4.12 Importance of Water and Mineral Ions in Plants

Question 1

Why do plants need water?

Answer 1

• for photosynthesis
• to transport mineral ions
• to maintain structural rigidity
• to regulate temperature

Question 2

Why is water important in photosynthesis?

Answer 2

water is a reactant in the process

Question 3

How is water used to transport mineral ions?

Answer 3

mineral ions are dissolved in water and hence can be transported around the plant through the xylem

Question 4

How does water maintain the structural rigidity of the plant?

Answer 4

• vacuoles of plant cells are filled with water - aka are turgid
• this exerts pressure outward with the cell contents pressing out on the cell wall
• this turgor maintains the rigidity of the stem and so keeps it erect
• the plant will wilt without turgidity

Question 5

How does water regulate temperature in plants?

Answer 5

water evaporating from the leaves helps cool the plants down

Question 6

What are the main properties of water that are important to plants?

Answer 6

• cohesion and surface tension
• solvent properties
• thermal properties

Question 7

What is cohesion and surface tension and why is this useful for plants?

Answer 7

• cohesion and surface tension is caused by the hydrogen bonding between water molecules
• the strong cohesive force between water molecules means that water can move up through the xylem in a continuous column during transpiration
• surface tension means that small aquatic plants such as duckweed can be supported on the surface

Question 8

Why are the solvent properties of water useful to plants?

Answer 8

• substances can be dissolved in water and transported around the plant (e.g. mineral ions)
• in cells, the dissolved substances can move freely and react, often with water (e.g. photosynthesis)

Question 9

Why are the thermal properties of water useful to plants?

Answer 9

• a large amount of energy only causes a small increase in the temperature of water
• therefore water warms and cools slowly
• this means that plants avoid rapid changes in their internal temperatures and can maintain their internal temp. even if the external temp. varies

Question 10

What inorganic ions do plants need?

Answer 10

• nitrate ions
• calcium ions
• magnesium ions

Question 11

Why do plants need nitrate ions?

Answer 11

• for the production of amino acids
• for the production of other biological molecules such as chlorophyll, nucleic acids (for DNA), ATP, and plant growth substances (needed for plant growth, and food and seed production)

Question 12

How do plants use nitrate to produce amino acids and therefore proteins?

Answer 12

• organic molecules form photosynthesis are combined with nitrogen from nitrate ions through a sequence of enzyme-controlled reactions
• this produces all 20 amino acids
• proteins are produced from these amino acids (such as enzymes)

Question 13

Why do plants need calcium ions?

Answer 13

• they are important components of plant cell walls and so are required for growth (lack of calcium = stunted growth)
• they are important for the permeability of the cell membrane

Question 14

Why do plants need magnesium ions?

Answer 14

• required for the production of chlorophyll (pigment needed for photosynthesis)
• lack of magnesium means leaves turn yellow