B2 Topic one

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Animal cell.

Animal cells. 

They have 4 things:

  • Nucleus- Contains DNA which controls what the cell does. 
  • Cytoplasm- A gel-like substance where most of the chemical reactions take place.
  • Cell membrane- Holds the cell together and controls what goes in and out of the cell.
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Plant cell.

Plant cells. 

They have the same FOUR things that animal cells have BUT they have 3 extras:

  • Cell wall- Gives support for the cell.
  • Vacuole- Contains cell-sap 
  • Chloroplasts- where photosynthesis occurs. 
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Bacteria cell

Bacteria cells. 

They have NO nucles. 

They are much smaller than Animal and Plant cells. 

They have four things:

  • Chromosomal DNA- This floats free in the cytoplasm and controls what the cell does,
  • Plasmids- Small loops of extra DNA.
  • Flagella- Long hair-like structure which roates to make the bacteria cell move. 
  • Cell wall- Gives support to the cell. 
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  • DNA has two strands coiled together in the shape of a double helix. 
  • The two strands are held tofgetehr by chemicals called bases. 
  • There are FOUR bases; Adenine, Thymine, Cytosine and Guanine which are paired together by WEAK HYDROGEN BONDS, 

The discovery of DNA. 

There were FOUR people who discovered DNA:

  • Rosalind Frankilin
  • Maurice Wilkins
  • James watson
  • Francis Crick 

How they discovered DNA

Rosalind Franklin and Maurice Wilkins discovered that DNA had a helical structure. They discovered tihs by firing beams of x-rays on a crystal of DNA and looking at the patterns this made. 

THEN James Watson and Francis Crick used these findings to make a model of DNA. 

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A Mutation is a change to an organism's base sequence. 


  • Could change a order of amino acids in a protein and this could change the hsape of a protein.
  • Could chnage the features of an organism. 
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Enzymes in the body are called biological catalysts as they speed up chemical reactions in the cell.They are all proteins.They work INSIDE and OUTSIDE of cells.

 Enzymes are used for THREE things:

  • DNA replication- copy a cell's DNA before it divides. 
  • Protein synstheis- hold amino acids in place and forms bonds between them.
  • Digestion- They are used in the gut to disgest food.   
  • Every enzyme has an ACTIVE SITE. This is the part where it joins onto its substrate. 
  • Enzymes usually work with only ONE substrate. 
  • The substrate has to fit into the active site's shape for the enzyme to work, if it doesn't the reaction won't happen. 

The lock and key theory.- This is the theory that the substrate fits in to the enzyme like a key fits into a lock.

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factors that affect the rate of Enzymes.

The 3 Factors that affect Enzymes are:

  • Temperature- Enzymes like warm temperatures but NOT TOO HOT. If it gets too hot, the enzyme shape will get denatured.
  • pH- They don't want the pH too high or too low. The optimum pH is pH7.
  • Substrate concentration- The higher the substrate concentration, the faster the enzyme reaction because there are more substrate molecules to reaction with. 
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Genetic Engineering.

Genetic Engineering is when scientists can remove a gene from one organism and insert it into the gene of another organism. 


  • Can reduce Vitamin A deficiency because Golden Rice is a type of genetically modified and contains Beta Carotene and that is used in our bodies to make Vitamin A. 
  • Human Insulin can be made because the Human Insulin gene has been cut and put into the DNA of bacteria which is used to make Human inulin which can treat diabetes.
  • It can increase crop yield because GM crops have been made herbicide resistant and filds can be sprayed with herbicide and this would kill all the plants but not the GM crop. INCREASING OF CROP YIELD CAN LEAD TO MAKING MORE FOOD.
  • Disadvantages of Genetic Engineering are:
  • Some people think that GM crops are unsafe to eat.
  • Growing GM crops could affects insects and flowers that live by crops. 
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 Mitosis is a type of cell division and oocurs whenever new cells are needed. Mitosis happens when a part of the body has to be repaired, or needs to grow. 

Mitosis produces two diploid cells which are identical and contain the same number of chromosomes. 

Asexual reproduction also uses Mitosis. 

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Meiosis is used only in the reproductive organs and it is used to produce four haploid cells which don't have identical chromosomes. 

It is similar to Mitosis in only ONE way because it starts off  with a diploid cell, replicates and divides in two. Afterwards, it divides again to create four cells with only one pair of chromosome each.

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What is cloning?

  • cloning means making identical copies of something.
  • cloning is a type of asexual reproduction. becouse it produces cells that are genetically the same.


  • could help with the shortage of organs for transplants.
  • studying animal clones could develop our understanding of things like ageing and development of embryas.
  • could be use to help preserved endangered species.


  • reduced gene pool, cloned mammals don't live long, cloning processes often fail because it took hundred attempts to clone dolly the sheep and cloned mammal's immune systems are often unhealthy. 
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stem cells

What are stem cells?

Embryonic stem cells can differentiate into only cell type and are extracted from embryos. embryos are destroyed after remaving. stem cells. they can develop into any type of cell. adult stem cells are extracted from the body tissues of an adult. adult stem cells aren't as useful  embryonic stem cells becouse they can only differentiate into certain types of cells.


stem cells can cure diseases and replace cells that have been damaged by an disease or injury.


when embryonic stem cells are extracted,the embryo is killed. some people are against this becouse destroying embryos is murder. and each one is a potential human life.

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