NARAYANKAR NOTES

Plastids – Colourful and Storage Organelles of Plant Cells 1. Structure and Similarity with Mitochondria Plastids are double membrane-bound organelles found mainly in plant cells . Just like mitochondria, plastids also contain: DNA RNA 70S ribosomes These features allow plastids to synthesize some of their own proteins . However, plastids are usually larger in size than mitochondria and can be seen easily under a light microscope . 2. Classification of Plastids Based on Pigments Plastids are classified into three main types , based on the type of pigments they contain: Leucoplasts – Colourless plastids Chromoplasts – Coloured plastids (other than green) Chloroplasts – Green plastids involved in photosynthesis This section focuses on leucoplasts . 3. Leucoplasts – Nutrient Storage Units Leucoplasts are colourless plastids as they do not contain any pigments . They occur in various shapes and sizes , depending on their specific function. The...

Mitochondria – The Powerhouse of the Cell 1. Function and Occurrence Mitochondria are important cell organelles responsible for aerobic respiration , the process by which cells produce energy (in the form of ATP) using oxygen. They are absent in prokaryotic cells (like bacteria) and also in red blood corpuscles (RBCs) of mammals. 2. Shape and Appearance Mitochondria can have different shapes depending on the cell. They may be: Oval Spherical Spiral strip-like This variation in shape allows them to fit and function effectively within different types of cells. 3. Membrane Structure Mitochondria are double membrane-bound organelles , meaning they have two layers of membrane : Outer Membrane : This membrane is permeable to various metabolites (small molecules). This permeability is due to the presence of a protein called Porin (also known as Parson’s particles ). Inner Membrane : This membrane is selectively permeable , meaning it only allows ce...

  Glyoxysomes – Fat-to-Sugar Converting Organelles 1. Definition and Structure Glyoxysomes are membrane-bound organelles that are a special type of microbody . They contain specific enzymes that help in the conversion of fatty acids into sugars . 2. Function and Importance The main function of glyoxysomes is to convert stored fats into usable sugars through a biochemical pathway called reverse glycolysis( the breakdown of glucose by enzymes, releasing energy and pyruvic acid-a key molecule in cellular metabolism) . This process is especially important in germinating seeds , where the young plant cannot perform photosynthesis yet. 3. Role in Germination ( the process by which a plant grows from a seed into a seedling)  ( अंकुरण, मोड येणे, रुजवात.) During germination: The seed uses stored fats as a source of energy . Glyoxysomes help in converting these fats into glucose (sugar) , which the growing plant uses to carry out its life processes. This contin...

Vacuoles – Storage Sacs of the Cell 1. Location and Structure Vacuoles are membrane-bound sacs found inside cells. They are prominently seen in plant cells , whereas in animal cells , they are fewer in number and smaller in size . In most plant cells, there are two or three permanent vacuoles , but in some large plant cells, a single large vacuole fills the central region of the cell. This is known as the central vacuole . It can take up to 90% of the total cell volume , making it a very important organelle in plant cells. 2. Tonoplast Membrane The vacuole is surrounded by a semipermeable membrane known as the tonoplast membrane . This membrane controls the movement of substances in and out of the vacuole and maintains the unique composition of the liquid inside, which is called cell sap . The composition of the cell sap varies depending on the type of cell . In most cases, the central vacuole's sap contains a high concentration of ions , making it hypertonic (more c...

Lysosomes – The Dismantling and Restructuring Units of the Cell Definition and Structure Lysosomes are membrane-bound vesicles found in most eukaryotic cells . They are considered as dismantling and restructuring units of a cell because they help break down and recycle various substances. Enzymes in Lysosomes Lysosomes contain hydrolytic( a class of enzymes that use water to break down chemical bonds in molecules ) enzymes( Enzyemes are proteins that act as biological catalysts, significantly speeding up chemical reactions within living organisms, they use ) , which are special proteins that help in breaking down or digesting large molecules (called macromolecules ). These enzymes function best in an acidic pH (acidic environment). The types of enzymes found in lysosomes include: Amylases (which digest starch), Proteases (which digest proteins), and Lipases (which digest fats). These enzymes are stored in an inactive state inside the lysosome. They get activate...

🧬 What are they? Endoplasmic Reticulum (ER) and Golgi Body (or Golgi Apparatus) are cell organelles found in eukaryotic cells (cells with a nucleus). The ER is like a factory that makes proteins and lipids (fats) . The Golgi Body is like a post office or packaging center that modifies, sorts, and sends those proteins and lipids to their final destinations. 🏗️ Structure and Types of ER: The ER is a network of membrane-bound tubes and sacs connected to the nuclear envelope (the covering of the nucleus). There are two types of ER: Rough ER (RER) – has ribosomes attached, makes proteins Smooth ER (SER) – no ribosomes, makes lipids and detoxifies chemicals 📦 What does the Golgi Body look like? The Golgi Body is made up of flat, stacked pouches called cisternae . It is not connected directly to the nucleus or ER, but it receives materials from the ER through transport vesicles . 🔄 How do ER and Golgi Body work together? Let’s understand their coordin...

  Difference Between Vesicles and Vacuoles Feature Vesicles Vacuoles Size Small in size Larger than vesicles Function Transport substances inside the cell Store substances like water, food, and waste Presence Found in both plant and animal cells Large central vacuole in plant cells; small or absent in animals Structure Small, round, membrane-bound sacs Large, fluid-filled, membrane-bound sacs Mobility Move freely inside the cell Mostly fixed in place Examples Transport proteins from ER to Golgi apparatus Store water in plant cells Formation Formed from Golgi apparatus or cell membrane Formed from endoplasmic reticulum or Golgi apparatus Types Transport vesicles, secretory vesicles, lysosomes Food vacuole, contractile vacuole, central vacuole Role in Digestion Some vesicles (like l...

 

 

 Here is the complete list of cell organelles : Cell wall Plasma membrane / Cell membrane Cytoplasm Nucleus Nucleolus Chromatin / Chromosomes Ribosomes Endoplasmic reticulum (Smooth and Rough ER) Golgi apparatus / Golgi complex / Golgi body Lysosomes Vacuoles Mitochondria Plastids Chloroplasts Chromoplasts Leucoplasts Amyloplasts Elaioplasts Aleuroplasts Microbodies Peroxisomes Glyoxysomes Sphaerosomes Mesosomes Centrosome Centrioles Cytoskeleton Microtubules Microfilaments Intermediate filaments Cilia Flagella Basal body Plasmodesmata Oxysomes (in mitochondria) Thylakoids (in chloroplasts) Granum / Grana Lamella / Stromal lamellae Tonoplast (vacuole membrane) Nuclear envelope Nuclear pore Perinuclear space Karyolymph / Nucleoplasm 🧬 Cell Membrane (Plasma Membrane) 🌟 What is it? The cell membrane is a thin, flexible covering that surrounds the cell...