Plastids and Chloroplasts are important cell organelles found in plant cells. They play a key role in photosynthesis, storage, and pigmentation. These notes are based on NCERT Class 11 Biology and are useful for NEET preparation.
Functions of Plastids
- Chloroplast → Photosynthesis
- Chromoplast → Provide colour to fruits and flowers
- Leucoplast → Storage of food materials
Plastids & Chloroplasts
1. What are Plastids?
Plastids are found in all plant cells and in euglenoids. They are large enough to be easily observed under the microscope. Based on the type of pigments, they are classified into three types:
 |
| Plastids |
Chloroplasts: Contain chlorophyll and carotenoid pigments (trap light energy for photosynthesis).
Chromoplasts: Contain fat-soluble carotenoid pigments like carotene and xanthophylls (give yellow, orange, or red colors).
Leucoplasts: Colorless plastids of varied shapes and sizes that store nutrients:
Amyloplasts: Store starch (e.g., Potato).
Elaioplasts: Store oils and fats.
Aleuroplasts: Store proteins.
2. Structure of Chloroplast
Chloroplasts are double-membrane-bound organelles.
 |
| Sectional view of Chloroplast |
Stroma: The fluid-filled space limited by the inner membrane.
Thylakoids: Flattened membranous sacs present in the stroma.
Grana: Thylakoids are arranged in stacks like piles of coins called grana.
Stroma Lamellae: Flat membranous tubules connecting the thylakoids of different grana.
Matrix Contents: The stroma contains enzymes required for the synthesis of carbohydrates and proteins.
3. Semi-autonomous Nature (Like Mitochondria)
Chloroplasts also have their own:
Small, double-stranded circular DNA molecules.
70S Ribosomes (smaller than the cytoplasmic 80S ribosomes).
They also divide by fission.
Don't Forget for NEET:
Amyloplasts = Stores Starch (PotatoElaioplasts = Stores Oils & Fats,Aleuroplasts = Stores Proteins.
(Direct Match the Column question comes from here!)
Both Mitochondria and Chloroplasts have 70S Ribosomes and Circular DNA.
"Quick Revision Quiz"
Q1. A student observes a colorless plastid in a potato tuber cell. Which specific type of plastid is he looking at?
A) Chromoplast
B) Aleuroplast
C) Amyloplast
D) Elaioplast
Answer: C) Amyloplast Explanation: Leucoplasts are colorless plastids. Among them, Amyloplasts are specialized for storing carbohydrates (starch), like in potato tubers.
Q2. Which of the following features is common to both Mitochondria and Chloroplasts?
A) Presence of 80S Ribosomes
B) Absence of DNA
C) Presence of 70S Ribosomes and Circular DNA
D) Single membrane-bound structure
Answer: C) Presence of 70S Ribosomes and Circular DNA Explanation: Both are semi-autonomous organelles containing their own genetic material (circular DNA) and prokaryotic-type (70S) ribosomes.
Q3. The flattened membranous sacs forming the 'stacks' within the stroma of a chloroplast are called:
A) Cristae
B) Thylakoids
C) Stroma Lamellae
D) Matrix
Answer: B) Thylakoids Explanation: Thylakoids are flattened sacs arranged in stacks called grana. Cristae are found in mitochondria, not chloroplasts.
Q4. Match the following plastids with their storage products:
i. Elaioplast — a. Protein
ii. Aleuroplast — b. Starch
iii. Amyloplast — c. Fats/Oils
A) i-c, ii-a, iii-b
B) i-a, ii-b, iii-c
C) i-b, ii-c, iii-a
D) i-c, ii-b, iii-a
Answer: A) i-c, ii-a, iii-b Explanation: Elaioplasts store oils/fats, Aleuroplasts store proteins, and Amyloplasts store starch. (This is a very frequent NEET question)
Q5. Anthocyanins are water-soluble pigments responsible for red/purple colors in flowers. Where are they located?
A) Chloroplasts
B) Chromoplasts
C) Vacuoles
D) Leucoplasts
Answer: C) Vacuoles Explanation: Unlike fat-soluble carotenoids in chromoplasts, water-soluble anthocyanins are found in the cell vacuole. (A common trap for students!)
Conclusion
Plastids, especially chloroplasts, are essential for plant survival as they perform photosynthesis and store food. Understanding their structure and function is important for NEET exams.
){kind=link}
0 Comments