Topic 3 - Organisms Exchange Substances With Their Environment

Question 1

In small organisms, why is diffusion across their body sufficient?

Answer 1

• Distances are short (less than 0.5mm).
• Surface area is relatively large.
• The body/cell surface acts as the exchange surface.

Question 2

In large organisms, why can they not rely upon their body surface?

Answer 2

• Surface area relative to volume is insufficient for exchange.
• Diffusion distances are too great.

Question 3

What effect does an increase in size have on the need for a specialist exchange surface in larger animals?

Answer 3

• As size ⬆️, volume ⬆️ disproportionately compared to surface area.

Question 4

What does it mean if the demand of cells for nutrients and waste removal also increased disproportionately?

Answer 4

• The surface does not increase sufficiently to accommodate these extra demands.
• Must be met by a specialist exchange surface with enhanced surface area.

Question 5

Does breathing in (inspiration) require energy?

Answer 5

Yes

Question 6

Does breathing out (expiration) require energy?

Answer 6

No.

Question 7

What happens during INSPIRATION?

Answer 7

+ The diaphragm contracts and flattens.
+ The external intercostal muscles contract, pulling the ribs up+out.
+ Volume of the thorax increases, so pressure in the lungs decreases.
+ Air is pushed in the equalise the pressure.

Question 8

What happens during EXPIRATION?

Answer 8

+ The diaphragm relaxes and forms a dome shape.
+ The external intercostal muscles relax, pulling the ribs in+down.
+ Volume of the thorax decreases, so the pressure in the lungs increases.
+ Air is pushed out to equalise the pressure.

Question 9

2 ways in which the diffusion gradient is maintained in the alveoli :

Answer 9

• Blood is continuously moving.
• Constantly breathing = fresh oxygen.

Question 10

Why is diffusion rapid in the alveoli?

Answer 10

-Red blood cells are slowed as they pass through pulmonary capillaries.
-The distance between the alveoli and red blood cells is reduced hours the red blood cells are flattened against the capillary wall.
-The walls of the alveoli capillaries are very thin = short diffusion distance.
-Surface area of alveoli (due to folds) and capillaries (there are many) is large.
-Breathing (ventilation) and blood movement (due to heart) ensure a concentration gradient is maintained.

Question 11

What are the essential features of exchange surfaces?

Answer 11

• Large surface area to volume ratio ➡️ speed up the rate of exchange.
• Very thin e.g. one cell thick ➡️ keep the diffusion pathway short.
• Partially permeable ➡️ to allow selected materials to diffuse easily.
• Movement of external medium e.g. air ➡️ to maintain a diffusion gradient.
• Movement of internal medium e.g. blood ➡️ to maintain a diffusion gradient.

Question 12

4 Alveoli facts :

Answer 12

• Each alveolus is lined with a single layer of flattened epithelial cells.
• Around each alveolus is a network of pulmonary capillaries lined with a single layer of endothelial cells.
• The capillaries are narrow so that red blood cells are flattened and squeezed through.
• The capillaries have thin walls (one layer of cells thick).

Question 13

The respiratory system in mammals is made up of :

Answer 13

The mouth and nose, the trachea, the bronchi, the bronchioles and the alveoli.

Question 14

The mouth and nose in the respiratory system in mammals …

Answer 14

… Is the entrance to the rest of the respiratory system.

Question 15

The trachea in the respiratory system in mammals …

Answer 15

… Connects the mouth and nose to the lungs; a tough tube, surrounded by c-shaped rings of cartilage to prevent kinking, also lined with ciliates epithelial cells to trap dust and pathogens and waft back to the mouth in a sea of mucus.

Question 16

The bronchi in the respiratory system in mammals …

Answer 16

… Is two branches from the trachea that transfer air to and from each lung; these are similar in structure to the trachea.

Question 17

The bronchioles in the respiratory system in mammals …

Answer 17

… Are increasingly smaller branches from the bronchi that transfer air to and from the alveoli; these start with a similar structure to the bronchi but lose the cartilage lining and ciliates epithelial cells the closer they get to the alveoli.

Question 18

The alveoli in the respiratory system in mammals …

Answer 18

… Is the site of exchange of the gases oxygen and carbon dioxide; they are tiny sacs, lined with flattened epithelial cells and surrounded by a dense network of capillaries.

Question 19

What is Fick’s Law of Diffusion?

Answer 19

Diffusion is proportional to : (surface area x difference in concentration) / length of diffusion path

Question 20

What is the primary function of the lungs and breathing?

Answer 20

To supply oxygen for aerobic respiration. To remove carbon dioxide which is one of the waste products of respiration. Carbon dioxide produces an acid solution and as it accumulates the pH of the cells and blood is lowered that could interfere with enzymes function.

Question 21

What is the volume of air inspired know as?

Answer 21

The tidal volume.

Question 22

What is the volume of air inspired per minute known as?

Answer 22

The ventilation rate.

Question 23

Ventilation is approximately _ _ _ _ _ _ _ _ when at rest but increases during exercise since both the tidal volume and number of breaths per minute increases.

Answer 23

constant

Question 24

By what adaptions is efficient gas exchange in the lungs achieved?

Answer 24

• The millions of alveoli in the lungs have a combined area of approximately 70m², thereby significantly increasing the surface area to volume ratio of the human body. To prevent the walls of the alveoli is from sticking together a substance called surfactant is secreted by cells in the alveoli walls, which consist of phospholipids that reduces the surface tension of the water. 
  - A short distance for diffusion is achieved by the alveoli epithelial cells and capillary endothelium cells being very thin. The capillaries are also touching the alveoli so the oxygen and carbon dioxide have to travel through very little or no tissue fluid.
• The constant movement of blood through the capillaries, as well as breathing movements, ensure that a steep concentration gradient is maintained. The flow of air in and out of the lungs is called ventilation and has two stages: inspiration and expiration. Lungs are not muscular and cannot ventilate themselves, but instead the whole diaphragm moves and changes size, due to the action of two sets of muscles: the intercostal muscles and the diaphragm. 

Question 25

What is the pathway taken by an oxygen molecule from an alveolus to the blood?

Answer 25

An oxygen molecule would diffuse from the alveolus, across the alveolar epithelium and through the endothelium capillary membrane into the blood.

Question 26

How does one feature of an alveolus allow efficient gas exchange to occur?

Answer 26

The capillaries and alveoli war is only one cell thick, this means that the diffusion pathway is short and therefore efficient gas exchange can occur.