2.4 Exchanging Gases Questions and Answers

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.

aComplete the following table that summarises the structure and function of respiratory systems in different kinds of animals.

bList 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

Organism / Name of respiratory surface / Diagram of respiratory system / Description of process by which gas exchange occurs
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 / 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

bThin, 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

aLabel the following diagram of a stomate.

bDescribe the role of stomates.

cExplain the mechanism by which stomates open and close.

A4.

Bk Ch2 S2.4 A4

aX: stomatal pore; W: guard cell.

bStomates 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.

cThe 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

aDefine ‘lenticel’.

bOutline the role of lenticels.

A5.

Bk Ch2 S2.4 A5

aLenticels are pores in the woody stems of plants.

bLenticels 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:

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

aDefine ‘transpiration’.

bDescribe 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.

cDiscuss the factors that affect the rate of transpiration.

A9.

Bk Ch2 S2.4 A9

aTranspiration is the diffusion of water vapour from the leaf surfaces of plants through the stomates.

bWater 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.

cFactors 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.

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 QApage 1 of 5