الأسبوع 15 · مراجعة الفصل الدراسي الأول: العلاقات الغذائية بين الكائنات الحية وحركة الجسيمات · 3 دروس
1
Review: plants and food webs
Discovery Education Science P5: Term 1, Unit 1, pp. 1–99
GoalReview what plants need, how leaves make food, and how energy and changes move through food chains and food webs.
New words
producer · a living thing, such as a plant, that makes its own fooddecomposer · a living thing that breaks down dead plants and animalsfood web · many food chains joined together
Explanation
Plants need water, air and light. A seed germinates with water and warmth, using food stored inside it. Roots take in water and minerals, and xylem tubes carry them up the stem. In the leaves, light, water and carbon dioxide are used to make sugar, and oxygen is let out. Phloem tubes carry the sugar to the rest of the plant. Every food chain starts with a producer that gets its energy from the Sun. Consumers get energy by eating producers or other consumers, and decomposers return nutrients from dead matter to the soil. Arrows point from the food to the eater, because that is the way energy moves, and some of it is lost as heat at each step. Chains join into food webs. When one link changes, because of drought, lost habitats or plastic pollution, the other living things in the web change too.
Worked examples
light + water + carbon dioxide→the leaf makes food→sugar + oxygen
The leaf is a little kitchen. It takes in sunlight, water from the roots and carbon dioxide from the air, and it makes sugar. The oxygen is let out into the air.
A chain on a farm: wheat is eaten by a mouse, the mouse by a snake, and the snake by an eagle. The arrows show how energy moves. The wheat is the producer. The mouse, snake and eagle are consumers.
Part
Job
roots
take in water and minerals
xylem
carries water and minerals up
leaves
make sugar and let out oxygen
phloem
carries sugar around the plant
Each plant part has a job. Use the table to check your memory.
Class activity
Draw your own food web (a grown-up helps). Choose six living things from a place you know, such as a farm or a pond near the Nile. Write each name on a card and join the cards with arrows from the food to the eater. Then remove one card and talk about what will happen to the others.
Practice
1
A bean seedling grown in a dark cupboard is tall, thin and pale. Which basic need was missing?
Light. Without light the plant cannot make its food properly.
2
In the chain algae → small fish → heron, which is the producer and which are consumers?
The algae are the producer. The small fish and the heron are consumers.
3
Look at the web. If the small fish disappear, which two animals lose a food source?
The heron and the snake, because the arrows from the small fish go to both of them.
4
Why do the arrows in a food chain point from the plant to the animal that eats it?
