Plant Nutrition

Plant Nutrition In this topic you will learn:

Photosynthesis is the fundamental process by which plants manufacture simple sugars from raw materials.

Starter Question A tree is planted in a

meadow. After 20 years it has grown into a big tree, weighing 250kg more than when it was planted. Where do the extra

250kg come from? Explain your answer as

fully as you can.

Learning Outcomes Define photosynthesis and state the equation

for the production of simple sugars and oxygen in words.

State the equation for photosynthesis in symbols

Plant Nutrition Photosynthesis is the process in which light

energy, trapped by chlorophyll, is used to convert carbon dioxide and water into glucose and oxygen.

Word Equation Light energy

Carbon dioxide + water glucose + oxygen Chlorophyll

PhotosynthesisWord equation

Light energyCarbon dioxide + water glucose + oxygen

chlorophyll

Balanced Symbol Equation

Light energy6CO2 + 6H2O C6H12O6 + 6O2

chlorophyll

Learning Outcome Describe the intake of raw materials, the

trapping and storing of energy (conversion of light energy into chemical energy), the formation of food substances and their subsequent storage.

THINK!! What are the raw materials in

photosynthesis?

Where does the plant get them from?

What are the products of photosynthesis?

What happens to them?

Process of photosynthesis Carbon dioxide diffuses into the leaves of

green plants Water is absorbed by osmosis through plant’s

roots and transported to the leaf through xylem vessels

Chloroplasts, containing chlorophyll, are responsible for trapping light energy (energy is used to break up water molecules and then bond hydrogen and carbon dioxide to form glucose)

Process of photosynthesis Glucose is usually changed to sucrose for

transport around the plant, or to starch for storage

Oxygen is released as a waste product.

Leaves – a factory for photosynthesis Leaves are adapted to make them very

efficient for photosynthesis

Network of veins carry water and minerals to the leaf and food away from it.

Leaf is green, as it contains chlorophyll to absorb light

Petiole holds the leaf at an angle so it faces the sun and absorbs as much light as possible

Leaf is broad to give a large surface area to absorb light

Leaf is thin to allow substances to move quickly between and into cells (diffusion)

Testing a leaf for starch Dip a leaf into boiling water for

about a minute to soften it. Turn off the Bunsen burner. Put the leaf into a test-tube of

ethanol. Stand the test-tube in a beaker of

hot water for about 10 minutes. Wash the leaf in cold water Spread the leaf out flat on a petri

dish and cover it with iodine solution.

If the leaf goes blue-black, starch is present.

Is light needed for photosynthesis? Take a de-starched geranium plant.  Cover part of a leaf with some tin foil (this

prevents light getting through). Leave the plant in sunlight for a few hours Test the leaf for starch.

Is light needed for photosynthesis?Questions: Which parts of the leaf went blue black?

Why do parts that were not covered contain starch?

Photosynthesis

Is carbon dioxide needed for photosynthesis?

Take a de starched geranium plant

Enclose it in a plastic bag with a chemical that absorbs carbon dioxide. (e.g. soda lime or sodium hydroxide pellets).

Leave the plant in sunlight for a couple of hours

Test the leaf for starch.

Is carbon dioxide needed for photosynthesis?Questions: Does the leaf contain starch? Why not?  Has the plant carried out photosynthesis? What would be your control plant?

(Hint: a control plant should have everything it needs for photosynthesis including carbon dioxide).

Learning Outcomes Define the term limiting factor and interpret

(as limiting factors that affect photosynthesis) the effects of light and carbon dioxide concentration.

Limiting Factors The factors which if increased will increase

the rate of photosynthesis.

The process of photosynthesis depends on: Availability of light Presence of a pigment to absorb the light Supply of carbon dioxide and water A temperature suitable for enzyme activity

Limiting factors If any of these factors are in short supply

the rate of photosynthesis will be less then its maximum possible rate

The factor furthest from it’s optimum level is controlling the overall rate of photosynthesis!

The effect of light on the rate of photosynthesis Graph

As light intensity increase, so does the rate of photosynthesis, until a point where another factor becomes limiting

If the limiting factor in the graph was carbon dioxide concentration and the plants were given more carbon dioxide the graph would level off at a higher rate of photosynthesis.

The effects of carbon dioxide on the rate of photosynthesis graph

Effect of temperature on the rate of photosynthesis Temperature affects the enzymes that

control the rates of the chemical reactions of photosynthesis.

Graph

Compare this graph to the graphs showing the effect of temperature on enzyme activity.

Learning Outcome Explain the use of carbon dioxide enrichment,

optimum light and optimum temperatures in greenhouse systems

Optimum conditions in greenhouse systems Greenhouses are used to control the

conditions for plant growth The atmospheric conditions can be controlled

and the glass traps heat inside

Carbon dioxide enrichment 0.04% carbon dioxide in the air, so it can

easily limit the rate of photosynthesis Carbon dioxide concentration in a greenhouse

can be increased by: Burning fossil fuels Releasing pure carbon dioxide from a gas cylinder

Optimum light and temperature Optimum light

Light conditions for growth can be improved by using artificial lights

Optimum temperature Can be raised by using a heating system

Learning outcomes Identify the cellular and tissue structure if a

dicotyledonous leaf, as seen in cross section

Leaf Structure Revision:

How external features if a leaf design it to be a factory for photosynthesis

Activity – Bioviewers Observe and draw a cross section of a

dicotyledonous leaf

Internal Structure of a leaf Use the words below to

label your diagram of a leaf Waxy cuticle Upper epidermis Palisade mesophyll Spongy mesophyll

Lower epidermis Guard cell Stoma Phloem xylem

Functions of structures Pupil Activity

Cut out the internal structures and functions of a leaf

Match up the structure to the function

FunctionsStructure FunctionWaxy cuticle Prevents water loss from the leaf

Upper epidermis Transparent, Allows light to travel to cells within the leaf

Palisade mesophyll Cells tightly packed together, Main region of photosynthesis, Cells packed with chloroplasts

Spongy mesophyll Cells spherical and loosely packed, air spaces between cells allow for gas exchange

Vascular bundle Contains the xylem (transports water and minerals to the leaf) and phloem (translocation)

Lower epidermis Acts as a protective layer

stomata Regulates water loss (transpiration)Site of gaseous exchange in the leaf

Guard cells Control the opening and closing of stomata

Annotating a diagram Using the information you have already been

provided with Label the diagram Write a statement for each structure that you

have labelled.

Learning Outcomes Describe the importance of nitrate ions for

protein synthesis and magnesium ions for chlorophyll synthesis

Explain the effects of nitrate ions and magnesium ion deficiency on plant growth

Describe the uses and the dangers of overuse of nitrogen fertilisers

Nitrate ions Importance

Needed for synthesising amino acids

Amino acids form long chains to make proteins

Deficiency Plant growth is

stunted Weak stem Yellow, dying lower

leaves Upper leaves turn

pale green

Magnesium ions Importance

Forms part of chlorophyll molecules

Plants need chlorophyll to trap light to provide energy for photosynthesis

Deficiency Chlorosis

Leaves turn yellow Lack of

photosynthesis limits plant growth

Nitrogen fertilisers Nitrogen fertilisers can be used

To increase crop yields To replace the nitrate ions removed by intensive

farming

Nitrate can also be replaced by Applying animal manure Crop rotation

Grow leguminous plants in the field every 2/3 years

Dangers of overuse of fertilisers Too much nitrogen fertiliser can cause plant

roots to lose water by osmosis The plant wilts and dies

Eutrophication Fertilisers are soluble in rainwater and are washed

out of the soil This is known as leaching

Eutrophication

Stages of Eutrophication Fertilisers used by farmers may be washed into lakes

and rivers Rapid growth of water plants cause by the fertilisers Death of some of these plants due to lack of light

from overcrowding Microbes which feed on the dead organisms now

increase in number Oxygen is used up quickly by the microbes Suffocation of fish and other aquatic animals due to

the lack of oxygen in the water.

Pupil Activity Using the 5 main stages of eutrophication

leaching Rapid algal growth Death of algae Decay by bacteria Death of aquatic animals

Design a cartoon strip that summarises the process of Eutrophication

Progress Question – easy ones1. Plants need a supply of nitrate ions. State

the use made of nitrate ions in plants. [1]2. Many farmers regularly add nitrate

fertilisers to their fields. Explain why this is necessary. [2]

Progress Question – difficult one3. A farmer spreads a nitrate-rich fertiliser

over his fields. Each time he does this, he washes out his spreading equipment in a farm pond.

Suggest and explain what the likely effects of such pollution will be on the plants and animals in the pond. [5]