Form 5 · Paper 2 essay guide

Nutrition in Plants, Paper 2 essay guide

How Nutrition in Plants appears in Paper 2 essays: themes, a planning grid, a model answer structure and the keyword list.

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Essay themes this chapter supports

Comparing the uptake of water and mineral ions by roots: Describe how water enters root hair cells by osmosis, moving down a water potential gradient → Describe how mineral ions are absorbed by active transport, often against a concentration gradient → Explain why active transport requires energy from respiration while osmosis does not → Link root hair cell structure (large surface area, thin wall, large numbers) to efficient absorption of both
How deficiency symptoms reveal the role of a mineral nutrient: Explain the roles of nitrogen, phosphorus, potassium and magnesium in the plant → Describe the deficiency symptom linked to each nutrient and relate it back to the nutrient's role → Compare nitrogen deficiency and magnesium deficiency, and iron deficiency and magnesium deficiency, in terms of which leaves are affected first → Explain how a water-culture experiment with a missing-ion set-up and a control was used to establish each role
Three unusual strategies for obtaining nutrients: parasitic, epiphytic and insectivorous plants: Define and give one named example of a parasitic, an epiphytic and an insectivorous plant → Explain exactly how and why each obtains extra nutrients in its own way → Distinguish which of the three harms its host and which does not → Explain why an insectivorous plant still needs to photosynthesise despite trapping insects
Mutualism in plant nutrition: root nodules and mycorrhizae: Describe the Rhizobium-legume relationship inside a root nodule and what each partner provides → Describe the mycorrhizal association between plant roots and soil fungi and what each partner provides → Explain why both relationships are described as mutualistic rather than parasitic → Discuss the agricultural relevance of growing legumes in crop rotation to enrich soil nitrogen

How to structure your essay

Open with one or two sentences that define the topic and set the scope.
Devote one paragraph to each key concept, in a logical order.
Use precise biological terms and, where relevant, a labelled diagram.
Give an example or state where the process happens in the body or plant.
Close by linking the ideas back to the question.

Planning grid

Question	Answer
Introduction	State that plants obtain nutrients through root absorption, photosynthesis, and in some cases unusual partnerships or strategies
Point 1	Describe macronutrient roles and deficiency symptoms (nitrogen, phosphorus, potassium, magnesium)
Point 2	Compare water uptake (osmosis) and mineral ion uptake (active transport) and link to root hair structure
Point 3	Describe the water-culture method for establishing a nutrient's role, including the control set-up
Point 4	Describe diversity in nutrition: parasitic, epiphytic, insectivorous plants, and mutualism (Rhizobium, mycorrhiza)
Conclusion	Summarise how each strategy or mechanism ensures the plant obtains the specific nutrients it needs

Key terms to include

macronutrient
micronutrient
active transport
root hair cell
interveinal chlorosis
hydroponics
Rhizobium
root nodule
mycorrhiza
parasitic plant
epiphyte
insectivorous plant

A model essay outline

Main inorganic nutrients, Macronutrients (e.g. nitrogen, phosphorus, potassium) are needed in large amounts; micronutrients are needed in small amounts.
Role of nutrients, Nitrogen is needed for proteins, magnesium for chlorophyll; a lack of a nutrient causes a specific deficiency symptom.
Uptake of water, Water enters root hair cells by osmosis, moving down the water potential gradient.
Uptake of mineral salts, Mineral ions are absorbed by active transport, which needs energy because the soil is often more dilute than the cell.
Root hair adaptations, Root hair cells are long and thin with a large surface area to speed up absorption.

Frequently asked questions

How do roots absorb water and mineral salts?

Water is absorbed into root hair cells by osmosis, moving from the more dilute soil solution into the more concentrated cell sap. Mineral salts are absorbed as ions by active transport, which uses energy from respiration because the ions often move from the more dilute soil into the more concentrated cell against the concentration gradient.

Why does a plant need mineral nutrients if it makes food by photosynthesis?

Photosynthesis only makes carbohydrates from carbon dioxide and water. To make other molecules the plant needs mineral ions from the soil, for example nitrogen to make proteins and magnesium to make chlorophyll. A shortage of any of these causes a specific deficiency symptom such as yellow leaves.

Why are root hair cells good at absorbing water?

A root hair cell has a long, thin extension that greatly increases the surface area in contact with the soil, so more water and ions can be absorbed at once. Its thin wall gives a short distance for water to enter, and there are very many root hairs, which together make absorption efficient.