The cytoplasm comprises
- Cytosol — the gel-like substance enclosed within the cell membrane
- The organelles — the cell’s internal sub-structures, including (in eukaryote cells) the nucleus
- All of the contents of the cells of prokaryote organisms (such as bacteria, which lack a cell nucleus) are contained within the cytoplasm
- Within the cells of eukaryote organisms, the contents of the cell nucleus are separated from the cytoplasm and are then called the nucleoplasm
- The cytoplasm is about 70% to 90% water and usually colourless
Function of Cytoplasm
- In the cytoplasm, most cellular activities occur, such as many metabolic pathways including glycolysis, and processes such as cell division
- The inner, granular mass is called the endoplasm and the outer, clear and glassy layer is called the cell cortex or the ectoplasm
- The part of the cytoplasm that is not held within organelles is called the cytosol
- The cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell
- Due to this network of fibres and high concentrations of dissolved macromolecules, such as proteins, an effect called macromolecular crowding occurs and the cytosol does not act as an ideal solution.
- Plastids are major organelles found in the cells of plants and algae.
- They are the site of manufacture and storage of important chemical compounds used by the cell.
- Plastids often contain pigments used in photosynthesis and the types of pigments present can change or determine the cell’s colour
- They possess a double-stranded DNA molecule, which is circular, like that of prokaryotes.
Function of Plastids
- Plastids carry out photosynthesis, the storage of products like starch and the synthesis of many classes of molecules such as fatty acids and terpenes which are used for energy production and as raw material for the synthesis of other molecules
- All plastids are derived from proplastids (formerly “neoplastic”, to-: dawn, early), which are present in the meristematic regions of the plant
- Proplastids and young chloroplasts commonly divide by binary fission, but more mature chloroplasts also have this capacity.
Types of Plastids
- Proplastids: The newly developed plastids
- Etioplast: Colorless plastids developing in dark. Can develop into a variety of plastids
- Chromoplast: Colored plastids found in many flowers and fruits
- Chloroplast: Green plastids involved in photosynthesis
- Leucoplast: Colorless plastids. Involved in the storage of food. Found in may underground organs. E.g. root cells or onion bulb