AQA · GCSE · Biology

    Course version: 8461 · Version from Sept 2018

    Knowledge of ions is limited to nitrate ions needed for protein synthesis…

    Full specification wording

    Detection and identification of plant diseases: Knowledge of ions is limited to nitrate ions needed for protein synthesis and therefore growth, and magnesium ions needed to make chlorophyll.

    Plants absorb mineral ions from soil water, and two are specified.

    Checked against the AQA 8461 specification (opens in a new tab) on .

    • Point 6 of 6
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Plants absorb mineral ions from soil water, and two are specified. Nitrate ions supply nitrogen that is built into amino acids, which are joined into proteins; proteins include enzymes and structural components, so without nitrate ions a plant cannot synthesise protein and its growth is stunted, with older leaves often yellowing first. Magnesium ions are incorporated into chlorophyll, the green pigment that absorbs light for photosynthesis; a shortage causes chlorosis, so leaves look pale or yellow and less light energy is captured, reducing glucose production and growth. A useful method is to compare plants given complete nutrient solution with those lacking one ion, then link each deficiency symptom to its biochemical role.

    What earns the marks

    • Nitrate ions are absorbed from the soil and their nitrogen is used to make amino acids, which are assembled into proteins.
    • Because proteins include enzymes and growth materials, a shortage of nitrate ions reduces protein synthesis and therefore restricts growth.
    • Magnesium ions are needed to make chlorophyll, the pigment that absorbs light energy in photosynthesis.
    • A shortage of magnesium ions causes chlorosis, so less light is absorbed and less glucose is made, which also limits growth.
    • A valid comparison is a plant given all mineral ions against one deprived of nitrate or magnesium, with leaf colour and growth measured.
    • The specification limits required ion knowledge to nitrate ions and magnesium ions, so other named ions are not needed.

    Common mistakes and how to put them right

    • Saying magnesium is needed for protein synthesis.

      Put it right by linking magnesium to chlorophyll and nitrate to protein.

    • Saying nitrate ions are used directly as an energy source.

      Put it right by stating that nitrate supplies nitrogen for amino acids and proteins.

    • Confusing chlorosis with wilting.

      Put it right by describing chlorosis as pale or yellow leaves caused by too little chlorophyll, not loss of water support.

    Exam tips

    • Name the ion and its product in the same sentence, for example nitrate ions for protein synthesis and magnesium ions for chlorophyll.
    • When explaining poor growth, trace the chain: missing ion, missing molecule, reduced process, reduced growth.
    • Use deficiency symptoms as evidence, such as yellow leaves indicating chlorosis from insufficient magnesium.

    Try the lesson

    The start of the Detection and identification of plant diseases: Knowledge of ions is limited to nitrate ions needed for protein synthesis and therefore growth, and magnesium ions needed to make chlorophyll. lesson, made from checked teaching notes for this specification point.

    Have a go first

    A gardener notices that a plant has yellow leaves because it cannot make enough chlorophyll. Which ion is the plant most likely to be short of?

    Listen

    Plants absorb mineral ions from soil water, and two are specified. Nitrate ions supply nitrogen that is built into amino acids, which are joined into proteins; proteins include enzymes and structural components, so without nitrate ions a plant cannot synthesise protein and its growth is stunted, with older leaves often yellowing first. Magnesium ions are incorporated into chlorophyll, the green pigment that absorbs light for photosynthesis; a shortage causes chlorosis, so leaves look pale or yellow and less light energy is captured, reducing glucose production and growth. A useful method is to compare plants given complete nutrient solution with those lacking one ion, then link each deficiency symptom to its biochemical role. A strong answer earns marks for these points. Nitrate ions are absorbed from the soil and their nitrogen is used to make amino acids, which are assembled into proteins. Because proteins include enzymes and growth materials, a shortage of nitrate ions reduces protein synthesis and therefore restricts growth. Magnesium ions are needed to make chlorophyll, the pigment that absorbs light energy in photosynthesis. A shortage of magnesium ions causes chlorosis, so less light is absorbed and less glucose is made, which also limits growth. A common slip: Saying magnesium is needed for protein synthesis. Instead, linking magnesium to chlorophyll and nitrate to protein. Exam tip: Name the ion and its product in the same sentence, for example nitrate ions for protein synthesis and magnesium ions for chlorophyll.

    See it

    A top-down flowchart. On the left, a node labelled Nitrate ions from soil leads to Nitrogen for amino acids, which leads to Proteins made, which leads to Growth. On the right, a node labelled Magnesium ions from soil leads to Chlorophyll made, which leads to Light absorbed for photosynthesis, which leads to Glucose produced, which also leads to Growth. Two further branches show shortages: Nitrate ions from soil leads to Shortage: less protein synthesis, stunted growth, and Magnesium ions from soil leads to Shortage: chlorosis, pale or yellow leaves.
    Shows how nitrate ions lead to protein synthesis and growth, how magnesium ions lead to chlorophyll and photosynthesis, and the deficiency symptoms of each.

    Key words

    Say what each word means before you turn the card.

    Nitrate ions

    Try answering aloud or in your head before turning the card.

    Magnesium ions

    Try answering aloud or in your head before turning the card.

    Chlorophyll

    Try answering aloud or in your head before turning the card.

    Chlorosis

    Try answering aloud or in your head before turning the card.

    See every definition
    Nitrate ions
    Absorbed from the soil, their nitrogen is used to make amino acids, which are assembled into proteins, so a shortage reduces protein synthesis and restricts growth.
    Magnesium ions
    Needed to make chlorophyll, the pigment that absorbs light energy in photosynthesis, so a shortage causes chlorosis and less glucose is made.
    Chlorophyll
    The green pigment that absorbs light energy in photosynthesis.
    Chlorosis
    Pale or yellow leaves caused by too little chlorophyll, so less light is absorbed and less glucose is made, which also limits growth.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. On the left, a node labelled Nitrate ions from soil leads to Nitrogen for amino acids, which leads to Proteins made, which leads to Growth. On the right, a node labelled Magnesium ions from soil leads to Chlorophyll made, which leads to Light absorbed for photosynthesis, which leads to Glucose produced, which also leads to Growth. Two further branches show shortages: Nitrate ions from soil leads to Shortage: less protein synthesis, stunted growth, and Magnesium ions from soil leads to Shortage: chlorosis, pale or yellow leaves.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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