Gas Exchange.

Question 0

What happens as an object increases in sise?

Answer 0

The (surface area)/ volume ratio decreases.

Question 1

What does gas exchange refer to?

Answer 1

The uptake of oxygen and the removal of carbon dioxide by diffusion across the membrane of a cell.

Question 2

Why can’t a single cell grow bigger than 1mm?

Answer 2

Because beyond this sise the surface area becomes too small to supply the whole volume with oxygen and remove the Carbon dioxide produced.

Question 3

How have large organisms (bigger than 1mm) overcome the surface area to volume ratio problem?

Answer 3

By becoming multicellular with millions of tiny cells with a large surface area to volume ratio.

Question 4

How do flatworms survive without a specialised gas exchange surface?

Answer 4

By reducing the diffusion distance to a minimum by remaining very thin. The problem with this is that these animals cannot develop internal organs and therefore remain at a primitive level of development. So many of them become parasites.

Question 5

How do earthworms survive without a specialised gas exchange surface?

Answer 5

These animals carry out gas exchange through wet epithelium below which there are millions of blood capillaries which are part of a closed blood system with veins, arteries, capillaries and pseudo hearts. They reduce the need for oxygen to a minimum by not doing very much.

Question 6

Why would an animal require a specialised gas exchange surface?

Answer 6

Because for an animal to be large and active large amounts of oxygen are required and large quantities of Carbon dioxide are produced.

Question 7

What is the gas exchange surface found in fish?

Answer 7

The gills

Question 8

What is the gas exchange surface in vertebrates from amphibians onwards?

Answer 8

Lungs

Question 9

What is the gas exchange surface found in insects?

Answer 9

The tracheal system.

Question 10

What features do all gas exchange surfaces have in common?

Answer 10

1 - large surface area produced by folding or pocketing.

2 - thin walls/membranes to reduce diffusion distance to a minimum.

3 - they are moist because gasses diffuse faster across a wet surface.

Question 11

Outline a feature common to gills and lungs?

Answer 11

The surface is highly vascularised.

Question 12

Why is a ventilation system necessary for some animals?

Answer 12

For highly active animals in water and on land a ventilation system is required to force air or water across the exchange surface by muscle contraction which keeps oxygen and carbon dioxide diffusion gradients very steep.

Question 13

How many pairs of gills do boney fish have?

Answer 13

Four pairs.

Question 14

Describe the structure of a gill.

Answer 14

They consist of a curved bone called the gill bar from which project two lines of thin gill filaments. Each filament has its own blood supply.

Question 15

Where are the gills positioned?

Answer 15

They are positioned in the pharynx, just beneath the operculum and just behind the buccal cavity.

Question 16

Outline the process of inspiration in fish.

Answer 16

1 - the mouth opens
2 - the floor of the buccal cavity falls, increasing the volume and decreasing the pressure at the front of the mouth compared with outside. As a result, the water moves in.
3 - the operculum on both sides expands, increasing the volume and decreasing the pressure in the pharynx. As a result water is pulled across the gill filaments, right to the back of the mouth. It is during this time that gas exchange occurs.

Question 17

Outline the process of expiration in fish.

Answer 17

1- the mouth closes
2- the floor of the buccal cavity is raised, forcing all the water into the back of the mouth
3- the operculum on both sides now flatten, increasing the pressure in the pharynx and forcing water out through the opercular valve I.e beneath the operculum.

Question 18

Describe the “flow” in a fish’s ventilation system.

Answer 18

Water flow is one way.

Question 19

How is each gill filament supplied with deoxygenated blood?

Answer 19

Through an afferent blood vessel. In the filament a capillary runs along the left hand margin and curves at the end of the filament and comes back down the right hand margin. In addition, many capillaries pass across the gill filament from the left hand margin to the right. Eventually the blood enters an efferent vessel. In this system gas exchange occurs when the blood moves into the capillaries.

Question 20

What is parallel flow?

Answer 20

This is where the blood in the gill filaments flows in the same direction as the water.

Question 21

What is counter flow?

Answer 21

This is where the blood in the gill filaments flows in the opposite direction as the water.

Question 22

What direction of flow is most effective and explain why.

Answer 22

Counter flow is more efficient at extracting oxygen because the oxygen diffusion gradient is maintained across the whole distance because the blood is moving towards water that has a higher oxygen saturation. Tis is not the case in parallel flow where the oxygen in the blood and water quickly reach an equilibrium.

Question 23

Why don’t gas exchange systems that work in water not work n land?

Answer 23

1 - Air does not support a thin gas exchange surface.

2 - A thin, moist surface will dry out rapidly when exposed to air. Therefore it must be protected by being placed inside the body.

Question 24

Outline how the gas exchange systems in terrestrial animals developed?

Answer 24

Seen first in the development of internal lungs in amphibians and the tracheal system developed in insects.

Reptiles, birds and mammals developed more complex gas exchange systems whilst the tracheal system in insects did not develop any further.

Question 25

Outline the anatomy of the mammalian thorax.

Answer 25

The thorax is like an airtight box which is bounded below by the Diaphram and at the front and sides by the sternum and ribcage and at the back by the backbone. The trachea is the entry point for air. The lungs themselves are not muscular therefore pressure changes are caused by contraction of the intercostals and diaphram.

Question 26

Outline the process of inspiration in mammals.

Answer 26

1. ) the diaphram and intercostals contract, causing the Diaphram to flatten and the ribcage to expand.
2. ) this pulls the outer pleural membrane away from the inner pleural membrane causing the volume of the pleural cavity to increase.
3. ) as a result, pressure in the pleural cavity goes down and the lungs expand into the space.
4. ) As a result, air is drawn in and gas exchange occurs in the alveoli.

Question 27

Outline the process of expiration in mammals (quiet breathing)

Answer 27

1. ) the diaphram and intercostals relax
2. ) the ribcage falls under its own weight and the diaphram springs back to its curved position.
3. ) as a result, volume in the pleural cavity goes down, causing pressure to go up above one atmosphere. This forces air out of the lungs.

Question 28

Where does gas exchange take place in the lungs?

Answer 28

In thin walled pockets called alveoli.

Question 29

Outline the structure of alveoli.

Answer 29

These are made from very thin epithelial tissue which reduces the diffusion distance for gas exchange. Each alveolus has a thin layer of water the inside to protect it from drying out (also to speed up diffusion) because this water is in contact with the air it evaporates into and I eventually breathed out of the body.

Question 30

Describe the position of the alveoli in the lungs.

Answer 30

Each alveolus is surrounded by a dense network of capillaries which also have a thin wal called the endothelium. This places the lumen in the alveoli about 3μm away from the blood.

Question 31

Why is the surface area for gas exchange so large in the lungs?

Answer 31

Because the alveoli are curved and there are so many of them.

Question 32

What does the efficiency of the gas exchange system in mammals depend on?

Answer 32

Maintaining steep diffusion gradient between the alveolar air and the blood. Which is in turn dependant upon muscle contraction because contraction o the heart keeps blood flowing around the body, and intercostal and Diaphram contraction ventilate the lungs.

Question 33

What is the gas exchange system in insects?

Answer 33

The tracheal system.

Question 34

What are spiracles?

Answer 34

These are muscular openings in the exoskeleton of an insect through which gas exchange occur. There are two spiracles to each segment of the body.

Question 35

What do the spiracles lead to in the tracheal system?

Answer 35

The spiracle then opens into a large tracheal tube lined with chitin.

Question 36

What comes after the tracheal tubes in the tracheal system?

Answer 36

These divide into hundreds of tracheoles which get progressively smaller and smaller and are not lined with chitin. The living cells of the small tracheoles are lined with water just like the alveoli. There is usually a small pool of fluid found at the bottom of the terminal tracheoles.

Question 37

What is the result of the tracheal system?

Answer 37

This means that no cell in the body of an insect is more than 1μm from air.

Question 38

How does gas exchange occur In The tracheal system?

Answer 38

By diffusion across the wet tracheole walls.

Question 39

Outline the process of ventilation in insects.

Answer 39

For most of the time insects mainly rely on diffusion I.e oxygen in, CO₂ out. However the tracheal system can be ventilated by expanding and contracting the width of the thorax or abdomen.

Question 40

What are the main advantages of the tracheal system?

Answer 40

1. ) every living cell is close to air so the system is more efficient than that used in mammals.
2. ) this system limits water loss better than the lungs in mammals. Making insects better adapted to life on land than mammals.

Question 41

What is the main disadvantage of the tracheal system?

Answer 41

Because the system relies on mainly diffusion an insects body is limited to a maximum width of about 3cm.

Question 42

What problems are faced by plants on terms of gas exchange?

Answer 42

Similar problems faced by animals terrestrial animals. I.e preventing/limiting waterloss during gas exchange.

Question 43

How is the problem of waterloss overcome in plants?

Answer 43

By covering the surface with a waxy cuticle and by placing the gas exchange surface inside the leaf.

Question 44

Outline the structure of a leaf.

Answer 44

It consists of a waxy cuticle, beneath which is the upper epidermis, beneath which is the palisade mesophyll beneath which is a thick layer of spongy mesophyll, beneath which is the lower epidermis containing stomata and guard cells. Veins run through this structure consisting xylem tissue and phloem tissue.

Question 45

What is the role of the waxy cuticle in the leaf?

Answer 45

To prevent waterloss.

Question 46

What is the role of the upper epidermis in the leaf?

Answer 46

This is a protective, transparent covering for the palisade mesophyll.

Question 47

What is the role of the palisade mesophyll in the leaf?

Answer 47

This is the photosynthetic layer, containing chloroplasts.

Question 48

What is the role of the spongy mesophyll in the leaf?

Answer 48

This allows gas exchange between the palisade layer and the air outside.

Question 49

Outline the process of gas exchange in plants.

Answer 49

Gasses move easily through the spongy mesophyll so that CO₂ is taken up by the palisade mesophyll layer which produces O₂ by photosynthesis. These gasses enter and leave though the stomata during the day. At night the stomata close to reduce waterloss because photosynthesis comes to a stop.

Question 50

Where are guard cells positioned in the leaf?

Answer 50

Either side of the stomata in the lower epidermis of the leaf.

Question 51

Outline the structural adaptions of a guard cell?

Answer 51

1. ) a thickened inner wall. I.e the guard cell wall next to the stoma is thicker than the opposite wall.
2. ) chloroplasts are present
3. ) starch grains are present.

Question 52

Outline the mechanism of guard cell movement.

Answer 52

1. ) During the day, photosynthesis occurs and create A.T.P, also pH is high because of low CO₂ concentrations therefore little carbonic acid is present.
2. ) high pH signals the K⁺ pumps to bring in K⁺ by active transport from surrounding cells. The energy for which comes from A.T.P
3. ) High concentrations of K⁺ in guard cells during the day (due to abundance of A.T.P) lowers water potential in the guard cell causing water to move in by osmosis and the cell to become turgid.
4. ) As the guard cells become turgid they curve away from eachother due to the thick inner wall expanding more slowly than the thin outer wall as a result stomata open during the day.

At night stomata close because guard cells lose water and become flaccid. This is because CO₂ concentration increases, pH goes down and the pump stop. As a result ψcell increases and the cell loses water, becoming flaccid.