Additional Biology Topic 3

Additional Biology Topic 3

1. Evidence for Evolution

   • Fossils
     • They can be formed in 3 ways: From gradual replacement by minerals. Things like bones don't decay easily. They are eventually replaced by minerals, and form a rock-like substance, shaped like the original hard-part. They can also be formed by casts and impressions. This is when an organism is buried in a soft material like clay. They clay hardens around it and the organism decays leaving a cast of itself. The last way is from preservation, where the conditions aren't suitable for microbes to work, so the organism doesn't decay.
     • Fossils tell us what the creatures looked like, how long ago they existed and how they've evolved.
     • The fossil record is incomplete because very few dead plants and animals actually turn into fossils, some body parts decay completely and there are fossils yet to be discovered.
   • The pentadactyl limb provide evidence for evolution.
     • This is a limb with 5 digits.
     • This is found in many species. In these species, the pentadactyl limb has similar bone structures, but usually a different function. This proves that species with a pentadactyl limb have all evolved from a common ancestor.

2. Growth and Development

   • Growth is an increase in size and mass. Wet mass is the mass of an organism including all the water in its body. Dry mass is the mass of an organism with no water in its body. This can only be measured once the organism is dead.
   • Growth involves cell differentiation, division and elongation. Cell differentiation is when a cell changes to become a specialised cell. Cell division is by mitosis. Cell elongation is where a cell expands, making the cell bigger. This is only in plants.
   • Percentile charts are used to assess a child's growth over time, so an overall pattern in development can be seen.

3. Cell Organisation and the Circulatory System

   • Cells make up tissues, organs and systems.
     • A tissue is a group of similar cells that work together to carry out a particular function.
     • An organ is a group of different tissues that work together to perform a particular function.
     • A system is a group of organs working together to perform a particular function.
   • The heart has four chambers and four major blood vessels.
     • The right atrium receives deoxygenated blood from the body through the vena cava. This then moves to the right ventricle, which pumps it to the lungs through the pulmonary artery
     • The left atrium receives oxygenated blood from the lungs through the pulmonary vein. this then moves to the left ventricle which pumps the blood around the whole body through the aorta.
     • Valves prevent the backflow of blood.

4. The Circulatory System

   • Blood
     • Red blood cells carry oxygen from the lungs to all the cells in the body. They have a biconcave disc shape, which gives them a large surface area for absorbing oxygen. They contain haemoglobin, which contains a lot of iron. They don't have a nucleus, so it allows more room for haemoglobin.
     • White blood cells defend against disease. They can change shape to "gobble" up unwelcome microorganisms. They produce antibodies to fight the microorganisms and antitoxins to neutralise any toxins produced by the microorganisms.
     • Platelets are small fragments of cells. They help blood to clot a wound. This helps to stop blood loss and microorganisms getting in.
     • Plasma is the liquid that carries everything in the blood.
   • Blood Vessels
     • Arteries carry blood away from the heart under pressure.The artery walls are strong and elastic. They contain thick layers of muscle to make them strong.
     • Capillaries are involved with the exchange of materials with the tissues. Arteries branch into capillaries. Capillaries are one cell thick, so they can carry blood really close to every cell in the body to exchange substances with them. They have a permeable wall, so substances can diffuse in and out. They supply fodd and oxygen and take away waste like carbon dioxide.
     • Veins take the blood back to the heart. The walls aren't as thick as the arteries, since the blood is at a lower pressure. They have valves to help keep the blood flowing in the right direction.

5. Digestion

   • Enzymes
     • Carbohydrases digest starch to sugars.
     • Proteases digest proteins to amino acids.
     • Lipases digest fat to fatty acids and glycerol.
   • Mouth - The food is moistened with saliva. The amylase enzyme breaks down the food. The tongue makes the food into a ball (bolus), before swallowing.
   • Oesophagus - A tube which takes the food from the mouth to the stomach. The food is moved along by peristalsis.
   • Stomach - The enzyme pepsin, is a protease enzyme. The stomach produces hydrochloric acid to kill bacteria and give the right pH for pepsin.
   • Liver - Bile is produced here and stored in the gall bladder. It emulsifies fat and neutralises stomach acid.
   • Pancreas - Produces enzymes which are released into the small intestine.
   • Small Intestine - Food is absorbed into the blood stream from the digestive system.
   • Large Intestine - Excess water is absorbed for the food.
   • The faeces is stored in the rectum to be egested.
   • Peristalsis
     • Longitudinal muscles down the length of the gut and circular muscles running in circles around the gut squeeze food along. The circular muscles push the food along the gut and the longitudinal muscles run ahead to keep the food in a ball.
   • Villi
     • They are on the inside of the small intestine.
     • They have a big surface area, so digested food is absorbed into the blood quicker.
     • They have a single layer, so the digested food diffuses quicker over a short distance.
     • They have a very good blood supply, via capillaries to assist quick absorption of digested food.

6. Functional Foods

   • Probiotics - These are live bacteria such as bifidobacteria and lactobacillus. They are found in foods such as yogurts and they are thought to keep your digestive system healthy and your immune system strong.
   • Prebiotics - They are carbohydrates that we can't digest. E.g. oligosaccharides. They occur naturally in foods like onions and leeks. They are food supply for the good bacteria in your gut, which could improve the health of your digestive system.
   • Plant Stanol Esters - They can help to lower cholesterol and reduce the risk of heart disease. They occur naturally in plants. They can be used in spreads and dairy products.