1. Unit B: Cells and Systems
Topic 3: The Cell and its Structures

2. Cells = Life
Remember that one of the principles of cell theory says that all living things are either cells or made up of cells.
Unicellular organisms: Organisms made up of only one cell (eg. paramecium).

3. Cells are the Basis for Life
Multicellular Organisms – An organism that is made up of multiple, specialized cells. (eg. fungi, plants, animals, us).

4. Limitations of Unicellular Life
Unicellular organisms must always be in contact with water to help transport food and wastes. Therefore unicellular organisms must be near oceans.
Multicellular organisms get around this by taking in water from the environment and keeping water internally. (eg. blood is very similar to ocean water).
Another limitation is that to keep wastes moving out quickly enough and food coming in, unicellular organisms must be small in size.

5. How Cells Work
Organisms have organs and systems to carry out basic functions: reproduction, eliminate wastes, take in energy, adapt to environment, and growth.
Cells have organelles (little organs) to carry out the same functions. Cells have the same basic needs that all living things do.

6. Cytoplasm and Cell Membrane
Cytoplasm is the part of the cell that acts as the circulatory system. Nutrients, wastes and vacuoles all move throughout the cytoplasm. It is a jellylike goop surrounding all the other organelles.
Cell Membrane – is the covering of the cell, acting as its skin. It keeps out wastes and lets food and nutrients in. The one substance that can pass through the membrane is water.

7. Nucleus and Mitochondria
The ‘brain’ of the cell. It controls the cell’s activities. It also contains all of the genetic material of the cell. The nucleus is responsible for growth and reproduction of cells. (Cell splitting). It is a large circular object in a cell that is easily seen in a compound microscope.
Vacuoles are bubble-like organelles that store and transport food, wastes, and other materials. They have their own membrane.

8. Plant Organelles: Cell Wall and Chloroplasts
The cell wall occurs only in plants and fungi. It acts as the skeleton of a plant, giving it structural support. They are made of a tough, rigid material called cellulose.
Chloroplasts only occur in plants. Inside chloroplasts is a chemical, chlorophyll, which is green in color giving the cell and the plant its green color. This is where photosynthesis takes place.