Growing crop plants is basically a section about maximising rates of photosynthesis.  If a plant is photosynthesising at the fastest rate, it will be growing fast thus increasing the rate of food production.

One of the simplest ways of maximising photosynthetic rates is to grow crops in a greenhouse (laughably called a glasshouse in the syllabus to avoid confusing you) or a polytunnel.  Greenhouses are made of glass; polytunnels are much cheaper to build as they are made of transparent plastic.

What are the advantages of growing crops in a greenhouse or polytunnel?

Temperatures are increased due to the insulating effects of the glass or plastic.

Watering can be controlled.  Artificial lighting can be used to optimise the light intensity for a maximum photosynthetic rate.

Carbon dioxide concentrations in the air can be artificially increased if the doors to the greenhouse are kept closed.  Often carbon dioxide is released into the greenhouse – this is good for the environment as it reduces emission of greenhouse gases and good for the farmer as crop yields increase.

These points above link into the work you will have done on rates of photosynthesis.  (For more information on this, please refer to my posts on section 2.19)

https://pmgbiology.com/2014/12/03/factors-affecting-rates-of-photosynthesis-a-understanding-for-igcse-biology-part-1/

https://pmgbiology.com/2014/12/03/factors-affecting-rates-of-photosynthesis-part-2-a-understanding-for-igcse-biology/

Fertilisers can be added to the soil (see posts on section 2.21 and 5.3).

Pests can easily be kept out or removed (see posts on section 5.4)