In spite of the differences in size and complexity, all cells are mostly composed of the same substances and they all carry out similar life functions. These include growth and metabolism and reproduction by cell division.
Cells are made up of subcellular structures that are responsible for different and specific functions. These structures are known as organelles. A number of these organelles are common to both animal and plant cells. This section will focus on those parts which plants have.
Cell Structures (Cell Organelles)
- Cell Wall: This is the rigid outermost layer of a plant cell. It makes the cell stiff -providing the cell with mechanical support – and giving it protection. Animal cells do not have cell walls.
- Cell Membrane: This is a protective layer that surrounds every cell and separates it from its external environment. It is found just inside the cell wall and is made up of complex lipids (fats) and proteins.
- Cytoplasm: The cytoplasm is a thick, aqueous (water-based) solution in which the organelles are found. Substances such as salts, nutrients, minerals and enzymes (molecules involved in metabolism) are dissolved in the cytoplasm.
- Nucleus: The nucleus is the ‘control center’ of the cell. It contains Deoxyribonucleic acid (DNA), the genetic material that directs all the activities of the cell. Only eukaryotic cells have nuclei (plural for nucleus), prokaryotic cells do not. The nucleus is separated from the cytoplasm by a specialized membrane called the
- Nuclear membrane.
- Ribosomes: These are little round structures that produce proteins. They are found in the cytoplasm or attached to the endoplasmic reticulum.
- Endoplasmic Reticulum (ER): The ER is a membrane system of folded sacs and tunnels. The ER helps move proteins within the cell as well as export them outside of the cell. There are two types of endoplasmic reticulum.
- Rough endoplasmic reticulum. The rough endoplasmic reticulum is covered with ribosomes. Smooth endoplasmic reticulum (no ribosomes)
- Golgi body: The Golgi body is a stack of membrane-covered sacs that prepares proteins for export from the cell.
- Mitochondrion (plural mitochondria): This is the ‘powerhouse’ of the cell. It converts the energy stored in food (sugar and fat) into energy-rich molecules that the cell can use (Adenosine triphosphate – ATP for short).
- Lysosome: The lysosome is the digestive center of a cell that produces many different types of enzymes which are able to break down food particles and recycle worn out components of the cell.
- Vacuoles: These are large membrane-enclosed compartments that store toxic wastes as well as useful products such as water. These are mainly found in plants.
- Chloroplast: Chloroplasts contain a green pigment that traps sunlight and converts it into sugars by a process called photosynthesis. The sugars are a source of energy for the plants and the animals that eat them.