Subject:
Biology
Type of Lesson:
Lecture /discussion and practical
activity/ Use of textbook & internet
Grade:
10
CSEC OBJ:
B 2.2 Students should be able to
describe photosynthesis as the
process by which green plants
manufacture organic substances from
inorganic substances
Term:
Easter
UNIT: 5
Nutrition - Photosynthesis
Duration:
2 x 40mins
Lesson: 9
How does the process of
photosynthesis occur?
Week: 3
Objectives
As a result of this lesson, you will be able to:
1 ) distinguish between autotrophic and heterotrophic nutrition.
2 ) describe the process of photosynthesis, including the reactants (substances needed) and
the products.
3 ) name the conditions necessary for photosynthesis.
4 ) write a word equation and a chemical equation for the process.
5 ) describe what happens to the glucose made in photosynthesis.
6 ) evaluate the importance of photosynthesis to all living organisms including plants.
Prerequisite Student Knowledge
You should be familiar with:
1) characteristics of living things.
2) introduction to differences and similarities between animals and plants in respect of nutrition.
3) knowledge of photosynthesis as a process that plants use to make food.
Important Points
Important points in this lesson are:
1) All organisms need food, and may be grouped on the basis of how they obtain this food. The
main difference between nutrition in plants and animals is that plants make their own food
from simple inorganic substances (autotrophs), while animals need ready made complex
organic substances which they obtain from other living organisms (heterotrophs). Animals
obtain their food from plants or other animals.
2) During photosynthesis, plants make these complex organic substances from inorganic simple
materials. The products of photosynthesis are very important for all life, since they include
oxygen as well as glucose. The energy used to make photosynthesis occur comes from light
energy, which is absorbed by the chlorophyll and then converted into chemical energy (as
part of the food made). Thus the energy in plants comes directly from sunlight energy, while
the energy in animal foods comes secondarily, as a result of the animal taking in energy from
plant food.
Key Terms
autotrophic
heterotrophic
organic
organic
inorganic
Challenge Areas
Your teacher will ask you to research the following
1) Which plants have the fastest rate of photosynthesis?
2) In what regions of the world are these plants found?
3) Why are forests said to be carbon dioxide SINKS?
Equipment/Material Needed
1. Stems of submerged water plants such as Elodea
Figure 9.1: Part of Elodea plant (water weed)
2.
3.
4.
5.
6.
A large sink or large dish pan in which to set up the apparatus
sharp razor blade
matches and a wooden splint
A lamp or access to sunlight
Apparatus to be set up as shown in Figure 9.2
Note to student
1) Many of you even at this level still hold the misconception that plants get their food from the
soil. The activities in this lesson and those to follow should provide you with experiences
that should help you to form acceptable scientific ideas about this. Practical activities are
important in helping you form these new ideas.
2) Remember that photosynthesis uses carbon dioxide from the air as an inorganic, simple
substance and water to make complex organic substances, (glucose).
3) While plants are photosynthesizing, they use up carbon dioxide and give out oxygen.
However, they respire all this time, and so they need to use up some of this oxygen for their
own respiration, to obtain energy for their own activities.
Introduction
1) Introductory Activity: Reviewing feeding among living organisms
A ) Can you recall the lessons you did earlier on food chains, food webs and trophic
levels? Try to answer the following questions
i. Why are plants at the start of all food chains?
ii. Can you explain why the animals in a food chain or web are called
consumers?
B ) In today’s lesson you will learn two new terms used to distinguish how plants and
animals obtain their nutrition. You will also learn the process by which plants make
their own food.
Body of Lesson
1) Distinguishing between autotrophic and heterotrophic nutrition
A ) Here are two new terms ‘autotrophic’ and ‘heterotrophic’. One refers to how plants
feed and the other to how animals feed. Try to figure out which is which. Remember
you already know that trophic means feeding. Do you know the meaning of ‘auto’?
You should now be able to infer that plants are autotrophic while animals are
heterotrophic.
B ) To further distinguish between autotrophic and heterotrophic: you also need to say
whether plants or animals use simple substances obtained from their surroundings
(inorganic) to make food or they take in complex substances made by living things
(organic). From examining how plants and animals feed you should be able to make
the distinction here. Write a sentence to describe the difference.
C ) Can you think of examples of inorganic and organic substances? You will now learn
the process by which plants make food.
2 ) The process of photosynthesis
Important Point
What does ‘auto’ mean?
(self)
What does ‘trophic’
mean? (feeding)
So ‘auto-trophic’ means
self-feeding.
Consider now what
could ‘hetero-trophic’
mean?
iii.
iv.
A ) Consider the following questions:
I . Can you think of the things that plants need to stay alive?
Write them down. Your teacher will check your answers.
I I . How do you think each of the things you named helps to
keep the plant alive? Write down your answer. Check
yourself later as the lesson progresses and make any
corrections.
B ) You know from previous lessons that plants are living things so
they need food. But plants do not have mouths to take in food. So
how do they feed? Try to figure this out. Let us see what we
know that could help us find the answer.
i.
Plants cannot move around
ii.
They have roots that grow and branch into the soil
Their branches grow into the air and their leaves are spread out
Their leaves are mostly green
v.
vi.
vii.
viii.
Some of the components of soil are water, minerals (mineral salts), soil
particles and humus.
Air contains gases like carbon dioxide and oxygen
Plants die when there is no light even if they have water and air.
Plants die if they get no water for long periods.
When we examine each point above, we may get some clues to how plants feed. Can you
suggest some other clues before reading ahead?
C ) Let us consider what points might follow on from the above.
i. Since plants do not move about to get food they must get their food right
where they are.
ii. Maybe their roots take things from the soil…Is it water? or minerals or both?
or something else?
iii.
Maybe their leaves take something out of the air….What could it be?
iv.
Their green leaves are due to a green substance called chlorophyll which is
found in all green parts of plants especially the leaves. The chlorophyll is
found inside chloroplasts as you remember from studying cells. Since all
plants have this it must be a clue. Agree? Great so far.
v.
Water and sunlight are definitely two things needed.
D ) Read passage in Box 9.1
Box 9.1
Scientists have found out that plants are able to use energy from sunlight to make all
their food using water and minerals from the soil and carbon dioxide from the air.
These are all simple inorganic substances. The chlorophyll in the chloroplasts is able
to absorb light energy and convert it into chemical energy which the foods contain.
The process by which plants make their food is called photosynthesis. The word
photosynthesis is made up of two words ‘photo’ meaning light and ‘synthesis’
meaning putting together.
One way that scientists express what takes place in a chemical reaction is to write
what they call a formula or an equation as shown below.
The formula or chemical equation for the photosynthesis reaction is shown below
written in words.
sunlight
carbon dioxide + water       sugar + oxygen
chlorophyll
The formula may also be written using chemical symbols as shown below.
sunlight
6CO2 + 6H2O
C6H12O6 +
6O2
chlorophyll
The equation gives the overall reaction as the process is more complex than shown.
Carbon dioxide and water are called the reactants while the sugar and oxygen are the
products made during the reaction. Sunlight and chlorophyll are also shown to
indicate that those conditions must be present.
E ) Go to the internet site below and read what it tells you about photosynthesis:
http://www.biology4kids.com/files/plants_photosynthesis.html
This will give you a short summary of the process.
F ) Now let us consider the roles of the various substances – that is, what they do in
photosynthesis. Read the information in Table 9.1 and note the points.
Table 9.1: The Roles of Water, Light, Carbon Dioxide, Chlorophyll in the Process of
Photosynthesis
Role of light
Light supplies the energy for the process
is absorbed by the green pigment
in the chloroplasts.
Role of chlorophyll
Chlorophyll absorbs light energy and
chemical energy which is present in the
photosynthesis
Chloroplasts are found mainly in the
occurs mainly in the leaves
Role of water
Water is made up of hydrogen and
absorbed by chlorophyll is used to split
The oxygen formed is released as a waste
use what is needed for respiration. The
in making carbohydrate e.g. glucose by
dioxide.
of photosynthesis. The light
chlorophyll which is found
Try This!
These texts may be
helpful:
Chinnery, L. et al CXC
Biology, 3rd edition, pages
35 -36
Glucose is used in many
ways
Roberts and Mitchelmore,
Biology for CXC, page 164
What happens to sugar
which a leaf makes?
Atwaroo-Ali CXC Biology
page 164 Products of
photosynthesis
converts this energy into
foods formed as a result of
leaves so photosynthesis
oxygen. The energy
water into its components.
product after the plant cells
hydrogen from water is used
combining with carbon
Role of carbon dioxide
Carbohydrates contain carbon, hydrogen
and oxygen.
Carbon dioxide supplies the carbon and oxygen of carbohydrates (while water supplies the
hydrogen.)
3 ) Oxygen is released during photosynthesis.
A ) The practical activity that follows identifies one of the products of photosynthesis.
I.
Work with your group and using Worksheet 9.1 as your guide, collect the
necessary pieces of equipment and set them up correctly.
I I . After about five minutes, you will notice something happening. What is it?
I I I . Draw in your notebook, a diagram of the equipment used, and write up this
activity in the book. Make your own conclusions on how the intensity of light
affects the rate at which oxygen comes out and hence the rate of
photosynthesis.
4) Glucose is formed during photosynthesis. What happens to it?
A ) Read from your regular textbook to find out what happens to the glucose made during
photosynthesis.
B ) Did you read about the following things that might happen to the glucose produced?
i. Some glucose used in respiration to supply energy for the use of the plant
ii. Some stored temporarily in the leaf as starch or in some plants as sugar (e.g.,
in onion and skellion).
iii.
Some glucose is converted to sucrose and transported to other parts of the
plant. It can then be converted to carbohydrates, lipids and protein and used
in growth.
iv.
Cellulose which is found in the cell walls of plant is a complex carbohydrate
formed from glucose
5) Evaluating the role of photosynthesis in a habitat
A ) Think of the role of plants as producers in a habitat and then consider their usefulness.
Did you have the following points ?
i. Provides food for plants, animals, fungi
ii. Provides oxygen for respiration---plays vital role in the cycling of oxygen
iii.
Removes CO2 from air---plays vital role in carbon cycle
B ) Consider the fact the nowadays when people are building houses, they remove all the
trees from the building plot. What are some consequences of this action?
Closure
In-Class Assignments
1. Write up the experiment to show the rate of photosynthesis being affected by the amount of
light given to the plant.
2. Answer the following questions:
A ) In what organ of the plant does photosynthesis occur?
B ) Where, inside that organ, does the process occur?
C ) What substances/reactants are required for photosynthesis to occur?
D ) What are the main products of photosynthesis?
E ) What are some conditions needed for photosynthesis?
F ) What would happen if photosynthesis stopped on earth?
Out-of-Class Assignment
1 ) Make a table to compare autotrophic with heterotrophic nutrition
2 ) In groups, draw a diagram to explain how the process of photosynthesis occurs highlighting,
the reactants, the products and the condition necessary for the process to occur.
3 ) Prepare for next lesson by collecting different samples of leaves. Remember that the whole
leaf must include the stalk that attaches it to the stem. Note that some leaves like ackee are
compound leaves, so what you may think is a leaf is really a leaflet. Try to include leaves
with colours other than green.
Supplemental
Glossary of Terms
Autotrophic nutrition
A type of nutrition in which simple inorganic substances
obtained from the surrounding is used to make feed. It is
carried out by plants. They make their own food.
Heterotrophic
nutrition
Nutrition in which ready-made organic food is taken it.
Has to obtain food by eating other organisms (plants,
animals). Animals, fungi and most bacteria carry out this
type of nutrition
Inorganic substance
Minerals, metals, non-metals, elements (except carbon)
and the compounds formed from them.
Organic substance
Mainly compounds of carbon (few exceptions)
Complex substances made by living things, e.g.
carbohydrates such as glucose and starch, protein and
fats/lipids
Photosynthesis
Made up of two words ‘ photo/light’ and ‘synthesis/ to
put together’ A process in plants that uses light energy
absorbed by chlorophyll to make food from water and
carbon dioxide.
Products
Substances produced by a reaction
Reactants
Substances which cause a reaction to occur
Trophic
Pertaining to feeding, feeding level in a food chain, a
habitat
CSEC Questions
1) Describe the process by which carbon dioxide and water are made into carbohydrates by
green plants. (2001) Q1 part (a)
2) Write a balanced equation that effectively summarises photosynthesis. (June 2007) Q1 (a)
(ii)
3) Explain five ways in which the various parts of a plant may be adapted to carry out the
process of photosynthesis. (1997)
Recommended Materials
1) Worksheet 9.1
2) The following is a useful website:
http://www.biotopics.co.uk/plants/psfac2.html
Bibliography
Carrington, C., Agard, M., Sealy, L. (1995). Biology – Skills
for Excellence. Harlow, UK: Longman Caribbean
Chinnery, L., Glasgow, J., Jones, M., Jones, G. (2001). CXC Biology. London: Cambridge
University Press.
Roberts, M. B. V. & Mitchelmore, J. (1985). Biology for CXC. Cheltenham, UK: Thomas Nelson
and Sons, Ltd.
Soper & Smith with King. (DATE). Caribbean biology for CXC: An integrated approach.
London: Macmillan Caribbean.
Worksheet
Worksheet 9.1: Identifying one of the products of photosynthesis (oxygen)
1) Materials needed:
a. Small piece of Elodea (water weed)
b. water with a little bicarbonate dissolved
c. matches
d. splint
e. large beaker
f. funnel
g. test tube
2) Procedure:
a. Set up the apparatus as shown in Figure 9.2. N.B. Cut the end of the
stem again under water so as not to introduce air bubbles.
b. You will need a large sink or dishpan filled with water. which was left
overnight to remove chlorine.
c. Cut the stem of the Elodea under water.
d. Leave for a few minutes/half an hour or until about 2cm of gas has
collected in the top of the inverted test tube
i. Carefully remove the test tube so that the gas does not
escape.
ii. Light the wooden splint then extinguish it.
iii. Insert the glowing splint into the test tube.
e. Check for the splint to glow brighter or to be rekindled.
f. Write up the report in the lab book. Interpret the results.
gas collecting in test tube
gas bubbles from cut end of stem
inverted test tube originally full of water
beaker
water with bicarbonate added
water plant
support to keep funnel off beaker
lamp
Apparatus for collecting gas given off by photosynthesizing water weed
Figure 9.2: The water plant Elodea photosynthesizing and releasing gas bubbles.
Answers
1) Introductory Activity: Reviewing feeding among living organisms
A ) Can you recall the lessons you did earlier on food chains, food webs and trophic
levels? Try to answer the following questions
i. Why are plants at the start of all food chains? Answer:They are
producers/they make their own food.
ii. Can you explain why the animals in a food chain or web are called
consumers?
Answer: They obtain food from plants or other animals. They cannot make
their own food.