gas exchange

Question 1

single celled organisms exchange gas across their body surface

Answer 1

• single celled organisms absorb and release gases by diffusion through their outer surface
• they have a large surface area, thin surface, and short diffusion pathway

Question 2

describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted for gas exchange (2 MARKS)

Answer 2

1. single layer of cells
2. reduces diffusion pathway

Question 3

suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and the alveoli (3 MARKS)

Answer 3

1. less carbon dioxide exhaled
2. so reduced concentration gradient between blood and alveoli
3. more carbon dioxide stays in blood

Question 4

explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system (2 MARKS)

Answer 4

1. blood and water flow in opposite directions
2. concentration gradient maintained along length of lamella

Question 5

describe and explain the mechanism that causes lungs to fill with air (3 MARKS)

Answer 5

1. external intercostal and diaphragm muscles contract
2. volume of thoracic cavity increases and lung pressure decreases
3. air flows from area of high to low pressure

Question 6

use your knowledge of gas exchange in leaves to explain why plants grown in soil with very little water grow only slowly (2 MARKS)

Answer 6

1. stomata close
2. less carbon dioxide uptake for less photosynthesis

Question 7

describe the pathway taken by an oxygen molecule from an alveolus to the blood (2 MARKS)

Answer 7

1. (oxygen diffuses) across the alveolar epithelium
   BY SIMPLE DIFFUSION
2. (into a capillary) across the capillary epithelium

Question 8

explain how one feature of an alveolus allows efficient gas exchange to occur (2 MARKS)

Answer 8

1. alveolar epithelium is one cell thick
2. short diffusion pathway

Question 9

how are alveoli adapted for gas exchange?

Answer 9

1. a thin exchange surface - the alveolar epithelium is one cell thick = short diffusion pathway
2. a large surface area - large number of alveoli = larger surface area for exchange
3. steep concentration gradient of oxygen and carbon dioxide - maintained by blood flow and ventilation = increases rate of diffusion

Question 10

describe the gross structure of the human gas exchange system and how we breathe in and out (6 MARKS)

Answer 10

GROSS STRUCTURE
1. trachea, bronchi, bronchioles, alveoli
2. (above structures named in correct order)

BREATHING IN
3. external intercostal and diaphragm muscles contract
4. increases thoracic cavity volume
5. decreases pressure in the lungs

BREATHING OUT
6. external intercostal muscles and diaphragm muscles relax
7. reduces thoracic cavity volume
8. lung pressure increases

Question 11

explain three ways in which an insects tracheal system is adapted for efficient gas exchange (3 MARKS)

Answer 11

1. tracheoles have thin walls = short diffusion distance to cells
2. large number of tracheoles = short diffusion distance to cells
3. large number of tracheoles = large surface area for gas exchange

Question 12

explain two ways in which the structure of fish gills is adapted for efficient gas exchange (2 MARKS)

Answer 12

1. many lamellae = large surface area
2. thin surface = short diffusion pathway

Question 13

inspiration (breathing in)

Answer 13

• external intercostal and diaphragm muscles contract
• ribcage moves upwards and outwards and the diaphragm flattens which increases the volume of the thoracic cavity
• lung pressure decreases as thoracic cavity volume increases
• air flows from an area of higher pressure to an area of lower pressure
• air flows down the trachea into the lungs
• inspiration is an active process = requires energy

Question 14

expiration (breathing out)

Answer 14

• external intercostal and diaphragm muscles relax
• ribcage moves downwards and inwards and the diaphragm becomes curved
• volume of the thoracic cavity decreases
• air pressure increases
• air is forced down the pressure gradient and out of the lungs
• expiration is a passive process = doesnt require energy

Question 15

forced expiration

Answer 15

• EXTERNAL intercostal muscles RELAX and the internal intercostal muscles CONTRACT
• pulls the ribcage FURTHER DOWNWARDS and IN
• movement of the intercostal muscles is ANTAGONISTIC (opposing)

Question 16

insects use tracheae to exchange gases

Answer 16

• insects have microscopic air filled pipes called tracheae that they use for gas exchange
• air moves into the tracheae through pores on the surface called spiracles
• oxygen travels down the concentration gradient to the cells
• the tracheae branches into smaller tracheoles which have thin, permeable walls and go into individual cells = oxygen diffuses directly into respiring cells
• carbon dioxide from the cells move down its own concentration gradient towards the spiracles to be released
• insects use rhythmic abdominal movements to move air in and out of the spiracles

Question 17

dicotyledonous plants exchange gases at the surface of the mesophyll cells

Answer 17

• mesophyll cells have a large surface area
• mesophyll cells inside the leaf - gases move in and out of the stomata
• guard cells control the opening and closing of stomata

Question 18

insects control water loss

Answer 18

• insects close their spiracles using muscles if theyre losing too much water
• insects have a waterproof waxy cuticle all around their body to reduce evaporation
• insects have tiny hairs around their spiracles to reduce evaporation

Question 19

plants control water loss

Answer 19

• water enters the guard cells and they become turgid which opens the stomatal pore
• guard cells close the stomata if the plant is dehydrated
• the guard cells lose water and become flaccid which closes the stomata

Question 20

xerophytic adaptations

Answer 20

• stomata sunk in pits that trap moist air = reduces concentration gradient of water between the leaf and the air - reduces amount of water diffusing out of the leaf
• layer of hairs on the epidermis = trap moist air around the stomata
• curled leaves with the stomata inside = protect them from wind (wind increases rate of diffusion and evaporation)
• reduced number of stomata = less places for water to escape
• thick, waxy, waterproof cuticles on leaves and stems = reduce evaporation