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AS BIOLOGY- UNIT 2
The Voice of the Genome-Cell Ultra structure
The 3 basic ideas about cells are:
They are building blocks of structure in living things
Are the smallest units of life
Are derived from other pre-existing cells by division
Contains a blueprint for their growth, development and behaviour…

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Smooth endoplasmic rectilium- have no ribosomes and are the site of synthesis of substances
needed by cells. Example- SER is important in the manufacture
Endoplasmic rectilium- has a network of folded single membranes forming interconnected
sheets, tubes or sacs. The origin of endoplasmic rectilium is the outer membrane of nucleus…

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Some cells are totally dependent on other cells for example nerve cells are adapted for the
transport of nerve impulses but are dependent on blood cells for oxygen, and on heart
muscle cells to pump the blood
Specialised cells in mulitcellular organisms become organised into tissues and organs during
development…

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In animal cells, division is by in-tucking of plasma membrane at spindle equator and pinching
cytoplasm in half
In plant cells the Golgi apparatus forms vesicles of new cell wall materials which collect along
the line of equator spindle a.k.a. the cell plate.
The vesicles coalesce and form new plasma…

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Without the reductive nuclear division the chromosome number would double with each
generation.
Mammals reproduce sexually only but plants can reproduce both sexual and asexual
reproduction
Self fertilisation is when the sperm and egg come from the same individual but cross
fertilisation comes from sperm and egg form different individuals.…

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Crossing over segments of individual maternal and paternal chromosomes- results in new
combinations of genes on chromosomes of the haploid cells produced. It involves:
1. Homologous chromosomes paired in a bivalent
2. If chromatids break at corresponding points along their length, their rejoing may
cross over
3. The chromatids finally…

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Steps leading to fertilisation
In mammals fertilisation occurs in upper oviduct and during intercourse the PH of the vagina
is quite acidic but the alkaline secretion of prostate gland helps to neutralise the acidity and
provide a neutral environment for the sperm
Waves of contraction of the muscular walls of…

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cell types of an adult organism (+200 different within a tissue type e.g. blood stem cells give
ones) rise to red and white cells and platlets only
Make up the bulk of the embryo as it Occurs in growing and adult body, with most
commences development from the inner cell…

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Eggs are then mixed with sperm in a shallow dish and are checked using a microscope to
ensure fertilisation
Zygotes then incubated at body temperature for 2-3 days
Microscope examination to confirm that the embryos have reached the 4-8 cell stage
Up to 3 embryos are transferred into uterus in…

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It is now possible to obtain ES cells from an It is an important overriding principal for some
embryo at the 8 cell stage without causing the people that humans should not tamper with
death of the embryo `nature' in a deliberate way
It is possible to regulate and control…

Comments

Divya Sareen


You amazing person!! Thankyou so much !! very detailed.

emily

thankyou! um look at my unit 1 notes and see if you like them as well

rumaysa

Thank you, What did you get for this exam? 

emily


Um I don't know because this is the first time I'm taking A levels- I'll tell you as soon as I get my results- and your welcome!

T.A

omg life saver!!! thankyou ! :)

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