A year in the life of a sugar factory

The leaves of plants are everywhere in Nowhere Wood, helping to keep the wood alive. Leaves are organs: collections of living tissues and cells, having adventures in time and space. This is the story of a year in the life of an oak leaf.

Leaves are factories for making sugar from sunlight, water and carbon dioxide from the air. No human factory can do this, which is why we, and all other organisms, are so dependent on plants. Leaves are the producers of food.

In is late November and the cells that will divide to make the new leaf are protected safely inside the scales of the bud. Early in March, when the days warm and get longer, stem cells within the bud start to divide many times, producing all of the cells of the new leaf. To start with, the cells are very small and all look the same.

Soon, the cells take up water and get much larger. They escape the protection of the bud and the new leaf emerges. The new cells no longer look the same: they are on different journeys of development, becoming all of the different cells and tissues that make up the leaf.

 

The leaf is a factory for making sugar. Like any factory, it has a source of energy and transport systems to get the raw materials into the factory.  It also moves the manufactured sugar out to the places in the plant where it is needed. The heart of the factory is the production line where sugar is made. These are called chloroplasts and the leaf has millions of them, all making sugar whenever the sun shines. The Spring and Summer are sugar making seasons.

Gradually, in the autumn, when the days get cooler and shorter, the sugar factories are shut down and abandoned. The chloroplasts lie in ruins as everything useful is recycled back into the branches of the tree. All that remain are the frameworks of cell walls, turning brown as they dry in the autumn air.

 

Finally, the oak tree makes a special layer of cells that separates the old leaf from the stem, and the leaf is ready to fall when the wind blows strongly. The fallen leaves are not wasted, becoming energy stores for the organisms that feed on them. Next year’s buds are forming and wait for spring and the production of new leaves.

If leaves are factories form making sugar, then trees are factories for making leaves.

Everything has its own season in Nowhere Wood.

  1. Think about how the leaf is a factory for making sugar. Where does its energy store come from? How do the raw materials get to the production line?
  2. The production of leaves is sustainable in Nowhere Wood. What do you think this sentence means?

Subterranean superheroes

All change!

When you next look into a mirror ask yourself if you are the same person as you were yesterday. Well, of course you are.

Even people who last met you ten years ago can still recognise you and call you by your name. Although they might add, “My, how you have grown!”

And yet, if we could see under your skin, we would find that you are not the same. One of the biggest mysteries in biology is how we can change all of the time, whilst still staying the same.

Your skin cells live for about two weeks, so every month they are completely replaced. Red blood cells live for about 100 days and about two million are made in your body in every second.

Some of the chemicals in your cells exist for only minutes or seconds.

There is an energy store called ATP, which is needed for muscle contraction. ATP is made and broken down within 15 seconds.  Cells need glucose to make ATP and this explains why muscle cells need a continuous supply of glucose to stay alive. This comes from our food.

Even large organs, like the liver, are replaced regularly. You grow a new liver every year. The cells in the alveoli of your lungs are renewed every eight days. Even the bone cells in our skeleton are replaced every three months. Your entire skeleton is remade every ten years.

 

So, when your friend sees you after ten years and calls out your name, there is not a single part of your body that was the same as when you last met. You have been completely remade and remodelled. And the same is true of your friend.

 

So, how can this be? New cells are made when one cell divides to make two cells. The information in the genome is copied before cells divide, so the new cells always receive the same information as the old cells.

The new cells use this information to grow bigger and to develop. So, you stay the same because of how your new cells use the information in their genomes.

Living organisms are alive because they actively remake themselves. No man-made machine can do this. Which is, perhaps, just as well.

  1. In what ways have you changed in the last ten years?
  2. In what ways have you stayed the same?
  3. Why do need to eat food everyday?

A year in the life of a sugar factory