7.1 Specialised exchange surfaces

Question 1

Why do amoeba not require any specialised exchange surface?

Answer 1

all oxygen needed and waste CO2 produced can be exchanged with external environment by diffusion through cell surface
- distances substances have to travel are very very small

Question 2

2 main reasons why diffusion alone is enough to supply the needs of single celled organisms

Answer 2

1. metabolic activity of a single-celled organism is usually low, so O2 demands and CO2 production of cell are relatively low
2. SA:V ratio of organism is large

Question 3

Why is Surface area to volume ratio important?

Answer 3

As organisms get larger, they can be made up of millions/ billions of cells, forming tissues, organs and organ systems
–> metabolic activity is much higher ( more oxygen required and more CO2 produced)
–> distance between cells where oxygen is needed is too far for effective diffusion to occur
–> larger organism= smaller SA:V ratio (gases cannot be exchanged fast enough or in large enough amounts for organisms to survive

Question 4

What makes an efficient exchange surface?

Answer 4

1. Increased surface area - provides area needed for exchange * overcomes limitations of SA:V ratio e.g. root hair cells & villi
2. Thin layers - diffusion distance is short, meaning it is fast and efficient
3. Good blood supply - the steeper the conc grad, the faster diffusion occurs so good blood supply ensures substances are constantly delivered and removed. This maintains conc gradient.
4. Ventilation to maintain diffusion gradient - gases: a ventilation system helps maintain concentration gradient and makes the process more efficient

Question 5

Human Gaseous exchange system

Answer 5

mammals have a small SA:V ratio & very large volume of cells & high metabolic rate

Question 6

Respiratory system features: Nasal cavity

Answer 6

• large surface area with a good blood supply (warms air to body temp)
• hairy lining, which secretes mucus to trap dust and bacteria (protecting delicate lung tissue from irritation and infection)
• moist surfaces, which increases the humidity of incoming air, reducing evaporation from exchange surfaces

Question 7

Respiratory system features: Trachea

Answer 7

main airway, a wide tube supported by incomplete rings of strong flexible cartilage (stops trachea from collapsing)
–> Rings are incomplete to allow it to bend when food is swallowed down oesophagus behind the trachea

Lined with ciliated epithelium & goblet cells
–> prevents dust and bacteria from entering the lungs

Question 8

Respiratory system features: Bronchus

Answer 8

Extensions of the trachea that split into two for the left and right lung
–> very similar structure to trachea but smaller

Question 9

Respiratory system features: Bronchioles

Answer 9

divisions of bronchus and have no cartilage, only smooth muscle (allows contractions for constriction/ relax and dilate)
–> lined with a thin layer of flattened epithelium facilitating some gas exchange

Question 10

Respiratory system features: Alveoli

Answer 10

tiny air sacs (main gas exchange surface)
–> diameter of 200-300 micrometers and are made up of a thin layer of flattened epithelial cells, along with some collagen and elastic fibres
–> The elastic tissue allows alveoli to stretch as air is drawn in (as they return, this helps squeeze air out, elastic recoil)

Question 11

Respiratory system features: Alveoli adaptions

Answer 11

1. Large surface area (300-500 million alveoli per adult lung)
2. Thin layers - both alveoli and capillaries are only a single epithelial cell thick so diffusion distance is very short
3. Good blood supply- 280 million capillaries maintain steep concentration gradient
4. Good ventilation - breathing moves air in and out, helps maintain steep diffusion gradient
5. Inner surface of alveoli is covered in a thin solution of water, salts and lung surfactant - allows alveoli to remain inflated & reduces water loss

Question 12

Ventilation

Answer 12

pressure changes in thoracic cavity brought about ventilation. The rib cage provides a semi-rigid cage in which pressure changes to facilitate

Question 13

Parts of the chest

Answer 13

diaphragm: broad domed sheet of muscle which forms the floor of the thorax
External intercostal muscles & internal intercostal muscles are found between ribs
Thorax is lined by pleural membranes
Pleural cavity (space between pleural membranes) are filled with a thin layer of lubricating fluid so membranes slide easily over each other

Question 14

Inspiration (taking air in/ inhalation)

Answer 14

Process takes up energy
- Diaphragm contracts, moving down
- intercostal muscles move up and outwards
- thoracic volume increases
- thoracic pressure decreases
- air flows into the lungs to equalise the pressure difference

Question 15

Expiration (breathing out/ exhalation)

Answer 15

passive process
- diaphragm relaxes and move up
- intercostal muscles relax, moving down and in
- thoracic volume decreases
- thoracic pressure increases
- airflow out of lungs