Making food, or taking it
There are only two answers to the question of how an organism gets its food, and you met both of them in grade 10.
Autotrophic — making it
Green plants produce the food they need inside themselves. Nothing has to be brought in ready-made.
Heterotrophic — taking it
The cow and the heron depend on other organisms for their food. They cannot make any of it themselves.
Everything else follows from the first column
Living things secure their own survival by depending on that food, either directly — the cow eating grass — or indirectly, through however many organisms lie in between. The heron is several steps removed from any plant, and it is still living on what a plant made.
Autotrophic does not mean needing nothing
A green plant still takes in water and carbon dioxide, and it still needs light. What makes it autotrophic is that none of those is food — they are raw materials and an energy source, and the plant assembles the food itself. Grade 10 made the same point the other way round: a plant still has to respire to get the energy out of the food it made.
One process feeds everything alive
Trace any meal back far enough and it ends at a green plant with sunlight falling on it. That is not a figure of speech — it is the reason this chapter exists, and it is why a single process happening inside a leaf is worth ten pages of a textbook.