In this deck, you will learn how plants get sick and how they defend themselves. We will explore the common signs of plant disease, including those caused by a lack of nutrients, and then look at the clever physical, chemical, and mechanical defences plants have evolved to protect themselves from pests and pathogens.

Just like animals, plants can suffer from diseases. These are often caused by microorganisms called pathogens, such as viruses, bacteria, and fungi. Pests like insects can also damage plants. However, sometimes a plant looks unhealthy not because of a pathogen, but because it's missing essential nutrients from the soil.

One of the most common signs of a mineral deficiency is when a plant's leaves turn yellow. This condition is known as chlorosis. It happens because the plant cannot produce enough chlorophyll, the green pigment essential for photosynthesis.

The mineral magnesium is a key component of the chlorophyll molecule. Therefore, if a plant cannot get enough magnesium ions from the soil, it will suffer from chlorosis, and its growth will be stunted.