Key principles of the cell theory:
r living organisms are composed
of cells r cells are the smallest units of life r all cells come from pre-existing cells.
Drawing cell structures When you draw cells as they appear under a microscope, always use a sharp pencil and draw single lines to show the relative sizes and positions of the structures you can see. Do not use shading or crosshatching on your diagram. Label each structure with a straight line so that the name of each part appears at the side of your diagram. Always include a title and the magnification of your drawing.You can see an example of how to do this in Figure 1.2.
The functions of life are: r metabolism r nutrition r growth r reproduction response (or sensitivity) r r excretion r homeostasis A unicellular organism such as Paramecium (Figure 1.2) needs to metabolise organic materials in order to make the chemicals needed to sustain life. It must also be able to excrete waste produced during metabolism and dispose of it. It must be able to detect changes in its environment, so it can respond to more favourable or less favourable conditions. Some unicellular organisms photosynthesise and they have a light spot that enables them to move to a brighter environment to maximise photosynthesis. A unicellular organism must also be able to control its internal environment (homeostasis), as large changes in water or salt concentrations may have a detrimental effect on metabolism and other cellular functions. It must also obtain food, whether produced from simple inorganic substances through photosynthesis (as in Chlorella, Figure 1.3) or ingested as complex organic materials from outside as a source of nutrition. If the species is to survive, an organism must be able to reproduce. This could be either asexual or sexual reproduction.
Investigations of some life processes in Paramecium and Chlorella Paramecium can be observed under a light microscope. Paramecia have cilia, which they flick in rhythmic waves to move about in water, and they also have a row of specialised cilia that waft food particles towards the 35 Îźm
plasma membrane
Figure 1.3 Chlorella is a unicellular organism containing a chloroplast (Ă— 1200).
2
cytoplasm
food vacuoles
nucleus
oral groove
contractile vacuole
cilia
Figure 1.2 Paramecium carries out all the life functions within its single cell (Ă— 323).