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Discuss Conditions that Impact Transpiration

Worksheet Overview

QUESTION 1 of 10

Did you know that plants only use about 5 - 6% of all the water they absorb for photosynthesis? So what happens to all that water?  Let's find out more below.
 

Image of photosynthesis

 

Plants can’t help but lose water continually to the air. This is called transpiration. 

Water is constantly lost from the leaves of a plant through pores called stomata. When a plant opens its stomata to allow carbon dioxide in for photosynthesis, water will evaporate and diffuse out of the stomata. More water is drawn up from the stem and the roots to replace the lost water. This is because a concentration gradient exists - there's more water in the roots than the leaves. Water is also naturally cohesive. This means that water tends to 'stick' together, which helps to pull it up through the xylem vessels.

Water moves by osmosis from a high concentration in the roots to a lower one in the leaves. As water moves from the roots to the leaves, more water is drawn up from the soil into the root hair cells. This occurs because the concentration of water in the soil is greater than in the roots - the soil has a higher water potential, so water moves by osmosis into the root hair cells. 

This process is known as the transpiration stream.

Although transpiration is inevitable, it's also quite useful! It helps the plant remain cool and allows minerals to be drawn up the plant along with the water. It also gives plants structure and support.

 


Factors affecting transpiration

Transpiration is affected by many factors:

Temperature - increasing the temperature makes transpiration happen faster - the plant loses more water from its leaves. This is because water evaporates at a faster rate when it's warmer, so there'll be a greater concentration gradient. Water will be drawn up from the roots to replace the 'missing' water in the leaves, moving from a high concentration of water (in the roots) to a lower concentration in the leaves.

Humidity - if it's really humid, it means there's a lot of moisture in the air. The concentration of water outside the plant is higher than inside the plant, so the plant doesn't transpire as much and doesn't lose as much water.  

Wind - if it's really windy, water vapour is blown away from the leaf.  The concentration of water outside the plant is lower than inside the plant, causing the plant to lose more water from its leaves.

Light intensity - if its really sunny, the stomata will open wide to let in more carbon dioxide for photosynthesis -  at the same time, the plant will lose water.


 

Plant adaptations

Plants have adaptations that allow it to do a particular job.

 

Root Hair Cell

 

Image of root hair cell

 

Root hair cells are specialised cells found at the roots of a plant (see image above). These cells are long and thin, making them useful to manoeuvre between soil particles in search of water. The large surface area of the root hair cell allows for a greater chance of contact with water.​ Root hair cells contain lots of mitochondria, which provides the cell with energy. This energy is essential for active transport, which is needed to take in minerals from the soil.

 

Stomata

 

Image of leaf anatomy

 

 

Another adaptation of the plant is found in the leaf​. The lower epidermis layer contains the stomata (stoma for one pore). These stomata allow gases in and out of the underside of the leaf. The stomata are found between guard cells which open or close the stomata depending on how turgid (full of water and swollen - stomata open) or flaccid (lacking water and shrunken - stomata closed) the guard cells are. The stomata will open to allow in carbon dioxide for photosynthesis during the day, but will close during the night when there's no sunlight. 


Xylem
 

 Image of xylem and phloem vessels

 

 

Water moves through xylem vessels.  A xylem vessel is a continuous hollow tube that transports water and minerals in one direction from a plant's roots to the plant's leaves, via the stem. This allows water to travel uninterruptedly up the stem to the leaves. Xylem vessels are made of lignin that strengthen the walls. This helps to support the plant.

 

Phloem

Another transport vessel the plant has is called the phloem. The phloem vessels move sucrose (a form of sugar) that the plant has made by photosynthesis to where it's needed (for example in growing parts of the plant and for storage). Food travels up and down the stem using energy. The cells that make up the phloem are living, and include cells called sieve tubes and companion cells which help to transport substances in the phloem. This is known as translocation.


 

Measuring transpiration

 

 

Image of a Potometer  Image of a potometer

 

Scientists have been able to work out how to measure transpiration in the science lab. A potometer (shown above) is used to measure how much water is being taken up by the plant and the rate at which it does so.

Here's how to use a simple potometer:

 

1) The potometer is filled with water.

2) A leafy plant is connected to it underwater through a rubber tube at one end of the potometer.

3) A bubble of air passes up the potometer when held upright and then placed back into the water.

4) The bubble is observed and the distance travelled by the bubble over a set period of time is measured.

5) The faster the bubble moves, the greater the rate of water uptake and so the greater the rate of transpiration.

The conditions can be varied depending on what you want to investigate -  for example, the effect of changing temperature, humidity,  light intensity or wind speed (for example, with a fan).


In the following activity, you will discuss the factors affecting transpiration.

Root hair cells have an important job to do - they allow water and minerals to be absorbed from the soil.


What two features of the root hair cell allow water and minerals to be absorbed by the plant?

 

Image of root hair cell

 

Thin walls to pass through

Thick walls to pass through

Small surface area to take up less space

Large surface area to absorb more water and ions

Helen and Aisha are investigating transpiration in their science lesson. They'll be setting up equipment to measure the transpiration rate of a plant. Their teacher gives them instructions to follow but they soon realise they're not in the correct order.

 

Help Helen and Aisha to place the instructions in the correct order.

 

  Image of a potometer

 

Step

 Instructions to measure transpiration rate

1  The faster the bubble moves, the greater the rate of water uptake and so the greater the rate of transpiration.
2

A leafy plant is connected to the potometer underwater through a rubber tube at one end of the potometer.

3

 The bubble is observed and the distance travelled by the bubble over a set period of time is measured.

4  The potometer is filled with water.
5   bubble of air passes up the potometer when held upright and then placed back into the water.
4, 2, 5, 3, 1

4, 5, 1, 2, 3

5, 4, 1, 3, 2

The phloem vessel allows substances to be transported up and down the plant. The xylem vessel doesn't have end walls between cells. 

 

 How do these adaptations help the plant? 

 

Image of xylem and phloem vessels

 

The phloem allows substances to be transported up and down to wherever they are needed most by the plant

The phloem allows water and minerals to be transported in one direction

A xylem vessel doesn't have end walls which allows water to be transported quickly

The xylem allows sucrose to be transported to where it's needed by the plant

The phloem vessels move sucrose that the plant has made by photosynthesis to where it's needed, such as in growing parts of the plant and for storage. Food travels up and down the stem using energy. 

 

What is this process known as?

Respiration

Transpiration

Transmission

Translocation

There are four main factors that affect transpiration, these are described below.

 

Match up the factors with their descriptions.
 

 Factors affecting transpiration 

 If there's an increase in this factor,​ the concentration of water outside the plant becomes higher than inside the plant - the plant doesn't transpire as much, so doesn't lose as much water.

B

 If there's an increase in this factor, water vapour is blown away from the leaf.  The concentration of water outside the plant becomes lower than inside the plant, causing the plant to lose more water from its leaves.

C

 If there's an increase in this factor, the stomata will open wider to let in more carbon dioxide for photosynthesis - this causes the transpiration rate to increase.

D

 If there's an increase in this factor, transpiration happens faster because water evaporates at a faster rate when it's warmer.

Column A

Column B

A
Temperature
B
Wind
C
Humidity
D
Light intensity

Are these statements about transpiration true or false? 

 TrueFalse
Plants lose water through the stomata when guard cells are turgid
Decreasing the humidity will increase the rate of transpiration
Increasing the light intensity will decrease the rate of transpiration
Xylem vessels transport water all over the plant
Translocation is the movement of sucrose to where it's needed in a plant
A windy day will cause an increase in the transpiration rate of a plant
Transpiration is the loss of water from a plant

George is investigating conditions affecting transpiration. He connects a plant to a potometer and calculates the rate of transpiration. He then adds a table fan and turns it on near the plant. George calculates the rate of transpiration again.

 

What do you predict will happen and why?

Image of a Potometer  Image of a potometer

 TrueFalse
Plants lose water through the stomata when guard cells are turgid
Decreasing the humidity will increase the rate of transpiration
Increasing the light intensity will decrease the rate of transpiration
Xylem vessels transport water all over the plant
Translocation is the movement of sucrose to where it's needed in a plant
A windy day will cause an increase in the transpiration rate of a plant
Transpiration is the loss of water from a plant

Jake left a potted plant in a hot, brightly lit room for ten hours. The plant wasn't watered during this period. He looked at how the average width of stomata changed over the ten-hour period. 

 

How did the width of the stomata change over the ten-hour period? 

The width got smaller over time

The width got larger over time

The width didn't change

Jake left a potted plant in a hot, brightly lit room for ten hours. The plant wasn't watered during this period. He looked at how the average width of stomata changed over the ten-hour period. 

 

The width of the stomata got smaller over time. Explain the advantage to the plant of this change.

It increases photosynthesis

It increases the rate of water loss

It reduces the rate of water loss

Compare the key features of xylem and phloem vessels. 

 XylemPhloem
Contains mitochondria for energy supply
Transports sucrose
Allows movement of substances in one direction only
Translocation occurs here
Made of dead cells
Made of living cells
Allows transpiration to occur
  • Question 1

Root hair cells have an important job to do - they allow water and minerals to be absorbed from the soil.


What two features of the root hair cell allow water and minerals to be absorbed by the plant?

 

Image of root hair cell

 

CORRECT ANSWER
Thin walls to pass through
Large surface area to absorb more water and ions
EDDIE SAYS
Root hair cells have thin walls which allow water and mineral ions to pass through really easily and quickly. The tiny projections of the root hair cell increase the surface area, allowing more water to be in contact with the cell. This means more water and minerals which are needed for the process of photosynthesis, can pass into the root hair cell.
  • Question 2

Helen and Aisha are investigating transpiration in their science lesson. They'll be setting up equipment to measure the transpiration rate of a plant. Their teacher gives them instructions to follow but they soon realise they're not in the correct order.

 

Help Helen and Aisha to place the instructions in the correct order.

 

  Image of a potometer

 

Step

 Instructions to measure transpiration rate

1  The faster the bubble moves, the greater the rate of water uptake and so the greater the rate of transpiration.
2

A leafy plant is connected to the potometer underwater through a rubber tube at one end of the potometer.

3

 The bubble is observed and the distance travelled by the bubble over a set period of time is measured.

4  The potometer is filled with water.
5   bubble of air passes up the potometer when held upright and then placed back into the water.
CORRECT ANSWER
4, 2, 5, 3, 1
EDDIE SAYS
It's important to set up the potometer correctly, especially when attaching the plant. Attaching the plant is usually done underwater so that air does not get trapped in the plant's xylem vessels.
  • Question 3

The phloem vessel allows substances to be transported up and down the plant. The xylem vessel doesn't have end walls between cells. 

 

 How do these adaptations help the plant? 

 

Image of xylem and phloem vessels

 

CORRECT ANSWER
The phloem allows substances to be transported up and down to wherever they are needed most by the plant
A xylem vessel doesn't have end walls which allows water to be transported quickly
EDDIE SAYS
How are you doing with getting your xylem sorted from your phloem? They are both important for transporting substances around the plant but it's vital to know which one is which! A two-way flow in the phloem helps the plant to get access to substances such as sucrose and amino acids needed for growth or storage. The xylem forms one continuous tube, so that water can flow directly from the roots to the leaves where it's used for photosynthesis.
  • Question 4

The phloem vessels move sucrose that the plant has made by photosynthesis to where it's needed, such as in growing parts of the plant and for storage. Food travels up and down the stem using energy. 

 

What is this process known as?

CORRECT ANSWER
Translocation
EDDIE SAYS
Several tempting ones to go for here! Hopefully, you weren't drawn to respiration or transmission. But how to choose between the other two? Both transpiration and translocation are to do with the movement of substances through a plant, but it is important to understand the difference. Translocation is the movement of sugars and amino acids by the pholem around the plant, whereas transpiration is the movement of water and minerals by the xylem from the roots to the leaves.
  • Question 5

There are four main factors that affect transpiration, these are described below.

 

Match up the factors with their descriptions.
 

 Factors affecting transpiration 

 If there's an increase in this factor,​ the concentration of water outside the plant becomes higher than inside the plant - the plant doesn't transpire as much, so doesn't lose as much water.

B

 If there's an increase in this factor, water vapour is blown away from the leaf.  The concentration of water outside the plant becomes lower than inside the plant, causing the plant to lose more water from its leaves.

C

 If there's an increase in this factor, the stomata will open wider to let in more carbon dioxide for photosynthesis - this causes the transpiration rate to increase.

D

 If there's an increase in this factor, transpiration happens faster because water evaporates at a faster rate when it's warmer.

CORRECT ANSWER

Column A

Column B

A
Humidity
B
Wind
C
Light intensity
D
Temperature
EDDIE SAYS
Look out for clues in the descriptions! A mention of stomata opening wide is normally referring to light intensity. Water evaporating quicker is often related to increased temperatures. Moisture in the air is to do with humidity and a mention of water vapour being blown away is related to wind. If you didn't get them all correct, it might be a good idea to read the Introduction again and then have another go at this question to consolidate your knowledge.
  • Question 6

Are these statements about transpiration true or false? 

CORRECT ANSWER
 TrueFalse
Plants lose water through the stomata when guard cells are turgid
Decreasing the humidity will increase the rate of transpiration
Increasing the light intensity will decrease the rate of transpiration
Xylem vessels transport water all over the plant
Translocation is the movement of sucrose to where it's needed in a plant
A windy day will cause an increase in the transpiration rate of a plant
Transpiration is the loss of water from a plant
EDDIE SAYS
This is a good summary activity to test your knowledge. How did you get on?
  • Question 7

George is investigating conditions affecting transpiration. He connects a plant to a potometer and calculates the rate of transpiration. He then adds a table fan and turns it on near the plant. George calculates the rate of transpiration again.

 

What do you predict will happen and why?

Image of a Potometer  Image of a potometer

CORRECT ANSWER
EDDIE SAYS
This isn't an easy concept to grasp, so don't panic if you found this hard. Remember that water moves from a high concentration to a low concentration. Where is the water more concentrated on a windy day? That's right - it is more concentrated in the leaf than in the air because the wind has blown the water vapour away from the plant. This means that more water will move from the leaf into the air. Diffusion will occur at a faster rate when there's a steep concentration gradient. The wind blowing water vapour away from the leaf causes this steep gradient.
  • Question 8

Jake left a potted plant in a hot, brightly lit room for ten hours. The plant wasn't watered during this period. He looked at how the average width of stomata changed over the ten-hour period. 

 

How did the width of the stomata change over the ten-hour period? 

CORRECT ANSWER
The width got smaller over time
EDDIE SAYS
What will happen to a plant in a hot, brightly lit place if it isn't watered? It will begin to dry up and be in need of water. This will cause the guard cells to become flaccid which will, in turn, close the stomata. This is an important adaptation designed to reduce the amount of water being lost through transpiration at a time when the plant needs to conserve water.
  • Question 9

Jake left a potted plant in a hot, brightly lit room for ten hours. The plant wasn't watered during this period. He looked at how the average width of stomata changed over the ten-hour period. 

 

The width of the stomata got smaller over time. Explain the advantage to the plant of this change.

CORRECT ANSWER
It reduces the rate of water loss
EDDIE SAYS
Consider what will happen to a plant in a hot, brightly lit room for a long period of time, without being watered. It is going to begin to dry up and need to be watered. Because of this, the plant will try to reduce the amount of water being lost through transpiration - it will try to conserve water. The plant does this as the guard cells become flaccid, which narrows the stomata. It's all very clever stuff!
  • Question 10

Compare the key features of xylem and phloem vessels. 

CORRECT ANSWER
 XylemPhloem
Contains mitochondria for energy supply
Transports sucrose
Allows movement of substances in one direction only
Translocation occurs here
Made of dead cells
Made of living cells
Allows transpiration to occur
EDDIE SAYS
Here you have a summary and quick comparison of the xylem and phloem vessels. Does it help you to understand them? This would be a great way to remember the main points for a longer exam question. Great work, that’s another activity completed!
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