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Plastids Definition,Structure,Types,Shape & Composition

Plastids Definition,Structure,Types,Shape &Composition

Roll no = 14

  • Sessional year = 2020 -2024
  • Department = B.S.Chemistry
  • Semester = third
  • Assignment # 01
  • Subject = Botony
  • Topic = Plastids
  • Submitted by: Anam Shahzadi
Plastids Definition,Structure,Types,Shape &Composition


  • Government Graduate College  Chowk Azam Layyah

Plastids Definition,Structure,Types,Shape &Composition

 Definition of  Plastid 

  • Plastids may be a double membrane-bound

Organelle involved in the synthesis and storage of food is commonly found within the cell of photosynthetic plants.

  • Plastids were founded and named by Ernst Heckle, but A.F.W Schimper was the first to provide a clear definition.
  • They are necessary for essential life processes, like photosynthesis and food storage.
  • A plastid Containing green pigment ( chlorophyll ) is known as Chloroplast whereas a plastid Containing pigment aside from green is known as Chromoplast. A plastid that lacks pigment is called a Lecuoplast and it is mainly in food storage

Plastids Definition,Structure,Types,Shape &Composition

Types of Plastids

  • An undifferentiated plastid is named Proplastid. It may develop later into any of the opposite plastids.
  1. Chloroplast

  • The Chloroplast is probably the most knowledgeable of the Plastids.
  • These are responsible for Photosynthesis.
  • The Chloroplast is crammed with thylakoids, which is where photosynthesis occurs, and chlorophyll remains.
  1. Chromoplast

  • Chromoplast is units where pigments are stored and synthesized within the plants.
  • These may be found in flowering plants, fruits and ageing leaves
  • The Chloroplast actually converts over to Chromoplasts.
  • The carotenoid pigment allows for the different colours seen in fruits and the fall leaves .one of the main reasons for this structure and the colours is to attract pollinators
  1. Leucoplast

  • Leucoplast are the non- pigmented organlles.
  • They are found within the non-photosynthetic parts of the plants like the roots.
  • Depending on what the plant needs, they may become essentially just storage points for starches, lipids, and protein.
  • They are more readily used for the synthesis of Amino acids and fatty acids.
  • A leucoplast may be an amyloplast that stores fat or a protoplast that stores proteins

Plastids Definition,Structure,Types,Shape &Composition

  1. Gerontoplast

  • Gerontoplast is basically a chloroplast that is going through the ageing process.
  • These are the Chloroplast of the leaves that are origination to convert into different organelles or are being repurposed since the leaf is no longer utilizing photosynthesis ( such as in the fall months ).
  • Depending on their morphology and functions plastids have the power to differentiate or differentiate, between these and other forms.

# Some other types of plastids and their functions are given below in the form of a diagram.

Plastids and their types.

Structure of Plastids

  • Chloroplast may be spherical, ovoid, or discoid in higher plants and stellate,cup-shaped, or spiral as in some algae.
  • They are usually 4 to 6 um in diameter and 20 to 40 in number in each cell of higher plants, evenly distributed throughout the cytoplasm.
  • The Chloroplast could also be bound with two lipoprotein membranes an outer and an inner membrane, with an intermembrane space between them.
  • The inner membrane contains a matrix, the stroma which contains a small cylindrical structure named Grana. Most Chloroplasts contain 10-100 grana.
  • Each granum has a number of disc-shaped membranous sacs named grana lamellae or thylakoids ( 80 – 120 A° across ) piled on over the other grana.
  • The grana are connected by a network of anastomosing tubules referred to as inter-grana or stroma lamellae.
# The Grana and thylakoids
  • Single thylakoids are named stroma thylakoids which may be found in the chloroplast
  • Electron dense bodies, osmophilic granules along with ribosomes (the 70S), circular DNA, RNA and soluble enzymes of Calvin Cycles are also present in the matrix of the stroma.
  • Chloroplast thus has three differentiated membranes, the outer, the inner and the thylakoid membrane
  • The thylakoid membrane contains lipoprotein with a greater amount of lipids which are galactolipids, Sulpholipids, and phospholipids.
  • The inner surface of the thylakoid membrane may be granulated or powdered in the organization due to small spherical quantosomes.
  • The quantosomes are the photosynthetic units and consist of two structurally distinct photosystems PSl and

PSll, Containing about 250 chlorophyll molecules, each photosystem has antenna chlorophyll complexes and one reaction centre in which energy conversion takes place. In higher plants, the pigments that are present may be chlorophyll-a, chlorophyll -b, carotene, and xanthophyll.

  • The two photosystems and the components of the transport chain are asymmetrically distributed across the thylakoid membrane. Electron accepted of both PSI and PSll are on the outer ( stroma) surface of the thylakoid membrane, and electron donors of the PS1 are on the inner ( thylakoid space) surface.
Functions of Plastids
  • All plant cells contain Plastids in some shapes or forms. the roll- call indicates their functional diversity and demonstrates that Plastids lie at the very core of plant cellular functions.
  • Pladtiy is the site of manufacture and storage of important chemical compounds used by the cells of autotrophic eukaryotes.
  • The thylakoid membrane contains all the enzymatic components required for Photosynthesis, the interaction between chlorophyll, electron carriers, coupling factors, and the other components that take place within the thylakoid membrane. thus the thylakoid membrane may be a specialized structure that plays a key role in the capture of sunshine and electron transport.
  • Thus chloroplasts are the centres of the synthesis and metabolism of carbohydrates.
  • They are not only important within the process of Photosynthesis but also in the storage of primary foodstuffs, particularly starch.
  • Its functions largely depend on the presence of stains. A Plastid involved in food synthesis typically contains pigments, which also are the ones liable for the colour of a plant part ( e.g green leaf, red flowers, yellow fruit etc).
  • Like mitochondria, Plastids may have their own DNA and ribosomes. hence they may b used in phylogenetic studies.

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