Class 11 Biology Chapter 3 Plant Kingdom, 1st Year

Chapter 3

  Plant Kingdom  


Q1. What is the basis of classification of algae?
Answer:  Algae are classified into three main classes on the basis of absence or presence of pigments. They are-
• Chlorophyceae are green in colour due to the presence of pigments chlorophyll a and b. They are also known as blue-green algae.
• Phaeophyceae are brown colour algae and this is due to the presence of xanthophyll pigment called fucoxanthin. They also possess chlorophyll a and c, and carotenoid.
• Rhodophyceae are commonly known as red algae because of the presence of red pigment called phycoerythrin.


Q2. When and where does reduction division takes place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?
Answer:  The saprophytic plant produces haploid spores after meiosis in the case of liverwort, moss and fern; meiosis occurs in antheridium and ovary in the case of gymnosperm and an angiosperm. These were occurs for the formation of pollen grain and ovules.


Q3. Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
Answer:  Three groups of plants that bear archegonia are bryophytes, pteridophytes and gymnosperms. Archegonium is the female sex organs that generate egg.
In bryophyte, the main body of the plant is haploid. It produces gametophyte. The male sex organ is antheridium which produces biflagellate antherozoids. Archegonium is the female sex organs that generate egg. The antherozoids are released into the water where they come in contact with archegonium. Antherozoid fuses with the egg and form zygote. Zygote produces sporophyte which is not free-living i.e., it is attached to the photosynthetic gametophyte. Some cells of sporophyte undergo reduction division to generate haploid spores. These spores germinate to produce 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: Protonemal cell of a moss: Haploid
Primary endosperm nucleus in dicot: Triploid, Leaf cell of a moss: Haploid
Prothallus cell of a ferm: Haploid
Gemma cell in Marchantia: Diploid
Meristem cell of monocot, ovum of a liverwort, and zygote of a fern:  Diploid; Diploid; Zygote.



Q5. Write a note on economic importance of algae and gymnosperms.
Answer: Almost 50% of the total carbon dioxide on earth is fixed by algae through photosynthesis and increase the level of dissolve oxygen in the air. They also formed the primary producers of energy-rich compounds which form the basis of the food cycles of all aquatic animals. Some species of marine algae are used as food. Some species of marine brown and red algae produce hydrocolloids which are water holding substances. Some species of algae are used as culture medium in laboratories.
Gymnosperms are widely used as ornamental plants. Fibers from conifer are used as paper pulp. Cornifers are also used in reforestation projects. Conifers also produced useful oils like pine, juniper, etc.



Q6. Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
Answer: Gymnosperms and angiosperms bear seeds but they are classified separately because gymnosperm’s seeds are naked whereas angiosperm’s seeds are covered.



Q7. What is heterospory? Briefly comment on its significance. Give two examples.
Answer: The megaspore germinates in heterospory to produce female gametophyte while the microspore germinates to produce the male gametophyte. This occurrence is a precursor of the habit of seed in higher plants. Example: 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: In bryophyte life cycle, it appears the earliest stage. It is like thread of chain of cells. It developed just after the germination of spores.  
ii. Antheridium: It is the male sex organ of a plant which produces the male gametes. It is found in the gametophyte phase of lower plants and in sporophyte phase of higher plants.
iii. Archegonium: Three groups of plants that bear archegonia are bryophytes, pteridophytes and gymnosperms. Archegonium is the female sex organs that generate egg.
iv. Diplontic : In diplontic, the diploid sporophyte is the dominant photosynthetic phase of the plant. Angiosperms and gymnosperms show this.
v. Sporophyll : A leaf which bears sporangia is known as sporophyll. Sporophylls can generate megaspores or microspores.
vi. Isogamy : In isogamy, gametes are similar in size. The gametes can be non-flagellated or flagellated.



Q9. Differentiate between the following:

i. Red algae and brown algae:
Rhodophyceae are commonly known as red algae because of the presence of red pigment called phycoerythrin. They store food as floridean starch.
Phaeophyceae are brown colour algae and this is due to the presence of xanthophyll pigment called fucoxanthin. They also possess chlorophyll a and c, and carotenoid. They store food as Mannitol, laminarin.

ii. Liverworts and moss:
In liverworts, thallus is dorsoventrally flattened and lobed liver like. Rhizoids are unicellular.
In moss, thallus is leafy and radially symmetrical. Rhizoids are multicellular.

iii. Homosporous and heterosporous pteridophyte
Pteridophytes which produce only one kind of spores are said as homosporous pteridophyte.
Pteridophytes which produce two kinds of spores are said as heterosporous pteridophyte.

iv. Syngamy and triple fusion
Syngamy is the fusion of one male gamete with the egg and form zygote.
Triple fusion is the fusion of second male gamete with secondary nucleus to form triploid endosperm.



Q 10. How would you distinguish monocots from dicots?
Answer:  Monocots are characterized by the presence of one cotyledon in the seed whereas dicots are characterized by the presence of two cotyledons in the seed.



Q11. Match the followings
    Column I                     Column II
a. Chlamydomonas       i. Moss
b. Cycas                          ii. Pteridophyte
c. Selaginella  iii. Algae
d. Sphagnum         iv. Gymnosprem
Answer: 
a. iii.
b. iv.
c. ii.
d. i.



Q12. Describe the importance characteristics of gymnosperms.
Answer: 
• The seeds of gymnosperm are naked.
• Roots are tap roots.
• The stems are branch or unbranched.
• The leaves may be simple or compound.
• The leaves are well-developed to withstand extremes of temperature, wind, and humidity.


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