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  • Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.

7. Name two cell organelles that are double membrane-bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.

Answers (2)

The two double membrane-bound organelles are mitochondria and chloroplast. 

Characteristics of Mitochondria- 

1. Mitochondria are cylindrical-shaped cell organelles which can be stained by Janus green and observed in the microscope. MItochondria consists of 60-70% proteins, 25-35 % lipids, 5-7% RNA, DNA etc. 

2. Mitochondria is made up of two membranes i.e. an outer membrane and an inner membrane. These two membranes are separated by pre-mitochondrial space. The outer membrane is smooth and porous. Porins are present in the outer membrane. 

3. The inner membrane of mitochondria is invaginated into folds that are called cristae. The electron transport chain and exosomes are found in the inner membrane.

4. Inside the mitochondria, a semi-fluid matrix is present which consists of protein particles, ribosomes, RNA, DNA and enzymes that are used in the Krebs cycle, amino acid synthesis etc. 

5. Mitochondria are semi-autonomous organelles as they possess their own DNA and protein synthetic machinery. The DNA of mitochondria is naked and circular.

Functions of mitochondria

1. Mitochondria are the sites of cellular respiration

2. Mitochondria provide important intermediates for the synthesis of several biochemicals like chlorophyll.

3. Synthesis of many amino acids and fatty acids occurs in the mitochondria. 

4. MItochondria may store and release calcium when required.

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Characteristics of chloroplast

The chloroplast is a green coloured plastid which possesses photosynthetic pigments like chlorophyll, carotenoids etc and takes part in photosynthesis. 

2. Chloroplasts can be variously shaped i.e. they can be plate-like, ribbon-like, cup-shaped etc.

3. Chloroplast consists of 50-60% protein, 25-30% lipids, 5-10% chlorophyll, 1-2% carotenoids, up to 0.5% DNA and 2-3% RNA. 

4. The structure of chloroplast consists of an envelope, matrix and thylakoids. 

5. The envelope of the chloroplast is made up of two smooth membranes separated by intermembrane space of 100-200 angstrom width. The outer membrane is more permeable than the inner membrane. 

6. The ground substance of a chloroplast is known as a matrix or stroma. It is a semi-fluid colloidal complex made up of 50% soluble proteins and RNA, DNA, ribosomes, enzymes etc. Throughout the stroma, membrane-lined flattened sacs are present. These take part in photosynthesis. Thylakoids are stacked one over the other to form grana. 40-60 grana may occur in 1 chloroplast. Each granum may have 2-100 thylakoids. In thylakoid membranes, photosystems are present. 

Functions of chloroplast

1. Chloroplasts are the site of photosynthesis.

2. Chloroplasts contain the enzymes for the synthesis of carbohydrates and proteins.

3. They temporarily or permanently store starch

Structure of Chloroplast

 

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Sonika

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Nudeus.endoplasmic relicolum Golgi bodies ly so sames mitochondria vacuoles are all different cell organelles

 

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Siddique Firdous sher ali

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