Exchange surfaces

Question 1

Why do single celled organisms not need exchange surfaces?

Answer 1

They can exchange directly over body surface, entirely exposed to external environment so diffusion is good enough.
Oxygen diffuses in, and Co2 out.

Question 2

How do small multicellular organisms exchange substances?

Answer 2

Directly over body surface. Good enough diffusion distances from environment, so is enough to supply cells with nutrients/O2.

Question 3

How do large multicellular organisms exchange substances?

Answer 3

Need specialised exchange surfaces and transport mechanisms. Cells within organism are too far from external environment - diffusion pathway is longer.

Question 4

Surface area to volume ratio of small organisms?

Answer 4

Relatively large SA compared to volume. Not need specialised exchange system.

Question 5

Why is SA:V useful?

Answer 5

As organism gets bigger, ratio decreases. Some organisms can be relatively large but have a low enough ratio to avoid needing an exchange surface.

Question 6

What also affects the need for a gas exchange surface?

Answer 6

Level of metabolic activity - need energy and O2 to release additional energy.
- low metabolism, need less nutrients and produce less waste.
- higher metabolism - require specialised exchange surface.

Question 7

What are common features that maximise exchange surface efficiency?

Answer 7

• SA
• thin barriers
• good blood supply

Question 8

Why is a large surface area useful?

Answer 8

More space for substances to pass through - can be maximised by folding and hairs
eg. cilia of ciliated epithelial cells

Question 9

Why are thin barriers useful?

Answer 9

Reduces diffusion distance for molecules to travel. Faster exchange.
eg. alveoli with 1 cell thick walls.

Question 10

Why is a good blood supply useful?

Answer 10

Blood supply can take important substances away and provide surface with waste to be removed from the body. Maintains a strong diffusion gradient.
eg. lungs ventilate to refresh air around alveoli.

Question 11

How does air enter the lungs?

Answer 11

Air is inhaled during ventilation - down the trachea - divides into bronchi then bronchioles. Many alveoli (site of gas exchange).

Question 12

What is the structure of the trachea and bronchi?

Answer 12

Wide - air flow unobstructed.
Supported by C rings of cartilage - flexible to prevent collapse during inspiration.
Smooth muscle - constrict to reduce air flow to/from alveoli.
Goblet cells and ciliated epithelial cells - remove dirt and pathogens from lungs as secrete mucus + waft away.

Question 13

What is the structure of the bronchioles?

Answer 13

Smooth muscle and epithelial cells - can constrict.
Carry air to alveoli.

Question 14

What are the features of alveoli?

Answer 14

Oxygen diffuses from air in alveoli to blood in capillaries. CO2 opposite.
Made of squamous epithelial tissue and elastic fibres (recoil during expiration).
Large surface area.
Capillaries in close contact with alveoli walls - maximum time for gas exchange.
Surfactant = thin layer of moisture on alveoli to stop collapse.

Question 15

Why is smooth muscle and elastic tissue necessary in the lungs?

Answer 15

Muscle can contract - decrease diameter of lumen so restrict airflow. Prevent inhalation of harmful substances. When begins to relax, elastic fibres recoil to OG shape/size so can dilate airway again.

Question 16

What structures in the lungs are needed for ventilation?

Answer 16

Intercostal muscles (internal -> expiration, external -> inspiration.
Diaphragm.

Question 16

What is ventilation?

Answer 16

The process of breathing in and out. To maintain gas exchange in alveoli.

Question 17

What happens during inspiration?

Answer 17

REQUIRES ATP.
- external intercostal muscles contract
- ribs pulled up and out
- diaphragm contracts + flattens
- volume of thorax increases, pressure decreases
- atmospheric pressure is greater
- air forced into lungs

Question 18

What happens during expiration?

Answer 18

LESS ATP (mostly passive).
- internal intercostal muscles contract
- ribs move down and in
- diaphragm relaxes + is pushed up
- volume of thorax decreases, increasing pressure
- pulmonary pressure is greater
- air forced out lungs

Question 19

What is used to measure the volume of the lungs?

Answer 19

Spirometer

Question 20

What is tidal volume?

Answer 20

Volume of air moved in and out of lungs with normal breath.

Question 21

What is vital capacity?

Answer 21

Maximum amount of air that can be moved by the lungs in 1 breath.

Question 22

What is the residual volume?

Answer 22

The volume of air left in the lungs after a forced expiration.

Question 23

What affects oxygen uptake?

Answer 23

Increased oxygen demand eg exercise.

Question 24

How is oxygen uptake calculated?

Answer 24

• mark 2 points of trace at same stage of ventilation
• measure time between
• measure difference in volume between
• divide difference in volume by time taken

Question 25

What is the structure of gills?

Answer 25

A series of bony arches with gill filaments. These have lamellae which increase SA. Each has a network of capillaries by a single layer of epithelial cells.
Protected by operculum.

Question 26

How do fish ventilate their gills to maintain a strong diffusion gradient?

Answer 26

Buccal-opercular pump.
When open buccal cavity, close opercular vents to draw fresh water in.
(some sharks not use and have to swim constantly instead).

Question 27

What is countercurrent flow?

Answer 27

2 liquids in close proximity to each other flowing in opposite directions.

Question 28

How does countercurrent flow work to ensure maximum efficiency of gas exchange in fish?

Answer 28

• blood through capillaries in opposite direction to water
• as water flows past, loses oxygen down diffusion gradient
• blood with very little O2 flows past H2O with slightly higher conc of O2 - diffuses.

Question 29

How do insects transport oxygen?

Answer 29

In an open circulatory system - exoskeleton prevents effective gas exchange –> tracheal system.

Question 30

How does the tracheal system work?

Answer 30

At rest, tracheal fluid seeps into tracheoles from cells.
When active, muscle contraction draws up tracheal fluid: provides O2 containing fluid, lowers pressure in tracheoles - more air in through spiracles, increases SA of tracheal wall exposed to air.

Question 31

How do larger insects ventilate their tracheal system?

Answer 31

• air sacs have flexible walls and can be squeezed by flight muscles
• flight muscles can alter volume of insect thorax
• specialised breathing mechanism - as abdomen expands, close spiracles at back of body but open those at the front. Vice versa when abdomen contracts.