Lab 4 - Plant Cell Structure PDF

Basic Cell Structure Plant Cell and Functions What is cell? – Cell is the basic structural and functional unit of living organisms. – In other words, cells make up living things and carry out activities that keep a living thing alive. Cell Theory –...

Basic Cell Structure Plant Cell and Functions What is cell? – Cell is the basic structural and functional unit of living organisms. – In other words, cells make up living things and carry out activities that keep a living thing alive. Cell Theory – Timeline Year Discovery 1665 Robert Hooke discovered cell 1674 Anton Van Leeuwenhoek observed living cell 1838 Matthias Schleiden proposed all plants are made up of cells 1839 Theodor Schwann proposed all animals are made up of cells 1845 Carl Heinrich Braun proposed cell is the basic unit of life 1855 Rudolf Virchow proposed all new cells arise from pre-existing cells 1883 Robert Brown discovered nucleus 1885 Felix Dujardin discovered fluid content of cell Cell Theory is a collection of ideas and conclusions from many different scientists over time that describes cells and how cells operate – All known living things are made up of one or more cells. – All living cells arise from pre-existing cells by division. – The cell is the basic unit of structure and function in all living organisms. Structure of cell  The detailed structure of a cell has been studied under compound microscope and electron microscope.  Certain structures can be seen only under an electron microscope.  The structure of a cell as seen under an electron microscope is called ultrastructure. Plant Cell 1. Nucleus 2. Golgi Body 3. Vesicle 4. Lysosome 5. Plasma membrane 6. Mitochondria 7. Chloroplast 8. Cell wall 9. Vacuole 10. Smooth endoplasmic reticulum 11. Rough endoplasmic reticulum 12. Nucleolus Functions of Plant Cell Components CELL WALL 1. Non-living and outermost covering of a plant cell 2. Can be tough, rigid and sometimes flexible 3. Made up of cellulose, hemicellulose and pectin 4. May be thin or thick, multilayered structure Functions  Provides definite shape, strength & rigidity  Prevents drying up (desiccation) of cells  Helps in controlling cell expansion  Protects cell from external pathogens PLASMA MEMBRANE 1. Extremely delicate, thin , elastic, living and semi- permeable membrane 2. Made up of two layers of lipid molecules in which protein molecules are floating 3. Can be observed under an electron microscope only Functions  Maintains shape & size of the cell  Protects internal contents of the cell  Regulates entry and exit of substances in and out of the cell  Maintains homeostasis CYTOPLASM 1. Jelly-like material formed by 80 % of water 2. Present between the plasma membrane and the nucleus 3. Contains a clear liquid portion called cytosol and various particles 4. Particles are proteins, carbohydrates, nucleic acids, lipids and inorganic ions 5. Also contains many organelles with distinct structure and function 6. Some of these organelles are visible only under an electron microscope CHLOROPLAST 1. Double membrane-bound organelles found mainly in plant cells 2. Usually spherical or discoidal in shape 3. Shows two distinct regions-grana and stroma 4. Grana are stacks of thylakoids (membrane- bound, flattened discs) 5. Thylakoids contain chlorophyll molecules which are responsible for photosynthesis 6. Stroma is a colorless dense fluid Functions  Convert light energy into chemical energy in the form of food  Provide green colour to leaves, stems and vegetables MITOCHONDRIA 1. Small, rod shaped organelles bounded by two membranes - inner and outer 2. Outer membrane is smooth and encloses the contents of mitochondria 3. Inner membrane is folded in the form of shelf like inward projections called cristae 4. Inner cavity is filled with matrix which contains many enzymes 5. Contain their own DNA which are responsible for many enzymatic actions Functions  Synthesize energy rich compound ATP  ATP molecules provide energy for the vital activities of living cells NUCLEUS 1. Nucleus has a double layered covering called nuclear membrane 2. Nuclear membrane has pores of diameter about 80- 100 nm 3. Colourless dense sap present inside the nucleus known as nucleoplasm 4. Nucleoplasm contains round shaped nucleolus and network of chromatin fibers 5. Fibers are composed of deoxyribonucleic acid (DNA) and protein histone 6. These fibers condense to form chromosomes during cell division 7. Chromosomes contain stretches of DNA called genes 8. Genes transfer the hereditary information from one Functions  Control all the cell activities like metabolism, protein synthesis, growth and cell division  Nucleolus synthesizes ribonucleic acid (RNA) to constitute ribosomes  Store hereditary information in genes VACUOLES 1. Single membrane sac filled with liquid or sap (water, sugar and ions) 2. In animal cells, vacuoles are temporary, small in size and few in number 3. In plant cells, vacuoles are large and more in number 4. May be contractile or non-contractile Functions  Store various substances including waste products  Maintain osmotic pressure of the cell  Provide turgidity and rigidity to plant cells Exercise 1 Objective: To prepare a stained temporary mount of an onion peel (Plant cell) Materials Required: Cover slip, glycerin, glass slide, onion, watch glasses, distilled water, safranin, forceps, brush, needle, microscope, blotting paper, dropper Procedure: See video in next slide Observation: Temporary mount of an onion peel (Plant cell) Video – Move the cursor in the middle of slide to play  PERMEABILITY OF BIOLOGICAL MEMBRANES Osmosis Plasmolysis Osmosis Passage of water from a region of low concentration of solute to a region of high concentration, across a semipermeable membrane How is Osmosis different from Diffusion? Isotonic: Same solute concentration Hypotonic: Low solute concentration Hypotonic: High solute concentration Semipermeable membrane Osmosis in plant cells - Plasmolysis  Plasmolysis Plasmolysis is the loss of water from the cell by osmosis, and this is evident when the cell contents pull away from the rigid cell wall as the water moves out. Steps of Plasmolysis TIME, (min) Steps of Plasmolysis  Plasmolysis Purpose: To demonstrate a biological principle observed in plant cells called plasmolysis. Materials and Methods: Microscope, clean slides and cover slips, dropper, salt, spatula, and elodea. Prepare a wet mount using a single leaf. Carefully add some salt crystals to the edge of the cover slip. You may need to add a drop more water onto the crystals with the dropper. Now place the slide on the microscope stage and observe the leaf cells on low and then high power. Experiment: As water moves out of the cells by osmosis, you should observe the cytoplasmic contents clumping away from the cell wall as Plasmolysi s Video – Elodea under hypertonic and hypotonic solution Wiltin g due to a loss of water!!  In this experiment what is Conclusion: considered hypertonic? What is considered hypotonic? In the diagram above, the right cell is plasmolyzed. The cell on the left is turgid. What does this mean and under what conditions would it be in this condition?