Question

Short note on microsporangium

Answer 1

Answer:

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Explanation:

Microsporangium is the sporangial structure which contains microspores which are the pollen sacs giving rise to male gametes in an angiosperm. A microsporangium is circular in outline in transverse section and is usually surrounded by four wall layers. The outermost is the single layer of the epidermis. The second layer is endothecium, where cells develop thickenings. The middle layer is made up of 2-4 cells. The innermost layer is tapetum, which provides nutrition to the developing pollen cells. The cells of tapetum may be multinucleate. The outer three layers are protective in function. They also help in dispersal of pollens by dehiscing themselves. There are four pollen sacs present inside. The centre of the microsporangium comprises of compact sporogenous tissue. These tissues undergo meiotic divisions to form microspore tetrads, that further divide to form pollen grains.

Microsporangium is a structure in the plant’s male reproductive organ where the development of pollen takes place.

Structure of Microsporangia

A microsporangium appears to have a circular outline when viewed transversely. It is surrounded by four layers:

Epidermis

Endothecium

Middle layers

Tapetum

The outer three layers protect the pollen and help in the splitting of anther to release the pollen. The tapetum nourishes the pollen grain. The cells of the tapetum are multinucleated and have dense cytoplasm. A young anther comprises of a group of compactly arranged homogenous cells called sporogenous tissue.

Sporogenous Tissue

These are located at the centre of each microsporangium in a young anther. With the development of the anther, the sporogenous cells undergo meiotic division to form microspore tetrads. Each sporogenous cell is known as pollen mother cell or microspore mother cell. This process by which a microspore is formed from the pollen mother cell is known as microsporogenesis. The microspores are arranged in the form of a tetrad. As the anther matures it dehydrates and the microspores dissociate from each other and develop into a pollen grain.

Pollen Grain

The matured pollen grain contains two cells: a generative cell and a pollen tube cell. The generative cell is present within the larger pollen tube cell. The tube cells form the pollen tube on germination. The generative cell migrates into the ovary through the pollen tube. Inside the pollen tube, the generative cell divides into two gametes or sperms. The anther matures and releases the pollen grains.

Answer 2

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★ A ᴛʏᴘɪᴄᴀʟ ᴍɪᴄʀᴏsᴘᴏʀᴀɴɢɪᴜᴍ ᴀᴘᴘᴇᴀʀs ᴄɪʀᴄᴜʟᴀʀ ᴀɴᴅ ɪs sᴜʀʀᴏᴜɴᴅᴇᴅ ʙʏ ғᴏᴜʀ ᴡᴀʟʟs:

(ɪ) ᴇᴘɪᴅᴇʀᴍɪs: ɪᴛ ɪs ᴛʜᴇ ᴏᴜᴛᴇʀᴍᴏsᴛ sɪɴɢʟᴇ ʟᴀʏᴇʀ ᴏғ ᴄᴇʟʟ ᴡʜɪᴄʜ ɪs ᴘʀᴏᴛᴇᴄᴛɪᴠᴇ ɪɴ ɴᴀᴛᴜʀᴇ.

(ɪɪ) ᴇɴᴅᴏᴛʜᴇᴄɪᴜᴍ: ɪᴛ ɪs ᴛʜᴇ sᴇᴄᴏɴᴅ ʟᴀʏᴇʀ ᴡɪᴛʜ ᴛʜɪᴄᴋ ᴄᴇʟʟs, ʜᴇʟᴘ ɪɴ ᴅᴇʜɪsᴄᴇɴᴄᴇ ᴀɴᴅ ɪs ᴘʀᴏᴛᴇᴄᴛɪᴠᴇ ɪɴ ɴᴀᴛᴜʀᴇ.

(ɪɪɪ) ᴍɪᴅᴅʟᴇ ʟᴀʏᴇʀ: ɪᴛ ɪs ᴛʜᴇ ᴛʜɪʀᴅ ʟᴀʏᴇʀ ᴄᴏᴍᴘᴏsᴇᴅ ᴏғ 1-3 ʟᴀʏᴇʀs ᴏғ ᴄᴇʟʟs, ʜᴇʟᴘ ɪɴ ᴅᴇʜɪsᴄᴇɴᴄᴇ ᴀɴᴅ ɪs ᴘʀᴏᴛᴇᴄᴛɪᴠᴇ ɪɴ ɴᴀᴛᴜʀᴇ.

(ɪᴠ) Tᴀᴘᴇᴛᴜᴍ: ɪᴛ ɪs ᴛʜᴇ ғᴏᴜʀᴛʜ ᴀɴᴅ ɪɴɴᴇʀᴍᴏsᴛ ʟᴀʏᴇʀ ᴏғ ᴄᴇʟʟ ᴡɪᴛʜ ᴅᴇɴsᴇ ᴄʏᴛᴏᴘʟᴀsᴍ ᴀɴᴅ ᴍᴀɴʏ ɴᴜᴄʟᴇɪ. ɪᴛ ᴘʀᴏᴠɪᴅᴇs ɴᴏᴜʀɪsʜᴍᴇɴᴛ ᴛᴏ ᴛʜᴇ ᴅᴇᴠᴇʟᴏᴘɪɴɢ ᴘᴏʟʟᴇɴ ɢʀᴀɪɴs.

★ᴛʜᴇ ᴄᴇɴᴛʀᴇ ᴏғ ᴇᴀᴄʜ ᴍɪᴄʀᴏsᴘᴏʀᴀɴɢɪᴜᴍ ɪs ғɪʟʟᴇᴅ ᴡɪᴛʜ ᴄʟᴏsᴇʟʏ ᴀʀʀᴀɴɢᴇᴅ sɪᴍɪʟᴀʀ ᴄᴇʟʟs ᴄᴀʟʟᴇᴅ sᴘᴏʀᴏɢᴇɴᴏᴜs.

★ᴀᴛ ᴍᴀᴛᴜʀɪᴛʏ, ᴘᴏʟʟᴇɴ sᴀᴄ ɪs ғᴏʀᴍᴇᴅ ʙʏ ғᴜsɪᴏɴ ᴏғ ᴛᴡᴏ ᴍɪᴄʀᴏsᴘᴏʀᴀɴɢɪᴜᴍ ɪɴᴇᴀᴄʜ ʟᴏʙᴇ.

★ᴀ ᴍᴀᴛᴜʀᴇ ᴀɴᴛʜᴇʀ ᴅᴇʜɪsᴄᴇs ʙʏ sʟɪᴛs ᴀɴᴅ ʟɪʙᴇʀᴀᴛᴇ ᴛʜᴇ ᴘᴏʟʟᴇɴ ɢʀᴀɪɴ.