3.3.4.2 Mass transport in plants

Front

What is the primary function of xylem in plants?

Back

Transport of water

Answer explanation

The primary function of xylem in plants is the transport of water from the roots to the leaves. This is essential for photosynthesis and nutrient transport, making 'Transport of water' the correct answer.

Front

Which theory explains the mechanism of water transport in the xylem?

Back

Cohesion-tension theory

Answer explanation

The cohesion-tension theory explains water transport in the xylem through the cohesive properties of water molecules and the tension created by transpiration, allowing water to move upward from roots to leaves.

Front

What is the primary function of phloem in plants?

Back

Transport of organic substances

Answer explanation

The primary function of phloem in plants is the transport of organic substances, primarily sugars produced during photosynthesis, from the leaves to other parts of the plant. This is essential for growth and energy.

Front

Which hypothesis explains the mechanism of translocation in plants?

Back

Mass flow hypothesis

Answer explanation

The mass flow hypothesis explains translocation in plants as the movement of nutrients and water through the phloem, driven by pressure differences. This mechanism contrasts with other theories like cohesion-tension, which focuses on water movement.

Front

What is the purpose of using tracers in plant experiments?

Back

To track the movement of substances

Answer explanation

The purpose of using tracers in plant experiments is to track the movement of substances within the plant. This helps researchers understand how nutrients and water are transported, rather than measuring growth or enhancing photosynthesis.

Front

What is a ringing experiment used to investigate?

Back

Transport in plants

Answer explanation

A ringing experiment involves removing a ring of bark from a plant stem, which helps to study the transport of nutrients and water in plants. This method directly investigates how substances move within the plant, confirming that the correct choice is 'Transport in plants'.

Front

In a ringing experiment, what is typically removed from the plant?

Back

Phloem

Answer explanation

In a ringing experiment, the phloem is typically removed from the plant. This process disrupts the transport of nutrients, allowing researchers to study the effects on plant growth and development.

Front

Evidence against the mass flow hypothesis:

• Bidirectional movement of substances
• Unidirectional flow of water
• Presence of sieve plates
• High pressure in phloem

Back

Bidirectional movement of substances

Answer explanation

The bidirectional movement of substances contradicts the mass flow hypothesis, which suggests that phloem transport is unidirectional. This evidence indicates that substances can move in both directions, challenging the hypothesis.

Front

What role do sieve plates play in phloem?

Back

Regulate flow of organic substances

Answer explanation

Sieve plates are crucial in phloem as they regulate the flow of organic substances, allowing for the efficient transport of sugars and nutrients throughout the plant.

Front

Characteristic of the cohesion-tension theory?

Back

Water is pulled up the plant

Answer explanation

The cohesion-tension theory explains that water is pulled up the plant through transpiration, creating a negative pressure that draws water from the roots to the leaves. Thus, 'Water is pulled up the plant' is the correct characteristic.