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4A Plant Structure and Function (Plant cells (Cell wall-surrounds the cell…
4A Plant Structure and Function
Plant cells
Cell wall-surrounds the cell outside of the cell surface membrane and is made of a polysaccharide called cellulose. It strengthens and supports the cell and prevents it changing shape. Contains pores to allow the movement of substances easily
Chloroplast-a small, flattened structure that contains a double membrane. The inner membrane is stacked into thylakoid. Contains chlorophyll which is green pigment that absorbs light for photosynthesis.
Amyloplast - an organelle found in some plant cells that synthesises and stores starch molecules and breaks them down to glucose when the cell requires it.
Vacuole- A membranous sac that contains a fluid called sap, which contains dissolved sugars and salts for the cell. Its function is to allow the cell to become turgid and also to isolate unwanted chemicals from the rest of the cell.
Tonoplast-The name of the membrane surrounding a vacuole
Plasmodesmata-Channels of cytoplasm that pass between adjacent cell walls of plant cells that allows fast communication and exchange of substances between cells.
Pits- Sections of the cell wall which adjacent plant cells can exchange fluid or communicate through
Middle lamella-A layer made of pectin that lies between adjacent plant cells, sticking the cell walls together.
The stages of drug testing
The drugs are tested on human tissues 2. The drugs are then tested on animals. 3. The final main stage is clinical trials which involve testing the rugs on human volunteers and is made of 3 main phases: Phase 1- testing on a small group of healthy volunteers-this again checks for side effects and is monitored to see the areas of the body it effects and how long it remains in the body for. Phase 2- Testing the drug on a small group of volunteers with the illness. This is done to start determining effectiveness in both treating and preventing the disease and also to find the optimum dosage. Phase 3- Once a drug has passed it is test on a large number of participants.
A placebo group- a placebo is a substance with no active ingredients, in other words, it does not contain the drug being tested and is normally just a sugar pill. When patients are taking medication there is what is known as 'the placebo effect' where the patient's condition improves because psychologically they believe the drug will make them better, so they do make some improvement. Drug testing need to compare to the placebo group of patients to observe whether the drug is more effective than the psychological effects.
Double-blind trials- A blind trials is where the patient does not know whether they have the active drug or the placebo drug; this is so the placebo effect can be observed. A double-blind trial is where neither the patient nor the doctor knows which drug they have; this is to stop any subconscious bias the doctor may have when assessing the patient and their improvement
Plant cell carbohydrates
Starch
Amylose-amylose is an unbranched chain of glucose molecules joined by 1,4 glycosidic bonds, as a result of that amylose is coiled and so it is a very compact molecule meaning it can store a lot of energy
Amylopectin - amylopectin is branched and is made up of glucose molecules joined by 1, 4 and 1, 6 glycosidic bonds, due to the presence of many side branches it is rapidly digested by enzymes therefore energy is released quickly.
Cellulose-Cellulose is a component of cell walls in plants and it's composed of long, unbranched chains of beta glucose which are joined by glycosidic bonds. Microfibrils are made of long cellulose chains linked together by hydrogen bonds formed between adjacent chains. These microfibrils form long threads that provide structural support in plant cells
The secondary cell wall is a cell wall formed between the primary cell wall and the cell surface membrane. It only begins to grow once the cell has stopped growing. Its structure is made of parallel layer of microfibrils of cellulose, with other polysaccharide additions.
Sclerenchyma fibres, phloem vessels and xylem vessels
Lignin is a polysaccharide that is added to the secondary cell wall of plant cells in the transport vessel xylem and the sclerenchyma fibres. The lignin makes the cell walls less flexible and more rigid, adding strength to the vascular bundle. The primary function of xylem vessels is to transport water and inorganic ions around the plant, whereas the main function of sclerenchyma fibres is to support the plant
Both the sclerenchyma fibres and xylem vessels are made from dead cells, the xylem vessels form hollow tubes of dead cells whereas the cells in sclerenchyma fibres are tapered at the ends.