cell structure n organisation

• cells are the basic unit of structure in an organism
• all organisms are composed of one (unicellular) or more cells (multicellular)
• protoplasm includes the cytoplasm and the nucleus.
• plasma / cell SURFACE membranes are partially permeable to control substances entering and leaving the cell. it surrounds the organelles within the cells and keep them in place
• the cytoplasm is all the contents inside the cell membrane, excluding the nucleus. And protoplasm includes cytoplasm and the nucleus of the cell.
• the nucleus is surrounded by a partially permeable membrane called the nuclear membrane
• the nucleus controls cell activities (growth, repair, cell division) ; it is responsible for cell division. cells without a nucleus are unable to divide (eg red blood cell). it contains genetic information in the form of chromosomes
• chromosomes are made up of proteins and a compound called dna, which store hereditary information that carries instructions for cell activities (eg growth and reproduction).
• when a cell is dividing, the chromosomes condense and shorten to become thick, rod shaped structures
• the cytoplasm is a gel like substance that surrounds the cell. it contains every organelle inside the cell except the nucleus
• an organelle is a cellular structure that performs specific functions/jobs within the cell
• the outer surface of the rough endoplasmic reticulum (RER) appears rough due to ribosomes attached to the surface.
• the RER functions as the site of protein synthesis and is a transport system that moves proteins from the ribosomes to the golgi body for secretion out of the cell.
• the rer is linked with the nuclear envelope
• the smooth endoplasmic reticulum (SER) does not have ribosomes attached to its membrane.
• the SER has two main functions: synthesis of fats and steroids (eg sex hormones) and detoxification (the conversion of harmful substances into harmless substances)
• ribosomes are small round structures that are either attached to the RER or lie freely in the cytoplasm
• ribosomes attached to the RER synthesise proteins to be transported out of the cell
• ribosomes floating freely in the cytoplasm synthesise proteins that are used within the cytoplasm of the cell
• vacuoles are a fluid filled space enclosed by partially permeable membrane. its main function is to store substances within the cell
• in a plant cell - the vacuole is large and central which contains cell sap (dissolved substances like amino acids, mineral salts). the vacuole is a storage of dissolved sugars, mineral salts and amino acids. it increases the cell size through water uptake to provide support (turgor) in plant cells
• in an animal cell - the vacuole is small, numerous and usually temporary. it stores water and food substances, and waste for removal
• mitochondria - plural
• mitochondrion - singular
• mitonchondrion functions as the site of aerobic respiration where energy is released (NOT produced) for cellular activities (eg cell division)
• mitochondria is commonly known as the powerhouse of the cell
• cells/organs that require a lot of energy usually have many mitochondria (eg sperm/muscle cell, liver)
• the golgi body is a stack of flattened, membrane bound sacs together w associated vesicles (small membrane bound sacs) called the golgi body
• the golgi body is NOT interconnected. it is also not continuous with the nuclear membrane of the ER)
• the golgi body chemically modifies substances made by the ER (eg proteins, fats and steroids)
• the golgi body stores and packages these substances in vesicles for secretion out of the cell (eg nerve cells secrete neurotransmitters etc)
• the cell wall is a rigid wall made up of cellulose (which is entirely made up of glucose molecules). the cell wall is fully permeable
• the cell wall protects the cell from injury and gives the plant cell a fixed shape
• chloroplasts contains a green pigment called chlorophyll. chlorophyll is essential for photosynthesis as it traps light for photosynthesis