Chapter 4

• How much of our blood is made up of red blood cells? What is their job?


  Red blood cells make up about half of our blood by volume. Their job is to carry oxygen from our lungs to our body tissues
• How are red blood cells adapted to their function?


  -they have a biconcave shape to give them a large surface area for absorbing oxygen.

  -they contain haemoglobin (a red pigment) which carries oxygen

  -they don't have a nucleus which allows more room for haemoglobin meaning they can carry more oxygen
• How is oxygen transported in the blood?


  -In the lungs, oxygen diffuses into the blood. The oxygen combines with haemoglobin in red blood cells to become oxyhaemoglobin

  -In body tissues, oxyhaemoglobin splits up into haemoglobin and oxygen, to release oxygen to the cells
• How much of our blood is made up of white blood cells? What is their job?

  White blood cells make up less than one percent of our blood. Their job is to defend against microorganisms that cause disease

  -they can engulf unwelcome microorganisms and digest them

  -they can produce antibodies to fight microorganisms

  -they can produce antitoxins to neutralise any toxins produced by the microorganisms
• What are platelets? What is their job?


  Platelets are tiny fragments of cells and have no nucleus.

  They help blood to clot at a wound. Clotting also prevents microorganisms from getting in at the wound. A lack a platelets can cause excessive bleeding and bruising
• What is plasma? What is its function?


  Plasma is a yellow liquid that transports all of your blood cells and hormones, proteins, carbon dioxide and nutrients around the body
• What is artificial blood?


  Artificial blood is a blood substitute that is usually made of salt solution. It adds volume to the circulatory system which allows the heart to keep pumping. However only 1/3 of our blood can be replaced by it
• What are arteries?


  Blood vessels that carry blood away from the heart
• How are arteries adapted to their function?


  - they have thick layers of muscle to make them strong enough to withstand the high pressure at which they carry blood

  - they have strong elastic fibres to allow them to stretch and spring back
• What are capillaries?


  Arteries branch off into capillaries. Capillaries are involved in exchanging materials at the tissue. They supply food and oxygen to the cells and take away waste products like carbon dioxide.
• How are capillaries adapted to their function?


  - they have permeable walls so that substances can diffuse in and out

  - their walls are only one cells thick which increases the rate of diffusion by decreasing the distance over which it occurs

  - capillaries are really close to every cell in the body to exchange surfaces with them
• What are veins?


  Capillaries join up to form veins. Veins carry blood to the heart
• How are veins adapted to their function?


  - the walls are not thick as blood is not carried at a low pressure

  - they have a big lumen to help blood flow

  - they have valves to keep blood flowing in the right direction
• How do you calculate the rate of blood flow?

  Rate of blood flow = volume of blood / number of minutes
• What is the function of the circulatory system?

  To circulate food and oxygen through the body and to remove wastes such as carbon dioxide and urea
• What is a double circulatory system?


  A double circulatory system is made up of two circuits joined together.

  -in the first circuit, the right ventricle pumps deoxygenated blood to the lungs to take in oxygen. The blood then returns to the heart

  -in the second circut, the left ventricle pumps oxygenated blood around all the organs of the body. the blood gives the oxygen to the body cells and the deoxygenated blood returns to the heart
• What is a heart?

  The heart is a pumping organ that keeps the blood flowing around the body. The walls of the heart are mostly made of muscle tissue, which contracts to pump blood.
• Describe the structure of the heart?


  The heart has four chambers with thick muscular walls surrounding them. The top chambers are called atria and the bottom chambers are called ventricles. Between the chambers are valves that prevent the backflow of blood.
• Describe blood flow through the heart


  1)Blood flows into the two atria from the vena cava (right) and the pulmonary vein (left)

  2)The atria contract, pushing the blood into the ventricles

  3)The ventricles contract forcing the blood into the pulmonary artery (right) and the aorta (left)

  4)The blood then flows to the organs through arteries and returns through veins.

  5)The atria fill again and the whole cycle starts over)

  
• What are stents used for?

  Stents can be used to keep narrowed or blocked arteries open to avoid coronary heart disease
• What are statins?


  Statins are a drug that reduce cholesterol levels in the blood, reducing coronary hear disease
• What is a pacemaker?


  There are a group of cells in the right atrium that act as a pacemaker for the heart. When these don't work doctors implant an artificial pacemaker send strong, regular electrical impulses to the heart that stimulate it to beat properly
• Why might valves have to be replaced?

  Valves have to withstand a lot of pressure so over time they might start to leak, become stiff or not fully open, making the heart less efficient
• What are mechanical valves?


  Mechanical valves are made of materials such as titanium and polymers. They last a very long time However you have to take medicine for the rest of your life to prevent blood clotting around it
• What are biological valves?


  Biological valves are taken from humans or other mammals. They work very well and the patient will not have to take any medicine. However they need replacing after 12-15 years
• When is an artificial heart needed?


  Artificial hearts are occasionally used to keep patients alive while they wait for a transplant, or for their heart to rest as an aid to recovery
• What is the purpose of the lungs?


  To get air into your bloodstream so that it can be used for cellular respiration and to get rid of the carbon dioxide in your blood.
• Describe the thorax


  The lungs are in the thorax. The thorax is the top part of your body. It's separated from the abdomen by the diaphragm. The lungs are protected by the ribcage and surrounded by the pleural membranes

  
• Describe the journey of air through the lungs?


  The air that you breathe in goes through the trachea. This splits into tubes called the bronchi (one going to each lung). The bronchi split into bronchioles and the bronchioles split into alveoli
• How are alveoli adapted for gas exchange?


  -Alveoli have very thin walls to improve diffusion

  -The spherical shape of the alveolus gives relatively large surface area for diffusion

  -The alveolus has a good blood supply to maintain concentration gradient for diffusion

  -The alveolus has good ventilation which helps maintain a steep concentration gradient

  
• What do epidermal tissues do?

  Cover the surfaces and protect them. These cells often create a waxy substance that waterproofs the surface of the leaf
• What does the palisade mesophyll do?

  Contains lots of chloroplasts which carry out photosynthesis
• What does the spongy mesophyll do?


  Contains big air spaces and a large surface area to allow gases to diffuse in and out of cells
• Describe the structure of a leaf


  -Carbon dioxide diffuses into the leaf through little holes called stomata which make up the lower epidermis

  -The carbon dioxide then moves up to the spongy mesophyll which has big air spaces to allow the gas to easily diffuse into the next layer

  -The next layer is called the palisade mesophyll layer. This is where most of the photosynthesis happens so the cells have lots of chloroplasts

  -The last layer is called the upper epidermis which is really thin so the sunlight can get through.

  -Once photosynthesis has produced sugar molecules they are carried to the rest of the plant through the phloem

  
• What do the stomata do?


  Stomata act as openings in a leaf, allowing carbon dioxide, water etc. to get inside. They are open for as little time as possible to prevent water loss and because they are sensitive to light. They are on the bottom of the leaf as it is more shaded so there will be less evaporation.
• What does the phloem do?


  Transports dissolved products of photosynthesis (cell sap) in various directions ​around the plant and to the storage organs where it provides an energy store for the winter.

  
• What is translocation?


  The movement of dissolved sugars from the leaves to the rest of the plant
• What does the xylem do

  Transports water and mineral ions to the stem and leaves.

  
• What is transpiration?


  The loss of water vapor through the stomata of leaves
• What is the transpiration stream?

  The continuous movement of water from the roots through the xylem and out of the leaves