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Molecules and cells - Edexcel GCE Biology Revision Notes

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´╗┐Cells and Organelles * The nucleus is a large organelle surrounded by a nuclear envelope ? which is double membrane. The membrane contains many nuclear pores. The nucleus contains chromatin and nucleolus (which makes ribosome) Chromatin is made of proteins and DNA. The pore allows substances (I.e. mRNA) to move between the nucleus and the cytoplasm. * Lysosome is a round organelle surrounded by a membrane with no clear internal structure. It contains hydrolytic digestive enzyme. It can be used to digest invading cells / break down old organelles. * Vesicle is a small fluid ? filled sac in the cytoplasm, it transports substances in and out of the cells. Most are formed by the Golgi apparatus and the cell surface. * Ribosomes are very small organelles that are free in the cytoplasm or are attached to the rough endoplasmic reticulum ? it?s the site of protein synthesis. * There are 2 types of endoplasmic reticulum, the smooth ER is a system of membrane enclosing a fluid filled space ? it synthesized and processes lipid. The rough ER is similar to sER but is covered in ribosome. ...read more.


Cell differentiation * Stem cells are unspecialized cells that can develop into any type of cells, they divide by mitosis to become new cells, which then become specialize. The process in which stem cell specializes is called differentiation. * In humans, stem cells are found in the embryo (where they differentiate into all the cells required to form a fetus) and in some adult tissues (where they differentiate into specialized cells that need to be replaced - i.e. Bone marrow can differentiate into red blood cells): - Totipotency: The ability to produce all cell types, including all the specialized cells in an organism & extraembryonic cells, i.e placenta & umbilical cord - Pluripotency: The ability of stem cells to produce all the specialized cells in an organism but not extraembryonic cells Totipotent cells differentiate into pluripotent cells and extraembryonic cells, and then the pluripotent cells will differentiate into the specialized in a fetus. * Plants have stem cells in the area where growth occurs, i.e. Roots and shoots. All stem cells in plants are totipotent, meaning they can produce all cell types and can grown into a whole new plant. ...read more.


- Decisions about important scientific work like stem cell research must be made upon taking into account everyone?s view on the topic. * Regulatory authorities have been established To consider both the benefits and ethical issue surrounding embryonic stem cell research: - Looking at proposal of research to decide whether or not it should be allowed ensuring the researches involving embryos is carried out for a good reason. This also makes sure the research isn?t repeated by different groups. - Licensing and monitoring centres involved in embryonic stem cell research ensures only fully trained staffs carry out the research. They will understand the implication of the research and won?t waste any precious resources - this also helps to avoid unregulated research. - Producing guidelines and codes of practice making sure all scientists work in a similar method, otherwise their results would be incomparable. This also ensures methods of extraction are controlled. - Monitoring development in scientific research makes sure any changes in the field are regulated appropriately and that all guidelines are up to date. - Provide info and advice to government and professionals helps to promote the science involved in embryo research, helping society to understand what?s involved and why embryonic stem cell research is important. ...read more.

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