Ins and Outs of Water
Plants need water. It serves several purposes:

It provides structural strength in certain tissues
by keeping their cells rigid. This is called
turgor.

It is a solvent. Solutions of nutrients and
organic compounds in water are transported
throughout the plant.

It is a raw material for various chemical
reactions that happen in plants, such as
photosynthesis.

Its loss by transpiration cools plant leaves,
protecting them from wide temperature
fluctuations.
water is lost through
plant leaves during
transpiration
water is transported
through the plants
stem and leaf veins
water gets into a
plant through its roots
This group of sheets is about the role that water plays in plants:

Plant roots

Plant cells and water

About water

Moving water through plants

Plant leaves and water

Water and plant structure
Studying the ins and outs of water in plants can bring together important scientific ideas in
biology, chemistry and physics. Relevant examples are summarised by statements taken from
the National curriculum for science in England at key stage 3:
In biology pupils should be taught about Cells and organisation, Nutrition and digestion, Gas
exchange systems and Cell respiration.

the role of diffusion in the movement of materials in and between cells

plants making carbohydrates in their leaves by photosynthesis and gaining mineral nutrients
and water from the soil via their roots

the role of leaf stomata in gas exchange in plants

aerobic and anaerobic respiration in living organisms, including the breakdown of organic
molecules to enable all the other chemical processes necessary for life

a word summary for aerobic respiration
In chemistry pupils should be taught about Particulate nature of matter, Pure and impure
substances and Energetics

the properties of the different states of matter (solid, liquid and gas) in terms of the particle
model, including gas pressure

changes of state in terms of the particle model

the concept of a pure substance

mixtures, including dissolving

diffusion in terms of the particle model
Science & Plants for Schools: www.saps.org.uk
Ins and Outs of Water: p. 1

energy changes on changes of state (qualitative)
In physics pupils should be taught about Forces, Physical changes, Particle model and Energy in
matter

forces as pushes or pulls, arising from the interaction between two objects

conservation of material and of mass, and reversibility, in melting, freezing, evaporation,
sublimation, condensation, dissolving

similarities and differences, including density differences, between solids, liquids and gases

Brownian motion in gases

diffusion in liquids and gases driven by differences in concentration

the differences in arrangements, in motion and in closeness of particles explaining changes
of state, shape and density, the anomaly of ice-water transition

changes with temperature in motion and spacing of particles
The activities also provide an opportunity to tackle some common misconceptions, including:
Particles are the same as visible grains as in rocks, for example.
Particles expand on heating.
When ice is heated its particles melt
The space between particles is full of air
Particles in a liquid are smaller than in a solid
Sugar disappears when it dissolves
Living things are made of cells, which are as small as atoms
Respiration is the same as breathing.
Plants don’t respire.
Plants only respire at night.
Plants get their food from the soil.
Plants breathe in oxygen at night and carbon dioxide during the day.
Science & Plants for Schools: www.saps.org.uk
Ins and Outs of Water: p. 2