Appendix

Interesting facts about…

Human Body

- The largest cell in the human body is the female egg and the smallest is the male sperm.

- A full bladder is roughly the size of a soft ball.

- Approximately 75% of human faeces is made of water.

- It takes the food seven seconds to get from your mouth to your stomach.

- One human hair can support 3 kg.

- Human thighbones are stronger than concrete.

- The attachment of human muscles to skin is what causes dimples.

- Your thumb is the same length of your nose.

- A woman's heart beats faster than a man's.

- If the average male never shaved, his beard would be 13 feet long when he died.

- Men without hair on their chests are more likely to get cirrhosis of the liver than men with hair.

- There are about one trillion bacteria on each of your feet.

- Side by side, 2000 cells from the human body could cover about one square inch.

- Women blink twice as much as men.

- The average person's skin weighs twice as much as his brain.

- When you are looking at someone you love, your pupils dilate, they do the same

when you are looking at someone you hate.

- It takes twice as long to lose new muscle if you stop working out than it did to gain it.

- Your ears secrete more earwax when you are afraid than when you aren't.

- Your body uses 300 muscles to balance itself when you are standing still.

- If saliva cannot dissolve something, you cannot taste it.

- The average woman is 5 inches shorter than the average man.

The Journey into the Cell

Life is both wonderful and majestic. Yet for all of its majesty, all organisms are composed of the fundamental unit of life, the cell. The cell is the simplest unit of matter that is alive. From the unicellular bacteria to multicellular animals, the cell is one of the basic organizational principles of biology.

There are two primary types of cells: eukaryotic cells and prokaryotic cells. Eukaryotic cells are called so because they have a true nucleus. The nucleus, which houses DNA, is contained within a membrane and separated from other cellular structures. Prokaryotic cells however have no true nucleus. DNA in a prokaryotic cell is not separated from the rest of the cell but coiled up in a region called the nucleoid.

As organized in the Three Domain System, prokaryotes include archaeans and bacteria. Eukaryotes include animals, plants, fungi and protists. Typically, eukaryoitc cells are more complex and much larger than prokaryotic cells. On average, prokaryotic cells are about 10 times smaller in diameter than eukaryotic cells.

Eukaryotes grow and reproduce through a process called mitosis. In organisms that also reproduce sexually, the reproductive cells are produced by a type of cell division called meiosis. Most prokaryotes reproduce through a process called binary fission. During binary fission, the single DNA molecule replicates and the original cell is divided into two identical daughter cells. Both eukaryotic and prokaryotic organisms get the energy they need to grow and maintain normal cellular function through cellular respiration. Cellular respiration has three main stages: glycolysis, the citric acid cycle, and electron transport. In eukaryotes, most cellular respiration reactions take place within the mitochondria. In prokaryotes, they occur in the cytoplasm and/or within the cell membrane.

The body is composed of many different types of cells, each with its own structure and function. Some, such as white blood cells, move freely, unattached to other cells. Others, such as muscle cells, are firmly attached one to another. Some cells, such as skin cells, divide and reproduce quickly; others, such as nerve cells, do not divide or reproduce except under unusual circumstances. Some cells, especially glandular cells, have as their primary function the production of complex substances, such as a hormone or an enzyme.

For example, some cells in the breast produce milk, some in the pancreas produce insulin, some in the lining of the lungs produce mucus, and some in the mouth produce saliva. Other cells have primary functions that are not related to the production of substances, for example, muscle cells contract, allowing movement. Nerve cells generate and conduct electrical impulses, allowing communication between the central nervous system (brain and spinal cord) and the rest of the body.