TOPIC 3 - surface area: volume + gas exchange

Question 1

how does an organisms size relate to their surface area to volume ratio?

Answer 1

the larger the organism the lower the surface area to volume ratio.

Question 2

how does an organisms surface area to volume ratio relate to their metabolic rate?

Answer 2

the smaller the surface area to volume ratio, the higher the metabolic rate.

Question 3

how might a large organism adapt to compensate for its small surface are to volume ratio?

Answer 3

CHANGES THAT INCREASE SURFACE AREA:
- folding of membranes
eg. villi / microvilli in small intenstines

Question 4

why do multicellular organisms require specialised gas exchange surfaces?

Answer 4

their smaller surface area to volume ratio means the distance needed to be crossed is larger and substances cannot easily diffuse at the cells as in a single-celled organism.

Question 5

name three features of an efficient gas exchange surface?

Answer 5

1. large surface area. eg folded membranes in mitochondria
   2.thin/short distance eg walls of capillaries
   3.steep concentration gradient, maintained by blood supply or ventilation. eg at the alveoli

Question 6

name and describe three adaptations of a leaf that allow efficient gas exchange?

Answer 6

1. thin and flat to provide short diffusion pathway and large SA:V ratio.
   2.Many minute pores in the stomata which allows gases to easily enter
   3.Air spaces in the mesophyll, allow gases to move around in the leaf, facilitating photosynthesis.

Question 7

how do plants limit their water loss while still allowing gases to be exchanged?

Answer 7

Stomata regulated by guard cells which allow them to open and close as needed. Most stay closed to prevent water loss, while some open to let oxygen in.

Question 8

what are xerophytes?

Answer 8

a species of plant that has adaptations to survive in an environment with little liquid water.

Question 9

how are xerophytes adapted to minimise water loss?

Answer 9

1.sunken stomata in pits - traps moist air, reducing the concentration gradient of water between the leaf and the air. This reduces the amount of water diffusing out of the leaf and evaporating away.

2. Hair on epidermis - traps moist air around the stomata
3. curled leaves with the stomata inside - protecting them from the wind.
4. reduced number of stomata - so less release of water

5.waxy, waterproof cuticles on leaves and stems to reduce evaporation

Question 10

why cant insects use their bodies as an exchange surface?

Answer 10

they have a waterproof chitin exoskeleton and a smal SA:V ratio in order to conserve water.

Question 11

name and describe 3 main features of an insects gas transport system.

Answer 11

Spiracles - holes on the body’s surface which may be opened or closed by a valve for gas or water exchange

Tracheae - large tubes extending through the body tissues, supported by chitin rings to prevent collapse.

Tracheoles - smaller branches dividing off the tracheae. Delivers oxygen to the cells and tissues of the insect.

Question 12

explain the process of gas exchange in insects?

Answer 12

• air enters the bodies of the insects through spiracles
  A diffusion gradient allows O2 to diffuse in and Co2 to diffuse out.
• Contraction of muscles in the tracheae allows mass movement of air in and out.
• spiracles transfer the air to thin tubes called the trachea, and the tracheae delivers oxygen to the cells and the tissues of the insect.

Question 13

why is the tracheae a good transport system?

Answer 13

• very extensive throughout the insects body and tissue which means every cell has a short diffusion pathway.

Question 14

why don’t the tracheae open or close?

Answer 14

The tubes have rings of muscles around them to keep them open and aid with gas exchange.

Question 15

why can’t fish use their bodies as a gas exchange surface?

Answer 15

They have a waterproof, impermeable outer membrane and a small SA:V ratio.

Question 16

Name and describe the two main features of a fish’s gas transport?

Answer 16

Gills= located within the body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles.

Lamellae= at right angles to the gill filaments, give an increased surface area.Blood and water flow across them in opposite directions (countercurrent exchange system)

Question 17

Explain the process of gas exchange in fish.

Answer 17

• the fish opens its mouth to enable water flow in,then closes its mouth to increase pressure
• water passes over the lamellae, and the oxygen diffuses into the bloodstream.
• waste carbon dioxide diffuses into the water and flows back out of the gills.

Question 18

How does the countercurrent exchange system maximise oxygen absorbed by the fish?

Answer 18

The counter-current system ensures the concentration gradient is maintained along the whole length of the capillary.Maintains a steep concentration gradient, as water is always next to blood of a lower oxygen concentration. Keeps rate of diffusion constant and enables 80% of available oxygen to be absorbed.

Question 19

describe the pathway taken by air as it enters the mammalian gaseous exchange system?

Answer 19

nasal cavity —> trachea —> bronchi —> bronchioles —> alveoli

Question 20

describe the function of the nasal cavity in the mammalian gaseous exchange system?

Answer 20

good blood supply warms and moistens air entering the lungs. Goblet cells in the membrane secrete mucus which traps dust and bacteria.

Question 21

describe the trachea and its function in the mammalian gaseous exchange system?

Answer 21

• wide tube
• supported by C-shaped cartilage = keeps air passage open during pressure changes. Prevents it from collapsing as air pressure decreases
• lined by ciliated epithelium cells which moved mucus towards the throat to be swallowed, preventing lung infections.
• carries air to the bronchi

Question 22

describe the bronchi and their function in the mammalian gaseous exchange system?

Answer 22

• supported by rings of cartilage that are lined by ciliated epithelium cells
• narrower and two of them in each lung
• allows passage of air into the bronchioles

Question 23

describe the bronchioles and their function in the mammalian gaseous exchange system?

Answer 23

• narrower than bronchi
• don’t need to be kept open by cartilage
• have muscle and elastic fibres so they can contract and relax easily during ventilation
• allow passage of air into the alveoli

Question 24

describe the alveoli and their function in the mammalian gaseous exchange system?

Answer 24

• mini air sacs
  -lined with epithelium cells
• site of gas exchange
• walls only one cell thick
  -each alveoli is surrounded by a network of capillaries
• 300 million in each lung
• collagen and elastic fibres = allow it to stretch as they fill with air when breathing in

Question 25

Explain process of inspiration and changes that occur throughout the thorax.

Answer 25

• external intercostal muscles contract ( while internal relax) = pulling ribs up and out
• diaphragm contracts and flattens
• volume of the thorax increases
• atmospheric pressure is greater than pulmonary pressure, so air is forced into the lungs

Question 26

explain the process of expiration and the changes that occur throughout the thorax.

Answer 26

• internal intercostal muscles contract ( whilst external relax) = bringing ribs down and in
• diaphragm relaxes and domes upwards
• volume of thorax decreases ( to increase pressure)
• pulmonary pressure is greater than atm, and so air is forced out the lungs.

Question 27

what is tidal volume?

Answer 27

the volume of air we breath in and out during each breath at rest

Question 28

what is breathing rate?

Answer 28

the number of breaths we take per min

Question 29

how do you calculate pulmonary ventilation rate?

Answer 29

tidal volume x breathing rate

• can be measured using a spirometer = device which records volume changes onto a graph as a person breathes.