Biology Today - April 2016

79 Pages·2016·9.43 MB·English

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Vol. XVIII No. 4 April 2016
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CONTENTS
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Morphology of Flowering Plants-I
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MTBIOLOGY TODAY | APRIL ‘16 7
The content for PMT Biology is
very vast and does not allow
students to engage in inquiry
and develop meaningful
knowledge. An essential topic
for PMT is presented here to
enable students grasp the
topic, analyse the type of
questions appearing in PMTs,
and SCORE HIGH.
MORPHOLOGY OF FLOWERING PLANTS-I
Plant morphology (Gk. morphe-form, logos-study) is the branch of botany that deals with the study of forms and features of different
plant organs like roots, stems, leaves, flowers, fruits, seeds etc.
CLASSIFICATION OF PLANTS
The body of a flowering plant can be divided into two fundamental parts : (i) root system and (ii) shoot system.
Plants can be classified on the basis of height and nature of stem, life span and frequency of flowering or fruiting. Classification of
plants on different basis is given in the following flow charts.
Herbs Trees
(cid:115)(cid:0) Small plants with soft, delicate and green stems (cid:115)(cid:0) Tall plants with a thick woody main stem called trunk.
normally growing to a height of less than 2 m. (cid:115)(cid:0) The trunk may remain unbranched (caudex) or
(cid:115)(cid:0) These may be annuals (e.g., mustard, pea, produce narrow lateral branches (excurrent).
rice etc.), biennials (e.g., beet, carrot etc.) or (cid:115)(cid:0) These are perennials e.g., Mangifera indica,
perennials (e.g., ginger, banana etc). Dalbergia, etc.
On the basis of
height and
nature of stem
Shrubs
(cid:115)(cid:0) These are usually taller than herbs, measuring 1-3 m in height and have woody stems.
(cid:115)(cid:0) These branch profusely from near the ground, and thus the plants become bushy in habit
without a clear trunk.
(cid:115)(cid:0) These are perennials e.g., Hibiscus rosa-sinensis, Capparis, etc.
8 MTBIOLOGY TODAY | APRIL ‘16
Annuals Monocarpic
Plants which complete their life cycle from germination They flower and fruit only once in their life. All annual
through flowering and seed production to death in a and biennial plants are monocarpic. However, some
single year or less. Examples include cereals, grains, perennial plants are also monocarpic e.g., bamboo
legumes etc. and Agave.
Biennials
On the basis of
Plants which complete their life cycle in
On the basis
two years. Flowering usually occurs during frequency of
of life span
the second year, after a year of vegetative flowering or fruiting
growth. Beets and carrots are biennials.
Polycarpic
Perennials
These plants bear flowers and fruits repeatedly after
Plants that live for few years to several hundred years,
e.g., trees like neem, Ficus etc. attaining maturity e.g., Acacia, Eucalyptus, Mangifera, etc.
MORPHOLOGY OF ROOT
The root is typically a non-green underground descending portion of the plant axis which gives rise to similar types of endogenous
lateral branches and does not possess nodes and internodes. They are positively geotropic, positively hydrotropic and negatively
phototropic.
A typical root possesses four zones:
(cid:58)(cid:79)(cid:78)(cid:69)(cid:0)(cid:79)(cid:70)(cid:0)(cid:68)(cid:73)(cid:70)(cid:70)(cid:69)(cid:82)(cid:69)(cid:78)(cid:84)(cid:73)(cid:65)(cid:84)(cid:73)(cid:79)(cid:78)(cid:15)
(cid:77)(cid:65)(cid:84)(cid:85)(cid:82)(cid:65)(cid:84)(cid:73)(cid:79)(cid:78)(cid:0)
Cells in this region are differentiated into
permanent tissues (viz. xylem, phloem,
pericycle, endodermis, cortex etc.)
depending upon the functions they have to
perform. Root hairs are also present in this
zone, which help in water absorption.
(cid:58)(cid:79)(cid:78)(cid:69)(cid:0)(cid:79)(cid:70)(cid:0)(cid:67)(cid:69)(cid:76)(cid:76)(cid:0)(cid:69)(cid:76)(cid:79)(cid:78)(cid:71)(cid:65)(cid:84)(cid:73)(cid:79)(cid:78)(cid:0)
Cells of this region have lost the
power of division, they elongate
rapidly and increase the length of
the root.
(cid:50)(cid:79)(cid:79)(cid:84)(cid:0)(cid:67)(cid:65)(cid:80)
It is cap-like parenchymatous, multicellular
structure, which covers the root meristem.
The cells of root cap secrete mucilage which
lubricates the passage of root through soil.
Cells also possess starch grains which take
part in graviperception. (cid:58)(cid:79)(cid:78)(cid:69)(cid:0)(cid:79)(cid:70)(cid:0)(cid:67)(cid:69)(cid:76)(cid:76)(cid:0)(cid:70)(cid:79)(cid:82)(cid:77)(cid:65)(cid:84)(cid:73)(cid:79)(cid:78)(cid:0)
(cid:79)(cid:82)(cid:0)(cid:77)(cid:69)(cid:82)(cid:73)(cid:83)(cid:84)(cid:69)(cid:77)(cid:65)(cid:84)(cid:73)(cid:67)(cid:0)(cid:90)(cid:79)(cid:78)(cid:69)(cid:0)
It is subterminal in positions. It consists
of compactly arranged small, thin-walled,
isodiametric and meristematic cells having
dense cytoplasm. Cells of this region are in
active state of division.
10 MTBIOLOGY TODAY | APRIL ‘16
There are three types of root systems occurring in plants: tap root system, fibrous root system and adventitious root system. A
comparative account between the three is summarised in the given table.
Table: (cid:35)(cid:79)(cid:77)(cid:80)(cid:65)(cid:82)(cid:73)(cid:83)(cid:79)(cid:78)(cid:0)(cid:66)(cid:69)(cid:84)(cid:87)(cid:69)(cid:69)(cid:78)(cid:0)(cid:84)(cid:65)(cid:80)(cid:0)(cid:82)(cid:79)(cid:79)(cid:84)(cid:0)(cid:83)(cid:89)(cid:83)(cid:84)(cid:69)(cid:77)(cid:12)(cid:0)(cid:108)(cid:66)(cid:82)(cid:79)(cid:85)(cid:83)(cid:0)(cid:82)(cid:79)(cid:79)(cid:84)(cid:0)(cid:83)(cid:89)(cid:83)(cid:84)(cid:69)(cid:77)(cid:0)(cid:65)(cid:78)(cid:68)(cid:0)(cid:65)(cid:68)(cid:86)(cid:69)(cid:78)(cid:84)(cid:73)(cid:84)(cid:73)(cid:79)(cid:85)(cid:83)(cid:0)(cid:82)(cid:79)(cid:79)(cid:84)(cid:0)(cid:83)(cid:89)(cid:83)(cid:84)(cid:69)(cid:77)
(cid:52)(cid:65)(cid:80)(cid:0)(cid:82)(cid:79)(cid:79)(cid:84)(cid:0)(cid:83)(cid:89)(cid:83)(cid:84)(cid:69)(cid:77) (cid:38)(cid:73)(cid:66)(cid:82)(cid:79)(cid:85)(cid:83)(cid:0)(cid:82)(cid:79)(cid:79)(cid:84)(cid:0)(cid:83)(cid:89)(cid:83)(cid:84)(cid:69)(cid:77) (cid:33)(cid:68)(cid:86)(cid:69)(cid:78)(cid:84)(cid:73)(cid:84)(cid:73)(cid:79)(cid:85)(cid:83)(cid:0)(cid:82)(cid:79)(cid:79)(cid:84)(cid:0)(cid:83)(cid:89)(cid:83)(cid:84)(cid:69)(cid:77)
(i) It is formed from the radicle of the It occurs in place of tap root system It may develop from any part of the plant
embryo. at the base of main stem. other than radicle.
(ii) It is always underground. It is always underground. It may be underground or aerial.
(iii) It consists of a single primary (main) Primary root is short lived. Instead Primary root is absent and it consists of
root. underground roots arise in groups roots forming a cluster.
from base of stem.
(iv) Primary root produces distinct secondary The main roots are of equal length The roots may be thick, thin or variously
roots, tertiary roots and rootlets in and give off small branches. Main modified.
acropetal succession. roots and their branches are thin
and thread like.
(v) It may be surface or deep feeder, the It is usually surface feeder. It is usually surface feeder.
deep feeder being the usual feature.
(vi) It is commonly found in dicots. It is commonly found in monocots. It is found both in dicots and monocots.
MODIFICATIONS OF ROOTS
To know about an
Primary functions of roots are anchorage (or fixation) of the plant and absorption of water
incredible forest
and minerals from the soil for their transport to the shoot system. However, roots undergo
growing in Poland
morphological modifications to perform various functions such as food storage, mechanical
support etc. as discussed briefly in the given flow charts. refer to page no. 68
Some plants are rootless e.g., Wolffia while green flattened roots are found in Podostemon.
MTBIOLOGY TODAY | APRIL ‘16 11
(cid:38)(cid:76)(cid:69)(cid:83)(cid:72)(cid:89)(cid:0)(cid:84)(cid:65)(cid:80)(cid:0)(cid:82)(cid:79)(cid:79)(cid:84)(cid:83) (cid:34)(cid:85)(cid:84)(cid:84)(cid:82)(cid:69)(cid:83)(cid:83)(cid:0)(cid:82)(cid:79)(cid:79)(cid:84)(cid:83)
Tap roots become swollen and fleshy with stored food. They are horizontal roots that arise jointly
These are of following types: from the bases of tap root and the trunk.
(cid:35)(cid:79)(cid:78)(cid:73)(cid:67)(cid:65)(cid:76)(cid:0)(cid:26)(cid:0)Thicker on the upper end and tapering at They provide extra support, e.g., pipal.
the lower end, e.g., carrot.
(cid:52)(cid:85)(cid:66)(cid:69)(cid:82)(cid:79)(cid:85)(cid:83)(cid:0)(cid:26)(cid:0)Swollen and without any definite shape,
e.g., Mirabilis.
(cid:46)(cid:65)(cid:80)(cid:73)(cid:70)(cid:79)(cid:82)(cid:77)(cid:0)(cid:26)(cid:0)Much swollen and spherical at the upper
end and taper downward into a thread like structure,
e.g., turnip.
(cid:38)(cid:85)(cid:83)(cid:73)(cid:70)(cid:79)(cid:82)(cid:77)(cid:0)(cid:26) Swollen in the middle and tapering on
both ends, e.g., radish.
Modifications
of tap root
(cid:46)(cid:79)(cid:68)(cid:85)(cid:76)(cid:65)(cid:84)(cid:69)(cid:68)(cid:0)(cid:8)(cid:52)(cid:85)(cid:66)(cid:69)(cid:82)(cid:79)(cid:85)(cid:83)(cid:9)(cid:0) (cid:48)(cid:78)(cid:69)(cid:85)(cid:77)(cid:65)(cid:84)(cid:79)(cid:80)(cid:72)(cid:79)(cid:82)(cid:69)(cid:83)(cid:0)
Root nodules (small swellings) (cid:8)(cid:50)(cid:69)(cid:83)(cid:80)(cid:73)(cid:82)(cid:65)(cid:84)(cid:79)(cid:82)(cid:89)(cid:0)(cid:82)(cid:79)(cid:79)(cid:84)(cid:83)(cid:9)
are present on the roots and Upright breathing aerial roots
their branches which help to which develop at short intervals,
perform biological N -fixation, found in plants growing in
2
e.g., leguminous plants. mangroves or saline swamps,
e.g., Avicennia.
U N S C R A M B L E M E
Unscramble the letters using the given clues.
Scrambled letters Clues Words
1. GAESNNEDIRSO Production of haploid plants from male gametophyte.
2. UBTTAROOR Part of ovary of a flower that chemically guides the .............................
growth of pollen tube.
3. HEATLAPAGNAEO Super order in which big sized, flightless running birds, .............................
without teeth are included.
4. OHECLCOTANIO A method used by some animals to detect object in dark. .............................
5. SEAPCASS Protease enzymes that initiate and carry out cascade of .............................
events during apoptosis.
6. GYNEOOTN The developmental course of an organism from fertilised .............................
egg to maturity.
7. XNIELATOYHP An antimicrobial substance produced by plants in response .............................
to infection against fungus and bacteria.
8. HRPYOOMAP Evolutionary trait unique to a particular species can be .............................
used as a defining character of a species.
9. YIRMISDAS Widening or dilation of pupil of the eye. .............................
10. ITLCESENL Aerating pores in the bark of plants. .............................
Readers can send their responses at [email protected] or post us with complete address by 25th of every month to win exciting prizes.
Winners’ names will be published in next issue.
12 MTBIOLOGY TODAY | APRIL ‘16
MORPHOLOGY OF STEM
Stem is an ascending part of the plant body that
develops from the plumule of the embryo and is usually
negatively geotropic and positively phototropic.
Buds
Stem grows by means of a terminal bud which represents
a condensed immature or embryonic shoot possessing
a growing point. The buds are generally small in size.
The largest bud is that of cabbage. According to(cid:0)their(cid:0)
nature/structure buds can be (cid:86)(cid:69)(cid:71)(cid:69)(cid:84)(cid:65)(cid:84)(cid:73)(cid:86)(cid:69)(cid:0)(form leafy
shoots only), (cid:109)(cid:79)(cid:82)(cid:65)(cid:76)(cid:0)(reproductive buds that develop
into flowers) or (cid:77)(cid:73)(cid:88)(cid:69)(cid:68)(cid:0)(both vegetative and floral
branches).
On the basis of position buds can be of different types
as summarised in the given flow chart.
On the basis of activity buds can be (cid:65)(cid:67)(cid:84)(cid:73)(cid:86)(cid:69) (usually
naked) or (cid:68)(cid:79)(cid:82)(cid:77)(cid:65)(cid:78)(cid:84)(cid:0)(remain inactive for short or long
periods, covered by protective scales or bud scales).
MTBIOLOGY TODAY | APRIL ‘16 13
Branching patterns of the stem
Diverse forms of stem
Stem may be aerial, subaerial or underground. Stems of flowering plants attain diverse forms in order to perform various functions
like food storage, vegetative propagation, mechanical support, photosynthesis, protection etc. Aerial stems are grouped under three
broad categories.
(i) (cid:50)(cid:69)(cid:68)(cid:85)(cid:67)(cid:69)(cid:68)(cid:0)(cid:83)(cid:84)(cid:69)(cid:77) (stem reduced to a small disc which is not differentiated into nodes and internodes.
(ii) (cid:37)(cid:82)(cid:69)(cid:67)(cid:84)(cid:0)(cid:83)(cid:84)(cid:69)(cid:77) (strong stem, remains erect or upright without any external support, e.g., wheat). Erect stems with swollen nodes
or jointed stems are called culms (e.g., bamboo). Unbranched erect stem is known as(cid:0)(cid:67)(cid:65)(cid:85)(cid:68)(cid:69)(cid:88) (columnar) while the branched
ones are either (cid:69)(cid:88)(cid:67)(cid:85)(cid:82)(cid:82)(cid:69)(cid:78)(cid:84) or (cid:68)(cid:69)(cid:76)(cid:73)(cid:81)(cid:85)(cid:69)(cid:83)(cid:67)(cid:69)(cid:78)(cid:84).
(iii) (cid:55)(cid:69)(cid:65)(cid:75)(cid:0)(cid:83)(cid:84)(cid:69)(cid:77) (thin and soft stem that needs support to stand erect).
Weak stems may be upright or prostrate. Upright weak stems are of two types:
(a) (cid:52)(cid:87)(cid:73)(cid:78)(cid:69)(cid:82)(cid:83)(cid:0)(cid:26) The stems are long, slender, flexible very sensitive and coil around an upright support on coming in its contact due to
a special type of growth movement called nutation e.g., Convolvulus, Lablab.
(b)(cid:0)(cid:0)(cid:35)(cid:76)(cid:73)(cid:77)(cid:66)(cid:69)(cid:82)(cid:83)(cid:0)(cid:26) The stem is weak and unable to coil around a support. It usually climbs up the support with the help of some
clasping or clinging structures. Accordingly, climbers of four types: tendril climbers, root climbers, scramblers, lianas etc.
Prostrate or sub-aerial weak stems take the support of ground for spreading and proper exposure of the leaves and reproductive
organs. They are of two types:
(a)(cid:0)(cid:0)(cid:52)(cid:82)(cid:65)(cid:73)(cid:76)(cid:69)(cid:82)(cid:83): The shoots trail or spread horizontally along the ground (cid:87)(cid:73)(cid:84)(cid:72)(cid:79)(cid:85)(cid:84)(cid:0)(cid:82)(cid:79)(cid:79)(cid:84)(cid:73)(cid:78)(cid:71)(cid:0)(cid:65)(cid:84)(cid:0)(cid:73)(cid:78)(cid:84)(cid:69)(cid:82)(cid:86)(cid:65)(cid:76)(cid:83), e.g., Convolvulus microphyllus,
Euphorbia prostrata, etc.
(b) (cid:35)(cid:82)(cid:69)(cid:69)(cid:80)(cid:69)(cid:82)(cid:83)(cid:26)(cid:0)They root at intervals. Breaking of different rooted parts help in vegetative propagation.
In technical usage, fetus is now the standard spelling throughout the English- speaking world, the spelling

foetus has no etymological basis but is still found in British English outside technical context.
Mucus (a noun), means a thick liquid produced inside the nose and other parts of the body, and mucous

in British English is an adjective which means relating to mucus.
14 MTBIOLOGY TODAY | APRIL ‘16
Underground stem modifications
In some plants, the main stem or its branches lie below the surface of soil (underground), store food materials, help in perennation
and vegetative propagation. Underground stems are non-green and resemble roots in their general appearance. However, they can
be distinguished by absence of root cap and root hair, presence of terminal bud, nodes and internodes, occurrence of foliage or scale
leaves on the nodes, exogenous branching and stem-like internal structure.
MTBIOLOGY TODAY | APRIL ‘16 15
Aerial stem modifications
Thorns (modified stems), spines (modified leaves) and prickles (superficial epidermal outgrowths of stems and leaves) are sharp,
pointed, straight or curved hard structures which protect the plant from grazing animals and excessive transpiration.
Table: (cid:36)(cid:73)(cid:70)(cid:70)(cid:69)(cid:82)(cid:69)(cid:78)(cid:67)(cid:69)(cid:83)(cid:0)(cid:66)(cid:69)(cid:84)(cid:87)(cid:69)(cid:69)(cid:78)(cid:0)(cid:80)(cid:72)(cid:89)(cid:76)(cid:76)(cid:79)(cid:67)(cid:76)(cid:65)(cid:68)(cid:69)(cid:0)(cid:65)(cid:78)(cid:68)(cid:0)(cid:67)(cid:76)(cid:65)(cid:68)(cid:79)(cid:68)(cid:69)
(cid:48)(cid:72)(cid:89)(cid:76)(cid:76)(cid:79)(cid:67)(cid:76)(cid:65)(cid:68)(cid:69) (cid:35)(cid:76)(cid:65)(cid:68)(cid:79)(cid:68)(cid:69)
(i) Both main stem and branches are modified to function Only the branches are modified to take over the function of
like leaves. leaves.
(ii) Phylloclade has unlimited or indefinite growth. Cladode has a limited or definite growth.
(iii) It consists of several nodes and internodes. Usually it is one internode long.
(iv) A phylloclade represents whole shoot. A cladode is 1-2 internode long stem branch.
(v) True leaves are commonly caducous. True leaves are either reduced to scales or modified to spines.
16 MTBIOLOGY TODAY | APRIL ‘16