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Explain Transpiration

In this worksheet, students will explain how transpiration occurs.

'Explain 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 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 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.  
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/air movement - if it's really windy water vapour is blown away from the leaf.  T
he concentration of water outside the plant 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 to let in more carbon dioxide for photosynthesis, this causes the plant to 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 also 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 storage). Food travels up and down the stem using energy. This is known as translocation.


In the following activity, you will explain how transpiration occurs in plants.

 

Which environmental factors can affect the rate of transpiration? 

 

Wind speed

Minerals

Humidity

Temperature

Light intensity

Image of xylem and phloem vessels

 

The xylem vessel doesn't have end walls between cells. How does this adaptation help the plant? 

 

It allows food to be transported quickly

It allows water to be transported quickly

It allows carbon dioxide to be transported quickly

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

Explain why transpiration happens at a slower rate if it's very humid outside?

 

Column A

Column B

High humidity means there's a lot of
decreases
The concentration of water outside the plant
water vapour in the air
The plant doesn't lose as much water to the air be...
water normally diffuses from a high concentration ...
The rate of transpiration
is higher than inside the plant

Image of xylem and phloem vessels

 

The phloem vessel allows substances to be transported up and down the plant.

 How does this adaptation help the plant?

It allows water to be transported quickly

It allows oxygen to be transported quickly

It allows substances to be transported to where ever they are needed most

What does the term translocation mean?

 

The movement of nutrients made through photosynthesis to where it's needed

The movement of water through the plant

The movement of gases in and out of the stomata

Fill in the blanks below explaining why transpiration is normally 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
stomata
B
photosynthesise
C
water
D
night

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

Explain how the guard cells open and close stomata to allow water to enter and leave the plant.

The stomata are found between guard cells which absorb water in the light and become turgid, opening the stomata

The stomata are found between guard cells which absorb oxygen in the light and become turgid

In the dark the guard cells lose water and become flaccid, closing the stomata

In the light the guard cells lose water and become flaccid, closing the stomata

The xylem vessel transports water in one direction whereas the phloem vessel transports sucrose up and down the plant.

How is the phloem vessel able to transport sucrose around the plant?

By using diffusion

By using osmosis

By using energy

  • Question 1

Which environmental factors can affect the rate of transpiration? 

 

CORRECT ANSWER
Wind speed
Humidity
Temperature
Light intensity
EDDIE SAYS
These four factors are often asked about in exam questions, so it's useful to remember these.
  • Question 2

Image of xylem and phloem vessels

 

The xylem vessel doesn't have end walls between cells. How does this adaptation help the plant? 

 

CORRECT ANSWER
It allows water to be transported quickly
EDDIE SAYS
As the xylem forms one continuous tube, water can flow directly to the leaves where it's used for photosynthesis.
  • Question 3

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 4

Explain why transpiration happens at a slower rate if it's very humid outside?

 

CORRECT ANSWER

Column A

Column B

High humidity means there's a lot...
water vapour in the air
The concentration of water outsid...
is higher than inside the plant
The plant doesn't lose as much wa...
water normally diffuses from a hi...
The rate of transpiration
decreases
EDDIE SAYS
Don't worry if you found this a little tricky! It's easy to get mixed up with humidity and heat/temperature. Remember, humidity is about how much moisture is in the air and not the actual temperature.
  • Question 5

Image of xylem and phloem vessels

 

The phloem vessel allows substances to be transported up and down the plant.

 How does this adaptation help the plant?

CORRECT ANSWER
It allows substances to be transported to where ever they are needed most
EDDIE SAYS
A two-way flow helps the plant to get access to substances such as sucrose and amino acids needed for growth or storage.
  • Question 6

What does the term translocation mean?

 

CORRECT ANSWER
The movement of nutrients made through photosynthesis to where it's needed
EDDIE SAYS
Translocation is the movement of mainly sugars and amino acids around the plant.
  • Question 7

Fill in the blanks below explaining why transpiration is normally 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.
  • 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

Explain how the guard cells open and close stomata to allow water to enter and leave the plant.

CORRECT ANSWER
The stomata are found between guard cells which absorb water in the light and become turgid, opening the stomata
In the dark the guard cells lose water and become flaccid, closing the stomata
EDDIE SAYS
The guard cells surround and control the stomata, which is why they have the name guard cells!
  • Question 10

The xylem vessel transports water in one direction whereas the phloem vessel transports sucrose up and down the plant.

How is the phloem vessel able to transport sucrose around the plant?

CORRECT ANSWER
By using energy
EDDIE SAYS
Transporting water is a physical process so doesn\'t require energy. Phloem and xylem vessels are almost opposites so that should hopefully help you to remember!
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