Biology Topic 4

• Cellulose is strong material that is a polysaccharide made up of beta glucose. They are a long unbranched chain. Carbon atom 1 links to carbon atom 2, so they have a 1,4 glycosidic bond.
• The physical properties of cellulose is extraordinary tensile strength, durable, insoluble and tough.
• The cell wall formation STEP 1: The middle lamella forms when the plant cell divides in 2 (in mitosis), and is made out of pectin (which acts like a glue to hold the cell walls of adjacent cells together).
• The cell wall formation STEP 2: layers of cellulose microfibrils and matrix are deposited producing a flexible structure.
• The cell wall formation STEP 3: more layers of cellulose are added to the inner surface, at right angles to each other which adds strength.
• The cell wall formation STEP 4: Lignin are added which hardens and further strengthens the wall, the material is also hydrophobic making the xylem impermeabe.
• Plasmodesmata are cytoplasmic bridges between primary cell walls.
• Pits are when the deposition does not occur in areas of the plasmodesmata. Pits in xylem allow water to move between xylem vessels.
• Amyloplasts are found in plants and not in animals =, they are colourless and store starch grains.
• Chloroplasts are found in plant cells but not in animal cells, they are large and long and green in colour.
• The thylakoids is a system of branching membranes which are formed by the folding of the inner layer.
• In between the membrane (in a chloroplasts) is the intermembrane space.
• Chloroplasts contains their own DNA.
• Chloroplasts are double membraned, with an outer and inner layer.
• Thylakoids are arranged in a flattened circular piles called gana.
• Grana contains chlorophyll.
• Lamellae are stacks of grana.
• Starch granules store energy from photosynthesis.
• The vacuole is a cavity filled with a fluid called cell sap.
• Xylem are hollow tubes of long dead cells that have heavily lignified walls.
• Xylem start of as living cells, protoxylem.
• Phloem consists of intact cells with living contents.Transport in the phloem is an active process called translocation.
• Chloroplasts and mitochondria are both large organelles with a biconvex shape. They contain their own DNA and are both surrounded by an outer membrane.
• Chloroplasts are the site of photosynthesis, yet mitochondria are the site of respiration.