Carbohydrate uses and mineral ions
Diperkenalkan| English | Makna |
|---|---|
| glucose/ˈɡluːkəʊs/ | A simple sugar with molecular formula C6H12O6, used by cells as a source of energy. |
| starch/stɑːtʃ/ | A storage polysaccharide in plants, made from glucose units. |
| cellulose/ˈseljuːləʊs/ | A structural polysaccharide made of glucose units, forming a major component of plant cell walls. |
| nectar/ˈnektə/ | The sugary liquid produced by flowers to attract pollinators. |
| sucrose/ˈsuːkrəʊs/ | A disaccharide sugar made from glucose and fructose. |
| nitrate ions/ˈnaɪtreɪt ˈaɪɒnz/ | Ions containing one nitrogen atom and three oxygen atoms with an overall charge of minus one; plants use them as a nitrogen source. |
| magnesium ions/mæɡˈniːzɪəm ˈaɪɒnz/ | magnesium ions |
Can extra sugar replace a missing mineral ion?
- A plant may have light, carbon dioxide and water yet grow poorly without essential mineral ions. Making carbohydrates does not supply every material needed for growth.
- Follow two different questions: what happens to the carbohydrates made, and which minerals supply materials that carbohydrates alone cannot provide?
Why can a sugar supply alone fail to support normal plant growth?
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Carbohydrates do not supply all the materials needed for growth.
Store, build and release energy
- Glucose 葡萄糖 can be used in respiration to release energy for cell processes. It can also be converted into starch 淀粉, an insoluble carbohydrate used as an energy store.
- Cellulose 纤维素 is used to build cell walls. Storage starch and structural cellulose have different roles, even though both can be made from glucose.
This diagram shows four uses. Nectar production is another use of carbohydrates, described below.
Transport sugars and attract pollinators
- A plant converts carbohydrate into sucrose 蔗糖 for transport in phloem. Sugars made in leaves can reach growing shoots, roots, fruits and storage organs.
- Sugars can also be secreted in nectar 花蜜, attracting insects that may transfer pollen between flowers. Nectar attracts pollinators; it does not itself become a seed or carry out fertilisation.
Follow a carbohydrate to its use
Distinguish respiration, storage, cell-wall structure and transport.
Match each carbohydrate form to its main role here.
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The same original carbohydrate can be converted into forms with different roles.
How can making nectar help a flowering plant reproduce?
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Nectar attracts potential pollinators; pollen transfer and fertilisation are separate processes.
Distinguish nitrate from magnesium
- Nitrate ions 硝酸根离子 supply nitrogen for making amino acids, which are used to make proteins. Without enough nitrate, protein production and growth are restricted.
- Magnesium ions 镁离子 are needed to make chlorophyll. A shortage can cause reduced chlorophyll and yellowing leaves, reducing the plant's capacity to absorb light for photosynthesis.
Two otherwise matched plants receive mineral solutions. Plant A lacks nitrate; plant B lacks magnesium. Poor growth in A is consistent with restricted amino-acid and protein production. Yellowing in B is consistent with reduced chlorophyll. The diagnosis depends on the controlled treatment, not colour alone.
Nitrate ions supply nitrogen for making amino ______, which are used to make proteins.
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Amino acids are used to build proteins; nitrate provides their nitrogen.
A controlled treatment removes magnesium ions. Which direct material role is affected?
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Magnesium is needed for chlorophyll, which absorbs light for photosynthesis.
Nitrate ions are an energy source that can replace glucose in respiration.
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Nitrate supplies nitrogen for amino acids; it does not replace carbohydrate as an energy source.
Use a complete solution as the control
- Compare similar seedlings in a complete mineral solution and a solution missing just one ion. Keep light, temperature, water, solution volume and growth period comparable; repeat with several plants.
- Record changes such as growth and leaf colour over time. Symptoms can have other causes in an uncontrolled garden, so yellow leaves alone do not prove a magnesium deficiency.
Mineral ions are not an energy source, and nitrate is not a substitute for carbon dioxide. Carbon dioxide supplies the carbon used to make carbohydrates; nitrate provides nitrogen for amino acids, and magnesium supports chlorophyll production.
Plan a comparison that tests the effect of nitrate absence on seedling growth. Include a control and at least two controlled conditions.
Use similar seedlings in a complete mineral solution and an otherwise matched solution lacking nitrate. Keep light, temperature, solution volume, water and the growth period comparable. Use several plants in each group and record changes in growth over time.
A garden plant has yellow leaves. What is the most careful conclusion?
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A controlled missing-ion treatment gives stronger evidence than a symptom with several possible causes.
Trace materials to a growing root
- A green shoot supplies a growing root with sucrose through phloem. Root cells take up nitrate and use energy released by respiration for cell processes.
- Explain why sugar supply alone cannot replace nitrate. Then distinguish using carbohydrate for respiration from using it to build a cell wall.
A shoot supplies sucrose to a growing root through phloem. Explain why that sugar cannot replace nitrate, and distinguish using carbohydrate for respiration from using it to build a cell wall.
Sucrose provides carbohydrate, but nitrate supplies nitrogen for amino acids and proteins needed for growth. Respiration releases energy from carbohydrate for cell processes; making cellulose uses carbohydrate as structural material for a cell wall. These roles require different materials and processes.
Give each material its role
- Carbohydrates can be used in respiration, stored as starch, built into cellulose, transported as sucrose or supplied in nectar.
- Nitrate supports amino-acid and protein production; magnesium is needed for chlorophyll.
- Compare a single missing-ion treatment with a complete mineral solution before attributing poor growth or yellowing to that ion.
Which pair is correctly matched?
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Keep the two mineral roles separate: nitrate for nitrogen in amino acids, magnesium for chlorophyll.