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
Small SA:V
Waterproof covering
Spiracles
How can spiracles help to conserve water?
Opening of the tracheae which can open or close
Occurs mostly when at rest
Why do insects have a waterproof covering?
Covering the body surface which is rigid outer skeleton of chitin that is covered with a waterproof cuticles
Why does an insect have a small surface area to volume ratio?
To minimise area over which water is lost
State five ways in which plants reduce water loss
Thick cuticles Rolling up of leaves Hairy leaves Stomata in pit or grooves Reduced surface area to volume ratio
Why can’t plants have a small surface area to volume ratio?
The slower the rate of diffusion
What are xerophytes?
The plants adapted to living in dry conditions where they limits water loss through transpiration
How does a thick waxy cuticle reduce water loss?
Forms a waterproof barrier. The thick of the cuticle, the less water escape by this means
How can rolling leaves reduce water loss?
Protects lower epidermis trapping a region of air (saturated with water vapours). The region becomes a very high water potential where there is no gradient between inside and outside therefore no water loss
How do hairy leaves reduce water loss?
Thick layer on the surface which traps are, leaving a moist surface area. The gradient stops water from being evaporated.
How does having stomata in pits or grooves help to reduce water loss?
Traps moist air reducing the water potential gradient
Why do plants found on beaches have to be well adapted?
The soil solution is very salty meaning a very low water potential, making it difficult for root hairs to draw water in by osmosis.
In winter, the soil is frozen and therefore cannot absorb water by a samosas
Why do mammals have to absorb large amounts of oxygen and release large amounts of CO2?
Large organisms with a large volume of living cells
Maintain a high body temperature due to having high metabolic and respiratory rates
Why are lungs located inside the body?
Air is not dense enough to support and protect these delicate structures
The body as a whole would otherwise lose a great deal of water and dry out
What are the lungs?
A pair of lube structure is made up a series of highly branched tubulars called bronchioles which end in tiny air sacs called alveoli
What is the trachea?
Flexible airway that is supported by rings of cartilage
What is cartilage?
Prevents the trachea collapsing as the air pressure inside falls when breathing.
What are the bronchi?
Two divisions of the trachea. Produce mucus mucus to trap dirt particles and have cilia that moves the dirt – laden you mucus towards the throat
What are bronchioles?
Series of branching subdivisions of the bronchi. The walls are made of mucus lined with epithelial cells. Which controls the flow of air in and out of the alveoli
What are alveoli?
Air sacs which have collagen and elastic fibres which allow the alveoli to stretch when filling in with air.
