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Biology Unit 1

Structure of an epithelial cell

The nucleus - contains the organisms hereditary material and controls the cells activities

o Nuclear envelope - Double membrane that surrounds the nucleus. Controls the entry and exit of
materials in and out of the nucleus. This is where reactions take place…

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Biology Unit 1

Lysosomes - contain many digestive enzymes. Breaks down unwanted substances.

Ribosomes - small cytoplasmic granules found in all cells

o 80s ribosomes found in eukaryotic cells
o 70s ribosomes found in prokaryotic cells

Microvilli - finger-like projections of the epithelial cell that increase surface area to allow…

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Biology Unit 1


Light microscope

Advantages Disadvantages

Can be used to observe living material Light has long wavelength
Material seen in natural colour Low resolution
Can't resolve object smaller than 250nm

2 Different types of electron microscope

o Transmission electron microscope (TEM) - consists of an electron gun that…

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Biology Unit 1

µm Micrometre 10-6
nm Nanometre 10-9

Cell Fractionation - Process when cells are broken up and the different organelles are separated out. Before
cell fractionation can begin tissue must be placed in a cold, isotonic buffered solution.

o Cold - to reduce enzyme activity that might break…

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Biology Unit 1

Cell surface membrane is the plasma membrane that surrounds cells and forms the boundary between cell
cytoplasm and the environment. Controls movement of substances in and out of the cell.

Molecules that from this structure:

o Phospholipids from a bilayer sheet. Consists of a molecule that is…

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Biology Unit 1

o Allow active transport across the membrane by forming ion channels for sodium and potassium

There are several methods by which molecules and ions can move across the cell membrane:

o Diffusion

o Osmosis

o Active transport

Diffusion - net movement of molecules or ions from a…

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Biology Unit 1

Osmosis - the passage of water from a region of high water potential to a region where it has a lower water
potential through a partially permeable membrane.

Pure water has a water potential of 1 which is the highest water potential, everything is negative.

Active transport…

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Biology Unit 1

Absorption in the small intestine

Villi and microvilli

Villi have thin walls, lined with epithelial cells on the other side of which is a rich network of blood capillaries,
they considerably increase the surface area of the small intestine and therefore accelerate the rate of
diffusion. Villi…

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Biology Unit 1

Mechanism by which glucose is absorbed from the small intestine is an example of co-transport because 2
molecules are involved. -> Sodium potassium pump

Digestion is the process in which large molecules are hydrolysed by enzymes to produce small molecules
that can be absorbed and assimilated.


Page 10

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Biology Unit 1

Biochemical tests

Reducing sugar

1. Add Benedicts test

2. Boil

3. Colour changes from blue to brick red. Blue if no reducing sugar is present and brick red is reducing
sugar is present

Non-reducing sugar

1. Check no reducing sugar is present (by using reducing sugar test)…


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