Learning Focus: To understand how plants grow and what they need for growth
Understand how the climatic conditions around the world affect which plants grow and how?
Time and time again, I’ve planned work with plants but then forgotten about sowing seeds or have done it too late for the plants to be of any use so now’s a good time for you to avoid making the mistake I usually make.
I find that sunflower plants are among the best to work with for speed of growth whilst broad beans or runner beans are great for seeing what happens when a seed germinates.
I love slipping in a little bit of work on genetics, mostly because it’s fun – and that’s what science should be all about, but it also gives an opportunity for hypothesising and then testing the hypothesis. It may be a KS3 or even KS4 topic but there’s no harm in using the basics of it in KS2.
Many schools are lucky enough to have a school greenhouse but even if you don’t, a warm windowsill somewhere will suffice. One school I worked at bought a polytunnel for the pupils to work in and funded it by growing and selling tomato plants to the parents – a great way of teaching about money too and involving a bit of maths!
A bit of forward planning is required for these experiments… Decide what kinds of experiment you’re going to attempt and check how fast the plants will grow.
Germination
Watching germination and getting a basic understanding of it will be simple to organise. Stuff jam jars with cotton wool or pieces of scrunched up kitchen roll and put two or three bean seeds down the side so they’re visible from the outside then just add water!
On the day you plant them, give the pupils a dry seed and ask them to carefully split it apart, drawing and labelling what they see. At this point they don’t need to use the scientific name; that can come later. There’s a good chance that at least one of the seeds won’t germinate but it will swell with the addition of water and by taking the seed apart, they’ll see the parts more clearly and be able to compare them to what they saw in the dry seed.
Bean seeds are expensive and are best used for experiments where visualisation is needed but if you’re also looking at ideal conditions for germination and growth, choose cress seeds.
Put some in the dark, some in the light, some warm, some dry, wet, etc. and see what happens. To do it properly you’ll need a combination of experiments so record keeping will be important.
Plants and Climates
To make the learning more relevant, compare the conditions to those around the world, e.g. dry and warm = Africa, dark and cold = UK in winter, warm and wet = Amazon. This can then lead on to finding out how plants grow in those locations, which ones grow there and why they survive.
An extension to the experiment can include trying to grow a selection of seeds in conditions similar to one or more of the locations. Germinate cress, a succulent plant such as mesembryanthemum and sunflowers in hot and wet conditions like that it the African rainy season, then don’t water it. Which survives best? Try the same in conditions similar to those experienced elsewhere.
Beyond the experiment, you can find out which plants are grown in those conditions and talk about why they survive. How does this help the food situation in a country?
Growing Conditions
Following the germination experiment, you can use the same conditions to find out the best growing conditions for the plants or even test different plant foods against just plain water. You can also test different growing mediums.
Extending the learning from these you can discuss what makes one better than another. You’ll find that doing all these experiments as part of a series is useful for many of the observations will be relevant to each.
Photosynthesis
Photosynthesis is a good topic for experiments. I like using big leafed plants – again sunflowers work great, and some masking tape.
Get the children to stick the tape over a leaf, perhaps spelling their name if it’s short enough and then leave the plant for a week before carefully peeling off the tape. They’ll get personalised plants!
Without light, that part of the leaf stops producing chlorophyll, the green pigment in leaves and the xanthophyll, usually disguised by the chlorophyll, shows through. As chlorophyll is essential for the growth of the plant, loss of too much of it is fatal for the plant.
Plants and Oxygen
Most pupils know that without plants, the world would be overcome with carbon dioxide and most life would die. How can we prove that plants produce the oxygen that life needs?
This experiment is great for two reasons. First it shows that plants exhale oxygen as a by-product of photosynthesis and secondly, it shows transpiration, or water loss from the leaves.
The first experiment definitely requires a risk assessment and is best done outdoors where possible. Choose a sunny day and place a glass jar or goldfish bowl over a large leafed plant. Leave it for a day or two and then carefully lift it, trying to open it to the air as little as possible. Now, using an adult assistant, light and extinguish a taper so it is still glowing and insert it into the opening – you should find that the taper relights. It’s the oxygen that does this! You could also find that there is a lot of condensation on the inside of the glass. Whilst some of this is caused by evaporation of water from the soil, more of it comes from transpiration from the leaves as plants give off water vapour from their stoma, or little holes in the leaves.
Growing Plants in the Dark
The hypothesis is that plants always grow towards the light but what would they do in a completely dark environment?
Use a fast growing plant and stand it on something inside a light-proof box so that it is positioned centrally. Close the box and seal the joins with black duct tape to ensure no light enters. Leave the box for a week and open it to see what happens? In the meantime ask your pupils to draw a picture of what they think it will look like when the box is opened. Open the box and see whose drawing is the closest to what the plant looks like.
Genetics
Read the pupils the story of Gregor Mendel and his experiments with plants.
The children can use sweet pea plants to mimic his experiments. You’ll need to grow them very early in the term so you can gather the seeds and grow a second batch from them later in the summer. It’s possible but a tight timescale – you don’t want to have to wait a year to complete the experiment!
Grow a batch of white sweet peas (don’t buy hybrid seeds – they won’t work!) and a batch of purple ones. When they are in bud, you’ll need to split them all up to avoid accidental cross-pollination. Give the pupils two white flowering plants and ask them to transfer pollen from a flower on one plant to the other. Then do the same with a pair of purple flowering plants and again with two sets of one purple and one white. On one use a purple flower to pollinate the white plant and on the other use a white flower to pollinate a purple plant.
You’ll need to keep the groups of plants separate until the seeds form then, when they are ripe, sow them, keeping them carefully labelled, and see what colour flowers you get. Again, it’s a great experiment for the children to practise hypothesising with. The theory is that you’ll get marbled flowers but then nature’s a funny thing!
