Chap 4 Bio Molecules Flashcards

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1
Q

What roles do water have in living organisms? [4]

A
  1. As a solvent for chemical reactions eg. photosynthesis and hydrolysis
  2. As a key component of tissues e.g. protoplasm
  3. Controlling body temperature
  4. Transporting dissolved substances
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2
Q

What roles do water have especially for plants?

A

Essential for photosynthesis
Needed to keep cells turgid or firm
Needed to transport mineral salts (through the xylem) and food substances (through the phloem)

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3
Q

Define “carbohydrates” and what they may be classified as.

A

Carbohydrates are organic molecules made up of the elements carbon, hydrogen and oxygen. The hydrogen and oxygen atoms are present in the ratio 2:1. They may be classified as monosaccharides, disaccharides, or polysaccharides.

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4
Q

What are the purpose of carbohydrates?

A

Carbohydrates are needed as a source of energy and to synthesise other organic compounds such as cellulose, amino acids, fats, nucleic acids (e.g. DNA), lubricants and nectar.

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5
Q

Name examples of monosaccharides.

A

Glucose, fructose, galactose

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6
Q

Name examples of monosaccharides.

A

Glucose, fructose, galactose

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7
Q

Name examples of disaccharides

A

Maltose, lactose, and sucrose. Maltose is formed from two glucose molecules joining together to form maltose, with the removal of one molecule of water.

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8
Q

Name examples of polysaccharides

A

Starch, glycogen and cellulose

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9
Q

What are the stores of glucose? What are their features?

A

Glycogen and starch are stores of glucose. Starch is the store of glucose in plants, whereas glycogen is the store of glucose in animals. Glycogen is stored mainly in the liver and muscles.

Insoluble in water. Does not change water potential in cells.
Large molecules. Cannot diffuse through cell membranes and will not be lost from the cell.
Can easily be hydrolysed to glucose when needed.
In the hydrolysis of starch, the bonds within the polysaccharide are broken and glucose molecules are released.
Have compact molecule shapes. Occupies less space to allow for more to be stored.
This makes glycogen and starch suitable storage materials.

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10
Q

What are the functions of carbohydrates

A

Carbohydrates are a substrate for respiration to provide energy for cell activities.
Forms supporting structures like cell walls in plants
Can be converted into other organic compounds like amino acids and fats
Needed to form nucleic acids such as DNA
Synthesise lubricants like mucus
Synthesise nectar in some flowers (nectar is a sweet liquid that is produced to attract insects).

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11
Q

What are fats?

A

Fats are organic molecules made up of carbon, hydrogen and oxygen. They contain much less oxygen in proportion to hydrogen, unlike carbohydrates.

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12
Q

What can fats be broken down into?

A

Fats can be broken down into fatty acids and glycerol through hydrolysis.
Fat molecule + three water molecules → Glycerol + three fatty acid molecules.

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13
Q

What are the functions of fats?

A

Fats are a source and store of energy.
An insulating material that reduces excessive heat loss (e.g. blubber in animals)
As a solvent for fat-soluble vitamins and other substances like hormones
Essential constituent of cell membranes
A way to reduce water loss from the skin surface by being secreted as an oily substance forming a thin layer over skin surfacing, reducing water evaporation and reducing the rate of heat loss.

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14
Q

What are proteins?

A

Proteins are organic molecules made up of the elements carbon, hydrogen, oxygen, nitrogen and (depends) sulfur. Proteins are always present in protoplasm, and are the largest and most complicated.

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15
Q

What are proteins made up of? [2 para]

A

Protein molecules are built up from simpler compounds known as amino acids, which is made up of an amino group, an acidic group, and a side chain. There are many different amino acids, and they can be combined in various ways to form millions of different protein molecules.

Amino acids link up to form polypeptides. The bond between two amino acids is known as a peptide bond.
These polypeptides are long, three-dimensional folds that cannot be quickly absorbed if not broken down by enzymes in digestion, which is a series of hydrolytic reactions.

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16
Q

What are the functions of proteins

A

Synthesis of new protoplasm for growth and repair of worn out body cells
Synthesis of enzymes and some hormones
Formation of antibodies to combat diseases.

17
Q

Name the food test for reducing sugars.

A

Benedict’s Test

18
Q

What are reducing sugars?

A

Glucose, fructose, galactose, maltose and lactose (and not sucrose) are reducing sugars.

19
Q

Explain process of benedict’s test.

A

Place 2 cm3 of food samples into a test tube.
Add 2 cm3 of Benedict’s solution to the food sample.
Shake the mixture and place the tube in a boiling water bath for 2 to 3 minutes.
Observe colour change of the solution:

Solution remains blue
No reducing sugar

Blue to green ppt.
Traces of reducing sugar

Blue to yellow/orange ppt.
Moderate amount of reducing sugar

Blue to brick-red ppt
Large amount of reducing sugar

20
Q

Explain iodine test for starch.

A

Add a few drops of iodine solution (starts off yellow-brown) onto the food sample.
If starch is present, the iodine solution will become blue-black in colour. Otherwise, starch is not present.

21
Q

Name what ethanol emulsion test is for.

A

fats

22
Q

Explain ethanol emulsion test for liquid food

A

Add 2 cm3 of ethanol to the liquid food in a test tube, and shake the mixture thoroughly. Note observations.
Add 2 cm3 of water to the mixture and shake. Observe again.
If a cloudy white emulsion (suspension of small drops of a liquid in another liquid) appears, fats are present.

23
Q

Explain ethanol emulsion test for solid food

A

Cut the food into small pieces and place into a test tube. Add 2 cm3 of ethanol and shake thoroughly.
Allow solid particles to settle, and then decant (pour off top layer) ethanol into another test tube containing 2 cm3 of water.
If the solution remains clear, then fats are absent.

24
Q

Explain biuret test for proteins.

A

The biuret solution is a blue solution made up of sodium hydroxide and copper(II) sulfate.
Add 2 cm3 of sodium hydroxide solution (40% or bench solution) to 2 cm3 of egg white solution in a test tube, and shake it thoroughly.
Add 1% copper(II) sulfate solution, drop by drop, shaking the test tube after every drop.
OR
Add an equal volume of biuret solution to 2 cm3 of egg white solution, and shake well.
Observe colour change of the solution: if the solution becomes violet (purple), proteins are present. If no colour change is observed, proteins are not present. If there is pink colouration, polypeptides are present.