Cell biology

• Eukaryotic cells contain their genetic material enclosed in a nucleus.
• Animal and plant cells have two other features which are unique to eukaryotic cells: a cell membrane and cytoplasm.
• Prokaryotic cells, such as bacteria, are different from eukaryotic cells as their genetic material is not enclosed in a nucleus.
• Prokaryotic cells are much smaller than eukaryotic cells.
• The genetic material of prokaryotic cells consists of a single loop of DNA.
• Prokaryotic cells may also have small wings of DNA which are called plasmids.
• Prokaryotic cells have a cell membrane and a cell wall.
• The cell membrane of prokaryotic cells is different from the cell membrane of eukaryotic cells.
• Prokaryotic cells contain cytoplasm.
• The size of cells is measured in units of the metre, but objects and biology are often much smaller than that.
• A German Shepherd is around 1 meter long, and if we divide 1 meter into 100 equal parts, we get 1 centimeter.
• The prefix centi means one hundredths, and one centimeter is one hundredth of a meter.
• Scientists often use standard form, where 1 centimeter is 1 times 10 to the power of minus 2 meters.
• The width of a ballpoint pen is around 1 millimeter, and the prefix milli means one thousandth, so one millimeter means one thousandth of a meter.
• A meter is 1,000 millimeters long, and in biology, one millimetre is pretty big, so scientists work with even smaller sizes.
• If we divide a meter into 1 million equal parts, we get a micrometer, and the prefix micro means one millionth, so one micrometer is one millionth of a meter.
• A typical human cell such as a red blood cell is around 10 to 20 micrometers in size, and biologists find a micrometer a very useful unit especially when looking at cells.
• Cells contain smaller parts such as ribosomes, and we'll look at those in a later video, which means that we need an even smaller unit to talk about the sizes of objects inside cells, the final unit we'll look at is called the nanometer, and the prefix nano means one billionth, so one nanometer is one billionth of a meter.
• Proteins and cells are measured using nanometers.
• Order of magnitude is a concept used by scientists to compare the approximate size of different objects.
• An apple and an orange are both around the same order of magnitude, despite not being the same size.
• A pineapple is around ten times larger than a lemon, making the pineapple one order of magnitude larger than the lemon.
• A dog is around 100 times longer than a woodlouse, making the dog two orders of magnitude longer than the woodlouse.
• The key idea behind order of magnitude is that every order of magnitude is ten times greater than the one before.
• To work out the order of magnitude, count the number of zeros in the number.
• Ten times is one order of magnitude, 100 times is two orders of magnitude, and 1000 times is three orders of magnitude.
• A fox is around 40 centimeters long, while a tick living on a fox is around 4 centimeters long.
• The Fox is two orders of magnitude longer than the tick, as there are two zeros in the number.
• Animal cells are eukaryotes, with their genetic material enclosed in a nucleus.
• The function of the nucleus is to enclose the genetic material.
• Nuclei are normally not that color inside the cell, but the cytoplasm is a watery solution where chemical reactions take place, including the first stage of respiration.
• The cell membrane controls the molecules that enter and leave the cell.
• Inside the cell, there are smaller structures called mitochondria, where cellular respiration takes place, and ribosomes, which are the sites of protein synthesis.
• In the exam, you could be asked to identify structures from a diagram of a cell such as the one shown.
• The structures in the diagram include the nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes.
• Plant cells have a regular shape unlike animal cells which can easily change their shape.
• Plant cells are packed full of green structures called chloroplasts which contain chlorophyll and other sites of photosynthesis.
• Plant cells are surrounded by a cell wall which is made from a chemical called cellulose and strengthens the cell.
• Plant cells contain a large permanent vacuole which is filled with a fluid called cytoplasm SAP because it's packed full of fluid the vacuole helps give the plant cell its shape.
• Plant cells have a regular shape unlike animal cells which can easily change their shape.