All around you, there are cells.
A cell is the smallest biologic unit that is able to live on its own or which has the potential to live. So how big is a cell? There are some cells that you can see without a microscope such as the egg yolks of birds. However, most cells cannot be seen with unaided human eyes. If you want to see actual cells, you need a microscope. All living things are made up of cells. While some organisms are unicellular which means one organism has one cell (e.g. bacteria), plants and animals are multicellular which means they have many cells. Plant cells are special in that they can manufacture the plant’s own food, unlike your own cells which have to be supplied with nutrients by eating.
What are the basic parts of a cell?
Although cells have different sizes, shapes and activities, all of them have three basic structures: the nucleus, the plasma membrane and the cytoplasm. These components make life possible for the cell.
- Nucleus. The nucleus contains the genetic material of the organism. This genetic material is deoxyribonucleic acid (DNA) for plants. Different plants have unique DNA compositions, which sometimes help scientists identify new species or classify existing ones. Plant cells are called “eukaryotic” because they have a nucleus. Organisms like bacteria, which lack a nucleus but have nucleic acid floating in their cytoplasm are called “prokaryotic”.
- Plasma membrane. This is the thin, outermost membrane that maintains the cell as a unit distinct from neighboring structures. It serves as a mold and a limit for the inner contents of the cell. This part of the cell serves two purposes. First, it allows the cell to undergo several metabolic processes independent of its surroundings. Second, it allows the cell to communicate with neighboring cells by allowing substances and chemical and electrical signals to travel through.
- Cytoplasm. This part of the cell is everything that is between the nucleus and the plasma membrane. It is semifluid and it is a place, which contains other structures called “organelles”. The cytoplasm is important for maintaining the integrity and stability of the cell and the organelles it contains have functions essential to the cell’s life.
What is the cell wall?
The cell wall characterizes all plant cells. It consists of cellulose. Cellulose is a polymer of glucose and is thus called a polysaccharide. The presence of cellulose in the cell walls of plants is the reason why eating fruits and vegetables are important. Humans lack the enzyme called “cellulase” which can break down cellulose. Without this enzyme, you cannot break down the cell walls of plants, which make up the plant fiber. This fiber then acts like a broom to clean your intestines and helps you maintain normal bowel habits.
What organelles are found in both plants and animals?
An organelle is a membrane-bound compartment or sac located within the cell that has a specialized function. The nucleus is an organelle that is found in plants and animals. The following organelles are also found in both plants and animals.
- Mitochondrion. This organelle is called the powerhouse or power generator of the cell because it is where energy, in the form of adenosine triphosphate (ATP), is released from glucose. Note that glucose is present in what you eat. Glucose is then carried by the blood to your cells. When glucose reaches the cell, it is directed to the mitochondria, where energy is released. This energy is needed for the other functions of the cell such as the production of proteins.
- Endoplasmic reticulum. This organelle, also referred to as ER, is the place where biomolecules such as proteins and lipids are routed and modified. Rough ER has ribosomes and serves as a place where polypeptides become proteins. Smooth ER has no ribosomes and serves as a place where lipids are synthesized. Plant seeds are rich in smooth ER because they provide the plant with food when it is still unable to utilize nutrients from the soil and from its environment.
- Golgi bodies. The final processing of proteins and lipids occurs in the Golgi bodies. These biomolecules are then shipped to different parts of the cells.
What are organelles found only in plant cells?
- Plastids. These organelles are specialized organelles for photosynthesis or storage. Plants have three types of plastids: amyloplasts, chloroplasts, and chromoplasts. Amyloplasts do not have pigments like the other two types of plastids but they store starch. Plenty of amyloplasts are found in the cells of plant stems, in underground stems (e.g. potato tubers) and in seeds. Chloroplasts are the organelles that contain chlorophyll and are responsible for the ability of plants to use sunlight (photosynthesis) to generate energy. This energy is then used to manufacture glucose and starch from carbon dioxide and water. Chromoplasts do not contain chlorophyll but they contain carotenoids. Carotenoids are pigments which give plants their red and yellow colors. They are particularly important for attracting pollinators (e.g. butterflies and bees) and other organisms which facilitate reproduction and seed dispersion.
- Vacuoles. Vacuoles are organelles which store different types of substances and help the cell grow. They can contain sugars, ions, or simply, water. A vacuole expands during cell growth.
What are the other non-membranous structures in cells?
Two important structures which are not considered organelles are the ribosomes and the cytoskeleton. Both of these are found in plant and animal cells. Ribosomes are responsible for the production of polypeptides which eventually become proteins. The cytoskeleton is important for maintaining the overall shape and organization of the cell and facilitates the movement of the cell’s internal structures from one place to another.
