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Biology Notes 2023 All Chapters 12th Class
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Notes All Chapters 12th Class Biology
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12th Class Biology Notes 2023 All Chapters
Diversity Among Plants Biology Notes Class 11
Table of Contents
Q.2 i) Define alternation of generation and give its importance.
Alternation of generation:
“The occurrence of two or more forms differently produced in the life cycle of a plant or animal usually involving the regular alternation of sex with an asexual generation.”
“Alternation of generation is a mode of reproduction in which there is an alternation of an asexual with a sexual generation. The sporophyte produces spores which on germination give rise to a gametophyte. The gametophyte gives rise to haploid cells (egg and sperms, the fusion of these results into a young sporophyte.”
Importance of alternation of generation:
Alternation of generation is an adaptation to land habitat which ensures diversity and variations in characters. These variations help the plant to adjust and survive the land habitat.
Define alternation of generation and give its importance
Q.2 ii) Define heterogamy.
“Heterogamy is a type of sexual reproduction in which the gametes differ in both size and forms. The larger gamete, or egg, is nonmotile; the smaller gamete, or sperm, is motile.”
“Heterogamy is a state of conjugating gametes (egg and sperm) that are different in size, structure, and function.”
Q.2 iii) What are an antheridium and an archegonium?
Answer: 1. Antheridium:
“The male sexual organ of algae, mosses, ferns, fungi, and other non-flowering plants is as the antheridium.”
Structure of antheridium:
The antheridium is a multicellular, short-stalk, club-shape body which is fill up with numerous small cells as antherozoid cells. The antheridium bursts at the apex and the antherozoid cells are liberate through it in a mass of mucilage. The mucilaginous walls surrounding antherozoid cells dissolve in water and the antherozoid are set free. They are very minute in size, spirally coiled and ciliated; after liberation, they swim in water that collects at the apex of the moss plant after rains.
“The female sexual organ of algae, mosses, ferns, fungi, and other non-flowering plants is as the archegonium.”
Structure of archegonium:
The archegonium is a multicellular body, but it is flask-shape in appearance. It is provided with a short, multicellular stalk and consists of two portions;
I– Venter (belly):
The lower swollen portion is as the center (belly).
The upper tube-like portion is call the neck. The neck is long, narrow and straight.
Within the venter there lies a large cell which is the ovum (egg-cell or noosphere) or female gamete; above this lies a small ventral canal-cell and higher up in the neck there are a few neck canal-cells. Except the ovum other cells mention above are functionless and soon get disorganize.
The neck at first remains closed at the apex by a sort of lid, but as the archegonium matures, the lid opens and allows the antherozoids to enter and pass through it where egg and sperm fuse to form a zygote which develops into the sporophyte.
Q.2 iv) Give differences between bryophytes and tracheophytes.
Bryophytes do not have a vascular system
Tracheophytes have a well-developed vascular system
They lack specialized vascular tissue
They have a well-developed vascular system which consists of xylem and phloem
Bryophytes are typically quite small and a few exceed 2cm in length
Tracheophytes range in size from few CMS up to 30m
Mosses, liverworts and hornworts are examples of bryophytes.
Tracheophytes include fern, gymnosperms and angiosperms.
Bryophytes do not have such transportation mechanisms; they do not have specialized cells and tissues to perform this function for them.
Tracheophytes have a well-develop vascular system through which water and nutrients are transport from the roots to the leaves and carbohydrates are transport from the leaves to the rest of the plant.
Bryophytes have no water system so they can only grow in or near water
Tracheophytes can grow almost in any habitat
Q.2 v) Give three examples of subphylum pillowside.
Examples of Pillowside:
Rhynia Psilophyton (Psilopsidom)
Q.2 vi) Give three differences between angiosperms and gymnosperms.
Angiosperms are seed-producing flowering plants whose seeds are enclose within an ovary.
Gymnosperms are seed-producing non-flowering plants whose seeds are unenclose or naked
Reproductive organs are present in flowers which can be unisexual or bisexual
Reproductive structures are cones which are unisexual
Leaves are flat in shape
Leaves are scalelike and needle-like in shape
Q.2 vii) What is the difference between microphylls leaf and megaphylls leaf?
1. Microphylls leaves:
Microphylls is a leaf with a single vein
A microphylls leaf is present in club moss and horsetails.
There are two possibilities for the origin of the microphylls leaf.
One possibility is that this leaf originated as an outgrowth, lacking vascular tissue, from the naked branches of the primitive plant. With an increase in size, it needed support and transport so vascular tissue in the form of one vein appeared in it.
Another possibility is that the microphylls leaf originated by the reduction in the size of a part of the leafless branching system of the primitive vascular plant.
2. Megaphylls leaves:
A leaf with more than one vein or vascular trace that is associate with a gap in the central stele.
A megaphylls leaf is found in many plants such as the leaf of Ginkgo.
The leaves are evolve by the evolutionary modification of the forked branching system. The branching system became flat during the evolution of megaphylls leaf. This step of the evolution of the megaphylls leaf is call a plantation. Next, in evolution, the spaces between the bundles and branches of vascular tissue became filled with photosynthetic tissue. This process is call webbing. The organ, now a leaf, looked superficially the webbed foot of a duck. The branches changed into veins which resulted in many veined leaves or megaphylls leaves.
Biology Notes class 11 Long Questions pdf
Q.3 i) Describe the adaptations shown by bryophytes to land life.
Answer: Land adaptations by bryophytes:
Bryophytes had invaded the land from water and therefore, they are called the first invaders of land among plants. They show the following adaptations for life on land or terrestrial habitat.
1. Multicellular plant body and conservation of water:
When the bryophytes migrated to land from water, they faced the danger of dehydration due to evaporation. To cope with this problem, they developed many structures which prevented the loss of water or dehydration. Plant body or thallus was of many cells which kept the needful water within them for a successful life. Moreover, for protecting dehydration due to evaporation from the surface of the cells, they formed a waxy waterproof layer called cuticle (made of cetin) on the epidermis. Despite these adaptations, if some bryophytes are dry, they become brittle and turn green soon after getting water from rain or any other source of water.
2. Absorption of carbon dioxide:
Bryophytes have evolved elaborate structures to absorb sufficient carbon dioxide. The epidermis is provided with many pores for the diffusion of carbon dioxide and oxygen. This carbon dioxide is absorbe by the wet surfaces of the photosynthetic cells for the life processes of the bryophytes.
3. Absorption of water:
Bryophytes have no roots or root-hairs for absorbing water from the soil. They have developed long hair-like structures called rhizoids from the lower surface of the thallus to absorb water from the soil which enables the bryophytes to live on land.
The universal occurrence of sexual reproduction of heterogamous type involving the union of sperm and egg in green plants like bryophytes is the most successful type of reproduction. The large, non-motile egg formed in heterogamy is full of stored food. After fertilization, this store food is use to nourish the early stages in the development of new offspring. The heterogamous sexual reproduction is best suite for life on land.
5. Protection of reproductive cells:
Reproductive cells should be safe and protected from any kind of injury for the plants to live on land. Fortunately, the bryophytes possess this important character which enables them to survive land habitat. The reproductive cells are sperms and egg or oosphere. The sperms remain protected in male sex organ or antheridium and the egg in the female sex organ or archegonium. The sex-organs are prevent from drying by the leaf-like structures and sterile hairs produce at the shoots which bear the sex organ. Moreover, the spores of these land plants are also well protect from drying. Spores are produce in multicellular sporangia.
6. Embryo formation:
In bryophytes, the sperms are transport to the egg and unite with it inside the female reproductive structure. A zygote is form here which develops into an embryo. The embryo remains protected in the female organ from drying out and from mechanical injury. In this way, the chances of survival are increase.
7. Alternation of generation:
The life cycle of bryophytes shows clear alternation of generation for its survival on land. Alternation of generation is an adaptation to land habitat which ensures diversity and variations in characters. These variations help the plant to adjust and survive the land habitat.
Q.3 ii) Explain the life cycle of flowering plants.
The life cycle of a flowering (Angiosperm) plant:
The angiosperms plant is a diploid sporophyte which is composed of root, stem, leaves, and flowers.
Flower the reproductive organ:
A flower is a reproductive organ, white stamens and the carpels are its reproductive parts.
Stamens are male reproductive parts. Each stamen consists of an anther with four pollen sacs. A large number of microspores are produced by meiosis in each pollen sac. The wall of microspore becomes thick and is known as pollen grain.
During pollination, the pollen grains are transferred to the stigma of the carpels. The pollen grain germinates and develops into male gametophyte or microgametophyte. The nucleus of the pollen grain divides into a generative nucleus and vegetative or tube nucleus. The generative nucleus divides into two male gametes. The pollen grain sends down a tube called the pollen tube which contains two male gametes and tube nucleus. Male gametophyte:
The pollen tube together with the two male gametes and a tube nucleus constitutes the male gametophyte.
Carpels are the female reproductive parts. The carpel consists of a basal swollen part, the ovary, which contains one or many ovules. The ovule consists of a tissue called nucellus, which is covered by the integument. Certain changes occur in the ovule, leading to the formation of megaspore.
Female gametophyte or embryo sac:
The megaspore generally develops into a seven-celled female gametophyte or embryo sac. One of these seven cells is the egg or oosphere and the other is the endosperm mother cell which is diploid.
The pollen tube enters the female gametophyte. The tip of the pollen tube ruptures and the two sperms are released into the female gametophyte. One sperm fuse with the egg to form zygote or oospore and the other sperm fuses with the endosperm mother cell to form fusion nucleus. The fusion of one sperm with the egg to form a zygote and that of the other with the endosperm mother cell to form fusion nucleus is called double fertilization, which occurs only in the angiosperms.
The oospore develops into an embryo which consists of a radical, hypocotyl, plumule and one or two cotyledons.
The fusion nucleus develops into a nutritive tissue called endosperm.
After fertilization, the ovule matures into a seed. The integuments of the ovule from the seed coats called teste and tegmen.
The wall of the ovary develops into fruit on ripening. Under favorable conditions, the seed germinates to produce seedling which on development becomes sporophyte. The two kinds of generation i.e., gametophyte and sporophyte, one after the other show alternation of generation.
Successful adaptation of angiosperm on land:
Angiosperms are successful because they can adapt to almost all kinds of environments. Moreover, they produce flowers, fruits, and seeds which show various adaptations for dispersal over large areas. Double fertilization is of common occurrence. They range in size from 1mm up to 100m. They possess broad leaves and maybe annual, biennial or perennial.
ife cycle of an angiospermmint plant
Q.3 iii) Write a detailed note on any two of the following:
This is the oldest group of most primitive rootless, leafless vascular plants. The sporophyte body shows little organ differentiation.
The stem is differentiated into an underground rhizome and an aerial part. The rhizome grows horizontally in soil and may bear rhizoids but no roots. The upright stem shows dichotomous or forked (Y-shaped) branching.
2. Reproductive organs:
The reproductive organs are sporangia (singular: sporangium) which are produced at the tips of the branches. The spores are formed in sporangia.
The two living genera are Psilotum and Tmesipeteris.
Examples of Psilopsida:
Rhynia, Cooksonia, Psilophyton (Pillowside), Psilotum and Mesenteries.
b. Sphenopsid (horsetails):
This group includes both extinct (e.g., Calamites) and living plants e.g., Equisetum, the only surviving genus. In this group, the individual plant is seldom more than a few feet high.
The plant is the sporophyte, distinguished into roots, stem and leaves.
The stem is not smooth but has ridges, furrows or ribs, and is divided into joints, nodes and internodes. Therefore, these plants are also called arthrophytes.
The leaves are reduced to scales and arranged into whorls at each node. Sporangia are closely packed to form terminal cones or strobilus.
The underground stem or rhizome branches frequently and is anchored by adventitious roots usually formed at the node.
4. Reproductive organs:
The upright green branches are numerous. Special lateral appendages called sporangiophores are developed which bear sporangia. Spores are produced in each sporangium.
The mature gametophyte body is a more or less flattened, irregularly shaped structure called a Prothallus. It is held to the substrate by slender root-like rhizoids. The antheridia and archegonia are borne on the upper surface. There is a distinct alternation of generation.
c. Lycopsida (Club mosses):
Lycopsida is commonly called club mosses. They are not mossing but called club mosses because their strobili are club-shaped and their leaves resemble the mosses.
Lycopsida includes both the living and fossil genera.
The living genera are Lycopodium, Selaginella, Isoetes and Phyllogenous.
The fossil genera are Liriodendron and Sigillaria etc.
The plants of glycosides are sporophytes, differentiated into roots, stem and true leaves.
The leaves are small and simple and are called microphylls (one veined leaf) leaves. The leaves usually densely surround the stem. Branching is dichotomous.
The spores are formed in sporangia. The gametophyte of glycoside is large, underground and independent. The sporangia develop singly on the upper side of the sporophylls. The sporophylls usually form strobila. At the base of sporophylls is a small outgrowth called ligule to retain moisture. In some glycoside, such as Lycopodium, the ligule is absent.
One example is Selaginella.
Selaginella comprises over three hundred species, most of which are tropical and grow abundantly on hills.
Selaginella grows in damp places in the hills and the plains. It is a slender, much-branched plant, either creeping on the wall or the ground.
The slender stem bears four rows of leaves—two rows of small leaves on the upper surface and two rows of larger leaves at the two sides.
A long slender, root-like organ is given off from the stem which is known as the rhizosphere (root-bearer).
Selaginella plant is the sporophyte. It bears two kinds of sporophylls – microsporophylls and megasporophylls. Both kinds of sporophylls may occur together in the same cone, or they may be borne in two separate cones either on the same plant or on two separate plants. All the sporophylls are near to equal size and spirally arranged, usually in four rows, around the apex of the reproductive shoot, in the form of a more or less distinct four-angled cone, called the splendiferous spike or strobilus. The sporophylls are similar to the vegetative leaves in appearance but are smaller in size.
Biology Notes FA FSC Chapter No 8 Diversity Among Plants 4
Q.3 iv) Give important characters of liverworts and hornworts.
Important characters of liverworts and hornworts (Bryophytes):
Liverworts and hornworts are nonvascular plants. Thus, the transportation of food, water and minerals occurs by diffusion.
The plant body is green branched thallus, lacking true roots, stems or leaves, but possessing hair-like rhizoids instead of roots.
The plant body is gametophyte, which bears multicellular male and female reproductive organs called antheridia (singular antheridium) and archegonia (singular archegonium) respectively.
The sex organs produce male and female gametes by mitosis. The male gametes are called sperms which are motile while the female gamete is called egg or oosphere which is non-motile and one in each archegonium.
The sperms swim towards the archegonium being attracted by the sweet fluid secreted by the neck of archegonium and fuses with it to form a diploid zygote. The fusion of sperm with the egg to form an oospore or zygote is called fertilization.
The zygote rests in the archegonium for some time and then develops by mitosis into a diploid embryo. Bryophytes are, therefore, called embryophytes. The embryo develops into a diploid sporophyte which produces haploid spores by meiosis. The spores develop into a gametophyte.
The sporophyte remains attached to the gametophyte for nourishment and protection.
They lack specialized fluid-conducting tissues (xylem and phloem). That limits their size because they cannot draw water and mineral nutrients more than about half a meter up to their stem.
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