Living Things Around Us
Primary 5 · Science and Elementary Technology
Living Things Around Us
Lesson 1 of 3
13 min
Let's begin
Uwase forgot to water the bean plant growing in a tin by her window. Three days later its leaves were hanging down like tired ears.
She poured in one cup of water in the morning. By the afternoon the leaves were standing up straight again. But think about it: the water went into the soil at the bottom. The leaves are at the top. A plant has no legs and no hands, so how did the water get up there?
A plant is a machine with four main parts, and each part has its own job. Today you will learn all four.
Do this before you read on. Go outside and pull a small weed out of soft soil. Look at the end that was buried. You will see pale threads with soil clinging to them. Those are the roots.
Two things you just noticed tell you exactly what roots are for.
Mineral salts are tiny amounts of substances, such as nitrogen, dissolved in the water in the soil. A plant needs them to grow strong and green — the same way you need beans and vegetables, not just water.
Pull up a bean plant. You find one thick root going straight down, with smaller hairs growing off it. That is a tap root. A mango tree has one. So does a carrot — in fact a carrot is a tap root, and it is fat because the plant stores food inside it.
Now pull up a maize plant, or a tuft of grass. There is no single thick root. Instead there are many thin roots of about the same size, spreading out in all directions. That is a fibrous root system. It is why grass holds a hillside together so well: thousands of thin roots gripping the soil like fingers.
Stand a stick of sugar cane beside a maize plant beside a tall avocado tree. They look nothing alike, yet each one has a stem. (On a big tree we call the stem the trunk.) The stem has two jobs.
See it for yourself. Put a white flower, or a stick of celery, into a cup of water coloured with red ink. Leave it overnight. In the morning the red colour has climbed to the top. You are looking straight at the water tubes doing their job.
Here is the biggest surprise in this lesson. A plant does not find its food. It makes its food. And it makes it inside the leaves.
Worked example
follow one drop of water. Uwase pours her cup of water into the tin. Let us follow a single drop.
Making food in the leaves like this is called photosynthesis. The word explains itself once you break it open: photo means light, synthesis means putting things together. Putting things together using light.
Now the shape of a leaf makes sense. It is flat and wide so it can catch as much sunlight as possible. It is green because it is packed with chlorophyll. And this is why a plant kept in a dark room slowly dies even if you water it every single day: you can give it water, but you cannot give it sunlight, and with no sunlight the kitchen is closed.
Watch a bean plant for a few weeks. First, small pale flowers open. Bees come and visit them. Then the flowers dry up and drop off — and exactly where each flower used to be, a small green pod starts to swell. Open a pod and what is inside? Beans. And a bean is a seed.
So the flower's job is to make seeds. When a bee (or the wind) carries pollen from one flower to another, the flower is pollinated and can begin making its seeds. The part that grows around the seeds becomes the fruit — a bean pod, a tomato, an avocado, a maize cob.
Every fruit you have ever eaten began life as a flower. And every seed inside it can become a whole new plant. That is how one bean plant turns into a whole field.
Tip
Touch a real plant from the bottom to the top and say this out loud:
Roots drink. Stem carries. Leaves cook. Flower makes seeds.
Four parts, four jobs, bottom to top. If you can say that line, you already have the whole lesson in your head.
Try each one first, then tap Show answer to check.
Habimana pulls up a maize plant and a bean plant. One has many thin roots of the same size; the other has a single thick root going down. Which is which?
Answer: The maize has the many thin roots — a fibrous root system. The bean has the one thick tap root.
A plant is left on a shelf in a dark store room and watered every single day. Three weeks later it is pale and weak. Why? It had plenty of water!
Answer: Water is not food. Leaves need sunlight to make food. In the dark there is no light for photosynthesis, so the plant slowly starves.
Which gas does a leaf take IN from the air, and which gas does it give OUT?
Answer: It takes in carbon dioxide and gives out oxygen. (These are easy to swap by mistake. Remember that the plant gives out the gas you need to breathe.)
Mutesi says, “A tomato is not a fruit, it is a vegetable.” Using this lesson, what can you tell her?
Answer: A tomato grows from a flower and has seeds inside it, so to a scientist it is a fruit. We may cook it like a vegetable, but the plant made it as a fruit to carry its seeds.
Someone cuts a ring of bark all the way around a young tree, cutting through the tubes in the stem. Why is that tree now in serious trouble?
Answer: The stem is the plant's road. Cut the tubes and water can no longer climb up to the leaves, and the food made in the leaves can no longer travel down to the roots. A plant with its road cut cannot survive.
What you learned today
Quick check
Match each part of a plant to its job.
Tap one on the left, then its partner on the right.
