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B4: Organising animals and plants (4.4: Helping the heart (Artificial…
B4: Organising animals and plants
4.1: The blood
Multicellular organisms need a transport system to move material between exchange surfaces - the human circulatory system consists of the blood, blood vessels, and the heart
Blood is a tissue - the liquid plasma contains red blood cells, white blood cells, and platelets
Blood plasma transports many substances including
Carbon dioxide from the organs to the lungs
Soluble products of digestion from the small intestine to the other organs
Urea from the liver to the kidneys, where urine is made
Red blood cells
Are bioconcave discs and do not have a nucleus
Contain the red pigment haemoglobin
Use their haemoglobin to combine with oxygen, which forms oxyhaemoglobin in the lungs
Carry the oxygen to all the organs, where the oxyhaemoglobin splits back into haemoglobin and oxygen
White blood cells
Have a nucleus
Form part of the body's defence system against microorganisms
Some produce, antibodies, antitoxins, and other engulf microorganisms
Platelets
Are small fragments of cells
Do not have a nucleus
Help the blood to clot at the site of a wound
Blood clotting is a series of enzyme-controlled reactions
The final reaction causes fibrinogen to change into fibrin
Fibrin forms a network of fibres that trap blood cells and form a clot
The clot dries and forms a scab
4.2: The blood vessels
Blood flows round the body in 3 main types of blood vessel - arteries, veins, and capillaries
Artreries
Carry blood away from the heart
Have thick walls containing muscle and elastic tissue
Veins
Carry blood towards the heart
Have thinner walls than arteries
Often have valves along their length to prevent backflow of blood
Capillaries
Are narrow, thin-walled vessels
Carry the blood through the organs
Allow the exchange of substances with all the living cells in the body
Double circulation
In humans and other mammals the blood vessels are arranged into a double circulatory system
One transport system carries blood from your heart to your lungs and back again
The other transport system carries blood from your heart to all other organs of your body and back again
4.3: The heart
The heart is a muscular organ that pumps blood around the body - it is made up of 2 pumps held together
Arteries carry blood away from the heart - veins carry it back
The right pump forces deoxygenated blood blood to the lungs where it picks up oxygen and loses carbon dioxide
After returning to the heart, the oxygenated blood is then pumped to the rest of the body by the left pump, which needs a bigger force
The heart has 4 chambers
The upper 2 are the atria
The right atrium receives blood from the vena cava
The left atrium receives blood from the pulmonary vein
The atria contract together to move blood into the lower chambers, the ventricles
When the ventricles contract they force blood out of the heart
The right ventricle pushes blood into the pulmonary artery
The left ventricle pushes blood into the aorta
The left ventricle has the thicker wall - valves in the heart prevent the blood from flowing in the wrong direction
The coronary arteries supply oxygenated blood (from the lungs) to the heart
Coronary heart disease occurs when the coronary arteries become blocked or narrower due to a buildup of fatty material inside them
Doctors can use a stent to open up the arteries, allowing the blood to deliver nutrients and oxygen to the heart again
Bypass surgery can also be used to replace damaged coronary arteries with lengths of vein
Statins are prescribed to lower cholesterol, which in turn reduces the fatty buildup in the arteries
4.4: Helping the heart
Doctors, scientists, and engineers have developed ways to solve problems with damaged hearts
Leaky valves mean the blood could flow in the wrong direction - artificial or animal valves can be inserted in the heart to replace damaged valves
Adults have a natural resting heart rate of about 70 BPM -the natural resting heart rate is controlled by a group of cells that act as a pacemaker
The natural pacemaker is located in the right atrium
Sometimes the rhythm of the heart becomes irregular if the natural pacemaker does not work properly
An artificial pacemaker is an electrical device that can be fitted in the chest to correct irregularities in the heart rate
If a person has a very weak or diseased heart they may require a transplant - donors are not always available so artificial hearts are being developed
Artificial hearts can be used to
Keep patients alive while waiting for a heart transplant
Allow the heart to rest as an aid to recovery
1 disadvantage of an artificial heart or artificial valve is that the person needs drugs to prevent the blood from clotting
4.5: Breathing and gas exchange
Moving air into and out of the lungs is called ventilating the lungs, or breathing
The lungs contain the exchange surface of the breathing system
The lungs are situated in the thorax, inside the ribcage and above the diaphragm, which separates the lungs from the abdomen
When you breathe in
The intercostal muscles, between the ribs, contract, moving the ribcage up and out
The muscles of the diaphragm contract and the diaphragm flattens
The volume of the thorax increases
The pressure in the thorax decreases and air is drawn into your lungs
When you breathe out
The intercostal muscles of the ribcage and the diaphragm relax
The ribcage moves down and in and the diaphragm becomes domed
The volume of the thorax decreases
The pressure increases and air is forced out
Adaptations of the alveoli
Your lungs are adapted to make gas exchange more efficient
Oxygen is absorbed from the air into the blood in the lungs - carbon dioxide is removed from the blood to the air
Efficient exchange surfaces have a large surface area, thin walls or a short diffusion path, and an efficient transport system
The lungs contain the gaseous exchange - the surface area of the lungs is icreased by the alveoli (air sacs)
The alveoli have a large surface area, thin walls, and a good blood supply
The lungs are ventilated to maintain a steep concentration gradient
Oxygen diffuses into the many capillaries surrounding the alveoli, and carbon dioxide diffuses back out into the lungs to be breathed out
4.6: Tissues and organs in plants
Plant tissues
Plant tissues are collections of cells that are specialised to carry out specific functions
Plant tissues include
Epidermal tissue
Covers the plant
Palisade mesophyll
Has many chloroplasts and can photosynthesise
Spongy mesophyll
Has some chloroplasts, many air spaces between the cells, and a large surface area for diffusion of gases
Xylem
Transports water and dissolved mineral ions from the root to the rest of the plant
Phloem
Transports dissolved food substances from the leaves to the rest of the plant
Plant organs
The plant tissues are arranged to form organs
Each plant organ has its own functions
Stems, roots, and leaves are plant organs
The plant organs form a plant organ system to transport substances around the plant
4.7: Transport systems in plants
Flowering plants have separate transport systems
Phloem tissue carries dissolved sugars from the leaves to the rest of the plant, including the growing regions and the storage organs - this process is called translocation
Xylem tissue transports water and mineral ions from the roots to the stem, leaves, and flowers
The importance of transport in plants
All the cells in the plant need the sugar produced in photosynthesis for respiration
The sugar and mineral ions are needed for growth
Water is needed for photosynthesis
Water is needed to support the cells, particularly in young plants and in the leaves
4.8: Evaporation and transpiration
Water loss from the leaves
Gases diffuse in and out of leaves through tiny wholes called stomata - the size of the stomata is controlled by the guard cells that surround them
Water is absorbed from the soil by the roots - the water passes through the plant to the cells in the leaves
In the leaves, water evaporates from the cells in the leaf into the air spaces between them - this water vapour diffuses out of the plant through the stomata on the leaf surface when the stomata are open - this is transpiration
The movement of the water through the plant is called the transpiration stream
The guard cells can close the stomata to prevent excessive water loss
4.9: Factors affecting transpiration
A plant could dehydrate if the rate of evaporation in the leaves is greater than the rate of water uptake by the roots
Factors that increase the rate of photosynthesis or increase stomatal opening will increase the rate of transpiration
The factors include
Temperature
Humidity
Air flow
Light intensity
Transpiration is more rapid in hot, dry, windy, or bright conditions
Plants can control water loss
Plants have a waxy, waterproof cuticle on the leaves that can be very thick and shiny in hot environments
Most of the stomata are on the underside of the leaf
Wilting of the whole plant can also reduce water loss - the leaves collapse and hang down, which reduces their surface area
The stomata can close, which stops photosynthesis but prevents more water loss and further wilting