The xylem and phloem are types of vascular tissue found in plants. 

Give one similarity between the structure of xylem and phloem tissue.

Describe three differences between the structure of xylem and phloem tissue.

Algae are small, photosynthetic organisms that rarely grow more than a few centimetres in height. They do not contain xylem tissue.

Suggest why algae do not need xylem tissue to survive. 

Describe the cohesion-tension theory of how water is transported in the xylem. 

Many animals and plants require specialised transport systems. 

Explain why large multicellular plants require a specialised transport system. 

Mass transport of sugars takes place through sieve tube elements and companion cells in the phloem.

Describe and explain one way in which sieve tube elements are adapted for the mass transport of sugars. 

Describe and explain one way in which companion cells are adapted for the mass transport of sugars.

Explain the mass flow hypothesis of transporting sucrose within a plant. 

A group of students investigated the rate of water uptake by a plant.

The set-up of their equipment is shown in the diagram below. 

Give one environmental factor the students should have controlled during this investigation. 

Describe how the students returned the air bubble to the start of the capillary tube during this investigation. 

Describe how the students would calculate the rate of water uptake in mm³ per minute. 

The uptake of water by the plant is not a true representation of the rate of transpiration.

Give two reasons why the rate of water uptake may not equal the rate of transpiration.

Plants contain two transport tissues, xylem and phloem tissue. 

Describe and explain three ways in which the xylem vessels are specialised for their function. 

Explain how hydrogen bonding facilitates the movement of water through the xylem. 

Xylem tissue is involved in the process of transpiration.

What is transpiration? 

State two environmental factors that affect the rate of transpiration.

For each factor given, explain how it affects the rate of transpiration.

A group of students used a potometer to investigate how wind speed affects the rate of transpiration in a leafy shoot.

The equipment used is shown in the diagram below. 

The students made sure to cut the plant shoot under water when placing it in the potometer.

Suggest why. 

Other than cutting the shoot under water, give two precautions the students should take when setting up the potometer to ensure they obtain reliable measurements. 

The results of their experiment are shown below. 

The air bubble moved 31.02 mm when exposed to a wind speed of 2 ms^-1 for 6 minutes.

The internal diameter of the capillary tube a 0.8 mm.

Calculate the mean rate of water uptake for the leafy shoot when exposed to a wind speed of 2 ms^-1.

Use the following formula:

volume of a cylinder = πr²l

where r is the radius and l is the length.

Describe and explain the results of the investigation. 

The xylem is a transport tissue found inside many plants. 

Name the two pathways that water takes to reach the xylem vessels at the base of a stem. 

Describe three differences between these two pathways. 

Explain how the Casparian strip prevents solutions from reaching the xylem of the plant.

Many plants contain phloem tissue that is responsible for transporting sucrose in cell sap from source to sink. 

Explain why starch is not transported in the sap.

Suggest why sucrose is transported rather than glucose.

Sucrose molecules are actively loaded into the phloem.

Describe how active loading takes place. 

Many plants contain fruits which act as ‘sinks’ in translocation.

Explain the role of a sink in this process. 

A scientist investigated the rate of water flow in the upper branches of a tree.

Their results are shown below. 

Describe and explain the change in water flow between 10:00 and 14:00.

The diameter of the tree trunk was at its lowest at around 13:00.

Suggest an explanation for this.  

Another scientist measured the rate of water flow in the trunk of the tree.

They found that the rate of water flow in the trunk increased later in the day compared to in the branches. 

Explain how these findings support the cohesion-tension theory. 

A student cut a stem from a plant in the process of transpiration.

The cut end of the stem was placed in an acidic solution, which kills plant cells.

Suggest why the transpiration stream was able to continue. 

Aphids are small insects that feed on plants by inserting tube-like structures into phloem tissue and extracting cell sap.

The diagram below shows how aphids are able to feed from the stem of a plant.

After an aphid stops feeding, cell sap continues to flow inside the phloem.

Explain why. 

Some plant tissues are described as being either sources or sinks.

State two examples of sinks. 

Explain why the stem tissue in the diagram above cannot be described as a source or sink.