1. A compound light microscope has two lens systems: the objective lens and the ocular or eyepiece lens.
Section 4.01
A compound light microscope has two lens systems: the objective lens and the ocular or eyepiece lens.

2. A compound light microscope has two lens systems: the objective lens and the ocular or eyepiece lens.
Section 4.01
A compound light microscope has two lens systems: the objective lens and the ocular or eyepiece lens.

3. A transmission electron microscope
A transmission electron microscope. The beam of electrons is emitted from an electron gun, a heated filament. Electromagnets bend the beam.
Section 4.01
A transmission electron microscope. The beam of electrons is emitted from an electron gun, a heated filament. Electromagnets bend the beam.

4. A transmission electron microscope
A transmission electron microscope. The beam of electrons is emitted from an electron gun, a heated filament. Electromagnets bend the beam.
Section 4.01
A transmission electron microscope. The beam of electrons is emitted from an electron gun, a heated filament. Electromagnets bend the beam.

5. The sizes of various biological structures.
Section 4.01

6. The sizes of various biological structures.
Section 4.01

7. Freeze-fracturing. An artist’s impression of how freeze-fracturing splits the bilipid layer of a cell surface membrane to reveal proteins embedded within the membrane.
Section 4.02
(a) Freeze-fracturing. An artist’s impression of how freeze-fracturing splits the bilipid layer of a cell surface membrane to reveal proteins embedded within the membrane.

8. Freeze-fracturing. An artist’s impression of how freeze-fracturing splits the bilipid layer of a cell surface membrane to reveal proteins embedded within the membrane.
Section 4.02
(a) Freeze-fracturing. An artist’s impression of how freeze-fracturing splits the bilipid layer of a cell surface membrane to reveal proteins embedded within the membrane.

9. A scanning electron micrograph of a freeze-fracture cell surface membrane. The spherical structures are thought to be proteins.
Section 4.02
(b) A scanning electron micrograph of a freeze-fracture cell surface membrane. The spherical structures are thought to be proteins.

10. A drawing of one of the plates that used to support the theory that plants and animals are made of similar cells, a theory that unified the sciences of botany and zoology. Numbers 1, 2, 3, and 14 are from plants, the other from animals. From Mikroskopische Untersuchungen, by Theordor Schwann, published in 1839.
Section 4.03
A drawing of one of the plates that used to support the theory that plants and animals are made of similar cells, a theory that unified the sciences of botany and zoology. Numbers 1, 2, 3, and 14 are from plants, the other from animals.

11. A drawing of one of the plates that used to support the theory that plants and animals are made of similar cells, a theory that unified the sciences of botany and zoology. Numbers 1, 2, 3, and 14 are from plants, the other from animals. From Mikroskopische Untersuchungen, by Theordor Schwann, published in 1839.
Section 4.03
A drawing of one of the plates that used to support the theory that plants and animals are made of similar cells, a theory that unified the sciences of botany and zoology. Numbers 1, 2, 3, and 14 are from plants, the other from animals.

12. Drawing of four cells from the epithelium of the small intestine seen with a light microscope.
Section 4.04
Drawing of four cells from the epithelium of the small intestine seen with a light microscope.

13. Drawing of four cells from the epithelium of the small intestine seen with a light microscope.
Section 4.04
Drawing of four cells from the epithelium of the small intestine seen with a light microscope.

14. Photomicrograph of some cells from the epithelium lining the small intestine. The small intestine is a tubular organ lined mainly with simple columnar epithelium. Scattered throughout the simple columnar cells are goblet cells that secrete mucus. Columnar epithelial cells form a single layer. The free surface of the columnar cell has tiny projections called a ‘brush border’, because they appear under the light microscope like the bristles of a brush. These are microscopic folds of the upper part of the plasma membrane (the membrane covering the surface of the cell) and are called microvilli. They increase the surface area for absorption.
Photo credit: P64 (bottom) Peter Arnold, Inc./Alamy.
Section 4.04
Photomicrograph of some cells from the epithelium lining the small intestine. The small intestine is a tubular organ lined mainly with simple columnar epithelium. Scattered throughout the simple columnar cells are goblet cells that secrete mucus. Columnar epithelial cells form a single layer. The free surface of the columnar cell has tiny projections called a ‘brush border’, because they appear under the light microscope like the bristles of a brush. These are microscopic folds of the upper part of the plasma membrane (the membrane covering the surface of the cell) and are called microvilli. They increase the surface area for absorption.

15. Electron micrograph showing ultrastructure of the micovilli of an intestinal columnar epithelial cell.
Photo credit: P65 Dennis Kunkel/Phototake Inc/Photolibrary.
Section 4.04
Electron micrograph showing ultrastructure of the micovilli of an intestinal columnar epithelial cell.

16. A columnar epithelial cell showing ultrastructures visible under an electron microscope.
Section 4.05
A columnar epithelial cell showing ultrastructures visible under an electron microscope.

17. A columnar epithelial cell showing ultrastructures visible under an electron microscope.
Section 4.05
A columnar epithelial cell showing ultrastructures visible under an electron microscope.

18. A transmission electron micrograph of part of the nucleus of an animal cell. The membrane system leading to the nucleus consists of rough endoplasmic reticulum characterized by ribosomes which appear as black dots.
Photo credit: P67 Science Photolibrary.
Section 4.05
A transmission electron micrograph of part of the nucleus of an animal cell. The membrane system leading to the nucleus consists of rough endoplasmic reticulum characterized by ribosomes which appear as black dots.

19. A transmission electron micrograph of mammalian smooth endoplasmic reticulum (magnification 12 000).
Photo credit: P67 Science Photolibrary.
Section 4.05
A transmission electron micrograph of mammalian smooth endoplasmic reticulum (magnification ).

20. False-coloured scanning electron micrograph of a mitochondrion (magnification 20 000).
Photo credit: P68 Telegraph Colour Library.
Section 4.06
False-coloured scanning electron micrograph of a mitochondrion (magnification ).

21. False-coloured transmission electron micrograph of Golgi apparatus (magnification 16 000).
Photo credit: P68 Telegraph Colour Library.
Section 4.06
False-coloured transmission electron micrograph of Golgi apparatus (magnification ).

22. Transmission electron micrograph showing a lysosome (magnification ). The lysosome (red) is a simple spherical sac bound by a single membrane.
Photo credit: P69 Telegraph Colour Library.
Section 4.06
Transmission electron micrograph showing a lysosome (magnification ). The lysosome (red) is a simple spherical sac bound by a single membrane.

23. A nematode worm in which you can see the individual cells.
Photo credit: P69 (bottom right) Sinclair Stammers/Science Photo Library.
Section 4.06
A nematode worm in which you can see the individual cells.

24. Cell fractionation: the preparatory stages.
Section 4.07

25. Cell fractionation: the preparatory stages.
Section 4.07

26. Cell fractionation: by differential centrifugation.
Section 4.07

27. Cell fractionation: by differential centrifugation.
Section 4.07

28. Cell fractionation: by density gradient centrifugation.
Section 4.07

29. Cell fractionation: by density gradient centrifugation.
Section 4.07