Biology (practical)

Cells

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Movement of substances

Passive transport e.g. Diffusion & osmosis :

Movement of a substance from a region of higher concentration to a region of lower concentration across a cell membrane, with no input of energy from the cell.

Active transport :

Movement of substances from a region of lower concentration to a region of higher concentration, and needs energy from cell respiration.

Possesses kinetic energy - move about constantly and randomly \n Molecules diffuse DOWN their concentration gradient. \n Steeper the concentration,  the faster the diffusion ~ rate of diffusion ÷ time

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Diffusion

Net movement of molecules from a region of higher concentration to a region of lower concentration that is, down a concentration gradient. \n \n Solute diffuse independently of each other in solution \n Some substances can diffuse across the cell surface membrane.

Osmosis

• Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

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Nutrients

Protease digest protein in amino acids.

Starch into maltose by amylase. >maltose into glucose by maltase

Lipase digest fats into glycerol + fatty acids

Protein into polypeptide by pepsin , polypeptide into amino acids by erepsin

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Enzyme

Nutrition in Man

Nutrition in Plants

Transport in Plants

Transport in Humans

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Tests:

Biuret solution- test for protein

1. Add 2cm^3 of biuret solution to 2cm^3 of food sample.

2. Shake the mixture thoroughly.

3. A purple or violet solution is formed if proteins are present.

   -biuret solution remained blue > protein absent

   -biuret solution turned from blue to purple > protein present

\n Ethanol emulsion test- test for fats

1. Add 2cm^3 of ethanol to 2cm^3 of food sample in clean and dry test tube.

2. Shake the contents of the tube vigorously.

3. Decant the liquid from step 2 into a new test tube.

4. Add 2cm^3 of distilled water into the test tube from step 3 and shake the mixture.

5. A white emulsion is formed if fats are present.

   -ethanol solution remained colourless > fats are absent

   -white emulsion formed > fats present

   Iodine solution - test for starch

6. Add 2cm^3 of food sample into clean test tube.

7. Add a few drops of iodine solution to the test tube.

8. A blue-black solution is formed if starch is present.

   - Iodine solution remained brown > starch is absent.

   -Iodine solution turns from brown to blue-black > starch is present.

\n Benedict’s test- test for reducing sugars

1. Place 2cm^3 sample of food sample into test tube.
2. Add 2cm^3 of Benedict’s solution to the food sample.
3. Shake the mixture and place the tube in a boiling water bath for 2-3 minutes.

\n Potato strips -shows osmosis in living tissues

\n Cellophane paper and thistle funnel- demonstrate osmosis \n Copper sulfate crystal - diffusion

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