ECOLOGICAL PLANTS GROUPS AND SUCCESSIONFlame Institute

Ecological plants groups

Water as an important ecological factor was first recognized by Warming. On the basis of water requirement plants are divided in to 3 major types :

(1) Hydrophytes : They live in abundance of water. They require abundance of water to complete their life cycle. They are of following types :

(i) Rooted submerged : The hydrophytes, which are rooted in mud at bottom and remain under water. e.g., Hydrilla, Vallisnaria.

(ii) Submerged floating : They are not rooted in the soil but completely submerged and floating e.g., Ceratophyllum, Utricularia.

(iii) Rooted with floating leaves : They are rooted in the soil but the leaves are floating on the surface of water e.g., Nelumbo, Trapa, Victoria.

(iv) Free floating : They are not rooted in soil and mud. These hydrophytes float freely on the surface of water e.g., Wolfia (Smallest angiosperm), Lemna, Spirodella, Pistia, Azolla, Salvinia.

(v) Rooted emergent : Roots are in soil shoots or leaves are partly outside and partly inside the water. Plants show heterophilly (Amphibious plants) e.g., Typha, Ranunculus, Sagittaria, Cyperus.

Morphological adaptations

(i) Roots of hydrophytes are poorly developed or completely absent in Wolfia, Ceratophyllum etc. Root hair absent but root pockets may be present e.g., Pistia, Eichornia, Trapa.

(ii) Stem is reduced in free floating plants e.g., Pistia, narrow and slender in submerged plants e.g., Hydrilla, Ceratophyllum and well developed in amphibious plants e.g., Typha.

(iii) Petioles become long, swollen and spongy for floating.

(iv) Leaves are usually long ribbon like e.g., Potamogeton, or finely divided e.g., Ranunculus or thin and broad e.g., Nelumbo, Victoria.

(v) In some hydrophytes leaves of different forms are produced by same plant. Aerial leaves are not dissected but submerged leaves dissected (Heterophilly) e.g., Ranunculuc, Limnophila.

Anatomical adaptations

(i) Cuticle absent or poorly developed.

(ii) Stomata are absent in submerged plants. Floating hydrophytes have stomata on upper surface e.g., Lotus (epistomatic).

(iii) Air spaces are extensively developed in root, stem and leaves. Well developed aerenchyma helps in buoyancy and gaseous exchange.

(iv) Leaves have spongy tissues and palisade is poorly developed. As light difuses from all palisade and spongy tissue. Epidermal cells contain chloroplasts for maximum capturing of difused light.

(v) Mechanical tissues like sclerenchyma (lignified tissues) and collenchyma are poorly developed or absent.

(vi) Vascular tissues are poorly developed.

Physiological adaptation

(i) Water and mineral nutrients are absorbed through general body surface.

(ii) Osmotic concentration or osmotic potential of cells is equal to or is slightly higher than external water.

(2) Xerophytes : They are adapted to grow in dry habitats. On the basis of pattern of life cycle, xerophytes are of three types :

(i) Ephemerals : They complete their life cycle in a very short period, evade dry season by disappearing, leaving their seeds. They are referred as drought escapers or drought evaderes e.g., Cassia toria, Argemone maxicana, Solanum xanthocarpum.

(ii) Succulents (Fleshy xerophytes) : They absorb large quantities of water during rainy season and store water in different body parts. They are common in deserts and referred as drought avoiding xerophytes e.g., Opuntia, Bryophyllum, Euphorbia, Mesembryanthemum (ice plant).

(iii) Non succulents : They are true xerophytes and called as drought resistant. They can with stand long drought periods e.g., Acacia, Calotropis, Casuarina, Nerium, Capparis, Prosopis.

Xerophytes are further divided in to different types :

(a) Oxylophytes : Plants growing on acidic soil.

(b) Psychrophytes : Plants growing on cold soil.

(d) Lithophytes : Plants growing on rocks.

(e) Chersophytes : Plants growing on waste land.

(f) Eremophytes : Plants growing in deserts and steppes.

(g) Psilophytes : Plants growing in savannah.

(h) Helophytes : Plants growing in mud.

Morphological adaptations

(i) Roots of xerophytes are extensively developed to increase water absorption. Roots are much more longer than the shoots. Root hairs and root caps are well developed. The roots reach to great depth.

(ii) Stems of xerophytes is usually stunted (dwarf), woody, dry, hard and covered with thick bark. Stem is modified into flat leaf like phylloclades or cladodes e.g., Opuntia, Ruscus, Asparagus.

(iii) Leaves of xerophytes are usually thick may be reduced to spines e.g., Opuntia, scales e.g., Casuarina or may become needle like e.g., Pinus (Microphyllous) or may absent e.g., Capparis. Leaves and stem become fleshy (Malacophyllous) e.g., Bryophyllum.

Anatomical adaptations

(i) Stomata are sunken and generally on the lower surface of leaves.

(ii) Epidermal cells thick walled and covered by hairs (Trichophyllous). e.g., Calotropis. Epidermis may be multilayered (Multiple epidermis) e.g., Ficus, Nerium.

(iii) Palisade generally on both sides (surfaces) of leaves e.g., Nerium.

(iv) In leaves spongy parenchyma are absent.

(v) Water storing parenchyma, conducting tissues and mechanical tissues are well develop.

(vi) Bulliform or motor cells are found in between the cells of upper epidermis. These cells cause rolling and unrolling of leaves e.g., Poa, Amnophila (grasses).

(vii) In Nerium leaf, upper as well as lower epidermis are multiseriate or multiple and are covered with thick cuticle. Mesophyll is different into palisade and spongy parenchyma palisade tissue occurs near both the epidermis while spongy parenchyma is located in between the palisade.

(viii) In Ficus leaf, upper epidermis is multiseriate and is thickly cuticularised. Cystoliths are present is the cells of inner layers of this epidermis.

Physiological adaptations

(i) Osmotic concentration or osmotic potential of cell sap is high.

(ii) They have resistance to dessication and mucilage to hold water.

(iii) They show less transpiration.

(3) Halophytes : They are special types of xerophytic plants which grow on saline soils with high concentrations of salts like NaCl, MgCl₂, MgSO₄ (Physiologically dry soil). Most of these are succulents. They have negatively geotropic roots for gaseous exchange called Pneumatophores. Halophytes show Vivipary (germination of seeds inside the fruits).

Halophytic communities growing on swamps are called helophilous halophytes which are of two types :

(i) Salt swamp and salt desert.

(ii) Littoral swamp forests which are most extensive in all tropical areas.

Swamp forest forms a characteristic vegetation called mangroves e.g., Rhizophora, Sonneratia, Avecenia, Heritiera, Salsola.

In India mangroves are quite common in sea shores of Bombay and Kerala, an in Andamans and Nicobar Islands.

(4) Mesophytes : Plants growing in places of moderate water supply. These plants cannot live for a long time either in water saturated or in moisture deficient soil. e.g., garden plants and crops.

Biotic or Ecological Succession

Community are never stable but keep on changing. This relatively definite sequence of communities over a period of time in the same area is called ecological succession.

Types : Succession is of two types :

(1) Primary succession : It includes changes which occur when living things become established on a previously uninhabited area such as a newly exposed sea floor, lake sediments or sand dunes.

(2) Secondary succession : It occurs where early communities have been damaged, leaving a few organisms and considerable organic matter. These remnant species, along with some new ones, regenerate a new community.

l According to another classification, the succession is of following types :

(1) Autogenic succession : When the succession has begun, the vegetation itself is responsible for replacing itself by changing existing environmental conditions.

(2) Allogenic succession : When in succession other conditions (not vegetation itself) are responsible for replacing communities, then it is called allogenic succession.

l Depending upon the substratum, succession are divided into three types :

(1) Hydrosere or Hydrarch : Succession beginning in fresh water, e.g., ponds, lakes, streams, etc.

(2) Xerosere or Xerarch : Succession beginning in dry conditions. It is further classified into three types :

(i) Lithosere : When succession starts on bare rocks.

(ii) Psammosere : When succession begins on sand.

(iii) Halosere : When succession starts in saline conditions.

(3) Mesarch : When succession begins in mesic conditions.

General processes of succession

Succession is completed in following steps :

(1) Nudation : Formation of bare area without any form of life is called nudation. The cause of nudation may be climatic, topographic or biotic.

(2) Invasion : Successful establishment of a species in this bare area is called invasion. It has three steps :

(i) Migration (ii) Ecesis or establishment (iii) Aggregation

(3) Competetion and coaction : Competetion may be interspecific or intraspecific.

Intraspecific competetion is called coaction.

(4) Reaction : Modification of environment due to organisms in it is called reaction.

(5) Stabilization : The terminal community becomes stabilized in the prevailing conditions.

Biotic succession on bare rock (Lithosere, Xerosere).

The sequence of successional stages that occur on bare rocks is called lithosere. Because the bare rock is deficient in water, the lithosere is also called xerosere.

The various seral stages are as follows :

(1) Lichen stage : Bare rock is invaded first by crustose lichens (e.g., Graphis). They corrode the rock at places causing foliose lichens to invade, eliminate crustose lichens and creating conditions for invasion by mosses. In tropics, blue green algae are pioneers instead of lichens.

(2) Moss stage : Mosses are of larger size, have gregareous habit and their rhizoids penetrate deeper in the rocks. They shade the lichens and hence replace the same. Mosses accumulate more soil and organic matter.

(3) Annual grass stage : Annual hardy grasses and herbs invade the humus rich moss dominated rock surface, e.g., Aristida, Poa. Their roots cause fragmentation of the rock, creating more soil, humus and moisture.

This increases moisture and soil. The soil becomes favourable for growth of longer lived annual grasses. The process of soil accumulation continues.

(4) Perennial grass stage : Annual grasses are replaced by perennial grasses due to increased moisture and soil in the rock crevices. The perennial grasses have runners and rhizomes which rapidly spread the grasses, e.g., Cymbopogon, Heteropogon, Shade, moisture, soil, perennial vegetation and seeds invite several small animals.

(5) Shrub stage : Shrubs begin to grow in area occupied by perennial grasses, e.g., Zizyphus, Caparis, Rhus, Rubus. Shrubs are larger and their roots reach greater depth causing further cracks in the rock substratum and hence helping in more soil formation. The shrubs shade the area, make it more moist and invite hardy trees and several types of animals.

(6) Climax community : Initially hardy light demanding small trees invade the area. They make the habitat shadier and more moist. Ultimately, trees shrubs and herbs representing the climax community begin to grow in the area.

Biotic succession in newly formed pond/lake (Hydrosere) : Seres of biotic communities that develop in a newly formed pond or lake is called hydrosere. It starts as soon as the muddy water becomes clear. The various successional or seral stages of hydrosere are :

(1) Plankton stage : Phytoplanktons (diatoms, flagellates, blue green and green algae) are the pioneers in a freshly formed water body. They are almost immediately followed by zooplanktons that feed on phytoplanktons.

(2) Submerged stage : The bottom lined by soft mud having organic matter is favourable for growth of submerged plants like Hydrilla and Najas. They are rooted in the mud and form dense growth. As a result sand and silt get deposited around the plants. The bottom level, therefore, rises slowly. The older plants and buried parts of other plants form humus on their death and decay.

(3) Floating stage : In the shallower regions appear plants with tuberous rhizomatous and creeping stems and leaves floating on the surface of water, e.g., Nymphaea, Nelumbo. At places, free floating plants also appear (e.g., Azolla, Wolffia, Lemna) to cover the water surface. Humus rich bottom begins to rise making water shallower.

(4) Reed swamp stage : Amphibious plants grow where the water body becomes shallow (0.3-1.0m), e.g., Phragmites, Typha, Scirpus, Sagittaria. The plants of swamp stage transpire huge quantities of water. They also produce abundant organic matter. Their tangled growth accumulates silt.

(5) Sedge/Marsh meadow stage : On newly built up shores, Carex (Sedge), Juncus, Cyperus, some grasses and herbs (Themeda, Caltha, Polygonum) grow rapidly and lower the water table. The plants transpire rapidly and add abundant humus. Therefore, soil is build up to invite next stage.

(6) Woodland stage : Rhizome bearing shrubs and small trees capable of tolerating excessive light and water logged conditions appear on the edges of sedge/marsh meadow, e.g., Cornus, Cephalanthus, Populus, Alnus.

The shrubs shade away the plants of sedge meadow stage. They invite invasion by trees capable of bearing bright sunlight and water logging, e.g., Populus (Cottonwood), Alnus (Alder). The plants of woodland stage lower the water lable by their transpiration. They also built up more soil. Shade loving plants come to grow below them.

(7) Climax forest : New trees, shrubs and herbs appear which are in perfect harmony with the climate of the area.

Importance of biotic succession

(1) Sequence of biotic succession is usually fixed. Ecologists can immediately recognise the seral stage of a biotic community found in an area.

(2) It tells us how a biotic seral stage like grasses and herbs of a pasture can be maintained by not allowing the biotic succession to proceed further through interference like grazing and fire.

(3) Information gained through biotic succession is used in having controlled growth of one or more species by preventing their superiors to invade the area, e.g., maintenance of teak forest.

(4) Dams are protected by preventing siltation and biotic succession to occur.

? Hult first of all gave the term ecological succession.

? The first group or community in succession is called as pioneer community.

? The last community in succession is called climax community.

? Climax community is always mesophytic.

? Different stages of succession are called seral stages and all these seral stages constitute a sere.

? Endophyte : A plant growing within an other as parasite or symbiont.

? Ectophyte : An external plant parasite.

? Retrogressive succession is in which continuous biotic influences have some degenerating influence on the process e.g., change of forest to shrubby or grassland community.

? Serule or microsere is the succession of micro organisms with in microhabitat.

? Euryhaline : Organisms which can tolerate wide fluctuations in salt concentration.

? Sternohaline : Organisms which cannot tolerate fluctuations in salt concentrations but live at nearly constant concentration.

? Tropophytes : Hygrophilous in rainy season, xerophilous at other times.

? Crinohalophytes : Salt secreting halophytes.

Avicennia, Rhizophora and Atiplex are [Orissa JEE 2005]

(a) Xerophytes (b) Halophytes

Which of the following is not a hydrophytic angiosperm

[RPMT 1997]

(a) Chara (b) Hydrilla

In ecological succession from pioneer to climax community, the biomass shall [CPMT 1991]

(a) Decrease

(b) Increase and then decrease

(d) Increase continuously

Mechanical tissue is undeveloped in [CPMT 1994]

(a) Xerophytes (b) Hydrophytes

Which one is partially submerged and fixed in mud

[RPMT 1996]

(a) Marsilea (b) Cyperus

(a) Chara is not a hydrophytic angiosperm, it belongs to the chlorophyceae or green algae.
(b) Mechanical tissues like sclerenchyma (lignified tissues) and collenchyma are poorly developed or absent.
(d) Typha is a rooted emergent. Roots are in soil shoots or leaves are partly outside and partly inside the water.

***

Ecological plant groups and Succession

Succession is

(a) Series of physical changes that occur in an area

(b) Development of biotic communities on a bare area

(d) Both (a) and (b)

In succession the seral forms are

(a) Large sized (b) Long lived

Succession on secondary bare area is

(a) Primosere (b) Xerosere

Secondary succession occurs on

(a) Burnt lands (b) Lumbered lands

Plant succession is a …………. process

(a) Definite (b) Haphazard

In submerged plants

(a) Anaerobic respiration is a rule

(b) Aerobic respiration occurs by utilizing dissolved oxygen of water

(d) None of the above

Mangrove forests are found in

(a) Uttar Pradesh (b) Madhya Pradesh

Water plants provide ……. to water animals

(a) O₂ and food (b) Water and CO₂

The early settlers on a barren area are [NCERT 1980]

(a) Ferns (b) Mosses

A community which starts succession in a habitat is

[AMU 1983, 89, 98; Manipal 1997]

(a) Pioneer community (b) Seral community

Mangrove vegetation is found in

[BHU 1986; Haryana PMT 2005]

(a) Dehradoon valley (b) Kullu valley

Alpine plants which are commonly found at the top of mountains show [MP PMT 1988]

(a) Xerophytism (b) Hydrophytism

Ephemerals are xerophytes that are [BHU 1990]

(a) Drought enduring (b) Drought escaping

Plants growing in saline and marshy conditions are called

[BHU 1990, 91; AFMC 1987, 90; CPMT 2002]

(a) Lithophytes (b) Mesophytes

The vegetation of Delhi is chiefly [CPMT 1991]

(a) Hydrophytic (b) Xerophytic

Extreme xerophytic condition is shown by [CPMT 1991]

(a) Brassica (b) Capparis

Desert can be converted into greenland by

[MP PMT 1994; AIIMS 2001]

(a) Oxylophytes (b) Psammophytes

In halophytes, pneumatophores are helpful in [CPMT 1993]

(a) Protein synthesis (b) Respiration

Rhizophora is an example of [RPMT 1995]

(a) Hydrophytes (b) Lithophytes

Acacia arabica is a [AFMC 1997; BVP 2000]

(a) Mesophyte (b) Hydrophyte

Casuarina equisetifolia is a [EAMCET 1995]

(a) Mesophyte (b) Xerophyte

The plants in which vascular tissues are absent and well developed aerenchyma is present, are [CPMT 1995]

(a) Xerophytes (b) Halophytes

Eichornia crassipes is a [MP PMT 1996]

(a) Desert plant (b) Parasite

Plants of salty seashore wet–lands are called [MP PMT 1996]

(a) Halophytes (b) Heliophytes

Pneumatophores plants are found

[CPMT 1999; JIPMER 2001]

(a) In desert (b) Near river banks

Excessive aerenchyma is characteristic of [CPMT 1999]

(a) Hydrophytes (b) Xerophytes

Mark the correct pair [KCET 1998]

(a) Plants growing in shady places – Heliophytes

(b) Plants growing in light – Sciophytes

(d) Roots are absent – Xerophytes

Pneumatophore roots are present in

[Pb. PMT 1999; RPMT 1999]

(a) Mesophytes (b) Xerophytes

Which is adapted for aquatic habit

[Pb. PMT 1999; RPMT 1999]

(a) Aldrovenda (b) Vallisneria

The first plants to reappear in a badly burned forest area will most probably be [CPMT 1988]

(a) Mosses (b) Liverworts

Last stabilised community in a plant succession is known as

[CPMT 1984; DPMT 2004]

(a) Seral Community (b) Pioneer Community

Intermediate community between pioneer and climax communities is called [AMU 1983]

(a) Seral Community (b) Biotic Community

Climax vegetation of a region is generally [CPMT 1987]

(a) Xerophytic

(b) Hydrophytic

(d) Depends upon the climate

Primary succession is development of communities on

[CBSE PMT 1995]

(a) Newly exposed habitat

(b) Cleared forest area

(d) Pond filled after a dry season

Succession showing changes in communities at a place is called [AMU 1997]

(a) Geographical succession (b) Biotic succession

Xeric environment is characterised by [CBSE PMT 1994]

(a) Precipitation

(b) Low atmospheric humidity

(d) High rate of vapourisation

What is wrong about xerophytes [CPMT 1994]

(a) Sunken stomata

(b) Small spiny leaves

(d) Larger number of stomata

Which one is not a trait of xerophytes [Bih. PMT 1995]

(a) Thick cuticle

(b) Sunken stomata

(d) Well developed mechanical tissue

Which one lacks both roots and stomata [RPMT 1996]

(a) Hydrophytes (b) Mesophytes

The vegetation of Rajasthan is

[CPMT 1996; Pb. PMT 2000; MHCET 2001, 03]

(a) Arctic (b) Alpine

Submerged hydrophytes exchange gases through

[AIIMS 1997; Pb. PMT 2000; CPMT 2001,
Bihar PMT 2001]

(a) Stomata (b) Hydathodes

Type of plants having adaptations to check transpiration is

[JIPMER 1998]

(a) Xerophytes (b) Lithophytes

The primary succession in a sere is [AMU 1998]

(a) Sub sere (b) Meso sere

One of them is a submerged hydrophyte [CPMT 1998]

(a) Ceratophyllum (b) Utricularia

Plants growing on sandstone are [RPMT 2000]

(a) Psammophytes (b) Oxylophytes

Plants like Rhizophora and Avecennia grow on the sea shores under saline condition. For this they have special roots for respiration which are called [CPMT 2000]

(a) Prop roots (b) Climbing roots

Last stage of plant succession is [RPMT 2000]

(a) Ecotype (b) Seral community

Plants growing in acidic soils are known as [JIPMER 2002]

(a) Psammophytes (b) Oxalophytes

A physiological xerophyte is [APMEE 2002]

(a) Salicornia (b) Euphorbia

Root cap is absent in [RPMT 2002; Manipal 2005]

(a) Halophytes (b) Hydrophytes

Plants growing in saline soil/high concentration of salts are

[CPMT 2002; RPMT 2002]

(a) Xerophytes (b) Halophytes

Which is not true of hydrophytes [Orissa 2002]

(a) Poorly developed root system

(b) Thin membranous leaves

(d) Poorly developed vascular bundles

A succulent xerophyte is [DPMT 2002]

(a) Capparis (b) Calotropis

Hydrophytes are characterised by [MP PMT 2003]

(a) Thick and large leaf

(b) Delicate and mucilagenous stem

(d) All of the above

Mechanical tissue is best developed in [CPMT 2003]

(a) Hydrophytes (b) Halophytes

Plants adapted to grow in shade are [CMC 2003]

(a) Psammophytes (b) Sciophytes

Halophytes are [Orissa JEE 2004]

(a) Salt resistant (b) Fire resistant

Rhizophora is a characteristic component of

[CPMT 1982; BHU 1984; MP PMT 2004; Orissa JEE 2004]

(a) Marsh plants (b) Swamp forests

Characteristic feature of mangrove plants is [HP PMT 2005]

(a) Vivipary (b) Heterospory

Plants near seashore is an example of [Bihar 2005]

(a) Halophyte (b) Mesophyte

In succession complexicities in structure[Haryana PMT 2005]

(a) Drastically increasing (b) Slowly increasing

Mangroves are [MP PMT 2005]

(a) Xerophytes (b) Hydrophytes

The waxy surface of the floating leaves of the hydrophytes prevents [Orissa JEE 2005]

(a) Respiration (b) Photosynthesis

Among the plants listed, point out one that does not fit into ecological group represented by other plants

[CPMT 1988; BHU 1999]

(a) Acacia (b) Rhizophora/Vallisneria

Succession in a 6 metre deep pond exhibits a sequence of

[CPMT 1989, 91]

(a) Submerged Plants ® Reeds ® Herbs ® Floating Plants ® Shrubs ® Trees

(b) Floating Plants ® Submerged Plants ® Reeds ® Herbs ® Shrubs ® Trees

(d) Submerged Plants ® Floating Plants ® Reeds ® Herbs ® Shrubs ® Trees

A nonsucculent xerophyte with thick leathery leaves having white sticky waxy coating is [DPMT 1999]

(a) Nerium (b) Calotropis

Ecological succession on sand is

[CPMT 1985; CET Chd. 2000, 02]

(a) Psammosere (b) Xerosere

Hydrophyte with both hydrophytic and xerophytic traits is

[CPMT 2001]

(a) Agave (b) Nerium

Biotic succession is caused by [AIEEE 2003]

(a) Competition amongst species

(b) Occurrence of diseases

(d) Adaptive ability to environmental changes

Submerged hydrophytes have commonly dissected leaves for [Haryana PMT 2003]

(a) Decreasing surface area

(b) Increasing surface area

(d) Increasing number of stomata

Read the assertion and reason carefully to mark the correct option out of the options given below :

(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion

(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion

(c) If the assertion is true but the reason is false

(d) If both the assertion and reason are false

(e) If the assertion is false but reason is true

Assertion : Aerenchyma is present in the leaves and petioles of hydrophytes.

Reason : Aerenchyma imparts buoyancy to the hydrophytes.

Assertion : Many mangrove plants possess high levels of organic solutes.

Reason : This is an adaptation to cope with the conditions of high salt concentration and osmotic potential.

Assertion : Presence of pneumatophores (the respiratory roots) is a special adaptation of hydrophytes.

Reason : Pneumatophores help to take up oxygen from the atmosphere and transport it to the main roots.

Assertion : Lichens and mosses are said to form the pioneer community in xerarch succession.

Reason : It is because these species get established later, during the course of succession.

Assertion : Community organisation, food chains and food web are complex in both seral and climax stages.

Reason : Seral and Climax stages are similar in structure and functions.

Assertion : Xerosere is a type of succession

Reason : It starts in water.

Assertion : Primary succession takes a very long time.

Reason : Succession taking place after forest fire is called primary succession.

Ecological plant groups and Succession

1	c	2	c	3	c	4	d	5	a
6	b	7	c	8	a	9	c	10	a
11	d	12	a	13	b	14	c	15	c
16	c	17	b	18	b	19	d	20	c
21	b	22	c	23	c	24	a	25	b
26	a	27	c	28	d	29	b	30	a
31	d	32	a	33	c	34	a	35	b
36	b	37	d	38	c	39	a	40	d
41	d	42	a	43	c	44	c	45	c
46	d	47	c	48	b	49	a	50	b
51	b	52	c	53	c	54	b	55	c
56	b	57	a	58	c	59	a	60	a
61	b	62	c	63	c

Critical Thinking Questions

1	b	2	d	3	b	4	a	5	d
6	d	7	c

Assertion and Reason

1	a	2	a	3	e	4	c	5	d
6	c	7	c

Ecological plant groups and Succession

(c) When the biotic succession that occurs on a previously sterile or primarily bare area are called primary succession.
(c) Size of individuals are small in the seral stage and large in the climax stage.
(c) Secondary succession or subsere is a biotic succession that occurs in an area which became secondarily bared due to destruction of the community previously present there.
(a) Water plants provide and food because they are the producers they give by the process of photosynthesis and water plants are eaten by the water animals as their food.
(c) Lichens are the early settlers on a barren area because they can tolerate desiccation heating during summer noon or excessive cooling during winter nights. They secrete lichen acids and carbonic acid. The acids slowly corrode rock surface and release minerals required for proper growth of lichens.
(a) The first biotic community which develops in a bare area is called pioneer community. It has very little diversity. This stage takes the longest time to change the environment for invasion of the next community.
(a) Because they can not absorb water due to ice-formation.
(b) Ephemerals complete their life cycle in a very short period, evade dry season by disappearing, leaving their seeds. They are referred as drought escapers or drought evaders.
(c) Halophytes are special types of xerophilous plants which grow on saline soils and marshy conditions with high concentrations of salts like and
(c) Because it has all the xerophytic character like modification of leaves into spines etc.
(b) Because plants which grow on sand are called psammophytes and deserts are made up of sand.
(b) Halophytes possess small negatively geotrophic vertical roots called pneumatophores. Pneumatophores have lenticels for gaseous exchange.
(c) Aerenchyma helps in floating of hydrophyte plants.
(a) Halophytes are plants of saline habitats which have not only the ability to tolerate high conc. of salts in their rooting medium but are able to obtain their water supply from the same. Halophytes grow in saline soils, mangroves, coastal dunes and tidal marshes.
(b) Pneumatophores are negatively geotropic specialised root branches produced in large numbers by some vascular plants growing in the water of tidal swamps (e.g., mangroves).
(a) In aquatic plants, the intercellular spaces in parenchyma develop to a considerable extent so as to form a connected system throughout the plant. Such a modified parenchymatous tissue is called aerenchyma. It helps in the circulation of air as well as provides buoyancy to plants.
(d) Pneumatophore roots are the aerial roots. It have important role in respiration of halophytic plants.
(d) Climax community is the stable, self perpetuating and final biotic community that develops at the end of biotic succession and is in perfect harmony with the physical environment.
(a) The various biotic communities that develop during biotic succession are termed as seral or transitional communities. The entire sequence of development stages of biotic succession from pioneer to a climax community is known as sere.
(a) Newly exposed sea floor, igneous rocks, sand dunes, lava sediments or newly submerged areas are some of the examples of primary bare area. It is quite hostile to first life or pioneer community. Primary succession takes a very long time.
(b) Communities are never stable but keep on changing. This relatively definite sequence of communities over a period of time in the same area is called ecological succession.
(d) In xerophytes stomata are sunken, less in number and restricted to lower surface of the leaves.
(c) Aerenchyma is a trait of hydrophytes.
(a) Roots of hydrophytes are poorly developed or completely absent in Wolfia. Stomata are absent in submerged plants. But floating hydrophytes have stomata on upper surface. e.g., Lotus.
(d) In Rajasthan, the rainfall is less and soil has little amount of water. Here, the vegetation is xerophytic.
(a) In xerophytes, a thick envelope of hairs on epidermis and around sunken stomata. This layer forms an insulating envelope and checks increase in temperature which is helpful to check transpiration.
(d) Pneumatophores is aerial root found in these plants which grow in marshy places. Its main function is respiration.
(b) Plants growing in soil which have acidic nature, rich amount of humans and lack of ions are known as oxalophytes.
(c) All hydrophytes show presence of large air chambers. The tissue that forms air chambers is called aerenchyma.
(c) In succulent xerophyte, plants have fleshy organs where water and mucilage are stored. Depending upon the organ where succulence occurs, the succulents show chylocauly e.g., Opuntia, and chylophylly e.g., Agave or chylorhizy e.g., Asparagus.
(b) In hydrophytes stem is long. Slender spongy and flexible which often covered with mucilage.
(c) Mechanical tissues like collenchyma and sclerenchyma are well developed in xerophytes.
(b) Sciophytes are shade plants which grow in areas having moderate to low intensity light, as below the shade of other plants. Optimum growth occurs with light of 10-30% of full sunlight.
(c) A few mangrove plants secrete salts from their roots. Some have water storage tissues to dilute salt, e.g., Rhizophora (Red Mangrove).
(a) Mangroves are halophytes and vivipary is its characteristic. Vivipary is the germination of seed inside the fruit while it is still attached to the plant. e.g., Avicenia, Rhizophora, Sonneratia, Salsola etc.
(a) Plants growing in mangroves are halophytes. Mangroves are marshy areas found in tropical deltas and saline ponds near seashore. The areas have not only excess salt but also excess water.

Critical Thinking Questions

(b) Acacia, Aloe and Euphorbia are xerophytic plants while Vallisneria is hydrophyte and Rhizophora belongs to the halophyte plant group.
(d) Seres of biotic communities that develop in a newly formed pond or lake is called hydrosere. It starts as soon as the muddy water becomes clear. Seral stages starts with the submerged plants and the climax community is represented by trees.
(a) When succession begins on sand is called Psammosere. Psammophilous plants growing in sandy swamps.
(c) Plants with both submerged and floating or emerged leaves show heterophylly or occurence of more than one type of leaves. The leaves below water are narrow and with cut or dissected margins to reduce effect of water current and leaves which are above water one broader and with entire margins.

Assertion and Reason

(a) Plants which remain permanently immersed in water are called hydrohytes. They may be submerged or partly submerged and show the presence of aerenchyma (large air space) in the leaves and petioles. Aerenchyma helps to transport oxygen produced during photosynthesis and permits its free diffusion to other parts, including roots located in anaerobic soils. These tissues also impart buoyancy to the plants. Presence of inflated petioles in Eichhornia (water hyacinth) keeps the plants floating on the surface of water.
(a) Mangroves are found in marshy conditions of tropical deltas and along ocean edges. For coping with conditions of high salt concentration and osmotic potential, Many mangrove plants have high levels of organic solutes, such as proline and sorbitol. Dunaliella species (green and halophytic algae found in hyper saline lakes) can tolerate saline conditions by accumulating Glycerol in the cells, which helps in osmoregulation. Some species of mangroves can excrete salts through the salt glands on the leaves. Some mangroves can exclude salts from the roots by pumping excess salts back into soil.
(e) Presence of pneumatophores (the respiratory roots) is a special adaptation of halophytes and not of hydrophytes. Halophytes are plants of saline environments, which are adapted to grow in high concentration of salt in soil or water. On the other hand, hydrophytes are the plants which remain permanently immersed in water (submerged or partly submerged). Since halophytes are exposed to saline and anaerobic conditions in wetlands, they have developed special adaptations like pneumatophores prop and stilt roots, and vivipary etc. The presence of pneumatophores (the respiratory roots) helps to take up oxygen from the atmosphere and transport it to the main roots. Prop and stilt roots, in many species of mangroves, give support to the plants in wet substratum, vivipary (seeds germinate while on the tree) permits plants to escape the effect of salinity on seed germination.
(c) The plants that invade the base land initially, are called pioneer community. Lichens and mosses form the pioneer community in xerarch succession species. The assemblage of pioneer species forms the pioneer. Lichens form a crust over the base rocks and begin to form soil from their organic remains and by stimulating chemical breakdown of the rocks. Lichens are normally followed by mosses, which speed up the process of soil accumulation by trapping wind blown particles. Mosses grow in bunch, and together with lichens, make a mat over the substratum. In this way, lichens and mosses get established on barren rock as pioneer species forming the pioneer community. Generally, the pioneer species show high rate of growth but short life span. In time, the pioneer community is replaced by another community with different species combination. This second community is replaced by a third community, and so on. The plant species which get established later, during the course of succession, are known as late successional species. These species are slow growing and long lived. The terminal stage of succession is represented by the climax community which is stable and does not show change is species composition, as long as the environmental conditions remain the same.
(d) The biotic communities are dynamic in nature and change with the passage of time. The different communities or stages represented by combinations of mosses, herbs shrubs and trees replacing one another during succession are referred to as seral stages or seral communities. The terminal stage of succession is represented by the climax community. The climax community is stable and does not show changes in species composition, as long as the environmental conditions remains the same. The seral stages differ from climax stages with reference to structure and functions. The average size of individuals generally increases and the community organisation becomes more complex in the climax community as compared to the seral community. The food webs become complex during successional stages. The efficiency of energy use and nutrient conservation increase as the community progresses towards the climax stage. The species composition at the climax stage is determined by the regional climate, as well as local conditions of soil, topography and water availability. The climax stage reflects the highest level of vegetation and the associated fauna that can be supported under the given environmental conditions.
(c) Succession that proceeds in an area where there deficiency of water is called xerosere. Succession which proceeds in water in called hydrosere.
(c) Primary succession is a biotic succession that occurs on a previously sterile or primarily bare area. Primary succession takes a very long time. It is often 1000 years or more. Secondary succession is a biotic succession that occurs in an area which became secondarily bared due to destruction of the community previously present there. Secondary succession occurs on the land bared due to forest fire.

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