A Level: Ethanol Emulsion For Testing Of Fats

Materials:

• Ethanol
• Brownies
• Sticky Rice
• Bread
• Whole
  Bread
• White Bread
• Oil
• Water

Equipments:

• Evaporating Dish
• Test Tube
• Test Tube Rack
• Filter Funnel
• Filter Paper
• Pestle/Mortar
• Pipette
• Tongs

Preparations of a solid sample:

1. Completely crushes adequate amount of food with a clean and dry mortar and pestle.

2. Transfer an adequate amount of crushed food sample to a clean test tube

3. Adds 2cm ethanol above the food sample

4. Shakes the test tube thoroughly and safely .

5. Allows the solid to settle for about 3 min

6. Decants the ethanol carefully into a clean,dry test tube without transference of food particles.

7. Adds 2cm of de-ionized water to the test tube

8. Compares each result with the negative control

9. Compares the heights of the emulsion layer of all the samples

Process:

1. Add the food sample to 2 cm3 of ethanol, shake well.
2. Allow to settle in a test tube rack for 2 minutes for food to dissolve in ethanol.
3. Empty any clear liquid into a test tube containing 2 cm3 of distilled H2O.
4. A MILKY-WHITE EMULSION is a positive result: lipid is present.
5. If the mixture remains clear, there are no fats present in the sample

RESULTS

SUBSTANCE TESTED	PRESENCE OF SPOT	LIPIDS PRESENCE
Brownies	Yes	Yes
Rice	-	-
Sticky Rice	-	-
Cooking Oil	Yes	Yes
White bread	Yes
Whole bread	No	No

By: Nadia Hasna Karimah

Cell Membrane And Transport

Phospholipids

A lipid that containing phosphate group in its molecule. From phospholipids, little bags can be formed in which chemicals can be isolated from the external environment. These bags are the membrane-bound compartments that we know as cells and organelles.

The basic structure of a membrane is a 7 nm thick phospholipid bilayer with protein molecules
spanning the bilayer or within one or other layer. Phospholipids and some proteins move within the
layers. Hence the structure is described as a fl uid mosaic – the scattered protein molecules resemble pieces of a mosaic.

Phospholipid bilayers are a barrier to most water 

soluble substances because the interior of the membrane is hydrophobic.

Structure Of Membrane

Cholesterol is needed for membrane

fluidity and stability.

Some proteins are transport proteins, transporting molecules or ions across the membrane. They may be either channel proteins or carrier proteins. Channel proteins have a fixed shape; carrier proteins change shape. Some proteins act as enzymes – for example, in the cell surface membranes of microvilli in the gut. Glycolipids and glycoproteins form receptors – for example, for hormones or neurotransmitters. 

They also form antigens, which are cell recognition markers.

Transport Across The Cell Surface Membrane

Th e cell surface membrane controls exchange between the cell and its environment. Some chemical reactions take place on membranes inside cell organelles, as in photosynthesis and respiration. 

Diffusion is the net movement of molecules or ions from a region of their higher concentration to one of lower concentration. Oxygen, carbon dioxide and water cross membranes by diffusion through the phospholipid bilayer. Diffusion of ions and larger polar molecules through membranes is allowed by transport proteins. This process is called facilitated diffusion.

Active transport – the sodium–potassium pump

By: Nadia Hasna Karimah