Chapter 6 - Exchange Flashcards
Name three things that organisms need to exchange with their environment
Oxygen, waste products and heat
What is passive exchange?
No metabolic energy is required
Give two examples of passive exchange
Diffusion and osmosis
What is active exchange?
Metabolic energy is required
Give an example of active exchange
Active transport
Why can substances diffuse directly out of the cells across the cell surface membrane in single-celled organisms?
They have a large SA:V which ensures efficient exchange
Why is diffusion across the cell membrane too slow in multicellular animals?
There is a large distance between cells deep inside the body and the outside environment
Large animals have a small SA:V so the exchange is inefficient
What is mass transport?
The use of an efficient system to carry substances to and from individual cells
What is the exchange system in mammals?
Circulatory system
What is the exchange system in plants?
The xylem and phloem
How are multicellular organisms adapted for efficient exchange?
They have a flat shape for a short diffusion pathway or they have specialised exchange surfaces to increase the SA:V
Why do specialised exchange surfaces normally have a large SA:V?
It increases the rate of exchange
Why are specialised exchange surfaces normally very thin?
The diffusion pathway is short so materials can cross the surface very rapidly
What is Fick’s law?
(Surface area x concentration gradient) / length of diffusion pathway
Why do smaller organisms generally need a higher metabolic rate?
Smaller organisms normally have a larger surface area, which means that much more heat is lost. They must have a higher metabolic rate in order to generate heat and stay warm
Why might an animal living in the Arctic have a round shape?
It has a small surface area which reduces heat loss and helps the animal stay warm
Why might an animal living in the desert have a pointed nose and long ears?
Both of these increase its surface area so it is easier to lose heat and stay cool
Why might animals with a high SA:V have kidney structure adaptations?
They tend to lose more water because of their large surface area so they produce less urine to compensate
Why might small mammals living in cold regions need to eat lots of high energy foods like nuts?
Because of their large surface area, they need fast metabolic rates
Why do elephants have large ears?
This increases their surface area so it is easier to cool down
What do most gas exchange systems have in common?
They have a large surface area and are often just one cell thick
What are tracheae?
An internal network of tubes, supported by strengthened rings
What are tracheoles?
Dead end tubes found on the end of tracheae
How does the insect respiratory system achieve a large surface area?
There are lots of tracheoles which span the whole body
How does the insect respiratory system achieve a small diffusion pathway?
The walls of the tracheoles are 1 cell thick
There is no chitin in the walls of the tracheoles for support
The tracheoles connect to the majority of cells
How does the insect respiratory system achieve the maximum diffusion gradient?
When the cells at the end of tracheoles are respiring, the oxygen is used up and this creates a steep concentration gradient between the outside air and the tracheoles. Respiration also produces carbon dioxide in the cells, which creates a steep concentration gradient in the opposite direction. Because of this, oxygen diffuses into the cells and carbon dioxide diffuses out
What are spiracles?
Tiny pores which cover the insect’s body and can be opened and closed on demand
How does the respiratory system of insects hinder their size?
Because the system relies mostly on the diffusion of gases into and out of the body, the diffusion pathway must be short, so insects must be a small size
Why do insects keep their spiracles closed for most of the time?
To avoid water loss by evaporation
How do insects move air into and out of the spiracles?
Their abdominal muscles can expand to lower the pressure and pull oxygen into the tracheoles, then contract to increase the pressure and force carbon dioxide out of the tracheoles
What happens when anaerobic respiration occurs?
Lactate is produced in the muscle cells around tracheoles, which lowers their water potential. Water, therefore, moves into these cells from the tracheoles by osmosis, lowering the volume of water in the tracheoles. Air gets drawn into the tracheoles because of the lower pressure. This increases the rate at which air is moved into tracheoles because diffusion is faster in a gas phase rather than in a liquid
What is the specialised gas exchange system in fish?
Gills
How do fish gills achieve a high surface area?
They consist of filaments and lamellae (which are at right angles to the filaments)
How do fish gills achieve a small diffusion pathway?
There is a network of blood capillaries, next to the lamellae, which have one cell thick walls
What is countercurrent flow?
The flow of water over the lamellae and the flow of blood inside them are in opposite directions. Therefore, the blood and water never reach equilibrium and oxygen continually diffuses into the blood
If fish didn’t have a countercurrent flow mechanism, what would be the maximum percentage of oxygen removed from the water?
50%, an equilibrium will be reached and no more oxygen will be extracted from the water because there is no concentration gradient
What percentage of oxygen is removed from the water?
80%
How does a countercurrent flow work?
Blood flows over the lamellae in one direction and water flows in the opposite direction. The concentration of oxygen in the blood is always lower than that of the water, so oxygen continually diffuses into the blood and the two never reach equilibrium
What are the two processes that plants conduct?
Photosynthesis and aerobic respiration
Equation for photosynthesis
6CO2 + 6H2O -> C6H12O6 + 6O2
The equation for aerobic respiration
C6H12O6 + 6O2 -> 6CO2 + 6H2O
When photosynthesis isn’t occurring, why is carbon dioxide still produced?
It is produced by aerobic respiration
State two ways in which gas exchange in plants is similar to that in insects
No living cell is far from the external air
Diffusion takes place in the gas phase
How do plants balance the conflicting needs of gas exchange vs water loss?
They have guard cells which can open and close stomata
Why are the stomata mainly at the bottom of the leaf?
Reduces transpiration and evaporation as not in direct sunlight
What is the function of guard cells?
To retain water when it is needed
What is the function of the waxy cuticle?
To stop evaporation from the leaf surface
Why must the cell surface be wet?
To allow the gases to dissolve
How are mesophyll cells adapted in the leaf?
They create big air spaces which increase the surface area available for diffusion
Why can a leaf be a maximum of 10 cells thick?
Must have a short diffusion pathway
State three ways in which insects minimise water loss
They have a small surface area to volume ratio
They are surrounded by a waterproof coating
Spiracles
How can spiracles help to conserve water?
They are surrounded by a ring of muscle which can contract to close the spiracles when gas exchange isn’t occurring
Why can’t plants have a small surface area to volume ratio?
Photosynthesis requires a large surface area to capture light and exchange gases
What are xerophytes?
Plants that are well adapted to reducing water loss through transpiration
State five ways in which plants reduce water loss
A thick, waxy cuticle The rolling of leaves Hairy leaves Stomata sunk in pits Small surface area to volume ratio of leaves
How does a thick waxy cuticle reduce water loss?
It reduces the amount of evaporation occurring
How can rolling leaves reduce water loss?
When leaves roll, the lower epidermis (where the stomata are found) is on the inside of the leaf. A layer of moist air is trapped, which becomes saturated with water and has a very high water potential. Because of this, there is no water potential gradient between the leaf and the air, so no water is lost
How do hairy leaves reduce water loss?
Still, moist air is trapped near to the surface. This means that the water potential gradient between the leaf and the air is reduced, so less water is lost by evaporation
How does having stomata in pits or grooves help to reduce water loss?
A layer of still, moist air is trapped next to the stomata. This means that the water potential gradient between the leaf and the air is reduced, so less water is lost by evaporation
Why do plants found on beaches have to be well adapted?
The water is quickly absorbed by the sand, so they must have long roots
It is windy and dry which means increased evaporation
The water is often salty, which means it is harder o pull water into cells by osmosis
How does having leaves with a smaller surface area to volume ratio help reduce water loss?
Having leaves with a smaller surface area means that the rate of water loss can be reduced because of the slower rate of diffusion, but this must be balanced with the need for a large surface area for photosynthesis
Why do mammals have to absorb large amounts of oxygen and release large amounts of CO2?
They are relatively large organisms
They maintain a high body temperature which is controlled by metabolic and respiratory rates
Why are lungs located inside the body?
The body would otherwise lose a great deal of water
Air isn’t dense enough to support and protect them
What are the lungs?
Lobed structures made of a series of bronchioles
What is the trachea?
A flexible airway supported by rings of cartilage. This stops the trachea collapsing when you breathe in
What are the bronchi?
Two mucus containing tubes which connect the trachea to each lung
What are bronchioles?
Subdivisions of the bronchi. They are surrounded by rings of muscle to control air flow to the alveoli
What are alveoli?
Minute air sacs across which gas exchange takes place. Elastic fibres allow them to stretch and contract
How is surface area maximised in the lungs? 5
The bronchioles are branching subdivisions of bronchi
Millions of alveoli which have the ability to stretch
Alveoli are highly folded
Large capillary network surrounding alveoli
Biconcave red blood cells
How is the length of the diffusion pathway minimised? 3
The walls of the alveoli are one cell thick
The lining of the capillaries are also one cell thick
Squamous epithelial cells
How is the concentration gradient maximised? 3
Lungs ventilated by a tidal stream of air which ensures the air within them is constantly replenished
Ventilation keeps oxygen high in the alveoli
Circulation keeps oxygen low in the capillaries
What is ventilation?
The movement of air into and out of the lungs
What is inspiration?
When the pressure inside your chest is lower than the outside pressure so air is forced into the lungs
What is expiration?
When the pressure inside your chest is higher than the outside pressure so air is forced out of your lungs
What are the three sets of muscles that control ventilation?
Internal intercostal muscles
External intercostal muscles
Diaphragm
When the internal intercostal muscles contract, what happens?
Expiration
When the external intercostal muscles contract, what happens?
Inspiration
What happens when you breathe in?
The external intercostal muscles and diaphragm contract
The ribs are pulled upwards and outwards and the diaphragm flattens, which increases the volume of the thorax
The increased volume results in reduced pressure in the lungs
Atmospheric pressure is now greater, so air is forced into the lungs
What happens when you breathe out?
The internal intercostal muscles contract and the diaphragm relaxes
The ribs move down and in, increasing the pressure of the thorax
The decreased volume results in increased pressure in the lungs
Atmospheric pressure is now less, so air is forced out of the lungs
Equation for pulmonary ventilation rate (dm3min-1)
tidal volume x ventilation rate
What is pulmonary ventilation rate?
Total volume of air taken in in one minute
What is tidal volume?
Volume taken in with each breath
What is ventilation rate?
Number of breaths per minute
Where does gas exchange take place in mammals?
The epithelium of the alveoli
How does oxygen diffuse from the alveoli into the blood?
The oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium and into the haemoglobin in the blood
Why are red blood cells slowed as they pass through capillaries?
Capillaries are so small that the red blood cells must flatten themselves against the walls of the capillaries to pass through
Why is it good that red blood cells are slowed down as they pass through capillaries?
There is more time for diffusion
Why is it beneficial that red blood cells are pushed against the capillary walls?
There is a shorter diffusion pathway
Why is it beneficial that the walls of both the alveoli and the capillaries are thin?
There is a shorter diffusion pathway
How is a steep concentration gradient maintained in the lungs?
Ventilation keeps oxygen concentration high in alveoli and circulation keeps it low in the blood
When does a correlation occur?
When a change in one of two variables is reflected by a change in the other variable
Name 5 risk factors for lung cancer
Smoking Genetics Air pollution Infections Occupation
What happens during digestion?
Large, insoluble food molecules are broken down into smaller, soluble food molecules by hydrolysis by enzymes
What is the function of the oesophagus?
It carries food from the mouth to the stomach
What is the function of the stomach?
A muscular sack that produces enzymes to digest food
Function of the retum
The faeces are stored here before egestion
What is the function of the large intestine?
It absorbs water
What do carbohydrates form when they are broken down?
Disaccharides
What do fats form when they are broken down?
Monoglycerides and fatty acids
What do proteins form when they are broken down?
Amino acids
What is the function of the small intestine?
It secretes enzymes to further digest the food
What is the function of the salivary glands?
Secrete amylase, which hydrolyses starch into maltose
What is the function of the pancreas?
Secretes enzymes to hydrolyse proteins, lipids and starch
What is the physical breakdown of food?
Structures such as teeth break down the food and increase the surface area for digestion
What is the chemical breakdown of food?
Enzymes use hydrolysis to add water to chemical bonds holding the molecule together and break it apart
How are lipids broken down?
Enzymes called lipases hydrolyse the ester bond found in triglycerides to produce fatty acids and monoglycerides
How are lipids emulsified?
Bile salts made by the liver turn larger lipids into smaller droplets with a larger surface area
What does lactose form when hydrolysed?
Alpha glucose + galactose
What does sucrose form when hydrolysed?
Alpha glucose + fructose
What are the three different peptidases?
Endopeptidases
Exopeptidases
Dipeptidases
What do endopeptidases do?
Hydrolyse the peptide bonds in the centre of polypeptide chains
Where are endopeptidases found?
The stomach
Where are exopeptidases found?
Small intestine
What do exopeptidases do?
Hydrolyse the peptide bonds at the ends of polypeptide chains
What do dipeptidases do?
Hydrolyse the peptide bond between just two amino acids
Where are dipeptidases found?
Attached to the membrane of the small intestine
How are carbohydrates broken down?
Saliva enters the mouth and is thoroughly mixed with the food via chewing
Saliva contains amylase, which begins to hydrolyse the glycosidic bonds in starch into maltose
The food is swallowed and enters the stomach, where the amylase denatures
The food then enters the small intestine where it is mixed with pancreatic juice
Pancreatic amylase hydrolyses any remaining starch into maltose
Salts are produced by the small intestine and pancreas to keep the solution alkaline, which is where amylase works best
Muscles push the food along the ileum
Maltase (a membrane-bound disaccharidase) is produced by the ileum
Maltase hydrolyses the maltose to form alpha glucose
How is glucose absorbed into the bloodstream?
Cotransport with sodium ions
How is galactose absorbed into the blood stream?
Cotransport with sodium ions
How is fructose absorbed into the blood stream?
Facilitated diffusion
How are amino acids absorbed into the blood stream?
Co-transport with sodium ions through sodium-dependent transporter proteins
What properties do villi possess which increases the efficiency of absorption? 5
They massively increase the surface area
1 cell thick walls = short diffusion pathway
Well supplied with blood vessels to maintain the concentration gradient
Microvilli increase surface area even more
They are able to move, which mixes the contents of the ileum and maintains the concentration gradient
How are monosaccharides absorbed into the blood?
Facilitated diffusion and co-transport
How are triglycerides absorbed into the blood?
Micelles come into contact with the villi and microvilli of the lumen
Micelles break down, releasing fatty acids and glycerol
They are small and uncharged so pass through the bilayer through simple diffusion
Monoglycerides and fatty acids recombined to form triglycerides
Triglycerides combined with cholesterol and lipoproteins to form chylomicrons
Chylomicrons move out of the cell by exocytosis
They enter lacteals at the centre of each villus
Chylomicrons in lymphatic system enter the blood system
Triglycerides in chylomicrons hydrolysed by cells of capillary walls
Monoglycerides and fatty acids diffuse into cells
How do chylomicrons exit cells?
Exocytosis - they are too large to leave otherwise
