SUMMARY OF UNIT 1 – CELLS
Key Area 1 – Cell Division and its role in growth & repair
All cells have a nucleus, cytoplasm and a cell membrane. Plant cells have three additional features: a cell wall, a vacuole and chloroplasts.
All new cells are made by existing cells dividing in two. Cell Division is important because:
a) It produces new cells for growth and repair in multi-cellular organisms (e.g mending cuts and broken bones)
b) It allows single celled organisms to reproduce (e.g bacteria & fungi)
During cell division, the parent cell divides to produce two identical cells, which contain the same number of chromosomes in their nuclei as the parent cell. Cancer is caused by uncontrolled cell division.
Key Area 2 – DNA, genes and chromosomes
Genes are located on chromosomes in the nucleus. Genes are made of DNA which carries the instructions to make proteins.
Key Area 3 – Therapeutic uses of cells
Genetic engineering involves the transfer of one or more genes from one organism (e.g human) to another organism (e.g bacterium). The diagram below shows the process of genetic engineering.
Other therapeutic uses of cells are the use of stem cells. Stem cells are cells that can make copies of themselves and can differentiate in many different types of cell. Stem cells are currently being used to grow new skin for burn victims. In the future they will hopefully be able to help scientists test new drugs, understand diseases and help find new treatments for diseases.
Key Area 4 – Properties of enzymes and use in industries
Enzymes are not living, they are chemicals made of protein. Enzymes speed up chemical reactions but are not used up or altered during the reaction so can be used again and again. Without enzymes, reactions that take place in living organisms (for e.g photosynthesis) would not occur fast enough to support life.
The substance an enzyme acts upon is called its substrate and what is made as a result of the enzyme reaction is the product. For e.g
Enzyme / Substrate / ProductAmylase / Starch / Maltose
Catalase / Hydrogen Peroxide / Water & Oxygen
Phosphorylase / Glucose / Starch
Enzymes are very specific, only working on one substrate. They come together with their substrate like a lock and key.
Key Area 5- Properties of microganisms and use in industries
Micro-organisms (bacteria and yeast) can be very useful in industry as they grow rapidly, have a wide food source and can make a lot of useful products.
Bacteria Industries
1) Yoghurt. The bacteria feed on the sugar in milk (lactose) and change it into lactic acid which causes the milk to clot forming yoghurt.
2) Cheese. Cheese making bacteria along with rennet cause milk to curdle into solid curds making cheese.
3) Treating sewage. Bacteria are used at the sewage works to break down harmful waste into harmless liquid that can be released back into water ways.
4) Biofuel. When bacteria feed on sewage in the absence of oxygen, methane is produced which can be collected and used as a fuel.
Yeast Industries
1) Bread. When yeast feeds on sugar in the absence of oxygen it produces carbon dioxide. When yeast is added to dough in baking, the carbon dioxide causes the dough to rise.
2) Brewing. When yeast feeds on sugar in the absence of oxygen it also produces ethanol. Yeast is therefore used in the brewing industry to make alcohol.
Key Area 6 – Photosynthesis – limiting factors
Photosynthesis:
Some of the glucose produced during photosynthesis is stored as starch. To test to see if photosynthesis has taken place in a plant, leaves can be tested for starch with iodine solution. Photosynthesis cannot work without carbon dioxide, water, light and a suitable temperature. If any of these is in short supply they are said to be ‘limiting factors’.
Key Area 7 – Factors affecting Respiration
Respiration is the process by which energy is released from food. There are two types.
Aerobic respiration in all cells (in the presence of oxygen)
Glucose + Oxygen Carbon Dioxide + Water + Energy
Anaerobic respiration in animals (in the absence of oxygen)
Glucose Lactic acid + Energy
Animals would undergo anaerobic respiration during intense exercise when they cannot get enough oxygen into their bodies to meet their needs. When lactic acid builds up in muscles it causes fatigue. You may have experienced this as muscle soreness and lack of strength during intense activity.
Anaerobic respiration in plants & yeast (in the absence of oxygen)
Glucose Carbon Dioxide + Ethanol + Energy
The products of anaerobic respiration in yeast are utilised in baking and brewing as described earlier.
Factors affecting respiration
Key Area 8 – Controversial biological procedures
You need to have knowledge of at least one controversial biological procedure and the pros and cons of its use. One example is Gene Therapy. Gene therapy is when defective genes are substituted for normal genes. One advantage of this technique is that rather than just treating the symptoms of a disease with drugs, replacing the defective gene provides a cure. One disadvantage is that is has the potential to be mis-used, for e.g the creation of ‘designer babies’.