Topic 3 - Gas exchange

Question 1

Where is the exchange system of oxygen in fish ?

Gills

Answer 1

The gills

Question 2

How do gills have a large surface area ?

Gills

Answer 2

The gills consist of thin plates called gill filaments. These are also covered in lamellae.

Question 3

How does lamellae speed up diffusion ?

Gills

Answer 3

They increase the surface area
They have lots of blood capillaries
They have a thin surface layer of cells

Question 4

How does the counter-current system in fish work ?

Gills

Answer 4

water enters the fish through its mouth. The blood flows through the gills in the opposite direction to the water. This maintains a large concentration gradient down the whole length of the gill - there’s always a higher concentration of oxygen in the water than the blood so that it can diffuse down its gradient into the blood.

Question 5

How does air enter an insect ?

Insects

Answer 5

Through pores on its surface called spiracles.

Question 6

Explain how gas exchange works in insects

Insects

Answer 6

Insects use rhythmic abdominal movements to move air into the spiracles by changing the pressure. Air enters the insect through pores called spiracles on the insect’s surface. The air enters tracheae (tubes with rings of chitin) and then these branch into tracheoles which are smaller tubes that are go into individual cells. The oxygen diffuses down its concentration gradient from the air in the tracheoles into the cells. Carbon dioxide then diffuses down its concentration gradient out of the cell and towards the spiracles.

Question 7

How does air move in and out of spiracles

Insects

Answer 7

Insects use rhythmic abdominal movements to move air into and out of the spiracles by changing pressure

Question 8

How are the tracheoles a good exchange surface ?

Insects

Answer 8

They have thin permeable walls so the diffusion distance is short
They are branched so there is a large surface area
They enter tissues so short diffusion distance

Question 9

How are tracheae strengthened ?

Insects

Answer 9

They have rings of chitin

Question 10

How is gas exchange in insects a fast system ?

Insects

Answer 10

There’s no need for gases to bind to pigments like haemoglobin, also oxygen doesn’t need to travel in the blood stream to get to cells

Question 11

Why can insects not be larger ?

Insects

Answer 11

Because gas is diffusing directly in and out of their body so bigger size would mean more cells and therefore a greater diffusion distance so gas exchange would not be efficient for the insect.

Question 12

What can happen to tracheoles when the insect is resting ?

Insects

Answer 12

Tracheoles can fill with fluid to limit diffusion

Question 13

What happens to active insects?

Insects

Answer 13

lactic acid concentration increases in the muscle cells, this draws water into the cells by osmosis

Question 14

What adaptations do insects have to minimize water loss ?

Insects

Answer 14

They have a small surface area to volume ratio
A tough waxy, waterproof exoskeleton which stops them from drying out
They have the ability to close spiracles using their muscles
Spiracles have hairs to trap humid air.
All of this reduces evaporation

Question 15

Where is the main exchange surface in plants ?

Plants

Answer 15

the mesophyll cells as they have a large surface area and air gaps.

Question 16

How do gases enter and exit a plant cell ?

Plants

Answer 16

gases move in and out of the cells through stomata, the stomata are opened and closed by guard cells.

Question 17

What adaptations to plant cells have for gas exchange ?

Plants

Answer 17

Many stomata in the lower epidermis open in the sun light to allow for gases to exchange in and out of the leaf.
Thin cell walls minimize the diffusion distance.
Close contact between cells and air spaces allow for efficient gas exchange for photosynthesis and respiration.

Question 18

How do guard cells open and close the stomata to control water loss ?

Plants

Answer 18

Stomata are usually kept open during the day for gas exchange. water enters the guard cells, making them turgid and open the stomata pores. If plants start to dehydrate the guard cells turn flaccid, closing the pore.

Question 19

How are xerophytic plants adapted to their dry environment ?

Plants

Answer 19

Stomata are sunk in pits and trap moist air, this reduces the concentration gradient of water between the leaf and the air. This reduces water loss by evaporation.
A layer of hairs on the epidermis trap humid air around the stomata.
Curled leaved with stomata inside, protect them from the wind and therefore evaporation
A reduced number of stomata limit water loss
waxy waterproof cuticle on leaf and stems reduce water loss by evaporation.

Question 20

What happens during inspiration ?

Ventilation

Answer 20

The diaphragm and external intercostal muscles contract causing the diaphragm to flatten and the ribcage to move upwards and outwards. This increases the volume of the the thoracic cavity resulting in lower pressure compared to the atmosphere. Air moves down this pressure gradient into the trachea and lungs.

Question 21

Which ventilation process in humans requires energy ?

Ventilation

Answer 21

Inspiration

Question 22

What happens during expiration ?

Ventilation

Answer 22

The external intercostal muscles and diaphragm muscles relax causing the ribcage to move down and in and the diaphragm curves into a dome shape.
This decreases the thoracic cavity volume causing pressure to increase higher than the atmospheric pressure. Air travels down this pressure gradient out of the lungs into the atmosphere.

Question 23

What happens during forced expiration ?

Ventilation

Answer 23

Internal intercostal muscles contract whilst the external intercostal muscles and diaphragm relax. this causes the diaphragm to curve into a dome shape and the ribcage moves more downwards and inwards causing the thoracic cavity’s volume to greatly decrease meaning the pressure increases higher than the atmospheric pressure. More air moves down this pressure gradient out of the lungs and into the atmosphere.

Question 24

How is the alveoli adapted for gas exchange ?

Ventilation

Answer 24

They have/ create a large surface area so more gas can diffuse in and out at once for gas exchange.
They have a thin exchange surface: The alveolar epithelium is only one cell thick so there’s a short diffusion path so gas exchange can occur quicker.
Theres a good blood supply through the network of capillaries, this maintains a steep concentration/ diffusion gradient for gas exchange to occur quicker.

Question 25

What happens to oxygen and carbon dioxide in the alveoli ?

Ventilation

Answer 25

Oxygen diffuses out of the alveoli down its concentration gradient across the alveolar and capillary epithelium into haemoglobin in the blood.
Carbon dioxide diffuses into the alveoli from the blood out is breathed out.

Question 26

What is tidal volume ?

Ventilation

Answer 26

the volume of air in each breath

Question 27

What causes an asthma attack ?

Lung Disease

Answer 27

Airways become irritated and inflamed due to an allergic reaction, the smooth muscle lining the bronchioles contract and a large amount of mucus is produced. this closes up the airways making it difficult to breathe

Question 28

What are symptoms of asthma ?

Lung Disease

Answer 28

wheezing
tight chest
shortness of breath

Question 29

How do inhalers relieve an asthma attack ?

Lung Disease

Answer 29

they cause the muscles lining the bronchioles to relax causing the airways to open up

Question 30

What are the layers of cells in a leaf ?

Photosythesis

Answer 30

Waxy cuticle
upper epidermis
palisade mesophyl
spongy mesophyl
lower epidermis
(guard cells and stomata)
waxy cuticle