GoalExplain the kinds of leaves (simple and compound), what leaves do, what photosynthesis and chlorophyll are, and why leaves change colour in autumn.
New words
photosynthesis · fotosintezchlorophyll · xlorofillstoma (tiny pore in a leaf) · stomacompound leaf · murakkab barg
Explanation
Leaves differ in shape, colour and size. A leaf with one blade is simple (plane tree, poplar); if several small leaflets sit on one stalk it is a compound leaf (horse chestnut, acacia). The leaf is vital to the plant: it makes food, breathes and gives off extra moisture. Through tiny pores called stomata, carbon dioxide enters and oxygen and water vapour leave. In photosynthesis, light energy turns carbon dioxide and water into sugar (glucose) and oxygen. The green substance chlorophyll does this work. In autumn the days get shorter and chlorophyll breaks down, so other pigments show: carotene makes leaves orange, xanthophyll yellow and anthocyanin red.
The orange of carrots and apricots also comes from carotene, so some autumn leaves look similar.
Class activity
“Leaf album”: collect five fallen leaves (do not pick from living trees!), sort them into simple or compound and glue them in your notebook. Write each colour next to it.
Practice
1
What is the difference between a simple and a compound leaf? Give an example.
A simple leaf has one blade, a compound leaf has several leaflets. For example: plane tree is simple, acacia is compound.
2
What is produced by photosynthesis?
Sugar (glucose) and oxygen.
3
What are stomata and where are they?
Tiny pores in the leaf; gases pass in and out through them.
4
Why do leaves turn yellow in autumn?
Chlorophyll disappears and the xanthophyll pigment shows.