3.3 Organisms exchange substances with their environment Flashcards
3.3.1 Surface Area to Volume Ratio
How does an organisms size relate to their surface area to volume ratio?
- The larger the organism, the smaller its surface area to volume ratio
How does an organisms surface area to volume ratio relate to their metabolic rate?
- The smaller the surface area to volume ratio, the higher the metabolic rate
How might a large organism adapt to compensate for its small surface area to volume ratio?
- changes that will increase that surface area for example body parts becoming larger, developing a specialised gas exchange surface
Why do multicellular organisms require specialised gas exchange surfaces?
- Due to having a smaller SA:V ratio, the distanced that needs to be crossed for the gases is larger
- substances cannot easily enter the cells as in single celled organism
3.3.2 Gas Exchange
What are three key features that make an efficient gas exchange surface?
- Large surface area
- Thin/short diffusion pathway
- Steep concentration gradient
Why cant insects use their bodys as an exchange surface?
- They have a waterproof exoskeleton made from chitin
- and a small SA:V in order to conserve water
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What are the three main features of an insects gas exchange system?
- Spiracles- holes on the bodys surface which open and close by a valve for gas or water exchange
- Tracheae- large tubes extending through all body tissues, supported by rings so they dont collapse
- Tracheoles-small branches coming off the tracheae
What are 3 ways the insect tracheal system is adapted for efficient gas exchange?
- Lots of tracheoloes-so larger surface area for gas exchange
- Fine/thin tracehole walls-shorter diffusion distance to cells
- Spiracles on the bodys surface which open and close by a valve for gas
Explain the process of gas exchange in insects
- Gases move in and out of the tracheae through the spiracles
- A diffusion gradient allows oxygen to diffuse into the body tissue and waste CO2 diffuses out
- Contraction of muscles in the trachea allows the mass movement of air in and out
Why cant fish use their bodys as an exchange surface?
- They have a waterproof, impermeable outer membrane and a small SA:V ratio
- instead they use a specialised gas exchange system
What are the two main features of a fishs gas exchange system?
- Gills- located within the body, have lots of gill filaments which are stacked up in piles
- Lamellae- at right angles to the gill filaaments which give and increased surface area. BLood and water flow across them in opposite directions (countercurrent mechanism)
What are 3 ways the fish is adapted for efficient gas exhange?
- lots of gill filaments-larger SA:V ratio for gases
- thinner lamellae- shorter diffusion distance
- countercurrent mechanism
Explain the process of gas exchange in fish?
- the fish opens its mouth to enable water to flow in, then closes its mouth to increase presuure
- the water passes over the lamallae, and the oxygen diffuses into the bloodstream
- waste carbon dioxide diffuses into the water and flows back out the gills
Explain the countercurrent mechanism
- Water and blood flow over the gills in opposite directions
- This maintains a steep concentration gradient over the along the length of the whole lamellae
- ensures equilibrium is not reached
Name and describe three adaptations of a leaf that allows efficient gas exchange
- thin and flat-short diffusion pathway, large SA:V ratio
- many stomata-allows gases to easily enter
- air spaces in the mesophyll allows gases to move around the leaf, facilitating photosynthesis
How do plants limit their water loss while still allowing gases to be exchanged?
- Stomata regulated by guard cells which allows them to open and close as needed
- most stay closed to prevent water loss while some open to let oxygen in
Describe the pathway taken by air as it enters the mammalian gaseous exchange system
- Nasal cavity–> trachea–> bronchi–>bronchioles–>alveoli
What is the function of the nasal cavity in the mammalian gaseous exchnage system?
- a good blood supply warms and moistens the air entering the lungs
- Goblet cells in membrane secrete mucus which trap dust and bacteria
Describe the trachea and its function in the mammalian gas exchange system
- wide tube supported by C-shaped cartilige to keep the air passage open during pressure changes
- lined by ciliated epithelium cells which move mucus towards the throat to be swallowed preventing lung infections
- carries air to the bronchi
Describe the bronchi and their function in the mammalian gaseous exchange system
- Like the trachea they are supported by rings of cartilage and are lined by ciliated epithelium cells
- however they are narrower and there are two of them, one for each lung
- allows passage of air into bronchioles
Describe the bronchioles and their function in the mammalian gaseous exchange system
- narrower than the bronchi
- do not need to be kept open by cartilage therefore mostly have only muscle and elastic fibres so that they can contract and relax easily during ventilation
- allos passage of air into alveoli
Describe the alveoli and their function in the mammalian gas exchange system
- mini air sacs lined with epithelium cells, site of gas exchange
- walls only one cell thick, covered with a network of capillaries which facilitates gas diffusion
Explain the process of inhalation/inspiration
- External intercostal muscles contract (while internal relax) pulling the ribs UP and OUT
- Diaphragm contracts and flattens
- Volume of thorax increases
- Air pressure outside the lungs is therefore higher than the air pressure inside so air moves in to rebalance
Explain the process of exhalation/expiration
- External intercostal muscles relax while internal intercostal muscles contract bringing the ribs DOWN and IN
- Diaphragm relaxes and it domes upwards
- volume in thorax decreases
- Air pressure inside the lungs is therefore higher than the air pressure outside, so air moves out to rebalance
What is tidal volume?
- the volume of air we breathe in and out during each breath at rest
What is breathing rate?
- the number of breaths we take per minute
How do you calculate pulmonary ventilation rate?
- tidal volume x breathing rate
- can be measured using a spirometer which is a device that records volume changes onto a graph as a person breathes
3.3.3 Digestion and Absorption
What is digestion?
- the hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes
Which enzymes are involved in carbohydrate digestions and where are they found?
- Amylase-mouth
- Maltase, sucrase, lactase-membrane of small intestine
What are the substrates and products of the carbohydrate digestive enzymes?
- Amylase–> starch into smaller polysaccharides
- Maltase–> maltose into 2x glucose
- Sucrase–> sucrose into glucose and fructose
- Lactase–> lactose into glucose and galactose
Where are lipids digested?
- the small intestine
What needs to happen before lipids can be digested?
- They must be emulsified by bile salts produced in the liver
- this breaks down large fat molecules into smaller, soluble molecules called micelles, increasing surface area
What is the role of micelles in the absorption of lipids?
- are water soluble
- increase surface area for absorption
How are lipids digested?
- lipase hydrolyse the ester bond between monoglycerides and fatty acids
How is the ileum adapted for efficient absorption?
- wall is covered in villi which have thin walls surrounded by a network of capillaries and epithelial cells have even smaller microvilli
- these features maximisie absorption by increasing the surface area, decreasing the diffusion distance and **maintaining a concentration gradient
Which enzymes are involved in protein digestion and what are their roles?
- Endopeptidases-break between specific amino acids in the MIDDLE of a polypeptide
- Exopeptidases- break specific amino acids at the END of a polypeptide
- Dipeptidases-break dipeptides into amino acids
How are certain molecules absorbed into the ileum despite a negative concentration gradient?
- through co-transport
Which molecules require co-transport?
- amino acids
- monosaccharides
Explain how sodium ions are involved in co-transport
- Sodium ions (Na+) are actively transported out of the cell and into the lumen
- This creates a diffusion gradient
- Nutrients are then taken up into the cells along with Na+ ions
Why do fatty acids and monoglycerides not require co-transport?
- The molecules are non-polar, meaning they can easily diffuse across the membrane of the epithelial cells
3.3.4 Mass Transport
What is haemoglobin?
- a protein with a quatenary structure
Describe the structure of haemoglobin
- globular, water soluble
- consists of four polypeptide chains each carrying a haem group (quatenary structure)
Describe the role of haemoglobin
- present in red blood cells
- oxygen molecules bind to the haem groups and are carried around the body to where they are needed in respiring tissues
What three factors affect oxygen-haemoglobin binding?
- Partial pressure/concentration of oxygen
- partial pressure/concentration of carbon dioxide
- saturation of haemoglobin with oxygen
How does partial pressure of oxygen affect oxygen-haemoglobin binding?
- As partial pressure of oxygen increases the affinity of haemoglobin for oxygen also increases
- so oxygen binds tightly to haemoglobin
- when partial pressure is low, oxygen is **released from haemoglobin
How does partial pressure of
carbon dioxide affect oxygen-haemoglobin binding?
- As partial pressure of carbon dioxide increases the conditions become acidic which causing haemoglobin to change shape
- The affinity of haemoglobin for oxygen therefore decreases so oxygen is released from haemoglobin
- This is known as the Bohr Effect
How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?
- It is hard for the first oxygen molecule to bind
- Once it does it changes the shape to make it easier for 2nd and 3rd molecules to bind known as positive cooperativity
- It is then slightly harder for the 4th oxygen molecule to bind because there is a low chance of finding a binding site
Why does oxygen bind to haemoglobin in the lungs?
- partial pressure of oxygen is high
- low concentration of carbon dioxide in the lungs, so affinity is high
- Positive cooperativity (after the first oxygen molecule binds, binding of subsequent molecules is easier)
Explain why oxygen is released from haemoglobin in respiring tissues
- partial pressure of oxygen is low
- high concentration of carbon dioxide in respiring tissues so affinity decreases
What do oxyhaemoglobin dissociation curves show?
- saturation of haemoglobin with oxygen plotted against partial pressure of oxygen
- curves further to the left show that haemoglobin has a higher affinity for oxygen
How does carbon dioxide affect the position of an oxyhaemoglobin dissociation curve?
- curve shifts to the right because haemoglobins affinity for oxygen has decreased
Name 3 common features of a mammalian circulatory system
- suitable medium for transport, water-based to allow substances to dissolve
- means of moving the medium and maintaining pressure throughout the body, such as the heart
- means of controlling flow so it remains unidirectional, such as valves
What are the 4 chambers of the heart?
- right atrium
- right ventricle
- left atrium
- left ventricle
Relate the structure of the chambers to their function
- Atria-thin walled and elastic, so they can stretch when filled with blood
- Ventricles-thick muscular walls, pump blood under high pressure, left ventricle is thicker than the right because it has to pump blood all the way around the body
What are the main blood vessels in the heart?
- Arteries
- Veins
- Capillaries
Relate the structure of the vessels to their function
- Arteries- have thick walls to handle pressure without tearing and are muscular and elastic to control blood flow
- Veins- have thin walls due to lower pressure therefore requiring valves to ensure blood doesnt flow backwards. They have less muscular and elastic tissue as they dont have to control blood flow
Why are two pumps (left and right) needed instead of one?
- to maintain blood pressure around the whole body
- when blood passes through the narrow capillaries of the lungs the pressure drops sharply therefore would NOT BE flowing strongly enough to continue around the whole body
- therefore it is returned to the heart to increase the pressure
Describe what happens during cardiac diastole
- The heart is relaxed
- Blood enters the atria which increases the pressure and pushing open the atrioventricular valves
- This allows blood to flow into the ventricles
- Pressure in heart is lower than in the arteries so semilunar valves remain closed
Describe what happens during atrial systole
- The atria contract, pushing remaining blood into the ventricles
Describe what happens during ventricular systole
- The ventricles contract
- The pressure increases which closes the atrioventricular valves to prevent backflow and semi-lunar valves open
- Blood flows into the arteries
How is the structure of capillaries suited to their function?
- walls are only one cell thick-short diffusion pathway
- very narrow so can permeate tissues and red blood cells can lie flat against the wall, effectively delivering oxygen to respiring cells
- numerous and highly branched which creates larger surface area
What is tissue fluid?
- A watery substance
- Contains glucose, amino acids, oxygen and other nutrients
- It supplies these to the cells, while also removing any waste materials
How is tissue fluid formed and how is it returned to the circulatory system?
- hydrostatic pressure of blood is high at arterial end
- water and fluids forced out
- large molecules remain because theyre to large
- this lowers the WP
- water moves back into the venous end of capillary via osmosis
- lymph system collects any excess tissue fluid which returns blood to the circulatotory system
- tissue fluid returned to **vein
How is water transported in plants?
- through xylem vessels
- these are long, continuos columns that also provide structural support to the stem
Explain the cohesion-tension theory
- water molecules form hydrogen bonds with each other
- this causes them to stick together (cohesion)
- the surface tension of the water also creates the sticking effect
- therefore as water is lost through transpiration, more can be drawn up the stem
What are the three components of the phloem vessels?
- sieve tube elements- form a tube to transport sucrose in the dissolved form of sap
- companion cells- involved in ATP production for active loading of sucrose into sieve tubes
- plasmodemesmata- gaps between cell walls where the cytoplasm links allowing substances to flow
Name the process whereby organic materials are transported around the plant
- Translocation
How does sucrose in the leaf move into the phloem?
- sucrose enters companion cells of the phloem vessels by active loading
- this uses ATP and a diffusion gradient of hydrogen ions
- sucrose then diffuses from companion cells and into sieve tube elements through the plasmodesmata
How do phloem vessels transport sucrose around the plant?
- As sucrose moves into the STE the WP inside the phloem is reduced
- this causes water to enter via osmosis from the xylem and increases hydrostatic pressure
- water moves along the STE and towards areas of lower hydrostatic pressure
- sucrose diffuses into surrounding cells where it is needed
Give evidence for the mass flow hypothesis of translocation
- Sap is released when a stem is cut therefore there must be pressure in the phloem
- there is a higher sucrose concentration in the leaves than in the roots
- increasing sucrose levels in the leaves results in increased sucroses in the phloem
Give evidence against the mass flow hypothesis of translocation
- the structure of STE seems to hinder mass flow
- not all solutes move at the same speed as they would in mass flow
- sucrose is delivered at the same rate throughout the plant, rather than to areas with the lowest sucrose concentration first
How can ringing experiments be used to investigate transport in plants?
- the bark and phloem of a tree are removed in a ring which leaves behind the xylem
- the tissues above the missing ring swells due to accumulation of sucrose as the tissue below begins to die
- therefore sucrose must be trsnsported in the phloem
How can tracing experiments be used to investigate transport in plants?
- plants are grown in the presence of radioactive CO2 which will be incorporated into the plants sugars
- using autoradiography we can see the areas exposed to radiation correspond to where the phloem is
