4. Seeing Cells - Background
|Animal cell: Image created by Mariana Ruiz Villarreal
||Plant cell: Image created by Mariana Ruiz Villarreal
||Bacterial cell: Image created by Mariana Ruiz Villarreal
Students often have difficulty conceptualizing that cells are the basic building block of all living things. Thus, it is essential for them to have experience making slides of familiar living things – onions, plants and their own cheek cells – and viewing them under a microscope to see that cells really do make up all living things.
Multicellular creatures such as plants and animals have different levels of organization, from organic molecules to organelles to cells to tissues to organs to organ systems to a whole organism. Cells are the smallest unit that can fulfill all the necessary characteristics of life – it can metabolize, grow, reproduce, maintain homeostasis, evolve, respond to its environment and so on. Its organelles (parts of a cell, each has a specific job similar to the organs in the human body) participate in fulfilling these various functions.
Important organelles in eukaryotes such as plants and animals (prokaryotes such as bacteria have much simpler cells):
- Cell membrane – the cell’s skin that protects the cell from changing environmental conditions and from invaders as well as letting selected molecules in and out of the cell
- Cell wall – a feature of plants cells that functions like stiff lattice-like wall which helps plant cells maintain their structure and shape
- Nucleus – the cell’s control center that contains the DNA
- Cytoplasm – a jelly-like liquid that fills the interior of a cell and surrounds and supports all the organelles
- Chloroplast – a feature of plant cells that allows plants to do photosynthesis and make their own glucose from sunlight, water and carbon dioxide
- Mitochondria – the cell’s power plant that turns glucose into energy that the cell can use to run its organelles
- Ribosome – tiny organelles that function as little protein factories (see Protein Factory activity)
- Golgi complex – a complex series of interconnected membranes that functions like a post office - it processes, sorts, and labels proteins, making the proteins more effective at their various jobs and helping them to end up in the right place
- Endoplasmic reticulum – a system of membrane-enclosed canals and passageways used to quickly transport proteins within the cell
- Vacuole – a prominent feature of certain plant cells, though animal cells also have vacuoles as well, that is used as a storage container for nutrients or other materials
- Lysosome – a cell’s garbage and recycling center for digesting wastes and recycling the building blocks for other purposes
- Centriole – a feature of animal cells important for coordinating cell division
Using a light microscope only the largest features of a cell can be observed (the first 5 organelles on the list above). Greater magnification is required to visualize other cell parts. Still students can discover how all living things are similar in that they are made of cells but also discover the great diversity in cells themselves.
Experience with light microscopes is helpful. A basic understanding of the parts of a cell is essential to the completion of this activity.