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Structure and Function of Plastids

Plastids are double-membranous organelles found in plant and algal cells. Food production and storage are tasks handled by plastids. These typically include cellular color-altering pigments as well as photosynthesis-related pigments. Lets learn more about structure and function of plastids.

What are Plastids?

Plastid is a double-membrane-bound organelle present in the cells of photosynthetic plants that is involved in the synthesis and storage of food. Ernst Haeckel discovered and called plastids, but A. F. W. Schimper provided the first precise definition.

They are needed for important things like photosynthesis and storing food. A chloroplast is a plastid that has the green pigment chlorophyll. A chromoplast is a plastid that has pigments other than green. A leucoplast is a plastid that doesn’t have pigments. Its main job is to store food.

Types of Plastids

There are different kinds of plastids, each of which has a specific job to do. Some of them are mostly sorted by whether they have biological pigments or not and what stage of development they are in.

  1. Chloroplasts
  2. Chromoplasts
  3. Gerontoplasts
  4. Leucoplasts
Structure and Function of Plastids

Figure 1: Structure and Function of Plastids.

Chloroplasts: Chloroplasts are organelles that are biconvex, semi-porous, and have two membranes. They are found in the mesophyll of plant cells. They are the sites for synthesizing food by the process of photosynthesis.

Chromoplasts: Chromoplasts is the name for the part of a plant where all the pigments are stored and made. Most of the time, these are found in flowers, leaves that are getting old, and fruits. They change from chloroplasts to chromoplasts. Chromoplasts have carotenoid pigments that give leaves and fruits their different colours. The main reason for its different colour is to attract insects that spread pollen.

Gerontoplasts: These are essentially age-related chloroplasts. When a leaf stops doing photosynthesis, typically in the fall, its chloroplasts, known as geronoplasts, help it transform into many other organelles.

Leucoplasts: They’re the colourless, non-pigmented organelles. Roots and other non-photosynthetic plant components typically include leucoplasts. Based on what the plant requires, they serve as warehouses for carbohydrates, lipids, and proteins. Protein and fat metabolism rely heavily on these enzymes.

Structure of Plastids

In higher plants, chloroplasts can be round, ovoid, or disc-shaped, while some algae have chloroplasts that are stellate, cup-shaped, or spiral. They are usually between 4 and 6 m in diameter, and there are 20 to 40 of them in the cytoplasm of each cell of a higher plant. 

The chloroplast is made up of two lipoprotein membranes, one on the outside and one on the inside, with a space in between them. The inner membrane encloses a matrix called the stroma, which has small cylindrical structures called grana. Most chloroplasts have between 10 and 100 grana.

Functions of Plastids

Plastids are the site of production and storage of chemical substances utilised by autotrophic eukaryotic cells. The thylakoid membrane includes all of the enzymes necessary for photosynthesis. Within the thylakoid membrane, interactions occur between chlorophyll, electron carriers, coupling factors, and other components.

Consequently, the thylakoid membrane is a specialised structure that plays a crucial function in light and electron transport. Thus, chloroplasts are the sites of glucose production and metabolism. Not only are they essential for photosynthesis, but also for the preservation of primary nutrients, particularly starch.

Its function depends significantly on the presence of pigments. Typically, plastids engaged in photosynthesis contain pigments, which are also responsible for the coloration of plant structures (e.g. green leaf, red flower, yellow fruit, etc.). plastids, like mitochondria, have their own DNA and ribosomes. Consequently, they can be utilised in phylogenetic research.

Inheritance of Plastids

There are many plants whose plastids come from just one parent. Many gymnosperms get their plastids from the male pollen, but angiosperms get theirs from the female gamete. The plastids in algae come from only one parent. The DNA in the plastids seems to come from only one parent. In hybridization, the plastid seems to be passed on in a more random way.


FAQs on Structure and Function of Plastids

Plastids are organelles with a double membrane that are found in the cells of plants and algae. Plastids are responsible for food production and storage. These frequently contain pigments used in photosynthesis and various pigment kinds that can alter the colour of the cell.

Types of Plastids

  1. Chloroplasts.
  2. Chromoplasts.
  3. Gerontoplasts.
  4. Leucoplasts.

Ernst Haeckel found and named plastids, but A. F. W. Schimper was the first person to explain what they were.