Cell and Cell Organelles Science Notes

Cell and Cell Organelles Science Notes

Important Points:

→ Cell: Cell is the structural and functional unit of living organisms.
→ Cells are of different sizes and structures based on cv their functions. They form every organ in the body.

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Components of a cell

Cell and Cell Organelles Science Notes 1

→ Activities that consume cellular energy

  • Endocytosis: The entry of some substances into the cell from outer environment is endocytosis.
  • Exocytosis: The removal or exit of some substances from inside the cell to the outer environment is called exocytosis.

→ Processes that do not consume cellular energy:

→ Diffusion: The movement of molecules from region of high concentration to the region of low concentration is called diffusion. Liquid molecules or Gaseous molecules like 02, C02 show diffusion.
→ Osmosis: The movement of solute or solvent molecules that take place through the semipermeable membrane is called osmosis. The solute molecules always move from region of low concentration to region of high concentration.
→ The solvent molecules move from region of their high concentration to region of their low concentration. It is a physical process and passive in nature as it does not require energy.

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→ For clear understanding

→ The solution is made up of a solute and a solvent. For convenience let’s use the word ‘water’ for solvent. The cell’s plasma membrane acts as a semipermeable membrane during osmosis.
→ When three similar cells are placed in three types of solutions, i.e. isotonic, hypotonic and hypertonic, the process of osmosis will take place differently.

Water will always move from region of its high concentration to region of its low concentration. Solute will always move from region of its low concentration to the region of high concentration. Therefore, in isotonic solutions, the cell will remain (in equilibrium) the same as there will be no movement of water molecules.

In hypotonic solution, the water from outside the cell will come inside the cell. The cell will thus swell. This process is endosmosis. In hypertonic solution, the water from cell will come out in the cell. The cell will thus shrink. This process is exosmosis.
Cell and Cell Organelles Science Notes 2

Cell and Cell Organelles Science Notes 3
Cell and Cell Organelles Science Notes 4

Cytoplasm

  • Protoplasm = Cytoplasm + Nucleus.
  • Cytoplasm – cell organelles = cytosol
  • Cytoplasm is the material bounded by plasma membrane.
  • Many cell organelles and nucleus are present in the cytoplasm.
  • Cellular chemical reactions take place in cytoplasm.
  • Vital substances like amino acids, glucose, vitamins, etc. are present in the cytoplasm.
  • Animal cell cytoplasm : More granular and dense.
  • Plant cell cytoplasm : Thin and pushed to the periphery with a larger central vacuole.

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Cell organelles

  • They are organs of the cell.
  • Specialized subunit with specific cellular function.
  • Each organelle has its own lipoprotein membrane.
  • Except nucleus and chloroplast, all other organelles can be seen only with electron microscope.

Nucleus:

Cell and Cell Organelles Science Notes 5

→ Structure

  • Covered by a double layered porous membrane.
  • Pores allow the passage of material in and out of the nucleus.
  • One round nucleolus present.
  • Network of chromatin fibres present.
  • Short, thick chromosomes formed from chromatin fibres by condensation at the time of cell division.
  • Functional segments on chromosomes are called genes.

→ Functions

  • Control of all metabolic activities of the cell and cell division.
  • Transmission of hereditary characters from parents to offspring.
  • Nucleus is lost in RBCS of mammals to accommodate more haemoglobin.
  • Nucleus is also lost in sieve tubes of phloem for making them hollow for transportation of food.

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Endoplasmic Reticulum (ER):

Cell and Cell Organelles Science Notes 6

→ Structure

  • Net like structure having interconnected miniature tubes and sheets filled with fluid.
  • Conducts various substances inside the cell.
  • E.R. is connected to nucleus from inner side to plasma membrane from outer side.
  • Rough ER has ribosome granules on its outer surface
  • Smooth ER are without ribosomes.

→ Functions

  • Framework for supporting cell.
  • Conduction of proteins.
  • Detoxication process. Toxins that have entered are made water soluble by ER for their rapid flushing out of the body.

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Golgi Complex:

Cell and Cell Organelles Science Notes 7

→ Structure

  • 5-8 cisternae which are hollow and flat sacs placed parallel to each other.
  • Cisternae have different enzymes.
  • The proteins coming from ER are enclosed in vesicles.
  • Vesicles come to Golgi complex via cytoplasm.
  • Vesicles fuse with the formation face of the Golgi membranes.
  • They empty their contents in the cisternae.
  • The secretory contents are chemically modified with the help of enzymes while passing through the cisternae.
  • They are again packed in the vesicles which exit from the maturation face.

→ Functions

  • Secretory organ of the cell.
  • It modifies, sorts, packs and dispatches materials synthesized in the cell (enzymes, mucus, proteins, pigments etc.) to plasma membrane, lysosome etc.
  • Production of vacuoles and secretory vesicles.
  • Helps in the formation of cell wall, plasma membrane and lysosomes.

Lysosomes

Cell and Cell Organelles Science Notes 8

→ Structure

  • Structure: Simple, single membrane bound sacs containing digestive enzymes.
  • Digesting the organic wastes produced through metabolic activities in the cell.

→ Functions

  • Immune system – Destruction of viruses and bacteria that attack the cell.
  • Demolition squads – It destroys worn- out cellular organelles and organic debris. (Autolysis)
  • Lysosomes are called suicidal bags of the cell as the old and damaged cells are digested by bursting and releasing the digestive enzymes. Thus, digesting their own cells.
  • Lysosomes digest stored proteins, fats during starvation.

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Mitochondria

Cell and Cell Organelles Science Notes 9

→ Structure

  • Double membrane bound structure.
  • Porous outer membrane and deeply folded inner membrane.
  • Folds are called ‘cristae’.
  • The inner cavity has matrix containing ribosomes, phosphate granules and DNA. It is like a proteinaceous gel.

→ Functions

  • Oxidation of carbohydrates and fats in the cell with the help of enzymes.
  • Release of energy. Energy is stored in the form of ATP in mitochondria.
  • To produce energy-rich compound – ATP.
  • Synthesis of proteins, carbohydrates, lipids, etc. by using the energy in ATP.

→ Important

  • Mitochondria produces its own proteins.
  • Plant cells have less mitochondria than animal cells.
  • Mitochondria are absent in RBCs. The oxygen transported by RBCS don’t use this oxygen due to lack of mitochondria.

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Vacuole

Cell and Cell Organelles Science Notes 10

→ Structure

  • Storage sacs for solid or liquid contents.
  • No typical shape or size.
  • Structure changes according to the need of the cell.
  • Bound by single membrane.

→ Functions

  • Maintain the osmotic pressure of the cell.
  • Storage of metabolic by-products and end products. Such as glycogen, proteins, water, etc.
  • In animal cell – storage of waste products and food, In amoeba storage food before digestion.
  • Plant cell vacuoles – full of cell sap and provide turgidity, rigidity to them.

Cell and Cell Organelles Science Notes 11
Cell and Cell Organelles Science Notes 12

Prokaryotic and eukaryotic cells

Main differences between the Prokaryotic and eukaryotic cells.

Point of distinction Prokaryotic cells Eukaryotic cells.
Nucleus Nucleoid resembling nucleus Well-formed nucleus with nucleolus and nucleoplasm
Nuclear membrane Absent Present
Number of chromosomes Only one Many in number. With fixed number for each species.
Cell organelles No membrane bound cell organelles. Self-replicating, membrane bound cell organelles.
Size 1-10 micrometre. 5-100 micrometre
Examples Bacteria Highly evolved unicellular and all multicellular organisms such as plants and animals.

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Work of Institutes

  • National Centre for Cell Science (NCCS) is an independent institute working under Biotechnology Department of Government of India.
  • Situated at Pune in Savitribai Phule Pune University campus. It is involved in research in cytology.
  • National Animal cell repository is also associated with this institute. Its main work is research about cancer treatment.

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