The Importance of Water and Minerals in Plants

Plant Structure and Function

Why do plants need water?

Plants need water for photosynthesis, support, transport of substances and cooling.

Why is water needed for photosynthesis?

Water combines with carbon dioxide to produce glucose using energy from light.

How does water provide support in non-woody plants?

Water enters cells by osmosis and fills the vacuoles, producing pressure that pushes the cytoplasm against the cell walls and makes the cells turgid.

What does turgid mean?

A plant cell that is swollen and firm because water has entered by osmosis.

Why is turgor pressure important in plants?

It provides support and helps non-woody plants remain upright.

What happens to a plant if its cells lose too much water?

The cells lose turgor and become flaccid, causing the plant to wilt.

What does flaccid mean?

A plant cell that has lost water and is no longer firm or turgid.

How is water involved in transport in plants?

Water carries dissolved mineral ions through the xylem and acts as a solvent for substances transported around the plant.

How are mineral ions transported from the roots?

They dissolve in water and are carried upwards through the xylem in the transpiration stream.

How is water involved in phloem transport?

Sugars are dissolved in water and transported through the phloem by translocation.

How does water help cool a plant?

Water evaporates from the leaves during transpiration, removing heat and cooling the plant.

Why do plants need mineral ions?

They need mineral ions to make important biological molecules required for healthy growth and metabolism.

Where do plants obtain mineral ions?

They absorb them from the soil through their roots.

Which three mineral ions are particularly important for plants?

Nitrate ions, calcium ions and magnesium ions.

Why do plants need nitrate ions?

Nitrate ions are needed to make amino acids and therefore proteins.

What important proteins are made using nitrogen obtained from nitrate ions?

Plant enzymes and other proteins required for normal cell function.

What other substances require nitrate ions for their production?

DNA, many hormones and other nitrogen-containing compounds.

What are the symptoms of nitrate deficiency in plants?

Older leaves turn yellow and die, growth is stunted and the plant may eventually die.

Why does nitrate deficiency cause stunted growth?

The plant cannot make enough amino acids and proteins needed to produce new cells and tissues.

Why do plants need calcium ions?

Calcium ions are needed to form calcium pectate in the middle lamella and are important in cell membranes.

What is the role of calcium pectate in plant cells?

It helps hold neighbouring plant cells together in the middle lamella.

What happens when plants lack calcium ions?

Growing points die back and young leaves become yellow and crinkled.

Why are growing tissues particularly affected by calcium deficiency?

Calcium is important for forming new cell walls and maintaining cell membranes.

Why do plants need magnesium ions?

Magnesium ions are needed to make chlorophyll, activate some plant enzymes and synthesise amino acids.

Why is magnesium important for photosynthesis?

Magnesium is required to produce chlorophyll, which absorbs light energy for photosynthesis.

What are the symptoms of magnesium deficiency?

Yellow areas develop on older leaves and plant growth slows.

Why does magnesium deficiency cause leaves to turn yellow?

The plant cannot produce enough chlorophyll.

What is chlorosis?

The yellowing of plant leaves caused by a lack or loss of chlorophyll.

Why are mineral deficiency symptoms useful?

They can indicate which essential mineral ion a plant is lacking.

How can the effects of different mineral deficiencies be investigated?

Plants can be grown in nutrient solutions that are identical except that each solution lacks a particular mineral ion.

What should be used as the control when investigating mineral deficiencies?

A plant grown in a complete nutrient solution containing all required mineral ions.

Why must other conditions be controlled in a mineral deficiency experiment?

So any differences in plant growth can be attributed to the mineral ion being investigated.

What variables should be controlled in a mineral deficiency experiment?

Plant species and starting size, light intensity, temperature, water availability, pH, nutrient solution volume and growth time.

What would a plant grown in a complete nutrient solution be expected to show?

Healthy, normal growth.

What would a plant lacking nitrate ions be expected to show?

Stunted growth and yellowing of older leaves.

What would a plant lacking magnesium ions be expected to show?

Yellowing of older leaves due to reduced chlorophyll production and slower growth.

What would a plant lacking calcium ions be expected to show?

Death of growing points and yellow, crinkled young leaves.

Why do deficiency symptoms often appear in particular parts of a plant?

Different mineral ions can be moved around the plant to different extents, so deficiencies may affect older or younger tissues first.

What is mineral uptake?

The absorption of mineral ions from the soil into plant roots.

How are many mineral ions absorbed by root cells?

By active transport, often against their concentration gradient.

Why is active transport needed for mineral ion uptake?

Mineral ions may need to move from a lower concentration in the soil to a higher concentration inside root cells.

What does active transport require?

Energy supplied by ATP from respiration and specific carrier proteins in cell membranes.

What is phytoremediation?

The use of plants to remove pollutants, such as toxic metal ions, from contaminated soil.

How can plants be used to remove toxic metals from soil?

Specialised plants absorb and accumulate the metal ions in their tissues and can then be harvested and removed.

What types of pollutants can phytoremediation remove?

Toxic heavy metals such as thallium and lead.

Why is phytoremediation useful?

It can make contaminated land safer for growing crops or grazing animals.

How can plants be used to extract valuable metals from soil?

Plants that accumulate large amounts of a metal are grown, harvested and burned, and the metal is extracted from the ash.

What is phytomining?

The use of plants to absorb valuable metal ions from soil so that the metals can later be extracted from the harvested plants.

Why can some plants be useful for phytomining?

They can accumulate unusually high concentrations of particular metals in their tissues.

What is an example of a metal that can be obtained using specialised plants?

Nickel.

How can nickel be recovered from plants used for phytomining?

The plants are harvested and burned, then nickel is extracted from the resulting ash.

What are the four major roles of water in plants?

Photosynthesis, maintaining turgor for support, transporting substances and cooling through evaporation.

What is the main role of nitrate ions in plants?

To provide nitrogen for making amino acids, proteins and other nitrogen-containing compounds.

What is the main role of calcium ions in plants?

To form calcium pectate in the middle lamella and help maintain cell membranes.

What is the main role of magnesium ions in plants?

To make chlorophyll and assist enzyme activity and amino acid synthesis.