QVprep Biology Lessons

Plasma membrane, Cytoplasm, Nucleus

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Plasma membrane: The plasma membrane is a bilipid membranous layer composed of proteins and carbohydrates. It is fluid in nature. The membrane separates the cell from its external environment, and is selectively permeable. It protects the cell and provides stability. Proteins are found embedded within the plasma membrane, with some extending all the way through in order to transport materials. Carbohydrates are attached to proteins and lipids on the outer lipid layer.


Cytoplasm: The cytoplasm is a jelly-like substance found within the plasma membrane and makes up most of the cell and it is constantly streaming. All the cell’s organelles are found embedded in the cytoplasm. The area of the cytoplasm outside of the individual organelles is called the cytosol. The cytosol is the largest structure in the cell. It composes 54% of the cells total volume. It contains many enzymes responsible for glycolysis, gluconeogenesis, biosynthesis of sugars, fatty acids, and amino acids. In order for respiration to occur, glucose is ingested and broken down into pyruvate in the cytosol, for use in the mitochondria. The cytosol also contains the structural component called cytoskeleton. This structure gives the cell its shape and allows it to organize many of the chemical reactions that occur in the cytoplasm. Additionally, the cytoskeleton can aid in the movement of the cell.


Nucleus: It is the largest organelle in the cell. It is dark and round, and is surrounded by a double membrane called the nuclear envelope or nuclear membrane. It contains genetic information (DNA) on special strands called chromosomes. The nucleus is the control center of the cell, and is responsible for cell metabolism and reproduction.