Download 2.4 Exchanging gases – Questions and answers Q1. Bk Ch2 S2.4

2.4 Exchanging gases – Questions and answers
Q1.
Bk Ch2 S2.4 Q1
Name and describe the roles of the three systems used to transport chemicals between the external and
internal environments of plants and animals.
A1.
Bk Ch2 S2.4 A1
Respiratory system: to obtain the oxygen required by cells in respiration and to get rid of unwanted
carbon dioxide.
Circulatory system: to transport or circulate materials around the body to supply cells with nutrients
and remove wastes.
Excretory system: to collect and remove waste materials from the body.
Q2.
Bk Ch2 S2.4 Q2
Identify the gases exchanged in both plants and animals and state the process for which each gas is
used.
A2.
Bk Ch2 S2.4 A2
Plants exchange both carbon dioxide and oxygen with their external surroundings. Carbon dioxide is
used for photosynthesis; oxygen is released in this process. Plants also use oxygen for cellular
respiration, releasing carbon dioxide. Animals use oxygen for cellular respiration and release carbon
dioxide as a by-product.
Q3.
Bk Ch2 S2.4 Q3
Most organisms require oxygen for respiration. This oxygen is obtained from the environment. Insects,
fish, frogs and mammals all have different structures to facilitate the exchange of gases with the
external environment.
a
Complete the following table that summarises the structure and function of respiratory systems in
different kinds of animals.
b
List the features that all respiratory surfaces have in common. Explain how each feature facilitates
gaseous exchange.
Organism
Name of respiratory
surface
Diagram of respiratory
system
Description of process
by which gas exchange
occurs
Insect
Fish
Frog
Mammal
A3.
Bk Ch2 S2.4 A3
a
Organism
Name of
respiratory
surface
Diagram of respiratory system
2.4 Exchanging gases QA
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Description of process
by which gas exchange
occurs
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Insect
Tracheae
Air enters the body
through pores or spiracles
and moves through a
series of fine tubules
bringing air directly to all
cells. Gas exchange
occurs by diffusion.
Fish
Gills
Water flows over the gills
allowing dissolved oxygen
to diffuse into the
capillaries and carbon
dioxide to diffuse out
Frog
Lungs and
skin
Simple lungs: Air moves in
and out, allowing the
diffusion of oxygen and
carbon dioxide into the
capillaries that line them.
Skin: Gases diffuse
directly across the thin,
moist skin that is richly
supplied with capillaries.
Mammal
b
Lungs
Air moves into the lungs
through a series of tubules
that end in small sacs
called alveoli where
diffusion occurs between
the alveolar sac and the
capillaries lining them
Thin, moist walls mean that gases diffuse across the respiratory surfaces efficiently. Large surface
area allows maximum exchange of gases to occur in a given time.
Q4.
Bk Ch2 S2.4 Q4
a
b
c
Label the following diagram of a stomate.
Describe the role of stomates.
Explain the mechanism by which stomates open and close.
2.4 Exchanging gases QA
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A4.
Bk Ch2 S2.4 A4
a
b
c
X: stomatal pore; W: guard cell.
Stomates provide the passage through which oxygen and carbon dioxide diffuse into and out of
leaves and stems. Water vapour also evaporates from plant surfaces through the stomates.
The opening and closing of stomates is regulated by the surrounding guard cells. When the
concentration of potassium ions inside the guard cells increases, water enters the cells by osmosis
and the cells become distended or turgid, causing the stomates to open. As potassium levels
decrease, water leaves the guard cells, causing them to become less turgid, and the stomates close.
Q5.
Bk Ch2 S2.4 Q5
a
b
Define ‘lenticel’.
Outline the role of lenticels.
A5.
Bk Ch2 S2.4 A5
a
b
Lenticels are pores in the woody stems of plants.
Lenticels provide a pathway by which gaseous exchange can occur between the cells within the
woody tissue of plants and the external environment.
Q6.
Bk Ch2 S2.4 Q6
Explain why multicellular organisms require specialised transport systems.
A6.
Bk Ch2 S2.4 A6
Multicellular organisms need specialised transport systems to carry nutrients to all body cells and to
remove waste materials. Without specialised transport systems cells away from the external
environment would not receive their nutrients and wastes would accumulate.
Q7.
Bk Ch2 S2.4 Q7
Prepare a cross-sectional diagram of a stem showing the arrangement of xylem and phloem tissue in
vascular bundles.
A7.
Bk Ch2 S2.4 A7
Example diagram:
2.4 Exchanging gases QA
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Q8.
Bk Ch2 S2.4 Q8
Prepare a chart comparing xylem and phloem tissue. Include substances transported, direction of flow
and description of the tissues.
A8.
Bk Ch2 S2.4 A8
Xylem
Phloem
Transports water and mineral ions
Transports organic materials produced in
photosynthesis
Transports materials in upwards direction only
Transports materials in both directions, up and
down the plant
Xylem vessels are composed of dead cells that
have become thickened with woody material.
The end walls of these cells have broken down
so that a continuous tube is formed. Xylem
vessels are accompanied by strengthening
fibres. Xylem gives rigidity to plants, providing
them with structural support.
Phloem is made of living cells called sieve cells.
Sieve cells have perforated end walls, allowing
cell contents to flow from one cell to another
along the sieve tubes. The cells of the phloem
have cells alongside them called companion
cells as well as other supporting tissue.
Q9.
Bk Ch2 S2.4 Q9
a
b
c
Define ‘transpiration’.
Describe the process of transpiration that occurs in plants from the entry point of water at the root
hairs, its route through the plant, to its exit at the stomates.
Discuss the factors that affect the rate of transpiration.
A9.
Bk Ch2 S2.4 A9
a
b
c
Transpiration is the diffusion of water vapour from the leaf surfaces of plants through the
stomates.
Water enters the plant at the roots via the root hairs and is carried upwards through the roots, stem
and leaves in the xylem. Inside the leaf water evaporates from cell surfaces into intercellular
spaces, diffusing out of the stomates into the surrounding atmosphere.
Factors that affect transpiration rate:
Temperature: Warm air can hold more water vapour than cold air, therefore higher external
temperatures increase the rate of water loss through transpiration.
Humidity: When the surrounding air is already saturated with water vapour the rate of
movement of water vapour from the leaf to the surrounding air is decreased.
Wind: Moving air carries water vapour away from the leaf it has just left; a high diffusion
gradient is maintained between the leaf and the surrounding air, thereby increasing the rate of
transpiration.
2.4 Exchanging gases QA
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Light: Intense light stimulates the movement of potassium into the guard cells which in turn
increases the movement of water into guard cells by osmosis, causing the stomates to open. The
greater the light intensity the more the stomates open and the greater the rate of water loss by
transpiration.
Soil: The amount of water and the concentration of mineral ions in the soil also affect the rate
of water uptake by plants.
Q10.
Bk Ch2 S2.4 Q10
Describe a key difference in the role of the circulatory system between insects and vertebrates.
A10.
Bk Ch2 S2.4 A10
The circulatory system of vertebrates is responsible for the transport of respiratory gases whereas in
insects the circulatory system does not perform this role.
Q11.
Bk Ch2 S2.4 Q11
Compare the efficiency of open and closed circulatory systems.
A11.
Bk Ch2 S2.4 A11
Closed circulatory systems are more efficient than open circulatory systems; they deliver nutrients to
and remove wastes from cells very quickly compared with open systems; however, more energy is
required by closed circulatory systems.
2.4 Exchanging gases QA
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