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Biology Unit 2 Notes

Topic 3: the voice of the genome

Cells and Organelles

Prokaryotic cells

o Small and simple cells.
o No nucleus and no membrane bound organelles.
o DNA is circular and free floating in the cytoplasm
o Always have a cell wall
o Contain plasmids (rings of…

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o Found in large numbers in cells that are active and require a lot of energy

Golgi apparatus:

o Group of flattened sacs
o Vesicles often seen at the edges
o The golgi processes and packages substances made by the cell, mainly lipids and proteins
o Also makes lysosomes


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5. Protein is chemically modified, processed and `finished off'
6. Vesicles are budded off the Golgi and move to the cell surface membrane, along
7. Vesicles fuse with the membrane and the contents are releases. This is called secretion or

Cell organisation:

Multicellular organisms like humans are made…

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o S phase: Synthesis of DNA ­ replicated.
o G2: gap phase. Period after DNA duplication and cell prepares for division.



o Chromatin condenses, getting shorter
and fatter, and form chromosomes with
each chromosome having two chromatids
joined by a centromere.
o The nucleolus breaks down
o Centrioles…

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3. Add 10 drops of stain (e.g. acetic orcein) so that the chromosomes darken and can
be seen under microscope ­ ratio of stain to hydrochloric acid should be 10:1
4. Warm the watch glass on a hotplate for 5 minutes
5. Place the root tip on a microscope slide…

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o Crossing over produces new combinations of alleles
o This increases the genetic variation

Independent assortment of chromosomes:

o Happens during meiosis 1
o The homologous pairs line up randomly
o Maternal and paternal chromosomes from parents are therefore randomly distributed into

Mammalian gametes


o Flagellum/tail: allows sperm…

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Fertilisation in plants:

1. Male gamete: Pollen grain, female gamete: inside ovule of ovary
2. Pollen grain lands on stigma of flower, and begins to germinate (The pollen grain
must be from the same species)
3. A pollen tube grows out of the pollen grain and moves down the style…

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o There are two main types of stem cells: embryonic and adult stem cells.
o Potency refers to the differentiation potential (the potential to differentiate into different
cell types) of the stem cell. The three types are:

1. Totipotency: The ability of a stem cell to produce all cell types,…

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o Can improve the quality of life for many people e.g. replacing damaged cells in the eyes of
people who are blind.

Arguments against the use of stem cells:

o Obtaining stem cells from embryos by IVF raises ethical issues ­ viable embryos are
destructed and could have been a…

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o Under the right conditions, some genes are activated and other genes are
o mRNA is only transcribed from the active genes
o This is then translated into proteins
o The proteins modify the cell ­ they determine the cell structure and control cell
processes (including activation of more…




Brilliant! Thank you!

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