Topic 3A- Exchange and Transport Systems

What substances do organisms need to exchange with the environment?

• Cells need to take in oxygen (for aerobic respiration)

• They need to excrete waste products like carbon dioxide and urea

• Most organisms need to regulate their body temperature so heat needs to be exchanged

Do small or large animals have a larger surface area:volume ratio?

• Smaller animals

• There is more surface area exposed on smaller animals per unit volume compared to larger animals

• This is because when animals become larger, their volume increases faster than their surface area

Why do single-celled and very small organisms not need specialised exchange systems?

• The interior cells of the organisms are not far from the surface

• This means that substances can just diffuse into the body because the diffusion distances is small so diffusion can happen quickly and reach all cells

Why do larger organisms need specialised exchange systems?

• The interior cells are deep within the organisms because it has a larger volume relative to it’s surface area

• This means that substances like oxygen cannot diffuse through and supply all cells in the organism because their volume is too large and the oxygen wouldn’t reach all the cells

• There is also not enough surface area to bring in an adequate supply of oxygen

What is mass transport?

• Systems involved with the transport and exchange of substances within larger animals

• In mammals this normally refers to the circulatory system which transports oxygen and glucose but also hormones

• In plants this is the transport of water and solutes through the xylem of phloem

What kind of energy is released in metabolic reactions?

Heat energy

How does surface area:volume ratio relate to heat loss and what does this mean for smaller organisms?

• The rate of heat loss from an organism depends on this ratio

• Small animals with a large surface area:volume ratio have a faster rate of heat loss because of their relatively large surface area

• This means smaller organisms must have a relatively high metabolic rate in order to generate enough heat to stay warm

What features of animals would you expect to see in cold and hot environments?

• Cold- compact shape in order to reduce surface area which minimises heat loss

• Hot- Less compact/more spread out to increase surface area which increases heat loss from their surface

What are some behavioural and physiological adaptations animals have to reduce or increase heat loss?

• Animals with a high SA:V ratio lose more water from their surface so some desert animals have kidney structure adaptation to produce less urine to compensate

• To support high metabolic rates, small mammals living in cold regions eat high energy foods like seeds and nuts

• Smaller mammals have thick layers of fur or hibernate when the weather is very cold

• Larger organisms living in hot regions find it hard to keep cool

  • Elephants have developed large flat ears to lose more heat

  • Hippos spend most of their day in water- a behavioural adaptation

What are the two major adaptations of gas exchange surfaces?

• They have a large surface area

• They are thin

How do fish exchange oxygen in water and why does it have to do it this way?

• Water containing oxygen enters the fish through it’s mouth and passes out though the gills

• Each gill is made of many small plates called gill filaments which provide a large surface area for the exchange of gases

• Gill filaments are covered in lots of tiny structures called lamellae which increase surface area even more

• The lamellae have a lot of blood capillaries and a thin surface layer of cells to speed up diffusion

• Water flows in the opposite direction that blood flows in the lamellae and we call this a counter-current system

• This maintains a high concentration gradient between the water and blood so the concentration of oxygen is the water is always higher than in the blood so oxygen diffuses from the water into the blood

• This means that a steep concentration gradient is maintained across the whole length of the lamellae so as much oxygen as possible diffuses into the capillaries

How do insects exchange gasses?

• The spiracles open to allow for gas exchange

• Insects have microscopic air-filled pipes called tracheae which they use for gas exchange

• Air moves into tracheae through pores on the surface called spiracles

• Oxygen travels down the concentration gradient towards the cells

• The tracheae branch off into smaller tracheoles which have thin permeable walls and go to individual cells. Then oxygen diffuses directly into respiring cells

  • This means the insects circulatory system does not transport oxygen

• Carbon dioxide moves through its own concentration gradient to the spiracles where it can be released into the atmosphere

• Insects use abdominal pumping to move air in and out of the spiracles which maintains a high diffusion gradient

How is the insect respiratory system adapted for gas exchange?

• Tracheae are strengthened by chitin rings to prevent them from collapsing

• Tracheoles extend through the whole insect and deliver oxygen directly to cells, reducing the diffusion pathway

• Tracheoles are highly branched- increased surface area

• Very thin walls of tracheoles

• Abdominal pumping- mass flow

Why are insects small?

They need a large SA:V ratio because otherwise it would take too long for oxygen to reach the trachea

What is oxygen and carbon dioxide needed for in plants?

• Plants need carbon dioxide for photosynthesis which produces oxygen as a waste gas

• They also need oxygen for respiration which produces carbon dioxide as a waste gas

How are gasses exchanged in the surface of the mesophyll cells in plants?

• This is the air exchange surface which has been well adapted to have a large surface area

• Gases move in and out the special pores in the epidermis called the stomata (single=stoma)

• The stomata can open to allow for the exchange of gasses and close if the plant is losing too much water

• Guard cells control the opening and closing of the stomata

How do plants control water loss?

• Stomata are open during the day to allow for gas exchange

• Water enters the guard cells, making them turgid which opens the stomatal pore

• If the plant begins to get dehydrated, the guard cells lose water and becomes flaccid, which closes the pore and conserves water

How do insects control water loss?

They can close their spiracles using valves periodically to conserve water and also have a waterproof waxy cuticle all over their body and tiny hairs around their spiracles which both reduce evaporation

What are xerophytes?

Plants that are adapted for warm, dry or windy habitats where water loss is a problem

What are some xerophytic adaptations?

• Stomata sunk in pits which reduces the concentration gradient of water between the leaf and the air

  • This reduces the amount of water diffusing out of the leaf and evaporating away by trapping a humid layer of air

• Layers of hairs on the epidermis to trap moist air around the stomata

• Curled leaves with the stomata inside to protect from wind

• A reduced number of stomata so there are fewer places for water to escape

• Waxy, waterproof cuticles on leaves and stems to reduce evaporation

Why are windy conditions not ideal for plants?

Windy conditions increase the rate of evaporation and diffusion of water out of a plant

What are the different parts of the human gas exchange system called and where are they located?

How is air moved through the human gas exchange system?

• As you breathe, air enter the trachea

• The trachea splits into two bronchi (singular=bronchus)

• Each bronchus splits into smaller tubes called bronchioles

• The bronchioles end is small sacs called alveoli where gasses are exchanged

• The ribcage, intercostal muscles and diaphragm all work together to move air in and our of the body

What is ventilation?

• The process of inspiration (breathing in) and expiration (breathing out)

• Its controlled with the diaphragm, internal and external intercostal muscles and ribcage

How does inspiration work?

• The external intercostal muscles and diaphragm contract and the internal intercostal muscles relax

• This causes the ribcage to move upwards and outwards and the diaphragm flattens increasing the volume of the thoracic cavity (the space where the lungs are)

• Due to this increase of volume, the pressure in the thoracic cavity decreases to below atmospheric pressure

• Air moves into the lungs due to the fact that are will move from a place of higher pressure to a place of lower pressure

• Inspiration is an active process requiring energy

How does expiration work?

• The external intercostal and diaphragm muscles relax

• The ribcage moves downwards and inwards and the diaphragm becomes curved/domed again as it relaxes

• Due to this decrease of volume, the pressure in the thoracic cavity increases to above atmospheric pressure

• Air is forced down the pressure gradient and out of the lungs

• Elastic tissue in the alveolar walls recoil to increase pressure and force air out of the lungs

• Inspiration is a passive process requiring no energy

What happens during forced expiration?

• The external intercostal muscles relax and internal intercostal muscles contract, pulling the ribcage further down and in

• During this time, the movement of the two sets of intercostal muscles is said to be antagonistic (opposing)

How does gas exchange in the alveoli work?

• There is a huge number of alveoli in the lungs which means there is a big exchange surface for oxygen and carbon dioxide

• The alveoli are surrounded by a network of capillaries

• Oxygen diffuses out of the alveoli, through the alveolar epithelium and the capillary endothelium into haemoglobin in the blood

• Carbon dioxide into the alveoli from the blood and is breathed out

What features of alveoli speed up the rate of reaction?

• A thin exchange surface- the alveolar epithelium is one cell thick meaning there is a short diffusion pathway

• Large surface area due to a large number of alveoli

• Steep concentration gradient of oxygen and carbon dioxide between the alveoli and capillaries which increases the rate of diffusion (good blood supply)

  • This is constantly maintained by the flow of blood and ventilation

• Moist

How do you calculate pulmonary ventilation rate (PVR)?

PVR=Breathing rate (breaths/min) x Tidal volume (dm³)

What is tidal volume?

The volume of air moving in and out of the lung during normal breathing

What is ventilation rate?

The number of breaths per minute

What is forced expiratory volume?

The maximum amount of air that can be expelled in one second

What is forced vital capacity?

The maximum volume of air that can be forcefully exchanged in one breath

What is residual volume?

The volume of air that remains after exhaling fully

What is inspiratory capacity?

The volume of air than can be inhaled after breathing out normally at rest

What is the inspiratory reserve volume?

The amount of air that can be inhaled after breathing in normally at rest

What is expiratory capacity?

The amount of air that can be exhaled after breathing out normally at rest

What is expiratory reserve volume?

The amount of air that can be exhaled after breathing out normally at rest

How does pulmonary tuberculosis affect breathing?

• Upon infection with the bacteria, immune system cells build a wall around bacteria in the lungs

  • This forms small, hard lumps called tubercles

• Infected tissue within the tubercles dies and the gaseous exchange surface is damaged so tidal volume is reduced

• It also causes fibrosis which further reduces the tidal volume

• A reduced tidal volume means less air can be inhaled with each breath so int order to take in more oxygen, patients have to breathe faster so ventilation rate increases

• Common symptoms are persistent coughs, coughing up blood and mucus, chest pains, shortness of breath and fatigue

How does fibrosis affect breathing?

• This is the formation of scar tissue in the lungs caused by an infection or exposure to asbestos or dust

• Scar tissue is thicker and less elastic that normal lung tissue

• This reduces the lungs ability to expand so not as much air can be held

  • This reduces tidal volume and FVC

• There is a reduction is gas exchange rate as diffusion is slower over thicker scarred tissue

• Symptoms- Shortness of breath, dry cough, chest pain, fatigue, weakness

• People who suffer fibrosis have a faster ventilation rate than normal to get enough air to oxygenate their blood

What effect does asthma have on breathing?

• The airways become irritated and inflamed and is usually caused by pollen or dust

• During asthma attacks, the smooth muscle lining the bronchioles contracts and a large amount of mucus is produced

• This constricts the airways so airflow in and out of the lung is greatly reduced

  - This makes it difficult for the sufferer to breathe properly so FEV₁ is greatly reduced and less oxygen is moving from the alveoli into the blood

• Symptoms include wheezing, a tight chest and shortness of breath

• Relieved by drugs in inhalers which causes the muscles in the bronchioles to relax, opening up the airways

How does emphysema affect breathing?

• Caused by smoking or long term exposure to air pollution

  • Foreign particles in the smoke/air become trapped in the alveoli

• This causes inflammation attracting phagocytes which produce an enzyme which breaks down elastin, a protein found in the walls of the alveoli

• Elastin is elastic and helps the alveoli return to their normal shape after inhalation and exhalation

• Loss of this elastic means alveoli cannot recoil to expel air- reduced concentration gradient

• It also can lead to the destruction of alveoli walls, reducing surface area and therefore the rate of gas exchange

• Symptoms of emphysema includes shortness of breath, wheezing and increased ventilation rate as they try to increase the amount of oxygen-containing air reaching their lungs