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B2 Topic 1 The building blocks of cells
Plant cells and animal cells

Even though they belong to different organisms, plant and animal cells have some features in common:
o Cell Membrane ­ separates the contents of the cell and its surroundings. It controls the movement of
substances like glucose,…

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Microscopes have improved greatly over the past 350 years. The best modern light microscopes can magnify
specimens more than 1500 times.
As a result, we can observe very small structures inside cells. For example, we can see inside bacterial cells.
In the 1930s, the electron microscope was invented. This casts…

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3. tRNA (transfer) codons are attached to amino acids, each codon has a different amino acid
4. tRNA codons join to the complementary codons (bases) on the mRNA
5. As more amino acids are brought by the tRNA they bond together with peptide bonds.
6. Long chain of amino acids…

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2. Put the beaker into a water bath at 60C for 15 minutes as this denatures the enzymes that could digest the
DNA and help soften the onion cells.
3. The beaker must be put into ice to cool down quickly which stops the DNA from breaking down.
4. When…

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b. Golden rice is a variety of GM rice which contains two genes from other organisms which together
enable the rice to produce beta-carotene.
c. Growing golden rice in these places will mean the people will eat them and fewer people will suffer
from vitamin A deficiency.
2. Producing human…

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Mitosis

This is the division of somatic/body cells. These cells are diploid which means they have the full number of
chromosomes ­ 46.
When a cell divides by mitosis it makes two cells identical to the original cell, each with a nucleus containing
the same 46 chromosomes.
This type of…

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Meiosis only occurs in reproductive organs. Four haploid nuclei are produced whose chromosomes are not
identical.
Two divisions occur during this process.

Division 1

As with mitosis, the cell duplicates its DNA.
The chromosome pairs line up in the centre of the cell.
The pairs of chromosomes are pulled apart…

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5. Implantation of embryo into surrogate mammal. (sheep 3)
6. The offspring born by the surrogate mammal is a clone of sheep 1 not sheep 2.
Making plant clones can be relatively easy; you start with a bit of leaf, stem or root of the original plant. The
plant cells…

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white blood cells. These will survive in the patient as their body would recognise the new white blood cells as
their own cells.
This technique could treat many more problems than adult stem cells could as embryonic stem cells can
differentiate into almost every kind of cell. However, that means…

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enzyme is incapable of working on the substrate any faster (all the active sites are full). Therefore, adding
more substrate molecules will make no difference.

Specific enzymes

Enzymes only work with a particular substrate, so we say they have a specificity for their substrate. Enzymes
are therefore named according to…

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