Lesson 2: Understanding cells
Download as PPT, PDF2 likes1,697 views
The document explains that all living organisms are made up of cells, which are the fundamental units that perform vital life processes. It details the structure and functions of both animal and plant cells, highlighting differences such as the presence of cell walls and chloroplasts in plant cells. Additionally, it provides insights into how to use a microscope to observe cells and outlines the functions of various cell structures.
Lesson 2: Understanding cells
- 2. Understanding Cells Cells •Living organisms are made up of one or more cells. •Cells are the most basic unit of organisms which can function on their own. Cells carry out life processes such as respiration, division, excretion and growth. •Cells are the building blocks of an organism. •Cells work together to keep an organism alive. •Cells of living things exist in many sizes and shapes. They can be round, oval, long, short, with tail and so on.
- 3. •Robert Hooke, a British Scientist, was the first person to study cells. The figure below shows some cork cells observed through a microscope by him. Cork cells as seen by Robert Hooke
- 4. Using a microscope •Cells are very tiny and cannot be seen with the naked eye. •Cells of living organisms can be observed using a microscope. A Microscope
- 5. Functions of the different parts of microscope Parts of a Functions microscope Eye piece •To magnify the image of the specimen Objective lens •To magnify the specimen Body tube •To hold the eye piece at a fixed distance away from the objective lens Coarse focus knob •To raise or lower the body tube gently for sharp focusing. Arm and base •For holding and supporting the microscope
- 6. Clip T hold the slide on the stage in position o Stage To put the slide on. Diaphragm To control the amount of light entering the lens. Mirror To direct reflected light towards the diaphragm. Condenser To concentrate light from the mirror onto the specimen
- 7. The correct way to use a compound light microscope a. Place the microscope on a flat surface in a well- lighted area. b. Position the low power objective lens above the hole of the stage. c. Raise the condenser as high as it can go and open the iris of the diaphragm fully. d. Look through the eye piece and adjust the mirror to obtain a bright field of view.
- 8. e. Place a slide with the specimen on the stage and hold it in place with the clip. f. Lower the objective lens using the coarse focus knob until it is adjust above the slide. g. Look through the eye piece. Turn the coarse focus knob counter – clockwise until the object is in focus. h. If necessary, change to a high power objective lens. i. Adjust the fine focus knob until a sharp image is obtained.
- 9. General structure of a cell •A typical cell is made up of cell membrane which contains a living substance called protoplasm. a.Protoplasm consists of a nucleus and cytoplasm. b.The nucleus is a spherical in shape and surrounded by a nucleus membrane. c.Cytoplasm is a colourless jelly – like material surrounded by cell membrane. d.The cell membrane is a thin film which is partially permeable to the surrounding substances.
- 10. Structure of animal cells •Generally, each animal cell is made up of cell membrane and protoplasm (which consists of cytoplasm and nucleus.) An animal cell
- 11. •Animal cells do not have cell walls or chloroplasts. •There is great variety of forms and functions among animal cells. The figure below shows some examples of animal cells Paramecium Red blood cell Nerve cell
- 12. Structure of plant cells •The figure below shows the general structure of a plant cell. A plant cell
- 13. •The basic structure of plant cells is similar to that of animal cells in having a cell membrane, cytoplasm and a nucleus. •All plant cells have a cell wall which gives them an almost fixed shape. •Plant cells often have one large vacuole, whereas animal cells usually have many small ones. •Most plant cells that are under the light contain chloroplasts which are green in colour.
- 14. •Plant cells vary in their shapes, sizes, structures and functions. Palisade Guard cells cells Epidermal cell in the root Examples of plant cells
- 15. The function of cell structures Structure Present in Function Cell membrane All cells •Enclose the cytoplasm. •Controls the movement of materials in and out of cells. Cell wall ( a non – Plant cell only •Supports and give shape to the living layer of cells cellulose) Cytoplasm ( jelly – like All cells •This is where chemical reactions substance) take place inside the cell. •Stores dissolved material
- 16. Cell membrane Cell wall Cytoplasm
- 17. Structure Present in Function Nucleus Almost all cells •Controls all cellular activities (mature red blood cells do not have nuclei) Chloroplast (contain Most plant cells •Chlorophyll absorbs light for green pigments called that are under light photosynthesis to produce food chlorophyll) and oxygen. Vacuole (cell sap) Most plant cells •Holds useful substances and and some animal wastes. cells •Supports the plant when it is full of water.
- 18. Nucleus Chloroplast Vacuole
- 19. Comparison between animal cell and plant cells Similarities Similarities Animal cells Plant cells •Have cell membrane •Have protoplasm •Able to carry out activities to life
- 20. Differences Differences Animal cells Plant cells •Generally smaller Size •Generally bigger •Usually irregular •Fixed by cell wall Shape and may vary during life •Have a cell wall •Many plant cell under •No cell wall light have chloroplasts •No chloroplast Contents •Often have a large •With a small or no vacuole vacuoles
- 21. •Usually at the •Maybe to one Position of centre of the side of the cells nucleus cells •Glycogen •Starch Food granules granules storage