Content Writer-SME | Updated On - Nov 9, 2024
The flower structure comprises of four main parts, or whorls—known as the calyx, corolla, androecium, and gynoecium. Flowering plants, also known as angiosperms, account for the vast majority of the plant kingdom. Flowers are categorized into two types based on the presence or absence of reproductive organs of a flower.
The reproductive parts of a flower develop into a fully developed fruit. Perfect flowers and imperfect flowers are the two types of flowers. In this article we will learn in detail about flowers and their structure as well as their functions.
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Structure of a Flower
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Flowers come in a range of shapes and sizes, but their anatomy is generally the same having sepals, petals, stamen, and carpel. A whorl, or circular arrangement, is created by arranging these parts in a circular pattern. Stamen is considered as the male reproductive whereas carpel is the female reproductive structures of flower.
- Based on the vegetative and reproductive parts, flowers are of four types-complete, incomplete, bisexual, and unisexual flowers.
- Flowers with both male and female parts are known as hermaphrodites.
- Sepals, petals, anther and carpels are the units of vegetative and reproductive parts of flowers.
- Complete flower has the sepals, petals, stamens, and pistil.
- Incomplete flower is one that lacks one or more of these structure.
Flower Structure Diagram
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A labelled diagram of the structure of a complete flower is shown in the figure below:
Flower Structure Diagram
Parts of Flower
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A complete flower structure consits of two parts- vegetative and reproductive parts.
Vegetative Parts of Flower
The vegetative parts of a flower is further divided into sepals and petals. Sepals and petals are considered as acessory whorls of a flower as they play a supporting role in sexual reproduction in flowering plants.
Petals
The petals are brightly colored parts of the flower that attract bees, insects, and birds. Petal color varies from plant to plant; some are brilliant, while others are pale. As a result, petals assist in distinguishing one flower from another.
Sepals
The green-colored portion beneath the petals that protect emerging buds is known as a sepal. Some flowers have fused petals and sepals, while others have petals and sepals that are separated.
Reproductive Parts of Flower
A flower has reproductive sections, such as stamen and pistil. A flower may have all-female parts, all-male parts, or both male and female parts. A flower's reproductive parts include the following.
Gynoecium
Gynoecium serves as a female reproductive organ of flower whose sole purpose is to participate in the process of reproduction. Pistil or carpel is a unit of gynoecium that consists of the following components:
- Stigma: The pistil's upper section is called the stigma. It collects pollen in order to influence reproduction.
- Style: The style is the pistil's long part. It serves as a home for the pollen tube. It also serves as a barrier against harmful pollen.
- Pollen Tube: The pollen tube is a part of the pistil found inside the style. It allows pollen to travel from the stigma to the style and then to the ovary.
- Ovary: The ovary is the enlarged part of the pistil at the style's tip. The ovary's purpose is to protect the ovules. The ovules' job is to fertilize the pollen and turn it into a seed. The ovary develops into the fleshy fruit that surrounds the inner seed in flowering plants.
- Ovule: The ovule is found within the ovary. These are the flower's eggs, in a nutshell. The pollen will travel from the stigma to the ovary through the style. This fertilization ensures that the ovule develops into a seed. In sompe plants, only seed will grow while other plants will produce both a seed and a fleshy fruit at the same time.
Androecium
The male reproductive organ of a flower is called androecium. Stamen is considered as a unit of androecium that consists of following parts:
- Anther: The anther is found at the filament's tip. It is usually quite compact and is where pollen is produced.
- Filament: The filament is the long, narrow portion of the stamen that holds the anther in place. It is the link that connects the anther to the rest of the flower.
Whorls of a Flower
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A flower is made up of four whorls, which are largely responsible for the radial arrangement of the flower. A typical flower has a circular section with a common center that can be seen and distinguished from the top of the flower. There are four whorls:
Calyx
The calyx is the flower's outermost whorl. It is made up of sepals. This shields the flower whorls from mechanical damage and desiccation. Petaloid plants have colored calyx sepals and are distinguished by their color.
- The calyx is called polysepalous if the sepals are free, and gamosepalous if they are joined.
- The sepals of many flowers fall off before the flower fully opens. Such sepals are referred to as caducous.
- After fertilization, the sepals of some plants fall off. Such sepals are referred to as deciduous.
- The persistent sepals are present until the fruiting stage.
Corolla
The second accessory whorl of a flower is called corolla. Petals are the unit structure of corolla that serve two main purposes in flowers:
- To attract pollinators.
- To protect a flower's reproductive parts
Petals are brightly colored and scented to attract pollinators such as animals and insects. The perianth is made up of the calyx and corolla. The corolla comes in a variety of shapes and sizes in the flowers:
- Polypetalous Regular
- Polypetalous Irregular
- Gamopetalous Regular
- Gamopetalous Irregular
Stamens (Androecium)
Stamen is the male reproductive part of the flower and is also known as the third whorl. It is made up of a filament, which is a thread-like structure with a circular anther on top. The anther produces pollen, which contributes to the plant's male reproductive process. All stamens do not produce fertile anthers.
Carpels (Gynoecium)
Carpels are a type of cartilage. The carpel is the flower's fourth whorl, located in the center. The pistil, the female reproductive part of the flower, is housed in the carpels.
Functions of Flower
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The parts of a flower play a significant role in attracting and uniting male and female gametes of plants. Flowers and fruits are the end product of sexual reproduction in plants. Here are some of the most important functions of flowers mentioned below:
- Nectar (pollen reward) is given by flowers to attract insects and birds for pollination in plants.
- The colourful petals of flower are also utilized for attracting pollinating agents.
- The development of a gametophyte takes place in flower only.
- Diaspores are formed in flowers even without fertilization.
- Both self pollination and cross pollination are promoted by flowers.
- Fruit development takes place after fertilization.
Things to Remember
- Flowers are the reproductive part of a plant.
- Flowers can either a complete or Incomplete in structure.
- A complete flower comprises sepals, petals, stamens, and pistils.
- An incomplete flower is one that lacks one or more of these structures.
- A complete flower includes two different parts: Vegetative and reproductive part.
- The number of petals, sepals, stamens, and pistils can vary in different plants.
- A flower is also composed of four whorls, which are largely responsible for the radial arrangement of a flower.
Previous Years Questions
- Meiosis takes place in...[NEET 2013]
- The sexual reproduction is absent in….[NEET 1995]
- For union between stock and scion in grafting which one is the first to occur….[NEET 1990]
- A clone is ......… [KCET 2011]
- Animals which possess cleidoic eggs exhibit….[KCET 2011]
- Which among these is not a post fertilization event ?...[KCET 2016]
- Type of asexual reproduction found in Hydra is..[KEAM]
- Which of the following is having longitudinal binary fission ?….[KEAM]
- In grafting, the stock and scion should be joined….
- The mode of asexual reproduction in Euglena is….[CUCET 2010]
- Isogamy is found in...[CUCET 2010]
- In these plants artificial vegetative reproduction is possible through….[GUJCET 2006]
- Apomixis in plant means development of a plant… [BHU UET 2008]
- Which one of the following plants reproduces vegetatively by epiphyllous buds?
- Vegetative propagation by leaves is seen in… [JKCET 2010]
Sample Questions
Ques. What are the essential components of a flower? (1 mark)
Ans. A flower's essential parts are as follows: Sepals, Petals, Stamens, and Pistil
Ques. What is the process by which flowers reproduce? (1 mark)
Ans. Pollination is the process by which flowers reproduce. The male gametes are transferred to the female ovules during this process, where fertilization occurs and the ovules grow into seeds within a fruit.
Ques. What do the reproductive parts of a flower look like? (1 mark)
Ans. The male reproductive part of a flower is the stamen, while the female reproductive part is the pistil. An anther and filament surround the stamen. Pollen grains are produced by the anthers.
Ques. What do the vegetative parts of a flower look like? (1 mark)
Ans. The vegetative parts of a flower are the sepals and petals.
Ques. What are the important Flower Functions? (3 marks)
Ans. The following are some of the most important functions of flowers:
- In the flowers, gametophytes grow.
- Without fertilization, the flowers can produce diaspores.
- The flower's ovary develops into a fruit containing a seed after fertilization.
- Flowers' most important function is reproduction. They contribute to the union of male and female gametes.
- Flowers provide nectar to certain birds and insects, which aid in pollen transfer from one flower to the next.
- Flowers can encourage selfing (the union of sperms and eggs from the same flower) or cross-fertilization (the union of sperms and eggs from different flowers).
Ques. Describe any two devices in a flowering plant which prevent both autogamy and geitonogamy.
Explain the events upto double fertilisation after the pollen tube enters one of the synergids in an ovule of an angiosperm. (2018)
Ans. Two devices in a flowering plant which prevent both autogamy and geitonogamy are:
- Dichogamy: Dichogamy is a process of cross-pollination in which bisexual flowers aids in cross-pollination by developing stamens before the carpels t different times. Examples - Protandry is when stamens develop before carpels and flowers include Jasmine, Sunflower. Protogyny is when carpels develop before stamens such as Rose and Ashoka.
- Self-incompatibility: In this procedure the flowers cannot self-fertilize because it stops the pollen from one flower to fertilize another belonging to the same plant. This is a genetically managed process and stimulates out-cross.
Events upto double fertilisation after the pollen tube enters one of the synergids in an ovule of an angiosperm:
When the stigma receives the fallen pollen grains it begins to germinate and the pollen tube develops that passes through the style and eventually gets inside the female ovule. After the first step the male gamete gets released when the pollen tube gets inside one of the synergids. One of the two male gametes gets infused with the egg cell nucleus which leads to the creation of the zygote. This procedure is known as syngamy. The other male gamete gets infused with two polar nuclei that are placed in the central cell and forms into a triploid primary endosperm nucleus that can also be termed as PEN. This process is also known as triple fusion because it includes the fusion of three haploid nuclei. Double fertilization takes place when two different kinds of fertilization syngamy and triple fusion occur.
Ques. A teacher wants his/her students to find the genotype of pea plants bearing purple coloured flowers in their school garden. Name and explain the cross that will make it possible. (2015)
Ans. The genotype of the plant can be found by the process of test cross which will help us in understanding whether the persistent character of the purple flower is coming from homozygous or heterozygous genotype.
The purple flowers needs to be crossed with the white one i.e., the homozygous recessive flower = 1
If the flowers in F1 are of the same colour that is purple then the genotype of such a flower is homozygous dominant.
If all the flowers in F1 are not of the same colour, i.e., 50% is purple and the rest 50% is white then the genotype can be termed as heterozygous dominant.
Ques. A tomato plant following the process of sexual reproduction produces 240 viable seeds. Answer the following questions giving reasons :
What is the minimum number of pollen grains that must have been involved in the pollination of its pistil?
What would have been the minimum number of ovules present in the ovary?
How many megaspore mother cells were involved?
What is the minimum number of microspore mother cells involved in the above case?
How many male gametes were involved in this case? (2015)
Ans.
- The minimum number of pollen grains that must have been involved in the pollination of its pistil are 240 as one single pollen fertilizes one ovule.
- The minimum number of ovules present in the ovary are 240 as one single ovule would reproduce one seed.
- The number of megaspore mother cells involved is 240 because one among 4 megaspore mother cells tetrade remains functional.
- The minimum number of microspore mother cells involved are 60 as each microspore mother cell produces 4 pollen grains through the process of meiosis.
- The number of male gametes involved is 240 as each male gamete gets infused with one single female gamete and produces zygote that interns grows to form a seed.
Ques. Can a plant flowering in Mumbai be pollinated by pollen grains of the same species growing in New Delhi? Provide explanations to your answer.
Draw the diagram of a pistil where pollination has successfully occurred. Label the parts involved in reaching the male gametes to its desired destination. (2017)
Ans. Yes the plant flowering in Mumbai can be pollinated by pollen grains of the same species growing in New Delhi through the process of artificial pollination. In this procedure stamens are removed (emasculation) which aids in stopping self pollination. At a later stage the emasculated flowers are pollinated with the help of the desired pollen.
Ques. Name the organic material exine of the pollen grain is made up of. How is this material advantageous to pollen grain ?
Still it is observed that it does not form a continuous layer around the pollen grain. Give reason.
How are ‘pollen banks’ useful ? (2016)
Ans. The organic material exine of the pollen grain is made up of sporopollenin. This material helps in providing protection to the pollen grains against acid, alkali, extreme temperatures. It cannot be degraded by any sort of enzymes as well.
Germ pores let the pollen tube grow or lead to the germination of the pollen. Exine doesn’t provide a continuous layer around the pollen grain, hence sporopollenin cannot be seen in certain parts which are known as the germ pores. Germ pores act as a pathway for the development and origination of pollen tubes.
Pollen banks help in storing the pollen grains for a long period of time so that it can be used as a crop programme at a later stage.
Ques. As a senior biology student you have been asked to demonstrate to the students of secondary level in your school, the procedure(s) that shall ensure cross-pollination in a hermaphrodite flower. List the different steps that you would suggest and provide reasons for each one of them.
Draw a diagram of a section of a megasporangium of an angiosperm and label funiculus, micropyle, embryonic and nucellus. (2016)
Ans. The procedure shall ensure cross-pollination in a hermaphrodite flower which are as follows:
- Emasculation: This procedure helps in making sure that the anther is removed to stop self-pollination.
- Bagging: In this method the emasculated flower is covered with butter paper to prevent contamination through foriegn pollens.
- Tagging: At this stage the emasculated flowers which are also bagged are tagged with the date. The emasculation and pollination date of male and female flowers is attached to keep a proper record.
- Pollination: In this stage the appropriate pollen grains are dusted over the required stigma with a brush.
- Rebagging: After the process of pollination the flowers are bagged again till it’s fruits start to ripe.
Ques. Pollen banks are playing a very important role in promoting plant breeding programmes the world over. How are pollen preserved in the pollen banks ? Explain.
How are such banks benefitting our farmers ? Write any two ways. (2019)
Ans. Pollen banks play a huge role in aiding the breeding of plant programmes throughout the world. The process of storing pollen under particular conditions is called cryopreservation. In this process pollen is stored in pollen banks by preserving them in a feasible ambience within liquid nitrogen and in a temp as low as -196OCelcius.
The farmers are are benefited in the following ways:
- The protected pollen helps in ensuring the agricultural biodiversity for a prolonged period of time.
- The preserved pollen helps in the production of cross-breed crops at the later stage.
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