Download Plants: How do plants grow?

Plants: How do plants grow?
Objectives

Observe and describe how seeds and bulbs grow into mature plants.
Plenary
Display a photograph of a young person and an old person. How do the pupils know which
person is older? Next, show a photograph of an old tree and a young tree. How do the pupils
know which tree is older? They may identify that the old tree is thicker, more gnarled and
less green.
How do plants begin?
Humans begin as tiny clumps of living matter and then grow. In a similar way, most plants
begin as seeds (which are produced by fully-grown plants) and then grow. Show a time lapse
video of the growth of a plant from a seed. Explain that when the plant sprouts from the seed,
this is germination.
Clarify that while many plants start as seeds, some begin as bulbs, tubers or cuttings.
It seems incomprehensible that something as large as a tree begins as a seed. Explain that
humans need food to grow and plants need food to grow too. Plants make their own food
using air, water and sunlight as well as some nutrients from the soil.
Pupils must note:
When a seed germinates, a plant begins to grow.
Measuring the growth of a plant
EXPERIMENT: This experiment takes place over four weeks. It is best to take routine
measurements e.g.: at morning registration every weekday. All pupils should water their
plants regularly.
Divide the class into halves. One half will grow runner bean plants and the other half will
grow sunflower plants. They should fill labelled, transparent pots (so roots may be observed)
with some compost and plant their seeds just below the surface. Explain that the seeds
contain some food so the plant can germinate but it still needs to be watered.
They should check the progress of their plant over the course of four weeks, measuring its
size in cm using a ruler (beginning with 0 cm before it germinates).
If possible, take a digital photograph each day of each pupil’s plant so that at the end of the
experiment, these can be put together to make a animation showing the plant’s growth.
© Education Umbrella 2015
Plants in the local environment
Take the pupils into the school grounds. Pupils search their surroundings for young plants,
such as weeds in a border and old plants, such as wide-trunked trees.
Some fast-growing plants can be studied over short time period e.g.: ivy growing on a wall.
Depending on the time of the year, they should look for other types of plant growth, such as
new leaves growing in spring or fruit growing in autumn. Can they identify young branches
growing on trees? Take a cutting from one of these branches to demonstrate that they are
damp and green on the inside. Explain that this is why people use the term ‘green’ to refer to
someone young or immature.
Pupils may record what they observe with notes or labelled sketches.
Possible extra-curricular questions
How do plants make their own food?
This is complicated process called photosynthesis. The plant takes in water from its roots and
air (specifically carbon dioxide) and sunlight from its leaves. Using these ingredients, the
plant produces oxygen and glucose, which is a type of sugar. The glucose is then stored in the
plant and used for growth.
How are seeds made?
Pollen from a flower must be transferred to another flower (pollination), often with the help
of insects. The pollen combines with the egg inside the flower and this causes a seed to form.
How does a seed know when to germinate?
A seed may look dead, but they are capable of sensing their surroundings. When it senses that
it is in damp soil at the right temperature, special chemicals (enzymes) cause it to activate, so
it uses its food store to begin growth.
How old are plants?
Some plants only live for one year while other plants can live for centuries. You can find out
how old a tree is by looking at the size of its trunk – an older tree has a thicker trunk. The
oldest tree in the world is a 5000 year old pine tree.
© Education Umbrella 2015