B2
Digestion
Molecules of life
Carbohydrates - source of energy, glucose is the main respiratory substrate
Protein - growth and repair
Lipids - Energy and essential for normal growth
Carbohydrates include sugars and starches
Starch is a polymer of glucose
Cellulose is also made of glucose and it makes up plant cell walls, so it makes up a part of our diet and cannot be digested so it is egested
Once absorbed into the body, glucose molecules are transported to cells and used for respiration or reassembled into the carbohydrate glycogen
Proteins are made of amino acids
Proteins are big molecules that are too large to pass through the gut wall and therefore need to be converted into amino acids
Once inside the body the amino acids are converted into the proteins that the individual needs in the process of protein synthesis and excess amino acids are broken down in the liver
Lipids are esters of fatty acid and glycerol
Lipids cannot pass through the gut wall and must be digested first
In body's cells they are reassembled into the lipids the body needs e.g. cell membrane
Food test practical
Benedicts reagent
Sugars - Add benedict's reagent to food and heat in a water bath
Will change (traffic light) colour when sugar is present - brick red if a lot of sugar is present and green if little sugar is present
Iodine
Starch - foods containing starch will show a black blue colour from brown when added to the food
Biurets reagent
Add 1 cm biurets A and mix the liquids and then add 1 cm biurets B a
Purple colour indicates a protein is present or a purple ring between layers
Sudan III
Fats/ lipids - Equal amounts food and water are added to a test tube, drops of Sudan III are added
A red stained layer will form on top of the mixture if lipids are present
Digestive system
Mouth - begins the digestion of carbohydrates
Stomach - begins the digestion of proteins and small molecules such as alcohol are absorbed
Small intestine (duodenum) - continues the digestion of carbs and proteins and starts the digestions of lipids
Small intestine (Ileum) - Completes the digestion of carbs and proteins into simple sugars and amino acids, absorbs simple sugars, amino acids, fatty acids, and glycerol
Large intestine - absorption of water and egestion of undigested food
Absorption is done by villi which are projections on the wall of the small intestine which allow for increased surface area meaning quicker and more efficient absorption
Digestive enzymes
Enzymes are biological catalysts - they speed up reactions
Each enzyme has an active site which only a specific substrate can fit into
Lock and key
Substrate collides with active site and becomes attached
Enzyme catalyses breakdown the of the substance
Products are released from the active site
Active site has a complementary shape to the substrate
The fit between an enzyme and substrate is like a lock and key
Enzyme molecule is unchanged and can be reused
Factors that effect
Temperature
Low temperatures - less collisions per second due to decreased kinetic energy so slow reaction
High temperatures - can denature the active site which means the substrate cannot fit into the active site
pH
Extreme pH differences can denature enzymes
Enzymes
Carbohydrase break down carbohydrates
The carbohydrase that breaks down starch is amalayse
Protease breaks down proteins
Lipase breaks own lipids
In the mouth and small intestine to break down into simple sugars and glucose
In the stomach and small intestine to break down into amino acids
In the small intestine to break down into fatty acids and glycerol
Circulatory system
Heart
Oxygenated blood
Pulmonary vein - Left atrium - Left ventricle - Aorta
Deoxygenated blood
Vena cava - Right atrium - Right ventricle - Pulmonary artery
Blood is prevented from flowing back by heart valves
Pumps blood around the body
Arteries carry blood away from the heart, veins carry blood towards the heart, capillaries flow very close to cells to enable substances to move between them
Lungs
Trachea - windpipe, air moves through
Bronchi - air from the trachea move here to flow to each lung
Alveoli - air sacs where gaseous exchange occurs
Upon gas exchange, alveoli fill with oxygen and the capillaries flow with deoxygenated blood and the oxygen moves down the concentration gradient into the blood
Plant tissues organs and systems
Epidermal tissue - covered with a waxy cuticle to prevent water loss to evaporation
Palisade mesophyll - lots of chloroplast for photosynthesis at the top of the leaf so it can happen rapidly
Spongy mesophyll - Lots of air space which allows gases to diffuse in and out
Xylem and phloem
Xylem
Found in the roots, stems and leaves
Made of dead cells joined together creating a continuous tube
Strengthened with lignin
Allows movement of water and mineral ions from the roots to the stem and leaves where it evaporates and leaves the plant (Transpiration)
Lignin is waterproof so water only leaves at specific places
Phloem
Elongated cells with holes in the cell walls
Food can be moved in both directions from either the leaves or roots from storage to wherei its needs (Translocation)
Meristematic tissue - can differentiate into different types of plant cell - allows plant to grow