3 Composition of cells

Materials to build and fuel cells Symbol Element C Carbon H Hydrogen N Nitrogen O Oxygen P Phosphorus S Sulfur

Table 3.1 Typical water content of some organisms Water — essential for life

Water is the major component of cells

Carbohydrates, proteins, lipids and nucleic acids are organic compounds. Metabolism refers to all the chemical reactions that occur in a living organism. Water is the predominant solvent in living organisms. Water molecules are highly cohesive because of the attraction between hydrogen and oxygen atoms. Substances vary in their ability to dissolve in water.

Organic compounds Figure 3.8 The four main groups of organic molecules in cells. Note the monomers that make up the polymers of each group.

Carbohydrates — energy-rich Table 3.3 Basic structure and function of various groups of carbohydrates

Proteins

Lipids

Nucleic acids

The major compounds that make up living cells are different kinds of carbohydrates, lipids, proteins and nucleic acids. Each major compound has a specific role. Some exist only in either plant or animal cells; others play an important role in both.

The body requires a number of minerals, some in relatively large amounts, others in trace amounts. Minerals play a role in metabolic processes of cells and are incorporated into many structures produced by cells. Copper is an essential mineral for cellular respiration. Vitamins are a group of organic compounds and are essential for many of the chemical reactions that occur in cells. Vitamins can be divided on the basis of their chemical nature into two groups: fat-soluble and water-soluble vitamins. Each enzyme acts on only one kind of substrate.

Producers at work: photosynthesis

Figure 3.18 The inputs and outputs of the process of photosynthesis

Chloroplasts: where the action is!

Figure 3.22 Absorption of light of various wavelengths for different plant pigments. Which pigment absorbs yellow light best? What wavelengths of light (colours) are best absorbed by chlorophylls?

Accessing energy: cellular respiration

Levels of biological organisation

Finally… Photosynthesis is the process of converting light energy to chemical energy stored in sugars. Organisms that can make organic molecules by photosynthesis are called autotrophs and include all plants, algae and some bacteria. Adenosine triphosphate (ATP) is formed when energy is released during cellular respiration of glucose, a carbohydrate.