2.2 cell structure

• Cells are made up of:

  • Cell membrane
  • Cytoplasm
  • Organelles
  • Cytosol
  • Cytoskeleton
  • Inclusions
• The cell membrane, AKA plasma membrane, separates cell contents from the environment outside of the cell, and other cells. It encloses contents of the cell and controls what is able to enter and leave.
• Cytoplasm is the jelly-like, watery material inside the cell, and is made up of cytosol and organelles.
• Cytosol is the liquid component of the cytoplasm. It is made up of 75-90% water, and a mixture of dissolved substances. Cytosol plays a role in controlling osmotic pressure and the flow of chemicals in and out of the cell.
• Organelles are structures within a cell.
• The nucleus is the largest organelle in the cell, and contains DNA. The nuclear membrane separates it from the cytoplasm. The nucleolus plays a part in manufacturing proteins.
• Ribosomes are small, spherical organelles. They consist of amino acids joint together to create proteins.
• Endoplasmic reticulum are pairs of parallel membranes extending from the cell membrane to the nuclear membrane. Membranes of the ER provide a surface for chemical reactions. Channels of the ER are for storing or transporting molecules.
• Rough ER is when there are ribosomes attached to the membranes of the ER. Smooth ER is when there are no ribosomes attached to the membranes of the ER.
• A Golgi body is a series of flattened membranes stacked upon one another. It modifies proteins and packages them for secretion from the cell. Proteins from ribosomes pass through the ER to the Golgi body. At the edges of the Golgi body, vesicles are formed and proteins are packaged into them.
• Vesicles are small sacs of liquid containing proteins.
• Lysosomes are small spheres formed from the Golgi body. They contain digestive enzymes that can break down large molecules, such as vesicles, and can similarly digest worn out organelles.
• Mitochondrion are spherical or sausage-shaped structures with double membranes. The outer membrane surrounds the mitochondria, and the second membrane, known as the cristae, is arranged into a series of folds. This provides a large surface area for reactions to take place, which make energy for the cell's activies, hence it is called the 'powerhouse of the cell'. Chemical reactions of cellular respiration occur in mitochondrion.
• Cilia and flagella are fine projections that can beat back and forth to move the cell or substances over the surface of the cell. If they the projections are short and numerous, and resemble tiny hairs, they are cilia. If the projections are longer, and there are only one or two, they are flagella.
• Inclusions are chemical substances that are not part of the cell structure, but are found in the cytoplasm.
• Organelles include:

  • Nucleus
  • Ribosomes
  • Endoplasmic reticulum
  • Golgi body
  • Lysosomes
  • Mitochondria
  • Cilia and flagella
• Centrioles are a pair of cylindrical structures near the nucleus. They are involved in the reproduction of the cell.
• The cytoskeleton is the framework of protein fibres that gives the cell its shape and assists in cell movement. It consists of:

  • microtubules - hollow rods that keep organelles in place or move them around the cell.
  • microfilaments - move materials around the cytoplasm or move the whole cell.
• Animal cell diagram

  A) cell membrane

  B) nucleus

  C) nucleolus

  D) nuclear membrane

  E) lysosome

  F) cytoplasm

  G) ribosomes

  H) rough endoplasmic reticulum

  I) Golgi body

  J) Mitochondria

  K) Smooth endoplasmic reticulum

  L) centrioles