AS Biology

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  • Created on: 09-12-12 22:51
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3.1 In the beginning:
Prokaryotic cell: Bacteria and cyanobacteria (photosynthetic bacteria) They have no nuclei
or other membrane-bound cell organelles. Diameter 0.5 and 5
Eukaryotic cells: contain membrane bound organelles- nuclei, Mitochondria. Larger than a
prokaryotic cell. Diameter 20 or more.
Mitochondria: Inner of its 2 membrane is folded, form finger
like projections called cristae. Later stages of aerobic
Nucleus: Contains chromosomes and a nucleolus. DNA in
chromosomes genes that control synthesis of proteins.
Nucleolus: Dense body within the nucleus where ribosome's are made.
RER: System of interconnected membrane-bound flattened sacs. Ribosome are attached to
the outer surface. Proteins made by these ribosome's are transported to the ER to other
parts of the cell.
Ribosomes: Made of RNA & protein, these small organelles are found free in the cytoplasm
or attached to ER. They are the site of protein synthesis.
Cell surface membrane: Phospholipids bilayer containing proteins and other molecules
forming a partially permeable membrane.

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SER: Like RER. Does not have any attached ribosome's. SER are make lipids are steroids. E.g.
reproductive hormones.
Golgi apparatus: stacks of flattened, membrane bound sacs formed by fusion of vesicles
from ER. Modifies proteins and packages them in vesicles for transport.
Lysosomes: Spherical sacs containing digestive enzymes and bound by a single membrane.
Involved in the breakdown of unwanted structures within the cell, and in destruction of
whole cells when old cells are to be replaced or during development.…read more

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Gamete cells are unusual:
Human cell: 46 chromosomes. 22 homologous pairs. 1 pair of sex chromosomes.
Fundemantal difference between sex cells are other cells is the no. of chromosomes they
How do gametes form: 2 types of cell divison in living organisms. MITOSIS AND MEIOSIS.
Mitosis produces new body cells as organism grows and develops. This retains the full no. of
chromsosomes called the DIPLOID NO. (2n).
Meiosis produces gametes with only ½ no. of chromos omes called HPLOID NO (n).…read more

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From one to many: the cell cycle.
The cell cycle can be divided into 2 distinct parts: interphase and division.
Preparation for division: Interphone:
Time of intense & organised activity during which the cell synthesizes new cell
components such as organelles and membranes, and new DNA.
Formation of new cellular proteins occurs
thrpughout interphase.
DNA synthesis occurs during the S phase.
The S phase separates the first gap or G1
from the second gap G2 phase.…read more

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Apart from usual mutation both strands are identical copies.
They are 2 chromosomes joined at 1 region called centromere.
Microtubules from the cytoplasm form a 3D structure called spindle.
The centrioles move around the nuclear envelope and position themselves at
opposite sides of the cell.
The breakdown of the envelope signals the end of prophase and the start of
The chromosomes' centromeres attach the spindle fibres at the equator.
When this has been completed the cell has reached the end of metaphase.…read more

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Potential use of human stem cells in medicine:
They may 1 day produce universal human donor cells which would provide new cell, tissues
or organs for treatment and repair by transplantation.
Their potential to develop into any cell type offers the greatest flexibility for development,
unlike adult stem cells which are committed to developing only into certain cell types.…read more


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