Unit 9: Kingdom Plantae, where the intricate tapestry of botanical life unfolds before us. As we delve into the rich diversity of plant species, their remarkable adaptations, and their profound significance in shaping the world we inhabit, these meticulously crafted notes will serve as your guide.
From the tiniest mosses to towering sequoias, this journey will unravel the mysteries of plant anatomy, physiology, and ecological interactions, offering a comprehensive understanding of the vital role that the Kingdom Plantae plays in the global ecosystem. So, embark on this educational odyssey as we navigate through the verdant landscapes of botany, gaining insights that will not only enrich your academic pursuits but also deepen your appreciation for the wonders of the natural world.
Unit 9 Biology of 1st Year Short Answers Questions
What is the purpose of classifying living organisms into various groups?
The purpose is to reflect their similarities and dissimilarities at different levels and predict natural relationships and origins.
What is the term used to describe the classification system based on evolutionary relationships?
It is called the Phylogenetic System of Classification.
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What are the main characteristics of organisms in Kingdom Plantae?
They are eukaryotic, autotrophic, multicellular, non-motile, and develop from embryos. They have cell walls made of cellulose.
How many known species of plants are there?
There are about 360,000 known species of plants.
How are organisms in Kingdom Plantae divided for convenience?
They are divided into two broad categories: non-vascular (Bryophyta) and vascular (Tracheophyta) plants.
What does the division of organisms into non-vascular and vascular plants reflect?
It reflects similarities and dissimilarities among different groups of plants.
What are the taxonomic ranks used in the classification of Plantae?
Each category is divided into Sub-divisions, Classes, Subclasses, and other taxonomic ranks.
What is the main component of the cell wall in plant cells?
The main component is cellulose.
What are the two main categories within Kingdom Plantae based on vascularization?
The categories are non-vascular (Bryophyta) and vascular (Tracheophyta) plants.
What were the first plants to colonize land?
Bryophytes were the first plants to colonize land.
How did bryophytes evolve from green algae?
Bryophytes are generally thought to have evolved from green algae.
Where are bryophytes mainly found?
Bryophytes are mainly found in damp shady places.
How do bryophytes transport water, minerals, and prepared food?
Bryophytes rely on diffusion and osmosis for transportation of water, minerals, and prepared food.
Why are bryophytes referred to as the “amphibians of the plant world”?
Bryophytes cannot live away from water and need water for reproduction.
What is the dominant generation in bryophytes’ life cycle?
The gametophyte is the dominant independent free-living generation.
What structures does the gametophyte of bryophytes resemble?
The gametophyte can be thalloid or differentiated into structures resembling stem, leaves, rhizoids, etc.
What is the relationship between the gametophyte and sporophyte in bryophytes?
The sporophyte is partially or totally dependent upon the gametophyte for its nutrition.
How are male and female gametes produced in bryophytes?
Male gametes (antherozoids) are produced within antheridia, and female gametes (eggs) are formed within archegonia.
Where does fertilization occur in bryophytes?
Fertilization takes place in water, as antherozoids are attracted to archegonia.
What characterizes the sporophyte of bryophytes?
The sporophyte consists of foot, seta, and capsule; it is diploid and produces homosporous spores.
What is the alternation of generations in bryophytes’ life cycle?
Bryophytes exhibit an alternation of multicellular haploid gametophytic and diploid sporophytic generations.
How does the sporophyte obtain nourishment in bryophytes?
The sporophyte remains attached to the gametophyte for nourishment since it lacks chloroplasts and can’t perform photosynthesis.
What are some adaptive characters of bryophytes for the terrestrial environment?
Bryophytes developed a compact multicellular plant body to conserve water and reduce surface area exposure. They have a cuticle to minimize water loss through evaporation.
How do bryophytes absorb carbon dioxide while minimizing water loss?
Bryophytes have specialized chambers within their photosynthetic tissues that allow them to absorb carbon dioxide without losing much water and while being exposed to light.
What is the function of rhizoids in bryophytes?
Rhizoids in bryophytes serve for water absorption and anchorage.
What is heterogamy in bryophytes?
Heterogamy refers to the production of two types of gametes: non-motile eggs with stored food and motile sperms.
How are gametes protected in bryophytes?
Gametes in bryophytes are produced within multicellular organs called antheridia and archegonia.
What is the significance of alternation of generations in bryophytes?
Alternation of generations allows bryophytes to produce and test diverse genetic combinations for adapting to varying terrestrial conditions.
How are liverworts categorized within bryophytes?
Liverworts belong to the subdivision Hepaticopsida and are the simplest among bryophytes.
What are the characteristics of liverworts’ plant body?
The plant body of liverworts can be thalloid or ribbon-like, often dichotomously branched. It is attached to the soil by rhizoids.
What is the dependency of the sporophyte in liverworts?
The sporophyte of liverworts relies on the gametophyte for nourishment and protection.
Where do the sex organs develop in liverworts?
The sex organs develop on the upper surface of the thallus near the branch tips or on special branches called antheridiophores and archegoniophores.
Where do most mosses typically inhabit?
Most mosses inhabit damp places, similar to liverworts.
How do mosses differ from other bryophytes in terms of growth conditions?
Mosses can grow equally well in fairly dry places, unlike other bryophytes.
What is the role of water in moss reproduction?
Water is essential for the reproduction of mosses.
How are adult moss plants differentiated in terms of structures?
Adult moss plants have structures resembling stems and leaves.
What are rhizoids in mosses?
Multicellular rhizoids are present in mosses; they are root-like structures.
Give examples of mosses. Examples of mosses include Funaria and Polytrichum.
Where do archegonia and antheridia develop in mosses like Funaria?
Archegonia and antheridia develop on the tips of different branches on the same plant, like in Funaria.
What does a moss spore develop into, unlike liverworts?
A moss spore develops into an alga-like structure called the protonema.
How do Anthoceropsida sporophytes differ from other bryophytes?
Anthoceropsida sporophytes have advanced characters such as stomata, chloroplasts, and a waxy cuticle.
What is the purpose of the meristematic tissue in Anthoceropsida sporophytes?
The meristematic tissue at the junction of foot and spore-producing region allows for continuous growth in the sporophyte.
What are the two distinct generations in liverworts, mosses, and hornworts?
The two generations are haploid gametophyte and diploid sporophyte.
Which generation is dominant in the life history of bryophytes?
The gametophyte generation is dominant.
What does the gametophyte generation produce?
The gametophyte produces gametes called spermatozoids/antherozoids and eggs.
What results from the fusion of a haploid spermatozoid and a haploid egg?
The fusion produces a diploid oospore.
What does the oospore develop into?
The oospore develops into a sporophyte, a different plant structure.
Where do spores develop within the sporophyte capsule?
Spores develop within the capsule by reduction division (meiosis) from spore mother cells.
What does the spore give rise to upon germination?
The spore gives rise to the gametophyte.
What is the phenomenon of alternating gametophyte and sporophyte generations called?
It’s called alternation of generations.
When does the gametophyte stage begin and end?
The gametophyte stage begins with spores and ends at gametes.
What occurs during meiotic division in spore mother cells?
Meiotic division in spore mother cells results in reshuffling of genes, producing diverse spores.
How does alternation of generations contribute to genetic diversity?
Alternation of generations leads to genetic recombination, creating varied gametophytes and spores.
What happens to the genetic variation as it passes from oospore to sporophyte to gametophyte?
The genetic variation is passed from oospore to sporophyte to gametophyte through natural processes, enhancing adaptation.
Why are tracheophytes called vascular plants?
Tracheophytes are called vascular plants due to the presence of xylem and phloem, which are vascular tissues responsible for transporting water, nutrients, and organic compounds throughout the plant.
What are the key evolutionary characteristics that enabled vascular plants to dominate land habitats?
The evolutionary characteristics that contributed to the dominance of vascular plants include root, stem, and leaf structures; vascular systems in stems, roots, and leaves; protected sporangia leading to seed evolution; pollen tube for safe gamete transmission; flowers and fruits; and heteromorphic alternation of generations.
What are the sub-divisions of tracheophytes?
Tracheophytes are divided into four sub-divisions: Psilopsida, Lycopsida, Sphenopsida, and Prteropsida.
Describe the characteristics of Psilopsida (Psilophyta).
Psilopsida plants have rootless sporophytes with dichotomously branched underground rhizomes and aerial parts. The aerial branches are green, leafless, and carry out photosynthesis. The reproductive organs are sporangia located on branches. The internal stem structure is simple, with narrow vascular tissue and a broad cortex.
What is the significance of the term “megaphyll” in plant evolution?
Megaphylls are large leaves with divided veins and veinlets, and they characterize ferns and seed plants. The evolution of megaphylls likely started with a dichotomous branching system in primitive psilopsids around 350 million years ago. The process involved steps such as overtopping, planation, and fusion/webbing, leading to the development of more complex leaf structures.
How did the process of leaf evolution occur?
The evolution of leaves involved gradual steps over a long period. It began with overtopping, where some branches grew faster than others. This was followed by planation, arranging unequal dichotomies in one plane. Fusion or webbing then connected these branches with parenchyma cells, forming a leaf blade with dichotomously branched veins. This process took over 15-20 million years.
What are the three main parts of the sporophyte in Lycopsida?
The sporophyte of Lycopsida consists of roots, stem, and true leaves.
What are the leaves in Lycopsida called, and how are they arranged?
The leaves in Lycopsida are called microphylls, and they are small and single-veined. They can be arranged spirally or opposite.
Where do sporangia develop in Lycopsida, and what may they form?
Sporangia develop singly on the upper side of sporophylls in Lycopsida. They may or may not be arranged to form strobili.
How is the sporangia development different in Lycopodium and Selaginella?
Lycopodium has sporangia of one kind, while Selaginella has microsporangia and megasporangia.
Why are Lycopsids referred to as club mosses/spike mosses?
Lycopsids are referred to as club mosses/spike mosses due to their club/spike-shaped strobili and small leaves resembling mosses.
What distinguishes Selaginella from Lycopodium in terms of spore production?
Selaginella is heterosporous, producing both microspores and megaspores, while Lycopodium is homosporous, producing one type of spore.
How is the gametophyte of Lycopsida primarily positioned?
The gametophyte of Lycopsida is mainly found underground.
What are the distinguishing features of Sphenopsida (Horsetails)?
Sphenopsida’s sporophyte has roots, stems, and leaves, with leaves arranged in whorls. The plant body is composed of many joints.
Where are the sporangia located in Sphenopsida?
The sporangia in Sphenopsida are borne on structures called sporangiophores, aggregated to form strobili.
What is circinate vernation, and where is it observed?
Circinate vernation is the coiled pattern of development observed in immature and young fronds of the class Filicineae in Pteropsida.
What type of conditions do most Filicineae (ferns) prefer?
Most ferns prefer shade and moisture-loving conditions, with few able to live in dry conditions.
Where do ferns typically grow in terms of geographical locations?
Ferns can be found growing on hills, in plains, and some are epiphytic, growing on the bark of trees.
Where are ferns especially abundant? Name a few important fern genera.
Ferns are particularly abundant in the tropics.
Dryopteris, Pteridium, Adiantum, and Pteris are some important fern genera.
Describe the characteristics of Adiantum (Maiden-hair fern).
Adiantum is a small herb with an underground rhizome, pinnately compound fronds, and black, smooth, shiny stalks (stipe). The leaves show dichotomous venation.
What is circinate vernation?
Circinate vernation refers to the characteristic unfurling pattern of young fern leaves, resembling a coiled fiddlehead.
How are the sporangia arranged in Adiantum?
Sori (groups of sporangia) are found on the underside of the margins of the leaflets, protected by a bent margin, forming a false indusium.
What is the life cycle of Adiantum like?
Adiantum exhibits heteromorphic alternation of generations, with a dominant sporophyte and a separate, small, and independent gametophyte.
What is the role of the annulus and stomium in sporangia?
The annulus contracts in dry weather, causing the thin-walled stomium cells to rupture, dispersing haploid spores by wind.
How does the germination of spores occur in Adiantum?
When a spore falls on moist soil, it germinates to produce a haploid gametophyte or prothallus.
Describe the structure and characteristics of the prothallus (gametophyte) in Adiantum.
The prothallus is autotrophic, heart-shaped, and horizontally placed on soil. It has unicellular rhizoids, absorbs nutrients, and is monoecious (male and female sex organs).
How does fertilization occur in Adiantum?
Spermatozoids are produced in antheridia and swim to archegonia, where fertilization takes place, leading to the formation of an oospore and subsequently, a sporophyte.
What is one of the most significant events in the history of land plants?
The development of the seed habit, which occurred approximately 390 million years ago, was a crucial change in the reproductive system of vascular plants.
When did the first complete seeds appear?
The first complete seeds appeared approximately 365 million years ago during the late Devonian times.
What is an ovule and what is its role in seed formation?
An ovule is an integumented indehiscent megasporangium. It plays a crucial role in seed formation as the structure that develops into a seed after fertilization.
What is the term for all seed-producing plants?
All seed-producing plants are called spermatophytes.
What are the various steps involved in the evolution of the seed habit?
The steps involved in the evolution of the seed habit include: 1) Evolution of heterospory, 2) Retention and germination of megaspore within the megasporangium, 3) Development of protective layers around megasporangium, 4) Reduction to a single functional megaspore per sporangium, 5) Development of an embryo sac within the sporangium, and 6) Modification of the distal end of the megasporangium for pollen capture.
What is heterospory, and how did it contribute to the evolution of seed plants?
Heterospory is the production of two different types of spores, microspores and megaspores. It played a crucial role in the evolution of seed plants by allowing the development of distinct male and female gametophytes.
How did the development of protective layers around the megasporangium contribute to seed formation?
The fusion of branch-like structures around the megasporangium to form protective integuments led to the evolution of the ovule, providing increased protection to the egg-containing apparatus in terrestrial environments.
What happens to the remaining three megaspores in a megasporangium during seed plant evolution?
In the evolution of seed plants, only one megaspore is selected for further development into a healthy female gametophyte, while the remaining three megaspores are aborted.
How does the megasporangium contribute to the formation of a seed?
After fertilization, the megasporangium (ovule) transforms into a seed, with its integuments becoming the seed coats, offering maximum protection to the developing embryo in unfavorable terrestrial conditions.
What is the final outcome of the evolution of seed habit for plants?
The development and evolution of the seed habit enabled plants to colonize land permanently, providing a successful reproductive strategy in diverse environments.
What does the term “Gymnospermae” mean?
The term “Gymnospermae” literally means ‘naked seeded’, where “Gymno” refers to naked and “spermae” refers to seed.
What is the main characteristic of gymnosperms regarding seed production?
Gymnosperms produce seeds but not fruits.
How are ovules in gymnosperms different from those in angiosperms?
Ovules in gymnosperms are not enclosed but lie naked on the surface of fertile leaves, whereas in angiosperms, ovules are enclosed within ovaries.
What are the two types of spores produced by gymnosperms?
Gymnosperms produce microspores and megaspores.
How are gymnosperms adapted for pollination without relying on water?
Gymnosperms use wind to transfer pollen grains, which are equipped with wings for air travel, making them independent of water for pollination.
What is the main method of pollination in gymnosperms like Pinus?
Pollen grains in gymnosperms like Pinus are transported by wind for pollination.
How is fertilization achieved in gymnosperms?
Pollen lands directly on ovules, and after pollination, pollen tubes deliver male gametes to the embryo sac for fertilization.
What is the defining characteristic of angiosperms in terms of seed development?
Angiosperms have ovaries formed from folded and joined fertile leaves, which turn into fruits containing seeds after fertilization.
What is the primary difference in seed development between gymnosperms and angiosperms?
Gymnosperms have naked seeds on megasporophylls, while angiosperms have seeds enclosed within ovaries that develop into fruits.
What are some key features of angiosperms?
Angiosperms are highly evolved plants that produce flowers, fruits, and seeds. They make up a vast majority of plant species on Earth.
What is the adult plant in the life cycle of an angiosperm?
The adult plant is a diploid sporophyte with roots, stem, and leaves.
What is a flower composed of in the angiosperm life cycle?
A flower consists of a pedicel, thalamus, and floral leaves (sepals, petals, stamens, and carpels).
What are the reproductive parts of a flower?
The essential reproductive parts of a flower are stamens and carpels.
What is the role of sepals and petals in a flower?
Sepals and petals protect the reproductive parts and attract pollinators.
What happens after pollination in the angiosperm life cycle?
After pollination, sepals usually and petals always fall off.
What is the term for the male gametophyte in angiosperms?
The male gametophyte is called pollen.
What structures make up the carpel in a flower?
The carpel consists of the ovary, style, and stigma.
How does double fertilization occur in angiosperms?
One male gamete fuses with the egg to form the oospore, while another fuses with the secondary nucleus to form the endosperm nucleus.
What does the ovary develop into after fertilization?
The ovary develops into the fruit.
How do seeds usually begin the process of germination?
Seeds undergo a period of rest before germinating under suitable conditions.
What does the alternation of generations refer to in angiosperms?
It refers to the alternating dominance of the sporophyte (2n) and gametophyte (n) generations.
What is double fertilization in Angiosperms?
Double fertilization involves the fusion of two male gametes with two cells simultaneously. One male gamete fuses with an egg to form a diploid zygote, which develops into an embryo. The other male gamete fuses with a fusion nucleus to create a triploid endosperm cell that becomes a food-storing tissue.
How does double fertilization benefit plants?
Double fertilization ensures that food storage in fertilized ovules only occurs upon fertilization, specifically the formation of the zygote. This strategy helps plants optimize their food resources.
What are Monocotyledonae and Dicotyledonae?
Monocotyledonae (Monocots) and Dicotyledonae (Dicots) are two sub-classes of the class Angiospermae. Monocots have one cotyledon in the embryo, while dicots have two. Plants in the Monocotyledonae sub-class are called Monocotyledonous plants or Monocots, and those in the Dicotyledonae sub-class are called Dicotyledonous plants or Dicots.
How are Monocots and Dicots different?
Monocots have one cotyledon, parallel venation in leaves, scattered vascular bundles in stems, and flower parts in multiples of three. Dicots have two cotyledons, reticulate venation in leaves, vascular bundles arranged in a ring in stems, and flower parts in multiples of four or five.
What is the economic importance of the Rosaceae family?
The Rosaceae family is economically significant for providing fruit and ornamentals. Fruits like apples, pears, peaches, and strawberries come from this family. Many ornamental plants, especially roses, are cultivated for their beautiful flowers. The family also has uses in providing wood and essential oils, such as rose oil, used in perfumes and medicinal preparations.
What is Solanaceae known as?
Solanaceae is known as the Nightshade or Potato Family.
How many genera and species are there in Solanaceae?
Solanaceae consists of about 90 genera and 2000 species of plants with tropical and temperate distribution.
How many genera and species of Solanaceae are reported in Pakistan?
In Pakistan, 14 genera and about 52 species of Solanaceae are reported.
Name some familiar plants from Solanaceae.
Familiar plants from Solanaceae include Solanum tuberosum (Potato), Nicotiana tabacum (Tobacco), Lycopersicum esculentum (Tomato), and Capsicum frutescens (Red pepper).
What are the vegetative characters of plants in Solanaceae?
Plants in Solanaceae can be herbs, shrubs, trees, or vines. The stem can be hairy or prickly, and leaves are alternate or occasionally opposite, simple, petiolate, or rarely sessile.
How are the flowers of Solanaceae arranged?
The flowers of Solanaceae typically have an axillary cyme or a combination of cymes. They are mostly bisexual, actinomorphic or weakly zygomorphic, and usually have a pentamerous arrangement.
What is the economic importance of Solanaceae?
Solanaceae provides drugs, food, ornamentals, and some members are poisonous. The most important plant in this family is Solanum tuberosum (Potato). Other plants like Lycopersicum esculentum (Tomato) and Capsicum frutescens (Red pepper) have economic significance.
What is the commercial value of Nicotiana tabacum?
Nicotiana tabacum is commercially valuable for producing tobacco used in making cigarettes. It belongs to the Solanaceae family.
What is FABACEAE also known as?
FABACEAE is also known as the Pea Family or Papilionaceae.
How many genera and species are there in FABACEAE?
FABACEAE comprises about 400 genera and 9000 species, occurring worldwide, particularly in warm temperate regions.
Name some familiar plants from FABACEAE.
Familiar plants from FABACEAE include Lathyrus odoratus (Sweet pea), Arachis hypogea (Peanut), Cicer arietinum (Chickpea), and Dalbergia sissoo (Shisham).
What are the vegetative characters of plants in FABACEAE?
Plants in FABACEAE can be trees, shrubs, or herbs. Their stems can be herbaceous, woody, or climbers with tendrils. Leaves are typically compound, sometimes modified into tendrils, and are alternate with stipules.
What are the floral characters of the plants in the family described?
Answer: The flowers are bisexual, zygomorphic, bracteate, pedicellate, perigynous, pentamerous, and papilionaceous. Calyx has 5 sepals, usually united in a tube, and corolla is papilionaceous with 5 petals forming standard, wings, and keel. Androecium has 10 stamens, mostly diadelphous, and gynoecium is 1-carpelled with superior ovary.
What is the economic importance of the family?
Answer: The family is important as a source of high-protein food, oil, forage, and ornamentals. Pulses like Gram, Pea, and Kidney bean are protein-rich foods. Plants like Alfalfa are used as forage crops. Trees provide timber for building and furniture. Plants like Arachis hypogea yield edible peanuts and oil. Medicinal plants include Glycyrrhiza glabra and Clitoria tematea.
What are some important fodder crops in this family?
Answer: Medicago sativa (Alfalfa), Vicia, Melilotus, and Trifolium are cultivated as main fodder crops.
What product is obtained from the seeds of Arachis hypogea?
Answer: Edible peanuts and peanut oil are obtained from the seeds of Arachis hypogea.
Which plants are used for obtaining indigo dyes?
Answer: Indigo dyes are obtained from Indigofera tinctoria and Butea monosperma.
What are some medicinal uses of plants from this family?
Answer: Glycyrrhiza glabra is used for cough and cold, Clitoria tematea is used against snake bites, and Cassia alata leaves are used to cure skin diseases.
Name a plant from the Caesalpiniaceae family.
Answer: Cassia senna (Senna) is a plant from the Caesalpiniaceae family.
What is the common name of Bauhinia variegata?
Answer: Bauhinia variegata is commonly known as Kachnar.
How are the leaves of Cassia alata used?
Answer: The leaves of Cassia alata are used to cure ringworm and skin diseases.
Which plant yields the dye Haematoxylin?
Answer: The heartwood of Haematoxylon (Longwood) yields the dye Haematoxylin.
How many genera and species are there in the Mimosaceae family?
The Mimosaceae family consists of about 56 genera and approximately 2800 species.
How many native genera and species of Mimosaceae are found in Pakistan?
In Pakistan, there are 4 native genera and 18 species of Mimosaceae, while the rest are introduced.
Name some familiar plants from the Mimosaceae family.
Some familiar plants from the Mimosaceae family include Acacia nilotica, Albizzia lebbek, Mimosa pudica (Touch me not), Prosopis glandulosa, and P. cineraria.
What are the vegetative characteristics of Mimosaceae plants?
Most Mimosaceae plants are trees or shrubs, sometimes climbers or herbs. They have woody stems and pinnate compound leaves with modified stipules into thorns.
Describe the floral characters of Mimosaceae plants.
Mimosaceae plants have bisexual, actinomorphic flowers with 5 fused sepals and 5 free or fused petals. The androecium consists of 5 to numerous stamens, and the gynoecium is a simple pistil with an ovary containing many ovules. The fruit is usually a legume.
What is the economic importance of Mimosaceae family plants?
Many trees in the Mimosaceae family, like Acacia, Albizzia, and Xylia, provide valuable wood for construction, furniture, and fuel. Acacia species yield Arabic gum, and Acacia nilotica leaves are used for blood purification. Some plants like Mimosa pudica and Acacia melanoxylon are grown for ornamental purposes.
How is the family Poaceae (Gramineae) distributed worldwide?
The Poaceae family is distributed worldwide wherever vascular plants can survive, with about 600 genera and 10,000 species.
What are some familiar plants from the Poaceae family?
Familiar plants from the Poaceae family include Triticum vulgare (Wheat), Zea mays (Corn), Avena sativa (Oats), Oryza sativa (Rice), and Saccharum officinarum (Sugar Cane).
What are the vegetative characteristics of Poaceae plants?
Poaceae plants are usually annual or perennial herbs with jointed, hollow stems and ligulate leaves that often wrap around the stem base.
How are the flowers of Poaceae plants structured?
Poaceae flowers are usually small, bisexual, zygomorphic, and lack a perianth. They have stamens ranging from 1 to 6, and the compound pistil consists of 3 united carpels with feather-like stigmas. The fruit is a caryopsis or grain.
What is the economic importance of the Poaceae family?
The Poaceae family is of great economic importance as it includes cereals like wheat, rice, and maize, which are major food crops for humans. Many fodder crops for animals also belong to this family. Grasses are used for lawns, ornamental purposes, and building materials like bamboo.
(i) (a) How are ferns better adapted to life on land than liverworts and mosses?
(Answer): Ferns have vascular tissues (xylem and phloem) that facilitate the transport of water, nutrients, and food throughout the plant. They also have true roots, stems, and leaves, which provide structural support and efficient resource uptake. In contrast, liverworts and mosses lack true vascular tissues and have simpler structures, limiting their ability to grow tall and transport water and nutrients effectively.
(i) (b) Which of the following are nutritionally self-supporting:
- Mature liverwort and moss gametophyte.
- Mature liverwort and moss sporophyte.
(Answer): Mature liverwort and moss gametophytes are nutritionally self-supporting through photosynthesis, as they possess chlorophyll and can produce their own food. The mature sporophytes, on the other hand, are dependent on the gametophytes for nutrition and lack the capability to photosynthesize on their own.
(ii) (a) Question: Why are the chances of survival and development of wind-blown pollen grains much less than those of spores of Adiantum?
Answer: Wind-blown pollen grains have a relatively lower chance of survival and development because they are exposed to external environmental conditions, such as desiccation, predation, and UV radiation. In contrast, spores of Adiantum (a fern) have protective coverings and are produced in sporangia, allowing them to withstand harsh conditions and better ensure successful germination.
(ii) (b) Question: Why are megaspores larger and microspores smaller?
Answer: Megaspores are larger because they give rise to the female gametophytes within the ovule. These gametophytes provide nourishment and protection to the developing embryo. On the other hand, microspores are smaller as they develop into male gametophytes (pollen grains), which need to be lightweight and easily transportable to reach the female reproductive structures.
(ii) (c) Question: What important advances have angiosperms made towards the seed plant life?
Answer: Angiosperms, or flowering plants, have made several important advances in seed plant life compared to gymnosperms (non-flowering seed plants). Some of these advances include:
Enclosed Ovules: Angiosperms have ovules enclosed within ovaries, offering greater protection and support for fertilization and seed development.
Double Fertilization: Angiosperms have a unique double fertilization process where one fertilization event leads to the formation of the embryo and the other forms endosperm, a nutritive tissue for the embryo.
Fruit Formation: After fertilization, angiosperms often develop fruits from the mature ovaries. Fruits aid in seed dispersal, protecting seeds and enhancing their chances of germination in new locations.
Efficient Pollination Mechanisms: Angiosperms have evolved various specialized mechanisms for pollination, including co-evolution with insects, birds, and other animals, increasing the chances of successful fertilization.
Diversity of Flower Types: The diversity of flower structures in angiosperms enhances the variety of pollinators they can attract, leading to increased reproductive success.
Reduced Gametophyte: Angiosperms have reduced gametophytes, which are dependent on sporophytes for nutrition and protection, contributing to the overall success of seed production.
These advances have contributed to the overwhelming success and dominance of angiosperms in terrestrial ecosystems.
Question iii: Write a note on the alternation of generations.
Answer iii: The alternation of generations is a reproductive phenomenon in plants involving two distinct phases: the gametophyte (haploid) and the sporophyte (diploid) generations. The gametophyte produces gametes (sperm and egg cells) through mitosis. Fertilization of gametes results in the formation of the diploid sporophyte, which produces spores through meiosis. Spores then develop into haploid gametophytes, completing the cycle. This alternation allows plants to have a multicellular, independent gametophyte phase and a dominant sporophyte phase.
Question iv: What is the importance of the following?
(i) Seed.
Answer iv: Seeds are essential for plant reproduction and survival. They protect and provide nourishment to the developing embryo, allowing it to withstand harsh conditions and disperse to new locations for germination. Seeds also play a crucial role in agriculture and horticulture, as they are used to propagate plants and produce food crops.
(ii) Double fertilization.
Answer iv: Double fertilization is a unique process in angiosperms where one sperm cell fertilizes the egg cell to form the embryo, while another sperm cell fuses with two polar nuclei to form the triploid endosperm. The endosperm serves as a nutritive tissue for the developing embryo, providing essential nutrients for germination and early growth. This process ensures successful seed development and contributes to the nutritional value of many food crops.
(iii) Heterospory.
Answer iv: Heterospory is the production of two types of spores – microspores and megaspores – in a single plant species. Microspores develop into male gametophytes (pollen grains), carrying male gametes for fertilization. Megaspores develop into female gametophytes within ovules, where egg cells are produced. Heterospory enables better reproductive efficiency and increased diversity in plants, as it enhances the chances of outcrossing and reduces competition between male and female gametophytes.
Unit 9 Biology of 1st Year Long Answer Questions
(i) To what does alternation of generations refer in the plants? Deine sporophyte and gametophyte. With which stage is an adult animal comparable? How are they reproductively dissimilar?
Alternation of Generations in Plants
Alternation of generations refers to a complex life cycle exhibited by many plants, where they alternate between two distinct multicellular stages: the sporophyte and the gametophyte. This life cycle involves both sexual and asexual reproduction, resulting in the production of spores, gametes, and ultimately, the development of a new generation.
Sporophyte: The sporophyte is the diploid (2n) phase of the plant’s life cycle. It originates from a zygote formed by the fusion of gametes during sexual reproduction. The sporophyte is characterized by its ability to undergo meiosis, resulting in the formation of haploid spores. These spores are released from sporangia (structures that produce spores) and develop into the gametophyte stage.
Gametophyte: The gametophyte is the haploid (n) phase of the plant’s life cycle. It develops from spores produced by the sporophyte. The gametophyte generation is responsible for producing gametes (sperm and egg cells) through mitosis. These gametes fuse during fertilization to form a diploid zygote, which then grows into the sporophyte stage.
Comparison with Animals: The concept of alternation of generations in plants is comparable to the metamorphosis seen in many animals, where an individual undergoes distinct developmental stages (e.g., larva, pupa, and adult). However, the key difference is that in alternation of generations, both the sporophyte and gametophyte stages are multicellular and capable of independent growth and reproduction.
Reproductive Dissimilarities: The sporophyte and gametophyte stages in the alternation of generations have different roles in reproduction:
The sporophyte produces spores through meiosis. These spores are the equivalent of animal gametes in that they are the starting point for the next generation. However, they are not directly involved in sexual reproduction themselves.
The gametophyte produces gametes (sperm and egg cells) through mitosis. These gametes fuse during fertilization to form a zygote, which then develops into the sporophyte.
Alternation of generations is a unique reproductive strategy in plants, involving the alternation between two multicellular stages, the sporophyte and gametophyte. This cycle allows plants to undergo both sexual and asexual reproduction, contributing to their diverse and adaptable life strategies.
(ii) What is a seed? Why is the seed a crucial adaptation to terrestrial life?
Seed: A seed is a mature, fertilized ovule of a flowering plant (angiosperm) or a gymnosperm. It is a reproductive structure that contains a developing plant embryo, stored nutrients, and a protective seed coat. Seeds serve as a means of propagation and dispersal for plants.
Seeds are a crucial adaptation for terrestrial life for several reasons
Protection: Seeds have a tough outer seed coat that provides protection to the developing embryo against mechanical damage, desiccation (drying out), and microbial attack.
Dormancy: Seeds can enter a state of dormancy, which allows them to survive unfavorable environmental conditions such as drought, extreme temperatures, and lack of nutrients. This ensures the survival of the plant species over time.
Dispersal: Seeds are often dispersed away from the parent plant, reducing competition for resources and enhancing genetic diversity. Various mechanisms, such as wind, water, animals, and even self-ejection, aid in seed dispersal.
Nutrient Reserve: Seeds contain stored nutrients in the endosperm or cotyledons that provide nourishment to the germinating embryo during the early stages of growth. This enables the seedling to establish itself before it can photosynthesize.
Independence from Water: Unlike spores, seeds do not require water for fertilization to occur. This adaptation allows plants to colonize drier terrestrial environments where water availability might be limited.
Longevity: Many seeds can remain viable for extended periods, sometimes even years or decades, under the right conditions. This allows plants to wait for favorable environmental conditions before germinating.
Adaptation to Varied Habitats: The diversity of seed forms and dispersal mechanisms enables plants to adapt to a wide range of habitats, from deserts to forests, and from open grasslands to alpine regions.
(iii) Describe evolution of leaf and its importance in vascular plants.
Evolution of Leaf and its Importance in Vascular Plants
The evolution of leaves played a significant role in the adaptation and diversification of vascular plants. Leaves are essential structures that facilitate photosynthesis, allowing plants to capture light energy and convert it into chemical energy. The evolution of leaves can be traced through various stages, each contributing to the success of vascular plants.
Evolutionary Stages of Leaves
Microphylls: The earliest vascular plants, such as the extinct group called the lycophytes, had small, simple leaves known as microphylls. These leaves were often single-veined and lacked the complex vascular systems found in later leaves.
Megaphylls: Over time, plants evolved more complex leaves known as megaphylls. Megaphylls have a branched vascular system, with multiple veins running through them. This branching allowed for better water and nutrient distribution within the leaf, enhancing photosynthetic efficiency.
Leaf Complexity: As plants continued to evolve, leaves became larger and more complex. They developed various forms, such as simple leaves, compound leaves (with leaflets), and deeply lobed leaves. Increased complexity led to a larger surface area available for photosynthesis and more efficient gas exchange.
Importance of Leaves in Vascular Plants
Photosynthesis: The primary function of leaves is to perform photosynthesis, a vital process that converts sunlight, carbon dioxide, and water into glucose and oxygen. This process provides energy for the plant’s growth, development, and reproduction.
Gas Exchange: Leaves facilitate the exchange of gases, allowing plants to take in carbon dioxide (used in photosynthesis) and release oxygen (a byproduct of photosynthesis) and excess water vapor through small openings called stomata.
Water Regulation: Leaves play a crucial role in regulating water balance within the plant. They contain stomata that can open and close to control transpiration, the loss of water vapor from the leaf surface. This helps prevent excessive water loss in arid environments.
Adaptation: Leaves have evolved diverse forms and structures to adapt to different environments. For example, needle-like leaves of conifers reduce water loss in cold and dry conditions, while large, broad leaves of tropical plants maximize photosynthesis in high-light environments.
Nutrient Transport: The vascular system within leaves transports water, minerals, and nutrients from the roots to the rest of the plant. This transport system ensures that all parts of the plant receive the necessary resources for growth and metabolism.
Reproduction: Leaves also play a role in plant reproduction. In some species, leaves may develop specialized structures for reproduction, such as spores or reproductive structures like cones in conifers.
(iv) Discuss the evolution of seeds and its significance.
The evolution of seeds marked a significant advancement in the reproductive strategies of plants. Here’s a detailed discussion of the evolution of seeds and its significance:
Evolution of Seeds
Transition from Spore to Seed: Early land plants relied on spores for reproduction. Spores were single-celled structures dispersed by wind or water. However, spores had limitations in terms of protection and nourishment for the developing embryo.
Origins of Seed Coat: Over time, plants developed integuments, protective layers around the embryo, leading to the formation of seeds. These integuments evolved into seed coats, providing physical protection against desiccation, pathogens, and mechanical damage.
Nourishment and Dormancy: A significant evolutionary development was the inclusion of stored nutrients within the seed. The endosperm, a tissue rich in nutrients, nourishes the developing embryo. This allowed seeds to remain dormant until suitable conditions for germination were present.
Reproductive Efficiency: The evolution of seeds conferred several advantages. Seeds are more resilient and have higher survival rates compared to spores. They can withstand adverse conditions and travel longer distances, increasing the plant’s ability to colonize new habitats.
Significance of Seeds
Dispersal: Seeds are crucial for the dispersal of plant species. They can be transported by wind, water, animals, or other means. This enables plants to occupy new habitats, escape competition, and establish in diverse environments.
Protection: Seed coats provide protection against physical damage, pathogens, and herbivores. This protection increases the chances of successful germination and establishment.
Dormancy: Seed dormancy ensures that germination occurs under optimal conditions. This adaptive trait prevents seeds from germinating during unfavorable seasons, promoting the survival of the plant species.
Nourishment: The endosperm or cotyledons store essential nutrients for the germinating embryo. This stored energy sustains the early growth stages until the seedling can establish photosynthesis.
Evolutionary Success: The evolution of seeds contributed to the proliferation and diversification of plant species. Seeds allowed plants to colonize diverse ecosystems, contributing to the development of complex terrestrial ecosystems.
Human Agriculture: Seeds have immense significance for human agriculture. Cultivated plants are propagated through seeds, ensuring the continuity of agricultural practices and food production.
Ecological Relationships: Seeds play a crucial role in various ecological interactions. They serve as a food source for animals, contributing to seed dispersal, and form the foundation of many food chains.
(v) In what way do the lowering plants differ from the rest of the seed plants? What is the stigma? Is fertilization in angiosperms direct or indirect? From what tissue does angiosperm fruit develop?
Flowering plants, or angiosperms, differ from other seed plants (gymnosperms) primarily due to the presence of flowers and enclosed seeds within fruits. Gymnosperms, on the other hand, typically produce naked seeds that are not enclosed in a protective fruit structure. Additionally, angiosperms have a more advanced reproductive system involving double fertilization and specialized floral organs for pollination.
Stigma
The stigma is a part of the female reproductive structure in a flower known as the pistil or carpel. It is located at the top of the style and is the receptive surface where pollen grains land during pollination. The stigma plays a crucial role in fertilization as it allows pollen tubes to penetrate and deliver male gametes to the ovules, facilitating the process of fertilization.
Is fertilization in angiosperms direct or indirect?
Fertilization in angiosperms is indirect. It involves a process called double fertilization, where two separate fertilization events occur. One sperm cell fertilizes the egg cell, forming the zygote which develops into the embryo. The other sperm cell fuses with two polar nuclei in the central cell, forming the triploid endosperm, which provides nourishment to the developing embryo.
From what tissue does angiosperm fruit develop?
Angiosperm fruit develops from the ovary tissue of the flower. After fertilization, the ovary swells and undergoes various changes to develop into a fruit. The fruit serves as a protective structure for the developing seeds and aids in their dispersal. It can have a variety of forms, such as fleshy fruits like apples or berries, or dry fruits like nuts or capsules.
(vi) What two classes comprise the angiosperms? How do the two classes structurally differ from one another? Which class derived from the other? Explain.
The two classes that comprise the angiosperms are Monocotyledonae (monocots) and Dicotyledonae (dicots). These two classes structurally differ from each other in several key ways.
Monocotyledonae (Monocots)
Cotyledons: Monocots have only one cotyledon (seed leaf) in their embryos.
Leaf Venation: Monocot leaves typically have parallel venation, where the veins run parallel to each other.
Stem Vascular Bundles: Vascular bundles in monocot stems are scattered throughout the stem.
Root Development: Monocots generally develop a fibrous root system with no main taproot.
Floral Parts: Floral parts are often in multiples of three (e.g., petals in multiples of three).
Secondary Growth: Monocots lack secondary growth (woody growth) due to the absence of a vascular cambium.
Leaf Arrangement: Leaves are usually alternate.
Dicotyledonae (Dicots)
Cotyledons: Dicots have two cotyledons in their embryos.
Leaf Venation: Dicot leaves typically have reticulate (net-like) venation.
Stem Vascular Bundles: Vascular bundles in dicot stems are arranged in a ring.
Root Development: Dicots often have a taproot system with a main primary root.
Floral Parts: Floral parts are often in multiples of four or five.
Secondary Growth: Many dicots exhibit secondary growth, leading to the development of woody tissue, facilitated by the vascular cambium.
Leaf Arrangement: Leaves can be alternate, opposite, or whorled.
Evolutionary Relationship
Dicotyledonae (dicots) are considered to have derived from Monocotyledonae (monocots). This is supported by evolutionary evidence, including fossil records and genetic studies. Monocots are generally considered more primitive, with simpler vascular arrangements and lack of secondary growth. Dicots, on the other hand, exhibit more advanced features like secondary growth and diverse floral arrangements. This suggests that dicots have evolved from monocot ancestors, adapting and diversifying over time to form a wide range of plant species with varying characteristics.