3.3.2 Gas exchange: Adaptations in Plants

What is the primary function of stomata in dicotyledonous plants?

• Absorption of nutrients

• Gas exchange

• Photosynthesis

• Water transport

Answer explanation

The primary function of stomata in dicotyledonous plants is gas exchange. They allow carbon dioxide to enter for photosynthesis and oxygen to exit, playing a crucial role in the plant's respiratory process.

Which part of the dicotyledonous plant leaf is primarily responsible for photosynthesis?

• Stomata

• Epidermis

• Mesophyll

• Cuticle

Answer explanation

The mesophyll is the leaf tissue where most photosynthesis occurs, containing chloroplasts that capture light energy. In contrast, stomata facilitate gas exchange, the epidermis provides protection, and the cuticle reduces water loss.

How do terrestrial insects minimise water loss while maintaining efficient gas exchange?

• By having a thick cuticle

• By closing their spiracles

• By increasing their surface area

• By living in water

Answer explanation

Terrestrial insects minimize water loss by closing their spiracles, which are openings for gas exchange. This action reduces water evaporation while still allowing for necessary oxygen intake.

What adaptation helps xerophytic plants reduce water loss?

• Large leaves

• Thin cuticle

• Sunken stomata

• High stomatal density

Answer explanation

Sunken stomata are an adaptation in xerophytic plants that help reduce water loss by creating a microenvironment with higher humidity around the stomata, minimizing evaporation. This is more effective than large leaves or high stomatal density.

Which of the following is a structural adaptation of leaves for gas exchange?

• Thick waxy cuticle

• Large surface area

• Deep root system

• High chlorophyll content

Answer explanation

A large surface area in leaves enhances gas exchange by maximizing the area available for carbon dioxide uptake and oxygen release, making it a key structural adaptation. The other options do not directly facilitate gas exchange.

What is the main compromise faced by terrestrial insects regarding gas exchange and water loss?

• High metabolic rate

• Limited mobility

• Balancing open spiracles for gas exchange and closed spiracles to prevent water loss

• Increased body size

Answer explanation

Terrestrial insects face the challenge of balancing gas exchange and water conservation. Open spiracles allow oxygen intake but increase water loss, while closed spiracles prevent dehydration but limit gas exchange. Thus, they must find a compromise.

Which of the following is NOT a feature of xerophytic plants?

• Thick cuticle

• Reduced leaf size

• High stomatal density

• CAM photosynthesis

Answer explanation

Xerophytic plants typically have adaptations to conserve water, such as a thick cuticle, reduced leaf size, and CAM photosynthesis. High stomatal density is not a feature, as it would increase water loss.

What role do guard cells play in the function of stomata?

• They transport water

• They open and close the stomata

• They produce chlorophyll

• They absorb sunlight

Answer explanation

Guard cells regulate the opening and closing of stomata, which are small pores on the leaf surface. This function is crucial for gas exchange and transpiration, making 'They open and close the stomata' the correct answer.

Which of the following adaptations is common in both terrestrial insects and xerophytic plants?

• High metabolic rate

• Thick cuticle

• High water content

• Large surface area

Answer explanation

Both terrestrial insects and xerophytic plants have a thick cuticle to reduce water loss. This adaptation helps them survive in dry environments, making it a common feature between the two.

How do mesophyll cells contribute to gas exchange in leaves?

• By storing water

• By facilitating the diffusion of gases

• By transporting nutrients

• By producing wax

Answer explanation

Mesophyll cells facilitate gas exchange in leaves by allowing the diffusion of carbon dioxide and oxygen through their intercellular spaces, which is essential for photosynthesis and respiration.