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In 1663, the English scientist Robert Hooke discovered cells in cork. This is a special Cells may be thought of as the building blocks of bark that is often used to stopper wine life, and come in an amazing variety of types and bottles and is similar to, but thicker than, sizes. Skin, muscles, blood and plants are all made up the paper-like bark that you often find on of different types of cells. Most cells are so small that context trees in the park or school grounds. hundreds would fit on a full stop. Our bodies contain over a hundred million, million cells. An example of a very large cell is a hen’s egg. Discovering cells A hen’s egg—a really big cell! Fig 4.2.2 Using an early microscope, Hooke studied many different objects including feathers, the stinger of a bee and the foot of a fly. When he placed a thin strip of cork under his microscope he saw empty box-like shapes that he thought looked like the small rooms, or cells, occupied by monks of the time. It was logical then to call these box-like shapes cells too. It was not until nearly 200 years later, in 1839, that German biologists Theodor Schwann and Matthias Schleiden proposed the cell theory of life. This theory states: 1 All living things, or organisms, are made up of cells. 2 New cells are created by old cells dividing in two. 3 All cells are similar to each other, but not identical.

The simplest type of cell is a bacterial cell. Bacteria (sometimes called germs) are Robert Brown again tiny cells that can have Robert Brown, in 1831, was either good or bad effects. the first biologist to observe the cell nucleus and There are different types of discover that it was in all bacteria that help us digest plant cells. This is the same food, break down dead plants Robert Brown mentioned in and animals in soil, and Chapter 2 who used the microscope to discover Hooke’s first sketch showing ‘cells’ in cork Fig 4.2.1 cause disease. Brownian motion. 94 44..22

Three different types of bacteria Fig 4.2.3 UNIT cell membrane UNIT cocci

vacuole

cell nucleus

cytoplasm

mitochondrion bacilli (not normally visible)

Fig 4.2.5 A diagram of an animal cell showing the main organelles

spirilla Animal cells Cells from animals such as humans, pigs or frogs have several organelles in common. Cells from cells? 1 Cell membrane—this is a Until 1855 it was thought that cells could thin, flexible outer layer that appear spontaneously encases the cell and controls from anywhere. Then what goes in or comes out. a German physician, Rudolph Virchow, found 2 Cytoplasm—this jelly-like that living cells can liquid fills most of the cell only come from other and contains hundreds of living cells through reproduction. different chemicals. New flagellum substances are made and cytoplasm energy is released and stored here. Think of the cytoplasm as the chemical factory of the cell. 3 Vacuoles—these are storage areas that may contain air, water, wastes and food particles. Animal cells often contain several small vacuoles. 4 Cell nucleus—this is the ‘control room’ of the cell containing the genes composed of DNA. Each gene contains the information responsible for the cell membrane cell wall production of chemicals. These chemicals control chemical reactions in a cell, and how the cell develops and functions. The genes contain instructions in chemical codes for building new cells. Fig 4.2.4 A diagram of a bacterium showing 5 Mitochondria—these small objects may be thought its main features of as energy capsules. Each mitochondrion uses sugar and oxygen in a series of chemical reactions to release energy. Mitochondria are so small that There are two main types of cells—animal and they cannot usually be seen using a light plant cells. Each cell is made up of parts called microscope. Mitochondria were first described in organelles. Each organelle does a separate job inside muscle cells by Rudolph von Kolliker, a Swiss the cell. anatomist and physiologist, in 1857.

95 Plant and animal cells >>>

a green chemical, chlorophyll, which traps the light energy plants need for photosynthesis. The cell wall contains a tough fibrous material called cellulose and provides the support needed by the plant cell. Plant cells contain a single large vacuole filled with cell sap.

Worksheet 4.1 Cell diagrams Prac 1 p. 98 Fig 4.2.8 Plant cells

Fig 4.2.6 Stained human cheek cells Plant cells As stated in the cell theory, all cells are similar but not identical. Plant cells have several features in common with animal cells, but there are also some differences. Unlike animals, plants need to make their own People in science food with the help of sunlight, carbon dioxide and water. They do this in a process known as Theodor Schwann (1810–1882) photosynthesis. Photosynthesis occurs in organelles Theodor Schwann was a German physiologist who called chloroplasts inside leaf cells. Chloroplasts may said that the cell was the basic unit of an animal’s be seen using a light microscope. Chloroplasts contain structure. In 1836, while investigating digestion, he isolated a substance responsible for digestion in A plant cell showing the main organelles Fig 4.2.7 the stomach and named it pepsin. He also observed the formation of yeast spores and said that the fermentation of sugar and starch was the result of large vacuole cell wall containing yeast reproduction. In 1839 Schwann extended chloroplast cell sap Matthias Schleiden’s work on plant cells to include animal cells. Together they proposed the cell theory of life. Schwann was the first to use the term ‘metabolism’ for the chemical changes that take place in living tissue. Schwann also observed that an egg is a single cell that eventually develops into a complete organism. cell nucleus cell membrane mitochondrion

96 44..22 . Questions [ ] UNIT 4 2 UNIT

Checkpoint 17 The digestive systems of sheep, cows and rabbits contain special bacteria which help break down a Discovering cells substance found in cell walls that humans are unable

UNIT 1 Identify who first used the term ‘cell’ to describe the to break down. State which substance this might be. small structures in a slice of cork. 2 State when Schwann and Schleiden proposed the Analyse cell theory. 18 Construct a table like the one shown here to compare 3 Write three points to briefly describe the cell theory. animal and plant cells. Make sure you include some 4 Identify the simplest type of cell. similarities and some differences. Animal cells 5 Identify the part of a cell that could be called: Feature Animal cell Plant cell a the ‘control room’ b the ‘chemical factory’ c the ‘gatekeeper’ d the ‘powerhouse’ e the ‘walls’ 19 Plant cells need to have thicker walls than animal cells. 6 Identify three types of body cells. Explain why. Plant cells 20 Explain why there are fewer types of plant cells than 7 Identify the green substance in plant cells and state animal cells. its function. 8 Clarify the following terms related to plant cells: a photosynthesis b cell wall [ Extension] c cellulose 9 Identify three differences between plant and animal Create cells. 1 Construct a 2D or 3D model of a plant or animal cell Think using any materials you can find. 10 Compare an organelle in a cell to an organ in the Investigate human body. How similar are they in what they do? 11 Clarify the term ‘organism’. 2 Investigate the dates of key discoveries relating to the microscope and cells. Include those covered in this 12 Identify how big cells are. chapter and others that you research. Draw a time line 13 State how many cells our bodies are thought to using this information. contain. 14 Draw a diagram of an animal cell and a plant cell side Surf by side. Compare the cells by labelling the parts that 3 The confocal microscope is currently being are common to both with one label. developed by an Australian company. 15 Muscle cells contain large numbers of mitochondria. Investigate this new type of microscope Explain this observation. and how it may be used to observe skin cells 16 Identify the contents of a vacuole if it is in a: without the removal of skin from the body. a plant cell Make your investigation easier by connecting to the b animal cell Science Focus 1 Companion Website at www.pearsoned.com.au/schools, selecting chapter 4, and clicking on the destinations button.

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