Lycopodium sp. root cross section

Volvox sp. coloniesWhite blood cells engulfing bacteria

Plant cells

Phloem

Xylem

Chapter 1 Chemical composition of cells

Learning objectives:

• Cell as the most basic unit of life.

• Functions of water.

• Functions of inorganic salt.

Cells

• The most basic functional and organizational level of life.

• Some organisms are composed of only one cell, i.e. the unicellular organisms.

• Unicellular organisms work together and form colonies.

Slime molds aggregate and form fruiting bodies when food is scare.

• Multicellular organisms have various levels of organization within them.

• Individual cells may perform specific functions and also work together for the good of the entire organism.

Chemical composition of cell

•有机 Organic substances• Compound with one or more carbon atom(s) covalent bond to other elements

•无机 Inorganic substances• Does not contain carbon

Some strong chemicals bonds

Covalent bond 共价键

sharing of electron pairs between atoms

Hydrogen bonds 氢键

electrostatic attraction between two polar groups, always involve hydrogen

Ionic bond 离子键complete transfer of valence electron(s) between atoms, generates ions

1.1 Water

Function of water

• Water is the main component of cells.

• Function of water includes:• Metabolism substrates

• Solvent

• Location of chemical reaction

• Medium of transportation

• Support and maintenance of shapes

• Secretions

• Heat regulation

• Reproduction

1. Metabolism substrates

代谢作用物• E.g. photosynthesis, hydrolysis (digestion etc.)

Function of water

Reactants Products

photosythesis Hydrolysis of maltose into two glucose molecules

maltose 2 glucoses

Function of water

2. Solvent 溶剂• Many compound are soluble in water

• Suitable for internal transportation of substances

• E.g. blood, tissue fluid, lymph fluid, cytoplasm, sap in xylem or phloem

Function of water

3. Location of chemical reactions• Water as a buffer for

temperature change.

• Water has the highest specific heat capacity 比热 of any liquid.• Specific heat is defined as the

amount of heat one gram of a substance must absorb or lose to change its temperature by one degree Celsius.

• For water, this amount is one calorie, or 4.184 Joules.

• Reaction can be carried out at a constant rate in temperature

4. Medium of transportation• Many molecules and elements are

soluble in water

• Easier to transport water with as a solution

• E.g. sap (plants), body fluids (blood, lymph)

• Transport nutrients, oxygen, waste products etc.

Function of water

5. Support and maintenance of shape

• Animal cells required water to maintain its shape and functions.

• Plants cells rely on turgidity 膨胀度to maintain rigidity 刚性.

• Some animals such as jellyfishs rely heavily on water to maintains its shape as they may contain up to 97% of water in their body.

Function of water 低渗溶液 等渗溶液 高渗溶液

6. Others

• Secretions of body e.g. digestion fluid, hormone, tear, saliva, semen etc.

• Temperature regulation through sweating, urination (animal) or transpiration (plant)

• Transfer of genetic material during reproduction• Surface water (gametophyte of plants

such as in ferns)• Body fluids (animal)

Function of water

Fern gametophyte Sperm cell of Drosophila

Quiz

• Which of the following is NOT a use of water in the human body?

1. Transport

2. Temperature regulation

3. Genetic information

4. Chemical reactions