Question

Chemistry, Nutrition, and Digestion Fill in the blanks with the appropriate molecule or organelle. Answers can be used more than once. 12. Allows some materials to enter a cell, but not others. 13. Functions in lipid and carbohydrate synthesis. 14. The buoyancy of phytoplankton is increased by the presence of Page 2-65 inside their cells. Fats and oils have Three organelles that are found in plant cells, but not animal cells: 15. kcal/g, while carbs and proteins have 16. and 17. 18. 19. Location where genetic information is stored. Proteins that function as defensive weapons of the immune system. Proteins that function in active transport through the cell membrane.

Answer 1

12. Cell Membrane: This is the first line of defence for a cell. It is made up of lipids and proteins. Lipids give the membrane flexibility whereas proteins assist in the movement of nutrients across the membrane. The membrane is selectively permeable. It allows necessary compounds to pass and restricts entry of harmful substances that can affect the cell adversely.

13. Smooth Endoplasmic Reticulum: The smooth ER is responsible for the synthesis of lipids, such as cholesterol and phospholipids, which helps form all membranes of an organism. In addition, it is also involved in carbohydrate metabolism. An enzyme from smooth ER catalyses the production of glucose from glucose-6-phosphate.

14. Lipids: Lipids and fats are only around 2-20% of the weight of algae. When they get accumulated in phytoplanktons above this value, they being lighter than water, reduce the overall density of the cells thus making them more bouyant than usual.

15. Fats have 9 cal/g and carbohydrates have 4 cal/g energy content. A reason for this is that carbohydrates are easily oxidised and provide energy more quickly. Fats require more oxidation to completely oxidise than carbohydrates. Because of this, oxidation of fats takes longer but it also provides more energy.