Topic 8 - exchange and transport in animals

why is it necessary to transport substances

it is necessary to transport substances into organisms which are vital for life, and to transport waste products out of the organism to prevent them from accumulating

what happens during photosynthesis

during photosynthesis, plants need to be highly specialised in taking in carbon dioxide and excreting oxygen (a waste product of photosynthesis) out, while at the same time being able to take in dissolved nutrient and mineral molecules and water from the soil and air

animal especially advanced system

animals have especially advanced systems to remove waste - such as the kidney. the kidney efficiently removes waste such as urea and excess ions. this is vital, as if excess urea is not removed it builds up in the body and becomes toxic. excess carbon dioxide can also build up and dissolve in the blood, causing it to become acidic - leading to a condition called acidosis

what does specialised exchange surfaces do

specialised exchange surfaces allow efficient transport of substances from one area to another (from outside to inside the organism, for example). exchange surfaces often have a short distance for diffusion and a large surface area.

what do some exchange surfaces include

• the root hair cells of plants: these are specialised to take up water and nutrients from the soil, as they have a large surface area and thin walls (meaning diffusion across the wall into the plant can occur quickly)

• the walls of the nephrons in the kidney: these also have thin walls and a very large surface area, as they are required to efficiently reabsorb substances like water and glucose

what happens in the lungs

in the lungs, oxygen is transferred to the blood and carbon dioxide is transfered to the lungs. this takes place across the surface of millions of air sacs called alveoli, which are covered in tiny capillaries, which supply the blood

what happens in the small intestine

in the small intestine, cells have projections called villi. digested food is absorbed over the membrane of these cells, into the bloodstream

what happens in the gills

the gills are where gas exchange takes place in fish. water which has oxygen passes through the mouth and over the gills. each gill has plates called gill filaments, and upon these are gill lamellae, which is where diffusion of oxygen into the blood and diffusion of carbon dioxide into the water takes place. blood flows in one direction while water flows in the other

what happens in the leaves

in the leaves of the plant there are many different tissues to aid with gas exchange. carbon dioxide diffuses through stomata for photosynthesis, whilst oxygen and water vapour move out through them. the stomata are controlled by guard cells, which change the size of the stomata based on how much water the plant recieved (the guard cells swell with lots of water and make the stomata larger)

adaptation: having a large surface area

why:

• the greater the surface area, the more particles can move through, resulting in a faster rate of diffusion

examples:

• lungs: the small, spherical alveoli (sites of gaseous exchange) in the lungs create a very large surface area (approximately 75cm² in humans)

• small intestine: the cells of the small intestine have millions of villi, which are projections which increase the surface area. this means digested food can be absorbed into the blood faster

• fish gills: these contain lamellae to increase the surface area

• leaves: the flattened shape increases the surface area. the air spaces inside the leaf increases the surface area, so more carbon dioxide can enter cells

adaptation: having a thin membrane

why?

• provides a short diffusion pathway, allowing the process to occur faster

examples:

• lungs: alveoli and capillary walls are extremely thin

• small intestine: villi have a single layer of surface cell

adaptation: having an efficient blood supply/being ventilated (in animals)

why?

• creates a steep concentration gradient, so diffusion occurs faster

examples:

• lungs: the lungs constantly supply oxygen to make the blood from alveoli capillaries oxygenated, by exchanging it for carbon dioxide that can be breathed out. this is a constant process meaning the concentration gradient is always steep

• fish: water flows in one direction and blood flows in the other - this means that a steep concentration gradient is maintained as the concentration of oxygen is always much higher in the water - so it will diffuse across

measure for how well an organism or cell can transport substances

the Surface Area to Volume Ratio. this is the size of the surface area of the organism compared to its volume

• calculated by finding the volume (length x width x height) and the surface area (length x width), and writing the ratio in the smallest whole numbers

• if this is large, the organism is less likely to require specialised exchange surfaces and a transport system because the rate of diffusion is sufficient in supplying and removing the necessary gases

• eg. 15 (surface area):5 (volume) is written as 3:1

how do multicellular organisms transport molecules

single celled organisms can use diffusion to transport molecules into their body from the air - this is because they have a relatively large surface area to volume ratio. due to their low metabolic demands, diffusion across the surface of the organism is sufficient enough to meet its needs

what about in multicellular organisms

in multicellular organisms the surface area to volume ratio is small so they cannot rely on diffusion alone. instead, surfaces and organ systems have a number of adaptations that allows molecules to be transported in and out of cels

larger organisms vs smaller organisms ratio

• larger organism often have a small surface area to volume ratio, as they have a large volume but relatively small surface area

• smaller organisms have a larger surface area to volume ratio, as they have a large volume relative to their surface area

benefits of large surface area to volume ratio

the greater the surface area to volume ratio, the better adapted the organism is for diffusion. if an organism increases its surface area, it can take in more nutrients and expel more waste products more efficiently

what are alveoli

alveoli are the small ‘air sacs’ in the lungs. they are surrounded by blood vessels with thin walls, allowing gas exchange between the lungs and blood.

how are alveoli adapted

• they are very small and arranged in clusters, creating a large surface area for diffusion to take place over

• the capillaries provide a large blood supply, maintaining the concentration gradient

• the walls of the alveoli are very thin, meaning there is a short diffusion pathway

factors affecting rate of diffusion

• concentration gradient (difference in concentration) - the greater the difference in concentration, the faster the rate of diffusion. this is because more particles are randomly moving down the gradient than are moving against it

• temperature - the greater the temperature, the greater the movement of particles, resulting in more collisions and therefore a faster rate of diffusion

• surface area of the membrane - the greater the surface area, the more space for particles to move through, resulting in a faster rate of diffusion

how to calculate rate of diffusion

rate of diffusion is proportional to (surface area x concentration difference)/thickness of membrane

structure of blood

blood is made up of plasm, red blood cells, white blood cells and platelets

1. plasma

   • this is liquid that carries the components in the blood: red blood cells, white blood cells, platelets, glucose, amino acids, carbon dioxide, urea, hormones, proteins, antibodies and antitoxins

2. red blood cells

   • they carry oxygen molecules from the lungs to all the cells in the body

   • their biconcave disc shape provides a large surface area

   • they have no nucleus allowing more room to carry oxygen

   • they contain the red pigment haemoglobin, which binds to oxygen and forms oxyhaemoglobin

3. white blood cells

   • they are a part of the immune system, which is the body’s defence against pathogens (microorganisms that can produce disease)

   • they have a nucleus

   • there are a number of types

     • 1 - those that produce antibodies (small proteins that clump them together) against microorganisms

     • 2- those that engulf and digest pathogens

     • 3 - those that produce antitoxins to neutralise toxins (poisons) produced by microorganisms

4. platelets

   • they help the blood clot form at the site of a wound

   • the clot dries and hardens to form a scab, which allows new skin to grow underneath while preventing microorganisms from entering

   • small fragments of cells

   • no nucleus

   • without them, cuts would result in excessive bleeding and bruising

what types of blood vessels does the body contain

three different types of blood vessels:

1. arteries carry blood AWAY from the heart

   • layers of muscle in the walls make them strong

   • elastic fibres allow them to stretch

   • this helps the vessels withstand the high pressure created by the pumping of the heart

2. veins carry blood TOWARDS the heart

   • the lumen (the actual tube in which blood flows through) is wide to allow the low pressure blood to flow through

   • they have valves to ensure the blood to flow through

3. capillaries allow the blood to flow very close to cells to enable substances to move between them

   • one cell thick walls create a short diffusion pathway

   • permeable walls so substances can move across them

what system is the heart in

the heart is an organ in the circulatory system. the circulatory system carries oxygen and nutrients to every cell in the body and removes the waste products.

what does the heart do

the heart pumps blood around the body in a double circulatory system. this means there are two circuits

1. deoxygenated blood flows into the right atrium and then into the right ventricle which pumps it to the lungs to undergo gaseous exchange

2. oxygenated blood flows into the left atrium and then into the left ventricle which pumps oxygenated blood around the body

structure of the heart

• muscular walls to provide a strong heartbreak

• the muscular wall of the left ventricle is thicker because blood needs to be pumped all around the body rather than just to the lung from the deoxidated blood

• 4 chambers that seperate the oxygen blood from the deoxygenated blood

• valves to make sure blood does not flow backwards

• coronary arteries cover the heart to provide its own oxygenated blood supply

process of the heart

1. blood flows into the right atrium through the vena cava, and left atrium through the pulmonary vein

2. the atria contract forcing the blood into the ventricles

3. the ventricles then contract, pushing the blood in the right ventricle into the pulmonary artery to be taken to the lungs, and blood in the left ventricle to the aorta to be taken around the body

4. as this happens, valves close to make sure the blood does not flow backwards

what is the natural resting heart rate

the natural resting heart rate (around 7p beats per minute) is controlled by a group of cells found in the right atrium that acts as a pacemaker - they provide stimulation through small electrical impulses which pass as a wave across the heart muscle, causing it to contract. without this, the heart would not pump fast enough to deliver the required amount of oxygen to the whole body

what to do if someone has an irregular heartbeat

an artificial pacemaker can be used if the individual has an irregular heartbeat. it is an electrical device that produces a signal causing the heart to beat at a normal speed

respiration

respiration occurs in every cell in the body, and it is the process of transferring energy from glucose so living processes can occur. all living things undergo respiration

• it is exothermic as energy is transferred to the enviroment

• it can take place aerobically (with oxygen) or anaerobically (without oxygen)

aerobic respiration

this uses oxygen. it yields the most energy. most of the reactions that make up aerobic respiration occur in the mitochondria

C₆H₁₂O₆ + O₂ → CO₂ + H₂O

C₆H₁₂O₆ = glucose

O₂ = oxygen

CO₂ = carbon dioxide

H₂O = water

anaerobic respiration

occurs when there is not enough oxygen. it does not yield as much energy as aerobic respiration. it is only used as a last resort, for example during a sprint where it is difficult to breathe in enough oxygen. the oxidation of glucose is complete

in animals:

glucose (C₆H₁₂O₆) → lactic acid

in plant and yeast cells it is called fermentation:

glucose (C₆H₁₂O₆) → ethanol + carbon dioxide (CO₂)

this reaction is used to make bread and alcoholic drinks

Core Practical: investigate the Rate of Respiration in living organisms

in this practical, builds a simple respirometer - a machine to measure the effect of temperature on the oxygen consumption of small organisms

method

1. pick a small organism that you would like to measure the rate of respiration (eg. maggots, or leaves)

2. place 5cm³ of soda lime into a test tube

3. place gauze on top and a small amount of the organism being tested on top of this.

4. attach a three-way tap, capillary tube and syringe to the test tube. plug the test tube with a stopper

5. insert a small amount of coloured liquid into the capillary tube

6. turn the 3-way tap to allow air to enter the test tube for 5 minutes. after 5 minutes, close the 3-way tap

7. record how far the coloured liquid has moved against a scale

how to measure how well the heart is working

can be measured by using the equation:

cardiac output = stroke volume x heart rate

stroke volume is the volume of blood expelled from the heart in one contraction, whereas heart rate is the number of contractions (beats) per minute