KS4 Biology
Plant Nutrition
1 of 57
© Boardworks Ltd 2004
Contents
Plant Nutrition
How do plants make food?
What is photosynthesis?
More about photosynthesis
The rate of photosynthesis
Minerals from the soil
Multiple-choice quiz
2 of 57
© Boardworks Ltd 2004
How do plants get the food they need?
All living organisms
need food to grow
and survive.
Plants are known as
producers because
they provide food for
many other organisms.
Plants cannot move
very much, so how
do they get the food
that they need?
3 of 57
© Boardworks Ltd 2004
Nutrition in green plants
Green plants are amazing
because they actually
make their own food!
Green plants are the
only living organisms
that are able to do this.
All other organisms rely
on plants because of the
food that the plants make.
What is the name of the
process by which plants
make their own food?
4 of 57
© Boardworks Ltd 2004
What is photosynthesis?
Plants make their own food by photosynthesis.
This process is a chemical reaction that uses light energy.
light energy
The word photosynthesis comes
from the Greek language:
“photo” means “light”
“synthesis” means “putting together”
Photosynthesis just means “putting together with light”.
What do green plants “put together” to make their food?
5 of 57
© Boardworks Ltd 2004
Contents
Plant Nutrition
How do plants make food?
What is photosynthesis?
More about photosynthesis
The rate of photosynthesis
Minerals from the soil
Multiple-choice quiz
6 of 57
© Boardworks Ltd 2004
Photosynthesis: raw materials
The raw materials
for photosynthesis
come from the air
and the soil.
What are these raw
materials called?
What else do plants
need to turn
carbon dioxide
and water into food?
7 of 57
carbon
dioxide
water
© Boardworks Ltd 2004
Photosynthesis: energy for the reaction
Photosynthesis is a
chemical reaction
between carbon
dioxide and water.
light
energy
Energy is needed
for this reaction to
take place.
Where do plants
get this energy
from?
carbon
dioxide
water
8 of 57
© Boardworks Ltd 2004
Photosynthesis: where it happens
Plants use light
energy from the
Sun to power
photosynthesis.
light
energy
Where in the leaf
does this reaction
take place?
Photosynthesis
takes place in what
part of plant cells?
carbon
dioxide
water
9 of 57
© Boardworks Ltd 2004
Photosynthesis: where it happens
Photosynthesis takes
place in plant cells
with chloroplasts.
light
energy
Chloroplasts contain
the green chemical
called chlorophyll.
Chlorophyll absorbs
the energy from
sunlight that allows
carbon dioxide and
water to react.
What are the products
of this reaction?
10 of 57
chlorophyll
carbon
dioxide
water
© Boardworks Ltd 2004
Photosynthesis: products of the reaction
The products of the
reaction between
carbon dioxide and
water are glucose
and oxygen.
light
energy
chlorophyll
Which of these
products is used
by plants?
What happens to the
‘waste’ product?
carbon
dioxide
oxygen
glucose
water
11 of 57
© Boardworks Ltd 2004
Photosynthesis: products of the reaction
Glucose is the useful
product for plants.
Some glucose is used
straightaway by plant
cells, some is
converted to starch
for storage and later
used for food.
light
energy
chlorophyll
carbon
Oxygen is the ‘waste’
dioxide
product. This gas is
transported out of the
leaf into the air.
Why is this important
for humans and other
living things?
12 of 57
oxygen
glucose
water
© Boardworks Ltd 2004
Photosynthesis: summary
Summarize the process of photosynthesis in one sentence.
Photosynthesis is a chemical reaction
that takes place in the chloroplasts
in green plant cells, where light energy
is used to convert carbon dioxide and water
into glucose and oxygen.
Photosynthesis is a chemical reaction which means it can
also be summarized in a word equation.
What is the word equation for this vital chemical reaction?
13 of 57
© Boardworks Ltd 2004
Photosynthesis: word equation
light energy
carbon
dioxide
water
glucose
oxygen
chlorophyll
light
energy
chlorophyll
carbon
dioxide
oxygen
glucose
water
14 of 57
© Boardworks Ltd 2004
Photosynthesis: word equation activity
15 of 57
© Boardworks Ltd 2004
Photosynthesis: chemical formulae?
Photosynthesis is a chemical reaction involving molecules.
light energy
carbon
dioxide
water
glucose
oxygen
C6H12O6
O2
chlorophyll
CO2
H2O
The chemical formula of a glucose molecule is C6H12O6.
What are the chemical formulae of the simple molecules
that make up carbon dioxide, water and oxygen?
16 of 57
© Boardworks Ltd 2004
Word equation to chemical equation
17 of 57
© Boardworks Ltd 2004
Photosynthesis multiple-choice quiz
18 of 57
© Boardworks Ltd 2004
Contents
Plant Nutrition
How do plants make food?
What is photosynthesis?
More about photosynthesis
The rate of photosynthesis
Minerals from the soil
Multiple-choice quiz
19 of 57
© Boardworks Ltd 2004
Leaves: maximizing photosynthesis
Leaves are the most efficient
solar panels on Earth!
Why can they be called this?
Light energy is absorbed
by the chlorophyll in leaves
and used to carry out
photosynthesis.
Leaves come in all shapes
and sizes but what features
do they have in common
to maximize photosynthesis?
20 of 57
© Boardworks Ltd 2004
Structure of a leaf
How are leaves designed to maximize photosynthesis?
Leaves are wide and flat
Leaves are thin so gases
to create a large surface
can reach cells easily.
area and to absorb
as much light as possible.
Leaves have lots of veins
to carry water to the cells
and carry glucose away.
21 of 57
Leaves have holes, called
stomata, on their
underside through which
gases move in and out.
© Boardworks Ltd 2004
Structure of a leaf activity
22 of 57
© Boardworks Ltd 2004
Take a look inside a leaf
23 of 57
© Boardworks Ltd 2004
What happens to the glucose?
24 of 57
© Boardworks Ltd 2004
Testing leaves for starch – procedure
25 of 57
© Boardworks Ltd 2004
Testing leaves for starch – experiment
26 of 57
© Boardworks Ltd 2004
Photosynthesis and respiration
Only green plants photosynthesize, but respiration occurs
in the cells of all living things to release energy.
Photosynthesis (energy needed)
light energy
carbon
dioxide
water
glucose
oxygen
chlorophyll
Respiration (energy released)
carbon
glucose
oxygen
dioxide
water
Compare the reactants, products and energy results of
these two chemical reactions. How are they connected?
27 of 57
© Boardworks Ltd 2004
Photosynthesis and respiration
How will the amounts of oxygen and carbon dioxide
in the air vary over 24 hours?
amount of
oxygen
amount
of gas
in the air
amount of
carbon dioxide
12 a.m.
12 p.m.
12 a.m.
What overall effect do photosynthesis and respiration have
on the levels of oxygen and carbon dioxide in the air?
28 of 57
© Boardworks Ltd 2004
Contents
Plant Nutrition
How do plants make food?
What is photosynthesis?
More about photosynthesis
The rate of photosynthesis
Minerals from the soil
Multiple-choice quiz
29 of 57
© Boardworks Ltd 2004
The rate of photosynthesis
Photosynthesis is a chemical reaction and so has a rate.
light energy
carbon
dioxide
water
glucose
oxygen
chlorophyll
Is the rate of photosynthesis always the same?
The rate of photosynthesis varies depending on three
main factors:
light
carbon dioxide
temperature
How do these factors affect the rate of photosynthesis?
30 of 57
© Boardworks Ltd 2004
Light and the rate of photosynthesis
Light energy has to be absorbed by chlorophyll
for photosynthesis to take place.
light energy
carbon
dioxide
water
glucose
oxygen
chlorophyll
The brighter the light, the more light energy there is,
so will photosynthesis be faster or slower?
More light energy means that photosynthesis will be faster.
If light intensity is too high plant cells can be damaged.
How is photosynthesis affected if this happens?
31 of 57
© Boardworks Ltd 2004
Investigating photosynthesis – apparatus
32 of 57
© Boardworks Ltd 2004
Investigating photosynthesis – experiment
33 of 57
© Boardworks Ltd 2004
Investigating photosynthesis – results
34 of 57
© Boardworks Ltd 2004
Carbon dioxide and the rate of photosynthesis
Carbon dioxide is one of the raw materials
used by plants to make their food.
light energy
carbon
dioxide
water
glucose
oxygen
chlorophyll
The concentration of carbon dioxide in the air (0.03%)
is actually quite low.
Why is the concentration of carbon dioxide in
commercial greenhouses often raised to about 0.1%?
More carbon dioxide means more photosynthesis,
so plants make more food and grow quicker.
35 of 57
© Boardworks Ltd 2004
Temperature and the rate of photosynthesis
Photosynthesis is controlled by enzymes.
Enzymes usually work best at warmer temperatures.
light energy
carbon
dioxide
water
glucose
oxygen
chlorophyll
Why is the rate of photosynthesis slower on a sunny day
in winter compared to in summer?
If the temperature gets too hot (above 40 °C), plant enzymes
begin to break down and are destroyed or denatured.
Why does photosynthesis stop under such conditions?
36 of 57
© Boardworks Ltd 2004
What is a limiting factor?
What is the ideal combination of factors
for the maximum rate of photosynthesis?
enough light
enough carbon dioxide
ideal temperature (not too hot or cold)
How is the rate affected if one of these factors is restricted?
If one of the factors is restricted, the rate of photosynthesis
will be below the maximum possible rate.
The restricted factor controls how quickly photosynthesis
occurs and so limits the rate. It is called the limiting factor.
37 of 57
© Boardworks Ltd 2004
Photosynthesis and light – limiting factors
rate of photosynthesis
How does the amount of light affect the rate
of photosynthesis on this labelled graph?
As the amount of light
increases, so does the rate.
The limiting factor is light.
2
Here, increasing the amount
of light has no affect on the
rate. The limiting factor is
now carbon dioxide or
temperature.
2
1
light intensity
38 of 57
1
What must be increased for
the rate to increase?
© Boardworks Ltd 2004
Photosynthesis and carbon dioxide – limiting factors
rate of photosynthesis
How does the amount of carbon dioxide affect
the rate of photosynthesis on this labelled graph?
As the amount of carbon
dioxide goes up, so does
the rate. The limiting
factor is carbon dioxide.
2
Here, increasing the
amount of carbon dioxide
has no affect on the rate.
Light or warmth is now
the limiting factor.
2
1
concentration of
carbon dioxide
39 of 57
1
What must be increased
for the rate to increase?
© Boardworks Ltd 2004
Photosynthesis and temperature – limiting factors
rate of photosynthesis
How does temperature affect the rate of
photosynthesis on this labelled graph?
2
1
0oC temperature 45oC
40 of 57
11. As temperature increases,
so does the rate because
photosynthetic enzymes
work best in the warmth.
Here, the limiting factor is
temperature.
2
Most plant enzymes are
destroyed at about 45°C.
Here, photosynthesis stops
and the rate falls to zero.
What is the limiting factor?
© Boardworks Ltd 2004
Limiting factors activity
41 of 57
© Boardworks Ltd 2004
Limiting factors in the greenhouse
42 of 57
© Boardworks Ltd 2004
Contents
Plant Nutrition
How do plants make food?
What is photosynthesis?
More about photosynthesis
The rate of photosynthesis
Minerals from the soil
Multiple-choice quiz
43 of 57
© Boardworks Ltd 2004
What do plants need for a balanced diet?
Plants need carbon dioxide and water for photosynthesis.
Do they need any other nutrients to keep healthy?
Just like humans, plants need a balanced diet
that includes small amounts of mineral elements.
What mineral elements do they need?
44 of 57
© Boardworks Ltd 2004
What minerals do plants need?
Plants need mineral elements for healthy growth.
Some of the most important minerals needed by plants are:
nitrogen
nitrates
phosphorus
phosphates
potassium
potassium ions
magnesium
magnesium ions
How do plants obtain these minerals?
The mineral elements are found in salts dissolved in water.
Plants obtain minerals when they absorb water from the soil.
What type of salt are each of these elements found in?
45 of 57
© Boardworks Ltd 2004
What are minerals needed for?
How do plants use these mineral elements?
Mineral element How mineral is used in plants
nitrogen (N)
phosphorus (P)
potassium (K)
magnesium (Mg)
46 of 57
making leaves
making roots
making flowers and fruit
making chlorophyll
© Boardworks Ltd 2004
Plant and minerals – summary activity
47 of 57
© Boardworks Ltd 2004
Where do minerals come from?
What are the sources of minerals in the soil?
Rocks: The minerals in rocks are
slowly dissolved by slightly acidic
rainwater. These minerals are
washed into the soil.
Natural fertilizers: Animal faeces
and the decay of dead plants and
animals return minerals to the soil.
Artificial fertilizers: These
contain a ready-made mixture
of the minerals needed by plants.
Why do farmers add fertilizers to their soil?
48 of 57
© Boardworks Ltd 2004
Not enough minerals!
What happens if plants do not get enough minerals?
Plants do not grow properly if they are deprived of minerals
and begin to look unhealthy.
If a plant does not get enough of a mineral it is said
to have a mineral deficiency.
Do mineral deficiencies affect a plant in the same way?
49 of 57
© Boardworks Ltd 2004
Mineral deficiency – no nitrogen!
Nitrogen is used for making leaves and is probably
the most important mineral for plant growth.
What is the effect of nitrogen deficiency?
upper leaves
pale green
lower leaves
yellow and dead
weak stem
50 of 57
© Boardworks Ltd 2004
Mineral deficiency – no phosphorus!
Phosphorus is used for making roots and is important
for all the other minerals used by plants.
What is the effect of phosphorus deficiency?
purple leaves
small roots
51 of 57
© Boardworks Ltd 2004
Mineral deficiency – no potassium!
Potassium is used for making flowers and fruit, so
crops are given extra potassium before they start to fruit.
What is the effect of potassium deficiency?
poor flower
and fruit growth
yellow leaves
with dead spots
52 of 57
© Boardworks Ltd 2004
Mineral deficiency – no magnesium!
Magnesium is used for making chlorophyll
and so is vital for the process of photosynthesis.
What is the effect of magnesium deficiency?
upper leaves normal
(leaves turn yellow
from bottom upwards)
lower leaves pale green
or yellow
53 of 57
© Boardworks Ltd 2004
Mineral deficiency experiment
54 of 57
© Boardworks Ltd 2004
Plant and minerals summary
Complete this table of plant mineral needs and deficiencies.
Mineral
Use in plant
Deficiency signs
nitrogen
making leaves
stunted growth and
yellow leaves
phosphorus making roots
potassium
making flowers
and fruits
poor roots and
purple leaves
yellow leaves with
dead spots
magnesium making chlorophyll leaves turn yellow
from the bottom
55 of 57
© Boardworks Ltd 2004
Contents
Plant Nutrition
How do plants make food?
What is photosynthesis?
More about photosynthesis
The rate of photosynthesis
Minerals from the soil
Multiple-choice quiz
56 of 57
© Boardworks Ltd 2004
Multiple-choice quiz
57 of 57
© Boardworks Ltd 2004