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RePResentative samPle Biology: moRPhology of floweRing Plants

Morphology of Flowering Plants7.55

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MORPHOLOGY OF FLOWERING PLANTS

angIospErms and thEIr classIfIcatIon

root, stEm and lEaf

InflorEscEncE

floWEr, fruIt and sEEds

dEscrIptIon of cErtaIn famIlIEs of angIospErms

CHAPTER 7

1. Introduction

Morphology of plants is defined as the branch of science that deals with the physical forms or the physical structure of plants with respect to their function.Physical characteristics of the plants are usually divided into those features that are generally present (a) below the ground such as roots and seeds, stems in some cases and (b) above the ground such as stem, leaves, flowers, fruits, seeds. The different parts of plant organ are evolved to perform specific major functions and generally help the plant to acclimatize and adapt to its specific environment.

Topics Discussed


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2. ObjectivesThe objectives of this chapter is to learn about the morphological characteristics of flowering plant, study their classification and specific examples with relation to their functions.

3. AngiospermsAngiosperms are seed, fruit as well as flower-bearing plants which are the epitome of evolution in the plant kingdom. All of them show sporophytic (possessing multiple cells and have atleast two sets of chromosomes), phanerogramic (possessing distinct reproductive organs) and spermatophytic (seed generation and enclosed in fleshy organs).

4. Classification of AngiospermsAngiosperms are classified into various types based on the following criteria

4.1 Based on Cotyledon NumberAngiosperms are classified into

1.Monocotyledons (Monocots) when they possess a single cotyledon. Eg: Rye (Lolium perenne), Wheat (Triticum aestivum). These are the most evolved.

2. Dicotyledons (Dicots). Eg: Rose (Rosa multiflora), Sunflower (Helianthus annuus).

4.2 Based on HabitatThe environment that a plant adapts and conquers for its survival is known as its habitat. Thus, plants are classified as

1. Land conquerors (Terrestrial environment). Eg: Cashew (Anacardium occidentale), Mango (Mangifera indica).

2.Water conquerors (Water environment). Eg: Water Lily (Nymphaea alba), Mangrove (Nypa fruticans).

4.3 Based on Life Cycle DurationPlants can also be classified based on the duration required by them to complete their entire life cycle are produced distinct types as listed in the table.


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Class Duration of life cycle Examples

Ephemeral 4-6 weeksBloodwort (Sanguinaria canadensis)

Thale cress (Arabidopsis thaliana)

Annual One season (6-12 months)Rice (Oryza sativa)

Lettuce (Lactuca sativa)

Biennial Two seasons (24 months)Parsley (Petroselinum crispum)

Cabbage (Brassica oleracea)

Perennial Several seasons (>2 years)Giant Sequoia (Sequoiadendron giganteum)

Apple (Malus domestica)

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Plants are classified as

Monocarpic when they flower and produce fruit only once in their life cycle. This category includes all annual, biennial and even certain perennial plants. Eg: Barley (Hordeum vulgare), Pineapple (Ananas comosus).

Polycarpic when they generate flowers and fruits every season after they have attained full maturity. Eg: Orange (Citrus maxima), Mango (Mangifera indica).

4.4 Based on nutritionAll plants with a few exception are Autotrophic/Photosynthetic in nature wherein they synthesize organic sugar such as glucose to be used as a source of food using solar energy and carbon dioxide. However, there are certain plants, known as Heterotrophs which are slightly or completely dependent on other sources of energy and nutrition.


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Knowledge Builder

Heterotrophs further subdivided into

(a) Parasitic plants are those that derive complete nutrition (Holoparasite) or some nutrition,

namely water and/or minerals (Hemiparasite) from other living plants which act as their

hosts.

Holoparasites include the Giant Dodder (Cuscuta europaea), Branched Broomrape

(Orobanche ramosa).

Certain examples of Hemiparasites include Yellow Rattle (Rhinanthus minor), Christmas

tree (Nuytsia floribunda).

(b) Insectivorous/Carnivorous plants are plants which derive their nutritional requirements

from trapping and ingesting small organisms such as arthropods, insects and protozoans.

Surprisingly, they are all photosynthetic which indicates that they only depend on predation

for nutrients while producing energy through photosynthesis. Eg: Pitcher plants (Nepenthes

khasiana), Venus flytrap (Dionaea muscipula), Common Bladderworts (Utricularia vulgaris).

(c) Saprophytic plants are those group of plants that use decaying organic matter as their

chief source of nutrition and energy due to their non-green appearance which indicates their

lack of photosynthesis. Eg: Indian-pipe (Hypopitys uniflora), Sugar stick (Allotropa virgata),

Pine drops (Pterospora andromedia).

trY it YourselF

1. ________________ are the most evolved plants.

2. Plants classified into _____________ classes based on their life cycle nutrition.

3. Holoparasites are completely dependent on other plants for nutrition. True/False.

4. Mangrove is an example of ___________________________.

5. Polycarpic plants are the plants which generate flowers and fruits only once in their life cycle. True/False.


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5. RootPlant roots are the structures which are usually seen below the soil (though some are aerial), are non photosynthetic, non nodal and shows positively geotropic (branching down, away from the ground level), positively hydrotropic (moving towards presence of water), negatively phototropic (moving away from direction of light) characteristics.

5.1 Parts of RootsPlant roots are composed of two types of tissues, namely primary tissues and secondary tissues. Many annual plants (live for one year) have only primary tissues in their roots while plants that live more than one year (biennials, perennials) have secondary tissues in their roots in addition to primary tissues.

5.2 Types of Roots1. Tap roots – The main requirement for the primary root formation is the direct elongation of the radical. This type of root is seen in nearly all dicot plants. From the primary roots, lateral roots branch out and are referred to as secondary roots or tertiary roots. Thus, the tap root system is made up of these primary roots and its branches. Eg: Dicot plants such as Rose (Rosa multiflora), Sunflower (Helianthus annuus), Mustard (Brassica juncea) etc.

2. Adventitious roots/Fibrous roots – The fibrous roots system, seen in all monocots and due to its short life span, consists of huge number of roots replacing the primary roots. These roots erupt from the stem base and not from radical elongation. Infact, these roots are the opposite of the tap root system. Eg: Monocot plants such as Garlic (Allivum sativum), Rye (Lolium perenne), Wheat (Triticum aestivum) etc.

Functions of the root system: Water and minerals absorption, supporting plant parts through proper anchorage, reserve food material storage, fixation and assimilation of nitrogen and plant growth regulators (PGR)/hormone production.

5.3 Modified Roots

Root are modified in shape to perform functions, other than their main function.

(i) Modified Tap Root System

1. Tap root system modified for food storage

a.. Fusiform/Spindle roots – They are thicker in the middle and tapering at the top and bottom forming a spindle. Eg: Radish (Raphanus sativus).

b. Conical roots – The upper side appears thicker while the basal end is tapered similar to an ice cream cone structure. Eg: Carrot (Daucus carota).

c. Tuberous roots – No particular shape and any portion of the roots becomes swollen & fleshy. Eg: Four O’ Clock plant (Mirabilis jalapa).


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a. Napiform roots – Shows swollen and spherical appearance at the upper end while tapering (like a thread) at the lower end so that the overall appearance looks like a round top. Eg: Turnip (Brassica rapa), Sugarbeet/Beet root (Beta vulgaris).

Modification of tap root A. Conical root of carrot; B. Napiform root of turnip and C. Fusiform root of radish

A B C

BA

C

Types of Roots: A. Taproot; B. Fibrous root and C. Adventitious root


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2. Nodulated roots for symbiotic association

Nitrogen fixing bacteria (Rhizobium, Azorhizobium, and Methylbacterium) form structures called ‘nodules’ on primary and secondary root branches. These nodules are rich in nitrogenase and help in fixation of nitrogen from the air. This kind of relationship between a bacteria and plant, which benefits both is known as ‘symbiotic relationship’. Eg: Members of the Leguminosae family – Soybeans (Glycine max), Pea (Pisum sativum), Alfalfa (Medicago sativa).

3. Tap root modified for respiration

Plants which thrive in the marshy/swampy areas show root adaptation wherein some branches of tap root start, instead of expanding horizontally into the ground, starts growing vertically due to low levels of oxygen, thus showing negative geotropism. Air enters within the plant through minute pores called pneumathodes/lenticels and the plant respires through these pores. These roots are known as pneumatophores. Eg: Red Mangrove (Rhizophora mangle), Sunder plants (Heritiera fomes).

Nodulated roots of Pea

A B

A. Main Mangrove plant with emerging pneumatophores (respiratory roots); B. Enlarged pneumatophore


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Knowledge Builder

1. Reproductive roots

Adventitious buds are formed on some tap roots to aid in vegetative propagation. Eg: Indian Rosewood tree (Delbergia sissoo), Poplar (Populus tremula).

2. Buttress/Stilt roots

Horizontally-aligned roots, running parallel to the ground surface so that the main parent tree gets extra support to prevent it from falling and also to search for nutrients in the surrounding. Eg: Rubber tree (Ficus elastic), Peepal (Ficus religosa).

3. Mycorrhizal rootsSymbiotic association between roots of certain higher plants and fungus.This results in exchange of carbohydrate and water from the plant to the fungus while also helping the tree colonize less habitual environments. Eg: Pine tree (Pinus contorta), Birch (Betula alnoides).

(ii) Modified Adventitious Root System:

1. Fleshy roots acting as food storage

a. Nodulose roots – Root tips appear thick and swollen throughout. Eg: Mango Ginger (Curcuma amada), Sweet-clover (Melilotus indicus).

b. Fasciculated roots – Formed as clusters of adventitious roots originating from the lowermost stem node and showing thick, swollen appearance. Eg: Asparagus officinalis, Dahlia pinnata.

c. Beaded/Moniliform roots – Swelling of roots in the shape of beads. Eg: Bitter gourd (Momordica charantia), Nine O’ Clock plant (Portulaca grandiflora).

d. Tuberous/Tubercular roots – The shape of these roots is swollen and does not have any particular shape due to food accumulation and storage. Eg: Tapioca/Cassava (Manihot esculenta), Sweet potato (Ipomoea batatas).

e. Annulated roots – These roots are shaped like a series of rings/discs placed in a stack. Eg: Cephalis ipecacuana.

f. Palmate roots – Swollen roots arranged to form the shape of human hand. Eg: Orchid (Orchis militaris).


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Modification of adventitious roots A. Tuberous roots of sweet potato; B. Fasciculated roots of Dahlia;

C. Nodulose roots of Mango ginger

Modification of adventitious roots A. Moniliform roots of Momordica; B. Annulated roots of Ipecac

A B C

A B


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2. Stilt/Brace roots – Shaped like spiral whorls, these roots emerge from the lower stem node and then grow obliquely like thin wires till they reach the ground. These roots mainly provide support but do not absorb water. Eg: Maize (Zea mays), Sugarcane (Saccharum officinarum), Screwpine (Pandanus amaryllifolius).

Modification of adventitious roots: A. Stilt roots of sugarcane; B. Screw pine

3. Columnar/Prop/Pillar roots – These roots originate from the plant branches and appear like they are hanging from the branches and positive geotropism since they move towards the ground. Providing support to the tree and water absorption from the environment are its function. Eg: Banyan tree (Ficus benghalensis).

Modification of adventitious roots: Prop roots of banyan

A B


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4. Clinging/Climbing roots – Usually these roots originate from the base of the stem and serve as anchorage support for plants with weak foundation and few or no branches. These roots helps these plants to colonize wall fissures or sticks placed vertically in the fields. Eg: Money plant (Epipremnum aureum), Betel (Piper betel), Black pepper (Piper nignum).

Modification of adventitious roots: Climbing root of Piper

5. Assimilatory/Photosynthetic roots – Certain roots are capable of photosynthesis and are green in color. Eg: Guduchi (Tinospora cardifolia), Orchid (Taeniophyllum), Water chestnut/Singhara (Trapa natans).

Modification of adventitious roots: Assimilatory roots of Singhara


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1. Foliar/Epiphyllous roots – On injury some plants can generate roots from leaves. Eg: Devil’s backbone (Bryophyllum daigremontianum), Hardy begonia (Begonia grandis).

2. Parasitic/Sucking/Haustorial roots – Similar to climbing roots, these roots also originate from the stem but derive nutrition and water from the host plant they invade. Eg: Alfalfa Dodder (Cuscuta approximate), Mistletoe (Viscum album).

3. Epiphytic roots - Highly hygroscopic roots that are mostly aerial (above ground soil) and absorbs moisture from the environment through spongy tissue known as velamen. These roots also are photosynthetic and lack root hairs and without root cap. Eg: Vandaka (Vanda roxburgii), Pink Rock Orchid (Dendrobium kingianum).

Modification of adventitious roots: Epiphytic roots of Vanda (Orchid)

4. Floating roots - These roots helps in the plant buoyancy by keeping the plant floating on the water surface. Thus, the plant does not submerge and also respires using the stored air within the roots. Eg: Water-primrose (Ludwigia hexapetala).

Modification of adventitious roots: Floating roots


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trY it YourselF

1. Roots are negatively are negatively geotropic. True/False

2. Name the two types of roots.

3. Carrots are example of modified roots known as _________________________.

4. Respiratory tap root system are called ___________________________.

5. Betel is an example of climbing roots. True/False.

6. StemStem is defined as the rising, shaped-like a cylinder extensions that is formed from the plumule of a germinating seed’s embryo. Stems are always demonstrates shows negatively geotropic (moving up, not reaching the ground), negatively hydrotropic (moving away from water), positively phototropic (moving in the direction of light), attributes which are almost the opposite of roots. A large number of nodes are present on the stem which serve as the origin and support of the other plant organs such as leaves, flowers, buds, fruits as well as seeds while the internodes is the area between two successive nodes. Stem being an extension of the nodal cells are thus exogenous in nature.

The chief function of the stem is to ensure that the area possessing the other plant parts such as leaves, flowers and fruits are arranged to ensure their proper functioning. Other functions include transport and conductance of minerals, salts, water and food namely sugar produced through photosynthesis. Some stems are also responsible for food storage, vegetative propagation, plant support and protection.

6.1 BudsYoung, embryonic shoots which are immature, dormant and condensed are known as buds. Located at the stem node, buds are capable of forming flowers or shoots and are generally shielded by a mass of leaves.

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5. Root thorns – Roots modified in the shape of thorns and/or spikes. Eg: Walking palm (Socratea exorrhiza).

6. Contractile roots – Abundant in the amount of glucose, these swollen roots aids the plant in reaching its correct depth. Eg: Bulb of Garden Hyacinth (Hyacinthus orientalis).

7. Leaf roots – In order to ensure they stay afloat on water, leaves of certain particular water plants which originate at the stem node are modified to form root bunches. Eg: Walking palm (Salvinia molesta).

8. Reproductive roots - Adventitious buds are formed on some adventitious roots to aid in vegetative propagation. Eg: Sweet Potato (Ipomoea batatas).


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Classification of Buds

Buds are classified based on the following parameters

1. Based on morphology

Buds are classified on the basis of the shape or structure into

a. Naked buds – Embryonic parts are unprotected.

b. Covered/Perulate/Scaly buds – Embryonic parts protected by scales.

c. Hairy buds – Hairs protect the embryonic parts.

2. Based on location

On the basis of location, buds are classified into

a. Terminal/Apical buds – Originating at the stem tip or branch tip.

b. Axillary/Lateral buds – Buds which are located axillary (location not at the apical position) and positioned in the leaf’s axil.

c. Adventitious buds – Buds formed at all the other parts such as roots or tree trunks. They are of the following types

i. Radical buds – Generated on roots. Eg: Sweet potato.

ii. Foliar buds – Generated on leaves. Eg: Genus Bryophyllum, Begonia.

iii. Cauline buds – Generated on stem. Eg: Jackfruit.

Adventitious buds: A. Radical buds of sweet potato; B. Foliar buds of Bryophyllum; C. Foliar buds of Begonia; D. Bulbil of Dioscorea.

DCBA


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3. Based on function

Buds are classified on the basis of function into

a. Reproductive/Flower buds – Produces embryonic shoots with flower.

b. Vegetative buds – Produces shoots with leaves.

c. Mixed buds – Generates both shoots with leaves and flowers.

4. Based on status

On the basis of status, buds are classified into

a. Dormant/Latent buds – Delayed, slow or no growth of bud.

b. Resting buds – Buds generated when the growth season ends but remains latent till the onset of the new growing season.

c. Accessory buds – Secondary buds generated despite the presence of main bud.

d. Pseudoterminal buds – Buds which are located axillary select and take up the terminal buds function.

Chart showing Classification of Buds by Location; by Status; by Morphology; by Function.


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Modified Buds

1. The largest apical bud in existence is Cabbage (Brassica oleracea). Cabbage acts as a food storehouse and due to its leafy nature is classified as a vegetative bud. Other examples include Lettuce (Lactuca sativa).

2. Swollen vegetative buds with leafy bases participating in vegetative propagation, while also simultaneously storing food are known as Bulbils. Eg: Garlic (Allium sativum), Tulip (Tulipa suaveolens), Small Bulbous-rooted Iris (Iris xiphsium).

3. Specialized food storage buds generated by aquatic plants so that they can survive during the less favorable winter season are termed as Turions. Eg: Common Bladderwort (Utricularia vulgaris).

4. Buds modified in the shape of tendrils. Eg: Gourd (Cucurbita maxima) and thorns Eg: Golden drewdrop (Duranta erecta).

6.2 Branching of StemBranches are positioned on the stem in specific pattern and this order is known as branching. Branching of stem is of two types:

1. Dichotomous – Dual similar branches appearing in a ‘fork-like’ pattern. Eg: Palm (Hyphaene dichotoma).

2. Lateral – Branching occurring from the axillary buds and stem sides rather than the apical bud which stays dormant. Lateral branching are further divided into the following two types.a. Racemose/Monopodial/Indefinite Branching – Continuous, aggressive growth of the apical bud far

outweighs the growth of lateral branches and these lateral branches are positioned in acropetal succession i.e. the branches are arranged in an age-based hierarchy where the relatively older branches are located at the bottom with the younger branches positioned at the top forming a pyramid or conical shape. Eg: Australian pine (Casuarina equisetifolia), False Ashoka (Polyalthia longifolia).

b. Cymose/Sympodial/Definite Branching – Finite growth of the apical bud leads to the axillary branches growing more actively and forming many branches leading to an inverted bell or dome-like shape. Cymose branching is further subdivided into three subtypes.

i. Uniparous/Monochasial Cyme – At one time, a single lateral branch from the axillary bud is produced. The successive branches are either arranged in the form of a helix on the same one side of the plant i.e. helicoid, Eg: Ashoka (Saraca asoca) or positioned on the plants alternate sided to form a zig-zag like pattern i.e. scorpioid, Eg: Common grape vine (Vitis vinifera). The apical bud is modified to form a flower/thorn structure.


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i. Biparous/Dichasial Cyme – At one time, two axillary/lateral branches are produced. Eg: Four O’ Clock plant (Mirabilis jalapa), Moonflower (Datura inoxia).

ii. Multiparous/Polychasial Cyme – Multiple (>2) axillary/lateral branches are produced. Eg: Jungle tulsi (Croton bonplandianum), Sun spurge (Euphorbia helioscopia).

Summarizing Chart

6.3 Stem Forms

1. Erect stem (Strong stem) – Relative stable, physical stem.

a. The thick stem completely free/devoid of branches is known as Caudex. Eg: Nettlespurge (Jatropha cathartica).

b. Caudex in which the location and arrangement of both nodes and internodes is prominently seen is known as Culm. Eg: Bamboo (Bambusa vulgaris).

c. Oval, shaped-like a disc stem is called Reduced. Eg: Turnip (Brassica rapa), Radish (Raphanus sativus)

d. Stem branched at many positions is known as Deliquescent. Eg: Neem (Azadirachta indica), Mango (Mangifera indica)

e. When the shape of the tree resembles a cone, it is termed as Excurrent. Eg: Red Pine (Pinus resinosa).

2. Weak stem – Fragile stems requiring support for their propagation.

Three types of weak stems

i. Trailing stem – Fragile stem that advances over a wide-area of the ground surface but the nodes lack rooting and thus are not reproductive. Eg: Prostrate Sandmat (Euphorbia prostrata).

(contd.)


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Objective Questions

Q.1 Radish is an example of –

A. Fusiform root B. Napiform root

C. Conical root D. Tuberous root

Q.2 Roots associated with nitrogen fixing bacteria are –

A. Fusiform root B. Napiform root

C. Nodulated root D. Conical root

Q.3 The edible part of turnip is –

A. Modified adventitious roots B. Modified tap root

C. Stem D. Underground stem

Q.4 Which is a modification of root that does not store food?

A. Napiform root B. Fusiform root

C. Tuberous root D. Stilt root

Q.5 Shoot/Stem develops from –

A. Plumule B. Radical

C. Both (A) and (B) D. None of the above

Q.6 Lateral branches of stem are - [CPMT-1979]

A. Endogenous in origin B. Exogenous in origin

C. Both D. None of the above

Q.7 Which is an example of offset?

A. Cynodon dactylon B. Eichornia

C. Fragaria D. Mentha

Q.8 Rhizome of ginger is a modification of stem because –

A. It bears adventitious roots B. It bears nodes and internodes

C. It is underground D. It stores food material

EXERCISE

(contd.)


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EXERCISE

Subjective Questions

Q.1 Roots obtain oxygen from air in the soil for respiration. In the absence or deficiency of O2, root growth

is restricted or completely stopped. How do the plants growing in marshlands or swamps obtain their O2

required for root respiration?

Solution: Plants like Rhizophora, which grow in marshy or swamps area bear pneumatophores or respiratory roots. These roots come out of soil, grow vertically and bear respiratory pores (pneumathodes) for respiration.

Q.2 Write floral formula for a flower which is bisexual; actinomorphic; sepals five, twisted aestivation, petals five; valvate aestivation; stamens six; ovary tricarpellary, syncarpous, superior, trilocular with axile placentation.

Solution: † (5) 5 4 (3)K C A G

Q.3 In Opuntia the stem is modified into a flattened green structure to perform the function of leaves (i.e., photosynthesis). Cite some other examples of modifications of plant parts for the purpose of photosynthesis.

Solution: Phylloclades of Meuhlebechia and Euphorbia royleana; cladode of Asparagus.

Q.4 In swampy areas like Sunderbans in West Bengal, plants bear special kind of roots called…..

Solution: Pneumatophores

Q.5 In aquatic plants like Pistia and Eichhornia, the roots are found near…..

Solution: Water surface

Q.6 Reticulate and parallel venation are characteristic of ….. and ….. respectively.

Solution: Discotyledonous plants, monocotyledonous plants.

Q 7: Which parts of ginger and onion are edible?

Solution: In ginger, edible part is underground stem. In onion, edible part is fleshly scales.

(contd.)


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Previous Years Questions

Q.1 In which of the following family, bacteria fix nitrogen in soil by symbiosis [RPMT 2007]

A. Leguminosae B. Solanaceae

C. Malvaceae D. Cruciferae

Q.2 In which family, oblique ovary is found [RPMT 2007]

A. Solanaceae B. Liliaceae

C. Compositae D. Cruciferae

Q.3 What type of placentation is seen ins sweet pea? [AIPMT 2006]

A. Basal B. Axile

C. Free central D. Marginal

Q.4 Pentamerous, actinomorphic flowers, bicarpellary ovary with oblique septa, and fruit a capsule or berry, are characteristic features of [AIPMT 2006]

A. Asteraceae B. Brassicaceae

C. Solanaceae D. Liliaceae

Q.5 Replum is present in the ovary of flower of [AIPMT 2008]

A. Sunflower B. Pea

C. Lemon D. Mustard

Q.6 Dry indehiscent single-seeded fruit formed from bicarpellary syncarpous inferior ovary is [AIPMT 2008]

A. Berry B. Cremocarp

C. Caryopsis D. Cypsela

Q.7 The floral formula is that of ⊕ ⚥ K(5)

(5) 5C A

G(2) [AIPMT 2009]

A. Tobacco B. Tulip

C. Soybean D. Sunn hemp

(contd.)


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Objective QuestionsQ.1 A Q.2 C Q.3 B Q.4 D Q.5 A Q.6 B

Q.7 B Q.8 B Q.9 D Q.10 C Q.11 D Q.12 A

Q.13 C Q.14 D Q.15 B Q.16 C Q.17 B Q.18 D

Q.19 B Q.20 B Q.21 A Q.22 B Q.23 B Q.24 B

Q.25 A Q.26 D Q.27 C Q.28 A Q.29 C Q.30 C

Q.31 A Q.32 C Q.33 A Q.34 C Q.35 C Q.36 C

Previous Years QuestionsQ.1 A Q.2 A Q.3 D Q.4 C Q.5 D Q.6 D

Q.7 A Q.8 B

ANSWER KEY

(contd.)

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