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Describe 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. As water moves from the roots to the leaves, more water is drawn up from the soil 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.


 

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.

Humidity - if it's really humid, it means there's a lot of moisture in the air - the plant doesn't transpire as much, so doesn't lose as much water.

Wind - if it's really windy, water vapour is blown away from the leaf. This causes the leaf to transpire faster, so the plant loses more water from its leaves.

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.

 

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 a greater chance of contact with water.​ 

 

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. 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. ​

 

 Image of xylem and phloem vessels

 

Water moves through xylem vessels.  A xylem vessel is a continuous hollow tube that transports water in one direction and minerals from a plant's roots to the plant's leaves, via the stem.

Another vessel the plant has is called the phloem. The phloem vessels move food substances that the plant has made by photosynthesis to where they are needed (for example in growing parts of the plant and storage). Food travels up and down the stem. 


 

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 in the picture 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 describe how transpiration occurs in plants.

Helen and Aisha are investigating transpiration in their science lesson. They will be setting up equipment to measure the transpiration rate of a plant.

 

What is the name of the piece of equipment used to measure transpiration?

The image below shows the structure of a leaf.


What is the name of structure X that water vapour is lost from? 

 

Image of leaf anatomy  

The xylem vessel doesn't have end walls between cells.

 

How does this adaptation help the plant? 

 

Image of xylem and phloem vessels

It allows food to be transported quickly

It allows water to be transported quickly

It allows carbon dioxide to be transported quickly

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

During photosynthesis, glucose and oxygen are made. Glucose is needed around the plant for many different processes.


What is the name of the cell that transports glucose around the plant?

Xylem

Phloem

Stoma

Describe transpiration.

Xylem

Phloem

Stoma

Environmental factors can affect the rate of transpiration. 

 

Give some examples of these factors.

Fertiliser

Temperature

Wind

Farming

What does the term translocation mean? 

The movement of nutrients made through photosynthesis to where they're needed

The movement of water through the plant

The movement of gases in and out of the stomata

Which of the following environmental factors would increase the rate of transpiration in a plant? 

A very sunny day

A very cold day

A very hot day

A very humid day

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.... This means that plants won't lose ...D...

Column A

Column B

A
Photosynthesise
B
Water
C
Stomata
D
Night
  • Question 1

Helen and Aisha are investigating transpiration in their science lesson. They will be setting up equipment to measure the transpiration rate of a plant.

 

What is the name of the piece of equipment used to measure transpiration?

CORRECT ANSWER
potometer
a potometer
EDDIE SAYS
A potometer is essentially made up of a capillary tube, plus a rubber tube and a container of water. If you're not sure about this, have a look at the image in the Introduction.
  • Question 2

The image below shows the structure of a leaf.


What is the name of structure X that water vapour is lost from? 

 

Image of leaf anatomy  

CORRECT ANSWER
Stomata
Stoma
EDDIE SAYS
The stomata are pores that allow gas exchange to occur. They are normally surrounded by cells called guard cells that open and close, controlling which gases enter or exit the leaf.
  • Question 3

The xylem vessel doesn't have end walls between cells.

 

How does this adaptation help the plant? 

 

Image of xylem and phloem vessels

CORRECT ANSWER
It allows water to be transported quickly
EDDIE SAYS
Can you remember what the xylem carry inside them? Xylem cells transport water and minerals from the roots of a plant up to the leaves. As the xylem forms one continuous tube, water can flow directly to the leaves where it's used for photosynthesis.
  • Question 4

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 5

During photosynthesis, glucose and oxygen are made. Glucose is needed around the plant for many different processes.


What is the name of the cell that transports glucose around the plant?

CORRECT ANSWER
Phloem
EDDIE SAYS
Don't worry if you found that tricky! Phloem cells transport food or glucose up and down the stem (this is called translocation). The glucose is needed for respiration, growth and storage. Xylem transport water and minerals from the root to the leaves - this is called transpiration. A stoma is the singular of stomata which are the pores in the underside of a leaf where gas exchange takes place.
  • Question 6

Describe transpiration.

CORRECT ANSWER
EDDIE SAYS
How are you getting on so far? Don't forget, transpiration is all about water loss. Some plants are great at reducing water loss, like cacti, which have waxy spines, rather than leaves.
  • Question 7

Environmental factors can affect the rate of transpiration. 

 

Give some examples of these factors.

CORRECT ANSWER
Temperature
Wind
EDDIE SAYS
There are several factors that can affect the rate of transpiration. There were two mentioned in this question - did you get them both? A higher temperature or a stronger wind can both speed up the rate of transpiration. Two other factors not mentioned above are humidity and light intensity. If it is sunny or with a low humidity, there will be a faster rate of transpiration too.
  • Question 8

What does the term translocation mean? 

CORRECT ANSWER
The movement of nutrients made through photosynthesis to where they're needed
EDDIE SAYS
It is important to not get muddled between transpiration and translocation. Translocation is the movement of mainly sugars and amino acids around the plant. This happens in the phloem cells. Transpiration is the movement of water and minerals from the roots to the leaves of a plant, in the xylem cells.
  • Question 9

Which of the following environmental factors would increase the rate of transpiration in a plant? 

CORRECT ANSWER
A very sunny day
A very hot day
EDDIE SAYS
It is important to understand the factors that affect transpiration. A very sunny day is great for photosynthesis! The stomata will open, allowing more carbon dioxide in but this will also allow water to escape. A high temperature will mean the water evaporates quickly, increasing the transpiration rate. The humidity affects the rate of transpiration too - the more humid the air around the plant, the lower the rate of transpiration.
  • Question 10

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.... This means that 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 since there's no sunlight to power photosynthesis. This means that water vapour can't escape from the leaf and allows plants to reduce water loss from transpiration. Well done for completing this activity!
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