1.1.2 Molecules Quiz

1. Explain why water is described as a dipolar molecule. -Water is described as a dipolar molecule because it has a negative end and it has a positive end also. The oxygen is more electronegative so it pulls the electron cloud away from the hydrogen’s. So the hydrogen’s become more positive and the oxygen more negative. (2)

2. Give examples of hydrogen bond formation contributing to the structure of molecules. - The structure is maintained through different groups of amino acid residues. Tertiary and Quaternary form bond between 4 water molecules. (1)

3. Explain why sodium chloride dissolves in water. -Sodium Chloride dissolves in water because the positive part of the water molecules attracts the negative chloride ions and the negative part of the water molecules attracts the positively sodium ions. The polarity of water molecules enables water to dissolve many ionically bonded substances. Polar molecule has an uneven charge distribution. (1)

4. Explain why some organic molecules, such as simple sugars and alcohols, form aqueous solutions but others, such as lipids, do not. - Simple sugars and alcohols have charged polar groups which can form hydrogen bonds with water molecules (1)

5. Why is water an important transport medium in animals? Write down as many examples of where water is important in transport as you can. - Water is an important transport medium in animals because substances such as polar and ionic will dissolve in it and then this can be transported around the body. These substances can be transported to respiring cells and waste products such as urea can be excreted. Also it is a good transport medium because water is an excellent solvent for ions and polar molecules because the water molecules are attracted. Also the polar substances such as lipids do not dissolve in water and tend to be pushed together by it. (3)

6. Suggest where in the human body, apart from the blood and the protoplasm of cells, you might find significant quantities of water. For each of your suggestions, suggest the function of the water. - In the bones it protects and moisturises our joints - In our eye tears from glands this protects the surface of the eye. (2)

7. The formula for stearic acid is C17H35COOH. It is often written out as CH3(CH2)16COOH . The formula for oleic acid (another fatty acid) is C17H33COOH. Suggest which of these two fatty acids is found in animal tissues and which in plants, giving reasons in support of your answer. Which one is likely to be liquid at room temperature. - Oleic acid has too less hydrogen atoms. Oleic acid is liquid at room temperature. - Steric acid is in animal tissues, it’s a saturated fatty acid it also has no double bonds. (3)

8. Explain how phospholipids are involved in the structure of cell membranes. - Phospholipids form the bulky part of the membrane. A phospholipid is a special type of lipid molecule. It’s made of glycerol molecule with a phosphate group and two fatty acid chains attached. Phosphate group is hydrophilic and the fatty acid chains are hydrophobic. In the phospholipids bilayer the hydrophilic heads face the water because they like water and the hydrophobic tails are on the inside hiding from the water. (3)

9. Explain by means of a diagram how a glycosidic bond is formed when two monosaccharides, such as glucose, undergo a condensation reaction to form a disaccharide.

-When two glucose molecules join together the disaccharide maltose is formed. The two molecules join together by a condensation reaction. Bond produced is called a glycosidic link.

(3)

10. Glycogen are important storage molecules. Explain how they are suited to this function. - Glycogen is insoluble in water and it’s a big molecule, therefore cannot pass through cell membranes. It also has an compact shape which helps it save space. It could easily be used by the body to provide energy. (3)

11. Describe how the structure of an α-helix is maintained. How does the structure of a β-pleated sheet differ? - A-helix the hydrogen bonds occur between the carboxyl carbon of one amino acid with the amino group of the amino acid four residues further down the chain. B pleated sheet- the structure can easily be broken by high temp and ph. (2)

12. Construct a table of differences between fibrous and globular proteins, giving an example of each.

|Fibrous |Globular |
|Are elongated and insoluble |Are spherical and soluble in water |
|Fibrous proteins only have up to primary and secondary |Tertiary and quaternary structrue |
|structure. | |
|Long and thin |Has a 3d shape |
|Hair and skin. |Hormones enzyme |
| | |
| | |
| | |

(4)

13. Make a table to show the substances which need to be taken up by living animal cells. For each substance give a reason for uptake.

SUBSTANCE REASON OXYGEN For aerobic respiration AMINO ACIDS For protein synthesis GLUCOSE Energy source WATER Involved in metabolism (4)

14. List the ways in which materials can be transported across membranes. For each method, state whether it is active or passive.
DIFFUSION-Passive
ACTIVE TRANSPORT-Active
OSMOSIS-PASSIVE
(3)

15. Define diffusion. -Molecules move from a highly concentrated area to a place where there a fewer molecules. It is an automatic process that carries oxygen to the blood in the lungs and oxygen from the blood to the rest of the rest of the body tissues. (2)

16. List the factors affecting the rate of diffusion. -Area- the bigger the area the faster the rate. -Concentration gradient- the greater the difference in concentration the faster the rate of diffusion. (2)

17. Explain what is meant by the term ‘facilitated diffusion’ and describe how it differs from simple diffusion. -Facilitated diffusion- Passive transport because of materials. Spontaneous passage of molecules or ions across a biological membrane passing through a specific transmembrane integral proteins. -Simple diffusion allows non polar molecules. Secondly a simple diffusion does not allow ions. It also does not allow other membranes. (3)

18. Define osmosis in terms of water potential. - The net movement of water molecules from a region of high water potential to a region of low water potential across a selectively permeable membrane.(2)

19. Describe the factors which affect water potential in living cells. - Solute concentration adding solute lowers the water potential - Pressure increases the water potential. (1)
20. How does active transport differ from diffusion? - Active transport requires energy in the form of ATP from respiration; Molecules or ions are accumulated against a concentration gradient; The energy is needed to transport the substances across the membranes.(2)

21. How do endocytosis and exocytosis differ from other transport mechanisms? - Exocytosis and endocytosis are processes by which material is encapsulated by a vesicle and either secreted or brought into cell. (3)

22. Phagocytosis is carried out by certain white blood cells. Draw a series of diagrams to show what happens when a bacterium is engulfed and broken down.

[pic]

(3)