THE HUMAN BODYPart B: Respiration, Transportation, Waste Removal and Exercise

V.C.E. BIOLOGY UNIT 1Exchanging Gases

Gas ExchangeDiffusion• Gas Exchange occurs by oxygen and carbon dioxide moving from areas of high concentration to areas of low concentration.

• In humans this means that oxygen diffuses into the bloodstream in the lungs as carbon dioxide diffuses out.

• In plants the situation is a little more complex, but gases are still exchanged through stomata by diffusion.

Why exchange gases?• OxygenTo release energy held in glucose, organisms need oxygen and produce carbon dioxide which is toxic in the body (cellular respiration)

• Carbon DioxidePlants need carbon dioxide to trap light energy and synthesise glucose (photosynthesis)

Animals

Exchange surfaces and Exchange organs

• For effective gas exchange in animals the surface must remain moist and have a large surface area to volume ratio.

• This is easier in fish (gills) and amphibians (their skin) which live in water, but in land dwelling animals the organs must be internal (lungs) as the air would dry them out.

Mammals• In mammals there are

two lungs at the ends of a series of tubes (trachea bronchus bronchiole alveoli)

• The alveoli are moist and surrounded by blood vessels. Gases diffuse across the thin membrane of the alveoli and the thin walls of the blood vessels. The alveoli exist in thousands creating a large surface area for the volume of the lung.

Transporting Gases

• In animals the gases need to be transported around the body by blood fluids.

• In humans haemoglobin on red blod cells is able to make weak chemical bonds with oxygen and carbon dioxide, this allows the oxygen to be carried from lungs to cells and then bring carbon dioxide back to the lungs.

Plants

• Plants also need to exchange gases.

• They require carbon dioxide to enter the plant when they are photosynthesising.

• They require oxygen to enter the plant for cellular respiration.

• They also need to release water vapour.

Stomata

• These are pores in the leaves of cells that allow for gas exchange.

• Surrounded by guard cells which can open and close the stomata.

• More stomata are found on the undersides of leaves than on the upper sides, so that plants can control water loss.

V.C.E. BIOLOGY UNIT 1Transport Systems

Transportation• As organisms grow larger they need to get oxygen, water

and nutrients to all cells and the wastes from cells and out of the body becomes more difficult.

• The answer that evolves is transportation systems.

Open Circulatory Systems• In many of the insects, such as spiders and snails, interstitial fluid (fluid surrounding the cells) is circulated throughout the body via open ended tubes pumped by a simple tubular pump.

• The fluid moves under low pressure and takes a long time to move about the body.

Closed circulatory system• Larger, more active organisms need a closed circulatory system in which blood pressure can be maintained and fluid moved around the body more efficiently.

• These organisms have developed arteries and veins and 2, 3 and 4 chambered hearts.

Mammalian Transport System• In mammals the evolution of a complex system of arteries, arterioles, capillaries, veins and venules powered by a four chambered double pump heart that efficiently and effectively exchanges gases and transports materials around the body.

Plant Transport Systems

• In plants there is no heart to pump material around the body, but there are two systems of tubes called xylem and phloem.

• Xylem are simple tubes in which water and dissolved substances move up the plant from the roots.

• They have strengthened walls, but are not living tissue.

Plant Transport Systems• The Phloem moves plant materials throughout the organism powered by diffusion and active transport in a process called TRANSPIRATION.

• Phloem vessels are living tissue with companion cells that contain nuclei and cell organelles, especially mitochondria.

Plant Transport System• Water and dissolved salts move up the xylem drawn by

the energy of the sun evaporating water from the leaves surface via stomata – this is called TRANSPIRATION.

• The pressure of water entering the roots and the cohesion between water molecules support this process.

V.C.E. BIOLOGY UNIT 1Removing Wastes

Managing Waste in animalsWaste in organisms falls into two groups:• Carbon Dioxide – the result of cellular respiration, which

we know is exchanged with oxygen through a respiratory surface.

• Nitrogenous Wastes – the result of biochemical processes in the body, such as the break down of proteins and cell components.

Nitrogenous WasteThis can take the form of ammonia, uric acid or urea.

• In water based organisms it is ammonia ( a highly toxic molecule) because the organism is able to exchange it with the surrounding water by diffusion.

• Land based organisms produce either uric acid (birds and some reptiles) which is highly concentrated and reasonably dry or urea (mammals) which is dissolved in water.

Mammalian Kidneys

• Mammals have two kidneys which are used to filter the blood.

• Wastes are removed and sent to the bladder.

• Water, sugars, amino acids, dissolved salts and gases are returned to the blood.

• This occurs in a structure called the nephron.

Excretory Organs in Animals

• The nephron is different in different organism depending on how wet or dry their environment is. For animals in very dry environments the Loop of Henle is very long so that the maximum amount of water can be removed from the urine and the urine is very concentrated.

Managing waste in plants• Plants produce less waste because they have a lower metabolism and usually reuse carbon dioxide in photosynthesis, therefore they lack specialised organs.

• The structure of plants is based on carbohydrates not proteins and most wastes are recycled.

• Plant wastes tend to be stored in plant structures such as leaves that are dropped in autumn and the bark of woody trees.