bio

• Life processes


  Maintenance functions of living organisms that must go on even when they are not doing anything particular
• Living organisms must keep repairing and maintaining their structures made up of molecules
• Maintenance processes in living organisms

  • Nutrition
  • Respiration
  • Transportation
  • Excretion
• Energy is needed for maintenance processes to prevent damage and break-down
• Nutrition


  Process to transfer a source of energy from outside the body of the organism (food) to the inside
• Types of organisms based on nutrition

  • Autotrophs
  • Heterotrophs
• Autotrophs


  Organisms that use simple food material obtained from inorganic sources like carbon dioxide and water
• Heterotrophs


  Organisms that utilise complex substances and have to break them down into simpler ones before they can be used
• Photosynthesis


  1. Absorption of light energy by chlorophyll

  2. Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen

  3. Reduction of carbon dioxide to carbohydrates
• Chlorophyll is essential for photosynthesis
• Plants take up carbon dioxide through stomata on the leaf surface
• Plants take up water and other raw materials like nitrogen, phosphorus, iron and magnesium from the soil
• Strategies for heterotrophic nutrition


  • Breaking down food material outside the body and then absorbing it
  • Taking in whole material and breaking it down inside the body
  • Deriving nutrition from plants or animals without killing them (parasitic)
• Compounds which have been prepared by bacteria from atmospheric nitrogen
• Heterotrophic Nutrition


  The form of nutrition differs depending on the type and availability of food material as well as how it is obtained by the organism
• Examples of organisms with different nutritive strategies


  • Fungi like bread moulds, yeast and mushrooms (break-down food material outside the body and then absorb it)
  • Others (take in whole material and break it down inside their bodies)
  • Some organisms (derive nutrition from plants or animals without killing them, parasitic nutritive strategy)
• How organisms obtain their nutrition

  1. Food may be taken in by the entire surface (in single-celled organisms)

  2. As complexity increases, different parts become specialised to perform different functions

  3. Amoeba takes in food using temporary finger-like extensions of the cell surface which fuse over the food particle forming a food-vacuole

  4. Inside the food-vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm

  5. The remaining undigested material is moved to the surface of the cell and thrown out

  6. Paramoecium has a definite shape and food is taken in at a specific spot, moved to this spot by the movement of cilia which cover the entire surface of the cell
• Nutrition in Human Beings

  The alimentary canal is basically a long tube extending from the mouth to the anus, with different parts specialised to perform different functions
• What happens to food once it enters the human body

  1. Food is crushed with teeth to generate small particles of the same texture

  2. Food is wetted with saliva to make its passage smooth

  3. Saliva contains an enzyme called salivary amylase that breaks down starch

  4. Food is mixed thoroughly with saliva and moved around the mouth while chewing by the muscular tongue

  5. Peristaltic movements occur all along the gut to move the food in a regulated manner

  6. In the stomach, food is mixed thoroughly with digestive juices like hydrochloric acid and pepsin

  7. Hydrochloric acid creates an acidic medium which facilitates the action of pepsin, and protects the stomach lining

  8. Food exits the stomach in small amounts into the small intestine

  9. In the small intestine, complete digestion of carbohydrates, proteins and fats occurs with the help of enzymes from the liver and pancreas

  10. Bile juice from the liver makes the food alkaline and acts on fats

  11. Enzymes in the intestinal juice convert proteins to amino acids, carbohydrates to glucose, and fats to fatty acids and glycerol

  12. The digested food is absorbed by the villi in the small intestine, and transported to cells for energy, tissue building and repair

  13. Unabsorbed food enters the large intestine where more water is absorbed, and the rest is removed from the body via the anus
• Dental caries or tooth decay causes gradual softening of enamel and dentine, starting when bacteria acting on sugars produce acids that soften the enamel
• Brushing the teeth after eating removes the plaque before the bacteria produce acids
• The energy released during cellular respiration is immediately used to synthesise a molecule called ATP which is used to fuel all other activities in the cell
• ATP


  The energy currency for most cellular processes, released when the terminal phosphate linkage is broken using water
• Aerobic organisms need to ensure sufficient intake of oxygen for the aerobic respiration pathway
• Plants exchange gases through stomata, and the large inter-cellular spaces ensure that all cells are in contact with air
• Animals have evolved different organs for the uptake of oxygen from the environment and for getting rid of the carbon dioxide produced
• During the day


  CO2 generated during respiration is used up for photosynthesis, hence there is no CO2 release. Instead, oxygen release is the major event at this time.
• Animals


  • They have evolved different organs for the uptake of oxygen from the environment and for getting rid of the carbon dioxide produced
• Terrestrial animals


  They can breathe the oxygen in the atmosphere
• Aquatic animals


  They need to use the oxygen dissolved in water
• Activity 6.6


  1. Observe fish in an aquarium

  2. Count the number of times the fish opens and closes its mouth in a minute

  3. Compare this to the number of times you breathe in and out in a minute
• Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms
• How fish breathe


  They take in water through their mouths and force it past the gills where the dissolved oxygen is taken up by blood
• Terrestrial organisms


  • They use the oxygen in the atmosphere for respiration
  • They have organs with a structure that increases the surface area which is in contact with the oxygen-rich atmosphere
  • The exchange of oxygen and carbon dioxide has to take place across this surface, so it is very fine and delicate
  • This surface is usually placed within the body, so there have to be passages that will take air to this area
  • There is a mechanism for moving the air in and out of this area where the oxygen is absorbed
• Human respiratory system


  1. Air is taken into the body through the nostrils

  2. The air passing through the nostrils is filtered by fine hairs

  3. The passage is also lined with mucus

  4. The air passes through the throat and into the lungs

  5. Rings of cartilage are present in the throat to ensure the air-passage does not collapse

  6. Within the lungs, the passage divides into smaller and smaller tubes which finally terminate in balloon-like structures called alveoli

  7. The walls of the alveoli contain an extensive network of blood-vessels

  8. When we breathe in, we lift our ribs and flatten our diaphragm, and the chest cavity becomes larger as a result, causing air to be sucked into the lungs and fill the expanded alveoli

  9. The blood brings carbon dioxide from the rest of the body for release into the alveoli, and the oxygen in the alveolar air is taken up by blood in the alveolar blood vessels to be transported to all the cells in the body

  10. During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released
• When the body size of animals is large, the diffusion pressure alone cannot take care of oxygen delivery to all parts of the body. Instead, respiratory pigments take up oxygen from the air in the lungs and carry it to tissues which are deficient in oxygen before releasing it.
• Haemoglobin


  The respiratory pigment in human beings which has a very high affinity for oxygen and is present in the red blood corpuscles
• Carbon dioxide is more soluble in water than oxygen is and hence is mostly transported in the dissolved form in our blood.
• If the alveolar surface were spread out, it would cover about 80 m2. The surface area of the human body is much smaller, making the exchange of gases very efficient.
• If diffusion were to move oxygen in our body, it is estimated that it would take 3 years for a molecule of oxygen to get to our toes from our lungs. Haemoglobin makes this process much faster.