Exchange Surfaces

Question 1

SA: VOLUME ratio

5

Answer 1

Single celled organisms= large
Molecules can move through membrane by diffusion and active transport
Multicellular organisms = small
Not adequate to obtain sufficient molecules therefore have specialised specialised gas exchange surfaces
Distance is too great, outer cells will use up nutrients and oxygen before they reach inner cells

Question 2

3 factors affecting heat exchange

Answer 2

Body size- sa:volume ratio
Small animals= large surface area so heat lost more easily so need a relatively high metabolic rate
Body shape= compact shape reduces heat loss
Adaptation= body sharpening is adapted to environment

Question 3

Relationship between factors and rate of diffusion

Answer 3

Diffusion~ SA X diff. In conc./ length of diffusion pathway

~ = proportional to

Question 4

Gas exchange in single called organisms and terrestrial insects
4

Answer 4

Single celled are small and have a large SA: volume

Insects are multi celled so need specialised structures

= internal network of tubes called tracheae which are used for gas exchange directly into respiring cells, does not transport oxygen

Tracheae have rings to keep their airways open, resist negative pressure and are divided into smaller tracheoles which extend through the tissue. This allows oxygen in the air entering the tracheoles to diffuse to body cells as the distance is small

Question 5

How do gases move in and out of the tracheal system

1+3

Answer 5

Gas enters and leaves the trachea through tiny pores called spiracle.
Moves through the trachea and into the tracheoles by:

1. Gases diffuse down conc. gradient:
2. Abdominal muscle contraction during movement
3. Loss of water by osmosis from the ends of tracheoles durimg anaerobic respiration

Question 6

How do gases move in and out of the tracheal system

1. Gases diffuse down conc. gradient:

Answer 6

1. Gases diffuse down conc. gradient: aerobic respiration at the tissue uses up oxygen so levels are low at the respiring tissue and higher in the trachea. So O2 diffuses down tracheoles to respiring cells. CO2 is higher at the respiring tissue and lower in the environment so diffuses through the tracheoles and out the spiracles

Question 7

How do gases move in and out of the tracheal system

2. Abdominal muscle contraction during movement

Answer 7

Squeezes the tracheas and so moves air in and out through the spiracles

Abdominal pumping, by pushing gasses into or out of the trachea and tracheoles they are helping to decrease the conc. gradient

Question 8

How do gases move in and out of the tracheal system

3. Loss of water by osmosis from the ends of tracheoles durimg anaerobic respiration

Answer 8

The ends of the tracheoles are filled with water, when Insects carry out a lot of activity, they will need to carry out anaerobic respiration which produces lactate whic is soluble and lowers the water potential in the respiring cells. Water from the tracheoles moves into the muscle cells( respiring) by osmosis. The loss of water draws more air into the tracheoles and also means diffusion can occur through a gas which is quicker

Question 9

Ways in which the tracheole system is adapted for efficient gas exchange
5

Answer 9

1. Thin walls so short diffusion distance
2. Highly branched/ large number of tracheoles so short diffusion distance and large surface area
3. Trachea provide tubes full of air so fast diffusion into insect tissues
4. fluid in the end of the tracheoles that moves out into tissues during exercise so larger surface area for gas exchange
5. Body can be moved, abdominal muscle contraction to move air so maintains conc gradient

Question 10

Insects reduce water loss by
3
+1

Answer 10

Small SA: volume ratio

Waterproof coating- chitin

Spiracles - valves closing trachea when at rest reduce water loss butnioem when insects are active

Larger insects have a larger surface area so water loss will be greater, this limits the maximum size of the insect

Question 11

Behavioural and physiological adaptations to aid exchange

4

Answer 11

Animals w high SA:V lose more water, desert mammals have a kidney structure adaptation so they produce less urine

Small mammals with high metabolic rates, in cold regions need to eat large amounts of high energy food

Small mammals have thick layers of skin/fur and hibernate

Larger organisms in hot regions, increase SA eg elephant ears, hippos stay in water

Question 12

Gas exchange in fish

Answer 12

Small SA;volume ratio

Lower conc of oxygen in water than air

Specialised gas exchange system m= gills

Question 13

Structure of gills

3

Answer 13

Found just behind the head and made up of Gill filaments

On each filament there are many lamallea that have many blood capillaries and a thin surface to reduce diffusion pathway

Lamellae increase surface area for exchange of gases

Question 14

Counter current system

3

Answer 14

Blood in the lamella flows in the opposite direction to water

This means that water with a relatively high oxygen concentration always flows next blood with a lower oxygen concentration

This maintains a step concentration gradient so as much oxygen diffuses into the blood as possible

Question 15

Fish adaptation to gas exchange

6

Answer 15

Filaments and lamelle provide large SA
Excellent blood supply to maintain concentration gradient
Continuous flow of water maintains concentration gradient
Counter current flow
Blood vessels are very close to the exchange surface so short diffusion distance
Flattened epithelial and endothelial cells so short diffusion distance

Question 16

Gas exchange in the lead of a plant

6

Answer 16

Most exchange through leaves, no transport system required

Plants need CO2 for
photosynthesis and O2 for respiration

Main exchange surface is surface of mesophyll cells

Gases move in and out through special pores in epidermis called stomata

Stomata can open to allow exchange of gases and close if the plant is losing too much water

Guard cells control opening and closing of stomata

Question 17

Lead adaptations for gas exchange

6

Answer 17

Guard cells can open and stomata

Leaves are thin so short diffusion distance

Large SA

Many small pores, no cell is far from stomata so short diffusion distance

Numerous interconnecting air spaces, diffusion is faster through gases

Cells use up gases so conc gradient maintained

Question 18

Structure of human gas exchange system

3

Answer 18

Large multicellular organisms need to absorb large volumes of o2 for aerobic respiration and remove co2
Mammals maintain a constant body temp which relates to them having a high metabolic and respiratory rate- they are very active
Diffusion alone is not fast enough and the distances are too great so specialised ventilation mechanism and exchange surface required

Question 19

Lungs

10

Answer 19

Made of a series of branching tubes called bronchioles which end in tiny air sacs- alveoli
Supported and protected by ribs which are moved by intercostal muscles
Air is constantly ventilated by tidal stream of air
Trachea is flexible and surrounded by rings of cartilage, prevent collapsing when pressure decreases
Tracheal walls contain muscles and lined with epithelial and goblet cells which=mucus
Tracheal branches to bronchi. Similar structure to T and produce mucus
Ciliates epithelial cells waft the mucus to the throat where they are swallowed and digested
Bronchi branch to bronchioles, smooth muscle contract and control air flow in and out alveoli
Bronchi also lined with CEC and GC
Alveoli small sacs at the end, one cells thick and made of squamous epithelial cells, collage and elastic tissue between- stretch and recoil

Question 20

Role of alveoli in gas exchange

4

Answer 20

Large SA- 300 million alveoli in each lung, allows more molecules to diffuse quickly
Thin and permeable- squamous epithelial cells are very thin and have a short diffusion pathway, gas can diffuse quickly, water is lost so walls are moist
Large pulmonary capillary network- oxygen away and returns co2, maintains a steep concentration gradient
Surfactant- produced which reduces surface tension and prevent alveoli sticking together

Question 21

Diffusion of gases between the alveoli and blood will be very rapid because
3

Answer 21

Red blood cells are slowed as they pass through capillary allowing more time for diffusion
Red blood cells flattened against capillary walls so short distance
Walls of alveoli and capillaries are very thin giving a small diffusion distance
Alveoli and capillaries have large total SA
Breathing movements ventilate the lungs and maint a steep concentration gradient
Heart pumping blood through the pulmonary capillaires maintain a steep gradient

Question 22

Mechanism of breathing

Answer 22

Air is constantly moved in and out of lungs to maintain conc gradient- ventilation
Inspiration and expiration caused by pressure changes in the lungs
Pressure changes are brought about by the contraction/ relaxation of the diaphragm muscle and the internal and external intercostal muscles
Diaphragm muscles separate the thorax from the abdomen
Muscles contract and relax whereas elastic tissue stretches and recoil

Question 23

Inspiration

6

Answer 23

Diaphragm muscle contracts and diaphragm flattens
External intercostal muscles contract and raise the ribs upwards and outwards
Volume of chest cavity increase
Pressure in the chest cavity drops below atmospheric pressure
Air enters the lungs down a pressure gradient
Alveoli stretch

Question 24

Expiration

7

Answer 24

Alveoli recoil due to elastic tissue, making volume smaller and expelling air
Diaphragm muscle relax and curves upwards
External intercostal muscles relax and ribs moves downwards and inwards
Volume of chest cavity decrease
Pressure in thoracic cavity increase above atmospheric pressure
Air leaves the lungs down a pressure gradient
The alveoli recoil due to elastic tissue, making volume smaller and and expelling air

Question 25

Forced expiration

4

Answer 25

Internal intercostal muscles contract
External intercostal muscles relax
Ribcage pulled further downwards and inwards
Example of antagonistic muscle action

Question 26

Tidal volume

Answer 26

The volume of air taken in a normal breath and is usually about 0.5dm3
Breathing rate is usually between 12-20 in a healthy adult

Question 27

Pulmonary ventilation rate equation

Answer 27

Tidal volume x breathing rate

Question 28

Forced vital capacity

Air breathed in is

Air breathed out is

Answer 28

Maximum amount of air that can be exhaled in one breath
Approx 5 dm3
Air breathed in is the inspiratory reserve volume
Air breathed out is the expiratory reserve volume

Question 29

Residual volume

Answer 29

Around 1.5dm3

Remains in the lungs after you have breathed out as deeply as possible

Question 30

Forced expiratory volume

Answer 30

Maximum volume of air that can be breathed forcefully out of the lung in 1 second

Decreases with age due to loss of elasticity of the internal intercostal muscles

Question 31

Risk factors for lung disease

5

Answer 31

Smoking

Air pollution

Genetic make up= genetics

Frequent chest infections

Occupation- some people may inhale harmful chemicals etc

Question 32

Intracellular digestion

Answer 32

Digestion that takes place inside the cells

Question 33

Extra cellular digestion

Answer 33

Digestion that takes place outside the cell

Question 34

Human digestive system made up of

Is

Answer 34

Made of a long muscular tube and glands which produce enzymes that hydrolyse large insoluble molecules into smaller ones for absorption into the blood stream

Is an exchange system through which food substances are absorbed

Question 35

The digestive system

6

Answer 35

Salivary glands are found in the mouth, secrete saliva containing enzyme amylase which hydrolyse starch to maltose

Food passes from mouth(bucal cavity) through oesophagus(gullet) to stomach(muscular sac)

Cells lining stomach produce HCl+ protease enzymes to hydrolyse proteins. HCl provide optimum PH for protease in stomach. Muscle in stomach contract-churn contents called chyme

Food passed through ileum- pancreatic secretions contain bile, pancreatic carbohydrates, lipases, proteases enzymes to hydrolyse carbohydrates, lipids, proteins

Epithelial walls of SI(ileum) has membrane bound carbohydrases. The inner walls of the ileum are folded into villi- large SA which is furthered by millions of microvilli. These are adapted for absorbing products of digestion into the bloodstream.

Undigested food passes into the LI where waters absorbed for secretions. Faeces formed and removed via anus- egestion.

Question 36

Physical digestion

2

Answer 36

When large food particles are broken down by the action of the teeth. Increases SA for chemical digestion.
Churning by muscles in stomach wall also break up food

Question 37

Chemical digestion

Answer 37

Due to specific enzymes carrying hydrolysis reaction using water to break chemical bonds

Question 38

Carbohydrate digestion

7

Answer 38

1. saliva enters the mouth from salivary glands. Food mixed with saliva by chewing. Saliva contains mineral salts to help maintain optimum PH for enzyme.
2. Amylase hydrolyse alternate glycosidic bonds in starch to produce disaccharide maltose
3. food swallowed and enters stomach, acid released, denature amylase to prevent further starch hydrolysis
4. Food enters SI, mixes with pancreatic secretions- pancreatic juice, contains pancreatic amylase to continue hydrolysis of remaining starch in maltose
5. Alkaline salts in bile, released by walls of SI, help neutralisé acidic contents, neutral PH for amylase in SI
6. Muscle contractions in wall of SI result in peristalsis, push food along
7. As it passes along SI encounters three membrane bound disaccharide enzymes, maltase, sucrase, lactase- hydrolyse single glycosidic bonds to produce monosaccharides

Question 39

Peristalsis

Answer 39

A series of muscle contractions that occur in digestive tract to move the contents along

Question 40

Lipid digestion

6

Answer 40

1. In the duodenum fats and oils are first emulsified by bile salts
2. Emulsification is when lipids are split to tiny droplets to increase SA for lipase enzyme and speed up rate of hydrolysis
3. Bile salts are found in bile. Bile produced by liver, stored in gall bladder, secreted by bile duct in SI
4. Lipase enzymes emulsify lipids, produced by pancreas and present in pancreatic juice released into SI
5. Lipases hydrolyse ester bond to form fatty acids+ monoglygeride= one fatty acid+glycerol
6. Micelles formed

Question 41

Protein digestion

Answer 41

Hydrolysed by a group of peptidase enzymes

Question 42

Endopeptidases

3

Answer 42

Hydrolyse the peptide bond in the central region forming a series of peptide molecules

Trypsin and chymotrypsin secreted by the pancreas and SI

Pepsin is also produced by the cells lining the stomach. Only works in acidic conditions- HCl released by the stomach

Question 43

Exopeptidase

2

Answer 43

Hydrolyse the peptide bond at the ends of a peptide formed by endopeptidases to release dipeptides and amino acids

Endopeptidases means there are more ends to hydrolyse so protein digestion is faster

Question 44

Dipeptidases

2

Answer 44

Complete protein digestion by hydrolysing the peptide bonds in dipetide to release amino acids

Dipeptidases are membrane bound

Question 45

Properties for efficient absorption

5

Answer 45

Ileum walls are folded and contain villi and microvilli- increase SA
Thin walled- reduce diffusion path
Muscle which allows them to move- helps maintain conc gradient for fast diffusion
Well supplied by blood vessels, carry absorbed molecules away which maintains conc gradient for faster diffusion
Cell surface membrane of the epithelial cells form microvilli which further increase SA

Question 46

Absorption of monosaccharides and amino acids

4

Answer 46

1. Na+/K+ pump actively pumps Na+ out of the epithelial cell of the villus into the blood stream and K+ into the cell
   2 this produces concentration gradient so Na+ enter the epithelial cells
2. Na+ enters by facilitated diffusion it also brings in glucose using a co transporter protein in the membrane of the epithelial cells by the process of facilitated diffusion. This ensures that glucose will always enter the epithelial cells and a conc gradient established
3. Glucose will then pass by facilitated diffusion into the blood stream

Question 47

Absorption of triglycerides

5

Answer 47

Monoglyceride, fatty acid and bile salts form micelles Which break down releasing the monoglyceride and fatty acids which can easily diffuse through cell surface membrane of epithelial cell of SI
Monoglyceride and fatty acids are resynthesized into triglycerides in smooth ER
Then passed to Golgi where they associate with cholesterol+ lipoproteins to form chylomicrons
Chylomicrons move out of epithelial cells by exocytosis and enter lymphatic capillaries called lacteals found in the centre of each villus.
Front there they will pass through lymphatic vessels and finally into the blood stream

Question 48

Degenerative disease -

Answer 48

symptoms get worse over time.

Question 49

• Acute diseases-

Answer 49

symptoms last a short time

Question 50

• Chronic diseases -

Answer 50

symptoms last a long time

Question 51

Asthma-

4

Answer 51

during asthma attacks the smooth muscle lining the bronchioles contracts and a large amount of mucus is produced.
This causes constriction of the airways making it difficult to breathe.
The air flow in and out of the lungs is severely reduced, so less oxygen enters the alveoli and diffuses into the bloodstream.
FEV (forced expiratory volume will be less as a result).

Question 52

Emphysema-

6

Answer 52

usually caused by long-term smoking.
Foreign particles become trapped in the alveoli, inflammation results and attract phagocytes the site and in turn causes the breakdown of elastic tissue as the phagocytes produce an elastase enzyme.
The reduction in elastin means the alveoli can’t recoil as much on expiration.
It also results in a breakdown of the alveoli walls and a reduction in the surface area of the alveoli.
This will lead to an increase in their ventilation rate as they will try to increase the volume of air containing oxygen into their lungs to compensate. Symptoms of emphysema are shortness of breath, and wheezing.
COPD is a combination of chronic bronchitis (inflammation of bronchi) and emphysema (destruction of walls of alveoli)

Question 53

Fibrosis-

5

Answer 53

this can occur due to the build-up of scar tissue as a result of infections or exposure to chemicals.
The scar tissue is thicker and less elastic than normal lung tissue. Consequently the lungs will not be able to expand as much or hold as much air As normal.
As a result the tidal volume is reduced and so is the FVC (forced vital capacity).
The rate of gas exchange by diffusion across the thicker scar tissue will also be slower.

Question 54

Pulmonary Tuberculosis-

3

Answer 54

a bacterial infection where tubercles are formed in the lungs which damage the gas exchange surface.
The tidal volume is decreased and individuals will have a higher ventilation rate to compensate.
Symptoms include persistent cough with blood laden mucus, shortness of breath, fatigue and weakness.

Question 55

Asthma, emphysema, TB and fibrosis will all

Answer 55

. reduce the rate of gas exchange in the alveoli and less oxygen will diffuse into the bloodstream and will result in a lower rate of aerobic respiration. Less energy will be released and sufferers will be weaker and more tired.

Question 56

Risk Factors for Lung Disease Risk factors include:

5

Answer 56

• Smoking: 90% of people suffering from COPD are, or have been smokers.
• Air pollution: Particles such as sulphur dioxide released in areas of heavy industry increase the
chances of COPD.
• Genetic make –up. Some people are genetically more likely to get lung disease. This is why some
life- long smokers may never get the disease.
• Frequent chest infections- there is a higher incidence of lung disease.
• Occupation- people who may frequently inhale harmful chemicals, gases and dust have a higher
risk of lung disease.