3.1 Surface area to volume ratio + 3.2 Gas exchange Flashcards
1
Q
What is surface area (of an organism)
A
The total area of an organism that is exposed to the external environment.
2
Q
What is volume (of an organism)
A
The total internal space inside the organism.
3
Q
How does surface area to volume ratio relate to the size of an organism
A
The larger the organism, the smaller its surface area to volume ratio.
4
Q
Why do larger organisms have a smaller surface area to volume ratio
A
Volume increases much more rapidly than surface area as size increases.
5
Q
What is metabolic rate
A
The amount of energy expended by that organism within a given period of time.
6
Q
What is basal metabolic rate (BMR)
A
The metabolic rate of an organism when at rest. It is significantly lower when an organism is actively moving.
7
Q
What are 3 methods that can be used to estimate/ measure the metabolic rate
A
- Oxygen consumption
- Carbon dioxide production
- Heat production
8
Q
How does body mass affect the metabolic rate
A
- The greater the mass of an organism, the higher metabolic rate.
- E.g. a single rhino consumes more oxygen within a given time period compared to a single mouse.
9
Q
How does surface area to volume ratio affect the metabolic rate
A
- The BMR per unit of body mass is higher in smaller animals (with larger surface area: volume).
- Smaller animals have a larger SA:V ratio so they lose more heat, meaning they have to use up more energy to maintain their body temperature.
10
Q
How do single celled organisms exchange substances and why is this possible
A
- They have a larger SA:V ratio, so can exchange substances via simple diffusion.
- The large surface area allows for maximum absorption of nutrients and gases and secretion of waste products.
- The small volume means the diffusion distance to all organelles is short.
11
Q
Why is it not possible for larger organisms to exchange substances via simple diffusion
A
- Larger organisms have a smaller SA:V ratio
- There is less surface area for the absorption of nutrients and gases and the secretion of waste products.
- The greater volume means there is a longer diffusion distance to the cells and tissues of the organism.
12
Q
How do larger organisms exchange substances
A
They have specialised exchange systems, e.g. gas exchange system and circulatory system.
13
Q
What are 3 things that effective exchange surfaces in organisms have
A
- A large surface area
- Short diffusion distance
- Concentration gradient (maintained)
14
Q
What are spiracles (insects)
A
- Openings in the exoskeleton which have valves, allowing them to open and close.
- They increase the surface area needed for gas exchange.
- Air enters through them and flows directly into the tracheal system.
15
Q
What are some adaptations of spiracles and why is this necessary
A
Water also leaves the insect through the spiracles, so they are often closed in order to minimise water loss.
16
Q
What are the trachea (in insects)
A
- Tubes within the insect breathing system which lead to tracheoles (narrower tubes)
- They are supported and strengthened by rings to prevent them collapsing as the air pressure inside them fluctuates.
17
Q
What are the tracheoles and what is an adaptation of them
A
- Narrower tubes at the end of the trachea.
- They extend through the body tissue and lead to the muscle fibres which is the site of gas exchange.
- They have water filled ends.
18
Q
How does the tracheal system in insects create and maintain a concentration gradient
A
- The muscle cells use up oxygen through aerobic respiration, causing the concentration inside the insect to fall.
- This creates an oxygen diffusion gradient.
- Carbon dioxide is produced and diffuses down its concentration gradient out of the tracheoles.
19
Q
What is mass transport in insects and why is it needed
A
- Very active/flying insects need a more rapid supply of oxygen.
- Muscle contraction squeezes the trachea, enabling mass movement of air in and out.
- ‘Abdominal pumping’ increases the pressure, causing CO2 to be pushed out along a pressure gradient.
20
Q
Why is it helpful that the ends of the tracheoles are filled with water
A
- Muscle cells may anaerobically respire, producing lactate (a soluble substance which dissolves in the water).
- This lowers the water potential of muscle cells, causing water from the tracheoles to move into them by osmosis which decreases the pressure in the tracheoles.
- This draws more air in.
21
Q
How do insects compromise between gas exchange and water loss
A
- Small insects living on the ground are surrounded by air and prone to drying out, so they have waterproof exoskeletons that prevent water loss.
- The waxy coating of the exoskeleton makes gas exchange by diffusion very difficult, so they have an evolved breathing system (the tracheal system).
22
Q
What are 3 reasons why fish need adapted gas systems
A
- There is a lower concentration of oxygen in water than air, causing a smaller concentration gradient between mediums and tissues.
- There is a lower rate of oxygen diffusion in water than air, so less oxygen in tissues.
- Water is denser and more viscous than air, so it is harder to maintain a concentration gradient.
23
Q
What are 3 structural adaptations of fish
A
- High surface area to volume ratio
- Rich blood supply
- Thin layers
24
Q
Why is a high surface area to volume ratio a useful adaptation
A
Causes a faster rate of diffusion as there is a steeper concentration gradient and more area for diffusion to occur across.
25
Why is a rich blood supply a useful adaptation
It maintains a steep concentration gradient for diffusion.
26
How is having thin layers a useful adaptation
Faster rate of diffusion as the diffusion distance is shorter.
27
Describe the structure of fish gills
- There is a series of gills on each side of the head.
- Each gill arch is attached to 2 stacks of filaments.
- Rows of lamellae on the surface of each filament.
- The lamellae surface consists of a single layer of flattened cells that cover a vast network of capillaries.
28
What is the name of the system used in fish gills
The counter-current system
29
What is the task of the counter-current system
To maintain a diffusion gradient along the entire width of the lamellae.
30
Describe the structure of a leaf (from top to bottom)
- Waxy cuticle
- Upper epidermis
- Palisade mesophyll layer
- Spongy mesophyll layer
- Stomata
- Guard cells
- Lower epidermis
31
What are the upper and lower epidermis
Layers of tightly packed cells.
32
What is the palisade mesophyll layer
A layer of elongated cells containing chloroplasts.
33
What is the spongy mesophyll layer
A layer of cells that contain an extensive network of air spaces.
34
What are the stomata
Pores (usually) on the under side of the leaf which allow air to enter.
35
What are the guard cells
Pairs of cells that control the opening and closing of the stomata.
36
Describe gas exchange in plants
- Carbon dioxide diffuses into the leaf through the stomata
- The air spaces within the spongy mesophyll layer allow carbon dioxide to rapidly diffuse into cells
- The carbon dioxide is used up in photosynthesis (by cells containing chloroplasts) which maintains the concentration gradient
37
How is photosynthesis linked to transpiration
If there is a greater rate of photosynthesis, more water will be drawn into the plant as water is a reactant which will increase the amount of water available to the plant and therefore increase the rate of transpiration.
38
What are 4 factors that affect the rate of transpiration
- Light intensity
- Temperature
- Humidity
- Air movement
39
How does light intensity affect the rate of transpiration
- As light intensity increases, the rate of transpiration increases.
- This is because light is needed for photosynthesis, so there will be a greater rate of photosynthesis so more water will be drawn into the plant which will increase the rate of transpiration.
40
How does temperature affect the rate of transpiration
- As temperature increases, the rate of transpiration increases.
- This is because water molecules will have more kinetic energy which will increase the movement of water vapour.
- This will increase the rate of evaporation and therefore transpiration.
41
How does humidity affect the rate of transpiration
- As humidity increases, the rate of transpiration decreases.
- This is because there is more water in the air (higher water potential) so there is a less steep concentration gradient.
- This causes water to diffuse out of the stomata at a slower rate.
42
How does air movement affect the rate of transpiration
- Greater air movement increases the rate of transpiration (or as air movement decreases, rate of transpiration decreases).
- This is because in still air, water accumulates around the stomata which reduces the water potential gradient so water will diffuse out of the stomata at a slower rate.
43
What happens when plants don't get enough water
- Water is a reactant for photosynthesis, so decreased rate.
- Lower rate of glucose production.
- Lower rate of aerobic respiration.
- Less ATP for active metabolic processes (e.g. active transport, protein synthesis).
- Essential active metabolic processes cannot occur.
- Cell death.
44
What happens when plants get too much water
- Less air in the mesophyll tissue.
- Lower rate of gas exchange through stomata (as harder to pass through mesophyll tissue).
- Reduced rate of CO2 uptake.
- Lower rate of photosynthesis.
- Same as when there is not enough water.
- Plant could also become water logged, making it too heavy so it could sink.
45
What is a xerophyte
Plants that live in dry places.
46
What are some adaptations of xerophytes
- Sunken stomata
- Thick waxy cuticle
- Low stomata density
- Stomatal hairs
- Rolled leaves
- Extensive roots
47
How do sunken stomata help xerophytes
Helps maintain humid air around the stomata which minimised the water potential gradient, so less water diffuses out of the stomata and at a slower rate.
48
How does a thick waxy cuticle help xerophytes
- The waxy layer stops uncontrolled evaporation through leaf cells.
- The thickness increases the diffusion distance, causing water to evaporate slower.
49
How does a low stomata density help xerophytes
Causes a smaller surface area for water to diffuse out of the plant.
50
How do stomatal hairs and rolled leaves help xerophytes
They maintain humid air around the stomata which minimises the water potential gradient.
51
How do extensive roots help xerophytes
They maximise the water uptake.
52
What is a hydrophyte
Plants adapted to a habitat with an abundance of fresh water.
53
What are some adaptations of hydrophytes
- Very thin/ no waxy cuticle
- High stomatal density
- Wide, flat leaves
- Small roots
54
What is the trachea
- Connects mouth and lungs
- Has 'C' shaped cartilage rings which provide support and prevent the airways from collapsing.
55
What is the role of goblet cells in the trachea and bronchi
They secrete mucus to trap pathogens.
56
What is the role of ciliated cells in the trachea and bronchi
They sweep away pathogens trapped in the mucus.
57
What is ventilation
- The flow of air in and out of the alveoli.
- Caused by muscle contractions and changes in air pressure.
58
Describe the passage of air from outside the body into it
- Nose/mouth
- Trachea
- Bronchi
- Bronchioles
- Alveoli
59
Describe the process of inhalation (also known as inspiration)
- Diaphragm contracts and flattens
- External intercostal muscles contract
- Internal intercostal muscles relax
- Ribs move up and out
- This increases the volume of the thorax and lungs which decreases the pressure
- Atmospheric pressure is now greater than the pressure inside the lungs, so air pulled in down a pressure gradient.
60
Describe the process of exhalation
- Diaphragm relaxes and arches/curves
- External intercostal muscles relax
- Internal intercostal muscles contract
- Ribs move down and inwards
- This decreases the volume of the thorax and lungs which increases the pressure
- Atmospheric pressure is now lower than the pressure inside the lungs, so air drawn out down a pressure gradient.
61
What are 3 ways in which the alveoli are adapted for gas exchange
- Large number of alveoli
- Thin walls
- Extensive capillary network
62
How does a large number of alveoli adapt them for gas exchange
The large number of them increases the surface area available for oxygen and carbon dioxide to diffuse across.
63
How do thin walls adapt the alveoli for gas exchange
- The walls of both the alveoli and capillaries are around one cell thick.
- This decreases the distance in which gases have to diffuse, so increases the efficiency of gas exchange.
64
How does an extensive capillary network adapt the alveoli for gas exchange
- Constant blood flow through the capillaries allows oxygenated blood to be taken away from the alveoli and deoxygenated blood to be brought to them which maintains a concentration gradient.
65
What happens to red blood cells during gas exchange and why is this useful
- The capillaries have a small lumen, so the red blood cells are squeezed through.
- This reduces the speed they travel at, allowing more diffusion to occur.
66
What are the alveoli walls made of and why is this necessary
They are made of collagen and elastic fibres, allowing them to stretch (during inhalation) which increases thee volume of gas they can contain.
67
What is pulmonary ventilation rate
The volume of air breathed in (or out) in one minute/ a given time.
68
What is the equation for calculating pulmonary ventilation rate
PVR (pulmonary ventilation rate) = tidal volume x breathing rate.
69
What is tidal volume
The volume of air normally taken in at each breath when the body is at rest (approx. 0.5dm3).
70
What is breathing rate
The number of breaths taken in 1 minute (approx. 12-20 breaths in a healthy adult).
71
What are some examples of symptoms of COPD (chronic obstructive pulmonary disease)
- Chest tightness, wheezing, difficulty breathing.
- When goblet cells become enlarged, they produce more mucus which destroys the cilia (can no longer sweep mucus away from lungs).
- Mucus contains dust and pathogens which can block the bronchioles which could cause an infection.
- This attracts phagocytes which damage the elasticity of the alveoli walls, causing them to merge togehter and not be able to stretch as much.
72
What factors can affect lung disease
- Smoking
- Pollution
- Illness
- Genetics, etc.
73
Explain the importance of one adaptation of the gas exchange surface in the tracheal system of an insect
1. Tracheal wall thin/one cell thick
2. So short diffusion pathway/distance
OR
1. Tracheoles enter/supply tissues/muscle fibres
2. So diffusion directly into cells
OR
1. Tracheoles are highly branched
2. So large surface area for diffusion
74
Explain the advantages for larger animals of having a specialised system that facilitates oxygen uptake (2 marks)
- Larger organisms have a smaller surface area to volume ratio
- Specialised system overcomes the long diffusion pathway
