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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Sexual Reproduction in Angiosperms Know More

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  • Floral Symmetry: Different types of symmetry shown by different flowers are as follows:

a.      Actinomorphic: When a flower can be divided into two equal halves by a vertical section passing through centre, it is said to be a regular flower or radially symmetrical flower or an actinomorphic flower. Example: Datura, mustard, etc.

b.      Zygomorphic: A flower can be called zygomorphic flower when it can be divided into two equal halves along only one plane. Such a flower is said to be bilaterally symmetrical. Example: Pea, bean, etc.

c.       Asymmetrical: As the name suggests, it is an irregular flower which cannot be divided into equal halves along any vertical plane. Example: Canna.

 

  • Calyx, corolla, androecium and gynoecium have their respective members as sepals, petals, stamens and carpels. When the sepals are united, the condition is called gamosepalous. Example: China rose.
  • When the sepals are free, the condition is called polysepalous. Example: Mustard. Similarly, a flower shows gamopetalous, i.e., united petals or polypetalous, i.e., free petal condition.
  • A stamen consists of a filament, anther and connective. Sometimes the filaments of stamens are attached with the petals to some extent. Such stamens are called epipetalous stamens. Example: Petunia. If the filaments of all the stamens are fused to form a single tube called staminal tube, then the condition is called monadelphous condition Example: China rose.
  • Attachment of anthers to the filament is by three ways such as:

a.      Dorsifixed: Here, the filament is attached to the anther from its dorsal side.

b.      Basifixed: Here, the filament is attached to the anther from its base.

c.       Versatile: Here, the filament is attached to the anther in the middle so that the anther swings freely. It is an important adaptation for wind pollination.

  • In some flowers, the stamens are sterile, i.e., they do not produce pollen grains. Such a non-functional stamen is called a staminode.
  • Depending upon the number of carpel, the gynoecium is:

1.      Monocarpellary: Gynoecium with one carpel.

2.      Bicarpellary: Gynoecium with two carpels.

3.      Polycarpellary: Gynoecium with more than two carpels.
The carpels are united or free. United carpels form syncarpous gynoecium while free carpels form apocarpous gynoecium.

  • Ovules are present inside the ovary. Each ovule attaches itself to placenta by a stalk called funicle. Hilum is the point of attachment of body of ovule to the funicle. Depending upon the number of integuments, the ovule can be unitegmic or bitegmic. Depending upon the position of the body of ovule, it can be erect, i.e., orthotropous or inverted, i.e., anatropous.
  • Placentation: Parenchymatous tissue in the inner wall of the ovary on which ovules are attached is called placenta. The arrangement of placentae in the ovary is called placentation. It is of different types such as axile, marginal, parietal, basal, etc.
  • Axile Placentation: In this type, the ovules are present along the central axis. Here, the ovary is multilocular. Example: China rose, lemon.
  • Marginal Placentation: Here, the ovary is with single carpel and ovules are attached on the edges of ovary. Example: Pea, bean etc.
  • Parietal Placentation:Here, the ovary is unilocular and syncarpous. The ovules are arranged on the walls of the ovary. Example: Cucumber.
  • Basal Placentation: Here, the ovary is unilocular, with a single ovule which is attached to the base of the ovary. Example: Sunflower.
  • Zoophily: The cross pollination carried out by animals as the agents is called zoophily. Here, the if it is by birds, it is ornithophily; by insects, it is entomophily and by bats, it is chiropterophily.
  • Xenogamy: When the pollination is between two flowers present on two different plants of same species, it is called xenogamy.
  • Geitonogamy: When the pollination is between two flowers present on the same parent plant, it is called geitonogamy.
  • Siphonogamy: In angiosperms, the male gametes are non-motile and are thus carried by the pollen tube for fertilisation. This process is called siphonogamy.
  • The pollen tube enters the ovule through micropyle or through chalazal end or through integuments. Depending upon this, the process is called porogamy or chalazogamy or mesogamy respectively.
  • Types of Inflorescence: Racemose and cymose inflorescence are the two main types of inflorescence. The subtypes of racemose inflorescence are depending upon the structure of main axis such as:

0.      Raceme, panicle, spike, catkin, spadix are the subtypes of racemose where main axis is elongated.

1.      Corymb, umbel, compound corymb and compound umbel are the subtypes of racemose where main axis is shortened.

2.      Capitulum is a subtype of racemose where main axis is flat to form a receptacle.

  • The subtypes of cymose inflorescence are depending upon the branching pattern of inflorescence axis such as:

0.      Monochasial: Here, only one lateral branch is produced. If the lateral branches develop on alternate sides, it is called scorpioid and if lateral branches develop on the same side, it is called helicoid.

1.      Dichasial: Here, two lateral branches are produced.

2.      Polychasial: Here, more than two lateral branches are produced.

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