Biology 2B

Biology 2B

1. Enzymes

   • how they work?
     • Enzymes are biological catalysts - substances that increase the rate of chemical reactions without being used up. Enzymes are proteins folded into complex shapes that allow smaller molecules to fit into them. The place where these substrate molecules fit is called the active site.
       • If the shape of the enzyme changes, its active site may no longer work. We say the enzyme has been 'denatured'.
   • As the temperature increases, so does the rate of reaction. But very high temperatures denature enzymes
   • Changes in pH also alter an enzyme’s shape. Different enzymes work best at different pH values. The optimum pH for an enzyme depends on where it normally works. For example, intestinal enzymes have an optimum pH of about 7.5. Enzymes in the stomach have an optimum pH of about 2.
   • bile
     • After the stomach, food travels to the small intestine. The enzymes in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach. A substance called bile neutralises the acid to provide the alkaline conditions needed in the small intestine. Bile is produced by the liver and stored in the gall bladder.

2. respiration

   • areobic
     • Respiration is a series of reactions in which energy is released from glucose. Aerobic respiration is the form of respiration which uses oxygen.
     • glucose + oxygen → carbon dioxide + water (+ energy)
       • energy is shown in brackets because it is not a substance. Notice that: Glucose and oxygen are used up Carbon dioxide and water are produced as waste products
     • Aerobic respiration happens all the time in the cells of animals and plants. Most of the reactions involved happen inside mitochondria
       • The reactions are controlled by enzymes.
     • Energy released during respiration is used by the organism in several ways. It may be used to build up larger molecules from smaller ones
       • Plants make amino acids from sugars, nitrates and other nutrients. These amino acids are then built up into larger molecules - proteins
     • Energy is used by animals to enable the muscles to contract so that the animals can move. Mammals and birds keep their body temperature steady. Energy from respiration is used to do this when their surroundings are colder than they are.
   • anaerobic
     • Not enough oxygen may reach the muscles during exercise. When this happens, they use anaerobic respiration to obtain energy. Anaerobic respiration involves the incomplete breakdown of glucose. It releases around 5% of the energy released by aerobic respiration, per molecule of glucose.
     • glucose → lactic acid (+ little energy)
       • The waste product is lactic acid rather than carbon dioxide and water
     • Muscle fatigue
       • Muscles become fatigued (tired) during long periods of vigorous activity. This means that they stop contracting efficiently. One cause of this is the build-up of lactic acid in the muscles from anaerobic respiration. The lactic acid is removed from the muscles by blood flowing through them.
     • fitness vs health
       • Fit people are able to carry out physical activities more effectively than unfit people. Their pulse rate is likely to return to normal more quickly after exercise. But being fit is not the same as being healthy. Healthy people are free from disease and infection - they may or may not be fit as well. It is possible to be fit but unhealthy, or healthy but unfit.

3. Cell division and inheritance

   • DNA & cell division
     • DNA (deoxyribose nucleic acid) molecules are large and complex. They carry the genetic code that determines the characteristics of a living thing. Except for identical twins, each person’s DNA is unique. This is why people can be identified using DNA fingerprinting. DNA can be cut up and separated, forming a sort of 'bar code' that is different from one person to the next
       • A gene is a short section of DNA. Each gene codes for a specific protein by specifying the order in which amino acids must be joined together.
         • The cell’s nucleus contains chromosomes made from long DNA molecules. The diagram shows the relationship between the cell, its nucleus, chromosomes in the nucleus, and genes.
     • Mitosis
       • The chromosomes contain the cell’s genetic information. They are normally found in pairs in body cells. Body cells divide by a process called mitosis.
         • When a body cell divides by mitosis: The genetic material is copied The cell divides once to form two genetically identical body cells Mitosis occurs during growth or to produce replacement cells.
     • stem cells
       • Stem cells can be made to differentiate to form different types of cell, such as nerve cells.
   • Inheritance