What are Plastids? – Class 9 Biology

The body of all living organisms is made up of cells. Based on the cellular organization, some organisms are made up of single cells which are unicellular, and more than one cell which is multicellular organisms. Single-cell is able to perform all the life processes like gaining food, respiration, excretion, growth, and reproduction. 

A cell is a tiny mass of protoplasm which is surrounded by a membrane and is capable of performing all functions of life. A typical cell is formed of three parts. 

• Plasma membrane-Outermost covering of the cell which is made up of lipids and proteins. It allows the entry and exit of some materials in and out of the cell.
• Nucleus-It is a spherical structure present in the center of the cell and is surrounded by cytoplasm.
• Cytoplasm-It is a jelly-like fluid that occupies the space between the cell membrane and the nucleus. A number of tiny components called cell organelles are present in the cytoplasm. All the chemical reactions and functions will take place in the cytoplasm. 
• Cells have some special components called organelles. They are;
  • Plastids, Vacuoles, Ribosomes, Lysosomes, Golgi bodies, Mitochondria, Endoplasmic reticulum. 

Plastids

Plastid is a two-layered membrane-bound organelle found in the cells of plants that are involved in the synthesis and storage of food. They are fundamental for photosynthesis and the storage of food. Plastids are absent in animal cells. They consist of their own DNA and ribosomes and have the ability to divide.

A plastid containing green shade (chlorophyll) is called chloroplast while a plastid containing colors separated from green is known as a chromoplast. A plastid that needs colors is known as a leucoplast and is involved primarily in food capacity.

Types of plastids

Based on the morphology, structure, and color of plastids, they can be divided into the following types. Undifferentiated plastids are called “proplastids” which are found basically in meristematic tissues. Proplastids might form later into any of the different plastids.

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

Chloroplasts

 The most discussed type of plastid is the chloroplast. These organelles are liable for making plants green and creating energy for the cells and the plants overall. They are loaded up with heaps of thylakoid circles called grana. Each thylakoid film contains the green color chlorophyll, and the space inside the circle is known as the lumen. The liquid part that encompasses the grana and fills the chloroplast, similar to the cytoplasm of a phone, is known as the stroma.

Photosynthesis happens in the thylakoid stacks as the energy caught from the sun is siphoned across the layer from the stroma to the lumen. The hydrogen protons rush back across the film into the stroma, where ATP synthase changes over that energy into adenosine triphosphate (ATP), the cell’s energy cash. The ATP is incorporated into glucose atoms to be put away for some time in the future.

Chromoplasts

Chromoplasts are the other pigmented plastids that are all not green. These are tracked down in flowering plants, organic products, and mature leaves. At times chloroplasts are considered as chromoplast since they are pigmented, but the difference is that the green chlorophyll plays in photosynthesis.

Gerontoplasts

Gerontoplasts are old chloroplasts. The thylakoid films and the leftover chlorophyll are separated by gathering plastoglobuli, lipoprotein particles, in the stroma.

This progress from chloroplast to gerontoplast happens when the leaves go through senescence or decay with age. During the pre-winter months, the leaves change the tone and afterward bite the dust and tumble off. As the leaf passes on, the gerontoplasts are overwhelmed and processed via autophagosomes.

Leucoplasts

Leucoplasts are the non-pigmented organelles that are found in the non-photosynthetic pieces of the plant, like the roots.
They might turn out to be basically stockpiling sheds for starches, lipids, and proteins based on the plant’s needs. They are all the more promptly utilized for orchestrating amino acids and unsaturated fats.

There are three types of leucoplasts:

• Amyloplasts-Amyloplasts store and synthesize starch.
• Proteinoplasts-They stores the proteins and can be typically found in seeds.
• Elaioplasts-They help in storing fats and oils.

Structure of plastids

• Chloroplasts might be circular, ovoid, or discoid in higher plants and stellate, cup-molded, or winding as in some green growth.
• The chloroplast is limited by two lipoprotein films, an external and an internal layer, with an intermembrane space between them.
• They are usu­ally 4-6 µm in breadth and 20 to 40 in number in every cell of higher plants, equally circulated all through the cytoplasm.
• The inward layer encases a network, the stroma which contains little cylindri­cal structures called grana. Most chloroplasts con­tain 10-100 grana.
• Each granum has various plate molded membranous sacs called grana lamellae or thylakoids (80-120å across) heaped one over the other.
• The grana are intercon­nected by an organization of anastomosing tubules called between grana or stroma lamellae.
• Single thylakoids, called stroma thylakoids, are additionally tracked down in chloroplasts.
• Electron-thick bodies, osmophilic granules alongside ribosomes (the 70S), roundabout DNA, RNA, and dissolvable catalysts of Calvin cycles are likewise present in the grid of the stroma.
• Chloroplasts hence have three distinct mem­branes, the external, the internal, and the thylakoid layer.
• The thylakoid layer comprises lipoprotein with a more prominent measure of lipids which are galactolipids, sulpholipids, and phospholipids.
• The internal surface of the thylakoid layer is gra­nular in the association because of little spheroidal quantosomes.
• The quantosomes are the photosynthetic units and comprise of two basically particular photosystems, PS I and PS II, containing around 250 chlorophyll atoms. Each photosystem has to receive wire chlorophyll com­plexes and one response community in which energy change happens. In higher plants, the pig­ments present are chlorophyll-a, chlorophyll-b, carotene, and xanthophyll.
• The two photosystems and the parts of the electron transport chain are lopsidedly appropriated across the thylakoid film. Electron acceptors of both PS I and PS II are on the external (stroma) surface of the thylakoid layer. Electron givers of PS I are on the internal (thylakoid space) surface.

Functions

All plant cells contain plastids in some shape or structure. 

• Plastids are the site of production and capacity of significant synthetic mixtures utilized by the cells of autotrophic eukaryotes.
• The thylakoid layer contains every one of the enzymatic parts expected for photosyn­thesis. Association between chlorophyll, electron transporters, coupling factors, and different parts happens inside the thylakoid film. Consequently, the thylakoid layer is a particular struc­ture that assumes a critical part in the catch of light and electron transport.
• They are critical in photosynthesis as well as in the capacity of essential groceries, especially starch.
• Plastids store starch and can integrate unsaturated fats and terpenes
• They are the site of assembling and stockpiling of significant substance compounds
• Plastids are liable for the trademark shade of leaves, blossoms, and natural product
• They help to trap the daylight by which chloroplasts make their food by photosynthesis.

Inheritance of Plastids

Plastid inheritance in plants is uniparental. In oogamous species, plastids are generally derived from maternal parents. Only some of the species are known to have paternal plastid inheritance. During pollen development, all plastids are distributed into vegetative cells at the microspore mitosis and the generative cells formed from sperm cells are free of plastids. In some of the species young generative cell contains few plastids, but maternal generative cells are free of plastids. In monocots, sperm cells have plastids but the plastids will not be transmitted into the egg cell. After zygote formation by specific nucleases, the paternal plastid DNA will be degraded in 10 min. The maternal plastid DNA is protected by methylation. Thus, plastid DNA is degraded at different stages from the very first step of pollen mitosis, before fertilization, or after zygote formation.

FAQs on Plastid

Question 1: What are the types of plastids that help in pollination?

Answer:

Chromoplasts are the other pigmented plastids that are all not green. These are responsible for the color of flowers and fruits. They are engaged with drawing in bugs, and different vectors for fertilization (pollination) and for natural product dispersal.

Question 2: What is the location of plastids?

Answer:

Plastids are two layered-membrane organelles that exist in the cells of plants and algae. These are characterized by the synthesis and storage of food. These might contain pigments that can be used in photosynthesis and other types of pigments that are responsible for changing the color of the cell.

Question 3: What are the different types of Leucoplasts?

Answer:

• Leucoplasts are colorless plastids found in non-photosynthetic plants. These are of three types;
• Amyloplasts-Amyloplasts store and synthesize starch.
• Proteinoplasts-They stores the proteins and can be typically found in seeds.
• Elaioplasts-They help in storing fats and oils.

Question 4: What are the functions of plastids?

Answer:

• Plastids store starch and can integrate unsaturated fats and terpenes.
• They are the site of assembling and stockpiling significant substance compounds.
• Plastids are liable for the trademark shade of leaves, blossoms, and natural products.
• They help to trap the daylight by which chloroplasts make their food by photosynthesis.

Question 5: Name the different types of plastids based on color.

Answer:

1. Chloroplasts-Green
2. Chromoplasts-Either yellow, orange or red
3. Leucoplasts-Colorless or white
4. Gerontoplasts-Senescent forms of chloroplasts