24.1 the chemistry of life > 1 copyright © pearson education, inc., or its affiliates. all...

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24.1 The Chemistry of Life 24.1 The Chemistry of Life >>

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Chapter 24The Chemistry of Life

24.1 A Basis for Life

24.2 Carbohydrates24.3 Amino Acids and Their Polymers24.4 Lipids24.5 Nucleic Acids24.6 Metabolism



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Most fish obtain oxygen as water flows across their gills.

CHEMISTRY & YOUCHEMISTRY & YOU

Where do fish get their oxygen?



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The Structure of Cells

What are the two major types of cells that occur in nature?

The Structure of CellsThe Structure of Cells



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Until recently, life was defined as the ability of an organism to grow and to reproduce its own kind.

• Recent discoveries made at the fringes of life seem to blur this definition.




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As difficult as it is to define life, you can generally regard tiny structures called cells as the fundamental units of life.




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As difficult as it is to define life, you can generally regard tiny structures called cells as the fundamental units of life.

• Organisms are composed of as few as one cell or as many as billions of cells.




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Two major cell types occur in nature: prokaryotic cells and eukaryotic cells.




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• The prokaryotic cell is the more ancient of the two.


– Microscopic examination of fossilized remains shows that prokaryotic cells were present on Earth at least 3 billion years ago.



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• The prokaryotic cell is the more ancient of the two.

• Eukaryotic cells did not appear until about 1 billion years ago.


– Microscopic examination of fossilized remains shows that prokaryotic cells were present on Earth at least 3 billion years ago.



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Both eukaryotic and prokaryotic cells contain all the chemicals necessary for life, encased in a cell membrane.




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Both eukaryotic and prokaryotic cells contain all the chemicals necessary for life, encased in a cell membrane.


• The cell membrane is a sac that holds the contents of a cell and acts as a selective barrier for the passage of substances into and out of the cell.



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Eukaryotic cells are considerably larger and more complex than prokaryotic cells.




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Eukaryotic cells are considerably larger and more complex than prokaryotic cells.


• But the chemical processes carried out by both types of cells are very similar.



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One major feature that distinguishes eukaryotic cells from prokaryotic cells is that eukaryotic cells contain membrane-enclosed organelles.




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One major feature that distinguishes eukaryotic cells from prokaryotic cells is that eukaryotic cells contain membrane-enclosed organelles.


• Organelles, meaning little organs, are small structures suspended in the interior cellular fluid, or cytoplasm.



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The organelles are the sites of many specialized functions in eukaryotic cells.


• For example, the nucleus, a structure that is important in eukaryotic cell reproduction, is not present in prokaryotic cells.



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• Mitochondria (singular: mitochondrion) are the source of cellular energy in eukaryotic cells that use oxygen.

• Mitochondria are often referred to as the powerhouses of the cell.



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• Lysosomes are the sites for the digestion of substances taken into a cell.



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• Yet another membrane-enclosed structure is the highly folded, netlike endoplasmic reticulum (ER).

• The ER serves as an attachment site for ribosomes.

– The ribosomes are the sites where essential substances called proteins are made.



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What is a major difference between prokaryotic and eukaryotic cells?



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What is a major difference between prokaryotic and eukaryotic cells?

Eukaryotic cells are larger and more complex, containing membrane-enclosed organelles that perform specialized functions in the cells. Both eukaryotic and prokaryotic cells carry out similar chemical processes.



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The Energy and Carbon Cycle

What compound is reduced during photosynthesis? What compounds are formed?

The Energy and Carbon The Energy and Carbon CycleCycle



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Organisms must have energy to survive.


• The ultimate source of this energy is the sun.



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Cells of green plants and certain algae contain organelles called chloroplasts that are able to capture solar energy and make food.


• Within a chloroplast is a light-capturing system of membranes that converts light energy into chemical energy by a process called photosynthesis.



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6CO2 + 6H2O + Energy → C6H12O6 + 6O2


Carbon dioxide (carbon in more oxidized state)

Water from sunlight

Glucose (carbon in more reduced state)

Oxygen

Photosynthesis uses the energy from sunlight to reduce carbon dioxide to compounds that contain C—H bonds, mainly in the form of glucose (C6H12O6).



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In the energy and carbon cycle, photosynthetic organisms produce necessary carbon compounds.


• Animals, which do not carry out photosynthesis, get these carbon compounds by eating plants or by eating animals that feed on plants.



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Both plants and animals get energy by unleashing the energy stored in the chemical bonds of these carbon compounds.


• The nutrients are oxidized back to carbon dioxide and water in the process.

C6H12O6 + 6O2 → 6CO2 + 6H2O + EnergyCarbon dioxide (carbon in more oxidized state)

WaterGlucose (carbon in more reduced state)

Oxygen



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Although plant life could survive without animals, animal life could never survive without plants.


• Without photosynthesis, the supply of carbon compounds that animals need to get energy would not exist.



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Oxygen is another product of photosynthesis.




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• Photosynthetic land-dwelling and aquatic organisms produce the oxygen found in Earth’s atmosphere, oceans, and lakes.



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• Oxygen is needed for most organisms to live.



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• Oxygen is needed for most organisms to live.

• The importance of photosynthetic organisms is a major reason for the concern about the loss of such organisms through the destruction of forests.



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Fish, like all animals, need oxygen to survive. What process produces oxygen?




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Fish, like all animals, need oxygen to survive. What process produces oxygen?


During photosynthesis, plants use energy from sunlight, water, and carbon dioxide to produce oxygen.



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List the forms carbon takes in the carbon and energy cycle and explain what causes the transformations between forms.



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List the forms carbon takes in the carbon and energy cycle and explain what causes the transformations between forms.

Carbon dioxide is taken from the air by plants, which reduce it to glucose. Decomposers return carbon compounds from dead organisms to the soil and air. Glucose and other carbon compounds are reduced by plants, animals, and other living things to carbon dioxide.



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The two major cell types that occur in nature are prokaryotic cells and eukaryotic cells.

Photosynthesis uses sunlight to reduce CO2 to compounds that contain C—H bonds, mainly in the form of glucose.

Key ConceptsKey Concepts



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Glossary TermsGlossary Terms

photosynthesis: the process by which green plants and algae use radiant energy from the sun to synthesize glucose from carbon dioxide and water



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