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Discuss Conditions Affecting Transpiration

In this worksheet, students will discuss conditions that affect transpiration.

'Discuss Conditions Affecting Transpiration' worksheet

Key stage:  KS 4

GCSE Subjects:   Biology: Single Subject, Biology: Combined Science

GCSE Boards:   Pearson Edexcel

Curriculum topic:   Plant Structures and Their Functions

Curriculum subtopic:   Plant Structures and Their Functions

Difficulty level:  

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 anyway?  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 water up through the xylem vessels.

Water moves via 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 cellsThis occurs because the concentration of water in the soil is larger than in the roots- the soil has a higher water potential, so water moves via 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:

1)  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 its 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.

 

2 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; the plant doesn't transpire as much so doesn't lose as much water.  


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


4)  Light intensity - if its really sunny, the stomata will open wide to let in more carbon dioxide for photosynthesis, at the same time 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 thin and long making them useful to manoeuvre between soil particles in search of water. The large surface area of the root hair cell allows 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 needed to take in minerals from the soil.

 

Stomata

Image of leaf anatomy

 

Another adaptation of the plant is found in the leaf of a plant​. 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.  Xylem vessels are a hollow continuous tube that transports water and minerals in one direction from a plants 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 of the xylem vessel. 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.

 

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

 

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 the descriptions below.

 

 Factors affecting transpiration

 If there's an increase in this factor,​ the concentration of water outside the plant is 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 is higher 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
Light intensity
C
Wind
D
Humidity

George is investigating conditions affecting transpiration during his science lesson. 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?

 

Column A

Column B

A
Temperature
B
Light intensity
C
Wind
D
Humidity

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. 

Discuss how the width of the stomata changed over the ten-hour period. 

The width got smaller over time

The width got larger over time

The width didn't change

Image of root hair cell

 

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?

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

Image of xylem and phloem vessels

 

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? 

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

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

The xylem 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

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

Explain what the transpiration stream is.

 12345
More water is drawn up from the stem and the roots to replace the lost water as there's a higher concentration of water in the roots than the leaves
Water travels up the stem to the leaves
As the plant opens its stomata to allow carbon dioxide in for photosynthesis water evaporates and diffuses out of the stomata
The concentration of water in the soil is larger than in the roots so water moves via osmosis into the root hair cells
As water moves from the roots to the leaves more water is drawn up from the soil into the root hair cells

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

Fill in the blanks below explaining why transpiration is slower at night than during the day.

 

This is because the ...A... are closed during the ...B... as plants can't ...C..., so plants won't lose ...D...

Column A

Column B

A
night
B
photosynthesise
C
water
D
stomata
  • Question 1

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
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.
  • Question 2

There are four main factors that affect transpiration, these are described below. Match up the factors with the descriptions below.

 

 Factors affecting transpiration

 If there's an increase in this factor,​ the concentration of water outside the plant is 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 is higher 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 normally is referring to light intensity. Water evaporating quicker is often relating 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.
  • Question 3

George is investigating conditions affecting transpiration during his science lesson. 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?

 

CORRECT ANSWER
EDDIE SAYS
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 4

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. 

Discuss how the width of the stomata changed over the ten-hour period. 

CORRECT ANSWER
The width got smaller over time
EDDIE SAYS
To reduce the amount of water being lost through transpiration the stomata will get narrower, especially as the plant isn't being watered.
  • Question 5

Image of root hair cell

 

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?

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 6

Image of xylem and phloem vessels

 

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? 

CORRECT ANSWER
The phloem allows substances to be transported up and down to where ever they are needed most by the plant
The xylem doesn't have end walls which allows water to be transported quickly
EDDIE SAYS
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. As the xylem forms one continuous tube, water can flow directly to the leaves where it's used for photosynthesis
  • Question 7

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
Because the plant wasn't being watered, the plant will try to reduce the amount of water being lost through transpiration.
  • Question 8

Explain what the transpiration stream is.

CORRECT ANSWER
 12345
More water is drawn up from the stem and the roots to replace the lost water as there's a higher concentration of water in the roots than the leaves
Water travels up the stem to the leaves
As the plant opens its stomata to allow carbon dioxide in for photosynthesis water evaporates and diffuses out of the stomata
The concentration of water in the soil is larger than in the roots so water moves via osmosis into the root hair cells
As water moves from the roots to the leaves more water is drawn up from the soil into the root hair cells
EDDIE SAYS
How are you getting on so far? This is a great activity to consolidate your knowledge. Have a few go's if you didn't manage it the first time!
  • Question 9

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 10

Fill in the blanks below explaining why transpiration is slower at night than during the day.

 

This is because the ...A... are closed during the ...B... as plants can't ...C..., so plants won't lose ...D...

CORRECT ANSWER

Column A

Column B

A
stomata
B
night
C
photosynthesise
D
water
EDDIE SAYS
The plant's stomata don't need to open at night as there's no sunlight to power photosynthesis. This allows plants to reduce water loss via transpiration.
---- OR ----

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