3.3 Exchange and Transport systems

Question 1

What substances do organisms exchange with their environment?

Answer 1

1. cells - take in oxygen and nutrients
2. Excrete waste like CO2 and Urea
3. Stay at same temp. therefore heat exchanged.

Question 2

Describe the surface area to volume ratio of a small animal.

Answer 2

Small animal e.g. Mouse:

- Has a higher surface area to volume ratio. In other words, has bigger surface area relative to its volume.

Question 3

What is the rate of diffusion proportional to?

Answer 3

(Surface area x difference in conc.) ÷ ( length of diffusion pathway)

Question 4

Why do large/multicellular organisms need exchange organs and mass transport systems?

Answer 4

Diffusion across the outer membrane is too slow for 2 reasons:

• Some cells deep in the body so big distance between them and the outside environment.
• Large animals have a low surface area to volume ratio - difficult to exchange enough substances to supply large volume of animal through relatively small outer surface.

Question 5

How does size of body affect heat exchange? What does rate of heat exchange depend on?

Answer 5

Rate of heat exchange depends on surface area.

Organisms has a large volume, surface area is relatively small - harder for it to lose heat from body.

If organism is small, has relatively large surface area so more heat lost easily therefore small organisms have a high metabolic rate (to generate heat).

Question 6

How does shape affect heat exchange? (hint: Arctic fox and African fox)

Answer 6

• Animals compact shape have small surface area relative to its volume, minimising heat loss.
• Animal with less compact shape (shit sticking out etc.), larger surface area to volume, increase heat loss

Question 7

Give 3 features of respiratory surfaces in man and amoeba.

Answer 7

1. Large surface area
2. Short diffusion pathway
3. Large difference in conc. (conc. gradient)

See how this links to: rate of diffusion directly proportional to (surface area x volume) ÷ length of pathway.

Question 8

Describe the story of how the tracheal system of an insect exchange gases? (Keywords: tracheoles, permeable walls, oxygen, trachea, spiracles, abdominal movements)

Answer 8

Air filled pipes called trachea for gas exchange.

• air moves into pores called spiracles
• O2 travels down conc. gradient towards the cells.
• Trachae –> Tracheoles that have thin, permeable walls and go to individual cells. This means oxygen diffuses directly into respiring cells.
• CO2 moves down conc gradient towards spiracles.
• abdominal moments have move are in and out of spiracles.

Question 9

Narrate the story of how fish use counter-current system for gas exchange. (Key words: Gill filaments, big S.A., lamellae, capillaries, conc gradient)

Answer 9

1. Water contains oxygen that fish use to pass through the mouth and through the gills.
2. Each gill made of thin plates called filaments (draw diagram) which give a large surface area for exchange of gases.
3. Gill filaments covered in structures called lamellae which increase the surface area.
4. Lamellae packed with blood capillaries and thin surface cells - speed diffusion.
5. Blood flows in one dir. and water in the other. Called countercurrent flow/system. Maintains a large concentration gradient OVER THE WHOLE FILAMENT. Conc of oxygen in water is always higher than in blood so as much oxygen diffuses in from water as possible.

Question 10

Draw the structure of dicotyledonous plants.

Answer 10

See online.

Question 11

How are dicotyledonous plants adapted for gas exchange and how does this happen?

Answer 11

• Main gas exchange is surface of the mesophyll cells in the leaf. They’re well adapted for their function - they have a large surface area.
• The mesophyll cells are inside the leaf. Gases move in and out through special pores in the epidermis called stomata (singular = stoma)
• Stomata can open to allow exchange of gases, and close if the plan is losing too much water. Guard cells control the opening and closing of stomata

Question 12

How are insects adapted to minimise water loss?

Answer 12

• Close their spiracles using muscles
• Have a waterproof waxy cuticle
• tiny hairs to reduce evaporation

Question 13

How are plants adapted to control water loss?

Answer 13

• Stomata usually kept open during the day to allow gaseous exchange. Water enters guard cells and make them turgid, which opens the stomatal pore. If the plant starts to get dehydrated, the guard cells lose water and become flaccid, which closes the pore.

Question 14

Plants that live in hot, dry and windy habitats where water loss can be an issue. They’re called XEROPHYTES. How are they adapted to minimise water loss?

Answer 14

Examples of xerophytic adaptations:

• Stomata sunk in pits that trap moist air, reducing the concentration gradient of water between the leaf and the air. Reduces the amount of water diffusing out of the leaf and evaporating away.
• Hairs on epidermis - trap most air around stomata.
• Curled leaves with stomata inside, protecting them from wind (windy conditions increase the rate of diffusion and evaporation).
• Reduced number of stomata, so there are fewer places for water to escape.
• Waxy, waterproof cuticles on leaves and stems to reduce evaporation.

Question 15

Draw a structure of the human lungs.

Answer 15

Following should be included:

• Intercostal muscles
• bronchus
• bronchiole
• alveoli
• lung
• diaphragm
• ribcage
• trachea

Question 16

What is the name of the 2 breathing mechanisms?

Answer 16

Inspiration and expiration.

Question 17

How does inspiration work? (5 key points)

Answer 17

1. Diaphragm muscles contracts & moves down.
2. External intercostal muscles contract and internal intercostal muscles relax.
3. Ribcage & lungs move up and out.
4. Volume increases and pressure decreases below atmospheric pressure.
5. Causes air to be drawn in.

Question 18

How does expiration work? (7 key points)

Answer 18

1. External intercostal and diaphragm muscles relax.
2. The ribcage moves downwards and inwards and the diaphragm becomes curved again.
3. The volume of the thoracic cavity decreases, causing the air pressure to increase.
4. Air is force down the pressure gradient and out of the lungs.
5. Normal expiration is a passive process - it doesn’t require energy.
6. Expiration can be forced through.
7. During forced expiration, external intercostal muscles relax and internal intercostal muscles contract, pulling the ribcage further down and in. During this time, the movement of the intercostal muscles is said to be ANTAGONISTIC.

Question 19

Label an alveolus and alveolar epithelium.

Answer 19

Should mention:

• alveolus epithelial
• capillary vessel
• fluid
• RED BC
  (- blood from and to pulmonary artery, pulmonary vein respectively)

Question 20

What are the essential features of alveolar epithelium as a surface over which gas exchange takes place? (3 - possibly 4)

Answer 20

1. A large surface area compared with the volume of the organism.
2. A short diffusion distance for gas - ONE cell thick and cells flattened.
3. A large difference in oxygen and CO2 conc. on opposite sides of the surface.
4. Partially permeable and moist surfaces (to allow O2 and CO2 to diffuse easily).

Extra info: The small and narrow capillary at alveolus allows RBC to be squished and slow down so take longer gives enough time for diffusion because RBCs are slowed down.

Question 21

What is used to break down large biological molecules?

Answer 21

Digestive enzymes.

Question 22

What are some examples of biological molecules that are digested?

Answer 22

Proteins –> Amino acids
carbohydrates –> Glucose
Lipids –> Fatty acids and glycerol

Question 23

What breaks down Carbohydrates to its products and what are the products? Where can this enzyme be found?

Answer 23

Amylase - digestive enzyme breaks down starch to maltose.
Amylase produced by salivary glands (which release amylase into the mouth) also by the pancreas.
Membrane bound disacchariDASES are enzymes that digest disaccharides into monosaccharides e.g. maltase on lining of ileum.

Question 24

How are lipids broken down? Where and what produces the enzyme?

Answer 24

Lipids are broken down by the enzyme lipase. Lipases are made in the pancreas and work in the small intestine.

Question 25

What produces bile salts? How are bile salts useful?

Answer 25

Bile salts are produced in the liver. They emulsify lipids - means they cause the lipids to form small droplets.
Important because several small lipid droplets have a bigger surface area than a large droplet so formation of small droplets increases the surface area of lipids that’s available for lipase to work on.

Question 26

What’s formed once lipids broken down?

Answer 26

Monoglycerides and fatty acids - stick with bile salts form micelles.

Question 27

Where are endopeptidase found? Give examples

Answer 27

Stomach and lumen of small intestine - work in middle of polypeptide chain. Hydrolyse peptide bonds within a protein.

• Trypsin and chymotrypsin are 2 examples of endopeptidases.

Question 28

Where do exopeptidases work on protein chain? Where is it found?

Answer 28

Exopeptidases act to hydrolyse protein on outside of chain. On the stomach & the lumen of the small intestine

Question 29

How are monosaccharides, monoglycerides and fatty acids and amino acids absorbed?

Answer 29

Monosaccharides:
- Absorbed by active transport via co-transport proteins. Fructose is absorbed by facilitated diffusion.

Monoglycerides and fatty acids:

• Micelles help to move monoglycerides and fatty acids to epithelium
• Micelles break and release monoglycerides and fatty acids - absorbed. They’re lipid soluble so can diffuse directly across Epithelial CM.

Amino acids:
- Co-transport like glucose.

Question 30

What are the 4 main steps for co-transport?

Answer 30

1. Na+ actively transported against conc. gradient into the bloodstream and out of the cells.
2. Creates a low concentration of Na+ inside the cell. Does this to allow Na+ to diffuse into the cell from the ileum by cotransport protein.
3. Cotransport of Na+ and glucose into the epithelial cells - this is a PASSIVE PROCESS.
4. Glucose diffuses down the concentration gradient into the capillary via facilitated diffusion.

Question 31

Mass Transport in animals.
Where is haemoglobin found? Give details about haemoglobin. See what you know and don’t know (write what you don’t in a different colour.)

Answer 31

• Red blood cells contain haemoglobin.
• Haemoglobin is a large protein with quaternary structure - more than one.
• Chain has a haem group which contains iron ion and gives HG the red colour.
• Has a high affinity for oxygen so can carry 4 O2 molecules.
• In lungs oxygen joins HG to form oxyhaemoglobin.
• reversible reaction so when oxygen leaves turns back to HG.

Question 32

Haemoglobin saturation depends on partial pressure. How does a high partial pressure of oxygen affect the saturation of HG?

Answer 32

Oxygen loads onto HG where there’s a high Partial pressure of Oxygen. Oxyhaemoglobin unloads its oxygen where there’s a lower O2 concentration.

Question 33

Dissociation curves show how affinity for oxygen varies. How does oxygen binding onto haemoglobin affect the affinity of o2?

Answer 33

When oxygen binds on to the haemoglobin, it causes a change in shape of the quaternary protein structure. Makes it easier for more O2 molecules to bind onto HG. As becomes more saturated, harder for molecules to join so it has steep part then levels off.

Question 34

What are the effects of carbon dioxide concentration on the oxygen dissociation curve?

Answer 34

• At higher partial pressures of CO2, haemoglobin gives up oxygen more readily.
• respiration = CO2 –> raises pCO2.
• INcreases rate of oxygen unloading - curve shifts right.
• Saturation of blood with oxygen is lower for a given pO2 - so more o2 released.

^ Called “The Bohr effect”