Making food or finding it: nutrition and photosynthesis
Science Prep 1 Term 1, Unit 3: pp. 64–71
GoalList the characteristics of living things and explain how plants make food by photosynthesis.
New words
autotroph · a living thing that makes its own food, such as a plantheterotroph · a living thing that gets food from other living thingsphotosynthesis · making glucose from carbon dioxide and water using light energychlorophyll · the green substance in chloroplasts that takes in light energy
Explanation
Living things do nine jobs: they feed, respire, transport substances, excrete wastes, move, grow, reproduce, sense and respond, and adapt to where they live. Feeding comes in two kinds. Autotrophs, also called producers, make their own food by photosynthesis. In a plant this happens in the chloroplasts, where chlorophyll takes in light energy. Heterotrophs, also called consumers, depend directly or indirectly on producers: a rabbit eats plants, and a fox eats rabbits. Bacteria can be either kind. In photosynthesis, carbon dioxide and water, with light energy, give glucose and oxygen. The light energy is stored in the glucose as chemical energy.
Living or not? A rabbit does all nine jobs. A seed is alive, although it waits and shows few signs until it can grow. A ball is not alive. A flame seems to grow and move, but it has no cells and does not reproduce, so it is not alive.
A food chain starts with a producer. Wheat makes its own food, a mouse eats the wheat, and a fox eats the mouse. The mouse and the fox are heterotrophs that depend, directly or indirectly, on the wheat.
Bacteria can be either kind. Some bacteria use light to make their own food, and many others get food from dead or living things. So we cannot say that all bacteria are autotrophs or all are heterotrophs.
Class activity
Living or not? Plan a table with four things: a ball, a rabbit, a seed and a flame. In the columns write the nine life jobs and tick the ones each thing does. Then draw photosynthesis as boxes and arrows: carbon dioxide and water go in, with light, and glucose and oxygen come out.
Practice
1
Name four things that all living organisms do.
For example feed, respire, grow and reproduce.
2
Where does photosynthesis happen in a plant cell, and what takes in the light?
In the chloroplasts; chlorophyll takes in the light energy.
3
What goes into photosynthesis and what comes out?
In: carbon dioxide and water, with light. Out: glucose and oxygen.
4
Is a rabbit an autotroph or a heterotroph? Explain.
A heterotroph: it cannot make its own food and eats plants.
