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AQA A-Level Biology > Chapter 6 - Exchange > Flashcards

Chapter 6 - Exchange Flashcards

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1
Q

Name three things that organisms need to exchange with their environment

A

Oxygen, waste products and heat

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2
Q

What is passive exchange?

A

No metabolic energy is required

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3
Q

Give two examples of passive exchange

A

Diffusion and osmosis

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4
Q

What is active exchange?

A

Metabolic energy is required

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5
Q

Give an example of active exchange

A

Active transport

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6
Q

Why can substances diffuse directly out of the cells across the cell surface membrane in single-celled organisms?

A

They have a large SA:V which ensures efficient exchange

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7
Q

Why is diffusion across the cell membrane too slow in multicellular animals?

A

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

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8
Q

What is mass transport?

A

The use of an efficient system to carry substances to and from individual cells

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9
Q

What is the exchange system in mammals?

A

Circulatory system

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10
Q

What is the exchange system in plants?

A

The xylem and phloem

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11
Q

How are multicellular organisms adapted for efficient exchange?

A

They have a flat shape for a short diffusion pathway or they have specialised exchange surfaces to increase the SA:V

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12
Q

Why do specialised exchange surfaces normally have a large SA:V?

A

It increases the rate of exchange

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13
Q

Why are specialised exchange surfaces normally very thin?

A

The diffusion pathway is short so materials can cross the surface very rapidly

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14
Q

What is Fick’s law?

A

(Surface area x concentration gradient) / length of diffusion pathway

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15
Q

Why do smaller organisms generally need a higher metabolic rate?

A

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

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16
Q

Why might an animal living in the Arctic have a round shape?

A

It has a small surface area which reduces heat loss and helps the animal stay warm

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17
Q

Why might an animal living in the desert have a pointed nose and long ears?

A

Both of these increase its surface area so it is easier to lose heat and stay cool

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18
Q

Why might animals with a high SA:V have kidney structure adaptations?

A

They tend to lose more water because of their large surface area so they produce less urine to compensate

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19
Q

Why might small mammals living in cold regions need to eat lots of high energy foods like nuts?

A

Because of their large surface area, they need fast metabolic rates

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20
Q

Why do elephants have large ears?

A

This increases their surface area so it is easier to cool down

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21
Q

What do most gas exchange systems have in common?

A

They have a large surface area and are often just one cell thick

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22
Q

What are tracheae?

A

An internal network of tubes, supported by strengthened rings

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23
Q

What are tracheoles?

A

Dead end tubes found on the end of tracheae

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24
Q

How does the insect respiratory system achieve a large surface area?

A

There are lots of tracheoles which span the whole body

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25
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
26
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
27
What are spiracles?
Tiny pores which cover the insect's body and can be opened and closed on demand
28
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
29
Why do insects keep their spiracles closed for most of the time?
To avoid water loss by evaporation
30
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
31
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
32
What is the specialised gas exchange system in fish?
Gills
33
How do fish gills achieve a high surface area?
They consist of filaments and lamellae (which are at right angles to the filaments)
34
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
35
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
36
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
37
What percentage of oxygen is removed from the water?
80%
38
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
39
What are the two processes that plants conduct?
Photosynthesis and aerobic respiration
40
Equation for photosynthesis
6CO2 + 6H2O -> C6H12O6 + 6O2
41
The equation for aerobic respiration
C6H12O6 + 6O2 -> 6CO2 + 6H2O
42
When photosynthesis isn't occurring, why is carbon dioxide still produced?
It is produced by aerobic respiration
43
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
44
How do plants balance the conflicting needs of gas exchange vs water loss?
They have guard cells which can open and close stomata
45
Why are the stomata mainly at the bottom of the leaf?
Reduces transpiration and evaporation as not in direct sunlight
46
What is the function of guard cells?
To retain water when it is needed
47
What is the function of the waxy cuticle?
To stop evaporation from the leaf surface
48
Why must the cell surface be wet?
To allow the gases to dissolve
49
How are mesophyll cells adapted in the leaf?
They create big air spaces which increase the surface area available for diffusion
50
Why can a leaf be a maximum of 10 cells thick?
Must have a short diffusion pathway
51
State three ways in which insects minimise water loss
Small SA:V Waterproof covering Spiracles
52
How can spiracles help to conserve water?
Opening of the tracheae which can open or close Occurs mostly when at rest
53
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
54
Why does an insect have a small surface area to volume ratio?
To minimise area over which water is lost
55
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 ```
56
Why can't plants have a small surface area to volume ratio?
The slower the rate of diffusion
57
What are xerophytes?
The plants adapted to living in dry conditions where they limits water loss through transpiration
58
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
59
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
60
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.
61
How does having stomata in pits or grooves help to reduce water loss?
Traps moist air reducing the water potential gradient
62
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
63
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
64
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
65
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
66
What is the trachea?
Flexible airway that is supported by rings of cartilage
67
What is cartilage?
Prevents the trachea collapsing as the air pressure inside falls when breathing.
68
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
69
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
70
What are alveoli?
Air sacs which have collagen and elastic fibres which allow the alveoli to stretch when filling in with air.

AQA A-Level Biology (22 decks)

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