OCR AS Biology Revision: Units 1.1.1, 1.1.2 & 1.1.3

Set of Notes for OCR AS Biology Unit 1, covering the following topics:

Unit 1.1.1 - Cell Structure and Microscopy

Unit 1.1.2 - Cell Membranes 

Unit 1.1.3 - Cell Division, Cell Diversity and Cellular Organisation

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Preview of OCR AS Biology Revision: Units 1.1.1, 1.1.2 & 1.1.3

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Tom Bartlett OCR AS Biology Unit 1
Biology Revision
1.1.1 - Cell Structure & Microscopy
Definitions and Key Facts

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Tom Bartlett OCR AS Biology Unit 1
Magnification: The degree to which the size of an image is larger than the object
itself (does not affect the level of detail).
Resolution: The degree to which it is possible to distinguish between two separate
An electron microscope has a higher resolution than a light microscope therefore
more cell organelles can be seen using an electron microscope.…read more

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Tom Bartlett OCR AS Biology Unit 1
The nucleolus of a cell is responsible for the production of ribosomes.
Nuclear Envelope:
The nuclear envelope is a double membrane `shell' of the nucleus. Nuclear pores penetrate the
envelope, and are large enough to
let relatively large molecules though.
Endoplasmic Reticulum:
ER is a series of cisternae (membrane
bound sacs) which are continuous
with the outer nuclear membrane.…read more

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Tom Bartlett OCR AS Biology Unit 1
Lysosomes are vesicles containing digestive enzymes used for breaking down cellular waste
products such as membranes, other organelles (i.e. mitochondria), food and engulfed microbes which
are taken into the cell through phagocystosis. Once broken down, these products are returned to the
cytoplasm as new cell-building materials. They are spherically shaped and found only in animal cells.
Chloroplasts are organelles found in plant cells that conduct photosynthesis.…read more

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Tom Bartlett OCR AS Biology Unit 1
No true nucleus. Has a nucleus.
Single chromosomes Several chromosomes
made up from nucleic acid. with nucleic acid.
Cell organelles absent. Cell division by mitosis
Cell division by binary and meiosis.
fission. Complicated internal
Single membrane cell. structure, where an
ATP production takes organelle performs a
place in special infolded specific role.
regions called All organisms except
mesosomes. prokaryotes have this
Sometimes have flagella. structure.…read more

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Tom Bartlett OCR AS Biology Unit 1
Phospholipid - A molecule consisting of a glycerol molecule, a fatty acid molecule and a
phosphate group covalently bonded together.
Cholesterol - Used to main the integrity of cell membranes, and also has a role in cell
Cell Signalling - The molecular mechanism whereby cells detect and respond to external
stimuli and send messages to other cells.…read more

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Tom Bartlett OCR AS Biology Unit 1
Channel proteins; which are used to transport smaller molecules and ions down a
concentration gradient, much like a hollow tube with the ability to open and shut. They do not
change shape.
Globular Proteins transport molecules through the membrane, and act as regulators within
the membrane.
Glycolipids are used for cell recognition and cell interaction.
The effect of changing temperature on membrane structure and
Increased Temperature:
At body temperature cells function their best.…read more

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Tom Bartlett OCR AS Biology Unit 1
Homologous chromosomes are chromosome pairs of the same length, centromere
position, and staining pattern, with genes for the same characteristics at corresponding loci.
Stem Cell - An undifferentiated type of body cell found in bone marrow, growing tissues and
embryonic tissue. The physical location of the stem cell, and the hormonal or growth
influences that surround it, will determine what type of adult cell it will become.…read more

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Tom Bartlett OCR AS Biology Unit 1
The chromosomes shorten and thicken (supercoil) and they can now be seen by a light
microscope which shows that they consist of a pair of sister chromatids.
The nuclear envelope then breaks down and disappears.
The centriole divides into 2 and each daughter centriole moves to opposite ends of the cell
to form the spindle (a protein thread structure that looks like the lines of longitude on a
globe).…read more

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Tom Bartlett OCR AS Biology Unit 1
Erythrocytes are specialised to transport oxygen and carbon dioxide. In humans, they have no
nucleus. In haemopoeisis, not only is the nucleus lost but also the mitochondria and organelles in
erythrocytes. The loss of organelles and the nucleus in the cell creates more space for the exchange
of oxygen and carbon dioxide within the cell.
Human erythrocytes are biconcave discs. Some argue that this shape maximises the surface area to
volume ratio and therefore speeds up diffusion.…read more


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