Chemical and Cellular Basis of Life Flashcards
How many elements are recognized in nature?
92
What percentage of those elements are essential to continue healthy life and reproduction?
20 - 25%
How many elements are essential for,
a) Humans
b) Plants
a) 25
b) 17
Elements that make up 96% of living matter?
C, H, O, N
Elements that make up most of the remaining 4%?
Ca, P, K, S
Elements found in minute amounts in living matter?
Na, Cl, Mg, B, Co, Cu, Cr, F, I, Fe
Two reasons why water is important?
- Vital chemical constituent of living cell
- Provides a biological medium for all organisms
Describe the chemical structure of water?
Small, polar, angular molecules.
Describe the polarity of water?
- Oxygen atom is slightly negative and hydrogen atom is slightly positive.
Define hydrogen bonds in water?
Weak attractions between the slightly polar hydrogen atom of one water molecule and an oxygen atom of an adjacent water molecule.
Nature of hydrogen bonds of water when it’s a liquid?
- Very fragile
- Form and break with great frequency.
Four major properties of water to maintain life on earth?
- Cohesive behaviour
- Ability to moderate temperature
- Expansion upon freezing
- Versatality as a solvent
Define,
1. Cohesion
2. Adhesion
- Attractions between water moelcules due to hydrogen bonding
- Attraction between water molecules and other substances.
Properties of water that allow it to act as a transport medium?
Cohesion, Adhesion
Use of cohesion in plants?
Water and dissolved substances such as minerals are transported as a continuous column through xylem against gravity.
Use of adhesion in plants?
Adhesion between water molecules and cell walls helps in conduction of water and dissolved subtances.
Why does water has high surface tension?
Due to cohesion between water molecules, the uppoer surface water molecules are attracted by lower surface molecules and it forms a water film.
Explain water’s ability to moderate temperature
Water can absorb/ release a relatively high amount of heat energy by a slight change in its own temperature.
Advantage of high specific heat of water?
Acts as a thermal buffer in living system and aquatic bodies during temperature fluctuations on earth.
Advantage of high heat of vaporization?
An organism can release much heat energy with minimum loss of water. This helps organisms to cool their body surfaces.
1. Evaporation of water from human skin helps to maintain the body temperature at consant level.
2. Transpiration in plants help to cool the plant body surface and prevent from becoming too warm in the sunlight.
Explain the expansion upon freezing in water.
When the temperature of water falls below 4 ˚C, it begins to freeze and forms a crystalline lattice called ice cubes. Therefore water has the maximum density at 4˚C. Hence, ice floats on the surface of water bodies