cells
Organelle: a specialised structure with a specific function inside a cell
Nucleus
Contains DNA
The DNA provides a template for DNA replication
Bounded by two membranes, called the nuclear envelope, with pores which allow the passage of large molecules, such as mRNA and ribosomes. The outer membrane is continuous with the endoplasmic reticulum
The granular material in the nucleus is nucleoplasm and contains chromatin
Also contains a nucleolus which is where the formation of rRNA happens
Mitochondria
Comprise of two membranes, separated by a narrow, fluid-filled inter-membrane space. The inner membrane is folded inwards to form Cristae. Also contains an organic matrix, which is a solution containing many compounds, including lipids and proteins
The function of mitochondria is to produce ATP in aerobic respiration
The Cristae provide a large surface area for the attachment of enzymes involved in respiration
Endoplasmic reticulum (ER)
Chloroplasts
Chloroplasts occur in the cells of photosynthesising tissue
Each chloroplast is surrounded by two membranes, comprising the chloroplast envelope
The stroma is fluid-filled and contain some of the products of photosynthesis, including lipid droplets and starch grains. Within the stroma are many closed, flattened sacs called thylakoids. A stack of thylakoids is a geranium. Each geranium comprises between two and a hundred parallel sacs
The endoplasmic reticulum is an elaborate system of parallel double membranes forming flattened sacs with interconnected, fluid-filled spaces between them, called cisternae
Rough ER (RER) has ribosomes on the outer surface and transports the proteins made there. RER is present in large amounts in cells that make a lot of protein
Smooth ER comprises of membranes that lack ribosome. it is associated with the synthesis and transport of lipids
Ribosomes
Ribosomes have one large and one small subunit. They are assembled in the nucleolus from ribosomal RNA and protein
They are important in protein synthesis, as they are the site of translation, where mRNA is used to assemble the polypeptide chain
Golgi body
Vesicles containing polypeptides pinch off from the RER and fuse with the stack of membranes which constitute the Golgi body
Proteins are modified and packaged in the Golgi body
The functions of the Golgi body include:
-Producing secretory enzymes, packaged into secretory vesicles
-Secreting carbohydrates
-Producing glycoproteins
-Transporting and storing lipids
-Forming lysosomes containing digestive enzymes
Lysosomes
Lysosomes are small, temporary vacuoles surrounded by a single membrane, formed by being pinched off from the Golgi body
They contain and isolate potentially harmful digestive enzymes from the remainder of the cell
Vacuole
Vacuoles contain cell sap, a solution which stores chemicals such as glucose, amino acids and minerals
Most plant cells have a large permanent vacuole which consists of a fluid-filled sacs bounded by a single membrane, the tonoplast
Cell wall
The cell wall of a plant cell consists largely of cellulose. Cellulose molecules are held together in microfibrils, which are aggregated into fibres, embedded in a polysaccharide matrix called pectin
The cell wall has the following functions:
-Transport- the gaps between the cellulose fibres make the cell wall fully permeable to water and dissolved molecules and ions
-Mechanical strength- The structure of cellulose microfibrils and their laminated arrangement make the cell wall very strong.
Communication between cells- Cell walls have pores, called pits, through which strands of cytoplasm, called plasmodesmata pass