Plants, Matter and Energy
Students’ Sheet
Introduction
Plant parts
To grow healthily, plants need






air
water
nutrients
light
warmth

Why? When a plant grows a vast numbers of chemical
reactions happen. These reactions change one set of
substances (starting materials) into other substances
(reaction products). During these reactions energy is
transferred.

Roots take up water and
nutrients from the soil. They
also hold the plant steady
and upright in the soil.
The stem carries water and
nutrients to different parts of
the plant.
Leaves use carbon dioxide
from the air, water and
sunlight to make its food
(photosynthesis).
Matter
Air, water and nutrients are the starting point for the chemical reactions that happen to ‘build’ a
plant. They are all forms of matter.
Energy
Light and warmth are about transferring energy. Light is one way that energy can be transferred
from place to place. Warming and cooling are two of the effects than may happen when energy is
transferred.
Activities
Activity 1: Matter and particles
Matter is anything that has mass. In other words, matter can be
weighed.
Solids, liquids and gases are the three states of matter. They
are made of particles.
For any substance the particles are the same whether it is
solid, liquid or a gas. The difference is how they are arranged
and the way they move.
Plants need three kinds of matter: air, water and nutrients.
Air has mass
Air doesn’t weigh anything?
Think again.
Weigh a 1 dm3 container full
of air. Suck out the air and
weighed it again. It weighs
about 1.3 g less. So 1 dm3
of air has a mass of 1.3 g.
Questions
1. Draw lines to match the state of matter to the correct description of how its particles are
arranged and the way they move.
Solid
Particles are arranged randomly. They are close together and move
around one another.
Liquid
Particles are arranged in a regular way, close together. They vibrate in
a fixed position, but cannot move from place to place.
Gas
Particles are arranged randomly. They are far apart and move quickly
in all directions.
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Plants, Matter and Energy: p. 1
2. There are forces of attraction between particles. For a
substance,
Changes of state
(a) in which state of matter are they strongest?
When a solid substance melts it
becomes a liquid. Its particles are
more loosely linked to each other.
(b) in which state of matter are they weakest?
When a liquid boils it becomes a
gas. Its particles are even more
loosely linked to each other.
3. 70% of Earth’s surface is covered in water, mostly
oceans and seas. In very cold places water is in its solid
state, as ice and snow. Air contains water vapour (water
as a gas). The amount varies from day to day and place
to place and is called ‘humidity’.
Remember: The particles of the
substance do not change. They
are the same regardless of the
state of matter – solid, liquid or
gas. It’s the strength of the
attractive forces between them
that changes.
(a) Sketch diagrams to show how particles are arranged
in (i) ice, (ii) water, (iii) water vapour. Describe their
movement in each state.
(b) If the temperature of water gets to 0 oC or lower it
becomes ice. What is this change of state called?
(c) What is formed when water evaporates?
Activity 2: Particles in air and water
Atoms are the building blocks from
which all materials are made.
The particle model uses the term ‘particle’, but how do
parrticles of one substacne differ from particles of
another substance?
Elements are substances made
from just one type of atom.
Compounds are substances made
from atoms of two or more elements.
In Dalton’s model, atoms are pictured as tiny spheres,
too small to be seen even using the most powerful
microscope.
Everything in our world is made from atoms, but the only substances whose particles are atoms
are the noble gases such as helium, neon and argon (Group 0 of the Periodic Table).
So what are the particles in air, water and nutrients?
Molecules are made when two of more atoms are joined together by a chemical bond.
You can represent atoms by drawing circles and
labelling them with the element’s symbol.
The particles in all gases or liquid at room
temperatures are molecules. They can be
represented using circle diagrams to show the
numbers and types of atoms used to make a
molecule.
Here are two examples.
H
O
C
Ar
hydrogen oxygen
argon
carbon
You may read in some places that
molecules are ‘made of atoms’ and the
expression ‘atoms in a molecule’.
This is convenient, but it’s more accurate to
say molecules are ‘made from atoms’.
Hydrogen gas consists of molecules each
made from two hydrogen atoms. Methane gas
consists of molecules each made from one carbon atom and four hydrogen atoms.
H
hydrogen
molecule, H2
H
H
methane
molecule, CH4
H
C
H
We can represent
these using circle
diagrams:
H
Important. The circle diagrams show which atoms are bonded to which in a molecule, but they
do not show the size or geometry of the particle.
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Plants, Matter and Energy: p. 2
Questions
1. Air is a mixture of several gases.
Gas
Percentage by volume
Forces and molecules
Nitrogen
78%
Oxygen
21%
Argon
0.9%
Carbon dioxide
0.037%
The forces of attraction between
atoms bonded in a molecule are
very strong, much stronger than
the forces between one
molecule and another.
These are the percentages in dry air.
(a) Which of the gases in air are elements and which are compounds?
(b) Which of these gases is used in photosynthesis?
2. Below are the formulae of particles that make up air:
Gas
Formula
Particle made from
Nitrogen
N2
two nitrogen atoms
Oxygen
O2
two oxygen atoms
Argon
Ar
one argon atom
Carbon dioxide
CO2
one carbon atom bonded to two oxygen atoms
(a) Draw circle diagrams to represent the particles in each gas.
(b) In which gases are the particles (i) atoms, (ii) molecules?
3. Water, H2O, is also present in moist air.
(a) Which atoms and how many of each are used to make a water molecule?
(b) Draw a circle diagram of a water molecule.
Activity 3: Particles in nutrients
Nearly all nutrients are salts, which are compounds
produced in neutralisation reactions between a base and
an acid. Salts are solid compounds. Many are soluble in
water. This is important because it is how nutrients get
into a plant – they dissolve in water and the solution is
taken up through a plant’s roots.
The particles in salts are not molecules. They are ions, which
means they have an electrical charge. Some examples are
shown on the next page.
Atom(s)
Positively charged ion
sodium
sodium, Na+
potassium
potassium, K+
nitrogen and hydrogen
ammonium, NH4+
magnesium
magnesium, Mg2+
calcium
calcium, Ca2+
aluminium
aluminium, Al3+
What is ‘charge’?
‘Charge’ is a property of matter
that causes a force when near
another charge. Charge can be
positive or negative. Particles that
have opposite charges attract one
another. Particle with the same
charge repel one another.
Atoms, and ions
An atom has no overall
electrical charge. However, it
contains even smaller
particles called electrons.
Each electron has a negative
charge.
If an atom gains an electron,
it becomes negatively
charged. If an atom loses an
electron, it becomes
positively charged. The
charged particles are called
ions.
Science & Plants for Schools: www.saps.org.uk
Plants, Matter and Energy: p. 3
Atom(s)
Negatively charged ion
chlorine
chloride, Cl-
nitrogen and oxygen
nitrate, NO3-
sulfur and oxygen
sulfate, SO42-
phosphorus and oxygen
phosphate, PO43-
Notice, when a negatively charged ion is made from atoms of two elements, one of which is
oxygen, the name always ends in -ate.
Ions may be represented using circle diagrams such as:
Na+
Mg2+
NH4+
sodium ion
magnesium ion
ammonium ion
Cl-
NO3
SO4
chloride ion
nitrate ion
sulfate ion
-
2-
All salts consist of positively charged ions and negatively charged ions. The charges on the ions
must balance one another.
+
Na
-
Cl
sodium chloride, NaCl
+
NH4
-
+
Cl
Na
ammonium chloride, NH4Cl
SO4
2-
+
Na
sodium sulfate, Na2SO4
You can represent the formula of a salt using these diagrams.
However, these do not represent particles of the salts. They simply
show the repeating group found of ions (these are the ‘particles’)
found in the solid structures.
The picture on the right shows the arrangement of
sodium ions and chloride ions in solid sodium
chloride. To differentiate between them of sodium
ions are represented by purple spheres and
chloride ions by green spheres.
Salts
sodium chloride lattice
‘Salts’ are not the same as ‘salt’ (sodium
chloride). A salt is formed when an acid
neutralises a base. Sodium chloride is
one example. It forms when hydrochloric
acid is neutralised by sodium hydroxide.
Questions
1. The salts listed below are often used as plant nutrients. Name the ions in these salts and write
chemical formulae for the salts.
(a) potassium chloride
(b) ammonium nitrate
(c) ammonium sulfate
(c) calcium phosphate
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Plants, Matter and Energy: p. 4
(d) magnesium sulfate
2. A chemist has been asked to make samples of potassium chloride and ammonium sulfate in
the laboratory.
(a) Which base and which acid could be used to make potassium chloride?
(b) Which base and which acid could be used to make ammonium sulfate?
3. The diagram on the right shows a layer of potassium ions and
chloride ions in a potassium chloride crystal. The ions pack
together at the corners of a cube.
Sketch the layer directly behind.
K+
-
Cl
Remember: particles with same type of charge repel, particles with
opposite charge attract.
4. Nutrients dissolve in water and are absorbed through the roots
of a plant. The ions in a salt are arranged in a regular threedimensional structure.
+
K
-
Cl
-
Cl
+
K
-
Cl
+
K
+
K
-
Cl
+
K
-
Cl
-
Cl
+
K
-
Cl
+
K
Describe what happens to the charged particles (ions) in a solid
salt when it dissolves in water.
Particles
Often we call something that is very small, like a piece of dust, a particle. But in science it has
a special meaning. It is used as a catch-all for the smallest bits that substances are made of:
atoms, molecules or ions.

It takes 3 000 000 000 000 atoms to make a fleck of dust.
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One grain of sodium chloride contains 1 000 000 000 000 000 000 ions.

A plant cell is made from 80 000 000 000 000 000 atoms joined in different ways to make
various molecules.
Unimaginably large numbers! So the ‘particles’ that scientists talk about are incredibly small.
Energy
Activity 4: Energy
Plants need light and warmth. Changes that happen in
plants, like any other change, involve the transfer of
energy from one place to another.
Energy is not a material. It does not
have mass, but we can measure
amounts of energy. It cannot be
created or destroyed, but it can be
moved from place to place.
The evaporation of water from leaves is an example of
a physical change. Photosynthesis and respiration are
examples of chemical changes. All involve
energy transfer.
Modelling energy
Energy is stored in substances by the forces
of attraction between its particles and the
movement of those particles. Put another
way, it’s the sum of the potential energy and
kinetic energy of particles that make up the
substance.
Two models can be used.
Light and heating are two of the ways that
energy can be transferred from one place to
another. Light is a type of radiation (visible
radiation) that carries energy as waves.
Heating can happen when energy is
transferred by conduction, convection or
radiation.
Nowadays, however, another model is
preferred by many scientists. It uses the idea
of energy stores and energy transfers.
One says that energy comes in comes in
different forms, like heat, light and chemical
energy. When change happens energy is
transformed from one form to another.
All substances store energy.
When a change happens energy is
transferred from one store to another,
mechanically, electrically, by heating or by
radiation (e.g. light).
Science & Plants for Schools: www.saps.org.uk
Plants, Matter and Energy: p. 5
Questions
1. What are the smallest particles of water: (a) atoms, (b) molecules, (c) ions?
2. Ice melts above 0 oC.
(a) Is energy transferred (i) to the ice from its surroundings, or (ii) from the surroundings to the
ice?
(b) Explain why the transfer of energy causes ice to melt.
2. Water in leaves evaporates and cools them.
(a) Is energy transferred (i) to the water from its surroundings, or (ii) from the surroundings to the
water?
(b) Explain why the transfer of energy causes a leaf to cool.
3. Energy is transferred to plant leaves when photosynthesis happens.
(a) From which energy store does the energy come and how is it transferred?
(b) Explain how energy stored in plant food is released (Hint: Think about respiration).
Science & Plants for Schools: www.saps.org.uk
Plants, Matter and Energy: p. 6