Cells are the basic building blocks of all living organisms.
A tissue is a group of cells with a similar structure and function.
Organs are groups of tissues performing specific functions.
Organ systems are groups of organs which work together to form organisms.
Organisms are groups of organ systems which work together
The digestive system is an example of an organ system in which several organs work together to digest and absorb food.
Organs: glands, stomach, small intestine, large intestine, liver.
Glands: produce digestive juices with enzymes to break down food.
Stomach: produces HCl to kill bacteria.
Small intestine: soluble molecules absorbed into blood.
Liver: produces bile, stored in gall bladder.
Large intestine: absorbs water from undigested food and produces faeces.
Bile: alkaline to neutralise hydrochloric acid in the stomach. It emulsifies fat to form small droplets and increases the surface area. The alkaline conditions and large surface area speeds up the breakdown of fat.
Enzymes: biological catalysts (increases rate of reaction without being used up).
The lock and key theory: the shapes of the substrate and active site must match for a reaction to take place. Enzymes require an optimum temperature (37o) and pH (7). If conditions aren't optimal, the enzyme gets denatured.
Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream.
Carbohydrases break down carbohydrates to simple sugars e.g. Amylase is a carbohydrase which breaks down starch.
Proteases break down proteins to amino acids.
Lipases break down lipids (fats) to glycerol and fatty acids. Works better with the high pH and high surface area.
The products of digestion are used to build new carbohydrates, lipids and proteins. Some glucose is used in respiration.
Benedict's test: sugars (turns brick red)
Iodine test: starch (purple)
Biuret test: protein (turns purple)
Emulsion test: lipids (add ethanol and it turns cloudy)
Sudan III test: lipids (red layer on top)
Heart: an organ that pumps blood around the body in a double circulatory system.
Right ventricle: pumps blood to the lungs where gas exchange takes place.
Left ventricle pumps blood around the rest of the body.
Deoxygenated blood flows into the right atrium then right ventricle then lungs for gas exchange.
Oxygenated blood flows to the left atrium then left ventricle then the rest of the body.
Heart structure: muscular walls (strong heartbeat, left is thicker), valves (stop blood flowing backwards), coronary artery (covers the heart and provides its own blood supply)
The ventricles contract, pushing blood. Then the valves close.
Blood vessels: tubes which carry the blood around the body.
Arteries: carry blood away from the heart and split up into tiny blood vessels called the capillaries. Thick walls, small passageways, high pressure.
Capillaries: where gas exchange takes place. These then join together to form veins. Thin walls, large lumen, low pressure, valves.
Veins: carry blood in towards the heart.
From the vena cava, blood enters the right atrium, then a valve to the right ventricle then to the pulmonary artery.
From there it moves to the lungs.
From the lungs, oxygenated blood is returned to the heart through the pulmonary veins.
Then, blood is forced into the left atrium, then into the left ventricle.
From the left ventricle, the blood passes a valve into the aorta then to the rest of the body.
The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker. Artificial pacemakers are electrical devices used to correct irregularities in the heart rate.