc
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g
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Herbs are small plants with soft, fleshy stem e
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Talinum triangulae, Ageratum conyzoides,
Lactuca sativa etc
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Annuals are plants that complete their life cycle in one season i
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one year e
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Oryza sativa, Zea
mays
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e
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g
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Perennials are plants that live for more than two years e
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Triplochyton scleroxylum, Milesia
excels, Hildergadia barterii etc
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Many plants have also developed features that
adapt them to their specific habitats
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e
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Tithonia diversifolia, Euphorbia heterophylla etc
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g
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, Euphorbia sp
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Hygrophytes are plants growing in moist aand shady places e
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Ferns, some grasses
Hydrophytes are plants growing in aquatic places e
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water lettuce (Pistia), water hyacinth
(Eichhornia sp), water lily,
Halophytes are plants growing in saline soil or water e
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Rhizophora sp
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,
Mangrove plants etc
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Erect plants are those with strong stem that can stand on their own without any support
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Scandent plants are called climbers if they attach themselves to other plants or objects by some
means
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g
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g
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g
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g
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, Vigna sp
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They
climb round their supports e
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Entada gigas
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Scramblers do not attach to their support but simply lean against nearby plants and
spread over them e
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Combretum sp while stranglers start their life from seed which grow on the
host or near the host
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They could be total parasites e
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Cuscuta or partial parasites eg
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Epiphytes: these are plants that grow on other plants but they produce their food by themselves
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g
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g
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g
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The relationship is called symbiosis e
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Lichen which is
the association of fungi and blue green algae which is seen as green patches on tree trunks and
old walls
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The three regions are for cell divisions, cell elongation and cell maturation
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The cells of the root cap is
regenerated as it is been worn off in the process of soil penetration
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Cells

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REGION OF CELL ELONGATION
The cells in this region undergo rapid elongation and enlargement and are responsible for the
growth in length of the root
REGIONS OF CELL MATURATION
Cells in this region undergo maturation and differentiation into various kinds of tissues
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FUNCTIONS OF THE ROOT
Absorption of water and mineral salts from the soil
Anchorage of the plant to the soil
Conduction of the absorbed water upwards to the stem
Storage of food in some plant species
TYPES OF ROOT
There are two main forms of root, namely the Tap root system and Fibrous root system
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The secondary roots can also produce smaller branch
roots called rootlets or tertiary roots
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g
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THE STEM
The stem is the ascending portion of the axis of the plant, developing directly from the plumule
and bears the leaves, branches and flowers
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Leaves and
branches develop from the nodes
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When the stem or branch ends in a vegetative bud, it continues to grow upwards or sideways
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Buds occurring in the axil of leaves
are termed axillary buds
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e
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Stem conducts water and mineral salts from the root to the leaves
Conduction of prepared food from the leaves to other parts of the plant
Storage of water and food in some species
Young green stems perform photosynthesis to compliment the leaves
Stem is used to for vegetative propagation in some plants species
Some stems especially the underground stems are useful for perennation
Types of stem
Stem could be either aerial or underground
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Underground stems are useful for food storage and perennation

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