Biology

• 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 by moving molecules around all the time
• Maintenance processes in living organisms

  • Nutrition
  • Respiration
  • Transportation
  • Excretion
• Energy is needed for the maintenance processes to prevent damage and break-down
• 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
• Types of 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
• Organisms adapted to their environment

  • Whether the food source is stationary (such as grass) or mobile (such as a deer), would allow for differences in how the food is accessed and what is the nutritive apparatus used
• Strategies for obtaining and using food

  1. Break-down the food material outside the body and then absorb it

  2. Take in whole material and break it down inside their bodies

  3. Derive nutrition from plants or animals without killing them (parasitic nutritive strategy)
• What can be taken in and broken down depends on the body design and functioning
• Nutrition in single-celled organisms

  The food may be taken in by the entire surface
• Nutrition in Amoeba


  1. Temporary finger-like extensions of the cell surface fuse over the food particle forming a food-vacuole

  2. Complex substances are broken down into simpler ones which then diffuse into the cytoplasm

  3. Remaining undigested material is moved to the surface of the cell and thrown out
• Nutrition in Paramoecium


  1. Cell has a definite shape and food is taken in at a specific spot

  2. Food is 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
• What happens to food once it enters our body

  1. Crushing the food with teeth

  2. Wetting the food with saliva to make its passage smooth

  3. Breaking down complex food molecules with enzymes
• Saliva


  Contains an enzyme called salivary amylase that breaks down starch
• Movement of food through the digestive tract

  Peristaltic movements of the muscular lining of the canal push the food forward
• Digestion in the stomach

  1. Muscular walls mix the food thoroughly with digestive juices

  2. Gastric glands release hydrochloric acid, a protein digesting enzyme called pepsin, and mucus
• Function of hydrochloric acid

  Creates an acidic medium which facilitates the action of the enzyme pepsin
• Function of mucus


  Protects the inner lining of the stomach from the action of the acid under normal conditions
• Digestion in the small intestine

  1. Food enters from the stomach in small amounts

  2. Bile juice from the liver makes the food alkaline for pancreatic enzymes to act

  3. Bile salts break down large fat globules

  4. Pancreatic juice contains enzymes like trypsin and lipase

  5. Intestinal juice contains enzymes that convert proteins to amino acids, carbohydrates to glucose, and fats to fatty acids and glycerol
• Small intestine


  • Has numerous finger-like projections called villi which increase the surface area for absorption
  • Villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body
• Removal of unabsorbed food

  1. Sent into the large intestine where more villi absorb water

  2. Remaining material is removed from the body via the anus
• Dental caries causes gradual softening of enamel and dentine
• Dental caries begins when bacteria acting on sugars produce acids that softens or demineralises the enamel
• Masses of bacterial cells together with food particles stick to the teeth to form dental plaque
• Saliva cannot reach the tooth surface to neutralise the acid as plaque covers the teeth
• Brushing the teeth after eating removes the plaque before the bacteria produce acids
• If untreated, microorganisms may invade the pulp, causing inflammation and infection
• 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