Gaseous Exchange, Digestion and Absorption

Question 1

What is the relationship between size and SA : Volume ratio?

Answer 1

As the size of the organisms increases the surface area to volume ratio decreases

Question 2

How have larger organisms evolved to maintain adequate rates of gaseous exchange?

Answer 2

-developed specialised exchange structures like lungs or gills

-also maintain body temp by changes in body shape/ structure such as large ears to increase surface area for heat loss

Question 3

What’s the correlation between the SA : Volume ratio and metabolic rate?

Answer 3

• as the surface area to volume ratio decreases, metabolic rate also decreases.

Question 4

Gas exchange system in mammals consists of?

Answer 4

Trachea- supported by incomplete rings of cartilage that prevent it collapsing during pressure changes which occurs in ventilation

Bronchi- repeatedly divides into smaller tubes (Bronchioles)

Alveoli- provides a large surface area where gaseous exchange occurs.

Question 5

how is the alveoli adapted for gas exchange (6)

Answer 5

• their shape and large number provide a large surface area
• Fluid lining the alveolus allows gases to dissolve and diffuse across
• An extensive network of blood capillaries surrounds each alveolus provides a large surface area for absorbing oxygen and releasing carbon dioxide
• Only two cell layers separate the blood and air (short diffusion pathway)
• a circulatory system maintains a high concentration gradient for gaseous exchange by transporting deoxygenated blood and removing oxygenated blood to and from the lungs
• ventilation mechanism maintains a high concentration gradient for gaseous exchange by providing oxygen concentrated air and removing CO2 concentrated air

Question 6

describe the steps of gas exchange in lungs

Answer 6

1 - oxygen in the alveolar air space dissolves in the fluid lining the epithelium of the alveolus

2 - oxygen diffuses across the flattened epithelial cells of the alveolus and the endothelial cells of the capillary wall

3 - oxygen combines with the haemoglobin in RBC to form oxyhaemoglobin and CO2 diffuses from the blood in the opposite direction

Question 7

What word describes how the external and internal intercostal muscles work together

Answer 7

• Antagonistically
• as one of them contracts one of them relaxes

Question 8

Inspiration (breathing in)

Answer 8

• diaphragm contracts and moves down and flattens
• external intercostal muscles on ribs contract and move ribs up while internal intercostal muscles relax
• as lungs expand, air is sucked in through mouth and nose

Question 9

expiration (exhalation)

Answer 9

• external intercostal muscles and diaphragm relaxes and the diaphragm moves upwards to its dome shape

-this decreases the volume of the thoracic cavity and the pressure inside the lungs increases above atmospheric pressure and air is forced out of the lungs

Question 10

What else can help exhalation?

Answer 10

• elastic recoil of the lung tissue helps to force air out the lungs during expiration
• internal intercostal muscles may also contract, pulling the ribcage downwards and inwards.

Question 11

What is pulmonary ventilation?

Answer 11

The total volume of air that is moved into the lungs during one minute

Question 12

How to calculate pulmonary ventilation?

Answer 12

tidal volume x ventilation (breathing) rate

Question 13

What is tidal volume?

Answer 13

• the volume of air taken in at each breath

Question 14

What is breathing rate?

Answer 14

• number of breaths per minute

Question 15

What is a risk factor?

Answer 15

• anything that increases the chance of getting a disease- eg, diet, smoking, age, occupation, etc.

Question 16

What risk factors are associated with Lung Disease?

Answer 16

• smoking, air pollution, infections, genetics and occupation (e.g. working with chemicals/gases and radiation)

Question 17

What does correlation mean?

Answer 17

• where a change in one of two variables is reflected by a change in the other variable. (variables may or may not be related)

Question 18

What does cause mean?

Answer 18

-a factor which is directly a cause of a disease

Question 19

What does Relative Risk mean?

Answer 19

the likelihood of harm occurring in those exposed to a hazard than with those who are not exposed to it

Question 20

What is the tracheal system in insects?

Answer 20

• a system of pipes that connects the air outside the animal to the tissues of the body that require the oxygen

Question 21

Describe how gaseous exchange occurs into and out of the tracheal system in insects? (extended answer)

Answer 21

• the opening of the trachea to the air is through tiny holes on the insect’s surface called spiracles
• the spiracles have valves so that they can close to reduce water loss via evaporation
• each spiracle leads into tubes called tracheae held open by spiral bands of cuticle
• the trachea branches repeatedly to form finer tubes called tracheoles
• oxygen diffuses from the air, through the spiracles along the trachea and tracheoles to the cells
• carbon dioxide leaves the insect’s cells and travels to the atmosphere by the reverse pathway

Question 22

Trachea System adaptations (insects)

Answer 22

• tracheoles are thin, providing a short diffusion distance and are numerous providing a large surface area

Question 23

What does the opening of the spiracles depend on?

Answer 23

Levels of carbon dioxide in the body.

• during rest the spiracles close which helps reduce water loss by evaporation

Question 24

What causes the spiracles to widen?

Answer 24

• carbon dioxide levels rise due to respiration and this causes the spiracles to open wider increasing the rate of diffusion of gases in the tracheal system

Question 25

When do the spiracles close?

Answer 25

- during rest the spiracles close to help reduce water loss by evaporation

Question 26

How do large/active insects speed up diffusion?

Answer 26

- the muscles contract to compress the trachea forcing air out then the muscles relax and the trachea springs back into shape drawing in fresh air that is rich in oxygen

Question 27

How are the gills adapted for gaseous exchange?

Answer 27

- the large number of gill filaments provide a large surface area. They possess lamellae increasing the surface area even further - a short diffusion pathway consisting of two cell layers - epithelial layer of the gill lamellae - endothelial layer of the blood capillaries

Question 28

How does increased activity affect diffusion?

Answer 28

- during increased activity, anaerobic respiration often occurs producing lactic acid in cells lowering the water potential - some of the water in the ends of the tracheoles moves into the cells by osmosis enabling more air to move in along the tracheoles and into the cells speeding up the diffusion of oxygen to the cells

Question 29

How does the circulatory system improve/increase the rate of gaseous exchange?

Answer 29

- ensures a continual flow of blood through the respiratory surface to absorb oxygen and remove carbon dioxide thus maintaining a high gradient for gas exchange

Question 30

How are gills constructed?

Answer 30

4 pairs of gill arches consisting of many gill filaments protected by the operculum

Question 31

What leaf adaptation increase rate of gaseous exchange?

Answer 31

Leaves are thin which provides a short diffusion pathway

Question 32

When do plants respire?

Answer 32

During the day and night

Question 33

How does the ventilation mechanism improve/increase the rate of gaseous exchange?

Answer 33

- provides a continual flow of water over the gills bringing more oxygen and removing carbon dioxide thus maintaining a high gradient for gas exchange

Question 34

How is a plant adapted for gaseous exchange?

Answer 34

- numerous mesophyll cells lining the intercellular air spaces providing a large surface area - respiration and photosynthesis produce CO2 and O2 which maintains the diffusion gradient - mesophyll cells have moist and thin cell walls/membranes

Question 35

How does the counter-current system improve/increase the rate of gaseous exchange?

Answer 35

- ensures that blood continually meets water with a higher oxygen concentration so that a high diffusion gradient is kept along the whole length of the lamellae

Question 36

What is a stomata?

Answer 36

Pores in the epidermis of leaves that gases diffuse in and out of protected by two guard cells

Question 37

When do plants photosynthesise?

Answer 37

During the day only

Question 38

Why is there a net uptake of CO2 and loss of oxygen during the day in plants?

Answer 38

The rate of photosynthesis is higher than the rate of respiration in the day.

Question 39

How is starch hydrolysed ?

Answer 39

- Salivary amylase breaks down some of it into maltose in the mouth - Pancreatic amylase hydrolyses the rest (into maltose) in the small intestine (Duodenum)

Question 40

Where does Starch get completely hydrolysed?

Answer 40

- in the ileum by the disaccharidases maltase, lactase and sucrase into alpha glucose - the enzymes form part of the cell-surface membrane of the epithelial cells lining the ileum.

Question 41

How are lipids hydrolysed?

Answer 41

- the enzyme lipase is secreted by the pancreas into the small intestine and breaks them down into glycerol, fatty acids and monoglycerides by hydrolysing the ester bonds.

Question 42

How are digested lipids absorbed (extended answer)

Answer 42

- bile salts emulsify the lipids into small droplets increasing the rate of hydrolysis - bile salts combine with fatty acids and monoglycerides to form micelles to transport the poorly soluble monoglycerides and fatty acids to the surface of the epithelial cell - the micelles break down next to the epithelial cell to release the fatty acids and monoglycerides. They are non polar and are therefore able to diffuse through the membrane - fatty acids, monoglycerides and glycerol are recombined in the SER to form triglycerides - they are packaged in protein and phospholipids by the Golgi body to form chylomicrons - chylomicrons are absorbed into the lacteals in the villi which eventually drain into the blood

Question 43

How are proteins hydrolysed?

Answer 43

- they are hydrolysed by endopeptidases, exopeptidases and dipeptidases to form amino acids which are then absorbed in the ileum

Question 44

How do Bile Salts speed up lipid hydrolysis?

Answer 44

- they emulsify the lipids causing them to form small droplets which increases their surface area

Question 45

Describe the hydrolysis of proteins

Answer 45

- Endopeptidases are released in the stomach and hydrolyse internal peptide bonds to form small polypeptides and peptides - the pancreas then secretes exopeptidases which hydrolyse the peptide bonds at either end of a polypeptide so that individual amino acids or dipeptides are removed - finally dipeptidases are membrane bound enzymes in the microvilli of the ileum and hydrolyse the bond in a dipeptide to release two single amino acids

Question 46

How is the ileum adapted for absorption? (6)

Answer 46

- large surface area due to its long length and the presence of villi and microvilli - large number of mitochondria = more ATP for active transport - carrier and channel proteins in the cell surface membrane for absorption of specific molecules by active transport and facilitated diffusion - the wall of each villus has a single layer of epithelial cells providing a short diffusion pathway - villi contain blood capillaries that absorb monosaccharides and amino acids maintaining a high diffusion gradient for further absorption - the lacteals in the villi absorb digested lipids that maintains a high diffusion gradient for further absorption

Question 47

How are monosaccharides and amino acids absorbed?

Answer 47

- via co-transport

Question 48

Describe how monosaccharides and amino acids are absorbed via co-transport (extended answer)

Answer 48

- sodium ions are actively transported out of the epithelial cells and into the blood via carrier proteins - this creates a low conc of sodium ion inside the epithelial cell - a higher conc of sodium ions will be present in the lumen - a conc gradient s created for the sodium to diffuse into the epithelial cells through a co-transport protein and glucose will move through the co-transport protein with the sodium - the glucose then moves out of the cell towards the blood capillary via facilitated diffusion through another protein