Chapter 6: Exchange

Question 1

All organisms need to exchange substances with the environment. Name some of the substances that need to be exchanged between an organism and its environment.

Answer 1

Cells need to:

• exchange heat with the enivronment
• take in oxygen for aerobic respiration
• nutrients for building organic material
• excrete waste products (carbon dioxide, urea)

Question 2

Do smaller organisms such as algae, bacteria and worms have a
a) higher surface-to-volume ratio
b) lower surface to volume ratio
Why is this?

Answer 2

The answer is a because smaller organisms have a bigger surface area compared to their volume

volume = L x W x H
surface are = H x W ()

Question 3

a cube hippo measures 2cm x 4cm x 4cm
volume = 2 x 4 x 4 = 32 cm3
total surface area = 64 cm2

a cube mouse only measures 1cm x 1cm x 1cm
volume = 1 x 1 x 1 = 1 cm3
total surface area = 6 x 1 x 1 = 6cm2

Who has the higher surface area to volume ratio?

Answer 3

The mouse because its surface area is six times larger than its volume. The total surface area : volume ratio of the hippo is 64:32 or 2:1 and the total surface area : volume ratio of the mouse is 6:1

Question 4

Why is diffusion enough for single celled organisms?

Answer 4

The substances they need can easily diffuse in and out of the single-celled organism and the rate of diffusion is also quick because of a short diffusion pathway - the sybstances don’t have to travel far from the outside

Question 5

Why do multicelluar organisms need specialised exchange organs and mass transport systems?

Answer 5

Diffusion is too slow and inefficient to supply the cells that are deep within the body, and most cells are too far away from the outside environment for substances to reach them in time.

Specialised exchange organs (lungs) are involved in exchanging substances directly with cells while mass transport systems (cirulatory system) are an efficient system for carrying substances to indivdual cells and taking away the waste they produce

Question 6

What system is used for gas exchange in fish

Answer 6

Fish use a counter-current system for gas exchange

Question 7

Gas exchange in insects

Answer 7

Insects use tracheae to exchanges gases with their environment, and in this way atmospheric air can be brought directly to respiring tissues

Question 8

Gas exchange in humans

Answer 8

Humans need to take in oxygen and get rid of carbon dioxide. The alveoli act as the exchange surface where this takes place.

Question 9

How do plants control water loss?

Answer 9

waxy waterproof cuticle
curled leaves to trap humid air
hairs to trap moist air
stomaa sunk in pits

Question 10

How do insects control water loss?

Answer 10

by closing their spriacles using muscles
waxy cuticle layer over their body
tiny hair around their spiracles
reduce evaporation

Question 11

Briefly describe the structure of the fills found in fish

Answer 11

• gills are made up of gill filaments
• stacked like pages in a book
• at right angles to the gill filaments are gill lamellae

Question 12

Decribe how the countercurrent exchange system works

Answer 12

• water and blood flow in opposite direction
• the concentration of 02 in the blood is always lower than in the water
• maintains a large difference in the concentration of oxygen
• also maintains a steep diffusion gradient across the whole length of the gill lamellae

Question 13

Describes the actions that take place during ventilation

Answer 13

Ventilation is breathing in and out.

Inspiration/inhalation or breathing in involves increasing the volume inside the lungs so that air is forced down a concentration gradient

Expiration/exhalation or breathing out involves decreasing the vlume inside the lungs so that air is forced out from a high conc. in the lungs to a low conc. in the atmosphere

Question 14

Decribe how the insects exchange gas?

• along a diffusion gradient
• mass transport
• ends of tracheoles are filled with water

Answer 14

• air moves into the tracheae through spiracles (pores on the surface)
• oxygen travels down conc. gradient
• tracheoles are in contact with individual cells; have thin permeable walls so adapted for exchange
• oxygen is able to diffuse directly to respiring cells
• CO2 moves down conc. gradient towards spiracles
• insects use rhythmic abdominal movements to move air in and out of spiracles (mass transport)
• water at the ends of tracheoles draw water into cells

Question 15

Inspiration/inhalation or breathing in involves increasing the volume inside the lungs so that air is forced down a concentration gradient. How is air forced into the lungs.

Answer 15

• external intercostal muscles and diaphragm contract
• ribcage moves upwards and outwards and diaphragm flattens
• increases volume of thoracic cavity
• lung pressure decreases
• air flows into lungs from area of high pressure (atmosphere) to an area of lower pressure

Question 16

Inspiration is an active process. What does this mean?

Answer 16

It requires energy

Question 17

Expiration/exhalation or breathing out involves decreasing the vlume inside the lungs so that air is forced out. How is air forced out of the lungs?

Answer 17

• external intercostal muscles and diaphragm relax
• ribcage moves down an inwards and the diaphragm moves upwards
• this decrases the volume inside thoracic cavity
• asthe volume decreases the pressure inside the lungs increases
• air is forced from an area of high pressure (lungs) to an area of lower pressure (atmosphere)

Question 18

Expiration is a passive process. What does this mean and what happens during forced expiration?

Answer 18

It doesn’t require energy.

Question 19

Expiration is a passive process. What does this mean and what happens during forced expiration?

Answer 19

It doesn’t require energy.

Question 20

tidal volume

Answer 20

volume of air in a single breath

Question 21

How are the alveoli adapted for gas exchange?

Answer 21

• thin
• moist
• large SA
• good blood supply from capillaries

Question 22

amylase

Answer 22

digestive enzyme
breaks down strach into maltose
produced by salivary glands and pancreas

Question 23

membrane bound disaccharides

Answer 23

enzymes that break down disaccharides into monosaccharides

attached to cell membranes of epithelial cells lining the ileum

Question 24

proteins are broken down by…

Answer 24

…endopeptidases and exopeptidases, which are enzymes that hydrolyse peptide bonds holding proteins together. The former are secreted into the small intestine and stomach and the latter is found on the cell membranes of epithelial cells in the small intestine

Question 25

What is the difference between endopeptidases and exopeptidases?
Hint: eNDo = iNsiDe and exO = Outside

Answer 25

endopeptidases - hydrolyse peptide bonds within proteins

exopeptidases - hydrolyse peptide bonds at the end of protein molecules

Question 26

How are lipids broken down?

Answer 26

Lipids are broken down by lipase enzymes with the help of bile salt

• lipase catalyses catalyses the breakdown of lipids into monoglycerides
• made in ancrease and secreted into small intestine

Question 27

How are lipids broken down?

Answer 27

Lipids are broken down by lipase enzymes with the help of bile salts

• lipase catalyses the breakdown of lipids into monoglycerides and fatty acids
• made in pancrease and secreted into small intestine
• bile salts emulsify lipids (cause them to form small droplets)
• made in liver
• increases the SA for lipase to act on
• lipid droplets and bile salts form micelles
• micelles release monoglycerides and fatty acids
• which diffuse across epithelial cell membrane

Question 28

What is haemoglobin?

Answer 28

A large protein found in red blood cells

Question 29

structure of haemoglobin

Answer 29

• quaternary structure of 4 polypeptide chains

- each with a haem group whcih contains an iron ion

Question 30

Haemoglobin has a high affinity for oxygen. What does this mean?

Answer 30

It means that each molecule of haemoglobin can carry 4 oxygen molecules

Question 31

When there is a high partial pressure of oxygen what happens?

Answer 31

Haemoglobin’s affinity to oxygen increase so oxygen readily loads onto it to form oxyhaemoglobin. The opposite happnes when there is a low partial pressure of oxygen.

Question 32

Why does haemoglobin unload its oxygen at respiring cells?

Answer 32

respiring cells use up oxygen which decreases the partial pressure of oxygen (pO2) so that haemoglobin has a lower affinity for oxygen and releases oxygen which can be used up by the cell

Question 33

When there is a high partial pressure of carbon dioxide what happens?

Answer 33

Haemoglobin’s affinity to oxygen decreases and it readily unloads its oxygen

Question 34

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. Mechanisms of breathing not required. [4 marks]

Answer 34

1) oxygen from the atmosphere enters the lungs
2) through the trachea and into the bronchioles
3) down a pressure gradient
4) oxygen diffuses across the alveolar epithelium down a diffusion gradient
5) oxygen diffuses across the capillary endothelium into the capillary down a diffusion gradient

Question 35

What is a counter-current system and what is the advantage of fish having one in their gills?

Answer 35

The counter current system is where water and blood are flowing in opposite directions. This maintains a steep concentration gradient between the water and the blood, across the whole lamella. because the conc. of oxygen in water is always higher than the conc. of oxygen in the blood.

Question 36

What are an insect’s spiracles

Answer 36

An insect’s piracles are tiny pores on the surface that allow air to move into the trachea!