3.8 Exercise Problems

Q1. What is the basis of the classification of algae?

Answer: Algae are classified into three main classes – Chlorophyceae, Phaeophyceae, and Rhodophyceae. These divisions are based on the following factors:
(a) Major photosynthetic pigments present
(b) Form of stored food
(c) Cell wall composition
(d) Number of flagella and position of insertion
Class I – Chlorophyceae
Common name – Green algae
Major pigments – Chlorophylls a and b
Stored food – Starch
Cell wall composition – Cellulose
Flagella number and position – 2,8; equal and apical
Class II – Phaeophyceae
Common name- Brown algae
Major pigments – Chlorophylls a and c, and fucoxanthin
Stored food – Mannitol and laminarin
Cell wall composition – Cellulose and algin
Flagella number and position – 2; unequal and lateral
Class III – Rhodophyceae
Common name – Red algae
Major pigments – Chlorophylls a and b, and phycoerythrin
Stored food – Floridean starch
Cell wall – Cellulose, pectin, and polysulphate esters
Flagella number – Absent

Q2. When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?

Answer: Liverwort – In liverworts, the main plant body is haploid (gametophytic). It bears the male and female sex organs which produce gametes. These gametes fuse to form a zygote. The zygote develops on the gametophytic plant body to form a sporophyte. The sporophyte is differentiated into the foot, seta, and capsule. Many haploid spores are produced as a result of the reduction division taking place inside the capsule.
Moss – In mosses, the primary protonema (developed in the first stage) develops into the secondary protonema. Both these stages are haploid or gametophytic. The secondary protonema bears the sex organs which produce gametes. These gametes fuse to form a zygote. The zygote develops into a sporophyte. Many spores are formed as a result of the reduction division taking place in the capsule of this sporophyte.
Fern – In ferns, the main plant body is sporophytic. Its leaves are known as sporophylls and these bear the sporangia. Reduction division takes place in these sporangia, thereby producing many spores.
Gymnosperm – In gymnosperms, the main plant body is sporophytic. They bear two types of leaves – microsporophylls and megasporophylls. Reduction division takes place in the microsporangia present on the microsporophylls (producing pollen grains) and on the megasporangia present on the megasporophylls (producing megaspores).
Angiosperm – In angiosperms, the main plant body is sporophytic and bears flowers. The male sex organ in the flower is the stamen, while the female sex organ is the pistil. Reduction division takes place in the anthers of the stamen (producing haploid pollen grains) and in the ovary of the pistil (producing eggs).

Q3. Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.

Answer: Archegonium is the female sex organ that produces the female gamete or egg. It is present in the life cycles of bryophytes, pteridophytes, and gymnosperms. Life cycle of a fern (Dryopteris)
Dryopteris is a common fern with pinnately-compound leaves. The main plant body is sporophytic. Many sporangia are borne on the lower surfaces of its mature leaves. Each sporangium has spore mother cells which undergo meiosis to produce haploid spores. On maturing, these spores dehisce and germinate to give rise to a heart-shaped gametophyte called prothallus.
The prothallus bears the male and female sex organs called antheridia and archegonia respectively. The antheridia produce sperms that swim in the water to reach the archegonia. The egg is produced by the archegonia. As a result of fertilization, a zygote is formed. The zygote forms an embryo, which in turn develops into a new sporophyte. The young plant comes out of the archegonium of the parent gametophyte.

Q4. Mention the ploidy of the following: protonemal cell of a moss; primary endosperm nucleus in dicot, leaf cell of a moss; prothallus cell of a ferm; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.

Answer: (a) Protonemal cell of a moss – Haploid
(b) Primary endosperm nucleus in a dicot – Triploid
(c) Leaf cell of a moss-haploid
(d) Prothallus of a fern – Haploid
(e) Gemma cell in Marchantia – Haploid
(f) Meristem cell of a monocot – Diploid
(g) Ovum of a liverwort – Haploid
(h) Zygote of a fern – Diploid

Q5. Write a note on the economic importance of algae and gymnosperms.

Answer: Economic importance of algae
Algae have diverse economic uses. They perform half of the total carbon dioxide fixation on earth by photosynthesis, acting as the primary producers in aquatic habitats.
(a) Food source: Many species of marine algae such as Porphyra, Sargassum, and Laminaria are edible. Chlorella and Spirulina are rich in proteins. Thus, they are used as food supplements.
(b) Commercial importance: Agar is used in the preparation of jellies and ice cream. It is obtained from Gelidium and Gracilaria. Carrageenan is used as an emulsifier in chocolates, paints, and toothpaste. It is obtained from the red algae.
(c) Medicines: Many red algae such as Corallina are used in treating worm infections.
Economic importance of gymnosperms
(a) Construction purposes: Many conifers such as pine, cedar, etc., are sources of the soft wood used in construction and packing.
(b) Medicinal uses: An anticancer drug Taxol is obtained from Taxus. Many species of Ephedra produce ephedrine, which can be used in the treatment of asthma and bronchitis.
(c) Food source: The seeds of Pinus gerardiana (known as chilgoza) are edible.
(d) Source of resins: Resins are used commercially for manufacturing sealing waxes and water-proof paints. A type of resin known as turpentine is obtained from various species of Pinus.

Q6. Both gymnosperms and angiosperms bear seeds, then why are they classified separately?

Answer: Gymnosperms and angiosperms are seed-producing plants with diplontic life cycles.
In gymnosperms, the sporophylls are aggregated to form compact cones. The microsporophylls are broad and are not distinguished into filaments and anthers. The megasporophylls are woody and lack the ovary, style, and stigma, because of which the ovules lie exposed. The female gametophyte consists of archegonia. The fertilisation process involves the fusion of a male gamete with the female gamete. Their endosperm is haploid. The produced seeds are naked as there is no fruit formation.
Angiosperms are also known as flowering plants. They have sporophylls that aggregate to form flowers with the perianth. The microsporophylls consist of stamens containing pollen sacs. These sacs bear the male gametes called pollen grains. The megasporophylls are delicate and rolled, forming carpels that contain the ovary, style, and stigma. The ovules are present inside the ovary. The archegonium is replaced by an egg apparatus. Two male gametes enter the egg apparatus at the time of fertilisation. One male gamete fertilises the egg and the other fuses with the diploid secondary nucleus to form an endosperm. The resulting endosperm is thus triploid. In addition, in angiosperms, the development of seeds takes place inside the fruits.

Q7. What is heterospory? Briefly comment on its significance. Give two examples.

Answer: Heterospory is a phenomenon in which two kinds of spores are borne by the same plant. These spores differ in size. The smaller one is known as microspore and the larger one is known as megaspore. The microspore germinates to form the male gametophyte and the megaspore germinates to form the female gametophyte. The male gametophyte releases the male gametes and these reach the female gametophyte to fuse with the egg. The development of the zygote takes place inside the female gametophyte. This retention and germination of the megaspore within the megasporangium ensure the proper development of the zygote. The zygote develops into the future sporophyte. The evolution of the seed habit is related to the retention of the megaspore. Heterospory is thus considered an important step in evolution as it is a precursor to the seed habit. Heterospory evolved first in pteridophytes such as Selaginella and Salvinia.

Q8. Explain briefly the following terms with suitable examples:-
(i) protonema
(ii) antheridium
(iii) archegonium
(iv) diplontic
(v) sporophyll
(vi) Isogamy

Answer: (i) Protonema – It is the first stage in the life cycle of a moss, developing directly from the spore. It consists of creeping, green, branched, and often filamentous structures.
(ii) Antheridium – It is the male sex organ present in bryophytes and pteridophytes and is surrounded by a jacket of sterile cells. It encloses the sperm mother cells, which give rise to the male gametes.
(iii) Archegonium – It is the female sex organ present in bryophytes, pteridophytes, and gymnosperms. In bryophytes and pteridophytes, it generally has a swollen venter and a tubular neck, and contains the female gamete called the egg.
(iv) Diplontic – It is the term used for the life cycles of seed-bearing plants (gymnosperms and angiosperms). In these plants, the diploid sporophyte is dominant, photosynthetic, and independent. The gametophyte is represented by a single-celled (or a few-celled) structure.
(v) Sporophyll – In pteridophytes, the sporophytic plant body bears sporangia. These sporangia are subtended by leaf-like appendages known as sporophylls. In gymnosperms, microsporophylls and megasporophylls are found. These bear microspores and megaspores respectively.
(vi) Isogamy – It is a type of sexual reproduction involving the fusion of morphologically similar gametes. This means that the gametes are of the same size, but perform different functions. This type of reproduction is commonly observed in Spirogyra.

Q9. Differentiate between the following:
(i) red algae and brown algae
(ii) liverworts and moss
(iii) homosporous and heterosporous pteridophyte
(iv) syngamy and triple fusion

Answer: (i) Red algae and brown algae

\(
\begin{array}{|l|l|}
\hline \text { Red algae } & \text { Brown algae } \\
\hline \begin{array}{l}
\text { 1. Red algae are } \\
\text { grouped under the class } \\
\text { Rhodophyceae. }
\end{array} & \begin{array}{l}
\text { 1. Brown algae are } \\
\text { grouped under the } \\
\text { class Phaeophyceae. }
\end{array} \\
\hline \begin{array}{l}
\text { 2. They contain } \\
\text { Floridian starch as } \\
\text { stored food. }
\end{array} & \begin{array}{l}
\text { 2. They contain } \\
\text { mannitol or laminarin as } \\
\text { stored food. }
\end{array} \\
\hline \begin{array}{l}
\text { 3. They contain the } \\
\text { photosynthetic } \\
\text { pigments chlorophyll a } \\
\text { and d, and } \\
\text { phycoerythrin. }
\end{array} & \begin{array}{l}
\text { 3. They contain the } \\
\text { photosynthetic } \\
\text { pigments chlorophyll a } \\
\text { and c, and fucoxanthin. }
\end{array} \\
\hline \begin{array}{l}
\text { 4. Their cell walls are } \\
\text { composed of cellulose, } \\
\text { pectin, and } \\
\text { polysulphate esters. }
\end{array} & \begin{array}{l}
\text { 4. Their cell walls are } \\
\text { composed of cellulose } \\
\text { and algin. }
\end{array} \\
\hline \text { 5. Flagella are absent } & \begin{array}{l}
\text { 5. Two flagella are } \\
\text { present }
\end{array} \\
\hline
\end{array}
\)

(ii) Liverworts and moss

\(
\begin{array}{|l|l|}
\hline \text { Liverworts } & \text { Moss } \\
\hline \begin{array}{l}
\text { 1. They have } \\
\text { unicellular rhizoids. }
\end{array} & \begin{array}{l}
\text { 1. They have } \\
\text { multicellular } \\
\text { rhizoids. }
\end{array} \\
\hline \begin{array}{l}
\text { 2. Scales are present } \\
\text { very often }
\end{array} & \text { 2. Scales are absent } \\
\hline \begin{array}{l}
\text { 3. They are generally } \\
\text { thalloid, with } \\
\text { dichotomous } \\
\text { branching. }
\end{array} & \begin{array}{l}
\text { 3. They are foliage, } \\
\text { with lateral } \\
\text { branching. }
\end{array} \\
\hline \begin{array}{l}
\text { 4. Gemma cups are } \\
\text { present }
\end{array} & \begin{array}{l}
\text { 4. Gemma cups are } \\
\text { absent }
\end{array} \\
\hline \begin{array}{l}
\text { 5. Sporophyte has } \\
\text { very photosynthetic } \\
\text { tissue little }
\end{array} & \begin{array}{l}
\text { 5. Sporohyte has } \\
\text { abundant } \\
\text { photosynthetic } \\
\text { tissue }
\end{array} \\
\hline
\end{array}
\)

(iii) Homosporous and heterosporous pteridophyte

\(
\begin{array}{|l|l|}
\hline \begin{array}{l}
\text { Homosporous } \\
\text { pteridophytes }
\end{array} & \begin{array}{l}
\text { Heterosporous } \\
\text { pteridophytes }
\end{array} \\
\hline \begin{array}{l}
\text { 1. They bear } \\
\text { spores that } \\
\text { are of the } \\
\text { same type. }
\end{array} & \begin{array}{l}
\text { They bear two } \\
\text { kings of spores } \\
\text { microspores } \\
\text { and } \\
\text { megaspores. }
\end{array} \\
\hline \begin{array}{l}
\text { 2. They } \\
\text { produce } \\
\text { bisexual } \\
\text { gametophytes. }
\end{array} & \begin{array}{l}
\text { They produce } \\
\text { unisexual } \\
\text { gametophytes. }
\end{array} \\
\hline
\end{array}
\)

(iv) Syngamy and triple fusion

\(
\begin{array}{|c|c|}
\hline \text { Syngamy } & \text { Triple fusion } \\
\hline \begin{array}{l}
\text { 1. It is the } \\
\text { process of } \\
\text { fusion of the } \\
\text { male gamete } \\
\text { with the egg } \\
\text { in an } \\
\text { angiosperm. }
\end{array} & \begin{array}{l}
\text { 1. It is } \\
\text { process of } \\
\text { fusion of the } \\
\text { male gamete } \\
\text { with the } \\
\text { diploid } \\
\text { secondary } \\
\text { nucleus in an } \\
\text { angiosperm. }
\end{array} \\
\hline \begin{array}{l}
\text { 2. A diploid } \\
\text { zygote is } \\
\text { formed as a } \\
\text { result of } \\
\text { syngamy. }
\end{array} & \begin{array}{l}
\text { 2. A triploid } \\
\text { primary } \\
\text { endosperm } \\
\text { is formed as } \\
\text { a result of } \\
\text { triple fusion }
\end{array} \\
\hline
\end{array}
\)

Q10. Match the following (column I with column II)

\(
\begin{array}{ll}
\text { Column I } & \text { Column II } \\
\text { (a) Chlamydomonas } & \text { (i) Moss } \\
\text { (b) Cycas } & \text { (ii) Pteridophyte } \\
\text { (c) Selaginella } & \text { (iii) Algae } \\
\text { (d) Sphagnum } & \text { (iv) Gymnosperm }
\end{array}
\)

Answer:

\(
\begin{array}{|l|l|}
\hline \text { Column I } & \text { Column II } \\
\hline \begin{array}{l}
\text { (a) Chlamydomonas } \\
\end{array} & \text { (iii) Algae } \\
\hline \text { (b) Cycas } & \text { (iii) Gymnosperm } \\
\hline \text { (c) Selaginella } & \text { (ii) Pteriodphyte } \\
\hline \text { (d) Sphagnum } & \text { (i) Moss } \\
\hline
\end{array}
\)

Q11. Describe the important characteristics of gymnosperms.

Answer: Important features of gymnosperms:
(a) The term gymnosperm refers to plants with naked seeds (gymnos – naked, sperma – seeds), i.e., the seeds of these plants are not enclosed in fruits.
(b) The plant body ranges from medium to tall trees and shrubs. The giant redwood tree Sequoia is one of the tallest trees in the world.
(c) The root system consists of tap roots. The coralloid roots present in Cycas are associated with nitrogen-fixing cyanobacteria.
(d) The stem can be branched (as in Pinus and Cedrus) or un-branched (as in Cycas).
(e) The leaves can be simple (as in Pinus) or compound (pinnate in Cycas). The leaves are needle-like, with a thick cuticle and sunken stomata. These help in preventing water loss.
(f) Gymnosperms are heterosporous. They bear two kinds of spores – microspores and megaspores.
(g) Flowers are absent. The microsporophylls and megasporophylls are arranged to form compact male and female cones.
(h) Pollination occurs mostly through wind and pollen grains reach the pollen chamber of the ovule through the micropyle.
(i) The male and female gametophytes are dependent on the sporophyte.
(j) The seeds contain haploid endosperms and remain uncovered.

Exemplar Section

VERY SHORT ANSWER TYPE QUESTIONS

Q1. Food is stored as Floridean starch in Rhodophyceae. Mannitol is the reserve food material of which group of algae?

Answer: Mannitol is the reserve food material of brown algae or phaeophyceae.

Q2. Give an example of plants with
a. Haplontic life cycle
b. Diplontic life cycle
c. Haplo-diplontic life cycle

Answer: a. Haplontic life cycle-Volvox, Spirogyra and some species of Chlamydomonas
b. Diplontic life cycle-AH seed-bearing plants, i.e. (gymnosperms and angiosperms)
c. Haplo-diplontic life cycle-Bryophyte and Pteridophytes

Q3. The plant body in higher plants is well differentiated and well developed. Roots are the organs used for the purpose of absorption. What is the equivalent of roots in the less developed lower plants?

Answer: In lower plants like algae, holdfast is present and in bryophytes, rhizoids are present instead of roots.

Q4. Most algal genera show haplontic life style. Name an alga which is
a. Haplo-diplontic
b. Diplontic

Answer: a. Haplo-diplontic-Ectocarpus, Polysiphonia and Kelps b. Diplontic-Fucus

Q5. In Bryophytes male and female sex organs are called _________ and _______.

Answer: In Bryophytes male sex organ is called antheridium and female sex organ is called archegonium.

SHORT ANSWER TYPE QUESTIONS

Q1. Why are bryophytes called the amphibians of the plant kingdom?

Answer: Bryophytes are also called amphibians of the plant kingdom because these plants can live in soil but are dependent on water for sexual reproduction.

Q2. The male and female reproductive organs of several pteridophytes and gymnosperms are comparable to floral structures of angiosperms. Make an attempt to compare the various reproductive parts of pteridophytes and gymnosperms with reproductive structures of angiosperms.

Answer:

\(
\begin{array}{|l|l|l|}
\hline & \text { Reproductive parts of pteridophytes and gymnosperms } & \begin{array}{l}
\text { Reproductive structures of } \\
\text { angiosperms }
\end{array} \\
\hline \text { (i) } & \text { Strobili/cone } & \text { Flower } \\
\hline \text { (ii) } & \text { Microsporophyll } & \text { Stamen } \\
\hline \text { (iii) } & \text { Megasporophyll } & \text { Pistil/Carpel } \\
\hline \text { (iv) } & \text { Microsporangium } & \text { Anther } \\
\hline \text { (v) } & \text { Megasporangium } & \text { Ovule } \\
\hline
\end{array}
\)

Q3. Heterospory i.e., formation of two types of spores – microspores and megaspores is a characteristic feature in the life cycle of a few members of pteridophytes and all spermatophytes. Do you think heterospory has some evolutionary significance in plant kingdom?

Answer: In majority of the pteridophytes all the spores are of similar kinds, such plants are called hom’osporous. Genera like Selaginella, Salvirtia, Marsilea and Azolla which produce two kinds of spores, macro (large) and micro (small) spores are known as heterosporous. The megaspores and microspores germinate and give rise to female and male gametophytes, respectively.
The female gametophytes in these plants are retained on the parent sporophytes for variable periods. The development of the zygotes into young embryos take place within the female gametophytes. This event is a precursor to the seed habit considered an important step in evolution.

Q4. How far does Selaginella one of the few living members of lycopodiales (pteridophytes) fall short of seed habit.

Answer: Selaginella produce two kinds of spores, macro (large) and micro (small) spores. The megaspores and microspores germinate and give rise to female and male gametophytes, respectively. But Selaginella falls short of seed habit due to lack of integument around the megasporangium.

Q5. Each plant or group of plants has some phylogenetic significance in relation to evolution : Cycas, one of the few living members of gymnosperms is called as the ‘relic of past’. Can you establish a phylogenetic relationship of Cycas with any other group of plants that justifies the above statement?

Answer: Cycas, one of the few living members of gymnosperms is called as the ‘relic of past’ because it shows many characteristics which are similar to pteridophytes, like, flagellated antherozoids, circinate ptyxis, megasporophyll is leaf like, presence of archegonia, etc.

Q6. The heterosporous pteridophytes show certain characteristics, which are precursor to the seed habit in gymnosperms. Explain.

Answer: In majority of the pteridophytes all the spores are of similar kinds, such plants are called homosporous. Genera like Selaginella, Salvinia, Marsilea and Azolla which produce two kinds of spores, macro (large) and micro (small) spores, are known as heterosporous. The megaspores and microspores germinate and give rise to female and male gametophytes, respectively.
The female gametophytes in these plants are retained on the parent sporophytes for variable periods. The development of the zygotes into young embryos take place within the female gametophytes. This event is a precursor to the seed habit considered an important step in evolution.

Q7. Comment on the lifecycle and nature of a fern prothallus.

Answer: The diploid sporophyte is represented by a dominant, independent, photosynthetic, vascular plant body. It alternates with multicellular, saprophytic/autotrophic, independent but short-lived haploid gametophyte called prothallus. Such a pattern is known as haplo-diplontic life cycle. All pteridophytes exhibit this pattern.
These gametophytes require cool, damp, shady places to grow. Because of this specific restricted requirement and the need of water for fertilisation, the spread of living pteridophytes is limited and restricted to narrow geographical regions. The gametophytes (prothallus) bear male and female sex organs ‘ called antheridia and archegonia, respectively.
Water is required for transfer of antherozoids-the male gametes released from the antheridia, to the mouth of archegonium. Fusion of male gamete with the egg present in the archegonium result in the fonnation of zygote. Zygote thereafter produces a multicellular well-differentiated sporophyte which is the dominant phase of the pteridophytes.

Q8. How are the male and female gametophytes of pteridophytes and gymnosperms different from each other?

Answer: Male and female gametophytes of pteridophytes are free living while in gymnosperms male and female gametophyte do not have free-living existence. They remain within the sporangia retained on sporophytes.
\(
\begin{array}{|l|l|l|l|}
\hline & \text { Pteridophytes } & & \text { Gymnosperms } \\
\hline \text { (i) } & \text { Flagellated male gamete } & \text { (a) } & \text { Non-flagellated male gamete } \\
\hline \text { (ii) } & \text { Water is essential for fertilisation } & \text { (b) } & \text { Water is not essential } \\
\hline \text { (iii) } & \text { Pollen tubes are not formed } & \text { (c) } & \text { Pollen tubes are formed } \\
\hline \text { (iv) } & \text { Archegonia with neck canal cells } & \text { (d) } & \text { Neck canal cells are absent } \\
\hline
\end{array}
\)

Q9. In which plant will you look for mycorrhiza and corolloid roots? Also explain what these terms mean.

Answer:Mycorrhiza: Mycorrhiza is the symbiotic association between a fungus and the roots of higher plants. It is observed in Pinus (a gymnosperm).

Coralloid roots: Coralloid roots are the roots containing cyanobacteria, which help in nitrogen fixation and are seen in Cycas (a gymnosperm).

LONG ANSWER TYPE QUESTIONS

Q1. Gametophyte is a dominant phase in the life cycle of a bryophyte. Explain.

Answer: The main plant body of the biyophyte is haploid. It produces gametes, hence is called a gametophyte. The sex organs in bryophytes are multicellular.
The male sex organ is called antheridium. They produce biflagellate antherozoids or biciliated sperms. The female sex organ called archegonium is flask-shaped and produces a single egg. The antherozoids are released into water where they come in contact with archegonium. An antherozoid fuses with the egg to produce the zygote. Zygote do not undergo reduction division immediately. They produce a multicellular body called a sporophyte.

Q2. With the help of a schematic diagram describe the haplo-diplontic life cycle pattern of a plant group.

Answer: In a sexually reproducing plant there is an alternation of generation between a haploid and a diploid phase of plant bodies. The haploid plant body is termed gametophyte while the diploid plant body is called sporophyte. The gametophyte produces gametes by mitosis while the haploid spores are produced by sporophyte following meiosis (reduction division). Two gamete fuse together to produce a zygote which develops into the diploid sporophyte.

In a haplodiplontic life cycle pattern, such as in bryophyta or pteridophyta both the phases of life are multicellular. However, in bryophytes, the gametophytes are small, photosynthetic, independent and represent dominant phase. The partly or totally dependent sporophyte is physically attached to the gametophyte. The ( \(n\) ) spores dispersed by sporophyte germinate into individual gametophytic plants. However, in pteridophytes the \(2n\) (diploid) phase is dominant, well organized, independent while the n phase though also free-living and independent is short lived and photosynthetic. In both of these groups of plants the mobile male gametes, antherozoid produced by sex organ antheridium, travel to archegonium (bearing an egg cell) via the medium of water. Egg cell is non-motile hence the reproduction is oogamous.

Q3. Lichen is usually cited as an example of ‘symbiosis’ in plants where an algal and a fungal species live together for their mutual benefit. Which of the following will happen if algal and fungal partners are separated from each other?
a. Both will survive and grow normally and independent from each other.
b. Both will die
c. Algal component will survive while the fungal component will die.
d. Fungal component will survive while algal partner will die.

Based on your answer how do you justify this association as symbiosis.

Answer: Lichen is usually cited as an example of symbiosis in biology where in a fungal and an algal species live together for mutual benefit. The algal component synthesizes the food through photosynthesis which is utilized by the fungal species for its survival. The fungal component in return provides shelter and waste products that are consumed by algal species.
Experiments though have shown that algal component can grow independently when separated from fungal species. But same is not true with the fungal component which dies when separated from algal component. This association is, therefore, a typical case of master-slave relationship where fungus (master) has trapped the algal components (slave) for its own survival while giving nothing in return to it. Some authors consider this association as controlled parasitism or helotism due to the fact that sometimes the fungus sends its haustoria into the algal cells to derive nourishment.

Q4. Explain why sexual reproduction in angiosperms is said to take place through double fertilization and triple fusion. Also draw a labelled diagram of embryo sac to explain the phenomena.

Answer: After entering one of the synergids, the pollen tube release the two male gametes into the cytoplasm of the synergid. In angiosperm one male gamete fuses with the female gamete to form zygote while the fusion of the male gamete and the secondary nucleus forms the primary endosperm nucleus or (PEN).

When two instances of fusion of nuclei take place this phenomenon is known as Double Fertilization. As the male gamete fuses with secondary nucleus having two polar nuclei results in the formation of endosperm which has \(3 n\) chromosome, this phenomenon is known as Triple fusion.

Q5. Draw labelled diagrams of
a. Female and male thallus of a liverwort.
b. Gametophyte and sporophyte of Funaria.
c. Alternation of generation in Angiosperm.

Answer: (a) Female and male thallus of a liverwort:

(b) Funaria, gametophyte and sporophyte: 

 

(c) Alternation of generation in Angiosperm: